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Uncommon and Unusual

Gastrointestinal Causes of the AcuteAbdomen: Computed Tomographic DiagnosisDouglas S. Katz, MD,* Benjamin Yam, BS,* John J. Hines, MD, Joseph P. Mazzie, DO,*Michael J. Lane, MD, and Maher A. Abbas, MD

There is a wide variety of uncommon and unusual gastrointestinal causes of acute

abdominal and pelvic pain that may be prospectively diagnosed on computed tomog-

raphy. We demonstrate 10 such diagnoses and briefly review the current computed

tomography and clinical literature on intussusception occurring beyond early child-

hood, small bowel obstruction from internal hernia, cecal volvulus, intramural small

bowel hemorrhage, Boerhaaves syndrome, gastrointestinal luminal foreign bodies,small bowel diverticulitis, hemoperitoneum secondary to abdominal tumor; gallstone

ileus, and gallbladder torsion. Radiologists and clinicians need to be aware of these

disorders, particularly with the widespread utilization of computed tomography (CT) in

the management of patients with acute abdominal pain.

Semin Ultrasound CT MRI 29:386-398 2008 Elsevier Inc. All rights reserved.

In this article, we review 10 uncommon or unusual gas-trointestinal (GI) causes of acute abdominal and pelvicpain that may be diagnosed prospectively on computed

tomography (CT). The diagnosis may be apparent in some

of these disorders, but the CT findings and correct corre-

sponding diagnoses may be subtler in others. This is not

intended to be a comprehensive illustration and literature

review of all less common or rare causes of the acute

abdomen but highlights entities which, while not encoun-

tered on a routine basis, may occasionally be found in a

busy CT practice which images patients with acute ab-

dominal and pelvic complaints. Radiologists need to be

aware of the CT findings of these disorders, and clinicians

need to be aware that, although uncommon or unusual,

with the widespread use of abdominal and pelvic CT, these

diagnoses can be established prospectively.

Intussusception OccurringBeyond Early Childhood

Intussusception of the bowel is a different entity in older

children and adults than in young children. When the colon

is the primary or sole portion of bowel involved, in up to95%

of cases there is an identifiable pathologic leading point. This

point is a malignant tumor in between one-half and three-

quarters of colonic cases.1,2 Symptoms of colonic intussus-

ception in such patients may be acute, intermittent, or chro-

nic.2 The diagnosis should be established prospectively on

CT. Findings include a target- or sausage-shaped mass, with

the central portion representing the intussusceptum, sur-

rounded by eccentrically located fat, and then by the intus-

suscipiens. The leading point, particularly a lipoma, may be

identified (Fig. 1), but more frequently the underlying mass

may be difficult to distinguish from adjacent/edematous

bowel (Fig. 2).1,3 Surgical intervention is needed in the ma-

jority of colonic cases.

Pathologic processes underlie small bowel intussuscep-

tions in a minority of cases in older children and adults, eg,

due to small bowel metastases such as from melanoma, from

benign lesions such as a polyp or Meckelsdiverticulum, or in

transient intussusception such as may be seen in celiac dis-

ease or Crohns disease. However, the majority of such iso-

lated small bowel intussusceptions that arenow identified on

a relatively routine basis on CT are transient and have no

*Department of Radiology, Winthrop-University Hospital, Mineola, NY.

Department of Radiology, Long Island Jewish Medical Center, New Hyde

Park, NY.

Department of Radiology, South Texas Radiology Group, San Antonio,

TX.

Department of Surgery, Kaiser Permanente, Los Angeles, CA.

