Anteromedial Cervical Approach Vessel Lacerations Arterial lacerations and venous lacerations are rare, and the same treatment methods as mentioned in the chapter on lumbar vessel lacera
Trang 1reported to be superior to a staged procedure In a staged operation, the main decision must be made whether the condition of the patient will allow the opera-tion to be continued the next day This offers the advantage that the monitoring devices like pulmonary artery or peripheral artery catheters can be left in place
Single stage surgery is
generally advantageous but
in elderly patients caution
is warranted
The main problems are coagulation disorders requiring a longer period of time
between the two interventions Complication rates, costs (hospital stay) and patients’ preference are in favor of single day interventions when compared to staged procedures
Pitfalls and Salvage Strategies
Be prepared for typical
pitfalls
A knowledge of the typical pitfalls of an operation, and of strategies to cope with
them, is necessary before starting Pitfalls are either approach related or mentation related Instrumentation-related pitfalls often require special instru-ments or implants For example, unexpected pull-out of screws or hooks may require special implants which should be available (e.g., thicker screw, bigger hook, or bone cement augmentation)
Embolization
Consider preoperative
embolization for highly
vascularized tumors
Bleeding from a metastasis in the case of intralesional resection may be devastat-ing Preoperative angiographic embolization should be considered, especially in renal carcinoma and thyroid cancer
Profound Knowledge of Anatomy
This is as simple as it is obvious Nevertheless, it should be stressed that a thor-ough knowledge of the anatomy and a clear vizualization of the surrounding structures are crucial if complications are to be avoided
Patient Positioning Blood Loss
Prone position with a free
abdomen reduces blood
loss
Excessive diffuse blood loss can be prevented in posterior procedures by ade-quate positioning (see Chapter 13) of the patient prone on a Relton Hall frame
or other devices with a pendulous abdomen [70], which facilitates the draining of
the epidural vessels Excessive epidural bleeding can be minimized by:
) positioning of the patient with a hanging abdomen ) avoiding exploring the posterior surface of the vertebra (if not necessary) ) pushing aside epidural veins with the retractor before entering the disc space
) cauterization of veins which cannot be kept away [68]
Postoperative Blindness
Check the headrest to
avoid pressure on the eyes
There are numerous case reports of spinal surgeries which ended with unilateral
or bilateral visual loss [3, 65, 81, 112] The main cause is retinal artery occlusion
due to pressure on the eye globe by the headrest, ischemic optic neuropathy, and cerebral ischemia Most cases underwent posterior instrumentation with a long operation time [81] All precautions to avoid ocular compression must be taken
Trang 2Define your workflow
on perioperative changes
of evoked potentials
Paraplegia cannot be fully avoided, but any preventive measure with some
likeli-hood of reducing the incidence must be undertaken, including:
) intraoperative spinal cord monitoring [24, 108]
) thorough control of fluid volume, blood loss, and blood pressure
If evoked potentials show increasing potential latency or decreasing amplitude,
immediate reaction is required Somatosensory evoked potentials (SSEPs)
usu-ally have a delay in the response, so that a clear association with a certain
opera-Motor evoked potentials are more sensitive
tive step may not be obvious Motor evoked potentials (MEPs) are more sensitive
[90] so that reaction by either reducing correction or by removing a screw or a
hook can be done In the case of any doubt, a wake-up test is necessary If the
wake-up test indicates a neurological deficit, implant removal is required There
are no good comparative studies on the effect of implant removal after
pathologi-cal potentials and a pathologipathologi-cal wake-up test have taken place In view of the In cases with iatrogenic
neurologic deficit, complete implant removal is counter-productive if a floating spine will result
lack of clear evidence in the literature, implant removal is recommended, and
also in the light of medicolegal issues In some specific cases, however, there are
clear arguments for leaving the implants in place, for example in the case of
