However,thesenumbersareprobablyunderestimatedasnotall patientsaretested,especiallythosewhoareasymptomatic,orwith onlymildsymptomsandnoassociatedcomorbidities.Thestandard ofreferenceforco
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Trang 2COVID-19 pneumonia: A review of typical CT findings and differential
diagnosis
C Hania, N.H Trieua, I Saaba,b, S Dangearda, S Bennania, G Chassagnona,b,
M.-P Revela,b,∗
a Department of Radiology, Cochin Hospital, Assistance Publique-Hopitaux de Paris, 27 rue du Faubourg Saint-Jacques, 75014 Paris, France
b Université de Paris, Descartes-Paris 5, 75006 Paris, France
a r t i c l e i n f o
Keywords:
COVID-19 pneumonia
Tomography
X-Ray Computed
Cryptogenic Organizing Pneumonia
Pneumonia
a b s t r a c t
1 Introduction
Since March 11, 2020, the World Health Organization has
declared Coronavirus disease 2019 (COVID-2019) caused by
SARS-CoV-2tobeapandemicandpublichealthemergencyof
inter-nationalconcern[1].AsofApril8th,2020,theepidemichadspread
tomorethan199countriesandmorethanonemillionindividuals
havecontractedthevirusworldwidewith81,478reporteddeaths,
including82,048confirmedcasesinFranceand10,869deaths[2]
However,thesenumbersareprobablyunderestimatedasnotall
patientsaretested,especiallythosewhoareasymptomatic,orwith
onlymildsymptomsandnoassociatedcomorbidities.Thestandard
ofreferenceforconfirmingCOVID-19reliesonmicrobiologicaltests
suchasreal-timepolymerasechainreaction(RT-PCR)or
sequenc-ing[3].However,thesetestsmightnotbeavailableinanemergency
settingandtheirresultsarenotimmediatelyavailable.Computed
tomography(CT)canbeusedasanimportantcomplementto
RT-PCRfordiagnosingCOVID-19pneumoniainthecurrentepidemic
context[4,5].Indeed,whentheviralloadisinsufficient,RT-PCRcan
befalselynegativewhilechestCTshowssuggestiveabnormalities
[4,5].Alargeseriesbasedon1014patientsreporteda97%
sensitiv-ityofchestCTforthediagnosisofCOVID-19,whilethemeantime
intervalbetweeninitialnegativeandpositiveRT-PCRwas
approx-Abbreviations: CT, computed tomography; COVID-2019, Coronavirus disease
2019; GGO, ground glass opacities; MIP, maximum intensity projection; RT-PCR,
real-time polymerase chain reaction.
∗ Corresponding author.
E-mail address: marie-pierre.revel@aphp.fr (M.-P Revel).
imately5 days[5].Thus,CT canplaya pivotalrole intheearly detectionandmanagementofCOVID-19pneumonia[6],atleast forpatientswhohavebeensymptomaticformorethanthreedays
[4].Indeed,56%ofpatientsimagedduringthefirst2daysfollowing symptomonsetmayhavenormalCTfindings[7]
GiventheimportantroleofchestCT,itisimportantfor radiolo-giststobecomefamiliarwiththetypicalCTfeaturesassociatedwith thisnewinfection,aswellastheimagingcriteriaforanalternative diagnosis
Inthispictorialreview,wepresentthetypicalCTfeaturesof COVID-19pneumonia, theirchanges duringfollow-up, together withthemaindifferentialdiagnosisandcluesfortheirrecognition
AwidevarietyofCTfindingsinCOVID-19havebeenreported
inthedifferentstudies[8,9][9].However,allstudiesindicatethat themainCT featureof COVID-19pneumoniaisthepresenceof groundglassopacities(GGO),typicallywithaperipheraland sub-pleural distribution(Fig.1).The involvementof multiplelobes, particularlythelowerlobesisreportedinthemajorityofpatients withCOVID-19[10].These areasofGGO maybeadmixedwith areasoffocalconsolidation(Fig.2)andorassociatedwith superim-posedintralobularreticulations,resultinginacrazypavingpattern (Fig.3).Linearconsolidationsandothersignssuggestingorganizing pneumonia suchas thereversehalosign(i.e.,areasof ground-glasssurroundedbyperipheralconsolidation)areveryfrequently observed,mostlyinpatientsseveraldaysaftertheonsetofdisease
In thestudy bySalehiet al.,thefrequenciesof thedifferent
CTabnormalitieswereasfollows:GGOwasobservedin88.0%of
https://doi.org/10.1016/j.diii.2020.03.014
Trang 3Fig 1.Unenhanced CT images show typical findings of COVID-19 pneumonia in a 55-year-old man Peripheral GGO is seen in the upper portion of both lungs (A, B) (arrows), associated with linear consolidations in the lower lobes (C) (arrowhead) The results of first and second RT-PCRs were negative, with only the third test, repeated in view of
CT findings, becoming positive.
