Ebook Point of care - Ultrasound: Part 2

(BQ) Part 2 book Pocket protocols for ultrasound presents the following contents: Kidneys, bladder, abdominal aorta, peritoneal free fluid, testicular ultrasound, lower extremity deep venous thrombosis, central venous access, peripheral venous access, arterial access,...

20 Kidneys

Behzad Hassani

Background

Renal ultrasound provides a fast,

radiation-free, and cost-effective alternative to computed

tomography (CT) for the initial workup of

low-risk patients who present with acute

symp-toms ranging from undifferentiated abdominal

pain to painless hematuria.1 Ultrasound is the

imaging modality of choice for investigating

obstructive uropathy in pregnant and pediatric

populations, given the adverse effects of

ion-izing radiation

Focused renal ultrasound can accurately

detect and grade hydronephrosis in the context

of obstructive uropathy,2 directly visualize large

obstructing calculi,3 and characterize renal

cysts or solid masses.4 Renal ultrasound can be

incorporated into the assessment of any patient

with undifferentiated flank or abdominal pain

When clinical suspicion for renal calculus is

high, the presence of hydronephrosis on the

side of pain can be considered as de facto

evidence of obstructive uropathy Sensitivity

of ultrasound for detecting a calcified stone

can be improved with the addition of a single

plain film of the abdomen (kidneys, ureter, and

bladder, or KUB).5 Severity of hydronephrosis

observed may correlate with the duration of

obstruction6 and possibly with the size of the

obstructing calculus.7 When stone disease is

clinically less likely or an alternate pathology

such as abdominal aortic aneurysm, gallbladder disease, ovarian torsion, or ectopic pregnancy is being considered, the absence of hydronephro-sis effectively guides investigations elsewhere.Normal Anatomy

Kidneys are retroperitoneal organs that lie in

an oblique longitudinal plane with the inferior pole of each kidney more anterior and lateral compared to its superior pole (Figure 20.1) Therefore, the transducer must be positioned obliquely to image the kidney along its long axis The left kidney is located more superiorly and posteriorly compared to the right kidney The left kidney is usually visualized through the acoustic window provided by the spleen due to interference by bowel and stomach gas anteriorly, and the right kidney is often visual-ized through the acoustic window provided by the liver The right kidney is slightly larger than the left kidney, but both kidneys are normally within 2 cm of each other in any dimension Normal kidneys are 9–12 cm long, 4–6 cm wide, and 2.5–3.5 cm thick

Kidneys are divided into two distinct tomic parts: renal parenchyma and renal sinus (Figure 20.2) Renal parenchyma is further subdivided into renal cortex and medulla The medulla consists of cone-shaped medul-lary pyramids Renal parenchyma surrounds

4—ABDOMEN AND PELVIS

154

the sinus on all sides except at the hilum The

hilum is where the renal artery, renal vein, and

proximal ureter enter the renal sinus

Promi-nent fatty deposits within the renal sinus give

it a hyperechoic appearance and distinguish it

from the hypoechoic, grainy renal parenchyma

This difference in echogenicity is known as the

sonographic double density of the kidney.4,8

Image Acquisition

A low-frequency transducer with deep

penetra-tion, either phased-array or curvilinear type, is

used to image the kidneys The narrower beam

width of a phased-array transducer is ideal for

imaging between the ribs, but the wider beam

width of a curvilinear transducer allows

visual-ization of the entire kidney longitudinally in a

single view

When scanning a patient with a suspected

renal pathology, scan the unaffected side first

to obtain a baseline image to compare with

the affected side To image the right kidney,

place the patient in a supine position with the

transducer in a coronal plane in the

midaxil-lary to anterior axilmidaxil-lary line at the level of the

xiphoid process Center the kidney on the

screen and rotate the transducer 15-30 degrees

counterclockwise to aim the transducer marker

slightly posteriorly to capture a true long-axis

view of the right the kidney While holding

the transducer in the same location on the skin

surface, tilt or fan the transducer anteriorly and

posteriorly to assess the entire kidney from its

most anterior to posterior surface Rotate the

transducer 90 degrees counterclockwise from the long-axis view to obtain a transverse cross section of the kidney Tilt or fan the transducer superiorly and inferiorly to assess the superior and inferior poles of the kidney Figure 20.3illustrates transducer positions to obtain long- and short-axis views of the kidney

The left kidney is more posterior and superior than the right kidney Placing the patient in a right lateral decubitus position facilitates visualization of the left kidney and reduces interference from the ribs and bowel gas Requesting the patient to hold his breath

in maximal inspiration will shift the kidney caudally to further reduce interference from rib shadows Identify the left kidney with the transducer in a coronal plane on the posterior axillary line and then rotate the transducer 15-30 degrees clockwise aiming the transducer marker posteriorly to acquire a true long-axis view (Figure 20.4) Transverse or short-axis views are obtained by rotating the transducer

90 degrees counterclockwise from the long axis (Figure 20.5).4,8

Sagittal and transverse views of the bladder should be obtained for a complete evaluation of the urinary system (see Chapter 21, Bladder).Image Interpretation

Perinephric fat and Gerota’s fascia appear as

a hyperechoic stripe around the kidneys, and the fibrous capsule gives each kidney a hyper-echoic outline Normally, the renal cortex has

a homogeneous appearance on ultrasound

Figure 20.1 Anatomy of the urinary

system.

LiverRight

Inferiorvena cava

UrethraBladder

UreterAorta

RenalpelvisSpleen

that is less echogenic than the adjacent liver

or spleen Fluid-filled medullary pyramids

are seen as hypoechoic or anechoic triangular

prominences in a semicircular arrangement

around the sinus As a result, the renal medulla

is significantly less echogenic compared to the

surrounding cortex

The renal sinus normally appears

hyper-echoic due to fat content, and in the absence

of urinary tract obstruction, the sinus appears

homogenously hyperechoic with small

anechoic pockets of urine The ureter is usually

obscured by bowel gas but may be visible with

ultrasound when dilated When distended, the

ureter appears as a tubular structure extending inferiorly from the renal pelvis.4,8

pole

Inferiorpole

Lateralborder

MedialborderRenalarteryRenalveinRenalpelvis

RenalpelvisUreter

Ureter

Anterior surface of right kidney

Internal structure of right kidney

Pyramid

in renalmedullaRenal

cortex

Renalpapilla

Fibrous

capsule

Renalsinus

MajorcalyxMinor

calyxRenalcolumn

Hilum ofkidney

Figure 20.2 Cross-sectional anatomy of the kidney.

4—ABDOMEN AND PELVIS

156

distal renal stone Most algorithms incorporate

the degree of hydronephrosis into a clinical

decision-making pathway.1,7,9

Mild hydronephrosis is defined as

enlarge-ment of the calices with preservation of renal

papillae The renal sinus is normally

hyper-echoic but becomes anhyper-echoic due to mild

cen-tral dilation in mild hydronephrosis (Figure

20.7) As mild hydronephrosis progresses, the

degree of central dilation of the renal sinus

increases, but the structure of the

medul-lary pyramids is preserved (Figure 20.8) It is

preservation of medullary pyramidal ture, not the degree of renal pelvic dilation, that characterizes mild hydronephrosis and differ-entiates mild from moderate hydronephrosis (Video 20.1 )

architec-Moderate hydronephrosis is characterized

by rounding of the calices, obliteration of renal papillae, and blunting of medullary pyramids Progressive dilation of the calyces leads to glovelike splaying of the renal sinus and bal-looning of the medullary pyramids that has been called the classic bear-claw appearance

A B

Pocket ofurine

Sinus

Medullary

pyramid

Figure 20.4 Normal long-axis view of the kidney Note the prominent medullary pyramids and the

hyper-echoic renal sinus in the absence of hydronephrosis.

Cortex

Sinus

Figure 20.5 Normal short-axis view of the kidney.

Figure 20.6 Severity of hydronephrosis is graded by the degree of distortion of normal architecture Mild

hydronephrosis : enlarged calices with preservation of renal papillae and pyramids Moderate

hydronephro-sis : dilated calices with obliterated papillae and blunted pyramids Severe hydronephrosis: calyceal

balloon-ing, complete obliteration of papillae and pyramids, cortical thinning.

4—ABDOMEN AND PELVIS

A small amount of perinephric fluid due to calyceal rupture and urinary extravasation may

be seen with hydronephrosis (Figure 20.11) Perinephric fluid is associated with significant

Cortex Mildhydronephrosis

Sinus

Figure 20.7 Mild hydronephrosis.

Cortex Preservedpyramid

SinusMild

Figure 20.9 Moderate hydronephrosis.