resec-tion of vertebra where implant removal will cause the situaresec-tion to deteriorate
Approach-Related Complications
There is some overlap in procedure and approach related complications In
gen-eral, the anterior approach (Table 5) is more prone to serious complications than
Table 5 Incidence of complications in anterior thoracolumbar surgery
Anterior
lumbar
interbody
fusion
) mortality 0.15 % 684 mini-open anterior lumbar Brau (2002) [15]
1.0 % 207 anterior thoracolumbar Oskouian (2002) [88]
) direct vascular injuries 3.4 % 207 anterior thoracolumbar Oskouian (2002) [88]
) arterial injuries 0.8 % 684 mini-open anterior lumbar Brau (2002) [15]
0.08 % 1 223 anterior fusion Faciszewski (1995) [33]
) venous injuries 0.8 % 684 mini-open anterior lumbar Brau (2002) [15]
) deep venous thrombosis 2.4 % 207 anterior thoracolumbar Oskouian (2002)
1.0 % 684 mini-open anterior lumbar Brau (2002) [15]
) retrograde ejaculation 0.1 % 684 mini-open anterior lumbar Brau (2002) [15]
1.7 % 116 male retroperitoneal Sasso (2003) [99]
13.3 % 30 male transperitoneal Sasso (2003) [99]
17.5 % 40 male transabdominal Tiusanen (1995) ) ileus > 3 days 0.6 % 684 mini-open anterior lumbar Brau (2002) [15]
) superficial infection 1.0 % 1 223 anterior fusion Faciszewski (1995) [33]
) deep infection 0.6 % 1 223 anterior fusion Faciszewski (1995) [33]
Anterior
spinal
deformity
surgery
) pulmonary complications 4.9 % (2.2 %) 447 miscellaneous, deformities McDonnell [77]
) related to chest tube 1.8 % (2.7 %) 447 miscellaneous, deformities McDonnell [77]
) gastroenterological 1.1 % (2.9 %) 447 miscellaneous, deformities McDonnell [77]
) related to wound 1.1 % (2.7 %) 447 miscellaneous, deformities McDonnell [77]
) hematological 0.9 % (0.2 %) 447 miscellaneous, deformities McDonnell [77]
) operative 0.7 % (1.1 %) 447 miscellaneous, deformities McDonnell [77]
) neurological 0.7 % (1.8 %) 447 miscellaneous, deformities McDonnell [77]
) genitourinary 0.4 % (11.6 %) 447 miscellaneous, deformities McDonnell [77]
) cardiac 0.4 % (0.9 %) 447 miscellaneous, deformities McDonnell [77]
Note: When two rates are quoted, the first refers to major, and the second (in brackets) to minor, complications
Trang 3the posterior one, and some occur more often in the lumbar spine, others in the cervical spine For the purpose of this chapter, the complications are described where they occur most frequently
Anteromedial Cervical Approach Vessel Lacerations
Arterial lacerations and venous lacerations are rare, and the same treatment methods as mentioned in the chapter on lumbar vessel laceration can be applied The internal jugular vein may be ligated unilaterally Thrombosis of the internal jugular vein frequently occurs associated with hemodialysis catheters, and with-out important sequelae [116] Vertebral artery injury occurs in 0.3 – 0.5 % of ante-romedial interventions, especially in:
) complete corpectomy with resection of the lateral vertebral wall ) injuries by a burr
) lateral placement of an instrument ) excessive lateral disc removal ) intraoperative loss of the midline landmarks
An anomalous medial course of the artery is described and was found in an ana-tomic study in 2.7 % of patients Therefore, preoperative imaging is mandatory [61]
Superior Laryngeal Nerve Lesion
The superior laryngeal nerve (SLN) originates from the middle of the nodose ganglion of the vagus nerve and divides after an average of 15 mm into an inter-nal and exterinter-nal branch Caution is extremely important if the contralateral side
was operated on for thyroid surgery or neck surgery, or was irradiated A
bilat-eral lesion interrupts the afferent part of the cough reflex and can cause life-threatening aspiration [78] The external branch (ESLN) courses distally poste-rior to the supeposte-rior thyroid artery, and innervates the cricothyroid muscle, which
is responsible for regulating the tension of the vocal cords by rotating the cricoid cartilage A lesion causes slight hoarseness, voice fatigue, loss of high tonalities, and decrease in voice volume Therefore, prudence is particularly indicated in singers, teachers and professional speakers Treatment is not possible Caution is necessary in any cervical spine operation rostral to C4 [60]
Recurrent Laryngeal Nerve Lesion
Check larynx function
in case of previous surgery
or radiation
