IPR

Aatcbdam

ooaarao

RAAtddac

amuitccfi

D

A

2

maging of Abdomen andelvis: Uncommon Acute Pathologies

athachai Kaewlai, MD, Divya Kurup, MD, and Ajay Singh, MD

twtmtedraa

prcchtimavCdDi

cCwrcoaracswvd

cute abdomen is the most common cause of presentationto the emergency room. Although conditions such as

cute appendicitis, cholecystitis, pancreatitis, bowel obstruc-ion, and acute gynecologic pathologies are more commonauses of acute abdominal and pelvic pain, there are a num-er of uncommon acute pathologies that are important toiagnose because of either the high morbidity and mortalityssociated with them or their ability to mimic surgical abdo-en.We discuss the clinical findings, common imaging meth-

ds performed for diagnosis, and radiologic imaging featuresf uncommon abdominal pathologies that can present withcute abdomen. The conditions include ruptured abdominalortic aneurysm (AAA), acute mesenteric ischemia, perfo-ated peptic ulcer, volvulus, intussusception, internal hernia,cute epiploic appendagitis, and spontaneous splenic hem-rrhage.

upturedbdominal Aortic Aneurysm

AA is a permanent and irreversible localized dilatation ofhe abdominal aorta by � 1.5 times the expected normaliameter.1 Conventionally, the diagnosis is made when theiameter of the abdominal aorta is � 3 cm. They account forpproximately 15,000 deaths per year and is the 13th leadingause of death in the United States.2

The patients typically present with the triad of suddenbdominal or flank pain, shock, and pulsatile abdominalass. Most patients arriving at the emergency departmentsually have ruptures of the posterolateral wall, which leak

nto the retroperitoneal space. The aortic rupture of the an-erolateral wall is often associated with sudden death. In rareircumstances, rupture into the duodenum or inferior venaava may occur, resulting in aortoduodenal or aortocavalstula, respectively.

epartment of Radiology, Massachusetts General Hospital, Harvard MedicalSchool, Boston, MA.

ddress reprint requests to Ajay Singh, MD, Massachusetts General Hospi-tal, Harvard Medical School, 10 Museum Way, # 524, Cambridge, MA-

t02141. E-mail: mghpartners@yahoo.com

28 0037-198X/09/$-see front matter © 2009 Elsevier Inc. All rights reserved.doi:10.1053/j.ro.2009.05.004

Computed tomography (CT) is the modality of choice forhe diagnosis of ruptured AAA3-5 because of its high accuracy,ide availability, and short scan time. In addition, informa-

ion from CT can be helpful for surgeons to determine treat-ent options. Ultrasound (US) is considered less useful in

he diagnosis of this condition due to its limited ability tovaluate the entire abdominal aorta and operator depen-ency. Although magnetic resonance imaging can depictuptured AAA, it is not commonly used because of long im-ging time, difficulty in scanning an ill patient, and limitedvailability in the emergency department.

The most common CT finding of ruptured AAA are retro-eritoneal hematoma in the vicinity of AAA (Fig. 1).3,4 Ret-operitoneal hematoma appears on CT as hyperattenuatingollection predominantly in the retroperitoneal space, in-luding the perirenal and pararenal spaces. Retroperitonealematoma from ruptured AAA almost always involves mul-iple retroperitoneal compartments.3 If CT is performed withntravenous contrast administration, contrast extravasation

ay be visualized and is considered the most direct sign ofortic rupture. In most cases, even without the use of intra-enous contrast medium, aortic aneurysms are apparent.alcification of the aneurysm wall should be traced for evi-ence of discontinuity that can signify the site of rupture.isruption of calcification is a specific but uncommon find-

ng in ruptured AAA.6

Mural thrombi are common within the aneurysm sac andan have homogeneous or heterogeneous low attenuation onT. The crescent sign represents crescentic hyperattenuationithin the luminal thrombus or plaque in the aneurysm. A

adiologic-pathologic correlation study has shown that cres-ent sign may represent hemorrhage in the mural thrombusr in the aneurysmal wall that tracks from the lumen throughcleft in the thrombus within an aneurysm.7 It may be seen inuptured or impending-ruptured AAA on CT. The sensitivitynd specificity of crescent sign for the diagnosis of compli-ated AAA is 77% and 93%, respectively.8 “Draped aortaign” refers to an abnormal contour of the posterior aorticall, which is ill-defined and drapes around the anteriorertebral body instead on axial CT images. It represents aeficient posterior aortic wall that can be seen with a con-