Address correspondence to: Douglas S. Katz, MD,Vice Chair,Department of

Radiology, Winthrop-University Hospital,259 FirstStreet, Mineola, NY,

11501. E-mail:[email protected]

386 0887-2171/08/$-see front matter 2008 Elsevier Inc. All rights reserved.doi:10.1053/j.sult.2008.06.007
mailto:[email protected]:[email protected]:[email protected]


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identifiable lead point (Fig. 3).4-8 They are presumably re-lated to physiological intestinal peristalsis.3,4,6 Transientsmall bowel intussusceptions without underlying leadingpoints areusually short (4 cm)andnonobstructive.4-8 Mostcases can be managed conservatively. There is no consensuson the utility of follow-up testing, such as repeat CT, smallbowel follow-through, CT enterography, or capsule endos-

copy.3 In longer segment/longer diameter small bowel intus-susceptions, and when there is evidence of vascular compro-mise and/or associated inflammatory changes on CT, moreaggressive management should be considered.5,8,9

Small Bowel Obstructionfrom Internal Hernia

Internal hernia is a relatively rare cause of small bowel ob-struction (SBO). It is related to congenital mesenteric defects

Figure 1 Large bowel intussusceptiondueto a lipoma. A 61-year-oldwoman with myeloma. (A) Initial abdominal CT scan, obtained for

myeloma staging, shows incidental right colonic lipoma (betweencalipers). (B, C) CT scans for suspected right renal colic several

months later show intussusception related to the lipoma. Also notethe left iliac lesion related to the patients myeloma. Figure 2 Ileocolic intussusception due to lymphoma. A 16-year-old

with intermittent right lower quadrant pain. (A, B) CT scans showileocolic intussusception in the right lower quadrant, without ob-

struction. An underlying mass cannot be identified. High-grade B-

cell lymphoma involving the terminal ileum and cecum was discov-ered at emergency surgery.

Gastrointestinal causes of the acute abdomen 387


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or prior surgery.10,11 The presentation ranges from asymp-tomatic (with no associated obstruction) to intermittentsymptoms to acute small bowel obstruction with strangula-tion. Prospective CT diagnosis may be difficult. Distinguish-

ing SBO secondary to internal hernia from closed loop SBOdue to adhesions can be challenging. The radiologist needs tobe aware of the entity and maintain a high index of suspicionin the correct clinical setting (eg, a patient with no priorabdominal surgery, or prior gastric bypass or hepatic trans-

plantation).10-13 SBO related to an internal hernia, whethercongenital or postsurgical, should be managed surgically.

Imaging of internal hernias using CT has been the subjectof several excellent recent reviews.14-16 The CT findings of

internal hernias particularly in the previously operated abdo-menand features which distinguish SBO related to internalhernia from other etiologies and which may predict the spe-

cific type of internal herniacontinue to evolve.13,17

Internal hernias related to congenital mesenteric defectsaremost commonly left and right paraduodenal hernias, her-nias through the foramen of Winslow, and pericecal her-nias.14 CT findings (Fig. 4) include clustered dilated small

bowel loops in a sac-like mass between the pancreas andstomach or in their vicinity in left paraduodenal hernias. Inright paraduodenal hernias, loops of small bowel are notedbehind the superior mesenteric artery and inferior to thethird portion of the duodenum.10,14-16 Foramen of Winslow

hernias do not have an encapsulating membrane but are rel-atively similar on CT to left paraduodenal hernias, with clus-

tered bowel loops in the lesser sac.16Previously rare internal hernias are now well-described

complications following liver transplantation and Roux-en-Ylaparoscopic gastric bypass surgery. The most common typein most gastric bypass serieshasbeen the transmesocolic type(ie, at the mesenteric defect created to perform the gastroje-

junostomy),11,17 although the Peterson type (herniation of

small bowel behind theRoux loop, in a retrocolic or antecolicposition) was more common in a recent series.13 CT findingsof transmesocolic hernias include multiple small bowel loopscephalic to the transverse mesocolon between the stomachand spleen, a high position of the distal jejunal anastomosis,

an ascending course of tightly clustered vessels in the mes-entery, and a dilated efferent jejunal loop.17 In the series

composed primarily of Petersons hernias, mesenteric swirl-ing combined with a mushroom shape of the mesentery werethe best predictor on CT compared with a group of control

Figure 3 Transient small bowel intussusception. A 49-year-oldwoman with lower abdominal pain. CT scan shows short-segment

jejunal intussusception (between calipers),which was not identifiedon a small bowel follow-through performed 2 days later (not

shown).

Figure 4 Right paraduodenal hernia. A 50-year-old man with right upper quadrant pain and no previous surgical

history. (A, B) CT scans show a small bowel obstruction related to a cluster of small bowel loops in the right midabdomen. A right paraduodenal hernia was suspected on CT and confirmed at surgery.