Fig 2. Unenhanced CT examination performed 6 days after the onset of symptoms in a 64-year-old-man with COVID-19 pneumonia Axial (A) and coronal (B) CT images demonstrate bilateral ground glass opacities admixed with patchy areas of consolidation (arrow) in the central and peripheral portions of the lung.
Fig 3.Unenhanced CT images of an 86-year-old woman with a crazy-paving pattern due to COVID-19 pneumonia (a) CT examination performed 4 days after symptom onset (dry cough and chest pain) demonstrates moderate disease extent (10–25%) (b) Peripheral ground-glass opacities with superimposed intralobular reticulations (arrows) resulting in a crazy-paving pattern, are seen in both lower lobes.
patients,consolidationin31.8%,bilateralinvolvementin87.5%and
peripheraldistributionin76.0%ofpatients[8]
3 Various forms of severity
PatientswithCOVID-19pneumoniapresentwithvariable
dis-easeextent,rangingfrommild involvement,affectingless than
10%ofthelungparenchyma(Fig.4)toseverediseaseextentwith
a“white lung”appearanceonCT (Fig.5).Yuanet al.evaluated
imagingfindingsassociatedwithmortalityandreportedthatthe
frequencyofconsolidationsaswellasthemedianCTscorewere
bothhigherinthegroupofpatientswhodiedatthehospital,as
comparedtopatientswhocouldbedischarged[11].TheCTscore
inthisstudywascalculatedasfollows:CTattenuationwasgraded
usinga3-pointscale,with1fornormalattenuation,2forground glassand3forconsolidation.Thenthedegreeoflunginvolvement wasevaluatedfor6lungregions:upper,middleandlowerlung
oneachsideandgradedusinga5-pointscale:0noinvolvement,
1lessthan25%,2:25–50%,3:50–75%and4>75%.Themaximal
CTscorewas72.Usingacut-offvalueof24.5,theCTscore pre-dictedmortalitywithasensitivityof85.6%andaspecificityof84.5%
[11].Otherpredictivefactorsformortalityincludedolderageand highercomorbidity rate[12].Intheseriesby Lietal.,the inci-denceofconsolidation,linearopacitiesandcrazy-pavingpatternin severe/criticalpatientswassignificantlyhigherthanthatobserved
innon-severe(e.g.,ordinary)patients[13].Thisseriesbasedon83 patientsalsoconfirmedthatsevere/criticalpatientswereolderand withmoreco-morbidities[13]
Trang 4Fig 4. Unenhanced CT image in a 50-year-old woman with a mild form of
COVID-19 She has asthma with no respiratory symptoms except fever Her husband has
been recently diagnosed with COVID-19 CT demonstrates rounded ground-glass
opacities in both upper lobes, some in the sub pleural region (arrowhead) and others
more centrally distributed (arrow).