Figure 20.11 Longitudinal view of the right kidney

Note the small amount of perinephric fluid, tive of calyceal rupture and urinary extravasation.

indica-risk of infection or perinephric abscess

forma-tion and requires close follow-up.1

Several conditions can mimic the

ultra-sound appearance of hydronephrosis Two

general guiding principles should be followed

to distinguish between true hydronephrosis

and its mimics: (1) trace the anechoic areas

of suspected hydronephrosis to the renal

pel-vis where the areas should coalesce; and (2)

scan the kidney in both the longitudinal and

transverse planes to thoroughly delineate the

architecture of the area of suspected

hydro-nephrosis Medullary pyramids may appear

anechoic and can be mistaken for collections

of urine; however, the triangular pyramids are

separated from each other by cortical tissue

and should be seen as distinct entities from

the hyperechoic renal sinus Cortical and

par-apelvic cysts can also mimic hydronephrosis,

but they are distinguished by their

smooth-walled, spherical shape that is not

contigu-ous with the renal pelvis (Figures 20-12 and

20-13) Renal hilar vessels are also anechoic

and can be mistaken for hydronephrosis

Color-flow Doppler can differentiate

vascu-lature from hydronephrosis.8

Renal Calculus

Ultrasound has low sensitivity for detecting

ureteral calculi.3 Stones may be seen within the

renal parenchyma, at the ureteropelvic

tion proximally or at the ureterovesicular

junc-tion distally In general, ureters are obscured

by bowel gas and are difficult to assess as

they travel from kidney to bladder Stones are

hyperechoic and exhibit acoustic shadowing

(Figure 20.14 and Video 20.4)

Severity of hydronephrosis may correlate with stone size.7 Patients with renal colic and moderate or severe hydronephrosis are signifi-cantly more likely to have stones >5 mm than patients with mild or no hydronephrosis.7Stones <5 mm generally pass without interven-tion and stones 5–9 mm in size may pass sponta-neously, but stones >10 mm are unlikely to pass and will likely require urologic intervention.10Renal Cyst

Renal cysts are common and usually benign, but renal malignancies may present as cystic structures on ultrasound A benign cyst must fulfill all of the following criteria8:

1 Thin-walled and smooth, with no septations, internal echoes, or solid elements

Figure 20.13 Parapelvic cysts.

Renal calculus

Acousticshadowing

Figure 20.14 Large renal calculus in the right kidney

seen in along-axis view Note the associated nent acoustic shadowing.

promi-4—ABDOMEN AND PELVIS

160

2 Round or oval shape that is well

demar-cated from the adjacent parenchyma

and appears homogeneous in all

imag-ing planes

3 Posterior acoustic enhancement must be

evident behind the cyst

If the above criteria are not fulfilled, the

presence of a complex cyst (Figure 20.15),

renal abscess, or malignancy must be

consid-ered and warrants further workup

Multiple renal cysts are seen in polycystic

kidney disease (PCKD) and acquired renal

cystic disease (ARCD) PCKD represents

an extreme example on the spectrum of renal

cystic disease (Figure 20.16 and Video 20.5)

PCKD is characterized by an abundance of

irregular cysts of varying size that distort the

normal renal architecture bilaterally These

patients often present to acute care settings

with flank pain, hematuria, hypertension,

and renal failure ARCD is another condition

associated with multiple renal cysts that is

present in patients with end-stage renal

dis-ease on hemodialysis and is associated with

higher risk of renal malignancy While most

patients with chronic kidney disease have

bilaterally shrunken and hyperechoic kidneys (Video 20.6), those with ARCD have numer-ous cysts

Renal MassRenal malignancies detected incidentally dur-ing abdominal imaging are associated with lower morbidity and mortality rates.11 Any suspicious mass detected by point-of-care ultrasound warrants further investigation and expert consultation (Figure 20.17).11 Normal variants that can mimic renal malignancies include prominent columns of Bertin, which are hypertrophied cortical tissue that distort the calyces in the renal sinus (Figure 20.18).Renal cell carcinoma is the most common type

of renal malignancy in adults These tumors are

Septations

Debris

Figure 20.15 Large complex cyst with internal

sep-tations seen in a transverse view of the right kidney.

Figure 20.18 Hypertrophied column of Bertin.

appearance They can be isoechoic, hypoechoic,

or hyperechoic relative to adjacent parenchyma,

and they may have a partial cystic appearance that

can be mistaken for benign cysts.4

Angiomyoli-poma is the most common type of benign tumor

of the kidney The tumors are well-demarcated

hyperechoic masses located within the renal

cor-tex There is significant overlap in the appearance

of angiomyolipomas and echogenic renal cell

carcinoma.4 Therefore, providers using

point-of-care ultrasound should obtain additional

radio-graphic imaging and seek expert consultation

when incidental masses are detected

PEARLS AND PITFALLS

• Hydronephrosis may be

underrecog-nized in hypovolemic patients due to

transient collapse of calyces Sensitivity

of ultrasound in detecting

hydronephro-sis is increased after fluid resuscitation

in patients with volume depletion

• A bladder ultrasound exam should

accom-pany a renal ultrasound exam A distended

bladder due to bladder outlet obstruction

may cause bilateral hydronephrosis, and

performed after bladder decompression

• Varying degrees of hydronephrosis, most often on the right side, is common in pregnancy and may not be pathologic

• Renal calculi are common and detection

of a nonobstructing parenchymal stone may be unrelated to the patient’s clinical presentation

• Unilateral hydronephrosis may be due

to external ureteral compression by a mass lesion or retroperitoneal lymph-adenopathy, and these pathologies should be considered

• Absence of hydronephrosis does not rule out ureterolithiasis because small calculi may not create significant obstruction

• High-risk patients (age >50) who present with flank pain and hydronephrosis on bedside ultrasound exam may have a ruptured abdominal aortic aneurysm, and any abnormal ultrasound findings in these patients warrants additional workup

• All renal masses are malignant until

prov-en otherwise Detection of a rprov-enal mass

by point-of-care ultrasound requires ther workup with additional radiographic imaging and expert consultation

a left shift Your primary differential diagnosis includes pyelonephritis, diverticulitis, and kidney stone.

Ultrasound Findings

A focused bedside ultrasound exam of the abdomen is performed No free fluid is seen, but mild dronephrosis of the left kidney is detected (Video 20.7), suggesting renal colic as a possible etiology A comprehensive abdominal ultrasound confirms the presence of left-sided hydronephrosis ( Figure 20.19 ) and reveals a 6 mm partially obstructing calculus in the distal left ureter ( Figure 20.20 ) Bilateral ureteral jets are seen on the posterior bladder wall using color flow Doppler ultrasound ( Figure 20.21 ).

hy-Case Resolution

The patient is discharged with oral analgesics and a trial of medical expulsion therapy He is given outpatient urology follow-up He spontaneously passes the stone after days and recovers without complications.

Providers can accurately detect and grade hydronephrosis using bedside ultrasound When clinical suspicion of renal calculus is high, unilateral hydronephrosis serves as indirect evidence of obstructive uropathy due to a stone Moderate to severe hydronephrosis correlates with a stone size >5 mm, even though the actual stone may not be visualized Stones <5 mm usually pass spontaneously without any intervention.

Mild hydronephrosis

Figure 20.19 Longitudinal view of the left kidney

with mild hydronephrosis.

Ureteral stone withacoustic shadowing

Figure 20.20 Left distal ureter with an obstructing

calculus measuring approximately 6 mm Note the anechoic bladder on the right side of the screen.

Case 2

Case Presentation

A 62-year-old woman presents to the emergency department with a 2-hour history of right flank and lower quadrant abdominal pain She has a known history of renal colic but has been otherwise healthy without any previous hospitalizations or surgeries This episode is similar to her past renal colic epi- sodes, and she insists that she will be fine at home with oral analgesics and antiemetics She is afebrile, and her vital signs are remarkable only for mild tachycardia of 105 beats per minute, attributed to her pain Her exam is remarkable only for right costovertebral angle tenderness Urinalysis shows micro- scopic hematuria WBC count, hemoglobin, and creatinine are normal.

The patient is discharged home with oral analgesics and antiemetics Over the ensuing hours, her condition deteriorates She develops worsening right-sided flank pain, refractory vomiting, and progres- sive confusion She is brought to the hospital by ambulance, and she is febrile (40 º C), tachycardic at

120 beats per minute, and confused.

cystos-Hydronephrosis is graded by the degree of distortion of renal architecture Moderate phrosis is distinguished from mild hydronephrosis by rounding of the calices, obliteration of renal papillae, and blunting of medullary pyramids Severe hydronephrosis is characterized by cortical thinning Presence of moderate to severe hydronephrosis in a patient with renal calculus disease correlates with a stone size >5 mm Stones 5–9 mm might pass spontaneously, but stones

hydrone->1 cm are unlikely to pass without intervention.

Ureteral jet

Figure 20.21 Moderately filled bladder at the level

of trigone in a transverse view A left ureteral jet is visualized using color flow Doppler ultrasound.

20—KIDNEYS 161.e3

References

1 Swadron S, Mandavia D Renal In: Ma OJ, Mateer JR, Blaivas M, eds Emergency Ultrasound 2nd ed

New York, NY: McGraw-Hill; 2008

2 Dalziel PJ, Noble VE Bedside ultrasound and the assessment of renal colic: a review Emerg Med J

2013;30(1):3–8

3 Fowler KA, Locken JA, Duchesne JH, et al US for detecting renal calculi with nonenhanced CT as a

reference standard Radiology 2002;222:109–113.