ained rupture of AAA.9

AAaeioupclob

ac(

elblcdteettcso

m1m

Fotp(r

Fat(

Imaging of abdomen and pelvis 229

cute Mesenteric Ischemiacute mesenteric ischemia is an uncommon cause of acutebdominal pain, but can be life-threatening if not diagnosedarly in the course of disease. An end point of mesentericschemia is bowel necrosis, which can lead to high mortalityf 50%-93%.10-12 Patients with acute mesenteric ischemiasually present with nonspecific abdominal pain, often dis-roportionate to the clinical findings. There are 3 majorauses of acute mesenteric ischemia: arterial thromboembo-ism, venous thrombosis, and nonocclusive ischemia. An-ther possible cause is ischemia secondary to strangulatedowel obstruction.Arterial thromboembolism is the most common etiology of

cute mesenteric ischemia, accounting for 60%-70% of allases.11,12 It typically involves the superior mesenteric arterySMA), the occlusion of which is most frequently due to

igure 1 Ruptured AAA. Axial contrast-enhanced CT show a heter-geneous hyperattenuating collection (stars) in the right retroperi-oneal space, predominantly in the posterior pararenal space, dis-lacing the right kidney anteriorly. There is active extravasationarrows) of intravenous contrast material in the right para-aorticegion.

Figure 2 Superior mesenteric artery (SMA) embolism. Axshows total occlusion (arrow) of the SMA. Coronal-reforto ileocolic branch (arrowheads). The filling defect for

embolus.

mbolism from cardiac source (Fig. 2). The embolus usuallyodges within 3-10 cm from the origin of the SMA, or justeyond the origin of middle colic artery.13,14 Although iso-

ated occlusion of a single proximal mesenteric vessel may beompensated by collateral circulation, the occlusion of theistal segment usually results in bowel ischemia. Acutehrombosis of the mesenteric artery is less common thanmbolism. It usually occurs in patients with pre-existing ath-rosclerosis and is common within 2 cm from the origin ofhe SMA. It may occur because of mesenteric artery dissec-ion, secondary to extension of aortic dissection flap. Nonoc-lusive ischemia occurs in the setting of acute cardiogenichock or hypoperfusion state secondary to vasoconstrictionf mesenteric arteries. It accounts for 20%-30% of all cases.

Venous thrombosis of the mesenteric veins is the least com-on cause of acute mesenteric ischemia at less than 10%-

5% of all cases.12,14 Mesenteric venous thrombosis (Fig. 3)ay be secondary to portal venous thrombosis, hypercoagu-

trast-enhanced CT (A) in arterial phase of enhancementCT (B) shows an oblong filling defect (arrow) proximalacute angle with the arterial wall, consistent with an

igure 3 Intestinal ischemia due to venous thromboembolism. Anxial contrast-enhanced CT shows occlusion of the superior mesen-eric vein (arrow), bowel wall thickening (white stars) of the colonCo), and pneumatosis intestinalis (black arrows).

ial conmattedms an

ldcvcei

soasiwmtbp

sepscmitcwoptcmmflacc

fim

PSiotmumostiicfcpap

ctttepacs

CVoa

230 R. Kaewlai, D. Kurup, and A. Singh

ation, trauma, intra-abdominal neoplastic or inflammatoryiseases, vasculitis, or recent splenectomy. However, manyases are idiopathic. Isolated thrombosis of the proximaleins is usually well tolerated due to the presence of extensiveollaterals. In contrast, thrombosis of distal branches of mes-nteric veins has poorer outcome, often leading to bowelschemia and hemorrhagic infarction.12

There are 3 pathologic stages of bowel ischemia.12 The firsttage is a reversible ischemic change that involves the mucosaf the bowel resulting in erosion, ulceration, hemorrhage,nd necrosis. In the second stage, there is necrosis of the deepubmucosal and muscular layers of the bowel. The third stages transmural infarction of bowel wall. The degree of bowelall edema, hemorrhage, and congested mesenteric fat isore pronounced in bowel ischemia caused by venous

hrombosis compared with that of arterial causes. Whenowel ischemia occurs in the colon, there is usually superim-osed infection.Abdominal CT with CT mesenteric angiography has been

hown to be useful in the diagnosis of acute mesenteric isch-mia. One study used multidetector technology, appropriaterotocol, and predefined diagnostic criteria and demon-trated 96% sensitivity and 94% specificity.11 The most spe-ific CT signs of mesenteric ischemia are presence of pneu-atosis intestinalis, occlusion of SMA, combined celiac and

nferior mesenteric artery occlusion, embolus in the mesen-eric artery, and gas in the SMA or portal vein. The mostommon CT finding in acute mesenteric ischemia is bowelall thickening, which could be due to edema, hemorrhage,r superimposed infection. Bowel wall thickening is moreronounced in mesenteric ischemia resulting from venoushrombosis and colonic infarction. The former is likely be-ause of venous congestion and hemorrhage, while the latteray represent superimposed colonic infection. Other com-on CT findings include mesenteric fat stranding, dilateduid filled bowel, abnormal bowel wall enhancement, andscites.11,15 The presence of mesenteric fat stranding and as-ites with other evidence of small bowel ischemia may indi-ate transmural necrosis of the small bowel. However, these 2