COVID-19pneumoniaCTfeatureschangeovertime,with
dif-ferentpresentationsaccordingtothephaseandseverityoflung
infection.Panetal.investigatedlungchangesbytimeinpatients
whorecoveredfromCOVID-19[14].Theyclassifiedtheevolution
oflungabnormalitiesintofourstages(early0–4days,progressive
5–8days,peak9–13days,andabsorption≥14days)accordingto
timeperiods.TheyvisuallyquantifiedtheextentofCT
abnormal-ities.Eachofthe5lunglobeswasvisuallyscoredfrom0to5as
follows:0,noinvolvement;1,<5%involvement;2,25%
involve-ment;3,26%–49%involvement;4,50%–75%involvement;and5,
>75%involvement[14].ThetotalCTscorerangedfrom0toa
max-imalvalueof25.TheyfoundthatthetotalCTscoreincreaseduntil
about10daysaftersymptomonsetandthengraduallydecreased
RegardingthecategoryofCTabnormalities,stage2was
charac-terizedbyanincreaseofGGOextent,withacrazy-pavingpattern
morefrequentlyobserved[8].Ontheopposite, instage3,
con-solidationwasthemain featurewitha decreasedGGO ratio.In
aseriesof919patients,Salehietal.confirmedthis observation
and reported that CT findings in the intermediate stageof the
disease were characterized by an increase in the number and
sizeofGGOs,aprogressivetransformationofGGOintomultifocal
peakedonillnessdays6-11[10]
Inpatientswithclinicalworseningnotexplainedbyan exten-sion of lung opacities on CT, pulmonary embolism should be suspectedandacontrast-enhancedCTexaminationshouldbe per-formedifpossible,takingintoconsiderationtheclinicalseverity and therenal function.Ofnote,patientswithsevereCOVID-19 pneumoniahaveamarkedelevationofd-dimers,sothatthis d-dimer levelsdo nohelpidentifythosewho havesuperimposed pulmonaryembolism[16]
Amongdifferentialdiagnosis,onemajordifferentialis pneu-moniafrombacterialorigin.Community-acquiredpneumoniais usually characterized by an airspace consolidation in one seg-mentorlobe,limitedbythepleuralsurfaces.CTmayadditionally showground glassattenuation,centrilobular nodules,bronchial wallthickeningandmucoidimpactions(Figs.7and8)[17]
COVID-19pneumoniapresentationisverydifferent,withanabsenceof centrilobularnodulesandnomucoidimpactionsintheabsenceof superinfection
Pneumocystis Jirovecipneumonia is anotherinfectiouscause
of diffuse ground glass on CT, but occurs in immunocompro-mised patients Even though GGO is the main CT feature, its distribution withinthe lung parenchyma is not similar tothat observed in patients with COVID-19, it is more diffusely dis-tributedwithatendencytosparethesubpleuralregions(Fig.9)
[18]
ItismuchmoredifficulttodistinguishCOVID-19from pneu-moniaduetootherviralcauses.CTfeatureslargelyoverlap,even thoughit hasbeenreportedthatCT abnormalitiesinCOVID-19 pneumoniamore frequentlyexhibit aperipheralpredominance, withlessfrequentpleuraleffusionandlymphadenopathy(Fig.10)
[19].Itismainlythehighcurrentepidemiccontextwhichsuggests COVID-19asthecauseofGGOinpatientswithfeverandrespiratory symptoms
Fig 5.Unenhanced CT images of a “white lung” appearance in an 89-year-old man with respiratory distress due to COVID-19 pneumonia Axial (A) and coronal (B) CT images,
Trang 5Fig 6. Initial and follow-up CT images in a 71-year-old woman with COVID-19 pneumonia Unenhanced initial CT performed before RT-PCR confirmation (A,C) shows bilateral peripheral ground-glass in the dorsal segment of upper (a) and lower lobes (C) (arrows) Contrast-enhanced CT (B,dD) performed 6 days later to rule out pulmonary embolism demonstrates linear consolidations typical for an organizing pneumonia pattern (arrowheads).
Fig 7. Unenhanced CT images in a 55-year-old-patient with bacterial bronchopneumonia Centrilobular nodules (A) with a tree-in-bud pattern better seen on MIP reformatted images (B) (arrows) are seen in the right lower lobe, together with a segmental consolidation (arrowhead) (C).