4 Tublin M, Thurston W, Wilson SR The kidney and urinary tract In: Rumack CM, Wilson SR,

Charboneau JW, Levine D, eds Diagnostic Ultrasound 4th ed New York, NY: Elsevier; 2011.

5 Dalla Palma L, Stacul F, Bazzocchi M, Pagnan L, Festini G, Marega D Ultrasonography and plain

film versus intravenous urography in ureteric colic Clin Radiol 1993;47:333–336.

6 Brown DFM, Rosen CL, Wolfe RE Renal ultrasonography Emerg Med Clin North Am 1997;15:

9 Nobel V, Brown DF Renal ultrasound Emerg Med Clin North Am 2004;22:641–659.

10 Coll D, Varanelli MJ, Smith RC Relationship of spontaneous passage of ureteral calculi to stone size

and location as revealed by unenhanced helical CT Am J Roentgenol 2002;178:101–103.

11 Sweeney JP, Thornhill JA, Graiger R, McDermott TE, Butler MR Incidentally detected renal cell

carcinoma: pathological features, survival trends and implications for treatment Br J Urol 1996;78:

351–353

Stone withinrenal pelvis

Figure 20.22 Obstructing calculus in the renal pelvis

with associated moderate hydronephrosis.

21 Bladder

Behzad Hassani

Background

Bedside ultrasound evaluation of the

blad-der has several clinical applications

Esti-mation of bladder volume, confirEsti-mation of

proper urinary catheter placement,

detec-tion of stones, and assessment of ureteral

jets in suspected obstructive uropathy are the

core indications for point-of-care bladder

ultrasound

Many patients who present with a

com-plaint of “urinary retention” do not truly have

urinary retention.1 Evaluation of bladder

vol-ume based on physical exam is inaccurate due

to body habitus in a significant percentage

of patients Bladder ultrasound can precisely

determine bladder volume and avoid

unnec-essary urinary catheterizations When urinary

catheterization is necessary, bedside ultrasound

can confirm proper placement and functioning

of the catheter In pediatric patients, bladder

volume estimation can eliminate unnecessary

catheterizations,2 and real-time ultrasound

guidance can substantially reduce

compli-cations associated with suprapubic bladder

aspirations.3

Normal Anatomy

The bladder is a triangular organ positioned

in the pelvic cavity that is located inferior and

anterior to the peritoneal cavity and directly posterior to the pubic symphysis (Figure 21.1) Ureters enter the trigone of the bladder pos-teriorly and inferiorly (Figure 21.2) In males, the prostate encircles the bladder neck caudally and normally measures <5 cm in transverse diameter

Image AcquisitionThe curvilinear transducer (3.0–5.0 MHz) is ideal for imaging the bladder Its mid-range frequency allows for optimal resolution, and its wider footprint permits visualization of the entire bladder A fluid-filled bladder readily propagates sound waves resulting in posterior acoustic enhancement, or hyper-echogenicity, posterior to the bladder This artifact can obscure the far field of the image, and certain findings, such as pelvic free fluid, may be missed The far-field gain should be decreased to better visualize hypoechoic or anechoic entities posterior to the bladder.5The bladder is located posterior and infe-rior to the pubic symphysis and is best visu-alized from a suprapubic approach With the patient in a supine position, place the trans-ducer in a transverse plane at the superior edge of the pubic symphysis and aim the ultra-sound beam posteroinferiorly (Figure 21.3A)

K E Y P O I N T S

• The primary indications for performing bladder ultrasound at the bedside are estimation of bladder volume, confirmation of proper urinary catheter placement, detection of stones, and assessment of ureteral jets in suspected obstructive uropathy

• Bladder volume can be calculated using the following formula:

Volume = (0.75 × width × length × height)

• Detection of a bladder mass during a point-of-care ultrasound exam warrants further workup, including additional imaging and expert consultation

21—BLADDER 163

Tilt the transducer superiorly and inferiorly

to visualize the entire bladder in a transverse

plane Assess the bladder for its degree of

distention and for the presence of stones or

masses If the bladder is not filled, the

trans-ducer often has to be pointed caudally into the

pelvic cavity to identify the bladder The

pros-tate gland is hyperechoic and can be visualized

in a transverse plane adjacent to the inferior

bladder wall Rotate the transducer 90 degrees

clockwise to obtain longitudinal views of the

bladder in a sagittal plane (Figure 21.3B) Scan

the bladder thoroughly in a sagittal plane by

tilting the transducer to visualize the leftmost and rightmost walls

In patients with renal colic, visualization of ureteral jets, or intermittent expression of urine into the bladder, rules out complete obstruc-tion of the ureter To visualize ureteral jets, scan slowly through the bladder in a transverse plane and focus over the trigone.4–6 Ureteral jets can be detected using two-dimensional gray-scale sonography, but they are best visu-alized with power Doppler on a low-flow set-ting (i.e., low PRF setting) Power Doppler demonstrates flow regardless of direction and

Prostate

Laminapropria

Urethral

sphincter

UrethralsphincterUrethra

Figure 21.3 A, Transducer position to visualize the bladder in a transverse plane Caudal tilting of the

transducer helps visualize the bladder in the pelvic cavity B, Transducer position to visualize the bladder in a sagittal plane The transducer is rocked inferiorly to visualize the bladder in the pelvic cavity.

21—BLADDER 165

is particularly suited for detecting low-flow

states, such as ureteral jets The jets appear as

colorful emissions streaming from the base of

the bladder toward its center (Figure 21.4) In

well-hydrated patients, they appear at regular

intervals every 15–20 sec and last <1 sec.7

The presence of bilateral ureteral jets in a

well-hydrated patient rules out significant

obstruc-tive uropathy with high specificity.8,9 Ureteral

obstruction is suspected when a jet is not

visualized on the affected side but is visualized

unilaterally on the unaffected side

Bladder volume= (0.75 × width × length × height)

The width and anteroposterior dimension

(i.e., length) are measured in a transverse plane

(Figure 21.5A) The superior-inferior

dimen-sion (i.e., height) is measured in a sagittal plane

(Figure 21.5B) Past research10 has demonstrated

close correlation between the estimated bladder

volume using the formula above and the actual

catheterized volume (correlation factor = 0.983)

A qualitative assessment of bladder

disten-tion can be performed by noting the locadisten-tion

of the bladder dome relative to the umbilicus.1

Center the bladder dome on the screen in a

sagittal plane The center of the transducer on

the skin identifies the location of the dome

relative to the umbilicus The bladder dome

extends at least halfway to the umbilicus in

the majority of patients with urinary tion (Video 21.1 ).1 The presence of urinary retention should prompt a scan of the kidneys

reten-to rule out bilateral hydronephrosis, a finding that has prognostic implications in the setting

of chronic outlet obstruction

Although bedside transabdominal sound can readily detect prostatic hypertrophy (transverse diameter >5 cm), it cannot distin-guish benign hypertrophy from malignancy (Figure 21.6) If clinically indicated, urology consultation and additional imaging and/or biopsy should be pursued

ultra-BLADDER STONES

Bladder calculi are most often seen after cessful passage of renal calculi from the ureters into the bladder Bladder stones may also form

suc-de novo secondary to bladsuc-der stasis in patients with chronic retention.4 Bladder stones appear

as hyperechoic, mobile entities that demonstrate posterior acoustic shadowing (Figure 21.7)

Right ureteral jet

Figure 21.4 Transverse view of the female bladder

revealing a prominent right-sided ureteral jet on

color power Doppler originating in the trigone area.

Iliac vessels

Bladder

length (A)

& width (B)A

B

Bladder

height (A)

Figure 21.5 A, Measurement of the width (W) and

length (L) of the bladder is performed in a transverse plane B, Measurement of the height (H) of the

bladder is performed in a sagittal plane Bladder volume is calculated using the following formula:

Volume = 0.75 × W × L × H.

BLADDER MASS 4–6

Bladder masses typically appear either as

irreg-ular, echogenic projections from the bladder

wall or as foci of increased bladder wall

thick-ness (Figure 21.8) The bladder wall is

nor-mally 3–6 mm thick but varies depending on

the degree of bladder filling Transitional cell

carcinoma accounts for the majority of bladder

masses The differential diagnosis of a bladder

mass includes malignancy, bladder diverticula,

congenital outpouchings of the bladder wall,

and bladder wall thickening due to chronic

or recurrent cystitis Blood clots can be

mis-taken for a bladder mass, and repeat ultrasound

should be performed after adequate continuous

bladder irrigation Additional workup,

includ-ing imaginclud-ing and expert consultation, is always

warranted to further evaluate bladder masses

Foley

balloon

Enlarged

prostate

Figure 21.6 Transverse view of a male bladder with

a urinary catheter balloon and an enlarged prostate

in the far field.