388 D.S. Katz et al


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patients.13 In transmesenteric hernias following liver trans-plantation, clustered small bowel loops adjacent to the ab-dominal wall without overlying omental fat and centrallydisplaced colon were themost common CT findings.12 Bowelobstruction secondary to internal hernia following gastricbypass requires urgent operative intervention.

Cecal Volvulus

Colonic volvulus causes up to 10% of large bowel obstruc-tions. Untreated, this closed-loop obstruction can lead to

colonic ischemia and infarction, which may be fatal. Up to25% of the population have failure of peritoneal fixation,allowing the proximal colon to be more mobile.18 Sigmoidvolvulus is the most common type of colonic volvulus. Cecalvolvulus is less common. Transverse colonic volvulus is therarest form.

Plain films may show the classic coffee bean appearance ofcecal volvulus, a dilated inverted U-shaped formation producedby overlapping limbs of colon. However, plain films are equiv-ocal in up to one-half of cases, with nonspecific findings. Al-though a contrast enema is diagnostic, radiologists need to rec-ognize cecal volvulusonCT, as itmay bethefirst testperformedor may follow nondiagnostic plain films.18

There are surprisingly few publications on the CT findingsof cecal volvulus. Initial reports noted colonic obstruction,torsion of the colon around the mesocolon with a whirlsign, tapered narrowing of the efferent and afferent loops,

and the coffee bean appearance (Figs. 5 and 6).18 Multipla-nar reformations may be helpful.19 There is usually markeddilatation of the cecum, although it may not be initially ob-vious that the cecum is the dilated portion of bowel. In aboutone-half of cases, the cecum twists in the axial plane andremains in the right lower quadrant, whereas in the other

Figure 5 Cecal volvulus. A 48-year-old woman with left lower quadrant pain. (A, B) CT scans show a distended cecumin the left upper quadrant,with associated largebowel obstruction.The terminal ileum is located posteriorto thececum

(B, arrow). (Color version of figure is available online.)

Figure 6 Cecal volvulus. A 21-year-old woman with abdominal pain. (A, B) CT scans show a dilated cecum in the

midline of the abdomen anteriorly (arrows, B), with associated swirling of the collapsed terminal ileum (arrow, A) andmesentery, and collapse of the descending colon. (Color version of figure is available online.)



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half, the cecum twists and inverts, migrating into the leftupper quadrant. A recent series of 10 patients classified theformer type as the axial torsion type (with a clockwise whirlsign); the latter was classified as the loop type (with a coun-terclockwise whirl sign). The CT appearance of a cecal bas-

cule, a distended cecum which folds on itself anteriorly with-out torsion, was also reported.19 If there is bowelstrangulation, mesenteric edema, bowel thickening, andpneumatosis may be seen.18

Cecal volvulus requires operative intervention, with noestablishedrole for endoscopic reduction. A right hemicolec-tomy is performed when the cecum is ischemic. A cecopexy,fixation of the cecum to the abdominal wall, is performedwhen the cecum is viable.

Intramural Small

Bowel HemorrhageIntramural small bowel hemorrhage is relatively rare but islikely underdiagnosed. It can be trauma-related or can occurspontaneously. In adults, spontaneous hematoma is usuallyrelated to anticoagulation or an underlying bleeding disor-der. It may also be secondary to ischemia or closed loopobstruction.20-22 Gastrointestinal bleeding occurs in half orfewer patients. Symptoms are usually vague and subacute,andsome patients are asymptomatic. The correct diagnosis isoften unsuspected and delayed.20,22

CT findings are best seen on non-enhanced images, as IVcontrast may obscure the hyperdensity within the bowel

wall. There is homogeneous and symmetric small bowel wallthickening, usually involving a single site within the duode-

Figure 7 Intramural small bowel hemorrhage. A 64-year-old man on

coumadinwithmarkedlyelevatedINRanddiffuseabdominal pain. (A,B) CT scans through the lower abdomen following oral but not IV

contrast administration demonstrate a segment of thick-walled smallbowel with mildly hyperdense mural attenuation (white arrows) rep-

resenting acute hematoma. A small amount of hemorrhage infiltratestheadjacent smallbowel mesentery(*). (C)CT scan through thepelvis

demonstrates a small volume of hemoperitoneum (h).

