Li, G

Peh, WCG

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Title Radiological conference. PneumoperitoneumAuthor(s) Li, G; Peh, WCGCitation Hong Kong Practitioner, 1999, v. 21 n. 4, p. 182-186Issued Date 1999URL http://hdl.handle.net/10722/44676Rights Creative Commons: Attribution 3.0 Hong Kong LicenseClinical History:A young man presented wi th sudden onset of abdominal pa in . An abdominal radiograph was performed(Figure 1).Figure 1: Supine abdominal radiographAnsweronpage 1 S3What is the diagnosis?a) Pneumoperitoneumb) Intussusceptionc) Caecal volvulusd) Sigmoid volvuluse) Necrotising enterocolitisThis radiology case was prepared by:182Dr. G. LiProfessor W.C.G. Peh,Department of Diagnostic Radiology,The University of Hong Kong,Queen Mary Hospital.Hong Kong Practitioner 21 (4) April 1999Answer:a) PneumoperitoneumRadiological findingsThere is dilatation of gas-filled small bowel loops.The transverse folds of the valvulae conniventes of thesmall bowel are well visualised because of intra luminalgas. Free intraperitoneal gas on the outside of the smallbowel allows identif icat ion of both the outer and innersurfaces of the bowel wall, which is seen radiographicallyas a thin white line (Figure 2).Figure 2: Same radiograph as Figure 1 with additionof arrows. Rigler's sign or the thin whitestripe of the small bowel wall is clearly de-lineated (arrows) due to intraluminal as wellas intraperitoneal gasDiscussionThe presence of in t raper i toneal air in acu te ly i l lpatients is an important radiographical observation thatusual ly indicates bowel perforation. Various causes offree air are listed in Table 1.. peptic ulcer..appendicitis. infarction•surgery'peritoneal dialysisPerforation of viscusIatrogenicPneumomediastinumIntroduction per vaginaPneumothoraxIdiopathicClassical experimental studies by Miller and Nelsonshowed that as little as 1 ml of air could be detected belowthe r ight hemidiaphragm on properly-exposed chestradiographs taken with the patient in an upright position.Larger amounts may result in the following signs onabdominal radiographs:1. Serosal or Rigler's signNormally, gas is found only in the lumen of the bowel.However, gas on both sides of the bowel may outlinethe bowel wall, rendering it v is ib le as a thin, linearstripe (Figure 2). Since its original description byRigler in 1941, this sign has been recognised as animpor tan t indicat ion of p n e u m o p e r i t o n e u m onabdominal f i lms taken with the patient in a supineposition. Overlapping loops of dilated small bowelin the mid-abdomen may however mimic th i s sign,so care should be taken in radiographical evaluation.2. Increased lucency in the right upper quadrantAir accumulating superiorly in the free space betweenthe anterior aspect of the liver and the abdominal wallmay cause increased lucency in the r ight upperquadrant. This sign can be quite subtle. Dependingon the habitus of the patient, the lateral border of theair collection may be linear.3. Visualisation of the undersurface of the diaphragmAir may be trapped anteriorly in the cupola of thed i a p h r a g m , p e r m i t t i n g v i s u a l i s a t i o n o f t h e(Continued on page 185)183Hong Kong Practitioner 21 (4) April 1999undersurface of the central portion of the diaphragm.This sign is affected by the amount of air present andthe orientation of the diaphragm.4. Air in Morison's pouches (posterior hepatorenalspace)Morison's pouch is an intraperitoneal recess that isbounded anteriorly by the liver and posteriorly by theright kidney. Air in Morison's pouch is characterisedradiographically by a linear or triangular collectionof gas in the right upper quadrant outside the expectedlocation of the bowel.5. Outline of the normal peritoneal ligamentsWith larger amounts of free air, structures such as thefalciform ligament in the upper abdomen, the lateralumbilical ligaments (inverted V sign) in the lowerabdomen, and the urachus may occasionally bevisualised.6. "Football" signOriginally described by Miller in infants, this signindicates a large amount of free air f i l l ing the oval-shaped peritoneal cavity, mimick ing an Americanfootball. This sign has l imited value in adults.7. Air in the lesser sac of the peritoneal cavityIntraperitoneal air may occasionally enter the foramenof Winslow and become loculated in the lesser sac.This gas collection may manifest as an ill-definedlucency above the lesser curvature of the stomach.IntussusceptionIntussusception is defined as the telescoping of onesegment of bowel into an adjacent one. It accounts forapproximately 80% - 90% of bowel obstruction in infantsand children. In children, the usual site of intussusceptionbegins in the distal ileum; in 90% of cases, the cause isidiopathic. In contrast, intussusception in adults isrelatively rare; accounting for only 5% of mechanicalin tes t ina l obstruction. The presence of an abdominalmass and passage of blood per rectum raises suspicion ofthis diagnosis. Because adult intussusception is oftenchronic