Figure 4 Gastric ulcer perforation. Axial contrast-enhanc(between arrowheads), resulting perforation into the les

minal air bubbles (arrows) in the left subhepatic space.

ndings are not useful in differentiation between nontrans-ural and transmural colonic ischemia.12

erforated Peptic Ulcerurgical complications of peptic ulcer disease have dimin-shed in the past several years, owing to better understandingf pathophysiology and improved medical treatment of pep-ic ulcer disease. Acute duodenal ulcer perforation is esti-ated to occur in 2%-10% of patients with ulcers.16 Peptic

lcers on the anterior wall of the stomach and duodenumay perforate into the peritoneal cavity, as opposed to the

nes on the posterior wall that may perforate into the lesserac or retroperitoneal spaces. The most common site of pos-erior wall peptic ulcer perforation is the pancreas, resultingn pancreatitis or abscess. Perforated ulcers may seal off rap-dly; therefore, little extraluminal air can be seen in someases. CT may be valuable in evaluation for possible cause ofree air and the site of perforation.17 CT is more sensitive thanonventional radiography for detection of subtle pneumo-eritoneum, and is far superior in demonstration of free fluidnd abscess formation.18-20 In addition, CT may show a site oferforation in up to 53%-86% of cases.17,20

The imaging signs of peptic ulcer perforation on CT in-lude presence of pneumoperitoneum, localized fluid, andhickening of gastric or duodenal wall. The location of ex-raluminal air is helpful to differentiate peptic ulcer perfora-ion from other causes of perforation. The predominance ofxtraluminal air in the vicinity of stomach or duodenum andresence of fluid collection between duodenum and pancre-tic head may suggest peptic ulcer perforation.21 In rare cir-umstances, a focal bowel wall defect (perforation site) iseen (Fig. 4).

olonic Volvulusolvulus is a form of closed-loop bowel obstruction thatccurs when the loop of bowel, usually colon, rotates aroundfixed point. Most frequently, volvulus involves the sigmoid

(A) shows a defect in the posterior wall of stomach (S). Axial contrast-enhanced CT image (B) several extralu-

ed CTser sac

claitad

vlplcoa

sssatbcnlsaa

tt

Imaging of abdomen and pelvis 231

olon and cecum.22 Persistent twist of colonic loop in volvu-us results in mechanical obstruction, followed by ischemiand necrosis of colonic wall. The patients with volvulus typ-cally present with abdominal pain, distention, and obstipa-ion. Frequently, they have experienced recurrent episodes offorementioned symptoms and have history of previous ab-ominal surgery.22,23

Sigmoid volvulus is the most common form of colonic vol-ulus, seen more commonly in men in the sixth decade ofife.24 Elderly patients with chronic constipation, and youngregnant women are at higher risk of having sigmoid volvu-

us.25 Although abdominal radiograph can be diagnostic,lassic findings on radiograph are present in only 37%-65%f the time.22,24 In classic sigmoid volvulus cases, a supinebdominal radiograph shows an area of hyperlucency, re-

Figure 5 Sigmoid volvulus. Supine abdominal radiographconfiguration. Axial contrast-enhanced CT (B) show a mabdomen, a bird-beak appearance (arrowheads) at the

enema (C) shows complete obstruction of the sigmoid colon w

embling a shape of coffee bean arising from the pelvis. Theuperior part (apex) of volvulus may lie in the right- or left-ided abdomen, or in the midline, and may occupy the entirebdomen.25 If abdominal radiograph is nonrevealing in pa-ients with suspected volvulus, a single contrast enema maye performed and show an abrupt termination of colonicontrast medium in a bird-beak appearance.26 CT and mag-etic resonance imaging showed dilated loop of sigmoid co-

on with bird-beak appearance of the afferent and efferentegments. There is a whirl-like pattern of sigmoid mesocolonnd vessels (whirl sign).27 The whirl sign is highly suggestive,nd is a key feature of bowel volvulus (Fig. 5).28,29