Figure 8 Intramural small bowel hemorrhage. A 76-year-old womanwith abdominal pain and upper gastrointestinal bleeding, on cou-

madin. Non-enhanced CT scan shows hemorrhage in the anteriorand posterior walls of the proximal jejunum (between calipers).

There is also edema of the abdominal wall.

390 D.S. Katz et al


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num or proximal jejunum, or less commonly the ileum, withvariability of the average length of the segment of involve-ment (Figs. 7 and 8).20-23 Patients are usually managed con-servatively. The prognosis is guarded if greater than one-halfof the small bowel length is involved.23 Repeat CT as early asseveral days may show findings of resolution.

Boerhaaves Syndrome

Esophageal intramural hematoma and frank esophagealperforation (Boerhaaves syndrome) have a variety of eti-ologies, including iatrogenic (approximately 75%, eg, fol-

lowing endoscopic procedures) and self-induced (partic-ularly postemetic, following excessive food and/or alcoholintake). Mucosal injury often occurs at the esophagogas-tric junction, with associated hemorrhage (MalloryWeisstear). A transmural perforation (Boerhaaves syndrome)may occur into the mediastinum, typically on the left sideposterolaterally.24 Other thoracoabdominal emergenciesmay be suspected clinically, such as aortic dissection ormyocardial infarction.

Although plain films may show evidence of perforation,with subsequent confirmation on an esophagram, CT hasutility to rule in or exclude the diagnosis (Fig. 9). CT

findings include pneumomediastinum/mediastinal orpleural air-fluid levels, evidence of communication be-

Figure 9 Boerhaaves syndrome. An 81-year-old man with suddenonset of chest pain. (A, B) CT scans of lower thorax with abdominal

(A) and lung (B) window settings. Bilateral pleural effusions (*),pneumomediastinum (black arrows), and bilateral pneumothoraces

(ptx) are noted. The left effusion is high in density (81 HU), consis-tent with extravasation of oral contrast from the esophagus. (C)

Image from an esophagram performed with water-soluble contrastseveral hours after CT demonstrates marked contrast extravasation

from the esophagus into the mediastinum (*) and into both pleuralspaces (black arrows). e esophagus.

Figure 10 Unexpected jejunal foreign body on non-enhanced CT

performed for suspected left renal colic. A 16-year-old female withleft flank pain for several days. CT scan shows small vertically ori-

ented metallic density in a proximal jejunal loop, which appeared to

extend through the bowel wall posteriorly. A short-segment wirewas removed by a pediatric surgeon through a pediatric endoscope,

and the patient did not require subsequent surgery.



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tween the esophagus and mediastinum (especially whenwater-soluble oral contrast is given), pericardial effusion,esophageal thickening, and associated inflammatorychanges.25,26

Most submucosal esophageal hematomas are iatrogenic.Some are posttraumatic, and others are related to antico-agulation or bleeding disorders. CT demonstrates submu-cosal thickening with an attenuation consistent with hem-

orrhage. Intramural hematoma is usually managedconservatively, whereas the majority of patients with Boer-haaves syndrome need emergent surgery.24,27 Conserva-tive management is possible in a minority of patients, ifthere is a combination of a contained tear, minor symp-toms, no pleural contamination, and no systemic infection(eg, with a small tear of the cervical esophagus followingan endoscopic procedure).24

GI Luminal Foreign Bodies

Few reports of CT identification of nonmetallic luminal GI

tract foreign bodies have been published. The diagnosis ofGI tract perforation related to an ingested foreign body isusually not established prospectively without cross-sec-

tional imaging.28 There may be a substantial lag time be-

tween ingestion and the development of symptoms, and

for nonmetallic foreign bodies (eg, fishbones) the object(s)

may be obscured by contrast media.28,29 The radiologist,

therefore, needs to be aware of these potential pitfalls.