Fig 8.Unenhanced CT images of a 45-year-old man with bacterial pneumonia Ground glass opacities (arrow) limited to the posterior and lateral segment of the right lower lobe are demonstrated (A), associated with endobronchial secretions (arrowhead) (B) more proximally.
PulmonaryedemaisaverycommoncauseofdiffuseGGO,but
ischaracterizedby acentral predominancewithsparingofthe
peripheralportionsofthelungcontrarytoCOVID-19.Itis
asso-ciatedwith othersuggestive signs such as septal lines, pleural
effusion,largepulmonaryveinsandmediastinal
lymphadenopa-thy.IthasbeenreportedthatCOVID-19mightberesponsiblefor
acutemyocarditis[20].Thisdiagnosisshouldbesuspectedifthere aresignsofinterstitialpulmonaryedema suchasseptallinesin youngerpatients(Fig.11).Intraalveolarhemorrhageduetosmall vesselvasculitisisalsocharacterizedbydiffuseGGO,butpatients usuallypresentwithmildhemoptysis andacuterenal failureis associatedespeciallyinGoodpasturesyndrome.Thereisno sub-pleuralpredominancecontrarytothatseeninCOVID-19(Fig.12)
[21] Drug-induced pneumonitis manifesting as nonspecific
Trang 6Fig 9. Unenhanced CT images of a 30-year-old man with Pneumocystis Jiroveci infection Bilateral ground glass opacities with right lung predominance are demonstrated Note the relative subpleural sparing (arrows) on both axial (A) and coronal (B) CT images.
Fig 10.Unenhanced CT image in a 45-year-old-patient with Influenza
virus-associated pneumonia Bilateral diffuse ground glass opacities are demonstrated.
Differential diagnosis with COVID-19 pneumonia is not possible and relies on
RT-PCR results, even though peripheral predominance is less common RT-PCR result
for SARS-Cov-2 was negative but positive for influenza A.
interstitial pneumonia is another cause of ground glass
Sub-pleural sparing, history of drugexposurehelp diagnosis Those
manifestingasorganizedpneumoniahavesimilaritiesto
COVID-19, but are associated with GGO and occur in a very different
context[22]
Fig 12.Unenhanced CT performed in a 48-year-old woman with Goodpasture syn-drome CT image shows bilateral ground glass opacities with central predominance, associated with pleural effusion, which is very uncommon in COVID-19 pneumonia The patient presented with mild hemoptysis related to intra alveolar hemorrhage and acute renal failure Histopathological analysis of tissues samples obtained from renal biopsy confirmed Goodpasture syndrome.
Inthisepidemicsituation,CTundoubtedlyplaysanimportant role,forearlyidentificationofCOVID-19pneumonia.TypicalCT featuresincludeperipheralGGOswithmultifocaldistribution,and
aprogressiveevolutiontowardsorganizingpneumoniapatterns
Fig 11.Unenhanced CT images of a 64-year-old man with COVID-19 and pulmonary edema Ground glass opacities admixed with patchy consolidation are seen in both lungs and associated with linear consolidation in the subpleural region of the left lower lobe (arrow) (A) The associated smooth thickening of the interlobular septa (B),
Trang 7patientshavingimportantdiseaseextentandmoreconsolidative
formsandalsotoearlydetectcomplicationsinpatientswhorequire
furthermechanicalventilation[23].Centrilobularnodules,mucoid
impactionsandunilateralsegmentalorlobarconsolidations
sug-gest a bacterialoriginof pneumonia, or superinfection.RT-PCR
remains needed for final confirmation but its positivity canbe
delayed,withtheneedtorepeatthetest iftheCTfeatures are
suggestive
AllauthorsattestthattheymeetthecurrentInternational
Com-mitteeofMedicalJournalEditors(ICMJE)criteriaforAuthorship
Disclosure of interest
Theauthorsdeclarethattheyhavenocompetinginterest
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