Reviews and Commentary n Review for Residents 651 ------1

www.rsna.org/rsnarights. aging findings in multiple causes of large-bowel obstruc aging findings in multiple causes of large-bowel with acute colonic pseu and compared illustrated tion are do-obstruction. © RSNA, 2015 Large- is an abdominal emergency with emergency abdominal an is obstruction Large-bowel Al if left untreated. mortality rates high morbidity and is usually the initial imag though abdominal radiography large- having of suspected in patients study performed ing not be sufficient to distinguish obstruction, it may bowel other causes of colonic dilatation. Com obstruction from it as choice of method imaging the is tomography puted ob of large-bowel can establish the diagnosis and cause be used to confirm agent enema may struction. A contrast the im obstruction. In this review, large-bowel or exclude Classic Radiographic and and Radiographic Classic

Adult: and Mimics Etiology, CT Findings, Large-Bowel Obstruction in the in Obstruction Large-Bowel radiology.rsna.org

n T.J. T.J.

e 2015 This copy is for your personal non-commercial use only. To order presentation-ready presentation-ready order To personalonly. use non-commercial for your is copy This

Jun ). Note: at us contact clients, or colleagues distribution for copies to your Address correspondence to Volume 275: Number 3— 275: Volume [email protected] RSNA, RSNA, 2015 From the Department of Radiology, Duke University the Department of Radiology, From

q Received April 16, 2014; revision requested June 9; April 16, Received revision received July 3; accepted July 21; final version accepted July 31. (e-mail: Medical School, Box 3808, Durham, NC 27710 (T.J.); NC 27710 (T.J.); Durham, 3808, Box Medical School, Administration Hospital, Veterans Department of Radiology, and Department of Radiology, NM (W.M.T.); Albuquerque, NM (W.M.T.). Albuquerque, University of New Mexico, 1 Radiology: Tracy Jaffe, MD MD Jaffe, Tracy MD Thompson, William M. Review for Residents: Large-Bowel Obstruction in the Adult Jaffe and Thompson

cute complete large-bowel obstruc- The purpose of this review is to fa- stalsis (8). In the setting of vascular tion (LBO) is an abdominal emer- miliarize radiologists and radiology res- compromise and , patients of- Agency, with high morbidity and idents with basic knowledge of the im- ten demonstrate substantial abdominal mortality rates if left untreated (1,2). aging findings diagnostic of LBO and to tenderness. While LBO may develop over a pro- review the complications that require The competence of the ileocecal tracted period of time, the clinical pre- emergent surgical and endoscopic in- valve influences the response of the co- sentation is often acute and includes tervention. This review will focus on the lon. If the ileocecal valve is competent, abdominal pain, or obsti- most widely used imaging methods for which occurs in about 75% of patients, pation, and abdominal distension (3). the evaluation of LBO: radiography, con- an LBO will result in a closed -loop ob- The marked distension of colon proxi- trast agent enema, and multidetector struction, which cannot decompress mal to the level of obstruction leads to computed tomography (CT). The final into the small bowel (4). According to mucosal edema, bowel ischemia, and, if portion of this review describes the ma- the La Place law, the intraluminal pres- not treated, bowel and perfo- jor mimic of LBO, acute colonic pseudo- sure needed to stretch the wall of a hol- ration. While the same principles of obstruction (ACPO). low tube is inversely proportional to the initial management of small-bowel ob- radius of the tube. Because the cecum struction (SBO) (attention to strangula- is the largest diameter of the colon, it tion, hydration, and nasogastric suction) Clinical Findings and Pathophysiology requires the least amount of pressure are used in LBOs, emergency surgery An LBO occurs when there is occlusion to distend (9,10). Cecal distension will or colonoscopy is usually required to of the lumen of the colon anywhere lead to increased wall tension and with- relieve the obstruction (4). along its course and dilatation of the out intervention, will progress to ische- LBO is four to five times less frequent large bowel proximal to the site of ob- mia and necrosis. The exact size of the than SBO and the causes of LBO and struction. Both the clinical findings and cecum at risk for perforation ranges in SBO differ substantially (5) (Table 1). Co- the pathophysiology of LBO differ sub- the literature from 9 to 12 cm (5). In lonic malignancy remains the most com- stantially from SBO. Patients with LBO intermittent or chronic obstruction, mon cause of LBO (. 60%) (4,6). Addi- are usually elderly and the signs and however, the cecal wall may become hy- tional causes of LBO include entities such symptoms of LBO are often insidious in pertrophied and the colon may greatly as , colonic , and ad- contrast to the abrupt onset of symp- exceed 10 cm in diameter without per- hesions. Colonic obstruction is most of- toms seen in most SBOs; these symp- foration (11). It is important to note ten seen in elderly individuals, as the toms include abdominal pain, constipa- that the exact size of the cecum is less aforementioned causes of obstruction are tion or obstipation, and abdominal important than the duration and rapid- more common in advanced age groups. distension (3,5). The major sites of ob- ity of cecal distension (12–13). An in- Of note, the etiology of LBO worldwide struction include the cecum, hepatic competent ileocecal valve will decom- varies substantially as does the patient and splenic flexures, and recto-sigmoid press the LBO into the small bowel. population affected; in Africa and India, colon. LBO occurs more frequently The resultant small-bowel distension volvulus is the primary cause of LBO within the left colon (5). may mimic a distal SBO. (50%), and patients in these areas are The etiology of the LBO may be sug- usually young and healthy (7). gested by the specific symptoms and presentation of the patient. LBO caused Abdominal Radiography Technique by obstruction in the left colon mani- Abdominal radiography is usually the fests earlier than that caused by ob- first imaging study performed in pa- Essentials struction in the right colon because the tients suspected of having LBO (4,5,14). nn Large-bowel obstruction (LBO) lumen of the sigmoid and descending The examination should include supine differs substantially from small- colon is smaller and the stool is more and nondependent (either upright or bowel obstruction (SBO), and inspissated in the distal colon (3). Ob- left lateral decubitus) radiographs to aid LBO is an abdominal emergency. struction from sigmoid diverticulitis in the diagnosis of LBO and exclude an nn Abdominal radiography can differ- may manifest with symptoms of left SBO and to detect . entiate LBO from SBO. lower quadrant pain, fever, and a palpa- ble mass. Colonic volvulus, especially in Published online nn CT has become the standard im- the setting of chronically distended co- 10.1148/radiol.2015140916 Content code: aging procedure for patients with lon, may include symptoms of chronic both SBO and LBO. Radiology 2015; 275:651–663 abdominal distension and abdominal nn CT is highly accurate and well tol- pain. At the time of the acute volvulus, Abbreviations: erated and allows acquisition of these patients rapidly develop acute ACPO = acute pseudo-obstruction images in all patients; CT also pain and distension. Bowel sounds are LBO = large-bowel obstruction SBO = small-bowel obstruction helps distinguish the cause of LBO usually hypoactive in patients with LBO; and its complications. this is caused by the cessation of peri- Conflicts of interest are listed at the end of this article.