Correspondingly, we have recently identified several GI

tract foreign bodies on CT, where the diagnosis was not

suspected clinically (Figs. 10 and 11).Although affected patients are commonly elderly, neu-

rologically compromised, or alcoholics, GI tract foreign

bodies may be seen in otherwise healthy adults. The ma-

jority (80-90%) pass without complication, but perfora-

tion may occur anywhere along the GI tract, most com-

monly at physiologic or pathologic sites of narrowing.30

Free air, localized pneumatosis, adjacent inflammatory

changes, bowel obstruction, and other complications are

demonstrated on CT, along with the foreign body. Com-

mon causes of perforation include fish or chicken bones,

and toothpicks.29,31

In a recent series of seven patients with fishbone perfo-ration of the GI tract, the clinical diagnosis was not appar-

ent in any of the patients. The correct diagnosis was estab-

Figure 11 Unexpected ileal foreign body on CT performed for suspected bowel ischemia. A 78-year-old woman with

right abdominal pain. (A, B) CT scans show a subtle vertically oriented linear density which was correctly identifiedprospectively as a fishbone, which had perforated the adjacent ileum and resulted in inflammatory changes. FollowingCT, the patient underwent emergency surgery.

Figure 12 Duodenal, jejunal, and ileal diverticulitis. A 78-year old woman with lower abdominal pain, nausea, and

vomiting; 67-year-old woman with abdominal pain; and 88-year-old woman with metastatic breast cancer, now withbloody diarrhea, respectively. (A, B) Initial CT scan with oral contrast only, shows duodenal diverticulum (between

calipers) containing gas and a lith with central gas, with surrounding inflammatory changes (A). CT scan several dayslater (B) shows progressive soft-tissue swelling and inflammatory change in the same region related to duodenal

diverticulitis. (C, D) CT scans with oral contrast only, show free gas under the diaphragm (C) and a prominent jejunaldiverticulum that contains feces-like material and is associated with small bowel thickening and inflammatory changes

in the adjacent fat (D). (E, F) CT scans with oral and IV contrast show diverticulitis of the terminal ileum, withdiverticular disease and inflammatory changes.

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lished prospectively on CT in five of the patients, and thediagnosis was evident retrospectively in the other two.28

Small Bowel Diverticulitis

With the exception of Meckels diverticula, small boweldiverticula are acquired and involve only the mucosal andsubmucosal layers, usually along the mesenteric border.The pathogenesis of small bowel diverticulosis is unclear,although intestinal dyskinesis and high intraluminal pres-sures have been implicated. They are typically found inolder patients, often incidentally on imaging studies. Du-odenal diverticula are the most common and are solitary,

whereas small bowel diverticula in other locations are of-ten multiple.32-34 Small bowel diverticulitis is almost neversuspected clinically, and previously was almost never di-agnosed prospectively, until the advent of routine CT im-aging for acute abdominal pain. Patients present with in-termittent pain or an acute abdomen. Perforation,bleeding, or fistula formation may occur.32

CT findings of small bowel diverticulitis include a round oroval collection containing air and other feces-like material butusually not oral contrast, representing an outpouching on themesenteric side of the bowel, with associated inflammatorychanges and thickening of the adjacent bowel. There may alsobe an associated abscess in cases of frank perforation as well as

Figure 13 Meckels diverticulitis. A 13-year-old male with abdominal pain and Guaiac-positive stool. (A) CT scan

through the mid abdomen demonstrates the mouth of the diverticulum as a thick-walled structure (black arrows)adjacent to normalsmallbowel. Note thatthis proximal portion of thediverticulumopacifieswith oral contrast. Several

small pockets of extraluminal gas are present (arrowhead) adjacent to the diverticulum. (B) CT scan at a slightly lowerlevel shows inflammation of the peridiverticular fat, and avid mural enhancement of the diverticulum (black arrows) is

noted. Perforated Meckels diverticulitis was confirmed at laparotomy.

Figure 14 Perforated Meckels diverticulitis. A 4-year-old boy with severe abdominal pain. (A, B) CT scans show a rightlower quadrant abscess with an associatedtubular structure representing theportion of thediverticulum which has not

perforated (arrows, A) and inflammatory changes. A normal or abnormal appendix cannot be identified separate from

this process. Perforated Meckels diverticulitis with secondary appendicitis was found at surgery. (Color version offigure is available online.)