PEARLS AND PITFALLS

• Maximal dimensions should be used to

calculate bladder volume accurately The

maximal dimensions should be captured

by freezing the image while tilting or

fanning the transducer through the

blad-der Use the following formula: Bladder

volume = (0.75 × width × length × height)

• When conducting a qualitative

assess-ment of bladder volume for urinary

retention, recall that in the majority of

patients with urinary retention, the

blad-der dome extends at least halfway to the

umbilicus

Bladdercalculus

Figure 21.7 Transverse view of the bladder revealing

a hyperechoic calculus in the far field Note the nent posterior shadowing associated with the stone.

promi-Bladdermass

Figure 21.8 Sagittal view of the bladder revealing

bladder cancer.

• Ureteral jets may be infrequent or not sualized in many patients Although their presence rules out obstruction with high specificity, their absence by ultrasound imaging does not rule in obstructive uropathy

• Free fluid in the pelvis can easily be mistaken for the bladder Always scan the bladder and surrounding tissues thoroughly in transverse and longitudinal planes Filling the bladder or identifying

an inflated urinary catheter balloon can help distinguish the bladder from pelvic free fluid

• Blood clots may appear as a bladder mass

on ultrasound Continuous bladder tion often resolves blood clots and helps distinguish blood clots from a true mass

Ultrasound Findings

Bedside ultrasound reveals a grossly distended bladder with the dome at the level of the umbilicus (Video 21.2) A Foley catheter is inserted and its correct placement is confirmed by ultrasound (Video 21.3) The prostate is grossly enlarged, and bilateral moderate hydronephrosis is evident on renal ultra- sound (Videos 21.4 and 21.5).

Case Resolution

The Foley catheter drains 2 L of urine with minimal clots The urology service is consulted and the tient is admitted for observation His hospital course is complicated by post-decompression hematuria requiring blood transfusion He also suffers from post-obstructive diuresis (urine output of 4000 mL in

pa-24 h) requiring intravenous fluids His creatinine returns to baseline, and he is discharged home with

an indwelling urinary catheter He undergoes a transurethral resection of the prostate as an outpatient several weeks later.

A bladder ultrasound exam can be performed easily at the bedside In patients with decreased urine output, a bladder ultrasound exam can readily differentiate urinary retention or urinary catheter blockage from decreased urine production The bladder volume can be quantitatively assessed using the formula:

Bladder volume = ( 0.75 × width × length × height )

Case 2

Case Presentation

A 47-year-old woman presents with a 3-week history of lower urinary tract symptoms She received numerous courses of antibiotics for presumed urinary tract infection by her primary care provider and urgent care clinics She admits to bilateral flank pain, dysuria, frequency, urgency, and occasional epi- sodes of gross hematuria She also complains of straining, hesitancy, and incomplete voiding She denies prior history of renal colic or hematuria and is otherwise healthy She has a 20 pack-year smoking history Vital signs are normal, and her physical exam is unremarkable Lab results reveal mild anemia with slight elevation in creatinine Urinalysis shows leukocytes and blood.

Ultrasound Findings

A bedside bladder ultrasound exam is performed The bladder is distended with a postvoid residual of

700 mL Additionally, several bladder masses are noted (Video 21.6).

1 Skinner A Bladder EDE In: Socransky S, Wiss R, eds Point-of-Care Ultrasound for Emergency Physicians—“The EDE Book” Sudbury, ON: The EDE 2 Course Inc.; 2012.

2 Gochman RF, Karasic RB, Heller MB Use of portable ultrasound to assist urine collection by

suprapu-bic aspiration Ann Emerg Med 1991;20:631–635.

3 Kiernan SC, Pinckert TL, Keszler M Ultrasound guidance of suprapubic bladder aspiration in

neo-nates J Pediatr 1993;123:789–791.

4 Tublin M, Thurston W, Wilson SR The kidney and urinary tract In: Rumack CM, Wilson SR,

Char-boneau JW, Levine D, eds Diagnostic Ultrasound 4th ed New York, NY: Elsevier; 2011.

5 Hwang JQ, Poffenberger CM Renal and urinary system ultrasound In: Carmody KA, Moore CL,

Feller-Kopman D, eds Handbook of Critical Care & Emergency Ultrasound New York, NY:

McGraw-Hill; 2011

6 Hagen-Ansert SL Textbook of Diagnostic Sonography 7th ed New York, NY: Mosby; 2011.

7 Bates JA Abdominal Ultrasound: How, Why and When 3rd ed New York, NY: Churchill Livingstone;

2010

8 Burge HJ, Middleton WD, McClennan BL, et al Ureteral jets in healthy subjects and in patients with

unilateral ureteral calculi: comparison with color Doppler US Radiology 1991;180:437–442.

9 Strehlau J, Winkler P, De La Roche J The uretero-vesical jet as a functional diagnostic tool in

child-hood hydronephrosis Pediatr Nephrol 1997;11:460–467.

10 Chan H Noninvasive bladder volume measurement J Neurosci Nurs 1993;25:309–312.

The abdominal aorta is a vital retroperitoneal

structure with the potential for catastrophic

pathology that is often difficult to diagnose

In the words of Sir William Osler, “There is

no disease more conducive to clinical humility

than aneurysm of the aorta.” When a diagnosis

of aortic pathology is identified, appropriate

interventions may improve outcomes for this

often time-sensitive presentation.1

Abdominal aortic aneurysms are the most

commonly identified aortic abnormality They

may be complicated by thrombosis, dissection

of the intimal layer, or rupture, which carries

a particularly high mortality of approximately

90%.2 The incidence of abdominal aortic

aneurysm increases with age, family history,

male gender, and a history of smoking The

overall prevalence is approximately 4.7% and

3.0% in men and women, respectively.3 This

peaks around 5.9% in men 80–85 years old

and 4.5% for women over age 90.4

Aortic pathology should be considered in

any patient presenting with abdominal

dis-comfort, especially in patients with known

risk factors and those that present with

classic histories or exam findings

(hypoten-sion, back pain, pulsatile abdominal mass)

In addition, various recommendations have

been made for screening asymptomatic

patients, including a grade B

recommenda-tion by the U.S Preventive Services Task

Force, which recommends screening all men

between the ages of 65–75 with a history of smoking.5

Use of point-of-care ultrasound saves time, reduces cost, and avoids ionizing radiation and exposure to intravenous contrast when com-pared to other imaging modalities.1 Point-of-care ultrasound has demonstrated high sensitivity (97.5–100%) and specificity (94.1–100%) for detection of abdominal aortic aneu-rysm.6,7 It has high correlation with computed tomography (CT) and magnetic resonance imaging in diagnosing aortic dilation, but may slightly underestimate the exact diameter.8Normal Anatomy

The abdominal aorta is the section of aorta that extends from the posterior diaphragm where

it exits from the thoracic cavity and continues until its division into the common iliac arter-ies Through the abdomen, its major branches include the left and right renal arteries, celiac artery, superior and inferior mesenteric arteries, and gonadal arteries In addition, it has branches

to supply the diaphragm, adrenal glands, inal wall, and spinal cord Figure 22.1 illustrates the major branches of the abdominal aorta.Image Acquisition

abdom-Sonographic visualization of the abdominal aorta is achieved through a transabdomi-nal approach The proximal aorta can be viewed in the transverse (short-axis) plane by

K E Y P O I N T S

• Ultrasound is the preferred initial screening modality for abdominal aortic aneurysm

• The entire abdominal aorta should be imaged in two perpendicular planes (transverse and longitudinal) to avoid missing subtle abnormalities

• Oblique imaging planes may underestimate or overestimate aortic diameter and should be avoided

placing a phased-array or curvilinear

trans-ducer (3.5–5 MHz) just below the costal

margin in the center of the abdomen with the

transducer marker pointing to the patient’s

right Commonly, the celiac artery and

supe-rior mesenteric artery are seen in this

posi-tion, and occasionally left and right renal

arteries may be identified (Figure 22.2 and

Video 22.1) Evaluation of these structures is

typically less important when assessing for the

simple presence or absence of an abdominal

aortic aneurysm, but their identification

pro-vides useful landmarks A particularly useful

sonographic reference point is the vertebral

body and its characteristic shadow, which lies

immediately posterior and slightly to the right

of the aorta

Once the aorta is identified in a

trans-verse plane, slide the transducer inferiorly on

the abdominal wall, allowing for contiguous

imaging of the aorta With the transducer in

a transverse position just above the umbilicus

with the ultrasound beam directed

posteri-orly, the distal aorta is visualized as it divides

into the left and right common iliac arteries

(Figure 22.3 and Video 22.2 )

After evaluating the aorta in short axis, longitudinal views should be acquired to accu-rately assess the size of the aorta Place the transducer over the proximal abdominal aorta and rotate the transducer clockwise 90 degrees

so that the transducer marker is pointed toward the patient’s head Again, it may be possible to visualize the celiac and superior mesenteric arteries if the plane of the ultrasound trans-ducer is aligned with these vessels (Figure 22.4and Video 22.3)

Measurements of the aortic diameter should

be obtained in both transverse and longitudinal planes It is important to measure the aortic diameter with the transducer perpendicular

to the aorta to capture a true cross-sectional image because oblique images can underesti-mate or overestimate the diameter Calipers should be placed on the outer edges of the aor-tic walls The diameter of the aorta should be measured proximally and distally with calipers placed on the outer edges of the aortic walls

If interpretable images cannot be obtained

in the anterior mid-abdomen, usually due

to bowel gas or scarring, then an alternate approach is to image the aorta laterally from the

Diaphragm

Celiac artery

Common iliacarteries

Superior

mesenteric

artery

Inferiormesentericartery

Gonadalarteries

External iliacarteries

Internal iliacarteries

Left renalartery and vein

Figure 22.1 Anatomy of abdominal aorta.