In a study of 328 cases of anterior cervical spine surgeries, incidence of a lesion was 2.7 %, and lesions occurred with the same rate in right and left sided approaches [10] The main symptom of a unilateral lesion is hoarseness A bilat-eral lesion can cause severe problems to breath, but is assumed to be extremely rare in cervical spine surgery Continuous laryngeal nerve integrity monitoring did not decrease recurrent laryngeal nerve (RLN) complications in non-random-ized controlled studies regarding thyroidectomy Many false negative cases occurred during monitoring [97, 121] Spontaneous recovery occurs in about one-third of cases In the case of previous surgery on the contralateral side, in neurological disorders or after irradiation, preoperative laryngoscopy is neces-sary to avoid a bilateral lesion
Trang 4Hypoglossal Nerve Lesion
The hypoglossal nerve can be damaged in anterior approaches to the upper
cer-vical spine, and C1/C2 Magerl screws (Case Study 1) penetrating the anterior
cor-tex of the atlas A lesion causes tongue deviation to the ipsilateral side Treatment
is not possible but spontaneous recovery is frequent
Case Study 1
A 79-year-old female presented with severe neck pain 5 months after a fall The radiologic assessment (a) revealed a
dense non-union Non-operative measures failed and surgery was indicated based on a very painful atlantoaxial
instabil-ity A posterior atlantoaxial screw fixation was done with a 5-cm incision at the C1/2 level and a percutaneous screw
insertion under biplanar image intensifier control The skin entry points for the transarticular screws were at the level of
T2/3 and the screw trajectory could not be angled more steeply because of the upper thoracic kyphosis with
compensa-tory cervical hyperlordosis The screw placement and Gallie fusion with a titanium cerclage were carried out uneventfully
(b,c) The patient recovered from the surgery without any obvious neurological deficit However, on the second
postop-erative day, a deviation of the tongue was noticed A thorough neurological examination was otherwise unremarkable.
An MRI scan was done to rule out any central lesion or bleeding The T2-weighted MRI scan (d) demonstrated a
perfora-tion of the anterior cortex which was done intenperfora-tionally to increase screw purchase in an osteopenic bone However, the
screw had irritated the hypoglosseus nerve which runs in front of the axis The tongue deviation recovered
spontane-ously This case indicates that the anterior cortex should not be perforated with transarticular screws.
Trang 5Anterior Approach to the Cervicothoracic Junction
Lesions to the RLN and Horner’s syndrome are described in some case reports Lesions of large vessels can occur and care must be taken that the surgery can cope with this potentially life-threatening complication [13] The availability of a vascular surgeon should be clarified preoperatively
Thoracotomy Lung Lacerations
A laceration of the lung can be created during blunt dissection of pleural adhe-sions or by direct trauma with an instrument Air will exit and can be made visi-ble by irrigation fluid Treatment includes local closure of the leak and a chest
Suturing the lung is not
easy because the suture
tends to cut out
tube The pleura can be sutured using a 4/0 continuous suture, or synthetic mate-rial (Table 6) Fibrin sealant can be injected afterwards to make the lesion air-tight In order to avoid sutures cutting through the lung tissue, the suture has to
be placed with a perpendicular, grasping a larger piece of lung tissue to avoid cut-ting out
Table 6 Synthetic hemostatic materials
FloSeal Baxter bovine derived gelatine and
thrombin with mixing acces-sories and syringe
when control of bleeding by liga-ture is ineffective
epidural bleeding, lung lacera-tion
TachoSil Nycomed collagen sponge coated with
human fibrinogen and throm-bin
for supportive treatment of hemo-stasis where standard techniques are insufficient
pleural defects
Gelfoam Pfizer water-insoluble porous
prod-uct from purified pork skin gelatine Hemostatic mecha-nism not fully understood
as a hemostatic device, when other procedures are either ineffective or impractical
Avitene Davol Inc.,
Cranston,
RI, USA
a microfibrillar collagen product
apply pressure with a dry sponge.
the period of time may range from
a minute for capillary bleeding to
3 – 5 min for brisk bleeding or arte-rial leaks
in neurosurgery apply with a moist sponge For control of oozing from bone, it should be firmly packed into the spongy bone surface
Note: Extended indications are not quoted here! The product description of the company has been shortened For full details see the company description!