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adjacent diverticula in jejunalandilealdiverticulitis.32-35 The CTfindings are characteristic in our experience (Fig. 12).

The role of initial nonoperative management is not wellestablished, as there are few reported cases diagnosed pro-spectively with CT. The risk of recurrence or other compli-

cations following conservative management after initial CTidentification has also not been determined.

In contrast, Meckels diverticulum is congenital (from in-complete closure of the omphalomesenteric duct), containsall three intestinal layers, and is found along the antimesen-

teric side of the ileum. Diverticulitis occurs from obstruction,pepticulceration of ectopic gastric mucosa, or torsion. Meck-els diverticulitis may simulate appendicitis clinically and onCT (Figs. 13 and 14), but the diagnosis can be established ifthe diverticulum is identified on CT as being separate fromthe appendix and not contiguous with the cecal base.36,37

Rarely, Meckels diverticula may contain a lith or liths.38

In the largest seriesof CT findings of Meckelsdiverticulitisreported to date,36 11 patients had blind-ending pouches ofvariable size (short axis, 1.5 to 6 cm; long axis, 2 to 7 cm)with mural thickening. The diverticula contained gas, fluid,or particulatematerial,butnotoral contrast.There was muralenhancement and inflammation of the adjacent fat. The loca-tion was usually located in the midline but was also in theright lower quadrant in a minority, with a variable locationrelative to the terminal ileum (either superior or inferior).

A separate normal appendix was identified in seven pa-tients, and there was SBO in five.36 Definitive management issurgical.

HemoperitoneumSecondary to Abdominal Tumor

Although hemoperitoneumsecondary to abdominal tumor is

an uncommon scenario in Western countries, it is a relativelycommon presentation in parts of Africa and Asia. It is usually

Figure 15 Hemorrhagic hepatocellular carcinoma. A 67-year-oldman with severeacute abdominalpain, with no known

history of hepatitis or cirrhosis. At emergency laparotomy a large amount of acute hemoperitoneum and an activelybleeding hepatic mass were found. The liver lesion was oversewn and biopsy of the lesion revealed hepatocellular

carcinoma. (A) CT scan performed shortly after surgery shows a heterogeneously enhancing mass in the medial lefthepatic lobe (blackarrows) extendingto the liver surface. Acute hemoperitoneum is present aroundthe liver andspleen

(*). Note small pockets of pneumoperitoneum secondary to recent laparotomy (white arrow). (B) CT scan at slightlylower level demonstrates a second hepatic mass (black arrows) extending to the hepatic surface with hemorrhage (*)

adjacent to the tumor and in the left upper quadrant. The inferior portion of the first lesion (white arrow) extends intoa thrombosed left portal vein (arrowheads).

Figure 16 Unexpected hemorrhagic hepatocellular carcinoma. An80-year-old man with a history of bladder cancer, now with severe

abdominal pain. CT scan shows an exophytic left hepatic mass

(between calipers) which subsequently proved to be hepatocellularcarcinoma, with associated hemoperitoneum.



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related to capsular rupture of a hepatocellular carcinoma

(HCC) (Fig. 15). Occasionally, hepatic adenomas, metastases

(eg, hypervascular metastases such as melanoma, but also

from colon and lung, among others), or angiosarcomas can

also present with hemoperitoneum, as may other GI tract

tumors (such as GI stromal tumors).39-41 Patients present

with abdominal pain and signs of acute blood loss (hypo-

tension, tachycardia), increased abdominal girth, anemia,

and peritonitis. Bleeding related to HCC may occur at

initial presentation, and the diagnosis not suspected until

CT is performed (Fig. 16). Identification of the underlying

tumor may be challenging, depending on the extent of

intrahepatic hemorrhage and the size and extent of tu-

mor.39 HCC is generally highly vascular. Tumor necrosis

can lead to rupture of blood vessels penetrating the he-

patic capsule, although the mechanism by which HCCs (or

hepatic metastases) rupture is likely multifactorial and is

not entirely established.40,42

Rapid diagnosis is essential, especially in ruptured he-

patic malignancy, where the mortality is high even with

timely intervention. Long-term survival is poor, and he-

patic arterial embolization is an appropriate alternative to

surgery in some patients.42,43 Nonmalignant hepatic le-

sions are typically resected, as are other nonhepatic hem-

orrhagic tumors.