22—ABDOMINAL AORTA 169

right or left flank With the transducer marker

pointing toward the patient’s head, place the

transducer in the right or left midaxillary line

just below the costal margin to capture

longi-tudinal views of the aorta From the right flank,

a longitudinal view of two tubular, anechoic

structures is seen posterior to the liver at the

bottom of the image; the near-field structure is the inferior vena cava, and the deeper structure

is the abdominal aorta The transducer can be rotated 90 degrees clockwise to obtain trans-verse views of the aorta, but acquiring trans-verse images laterally can be challenging due

to the depth of the aorta The same technique

SMA

Ao Renal arteries IVC

Vertebral body

Splenic vein

SMA Splenic vein

C

LOGIQ E9

B A

Figure 22.2 A, Transducer position for transverse (short-axis) views of the proximal abdominal aorta

B, Celiac artery is seen branching into the common hepatic artery (HA) and splenic artery (SPL) C, Superior mesenteric artery (SMA) is seen along with the left and right renal arteries, splenic vein, aorta (Ao), and inferior vena cava (IVC) Note the position of the vertebral body posterior to the aorta.

can be used to obtain longitudinal views of the

abdominal aorta from the left flank (Figure

22.5 and Video 22.4)

Image Interpretation

An arterial aneurysm is defined as a

perma-nently localized dilation of an artery having at

least 50% increase in diameter compared to the

expected normal diameter of the artery in

ques-tion.9 For the abdominal aorta, this means that

an aneurysm is present whenever the diameter

exceeds 3.0 cm This provides a useful

thresh-old, though it may exclude some more subtle

aneurysms Fortunately, the complication rate

is directly related to the size of the aneurysm,

and smaller dilations are of less immediate

clin-ical significance Identification remains

impor-tant, as these aneurysms should be monitored.1

Point-of-care ultrasound can detect

abdom-inal aortic aneurysm with high sensitivity

(97.5–100%) and specificity (94.1–100%).6,7

Detection of an abdominal aortic aneurysm with a diameter of 3.0 to 4.5 cm should be followed with serial ultrasound examinations

at least annually, whereas an aneurysm with a diameter >4.5 cm warrants consultation with a vascular surgeon

Transesophageal echocardiography is the preferred ultrasound modality to evaluate for thoracic aortic dissection, but the sensitiv-ity and specificity of transthoracic ultrasound imaging of thoracic aortic dissection is less well established Estimates of sensitivity of trans-thoracic ultrasound to diagnose thoracic aortic dissection ranges from 67% to 80%.10,11 The presence of an undulating intimal flap portends

a very high specificity, approaching 100%.Pathologic Findings

ABDOMINAL AORTIC ANEURYSM

A distal abdominal aortic aneurysm is shown

in transverse and longitudinal planes where it

A

Right and left common iliac arteries

B

Figure 22.3 A, Transducer position for transverse views of the distal abdominal aorta B, Distal aorta in a

transverse plane showing division into the right and left common iliac arteries.

Figure 22.4 A, Transducer position for longitudinal views of the proximal abdominal aorta B, Proximal aorta

is seen in a longitudinal plane branching into the celiac artery and superior mesenteric artery (SMA) The splenic vein is seen in cross section as is crosses over the SMA.

Spleen

Aorta

Figure 22.5 Longitudinal view of the abdominal aorta as typically seen when imaging from the left flank.

B

Figure 22.6 Distal abdominal aortic

aneurysm seen in transverse (A) and

longitudinal (B) planes.

22.6 and Videos 22.5 and 22.6) An

abdomi-nal aortic dissection is shown in transverse

and longitudinal planes exhibiting an intimal

Color flow Doppler ultrasound can be used to evaluate a suspected intimal flap (Videos 22.9 and 22.10)

22—ABDOMINAL AORTA 173

Figure 22.7 An abdominal aortic

dissec-tion with an intimal flap (arrow) is seen in transverse (A) and longitudinal (B) planes.

A

B

PEARLS AND PITFALLS

• Aorta obscured by bowel gas: This effect

can be mitigated by exerting a firm,

con-stant pressure while rocking the

trans-ducer to displace loops of bowel with

gas In most cases, a few firm sweeps

will displace the loops of bowel and

permit ultrasound waves to penetrate to

the aorta

• Aorta mistaken for adjacent

struc-tures: The aorta can be confused with

vertebral bodies, para-aortic lymph

nodes, or inferior vena cava The aorta

should have pulsatile flow, which may be

confirmed by using Doppler ultrasound

Most nearby structures, except the

inferior vena cava, will not display flow

by Doppler The inferior vena cava may

be differentiated from the aorta by its

thin walls, position on the right side of

the vertebral bodies, presence of

respi-rophasic variation, and identification of

the celiac trunk and superior mesenteric artery arising from the aorta

• Underestimation of aortic diameter: This

is more likely to occur in the presence

of a mural thrombus, which can be confused with surrounding tissue To avoid this error, it is important to take the most conservative estimates of aortic diameter by always measuring from the outermost portion of the walls

• The “cylinder tangent” effect12: Diametric measurements taken across a cylinder are accurate only if they cross the center

of the cylinder (see Figure 18.5) Any other measurement between the edges can underestimate or overestimate the diameter if a measurement is obtained

in an oblique plane In order to increase accuracy, the diameter should always be measured in an axial plane, where the cross section of the aorta should appear

as a circle

Case Presentation

A 70-year-old man with a history of hypertension, hyperlipidemia, nephrolithiasis, and smoking presents with left-sided flank pain He reports having “more kidney stones than I can remember” and states the left-sided flank pain is typical of his past episodes of ureterolithiasis His vital signs are remarkable for elevated blood pressure His physical exam is limited by body habitus but reveals mild tenderness to palpation of his abdomen with no costovertebral angle tenderness Urinalysis and white blood cell count are normal Your primary differential diagnosis includes ureterolithiasis and abdominal aortic aneurysm.

Case Resolution

Pain and blood pressure control were initial priorities to minimize rupture risk of the aneurysm His pain subsided, and he was admitted for definitive management of his abdominal aortic aneurysm, including vascular surgery consultation.

Bedside detection of an abdominal aortic aneurysm with ultrasound can be lifesaving, especially when patients present with nonspecific flank or back pain Providers with limited training can perform

an ultrasound exam of the aorta with high accuracy The aortic diameter is normally 3 cm and should be measured in long and short axes..

A

B Figure 22.8 Abdominal aortic aneurysm (5.0 cm) seen in transverse (A) and

longitudinal (B) planes.

4—ABDOMEN AND PELVIS

173.e2

Figure 22.9 Measurement of the anteroposterior dimension

of the abdominal aorta from a transverse (short-axis) view that measures 3 cm.

Case 2

Case Presentation

A 75-year-old man is brought to the emergency department moaning in pain and pointing to his per abdomen and chest History is limited because he is non-English speaking and it is unclear what language he speaks He is hypotensive (BP 70/40) and tachycardic (pulse 115) He is diffusely tender to palpation over his abdomen with guarding.

up-Ultrasound Findings

A rapid bedside ultrasound exam is performed He is unable to stay still for the exam, but based on ited images, his abdominal aorta is not grossly dilated ( Figure 22.9 ); however, tissue flap pulsating in the aorta is identified on a zoomed image (Video 22.12 ) A focused cardiac ultrasound exam is performed due to his hypotension The parasternal long-axis view reveals a dilated ascending aorta and pericar- dial effusion ( Figure 22.10 and Video 22.13 ) The subcostal 4-chamber view confirms an acute, large pericardial effusion with diastolic right ventricular collapse—signs of cardiac tamponade (Video 22.14 ).

lim-Case Resolution

The patient is diagnosed with a thoracic aortic aneurysm complicated by dissection extending to the abdominal aorta Vascular and cardiothoracic surgery are emergently consulted while the patient re- ceives ongoing fluid resuscitation for impending tamponade A bedside transesophageal echocardio- gram confirmed presence of an ascending thoracic aortic aneurysm with dissection extending to the abdominal aorta The patient was taken emergently to the operating room for a lifesaving Bentall repair

of his aortic arch and aortic valve The patient was eventually discharged home after a lengthy erative hospitalization.

postop-Aortic dissection is visualized as a flap across the lumen and may occur with or without aneurysmal dilation Color flow Doppler can help confirm an aortic dissection by identifying the true and false lumens, and can help differentiate a dissection flap from mural thrombus Proximal and distal extension of an abdominal aortic dissection may be detectable with bedside ultrasound before obtaining additional imaging.