Use two chest tubes in case
of a hematopneumothorax
In the case of broad pleura adhesions, a large area of the pleura can be destroyed This area can be covered with Tachosil (Table 6) Air exiting from alveoli will not cause a problem It can be drained by the chest tube, and the lung will heal Air exiting from bronchi requires closure of the leak This is beyond the scope of an orthopedic surgeon, and a thoracic surgeon must be involved In any case, a chest tube has to be placed where the air is expected to accumulate, usually anterior to the lungs, if the patient is lying in the supine position
Lacerations of the Thoracic Vessels
Do not try to repair pulmonary artery lesions –
compress them until help
arrives!
The azygos or the hemiazygos veins are most likely to be injured, and can be ligated, as well as the segmental vessels The risk of anterior spinal artery syn-drome increases with bilateral ligation of segmental arteries If this is planned, clamping and neuromonitoring is required The aorta can be sutured as
Trang 6described below A lesion of a pulmonary artery requires the most experienced
thoracic/vascular surgeon available
Pneumothorax
A trocar guided chest tube insertion is dangerous
If air in the thorax is detected postoperatively, a chest tube is placed with local
anesthesia A trocar guided chest tube insertion is regarded as dangerous We
prefer a direct tube insertion after mini-thoracotomy (3 – 4 cm incision) In the
supine position, the drain must be beneath the anterior chest wall Tension
pneu-mothorax may occur, if not drained Findings are respiratory distress, tachypnea,
unilaterally decreased or absent respiration, tachycardia, and hypotension as the
key signs of tension pneumothorax
Hematothorax
Place the chest tube anteriorly to drain air and posteriorly to drain blood
If bleeding is expected, a chest tube has to be placed where blood is likely to
accu-mulate, usually lateral to the spine and posterior in a patient lying in the supine
position The chest tube will be removed after criteria established by the
depart-ment Some surgeons remove the tube after 24 h, others, if less than 200 ml per
day is collected There is no evidence in the literature on the best way If more
than 600 ml blood per hour is lost, revision thoracotomy must be considered If
hematothorax occurs after chest tube removal, ultrasound guided puncture may
be sufficient for minor bleedings
Chylothorax
Postoperative chylothorax
is treated by parenteral nutrition and chest tube
The chyle in the thoracic duct is a milky fluid In anterior approaches to the
tho-racic spine, especially in trauma or deformities, the thotho-racic duct may be injured
Ligation is possible, but the vessel is usually hard to find Therefore, it is better to
cover the area, where the leak is suspected, with synthetic material, e.g., Tachosil
(Table 6) A chest tube has to be placed posteriorly The loss of chyle may be
con-siderable and can range up to 6 L/day (average production is 40 ml/kg body
weight) Treatment is normally non-surgical with either total parenteral
nutri-tion or enteral low fat solid food or an enteral elemental diet supplemented with
intravenous lipid emulsion, until the lymph leak heals, which takes an average of
30 days Lymphocytopenia and hyponatremia are frequently seen [84]
Pleural Abscess
The stage of the disease decides the required procedure In early cases with liquid
pus, chest tube drainage is sufficient Failure to evacuate the pleural space or
per-sistent signs of infection should prompt surgical intervention by open
thoracot-omy or thoracoscopic evacuation In late cases with lung entrapment,
decortica-tion (resecdecortica-tion of the visceral pleura) may be necessary.
