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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_725_Библиотеки_им_академика_М_И_Перельмана
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AsherHirshberg,MD,contributedtothischapterinthefirsteditionofthisbook.
Chapter5
Abdominalimaging
MosheScheinandHansUlrichElben
Thediagnosticproblemoftoday
Hasgreatlychanged—thechangeshavecometo
stay;
Weallhavecometoconfess,thoughwithasigh
Oncomplicatedtestswemuchrely
Andusetoolittlehandandearandeye.
ZacharyCope,TheAcuteAbdomeninRhyme
Therearefundamentaldifferencesinhowphysicians,belongingtothe
different specialties involved in decision-making concerning the ‘acute
abdomen’,lookatabdominalimaging.Theradiologists’sharpeyessee
‘everything’ but they tend to see ‘too much’, and do not always
understand the clinical significance ofwhat theysee. They describe all
kinds of ‘findings’, densities here, enhanced fat there, but what you
REALLY want to know is the diagnosis, right? Some (not all) ER
physiciansdonotseemuchanddonotunderstandthemeaningofthe
littletheydosee;alltheycareaboutiswheretodumpthepatient.Some
doctors(yousurelyknowafewofthem)evendonotbotherlookingatthe
actual images, finding it easier reading the radiologist’s report. This
leaves us with ourselves, the surgeons. Armed with a better
understandingofthenaturalhistoryofthediseaseprocesses,and
abletocorrelateradiological imaging with the clinical scenario,or
previous operative observations, we should be well positioned to
interpretabdominal imaging—at leastaswellas theradiologists.
Wehavealreadydiscussed( Chapter4)theroleofabdominalimaging
intheevaluationofthepatientwithanacuteabdomen.Inthischapterwe
willtry toprovide youwith practicaltipsonhowtolookattheimages
andwhattolookfor.
PlainabdominalX-ray(AXR)
Tragically, thissimple, cheapandsafeX-rayis increasinglybypassed
in favor of an immediate computed tomography (CT) scan — which
deliversamuchgreaterradiationdose.Thisisapitybecausethereisso
muchthatyoucanlearnfromaquickglanceattheAXR.
Lookforabnormalgaspatterns
Gasoutsidethelumenofthebowel:
•
‘Freeair’(pneumoperitoneum)isbestseenonanerectchestX-ray
(CXR; Chapter4)butmayalsobeseenonanAXR( Figure5.1).
IftheCXRand AXR are ‘normal’andyou suspect perforation of a
viscus,aleftlateraldecubitusabdominalfilmmayshowfreegasin
theperitonealcavity.
Figure5.1.AbdominalX-rayintheuprightpositiondemonstratingapneumoperitoneum
withairunderbothdiaphragms(arrow).
•
Make a habit always to look for atypical gas patterns —
occasionallyyoumaybe rewardedwithan eye-poppingdiagnosis:
gas in the biliary tree (pneumobilia) implies either a cholecysto-
enteric fistula (see gallstone ileus; Chapter 21) or a previous
enterobiliary bypass or, more commonly, a sphincterotomy of the
sphincter of Oddi (via endoscopic retrograde
cholangiopancreatography[ERCP])( Figure5.2).Notethat gasin
the intrahepatic biliary ducts is seen centrally, while gas in the
periphery of the liver suggests portal vein gas. The gas finds its
way into the portal venous system through a breach in the bowel
wall — usually associated with mesenteric ischemia or severe
colitis—andrarelywithpylephlebitis.Commonly,gasintheportal
veinasaresultofischemicsmallorlargebowelisassociatedwith
pneumatosisintestinalis,i.e.thepresenceofintramuralgas.
Figure5.2.AbdominalX-raydemonstratingairinthebiliarytract(arrow).
•
Gas in the gallbladder wall signifies a necrotizing infection (
Chapter 20). A soap-bubble appearance signifies free gas inthe
retroperitoneum; in the epigastrium this isassociated withinfected
pancreaticnecrosis( Chapter19),intherightupperquadrantwith
aretroperitonealperforationoftheduodenum,andineithergutterit
isassociatedwithretroperitonealperforationofthecolon.