1 Hirsch AT, Haskal ZJ, et al ACC/AHA 2005 practice guidelines for the management of patients with peripheral arterial disease (lower extremity, renal, mesenteric, and abdominal aortic): a collaborative report from the American Association for Vascular Surgery/Society for Vascular Surgery, Society for Cardiovascular Angiography and Interventions, Society for Vascular Medicine and Biology, Society of Interventional Radiology, and the ACC/AHA Task Force on Practice Guidelines (Writing Committee

to develop guidelines for the management of patients with peripheral arterial disease): endorsed by the American Association of Cardiovascular and Pulmonary Rehabilitation; National Heart, Lung, and Blood Institute; Society for Vascular Nursing; TransAtlantic Inter-Society Consensus; and Vascular

Disease Foundation Circulation 2006;113(11):e463–e654.

2 Heikkinen M, Salenius J, et al The fate of AAA patients referred electively to vascular surgical unit

Scand J Surg 2002;91(4):345–352

3 Bengtsson H, Bergqvist D, et al Increasing prevalence of abdominal aortic aneurysms A necropsy

study Eur J Surg 1992;158(1):19–23.

4 Bengtsson H, Sonesson B, et al Incidence and prevalence of abdominal aortic aneurysms, estimated by

necropsy studies and population screening by ultrasound Ann N Y Acad Sci 1996;800:1–24.

5 U.S Preventive Services Task Force Screening for abdominal aortic aneurysm: recommendation

state-ment Ann Intern Med 2005;142(3):198–202.

6 Tayal VS, Graf CD, et al Prospective study of accuracy and outcome of emergency ultrasound for

abdominal aortic aneurysm over two years Acad Emerg Med 2003;10(8):867–871.

7 Costantino TG, Bruno EC, et al Accuracy of emergency medicine ultrasound in the evaluation of

abdominal aortic aneurysm J Emerg Med 2005;29(4):455–460.

8 Knaut AL, Kendall JL, et al Ultrasonographic measurement of aortic diameter by emergency

physi-cians approximates results obtained by computed tomography J Emerg Med 2005;28(2):119–126.

9 Johnston KW, Rutherford RB, et al Suggested standards for reporting on arterial aneurysms mittee on Reporting Standards for Arterial Aneurysms, Ad Hoc Committee on Reporting Standards, Society for Vascular Surgery and North American Chapter, International Society for Cardiovascular

Subcom-Surgery J Vasc Surg 1991;13(3):452–458.

10 Roudaut RP, Billes MA, et al Accuracy of M-mode and two-dimensional echocardiography in the

diagnosis of aortic dissection: an experience with 128 cases Clin Cardiol 1988;11(8):553–562.

11 Khandheria BK, Tajik AJ, et al Aortic dissection: review of value and limitations of two-dimensional

echocardiography in a six-year experience J Am Soc Echocardiogr 1989;2(1):17–24.

12 Reardon RF, Plummer D, et al Chapter 7 Abdominal aortic aneurysm In: Blaivas MO, Mateer JR, eds

Emergency Ultrasound 2nd ed New York: McGraw-Hill; 2008 http://www.accessemergencymedicine com/content.aspx?aID=107155 Accessed 20.02.13

Figure 22.10 Measurement of the diameter of the ascending

thoracic aorta from a parasternal long-axis view is 4.3 cm.

The gravitationally dependent anatomic

loca-tions where peritoneal fluid preferentially

accumulates have been recognized for over

a century.1–3 It has been known that physical

examination of the abdomen has low

sensitiv-ity for diagnosing intra-abdominal

patholo-gies.4–8 Providers can use ultrasound to detect

peritoneal free fluid and guide procedures like

paracentesis Collections of peritoneal free fluid

appear black, or anechoic, on ultrasound

imag-ing Although ultrasound is sensitive to detect

small amounts of peritoneal free fluid, it cannot

accurately differentiate types of peritoneal free

fluid Therefore, historical clues, such as recent

trauma or surgery and presence of preexisting

medical conditions, must be considered when

interpreting positive findings The minimum

amount of fluid in the peritoneal cavity

detect-able by ultrasound will vary depending on

several factors: patient positioning, etiology of

fluid accumulation, elapsed time from onset

of fluid accumulation, body habitus, quality

of the images, and provider skill level.9–13 A

range of 100–620 mL has been reported as the

minimum amount of intraperitoneal free fluid

detectable by ultrasound.14

Etiologies of peritoneal free fluid can be

divided into traumatic and nontraumatic

causes In trauma patients, the presence of

peritoneal free fluid is a surrogate marker for

solid organ injury Hemoperitoneum from

blunt trauma most commonly originates in the upper abdomen from injury to the spleen and liver.15 The hepatorenal recess is the most sensitive single area for hemoperitoneum sec-ondary to blunt trauma.16 Nontraumatic etiol-ogies of peritoneal free fluid include emergent causes, such as ruptured ectopic pregnancy, and nonemergent causes, such as chronic asci-tes due to cirrhosis

When used for procedural guidance, sound can guide site selection to perform a diagnostic or therapeutic paracentesis Ultra-sound guidance for paracentesis has been shown to improve procedural success rates and decrease complications, hospital costs, and length of stay.17,18

ultra-Normal AnatomyDetection of peritoneal fluid by ultrasound requires an understanding of the anatomic spaces where peritoneal free fluid accumulates The peritoneal cavity is subdivided into greater and lesser peritoneal sacs The greater peritoneal sac is further divided into supracolic and infra-colic compartments by the transverse mesocolon Pathologic fluid can pass between the supracolic and infracolic compartments via the paracolic gutters, the peritoneal spaces lateral to the ascend-ing and descending colon In a supine position gravity causes fluid in the upper abdomen to flow from the left upper quadrant and right para-colic gutter into the right upper quadrant In an

K E Y P O I N T S

• Focused abdominal ultrasonography is a sensitive and reliable bedside technique to detect intraperitoneal free fluid, although it cannot differentiate specific types of fluid

• Ultrasound improves the success rate and reduces complications related to paracentesis

• Ultrasound is the diagnostic modality of choice for the initial screening of unstable blunt trauma patients for peritoneal free fluid

flow into the pelvis.

In the upright and supine positions, the

most gravitationally dependent area of the

com-bined abdominopelvic peritoneal space is the

pelvis, specifically caudal to the sacral

promon-tory In the abdominal peritoneal space alone,

the hepatorenal recess, or Morison’s pouch, is

the most gravitationally dependent area above

the pelvic inlet If the source of fluid is above

the pelvic inlet and fluid accumulation begins

in a supine position, fluid gravitates toward the

hepatorenal recess for three reasons First, the

hepatorenal peritoneal reflection is more

poste-rior relative to other abdominal structures

Sec-ond, the lordotic curvature of the lumbar spine

and anterior location of the sacral promontory

relative to the hepatorenal recess prevents free

phrenicocolic ligament, a peritoneal reflection

in the left upper quadrant, shunts blood from the left upper quadrant toward the hepatorenal recess in the right upper quadrant.19 However,

if a patient has been upright for a significant amount of time, the pathologic fluid will pool

in the more dependent pelvis regardless of the site of origin

Image Acquisition

A low-frequency curvilinear or array transducer is needed to examine the abdomen and pelvis with ultrasound Three areas must be evaluated to detect peritoneal free fluid: right upper quadrant, left upper quadrant, and pelvis (Figure 23.1) The liver,

Spleen Kidney Lung Diaphragm

phragmatic space Splenorenal recess

Prostate Rectovesicular space

Female

Liver

Right Upper Quadrant Hepatorenalrecess

Kidney

Diaphragm

Kidney Spleen Diaphragm

Prostate Male Pelvis

Bladder Rectovesicular

space Uterus

Female Pelvis

Bladder Rectouterine

space

Figure 23.1 Transducer positions for detection of peritoneal free fluid A, Right upper quadrant window

Visualize the right subdiaphragmatic space, hepatorenal recess (Morison pouch, the most sensitive recess for upper abdominal free fluid), and the right paracolic gutter B, Left upper quadrant window Visualize the left subdiaphragmatic space (the most important area in the left upper quadrant), splenorenal space, and left paracolic gutter C and D, Pelvic window Visualize the rectouterine space in females (C) and the rectove- sicular space in males (D).