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Table 1 Figure 1 Figure 2 Causes of LBO Cause Specific Signs

Common Neoplasm (primary colon (.95%) carcinoma) (60%–80%) Volvulus (11%–15%) Sigmoid Cecum Transverse colon Diverticulitis (4%–10%) Uncommon Intussusception (,5%) Inflammatory bowel disease Extrinsic compression from abscess or other masses Intraluminal foreign body

Source.—References 16 and 86. Figure 1: Anteroposterior supine abdominal radio- graph in a 67-year-old man with LBO shows dilated Figure 2: CT scout radiograph in a 51-year-old ascending, transverse, and descending colon. A woman with chronic abdominal pain and cecal shows a distended and medially displaced cecum Merits of Abdominal Radiography transition point is identified in the region of splenic flexure from an obstructing colon carcinoma (arrow). (arrow). Gas is present throughout the entire colon. While the reported sensitivity of ab- CT showed no colonic obstruction. dominal radiography for the detection of LBO is similar to that for the detec- though intramural gas is recognized as tion of SBO (84% vs 82%, respec- a sign of necrosis and developing perfo- cent opiate use, critical illness, neurologic tively), the reported specificity is con- ration, the presence of pneumatosis in disorders, and metabolic disturbances siderably different (72% vs 83%, the setting of LBO does not always indi- (19). ACPO is described as an acute di- respectively) and as a result, it may be cate transmural infarction but should latation of the colon due to altered auto- difficult to distinguish between obstruc- be considered a worrisome finding for nomic innervation of the colon. Unlike tion and colonic pseudo-obstruction in threatened necrosis (12,17). Pseudo- in an adynamic ileus, perforation may a patient with a distended colon pneumatosis intestinalis, the appear- occur with ACPO. Both entities are (15,16). Normal colonic caliber ranges ance of gas trapped within feces or characterized by colonic dilatation with from 3 to 8 cm, with the largest diame- against the mucosal surface, may mimic preserved haustration, smooth inner ter in the cecum; the remainder of the pneumatosis and is commonly seen in wall contour, and normal colonic wall colon is dilated when it is greater than the cecum and the ascending colon thickness. Adynamic ileus is routinely 6 cm and the cecum is not larger than 9 (18), CT is helpful in distinguishing be- characterized by small-bowel dilatation cm in diameter. In the setting of LBO, tween these two diagnoses. as well (19). Colonic distension due to the colon is dilated proximal to the site these entities usually occurs with mini- of obstruction with a paucity or ab- Challenges of Abdominal Radiography in mal fluid; the presence of air-fluid sence of gas distal to the obstruction Patients with LBO levels should raise the suspicion of an (Fig 1). Air-fluid levels are often seen in One of the challenges facing radiolo- obstruction (19,20). Toxic , a the dilated colon on the upright or de- gists and clinicians is determining the complication of a variety of infectious, cubitus radiographs (5). The presence cause of a diffusely dilated colon ( 6 cm) ischemic, and inflammatory diseases of air-fluid levels suggest that the cause on abdominal radiographs. Pseudo- of the colon, is characterized by its of obstruction is more acute since the obstruction, dilatation of the colon with- hallmark feature of marked bowel wall colonic fluid has not been present long out mechanical obstruction, can occur thickening, loss of haustration, and enough to be absorbed. as a result of adynamic ileus, ACPO segmental parietal wall thinning (11,21). Abdominal radiography that in- (also known as ), or The presence of cecal distension may cludes an upright or decubitus radio- . Adynamic ileus can be be seen in LBO, colonic ileus, ACPO, and graph can also be used to identify com- characterized by diffuse small- and large- toxic megacolon. Johnson et al (22) de- plications of LBO, such as pneumatosis, bowel dilatation without a transition point. scribed the phenomenon known as ce- portal venous gas, and pneumoperito- Common causes of adynamic ileus in- cal ileus as the clinical condition that neum. It is important to note that al- clude recent gastrointestinal surgery, re- occurs when patients with a mobile ce-