Cecal volvulus accounts for 41% of all colonic volvulus andypically seen in young to middle-aged adults.22,23,26 In con-rast to sigmoid volvulus, cecal volvulus is usually associated

ows dilated sigmoid colon (arrowheads) in coffee beany dilated sigmoid colon (S) with air-fluid level in the leftof volvulus, and a whirl sign. Single-contrast barium

(A) sharkedlpoint

ith beak-shaped narrowing (curved arrow) at its tip.

wcputvlmaeafbmspmcftd

AIcapasstwaeiec

otttIsm

Tbefoiiwllipp

ibatitcrctrtps

Fca

Ftt

232 R. Kaewlai, D. Kurup, and A. Singh

ith anatomic variation when there is hypermobility of ce-um due to abnormal fixation of the cecum to the posteriorarietal peritoneum. However, this anatomic variant is notncommon; it is found in 11%-25% of the general popula-ion.30 Other predisposing factors associated with cecal vol-ulus are presence of abdominal mass, adhesions, or calcifiedymph nodes.23 Conventional radiograph of cecal volvulus

ay reveal a rounded air-filled distended colonic segmentrising from the right lower quadrant of the abdomen andxtending to the left upper quadrant. However, radiographsre diagnostic in only 38%-46% of cases.22,23 CT can be use-ul as it can show air- or fluid-filled dilated cecum with aird-beak appearance (Fig. 6).26 A whirl-like appearance ofesocolon and vessels can be visualized. CT findings may

uggest signs of complications, such as ischemia, necrosis, orerforation, when there is thickening of the cecal wall, pneu-atosis, or extraluminal gas.23,26 A variant of cecal volvulus is

alled cecal bascule. A cecal bascule occurs when the cecumolds anteriorly without torsion, resulting in a distention ofhe cecum. On CT, it appears as a dilated cecum in the mi-abdomen without twisting segment or a whirl sign.23,26

dult Intussusceptionntussusception is an uncommon condition in adult, ac-ounting for 1% of mechanical bowel obstruction and 5% ofll intussusceptions.31 Intussusception occurs when theroximal segment of bowel telescoping into the lumen of andjacent distal segment. Intussusceptum refers to the proximalegment that enters the lumen of distal intussuscipiens. Intus-usception may occur in patients of any age from the secondo ninth decade, with a mean age of 50 years.31 It may presentith abdominal pain of acute, intermittent or chronic onset,

nd symptoms of bowel obstruction.32 Intussusception is cat-gorized into enteric, enterocolic, and colonic types accord-ng to location. The frequency of enteric intussusception isqual to colonic intussusception in many surgical series, in

igure 6 Cecal volvulus. Axial unenhanced CT reveals a dilated ce-um (arrowheads) with an air-fluid level, a whirl sign (arrow), andscites (star).

ontrast with radiological series that enteric intussusception t

ccurs more often.33 The difference may be accounted byransient enteric intussusception often captured on cross-sec-ional imaging. Transient enteric intussusception is believedo be due to temporary abnormal rhythm of bowel peristalsis.t is common in proximal small bowel and frequently ob-erved in patients with celiac disease, Crohn disease, andalabsorption syndrome.34,35

Most adult intussusceptions have demonstrable etiology.31

he lead point of adult intussusception can be adhesionands and benign or malignant neoplasms. The mural andxtraluminal lead point cause intussusception by producingocal abnormal peristalsis at that portion, resulting in rotationr kinking of the adjacent bowel segment and subsequentntussusception.36 While presenting, lead points of colonicntussusception are more frequently neoplastic comparedith that of enteric intussusception. The lead point for co-

onic intussusception could be adenocarcinoma, adenoma,ipoma, or lymphoid hyperplasia. The lead point for entericntussusception could be adhesion, Meckel diverticulum,olyps, lipoma, metastatic disease (especially melanoma), orrimary small bowel adenocarcinoma.31

CT is the imaging method of choice for the diagnosis ofntussusception in adults and is not limited by the presence ofowel gas as opposed to US.34,37 On CT, intussusceptionppears as a complex soft-tissue mass (thickened segment ofhe bowel) that consists of outer intussuscipiens and innerntussusceptum (Figs. 7 and 8). Mesenteric fat and mesen-eric vessels are often visible and located eccentrically in theomplex mass of intussusception. Occasionally, curvilinearim of oral contrast medium is seen encircling the intussus-eptum. If CT was obtained perpendicular to intussuscep-ion, it appears as a rounded mass with rings of stratificationepresenting bowel wall edema or fluid trapped between in-ussusceptum and intussuscipiens. When CT scan plane isarallel to the intussusception, it is shown as a sausage-haped soft-tissue mass. Transient intussusception typically

igure 7 Small bowel intussusception due to gastrointestinal stromalumor (GIST). Axial contrast-enhanced CT shows small bowel in-ussusception (arrows) in the midpelvis. The central fat in the in-

ussusceptum represents the mesenteric fat.

sb

pscrs

iirl

IIacbsmccg

shltafTe

hcst

hlnCptadghpttarttdrdv

lWhbemrmootitqt

).