Insufficient Postoperative Oxygenation
Insufficient postoperative respiration can occur in patients with deformities and
severely impaired lung function, and in neuromuscular diseases such as
A thoraco-phrenico-lumbotomy decreases vital capacity by about 20 %
Duchenne’s disease An approach through the diaphragm (Hodgson approach)
causes a reduction of vital capacity of about 20 % for one year A rib hump
resec-tion may cause a decreased lung volume [71] Both measures can cause a
border-line sufficient respiration to deteriorate On the other hand, if correction does not
reduce lung volume, corrections can be performed even in patients with a vital
Trang 7capacity of less than 40 % Recently, Wazeka et al reported on deformity correc-tion in 21 patients with a mean predicted vital capacity of 32 %, who needed post-operative supplemental oxygen for 0 – 90 days Two developed pneumonia, two pleural effusions, and atelectasis was found four times There were no mortalities
or adverse neurological outcomes [115] Tracheotomy may be required if the patient is not able to breath sufficiently for days Exercises can increase the vital capacity as well In rare cases with no recovery, there is a need for a continuous oxygen supply via a transportable oxygen bottle
Thoracolumbar Approach
The same lesions as with the thoracic and lumbar anterior approaches can occur but the liver and the spleen are at risk during this approach
Liver Lesion
Repair of a bleeding liver
lesion requires a specialized
surgeon
A subcapsular hematoma does not require an intervention Open bleeding from the liver requires a specialized surgeon Postoperative suspicions should be investigated with ultrasonography
Splenic Injury
There are few case reports of accidental splenic injury during anterior spine approaches [20] especially the left sided approach to L1/L2 In other interven-tions like esophagectomy, the mortality and sepsis rate increase with splenec-tomy Therefore, preservation of the spleen should be the aim of treatment when-ever a splenic injury occurs Observation or hemostatic agents can be used for grade 1 and 2 (subcapsular hematoma < 50 % of surface) [79] Reconstruction or resection is the treatment of choice in grades 3 (> 50 %) to 5 (shattered spleen)
Anterior Lumbar and Lumbosacral Approach
Due to the high rate of anterior lumbar interventions and the proximity of ves-sels, the lumbar spine is the most common location of vessel lacerations
Arterial Laceration
After suturing an artery,
check for thrombosis
and monitor vascularization
by pulse oximetry
An intraoperative open arterial bleeding is usually caused by sharp dissection of the artery This can occur accidentally with a sharp instrument, or during dissec-tion in scar tissue A temporary vessel loop may facilitate the repair (Fig 1) How-ever, the inexperienced surgeon is at risk of increasing the problem when trying to prepare for the insertion of the vessel loop It is recommended that the less experi-enced surgeon is better to wait for the help of a vascular surgeon A simple incision
of the artery can be sutured with 3-0 monofilament double ended sutures for the aorta and 4-0 for thicker vessels like the common iliac artery (Fig 2) It is impor-tant to suture the entire wall of the artery including the intima; otherwise the intima can occlude the vessel (Fig 3) Occlusion of the vessel adjacent to the lacera-tion by vessel loops is mandatory Thrombectomy with a Fogarty catheter has to be done first, and intravascular heparin (5 000 IU) is administered before final clo-sure Just before the last knot is made, some blood is allowed to escape, in order to get the air out of the vessel To make the suture tight, synthetic hemostatic material (Table 6) may be administered Due to the risk of postoperative arterial thrombo-sis, it is recommended to consult a vascular surgeon in any case Postoperative monitoring of the blood circulation of the leg is required using a pulse oximeter
Trang 8Figure 1 Vessel loop
A vessel loop is put twice around the artery With this technique the artery can be closed by pulling on both ends.
Figure 2 Suture of a tear in a vessel
A monofilament double ended atraumatic suture is used One end of the suture is fixed, and then a continuous suture
is made with the first needle, and consecutively with the second needle In small children, single knots are better,
because a continuous unresorbable suture cannot grow This suture technique can also be used to repair a dural leak.
Figure 3 Suture of a tear in an artery
The suture canal should be oblique The intima is perforated further away from the tear than the serosa, in order to create
eversion of the vessel wall, and to avoid the intima occluding the vessel.