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cum develop an adynamic ileus with dis- to a transition point and decompressed Figure 3 placement of the cecum anteromedially bowel distal to the obstruction. The (Fig 2). Relative cecal size may be use- presence of a transition point is con- ful in determining if a large bowel is sidered a reliable finding for the diag- present; as Wittenberg (9) notes, if the nosis of LBO (3,24). colon is diffusely distended and the ce- cal diameter is clearly less than that of CT Technique the other colonic segments LBO is un- A reasonable scanning protocol for a likely. It may be difficult to distinguish routine abdominal and pelvic CT with a between a low colonic obstruction and 64-detector scanner would include the a colonic ileus as the absence of distal following acquisition parameters: heli- rectal gas is seen in both entities. The cal mode, 120 kVp; beam pitch, 0.8– converse is also true as small amounts 1.375; automated tube current modula- of distal rectal gas may be present in tion with minimum tube current, the setting of LBO as well as ileus. The 100–150 mAs; reconstruction section presence of rectal gas should not ex- thickness, 5 mm. If possible, the admin- clude the diagnosis of LBO, but frank istration of intravenous contrast agent distention of the implies a co- is recommended as it adds to the iden- lonic ileus. Acquisition of a prone or tification of the presence of a mass, as right lateral decubitus radiograph may well as signs of inflammation and bowel also be helpful in ruling out LBO: Gas wall ischemia. Iodinated intravenous will be restricted in a bowel obstruc- contrast agent can be given with a tion but will move to the distal colon weight-based protocol or in a routine and decompress in the setting of pseu- volume (eg, 150 mL) and a rate of 3 do-obstruction (Fig 3). Despite these mL/sec with a delay of 70 seconds, dissimilarities in presentation, the dif- which is sufficient for portal venous im- ferentiation between LBO and pseudo- aging in most patients. Oral contrast obstruction remains difficult and CT agent administration is controversial in should be used to better distinguish the setting of acute abdominal pain, between the two diagnoses. and its use is quite variable (26–29). Coronal and multiplanar reforma- tions aid in the identification of the Multidetector CT course of the distended bowel and the CT is the imaging modality of choice exact location of obstruction. If confu- Figure 3: Images in a 71-year-old man in a per- for the diagnosis of the cause of LBO. sion about the diagnosis of LBO per- sistent vegetative state after a pontine hemorrhage. Multidetector CT is a well-tolerated, sists, water-soluble rectal contrast (a) Anteroposterior supine abdominal radiograph shows rapid imaging examination that allows agent can be administered to better marked dilatation of the entire colon. (b) Right lateral acquisition of images in one breath document obstruction. decubitus radiograph shows gas filling the entire colon hold in the frail without the need for down into the sigmoid colon and rectum (arrows). the use of rectal contrast agent or air Pitfalls of CT Imaging of LBO insufflation. Thin sections and multi- Spasm at the splenic flexure in a nor- planar reformatting provide accurate mal colon may mimic a fixed narrow- short annular desmoplastic colonic le- delineation of large-bowel morphology. ing (25). It is important to note that sions on CT scans, particularly if CT can be used to diagnose intralumi- the transitional region in pseudo-ob- there is partial luminal obstruction nal, mural, and extramural causes of struction tends to be at or near the with limited distension of the proxi- LBO. In patients with LBO secondary splenic flexure (30). Dilatation of the mal colon to delineate the lesion. This to malignancy, CT offers the additional ascending and transverse colon with pitfall is more common in right-sided benefit of detecting local and regional distal collapse can be seen in both colonic tumors (19). metastases. CT is also an excellent im- ACPO and chronic colonic pseudo- aging modality for the detection of in- obstruction. Additionally, the “colon flammation and bowel ischemia. The cut-off” sign, an isolated gaseous dis- The Contrast Enema detection of LBO with CT has been tension of the ascending colon and Although CT has become the pre- reported to have a sensitivity and spec- hepatic flexure in the setting of pan- ferred imaging study for evaluation of ificity of 96% and 93%, respectively creatitis, can also mimic an LBO (31). LBO, there are some indications for (3,23–25). The diagnosis of LBO is Finally, as Beattie et al (25) note, performing a contrast enema. The based on dilated large bowel proximal there is also potential for missing major advantage of the contrast en-