Note that all these types of pathological air pattern are much
easiertodetectonCTimages.
Gaspatternwithinthelumenofthebowel:
•
Abnormalgaseousdistension/dilatationof smallbowelloops,with
or without fluid levels, implies a small bowel process — be it
obstructive(small bowel obstruction, Chapter21), paralytic ileus
( Chapter 45) or inflammatory (Crohn’s disease, Chapter 26).
Remember — acute gastroenteritis may produce small bowel
fluidlevels;thediarrheahintsatthediagnosis.
•
Abnormalgaseousdistension/dilatationofthecolondenotescolonic
obstruction or volvulus ( Chapter 27), colonic inflammation
(inflammatory bowel disease, Chapter 26) or colonic ileus
(pseudo-obstruction, Chapter27).
Figure 5.3. Abdominal X-ray: small bowel vs. large bowel. a) Small bowel obstruction.
Note the valvulae conniventes crossing the whole width of small bowel. b) Distal
obstructionofthecolon.Notethehaustracrossingaportionofbowelwidth.
Distinguishing small bowel from colon on an AXR is easy: the
‘transverselines’goall the wayacrossthe diameter of thesmallbowel
(thevalvulaeconniventes)andonlypartlyacrossthecolon(thehaustra).
Ingeneral,loopsofsmallbowelare situatedcentrally whilelarge bowel
occupiestheperiphery( Figure5.3).
Usefulhints:
Gaseousdistensionofsmallbowel+nogasinthecolon=
completesmall
bowelobstruction
.
Gaseousdistensionofsmallbowel+minimalquantityofcolonicgas=
partial
smallbowelobstruction
.
Significant gaseous distension of both the small bowel and the colon =
paralyticileus
.
Significant gaseous distension of the colon + minimal distension of the small
bowel =
colonic obstruction or pseudo-obstruction
. (The
magnitudeofsmallboweldistensionproximaltolargebowelobstructiondepends
onthecompetence,orincompetence,oftheileocecalvalve.)
Abnormalopacities
TheopacitieswhichyouareabletospotontheAXRarethecalcified
ones:gallstones in the gallbladder (visible in about one-fifthofpatients
withcholelithiasis),uretericstones(visibleinsomepatientswithureteral
colic), pancreatic calcifications (seen in some patients with chronic
pancreatitis), and appendicular fecaliths (occasionally seen in patients
withappendicitis)( Figure5.4).Clinicallyirrelevantcalcifiedlesionsthat
arecommonincludephlebolithsinthepelvisandcalcifiedlymphnodesin
therightiliacfossa,usuallyassociatedwithprevioustuberculosis.Fecal
matter may opacify the rectum and colon to a variable degree —
achievingextremeproportionsinpatientswithfecalimpaction.Notethat
amoderateamountoffecalmaterialintherightcolonisnormal,whilea
columnoffecesontheleftimpliessomeabnormality,ranginginseverity
fromsimpleconstipationtoearlymalignantobstruction.Anotheropacity,
whichmaysurpriseyou,isaforgottensurgicalinstrumentorgauzeswab.
Also,massiveasciteshasatypicalpictureonAXR( Figure5.5).
The simple abdominal X-ray is an extension of your clinical
evaluation,whichisnotcompletewithoutit.
Figure 5.4. Abdominal X-ray demonstrating an appendicular fecalith (arrow); when
visualized in a patient with symptoms and signs of acute appendicitis it is highly
diagnostic.
Figure 5.5. Abdominal X-ray demonstrating massive ascites. In the supine position the
bowel gas lies centrally and there is nothing peripherally. The lighter bowel loops are
practicallyfloatingonalakeofascitesintheabdominalcavity.
Computedtomographyinabdominalemergencies
The road to the operating room does not always have to pass
through the CT scanner but an appropriately indicated CT may
obviatetheneedforasurgicaljourney.