4—ABDOMEN AND PELVIS

176

spleen, and urine-filled bladder serve as the

major acoustic windows to evaluate the right

upper quadrant, left upper quadrant, and

pelvis, respectively An empty or ruptured

bladder, subcutaneous emphysema, bowel or

stomach gas, wound dressings, and asplenia

can reduce the sensitivity of ultrasound to

detect intraperitoneal free fluid from these

windows

RIGHT UPPER QUADRANT

In the right upper quadrant, three spaces

should be visualized: below the diaphragm,

between the liver and kidney, and the inferior

pole of the right kidney in the right

para-colic gutter Place the transducer in a coronal

plane in the midaxillary line between the 9th

and 11th intercostal spaces with the

trans-ducer marker pointing cephalad (Figure 23.2)

Adjust the transducer position and angle to

visualize the right upper quadrant,

focus-ing on the potential space between the liver

and kidney (hepatorenal recess, or Morison’s

pouch) (Figure 23.3) Fan the transducer from anterior to posterior through the entire hepa-torenal recess to visualize the inferior tip of the liver, looking for free fluid The inferior pole

of the right kidney should be visualized along with the right paracolic gutter Angle the transducer superiorly to image the right sub-diaphragmatic space Figure 23.4 and Video 23.1 demonstrate free fluid in the right upper quadrant

LEFT UPPER QUADRANT

In the left upper quadrant, three spaces should

be visualized: below the diaphragm in the parasplenic space, between the spleen and left kidney, and the inferior pole of the left kidney with the left paracolic gutter In contrast to the right upper quadrant, the left upper quad-rant is best visualized with the transducer in

a more posterior and superior position due to the location and size of the spleen Place the transducer in a coronal plane on the posterior axillary line between the 6th and 9th intercostal

Figure 23.2 In the right upper

quadrant, the transducer should be

placed in a coronal scanning plane

in the midaxillary line between the

9th and 11th ribs with the transducer

marker pointed cephalad and rotated

slightly posteriorly.

Liver

Free fluidFree fluid

StomachSpleen

KidneyKidney

Peritoneum

Hepatorenal

perisplenic space

Figure 23.3 Transverse cross section of the abdominal cavity Peritoneal free fluid accumulates in the

hepa-torenal recess (Morison's pouch) and perisplenic space.

spaces with the transducer marker pointing

cephalad (Figure 23.5) The image may be

improved by rotating the transducer 10-20

degrees clockwise with the transducer marker

pointing slightly posteriorly If repositioning

is possible, the patient can be placed in a right

lateral decubitus position to allow more

poste-rior access to the splenic window Evaluate the

left subdiaphragmatic and splenorenal spaces

for any signs of free fluid (Figure 23.6 and

Video 23.2) Similar to the right upper

quad-rant, fan the transducer through the

spleno-renal space from anterior to posterior The

inferior poles of the kidney and spleen should

be visualized along with the superior portion

of the left paracolic gutter

PELVIS

Peritoneal free fluid in the pelvis accumulates in

the rectovesicular space in men and the

recto-uterine space, or pouch of Douglas, in women

(Figure 23.7) To image the pelvic space, place

the transducer in a transverse plane just

supe-rior to the pubic symphysis with the transducer

Figure 23.4 A, Normal right upper quadrant B, Peritoneal free fluid in the hepatorenal recess in a patient

after blunt trauma.

Figure 23.5 In the left upper

quadrant, the transducer should be placed in a coronal scanning plane

on the posterior axillary line between the 6th and 9th ribs with the trans- ducer marker pointed cephalad and slightly posteriorly.

A

Kidney Spleen

Diaphragm

Blood

Left upper quadrant

Figure 23.6 A, Normal left upper quadrant

B, Peritoneal free fluid in the subdiaphragmatic space in the left upper quadrant.

4—ABDOMEN AND PELVIS

178

marker pointed toward the patient's right (

Fig-ure 23.8) Fan the transducer inferiorly into the

pelvis until the bladder is visualized Set the

imaging depth to view the bladder in the top

one-third to one-half of the screen Posterior

acoustic enhancement should be appreciated posterior to the bladder It is important to fan the transducer to visualize the entire bladder from fundus to neck to thoroughly evaluate the rectovesicular or rectouterine spaces for a free

Bladder

Pubicsymphysis

Uterus

Rectouterine space(pouch of

Douglas)RectumVagina

Vesicouterine

pouch

B

Figure 23.7 A, In males, pelvic free fluid accumulates in the rectovesicular space B, In females, pelvic free

fluid accumulates in the rectouterine space (pouch of Douglas).

Figure 23.8 The transducer should

be placed just above the pubic

sym-physis and angled slightly inferiorly to

image the male and female pelvis.

fluid collection (Figure 23.9 and Videos 23.3

and 23.4) Rotate the transducer 90 degrees

clockwise to obtain sagittal views of the bladder

and scan the entire bladder from left to right If

the bladder has been decompressed using a

uri-nary catheter, the bladder can be refilled with

while clamping the catheter distally to prevent drainage If the patient does not have a urinary catheter in place, a temporary catheter can be placed to inflate the bladder with saline.Image InterpretationThe peritoneum is a serous membrane com-posed of parietal and visceral layers The peri-toneal space normally contains a trace amount

of physiologic fluid that allows sliding of internal organs Excessive fluid accumulates

in pathologic states, and the patient's position, source of pathologic fluid, duration of fluid accumulation, and anatomic variability deter-mine where peritoneal free fluid will be detect-able by ultrasound

Free fluid in the peritoneal space collects

in gravitationally dependent areas and appears anechoic, or black Generally, all types of free fluid, including ascites, blood, bile, lymph, and urine, appear black Clotted blood and loculated fluid, especially pus, appear more echogenic due to higher protein content Solid debris from a ruptured hollow viscus appears heterogeneously echogenic

The liver and spleen have similar anatomic architecture and contain a large amount of blood The structure of these organs creates a homo-geneous sonographic appearance of the paren-chyma Changes in the sonographic appearance

of hepatic and splenic parenchyma following trauma vary and are subtle Since injured tissue within the liver and spleen are poorly visualized, presence of peritoneal free fluid is used as a sur-rogate marker for solid organ injury

The hepatorenal recess is the most tive location to detect peritoneal free fluid

sensi-in supsensi-ine patients when the source is sensi-in the upper abdomen.16 In the left upper quadrant, free fluid initially accumulates in the sub-diaphragmatic space, while in the right upper quadrant, fluid initially accumulates in the hepatorenal recess.19 In the absence of any anatomic obstruction, fluid in the perisplenic space eventually flows into the more dependent hepatorenal recess in the right upper quadrant Free fluid superior to the diaphragm may be

a pleural effusion or hemothorax If a mirror image of the spleen or liver is seen across the diaphragm, free fluid in the pleural space can

be ruled out (See Section 2, Lungs and Pleura, for additional information.)

Normally, there is no visible peritoneal free fluid in the abdominopelvic cavity in males

Figure 23.9 Normal (A) and abnormal (B) male

pelvis with free fluid collecting in the rectovesicular

space Normal (C) and abnormal (D) female pelvis

with free fluid collecting in the rectouterine space

(pouch of Douglas).

4—ABDOMEN AND PELVIS

180

In females, a small amount of physiologic fluid

may be present in the pelvis More than a small

amount of pelvic free fluid in females should be

considered abnormal and the source should be

investigated The urgency to evaluate free fluid

in the female pelvis depends on the patient's

stability and clinical situation

As fluid accumulates in the abdomen,

loops of small bowel begin to float freely and

are seen tethered posteriorly by the

mesen-tery The peritoneal space can fill with

sev-eral liters of fluid, which is accompanied by

progressive distention of the abdomen If

the peritoneal fluid is not removed,

intra-abdominal pressure will increase, causing

reduced diaphragmatic excursion and

poten-tially causing abdominal compartment

syn-drome (Figure 23.10)

Pathologic Findings

HEMOPERITONEUM

The focused assessment with sonography in

trauma (FAST) examination has evolved to

become the standard screening tool for

unsta-ble patients with blunt abdominal trauma (see

Chapter 41, Trauma) The most sensitive

loca-tions to detect small amounts of blood are the

hepatorenal recess in the right upper

quad-rant, subdiaphragmatic space in the left upper

quadrant, and rectovesicular or rectouterine

space in the pelvis The minimum amount of

free fluid that ultrasound can detect depends

on multiple factors but ranges from 100 to

620 mL.14 It is important to thoroughly

visu-alize the inferior tips of the liver, spleen, and

left kidney, where small amounts of fluid will

collect

ASCITES

Ascites is the most common complication of rhosis leading to hospital admission,20 and devel-opment of ascites is an important landmark in the natural history of cirrhosis, with 1- and 5-year mortality rates of 15% and 44%, respectively Ultrasound can differentiate gaseous abdominal distention from ascites and can guide diagnostic

cir-or therapeutic aspiration of ascites Large umes of ascites are often seen in addition to a small, fibrotic liver (Video 23.5)

vol-Other PathologiesThe vast majority of nontraumatic peritoneal free fluid collections are ascites due to cirrho-sis Other causes include congestive heart fail-ure, renal failure, and pancreatitis In females, pathologic conditions related to the ovaries are an important cause of peritoneal free fluid accumulation A positive pregnancy test in the absence of an identifiable intrauterine preg-nancy should be considered an ectopic preg-nancy until proven otherwise In this situation, free fluid present in the peritoneal space should raise significant suspicion for an ectopic preg-nancy Other sex-specific causes of peritoneal free fluid include ruptured hemorrhagic ovar-ian cysts and ovarian malignancies Malignant ascites can occur with multiple cancers in both sexes Less common causes of peritoneal free fluid include portal vein, hepatic vein, and infe-rior vena caval thrombosis