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Figure 4 necrosis or rarely air within the mass, the latter appearance may resemble an abscess (37). Recognition of proximal colonic dilatation aids in identification of the transition point at the site of tu- mor. Colonic malignancy may mimic diverticulitis if there is pericolonic spread with infiltration of the perico- lonic fat. The identification of perico- lonic lymph nodes larger than 1 cm in short axis should raise the suspicion of malignancy (38). It should be noted that not all enlarged pericolic lymph nodes contain tumor, and normal-sized nodes may have microscopic tumor in- Figure 4: Images in a 76-year-old man with LBO from a descending colon cancer. (a) CT scout image volvement (37). Nodal metastases can shows air-filled dilated colon terminating in the left upper quadrant (arrow).(b) Midline coronal reformatted be located in expected regional drain- CT image of the abdomen and pelvis after administration of intravenous contrast material shows obstructing age routes. Care should be made to left colonic adenocarcinoma (white arrow) with adjacent perforation and abscess (black arrow). review the entire colon for synchro- nous lesions, which occur in 2%–7% of patients (39). ema is that it usually allows easy dis- chronic colonic pseudo-obstruction. tinction between a LBO and colon The entities are presented in order of Volvulus pseudo-obstruction (4,5,32). It may frequency. Acute colonic volvulus accounts for ap- also be used to confirm a colonic vol- proximately 10%–15% of LBO (3). Vol- vulus (5). The goal of the examination Colon Carcinoma vulus is defined as a twisting of the in- is to fill the colon adequately enough Colon carcinoma is the most common testine upon itself that causes to detect the obstruction or demon- cause of LBO (. 60% of cases), and obstruction. If the twist is greater than strate dilated colon without a transi- mortality is high (10%–30%) in pa- 360°, the volvulus is unlikely to resolve tion point. Water-soluble iodinated tients requiring emergency surgery without intervention. The symptoms of contrast material should be used as it (3,17,33–35). The two most frequent obstruction, severe abdominal pain and is easily absorbed in the locations of obstruction due to colonic distension, are due to the narrowing should there be a perforation (32). malignancy are the sigmoid colon and produced at the site of torsion. Vascu- Additionally, if the enema is per- the splenic flexure (33). The most lar compromise at the site of volvulus formed first, water-soluble contrast common site of perforation in LBO is leads to ischemia, necrosis, and perfo- material does not cause an artifact on not at the site of the tumor but at the ration. Sigmoid volvulus is three to four CT scans. The study should be per- cecum, with a reported incidence of times more common than cecal volvulus formed under low pressure without perforation of 3%–8% (36). The clini- (60%–75% vs 25%–33%, respectively), inflation of the balloon. cal manifestation of LBO from a colon and volvulus of the transverse colon and To completely evaluate the colon, the malignancy depends on a number of splenic flexure is very rare (, 1%) patient must be able to rotate on the factors, including location of the tumor (4,5). A major predisposing factor lead- fluoroscopy table. This is particularly and competency of the ileocecal valve. ing to a colonic volvulus is a mobile re- true for the sigmoid colon, which can be Right-sided tumors with an incompe- dundant colon on a mesentery and a very redundant in the elderly patient. tent ileocecal valve can mimic SBO. fixed point about which the colon can For these reasons, the examination may Left-sided malignancies cause diffuse twist. Sigmoid volvulus commonly oc- be an insufficient diagnostic tool in the distension of the colon up to the level curs in the elderly, who have an elon- large, elderly, immobile, or uncoopera- of obstruction. gated and chronically dilated sigmoid tive patient. CT findings include asymmetric colon. The more proximal colon volvuli and short-segment colonic wall thick- occur due to a congenital defect in the ening or an enhancing soft-tissue mass cecum or transverse colon mesentery, LBO: Major Causes centered in the colon that narrows the which makes these segments of the co- The following section provides an colonic lumen with or without findings lon more mobile and prone to twisting overview of the clinical and radio- of ischemia and perforation (Fig 4). (40). Patients with a large-bowel volvu- graphic features of the various causes Obstructing colon cancers often pro- lus causing obstruction present with of LBO and a discussion of how to dif- duce a shouldering appearance and acute abdominal pain and abdominal ferentiate LBO from ACPO and may be large enough to have central distension.

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Figure 5 Figure 6

Figure 5: Anteroposterior supine abdominal radio- graph in a 58-year-old man with sigmoid volvulus and “northern exposure” sign shows markedly di- lated sigmoid colon (black arrow) extending above the transverse colon (white arrow).