ThesupremacyofCTintheimagingoftheabdomenisnotindispute.
CTshows details that no other diagnostic method does: free gas, fluid,
masses, tissue planes, inflammatory changes, opacities, blood vessels
andorgan perfusion.So whyshouldweobject to theindiscriminate
useofCTaspracticedtodayinmanycountriesaroundtheworld?
We object for the simple reason that in many patients the diagnosis
can be established without CT — the obtaining of which can delay
treatment, and confuse the picture by showing non-significant findings
(see Chapter4).Typically,wheneverradiologistspublishpapersonthe
use of CT in various abdominal emergencies they always declare
sensitivity and specificity rates approaching 100%. When surgeons,
however,lookobjectivelyattheoverallimpactofCTonthediagnosisand
treatment of specific conditions,the realimpact ofCTtends to be less
impressive.
Inaddition,rememberthattheradiationexposureofoneabdominalCT
examination can be several hundred times that of a chest X-ray.
AccordingtotheUSFoodandDrugAdministrationthisamountof
radiation exposure may be associated with a small increase in
radiation-associated cancer in an individual. This is particularly
relevantifpeopleweretoreceivethisexaminationrepeatedly,startingat
a young age — as in the young lady presenting with lower abdominal
paintoanERinBrooklyn,whereCTshowsanovariancyst.Twoweeks
latersheshowsupatanotherERintheBronxwhereanotherCTshows
(surprise!) the same cyst. Andof course,somebody hasto payfor the
CT, and radiologists have to possess the newest model of Mercedes.
Don’tthey?
ThekeywordintheeffectiveuseofabdominalCTis‘selectivity’.
Rather than indicating a need for exploration, CT is more useful in deciding when NOT to
operate—avoidingunnecessary‘exploratory’laparotomiesor‘diagnostic’laparoscopies.Also,
a ‘normal CT’ can exclude surgical abdominal conditions — allowing the early discharge of
patientswithouttheneedforadmissionforobservation.
Therecentintroductionoffastscannersthatimagetheabdomenfrom
the diaphragm to the pubis in a single breath has greatly improvedthe
image quality and reduced the time required to obtain the images.
However,itdoesrequirethatpatientsbetransportedtotheCTsuiteand
exposes them to the risks of aspiration of oral contrast media and
adverse reactions to intravenous (i.v.) contrast media such as
anaphylaxisandnephrotoxicity.Unenhanced(noi.v.contrast)helicalor
spiral CT scans are being increasingly used in suspected appendicitis,
while CTs without oral contrast have been reported as accurate in
patients suffering from blunt abdominal trauma. Whatever the CT
methodologyinyourhospital,you—whoknowtheabdomeninside
out and understand the natural history of abdominal diseases —
havetobeabletoanalyzetheCTimagesbetterthantheradiologist.
As is the case with all imaging studies, interpretation of CT scan
imagesrequiresasystematicapproach,andittakesplentyofpracticeto
become confident in one’s own ability. One also needs to spend time,
and the more time you spend the more findings — both negative and
positive— youpick up.We aregoing todescribe theway welookat a
CTscan of the abdomen;itis not ‘ideal’or ‘perfect’but it works for us,
especiallyinthemiddleofthenightwhenalltheradiologistsaresnoring
inbed.Inthemorningtheywill,withlatteinhand,dictatedetailedreports.
Thisiswhenyouhavetogoovertheimageswiththem—youwill
be surprised how often, now, equipped with the accurate clinical
informationyouprovide,theywillseesomethingthatwasmissedat
night.
Spenda fewhourson YouTubewhereyou willfind excellentclipson
howtolookatabdominalCTstudies.
Itisimportantto pay attention to a few technical aspects of the
studybeforebeginningtointerpretit.Whilethereisalotofliterature
tosupportthenotionthatthereisnoneedfororalorintravenouscontrast
material, the use of contrast improves your own diagnostic yield. One
exceptiontothisiswhenuretericcalculi areat thetopofthedifferential
diagnosis list anda non-contrast study gives almost all the information
required.
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