Imaging of abdomen and pelvis 233

hows only minor dilatation of the involved loop withoutowel obstruction.35

The CT signs suggestive of superimposed vascular com-romise of intussusception are fluid or gas collection in thepace enclosed by entering and returning walls of intussus-eptum (extraluminal fluid, gas) and hypoattenuation of theeturning wall of intussusceptum.38 The presence of asciteshould raise a suspicion of complicated intussusception.39

The findings that may favor a neoplastic etiology of adultntussusception include a longer length, larger diameter ofntussusception, and evidence of bowel obstruction.33 Indi-ect evidence of malignant lead point is the presence ofymphadenopathy or metastatic disease.

nternal Hernianternal hernia is herniation of abdominal viscera into anperture bounded by visceral peritoneum in the abdominalavity. One of the most frequently herniated viscera is theowel. Internal hernia usually causes abdominal pain andmall bowel obstruction,40 which can be persistent or inter-ittent. In some cases, symptoms may be mild and nonspe-

ific, leading to delayed diagnosis.41 The most feared compli-ations are strangulation, subsequent bowel ischemia, andangrene.41

There are several types of internal hernia, which are clas-ified by location of visceral peritoneal openings or where theerniated contents lie. This includes paraduodenal (right and

eft), pericecal, foramen of Winslow, transmesenteric andransmesocolic, pelvic and supravesical, sigmoid mesocolon,nd transomental internal hernias, in the order of decreasingrequency.42 Internal hernias may be congenital or acquired.he examples of acquired internal hernia includes transmes-nteric hernia liver transplantation and Roux-en-Y bypass.43

The CT finding helpful in making the diagnosis of internalernias includes abnormal bowel configuration in a saclikeluster. The other findings include mesenteric engorgement,tretching, and displacement of mesenteric vascular struc-

Figure 8 Colonic intussusception due to adenocarcinomafat (stars) sigmoid colon into the rectosigmoid junctionintussusceptum on the sagittal-reformatted CT image (B

ures (Fig. 9).42-45 q

Paraduodenal hernias are the most common type of internalernia and occur either to the right (fossa of Waldeyer) or to

eft of the duodenum (fossa of Landzert).41,43 Left paraduode-al hernias are 3 times more common than the right ones.41,43

T shows a saclike cluster of small bowel located between theancreatic body or tail and stomach, above and to the left ofhe ligament of Treitz. The inferior mesenteric vein is seennterior to the herniated sac.42 Inferior displacement of theuodenojejunal junction and transverse colon occurs. En-orgement, crowding, and stretching of vessels supplying theerniated bowel are noted at the entrance of the sac. In rightaraduodenal hernias, bowels herniated through a defect inhe right mesocolon into a fossa of Waldeyer inferior to theransverse segment of duodenum. Herniated sac is boundednteriorly by the mesentery, which contains the SMA andight colic vein at the anteromedial border, and posteriorly byhe aorta. SMA serves as an important landmark in charac-erizing right paraduodenal hernia on CT.42 Right paraduo-enal hernia is associated with developmental incompleteotation of the duodenum, which results in absent horizontaluodenum and abnormal location of superior mesentericein to the left and ventral to SMA.42,45

Foramen of Winslow is a 3-cm vertical slit between theesser sac and greater peritoneal cavity. Hernias of foramen of

inslow are uncommon, accounting for 8% of all internalernias.42 The CT shows an abnormal location of herniatedowel loops in the lesser sac or high subhepatic space. Mes-nteric fat is visualized between the inferior vena cava andain portal vein. There is absence of ascending colon in the

ight paracolic gutter if this part of colon herniates.42 Trans-esenteric hernias are hernias of bowel through a congenitalr acquired defect in the mesentery or omentum. Of all casesf transmesenteric hernias, 35% occur in children, possiblyhrough congenital defects near the origin (ligament of Tre-tz) or termination (ileocecal valve) of small bowel mesen-ery.42,43 In adults, hernias typically occur through an ac-uired defect due to previous gastrointestinal tract surgery,rauma, or intraperitoneal inflammation. They are more fre-

enhanced CT image (A) shows telescoping of mesocolics). A complex mass is shown at the lower end of the

. Axial-(arrow

uently seen at present due to increased rate of Roux-en-Y