Sigmoid Volvulus Sigmoid volvulus is the abnormal twist- ing of the sigmoid colon along the mes- enteric axis, which leads to a closed- loop obstruction. The diagnosis of Figure 6: Images in a 72-year-old woman with LBO caused by sigmoid volvulus. (a) CT scout image sigmoid volvulus is evident on abdomi- shows dilated, air-filled colon terminating in markedly dilated sigmoid colon folded upon itself with its apex nal radiographs in 57%–90% of cases (the “coffee bean sign”) in the midline upper abdomen (black arrow). The sigmoid also conforms to an “up- (40–42). There are several classic signs side down U” configuration. There is no gas in the rectum (white arrow).(b) Midline coronal reformatted CT describing the findings of colonic volvu- image of the abdomen and pelvis shows dilated, stool-filled colon proximal to the volvulus (black arrow) with lus; these include the coffee bean and a distal “whirl” of the mesentery at the point of volvulus (white arrow). bird beak signs. The coffee bean sign describes the appearance of the volvu- obstruction, there may be a substantial The whirl sign, the appearance of spi- lus, with apposition of the medial walls amount of gas in the more proximal co- raled loops of collapsed bowel with of the dilated loop of bowel forming the lon and the small bowel. Absence of enhancing engorged vessels radiating cleft of the bean and the lateral walls rectal gas is a common finding in sig- from the twisted bowel, is often evi- forming the outer walls of the bean; it moid volvulus. dent at the point of obstruction (Fig can be seen in both sigmoid and cecal CT is extremely helpful in the diag- 6b) (47–50). Macari et al (50) found volvulus (43–45). The bird beak sign, nosis of sigmoid volvulus. Levsky et al that the location of the whirl was seen in all colonic volvuli, describes the (46) reviewed the classic signs of sig- highly accurate in discriminating cecal smooth, tapering transition point of the moid volvulus on CT scans and found from sigmoid volvulus. CT is also used obstruction. The inverted U sign, an in- that the most sensitive signs on the CT to exclude findings of ischemia and verted ahaustral dilated sigmoid in the scanogram were the absence of rectal necrosis of the effected sigmoid. shape of an inverted “U” extending into gas (90%) and the U sign (86%), while The water-soluble enema is a help- the right upper quadrant, is specific to the most sensitive findings on cross- ful diagnostic tool in the confirmation sigmoid volvulus and is seen in 25%– sectional images were a single transi- of sigmoid volvulus. The examination 78% of patients (43,46) The northern tion point in the sigmoid (95%) and is performed under low pressure, exposure sign, also specific to sigmoid disproportionate enlargement of the without insufflation of the balloon (5). volvulus, describes the repositioning of sigmoid (86%). The coffee bean, kid- The classic beak sign is usually en- the dilated sigmoid colon out of the pel- ney bean, and bent inner tube signs, countered at the site of torsion, and vis to extend above the transverse colon all descriptors of the appearance of contrast material may not pass proxi- (Fig 5); among a series of 30 cases of air-filled closed loop of colon, can all mal to the transition point (Fig 7). In sigmoid volvulus, Javors et al (41) found be seen in the setting of sigmoid vol- some cases, however, the sigmoid vol- this sign in 26 (87%) of the cases. It is vulus (Fig 6). A “beak” can be found vulus does not produce a complete ob- by far the most specific sign described at the point of twisting of the sigmoid struction and contrast material may related to sigmoid volvulus. Because colon and if necessary, may be con- pass proximal to the beak, indicating a sigmoid volvulus can be a closed-loop firmed with colonic contrast material. partial LBO. In these cases, the right

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Figure 7 Figure 8

Figure 7: Anteroposterior supine abdominal radio- Figure 8: Coronal reformatted CT images of the abdomen and pelvis in an 81-year-old woman with LBO graph after administration of water-soluble enema in caused by cecal volvulus. (a) Image shows displaced cecum in the mid abdomen, with its apex located in the a 64-year-old man with sigmoid volvulus shows a left upper quadrant (arrow). The ileocecal valve is displaced toward the left upper quadrant as well (arrow- “beak” sign at the site of torsion (white arrow). head). (b) Image after administration of intravenous contrast material demonstrates the “whirl” sign (arrow), Some contrast material is noted to pass above the confirming the cecal volvulus originating in the right lower quadrant (arrow). level of obstruction (black arrow). Residual CT con- trast material is seen in the renal collecting systems and bladder (arrowheads). tates out of the right lower quadrant into ness of the twist is proportional to the the left upper quadrant and occasionally degree of rotation. Given the proximal into the left lower abdomen or mid line. location of this LBO, small-bowel dilata- colon and cecum are usually less di- There is often substantial cecal distension tion may also be an associated finding lated than the more distal colon. (. 9 cm), with little distal colonic gas. An (34). CT findings of ischemia associated incompetent ileocecal valve causes dilata- with cecal volvulus include wall thicken- Cecal Volvulus tion of distal small bowel. The key to di- ing, mural hypoenhancement, and pneu- Cecal volvulus is characterized by twist- agnosis with abdominal radiography is matosis. Mesenteric stranding and peri- ing of the cecum causing a proximal LBO. the recognition of displacement of the toneal fluid aid in the diagnosis of bowel This phenomenon occurs when the right cecum out of the right lower quadrant. If wall ischemia. colon is not fused to the posterior ab- a contrast enema is performed, a classic A variant of cecal volvulus, the cecal dominal wall (5,51). Pregnancy and re- beak sign will be demonstrated in the dis- bascule, occurs when the cecum folds cent colonoscopy, factors that result in placed ascending colon (5,52). It is im- anteriorly on itself without twisting dilatation of the right colon, predispose portant to recognize findings of ischemia (52,53). It appears as a dilated loop in patients to cecal volvulus (52). In half of in the cecum, which include pneumatosis the midabdomen. Johnson et al (22) patients with cecal volvulus, the cecum in the cecal wall, pneumoperitoneum, challenged this concept and felt most of twists in the axial plane, rotating along its and/or portal venous gas. these cases were due to focal ileus in an long axis, appearing in the right lower CT findings of cecal volvulus include anteriorly displaced cecum. It quadrant. The other half of patients has a marked distension of the cecum in an ab- is important to note that a distended “loop” type of cecal volvulus, with the ce- normal location, usually in the mid or left cecum, 9 cm or greater, is at risk for cum twisting and inverting, resulting in upper abdomen. The ileocecal valve is perforation. the apex of the cecal twist in the left up- also displaced into the left upper quad- per quadrant. The terminal usually rant. Coronal reformations confirm the Transverse Colon Volvulus twists with the cecum. Identification of abnormal location of the cecum (Fig 8). The transverse colon volvulus is very un- the displaced, gas-filled con- The two limbs of the looped obstructed common, accounting for between 1%– firms the diagnosis (34). bowel taper and meet at the site of the 4% of all colonic volvulus (5,54,55). It The diagnosis of cecal volvulus can be twist, forming an appearance that resem- occurs in patients with a redundant made in 75% of cases from the abdomi- bles a bird’s beak. The whirl sign can be transverse colon on a long mesentery; nal radiograph alone (5). The cecum ro- found at the site of the twist. The tight- failure of fixation of the mesentery may