Gallstone Ileus

Gallstone ileus is bowel obstruction secondary to a gall-

stone, which has eroded into the gastrointestinal tract as a

result of chronic cholecystitis. The gallstone (or occasionallygallstones) usually erodes into the bowel at the level of the

duodenum.Theobstruction occurs at a site of bowel narrow-

ing, especially the ileocecal valve, and less likely at the duo-

denaljejunal junction, at the sigmoid colon, or at a patho-

logic site of stricture.44-46 Rarely, obstruction occurs in the

stomach or proximal duodenum (Bouverets syndrome).47,48

TheCT findings of gallstone ileus arecharacteristic andare

the equivalent of Riglers triad (Fig. 17): bowel obstruction,

pneumobilia (in the gallbladder/bile ducts), and a ra-

diopaque stone at the transition zone of dilated to collapsed

bowel. The triad is not present in all patients, even on CT.

The pneumobilia is variable and the gallstone is difficult tovisualize if not well calcified.44,45,49 In a series of 27 patients

with gallstone ileus,with retrospective comparison of CT and

plain films findings, pneumobilia and an ectopic stone were

seen in 82% on CT, with Riglers triad present in 78% on CT,

whereas the triad could be identified on plain films in only

15%.50 In a series of 40 patients with gallstone ileus by the

same authors, there were five with multiple endoluminal

gallstones. Stone size was variable but usually measured

greater than 2.5 cm.50 The morbidity and mortality of gall-

stone ileus may be substantial, especially in elderly patients.

Treatment is surgery. As with other bowel obstructions, the

CT findings can be used by the operating surgeon as aroadmap.

Figure 17 Gallstone ileus. A 61-year-old man with known type Baorticdissection andacute abdominal pain. (A)CT angiogramdem-

onstrates pneumobilia (black arrow). (B) CT angiogram at slightlylower level shows pockets of gas within the gallbladder lumen

(black arrows). (*) Duodenum. (C) CT angiogram through lowerabdomen shows multiple fluid-filled loops of small bowel (*) and

intraluminal gallstone at the transition point (white arrow). Notecollapsed distal small bowel (small white arrows).

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Gallbladder Torsion

Gallbladder torsion (a.k.a. volvulus) is rare and rarely cor-rectly diagnosed preoperatively. In a review of 400 cases,only four such patients were identified prospectively prior tosurgery. Gangrenous changes were found at surgery and pa-thology in half.51 Torsion may be incomplete (180 degree

twist) or complete. First reported in 1898 by Wendell as thefloating gallbladder, gallbladder torsion is usually seen inolder women (3:1 ratio).51 Predisposing factors include along mesentery, a gallbladder without mesenteric attach-ments, large gallstones which may cause mesenteric elonga-tion,kyphosis, and vigorous gallbladder peristalsis, althoughthe true etiology is unknown. The clinical and radiologicalfindings are similar to that of usual acute cholecystitis.52

However, there are radiologic findings which when com-bined with the awareness of the entity may permit prospec-tive diagnosis on sonography or particularly on CT.52-54 Themost suggestive imaging findings are an unusual position of

the gallbladder, especially a horizontal lie; location of thecystic duct to the right of the gallbladder; and a conical struc-ture at the gallbladder neck (Fig. 18).52,53,55 Treatment isemergency surgery.

Summary

This potpourriof uncommon andunusual causesof theacuteabdomen as demonstrated by CT is not intended to be all-inclusive, but reflects what we believe to be representative ofentities which, while not encountered on a routine basis, canoccasionally be identified in radiology practices where CT

imaging of patients with acute abdominal and pelvic com-plaints occurs on a daily basis. Radiologists need to be awareof these disorders so that appropriate patient managementmay occur prospectively.

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