ParacentesisUltrasound guidance has proven to reduce com-plications and improve procedural success when performing paracentesis.17,18 Paracentesis is most often performed for diagnostic evaluation of new ascites or evaluation of new symptoms in patients with a history of ascites, and paracentesis can be performed for therapeutic relief of abdominal distention Before paracentesis, emptying the bladder by spontaneous voiding or placement

of a urinary catheter can prevent bladder injury Place the patient in a supine position with the head of the bed elevated 30 to 45 degrees to pool ascites in bilateral lower quadrants

Using a low-frequency curvilinear or phased-array transducer, scan the lower quad-rants of the abdomen in a longitudinal plane with the transducer marker oriented cephalad Scan lateral to the rectus abdominis muscles to localize the largest collection of peritoneal free

Ascites

Figure 23.10 Large amount of peritoneal free fluid

(ascites) with floating loops of small bowel tethered

by the mesentery.

fluid Site selection is ideally on the

antero-lateral abdominal wall, antero-lateral to the rectus

abdominis muscles but anterior to the thicker

lateral abdominal wall muscles (Figure 23.11)

If no free fluid is seen in the lateral lower

quad-rants, scan the most gravitationally

depen-dent areas of the abdominopelvic cavity in

the right and left upper quadrants and pelvis

as described above If only a scant amount of

fluid is seen in the gravitationally dependent

areas, paracentesis cannot be performed safely

When only a small amount of fluid is seen in

the lower quadrants of the abdomen, the risks

versus benefits of attempting paracentesis must

be weighed Thickness of the abdominal wall,

size and depth of fluid collection, and

proxim-ity to small bowel or other structures should be

carefully considered to guide decisions about

whether to attempt paracentesis, along with

site and needle selection Video 23.6

demon-strates a small amount of ascites with several

nearby loops of small bowel, a site where

para-centesis should not be performed

The abdominal wall has several superficial

and deep blood vessels that should be avoided

during paracentesis The inferior epigastric,

sub-costal, circumflex iliac arteries and veins, and

tho-racoepigastric veins are the major blood vessels

in the abdominal wall (Figure 23.12) Selecting

an insertion site lateral to the rectus abdominis

muscles should avoid the inferior epigastric sels in most patients, although the exact location, size, and branching of the inferior epigastric ves-sels varies in patients Other major vessels can be identified by evaluating the needle insertion site with a high-frequency linear transducer using color flow or power Doppler ultrasound (Video 23.7) If blood vessels are detected at the insertion site, slide the transducer a few centimeters away

ves-to select a site without any visible large vessels,

or consider performing the procedure using time ultrasound guidance to avoid the vessels.Real-time ultrasound guidance allows visu-alization of the needle traversing the soft tissues and entering the peritoneal cavity Tracking the needle tip in real time can help avoid punctur-ing large superficial blood vessels or bowel or inserting the needle too deep into the peritoneal cavity To perform paracentesis under real-time ultrasound guidance, cover the transducer with

real-a sterile shereal-ath real-and plreal-ace it in the sterile field

A transverse (out-of-plane) or longitudinal plane) approach can be used to guide the needle under direct visualization Anesthetize the skin and subcutaneous tract to the peritoneum under direct visualization to ensure that you have anesthetized the peritoneum Similarly, a large-bore needle or needle-catheter can be visualized entering the peritoneal cavity, and a diagnostic

(in-or therapeutic drainage can be perf(in-ormed

RectusabdominisLinea albaInferiorepigastricartery andveinsMuscular

aponeuroses

Thoracoabdominal

nerve, artery, and

veinExternal oblique

muscle

Transversus

abdominis muscle

Internaloblique muscle Endoabdominalfascia

Peritoneum

Figure 23.11 Transverse cross section of the abdomen showing the ideal window for paracentesis Note

the blood vessels in the anterior abdominal wall (inferior epigastric vessels) and lateral abdominal wall (thoraco-abdominal vessels) should be avoided The lateral abdominal walls, or flanks, are not preferred due to greater adipose tissue and musculature The avascular linea alba in the midline of the abdomen is an alternate site but the bladder must be decompressed before using this site for paracentesis.

4—ABDOMEN AND PELVIS

182

Internal thoracicartery and veinSuperiorepigastricartery and vein

Superficial

epigastric artery

and vein

Inferior epigastricartery and vein

Musculophrenicartery and vein

Deep circumflexiliac artery andvein

Inguinal ligamentFemoralartery and vein

Lateralthoracic vein

artery and vein

Figure 23.12 Abdominal wall vascular anatomy showing the location of inferior epigastric, subcostal,

cir-cumflex iliac, and thoracoepigastric vessels that should be avoided during paracentesis.

PEARLS AND PITFALLS

• Placing the patient in Trendelenburg or

reverse Trendelenburg position helps

pool peritoneal free fluid in gravitationally

dependent areas to facilitate

identifica-tion of small volumes of fluid.13,14,21

• Any previous abdominal surgeries may

alter fluid accumulation in gravitationally

dependent areas It is important to note

any surgical scars on the abdominal wall

while performing and interpreting an

abdominal ultrasound exam

• In urgent or emergent situations, patients

may have a fluid-filled stomach that can

cause a false-positive interpretation of

free fluid by an inexperienced

sonogra-pher22 (Figure 23.13)

• If fluid surrounding the kidneys does not

track into the peritoneum, the presence of

retroperitoneal fluid from a ureteral injury

or abdominal aortic aneurysm should be

considered Ultrasound is not sensitive

for evaluating retroperitoneal structures,

and a computed tomography (CT) scan of

the abdomen should be obtained

• In the absence of pathologic adhesions, peritoneal free fluid should disperse to dependent areas and will not appear well circumscribed A working knowledge

of abdominal anatomy and ultrasound appearance will enable providers to dif-ferentiate peritoneal free fluid from other fluid-filled structures, such as renal cysts,

a fluid-filled stomach, seminal vesicles, or perinephric fat (Figure 23.14)

• Subcutaneous emphysema from open wounds or pneumothorax prevents ad-equate ultrasound imaging of underlying organs Similarly, gas in the stomach, large bowel, or small bowel prevents adequate examination of underlying peritoneal space Firm pressure and gentle angling

of the transducer can often push overlying loops of bowel aside to allow better visual-ization of underlying structures

Stomach

Diaphragm

Spleen Kidney

Figure 23.13 Left upper quadrant window showing

a fluid-filled stomach Note that the fluid does not

layer under the diaphragm, appears well contained,

and the normally round edges of the spleen appear

sharp or pointed.

quadrant Liver

Renal cyst

Kidney

Figure 23.14 Right upper quadrant renal cyst

located in the hepatorenal space that could be mistaken for free fluid.

Ultrasound Findings

A bedside ultrasound exam per the Extended Focused Assessment with Sonography in Trauma (EFAST) protocol is performed Evaluation of the right and left upper quadrants reveals a large amount of free fluid in the hepatorenal space (Video 23.8) and left subdiaphragmatic space (Video 23.9) No free fluid

is detected in the pelvis (Video 23.10).

Case Resolution

Two large-bore peripheral IV catheters are placed, and he is bolused 3 L of normal saline Transfusion

of two units of blood is started, but his blood pressure remains low He is emergently transported to the operating room for exploratory laparotomy Splenic and liver injuries are found intraoperatively.

Trauma patients can be rapidly assessed using the EFAST exam to detect peritoneal free fluid, a surrogate marker of intra-abdominal injury Supine trauma patients initially accumulate free fluid in the hepatorenal space in the right upper quadrant and subdiaphragmatic space in the left upper quadrant before the fluid descends into the pelvis.

Ultrasound Findings

A bedside ultrasound exam of both lower quadrants reveals large amount of ascites A large collection

of fluid is seen in the left lower quadrant (Video 23.11) The right lower quadrant also has a large amount

of ascites, but there is an area of scar tissue with small bowel adhered to the abdominal wall (Video 23.12) The patient reports having prior drainage of an abdominal abscess at the site of the scar tissue

in the right lower quadrant.

Bedside ultrasound can readily differentiate abdominal distention due to ascites, gas-filled loops of bowel, and adipose tissue Ultrasound to guide paracentesis has been shown to reduce complication rates and increase procedural success rates Ultrasound can identify the largest collection of ascites that is safe to drain without any loops of bowel or large blood vessels in close proximity.