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lead to mobility of the ascending colon Figure 9 and hepatic flexure, leaving these pa- tients predisposed to transverse colon volvulus. Because the diagnosis may not be established early, and the twisting may occur at the root of the mesentery, the mortality rate in these patients has been reported to be 33% (46). A con- trast enema can confirm the diagnosis by demonstrating the classic beak at the point of obstruction in the transverse co- lon. Findings at CT include LBO proxi- mal to the twist in the mesentery. The right colon and cecum are midline or displaced to the left. By far the least common site for re- ported colonic volvulus is the splenic flexure (56). Causes include postopera- Figure 9: Images in a 47-year-old man with LBO caused by diverticulitis. (a) CT scout image shows air-filled tive adhesions, abnormal peritoneal at- dilated colon terminating in the left pelvis (arrow) (b) Transverse CT image of the pelvis after the administration tachments, and chronic constipation. A of intravenous contrast material shows dilated, stool-filled large bowel extending into the pelvis where the CT or contrast enema is usually needed sigmoid colon is thick walled and inflamed (white arrow). There is fluid in the root of the mesentery (black arrow). to establish the diagnosis. Findings will include marked distension of the distal transverse colon, with a whirl sign in the Figure 10 region of the splenic flexure (57,58).

Diverticulitis Although less common (10% of all cases of LBO), patients with acute di- verticulitis can present with LBO due to bowel wall edema and pericolonic inflammation (3). High-grade obstruc- tion is less common in the setting of diverticulitis; more commonly, ob- struction occurs in the setting of multi- ple episodes of diverticulitis, which causes narrowing and stricture forma- tion (5). Chronic diverticulitis can pro- duce both LBO and a chronically di- lated colon. While the most common Figure 10: Images in a 64-year-old man with LBO caused by a colocolonic intussusception. (a) CT scout location for obstructing diverticulitis is image shows air-filled dilated colon terminating abruptly in the left upper quadrant (arrow).(b) Coronal refor- the sigmoid, LBO caused by diverticu- matted CT image of the abdomen and pelvis shows a transverse colonic intussusception (arrow). The lead litis may occur at any location in the point for the obstruction was a tubulo-villous adenoma. colon and is not uncommon in the right colon in Asian countries (59). Patients with sigmoid diverticulitis Diverticulitis on CT scans is charac- the mesentery and vascular engorge- usually present with left lower quadrant terized by segmental, symmetric bowel ment favor the diagnosis of diverticulitis pain, fever, a palpable left lower quadrant wall thickening with hyperemia, which (61). In contrast, a short (, 10 cm) mass, and constipation. If there is accom- is typically in a longer segment (10 segment of colonic wall thickening and panying LBO, they will also have abdomi- cm) than malignant lesions (Fig 9) the presence of lymph nodes raise the nal distension. These symptoms may (38,60). Pericolonic inflammation and suggestion of mimic a colon carcinoma–producing fat stranding are hallmarks of diverticu- a colonic malignancy (38,60). In some LBO. Large LBO due to right colon or litis. If the inflammation is extreme, in- cases, it is impossible to distinguish be- cecal diverticulitis may mimic a distal tramural and extramural abscesses, as tween diverticulitis and a colonic malig- SBO, with dilatation of the small bowel well as perforation with pneumoperito- nancy without colonoscopy with biopsy. upstream of the inflammation. neum, may be seen. Fluid in the root of Although both the American Society of