Trang 9Arterial Thrombosis
Avoid pressure on lumbar
arteries by sharp-edged
retractors or pins
The rate of arterial thrombosis was 0.45 % in 1 315 consecutive cases undergo-ing anterior lumbar surgery at various levels from L2 to S1 [16] The main causes are either a tear in the intima, or compression of more than 50 % of the lumen Atherosclerotic plaques increase the risk A cautious surgical technique
can reduce the incidence of arterial thrombosis The pressure of sharp-edged
retractors or of pins should be avoided [66] and artery and veins should not be
separated in order to keep the lymph vessels and crossing blood vessels intact Even in posterior fusion, direct pressure on the inguinal region may cause occlusion [1]
Do not postpone treatment
by planning angiography
or ultrasound
Late symptoms are paralysis and sensory impairment usually of the left leg, and cyanosis of the toes Delayed thrombectomy after wound closure and
angi-ography will cause severe residual symptoms due to compartment syndrome
[19, 47, 66, 74, 94] Therefore, arterial thrombosis must be detected before symp-toms occur Similarly to arterial laceration, postoperative monitoring with a pulse oximeter is essential
Venous Laceration
Major vein lacerations are usually detected during surgery If a vein is com-pressed, a stab wound can be caused by a pin In anterior lumbar interbody fusion, the left ascending iliolumbar vein is recommended to be ligated in advance, because avulsion may be difficult to treat There are several opportuni-ties for treatment:
Suture
Usually, a 5-0 double ended monofilament suture is used (Fig 2) Direct repair is chosen if the defect is easily accessible, and if the resulting stenosis is expected to
be less than 50 % of the lumen Some stenosis can be accepted, and may be even beneficial, causing a higher speed of blood flow which may reduce thrombosis rate Postoperatively, heparin treatment for 5 – 7 days or during hospital stay is recommended followed by LMWH or other vitamin K antagonist treatment for
4 – 6 weeks, in order to prevent rethrombosis Heparin treatment can be per-formed for example with enoxaparin (Lovenox) starting 4 h after surgery (1 mg/
kg two times per day) Postoperative monitoring for thrombosis is also essential The recurrent thrombosis rate is 20 % Doppler sonography studies are recom-mended in the case of clinical suspicion
Compression and Hemostatic Agent
Most small venous lesions
are sealed by pressure only
The maintenance of pressure for about 5 min is essential, and is usually
per-formed with the help of a collagen sponge Hemostatic agents ( Table 6) are cho-sen either if the tear size is less than 5 mm or if the tear is difficult to access
Ligation
Ligation is the method of choice in catastrophic situations Before ligation of a large vessel, a vascular surgeon should be consulted Other measures including end-to-end anastomosis as well as interposition grafts or patches must be con-sidered The common iliac vein can be ligated in a life-threatening situation Even the inferior vena cava can be ligated below the renal veins, and sequelae like permanent edema of the legs are rare [111]
Trang 10The mortality from major abdominal vessel injuries
is high
In a recent study [86], 18 % of patients with iatrogenic injuries to major
abdomi-nal or pelvic veins died due to:
) uncontrollable bleeding
) multisystem organ failure
) pulmonary embolism
The blood loss ranged from 500 ml to 20 000 ml Therefore, any attempt must be
undertaken to avoid venous lacerations
Bowel Perforations
These are rare and usually occur during anterior procedures There are also some
case reports of perforations during microdiscectomy [42, 55, 58] A laceration of
Bowel perforations must be repaired
the serosa can be sutured superficially A perforation will require continuous
two-layer stitches, through the periphery of the mucosa and the entire muscle If a part
of the bowel is destroyed, resection will be necessary The likelihood of
contamina-tion and consequently of the formacontamina-tion of abscesses increases from proximal to
distal, with almost no danger of contamination in the small intestine, and a high
danger in the sigmoid colon Postoperative antibiotic treatment is required
Ureteral Injury
Some cases were reported which occurred during anterior lumbar surgery,
espe-cially in laparoscopic surgery [44] and disc prosthesis [39] The diagnosis is often
made postoperatively, and the main reasons are misplaced stitches or clips to stop
bleeding Treatment is an end-to-end anastomosis or implantation of the rest of the
ureter into the urinary bladder performed by a urologist A short-lasting
contu-sion by a stitch or a hemostat usually does not require surgical treatment, but
requires postoperative observation including ultrasonography of the kidney [49]
Urinary Bladder Injury
The incidence is rare The urinary bladder is sutured with two sutures After
suturing the muscularis and mucosa with continuous atraumatic 3-0 stitches, the
peritoneum is separately sutured A urethra or suprapubic catheter is applied for
10 days, and antibiotics are administered during this time [49]
Posterior Approach to the Cervical Spine
Postoperative Kyphosis
Postoperative kyphosis results can result from inappropriate technique
Failed reattachment of the semispinalis during laminoplasty may lead to
postop-erative kyphosis Reattachment should be performed, but anatomic variation has
to be considered [110] Resection of the C2 spinous process should be avoided in
order to prevent kyphosis
Vertebral Artery Injury
The lesion is rare and occurs in 4.1 % of transarticular (C1/2) screw fixations
[120] Biplanar imaging guidance has decreased the incidence Most patients
remain asymptomatic after the incidence The risk of neurological deficit from
vertebral artery injury was 0.2 % per patient or 0.1 % per screw, and the mortality
rate was 0.1 % [120] Devastating complications may occur in lesions of a
unilat-eral artery, or in the case of a contralatunilat-eral artery with thin lumen Preoperative