and re laps ing, the diagnosis is suggested byrecurrent episodes of subacute obstruction.If the intussusception is of the ileocolic or colocolicvariety, the "crescent" sign may be seen on radiographs.This sign is due to invagination of the intussusceptum(prolapsed segment of bowel) into the intussuscipiens(lumen of adjacent bowel). The intraluminal gas trappedbetween the two intestinal surfaces appears as a semilunarlucency. This lucent crescent is wider in diameter thannormal bowel and a round soft tissue density, representingthe mass created by the i n tu s suscep t ion , is oftensuperimposed. A more central and less distinctive lucentarc may be seen, representing trapped gas situated inlumen of the intussuscipiens. None of these clinical orradiographical signs were present in our patient.Caecal volvulusCaecal volvulus refers to a condition characterisedby a ro ta t iona l t w i s t of the r ight colon on its axisassociated with folding of the right colon, such that thecaecum is located in the mid-abdomen or left upperquadrant. Caecal volvulus occurs only when the rightcolon is incompletely fused to the posterior parietalperitoneum, an embryological variant present in 10% -37% of normal adults. On radiographs, a dilated, air-filled caecum in an ectopic location, usua l ly with thecaecal apex in the left upper quadrant is characteristicallyseen. The medially-placed ileocaecal valve may producea soft tissue indentation, so that the gas-filled caecum hasthe appearance resembling a coffee bean or kidney.Usual ly , little gas is seen in the distal colon. If theileocaecal valve is incompetent, refluxed gas within thesmall bowel may erroneously suggest small bowelobstruction. A contrast enema shows typical beaking atthe point of the volvulus in the mid-ascending colon.Caecal volvulus is likely to occur in a variety of clinicals e t t i ngs , i n c l u d i n g colonoscopy, b a r i u m enema,obstructive lesions in the distal colon, and pregnancy.These features were not seen in our case.Sigmoid volvulusThe radiographical appearance of sigmoid volvulusconsists of a dilated loop of sigmoid colon that has an185Radiological ConferenceRADIOLOGICAL CONFERENCEinverted U configuration and absent haustra. The dilatedbowel commonly extends into the upper abdomen abovethe transverse colon. The bowel may be located in themidline, or it may be directed towards the right or leftupper quadrants, where it can elevate the hemidiaphragm.Because s igmoid vo lvu lus represents a closed loopobstruction, there is usually a considerable amount of gasin the proximal colon. Gas may also be present in thesmall intestine. The apposed inner walls of the sigmoidcolon may occasionally form a dense white l ine whichpoints towards the pelvis. Absence of rectal gas is alsoan important finding. Sigmoid volvulus tends to occur inelderly males and residents of nursing homes and mentalhospitals, in whom chronic constipation and medicationare predisposing factors for gaseous distention of thesigmoid colon. Patients wi th sigmoid v o l v u l u s maypresent with abdominal pain and distention attributable tocolonic obstruction. Constipation and vomit ing are alsocommon findings. The symptoms are usual ly acute, butmay have a gradual onset in some patients.Necrotising enterocolitisNecrotising enterocolitis is a life-threatening processthat p r i m a r i l y a f f ec t s the g a s t r o i n t e s t i n a l t ract ofpremature infants. The following signs and symptomsusua l ly develop in the first two weeks of life: increasinggastric volume, abdominal distention, bloody stools,lethargy, and changing respiratory status. Specificradiographical features are pneumoperitoneum, fixedbowel loop on sequential studies, and portal venous gas.Other findings include gastric dilatation, a persistentlydilated bowel loop, or an unchanging bowel gas pattern.Pneumatos i s in tes t ina l i s presents later , and largecollections of intramural gas create a l inear streakypattern that parallels the bowel wall. In our patient, thisdiagnosis can be excluded based on the age group andradiographical features. •ReferencesRice RP. Thompson WM, Gedgandas TK. The diagnosis and significanceof ex l ra lumina l gas in the abdomen. Radiol Clin North Am. 1982:20:819-837.Grainger RG, All ison D. Grainger & Allison's Diagnostic Radiology: ATextbook of Medical Imaging. 3rd ed. New York: Churchi l l Livingstone,1997;pp897-900.Chapman S, Nakielny R. Aids to Radiological Differential Diagnosis. 2nded. London: Bailliere Tindall, 1990; pp168-169.Dahnert W. Radiology Review Manual. 4th ed. Baltimore: Williams &Wilkins. 1999;pp463.Miller RE. The technical approach to the acute abdomen. Semin Roentgenol1973:8:267-269.Figiel LS, Figiel SJ. Lesions of the large intest ine producing acutesymptoms. Radiol Clin North Am 1964:2:33-54.186

Radiological conference. Pneumoperitoneum

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Radiological conference. Pneumoperitoneum

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