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Figure 11 Figure 13

Figure 11: Transverse CT image of the pelvis in an 85-year-old woman with LBO caused by distal fecal impaction. Image obtained after administration of intravenous contrast material and displayed by using lung windows shows a dilated colon and large mass Figure 13: Images in a 59-year-old man with LBO caused by Crohn involving the distal descending of impacted stool in the rectum (arrow). Lung windows colon. (a) CT scout image demonstrates substantial colonic distension with stool. Arrow marks the site of aid in the delineation of air-containing structures. obstruction. (b) Midline coronal reformatted CT image shows wall thickening and hyperenhancement of the mucosa of the descending colon with a distal stricture from Crohn colitis (arrow). Figure 12 cases. Demonstration of a lead point is The CT findings of an ileocolic or co- [AQ14] found in more than 80% of adults (5). locolic intussusception include distended The most common cause of a coloco- colon (the intussuscipiens) with a thick- lonic intussusception is a primary colon ened wall, an intraluminal intussuscep- carcinoma (63). In addition, there are a tum telescoping within the intussuscipi- number of benign lesions that can serve ens, and a curvilinear area of fat as lead points in colonic intussuscep- representing the invaginated mesenteric tion, the most common being adenoma- fat of the intussusceptum (Fig 10). Invag- tous polyps and lipomas (64). Many inated vessels may also be seen accom- other lesions have been reported to panying the intussusceptum. The bowel cause intussusception, including gastro- has the appearance of a “target” in intestinal stromal tumors, as well as a cross-section or sausage-shaped mass if variety of appendiceal lesions, including in the longitudinal plane (63). the inverted appendiceal stump, endo- Figure 12: Anterior transverse CT image of the metriosis involving the appendix, and Intraluminal Contents Causing LBO abdomen and pelvis in a 67-year-old man with LBO benign masses such as a mucocele The most likely sites of colonic obstruc- caused by a colon-containing ventral hernia. Image (65,66). Other reported causes of LBO tion from intraluminal contents are the obtained after administration of oral and intravenous due to intussusception include eosino- rectum (70%) and sigmoid colon (20%) contrast material shows dilated, fluid-filled cecum philic colitis, pseudomem­braneous coli- (4,5). There are many reported causes (black arrow) and a portion of colon obstructed in a tis, and epiploic appendagitis (63,67– of intraluminal contents resulting in co- ventral hernia (white arrow). 69). lonic obstruction, including , Abdominal radiographs may show enteroliths, intentionally inserted foreign Colon and Rectal Surgeons and the only evidence of bowel obstruction, body, medications, and illegal drugs. The American College of Gastroenterology and if the lesion is in the right colon, most common cause is fecal impaction, routinely recommend that patients un- the findings may mimic a SBO. A con- a clinical entity occurring primarily in dergo colonoscopy to exclude colon trast enema can identify the obstruct- the elderly, chronically debilitated pa- cancer after an episode of acute diver- ing colonic mass and the classic “coil tients, and in those taking certain med- ticulitis, there are limited data to sup- spring” appearance as the contrast ications (3,71). Abdominal radiographs port this recommendation (62). material is trapped between the intus- will demonstrate colonic obstruction, susceptum and intussuscipiens (70). with a large amount of stool distal to Adult Intussusception However, with signs and symptoms of the obstruction (Fig 11). CT findings in- Intussusception accounts for only a a LBO, most patients will undergo an clude a large amount of stool located small number (, 1%–2%) of adult LBO abdominal CT. distal to the dilated colon.

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Figure 14 Table 2 Causes and Associations in ACPO Cause Association

Surgical Inflammatory Abscess, , , Trauma Fractures and orthopedic procedures, burns Urologic Renal tumor ablation, calculi Obstetric Normal pregnancy and delivery, cesarean section, hysterectomy, complications of pregnancy Organ transplantation … Other Emergency laparotomy, craniotomy, thoracotomy Medical conditions Cardiopulmonary Mechanical ventilation, pneumonia, myocardial infarction, congestive heart failure, chronic obstructive lung disease Metabolic Hypokalemia, hyponatremia, hypocalcemia, hypothyroidism, diabetes Neurologic Dementia, multiple sclerosis, Parkinson disease Infectious All system infections Oncologic All malignancies and their treatments Miscellaneous Organ failure, alcoholism Medications Narcotics, anticholinergics, antiparkinsonian, laxative abuse

Abdominal radiographs will demon- CT findings of colonic Crohn disease strate findings of LBO. Most of these include abscesses and fistulae. Stric- patients will undergo CT for definitive ture formation and obstruction is less diagnosis, where colon will be found common in and Figure 14: Images in a 55-year-old man with in a hernia with dilated proximal co- should raise suspicion of an underlying LBO caused by a metastasis from adenocarcinoma lon and decompressed distal colon. malignancy. of the lung. (a) CT scout image shows dilated, air- filled colon and small bowel terminating in the left Inflammatory Bowel Disease Adhesions upper abdomen (arrow). (b) Transverse CT image of Between 20% and 50% of patients the abdomen and pelvis after intravenous injection Adhesions are a very rare cause of with Crohn disease will have colonic of contrast material shows large necrotic metastasis LBO. Adhesive bands causing LBO from lung adenocarcinoma (black arrow) in the left involvement, and stricture formation have been reported in the right, trans- abdomen compressing and deviating the descend- of the large bowel occurs in 5%–17% verse, and sigmoid colon (5,76,77). ing colon posteriorly (white arrows). Both upstream of patients (73,74). It is important to Abdominal radiographs show a colonic small bowel and large bowel are dilated. exclude malignancy in these individ- obstruction, and contrast barium en- uals as the risk of colon cancer is two ema will demonstrate a short area of to three times higher in patients with circumferential narrowing with intact Crohn disease compared with age- mucosa. Similar to findings seen in Although a considerably less common matched standard populations (75). SBO, CT will demonstrate a colonic result of a hernia than a SBO, LBO Radiographic findings will demonstrate obstruction without an obvious cause. can occur secondary to inguinal, fem- an LBO. Contrast enemas are rarely oral, umbilical, Spigelian, incisional, performed in these patients, and most External Compression lumbar, and diaphragmatic hernias will undergo CT for diagnosis. The large bowel can rarely become ob- (Fig 12) (5). The most common inter- CT findings of colonic Crohn disease structed from external compression. nal hernia to produce an LBO is the include wall thickening, luminal nar- This type of LBO is most commonly foramen of Winslow hernia, the con- rowing with prestenotic dilatation, and caused by adjacent masses. Sources of dition in which small bowel and, in dilatation of the vasa recta supplying external compression are extensive one-third of cases, the right colon the affected bowel loop (Fig 13). Mural and include endometriosis, lymphade- herniate through the normal commu- stratification with hyperenhancement of nopathy, pancreatitis, intra-abdominal nication between the greater and the mucosal wall suggests active inflam- abscesses, mesenteric or colonic sur- lesser peritoneal cavities, between the mation, while homogeneous attenua- face involvement of peritoneal carcino- free edge of the lesser omentum and tion of the wall of the colon suggests a matosis, and direct invasion from gy- the hepatoduodenal ligament (72). more chronic fibrotic stenosis. Other necologic or prostatic malignancies

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Figure 15 obstruction (Table 2). Although the ex- domen and obtaining additional im- act pathophysiology is still unclear, the ages in a right lateral decubitus and/or treatment with neostigmine is based prone position after a few minutes on parasympathetic stimulation. This usually results in air filling the distal medication has been reported to show colon. This allows distinction between rapid resolution in more than 80% of LBO and pseudo-obstruction (83). ACPO patients (79). Treatment with Furthermore, patients with a chronic lower endoscopic decompression is colonic pseudo-obstruction can usually also very beneficial (80). be established with prior abdominal ACPO is most common in male pa- radiographs and a history of chroni- tients over 60 years of age, and most cally dilated large bowel (84). are already hospitalized with a severe Ultimately, if indistinguishable at illness (81). The symptoms of ACPO abdominal radiography, the diagnosis mimic those of LBO and include ab- may be made with a contrast enema dominal distension, pain, nausea, and (Fig 15) (22,80). If the differentiation vomiting. While they usually develop of LBO and ACPO remains problem- over 3 to 7 days, symptoms may occur atic, CT may play a role in the diagno- more quickly. Abdominal tenderness, sis of ACPO. CT will allow character- a common sign in the setting of LBO, is ization of the entire large bowel and not a prominent feature of ACPO and help identify the presence or absence its presence, especially in the presence of a transition point (85). of other signs of an acute abdomen, Disclosures of Conflicts of Interest: T.J. Ac- should prompt an immediate work-up tivities related to the present article: none to to exclude perforation. disclose. Activities not related to the present Abdominal radiographs in patients article: none to disclose. Other relationships: none to disclose. W.M.P. disclosed no relevant with ACPO often demonstrate marked relationships. colonic distension predominantly in- volving the cecum, ascending colon, and transverse colon. Gas may also ex- References Figure 15: Anteroposterior supine abdominal tend to the sigmoid colon and rectum 1. Lopez-Kostner F, Hool GR, Lavery IC. Man- radiographs obtained after cardiac surgery in a (Fig 15). Because the cecum is rou- agement and causes of acute large-bowel 55-year-old man with abdominal distension. (a) tinely distended in ACPO, cecal ische- obstruction. Surg Clin North Am 1997;77(6): Radiograph shows marked distension of the entire mia and perforation are a major con- 1265–1290. colon despite rectal tube (arrow) in place. (b) Radio- cern. The risk of spontaneous cecal 2. Sawai RS. Management of colonic obstruc- graph after administration of water-soluble enema perforation in ACPO is 3%–15%, with demonstrates patent colon without evidence of tion: a review. Clin Colon Rectal Surg 2012; a mortality of 50% (82). While there is 25(4):200–203. obstruction. The pseudo-obstruction resolved with no clear relationship between cecal di- colonic decompression tube placement. 3. Taourel P, Kessler N, Lesnik A, Pujol J, ameter and perforation, duration of ce- Morcos L, Bruel JM. Helical CT of large cal distension does correlate with risk bowel obstruction. Abdom Imaging 2003; (3). Abdominal radiographs will show of perforation. Prolonged cecal dilata- 28(2):267–275. LBO and occasionally a suggestion of tion beyond 2 to 3 days should prompt strong consideration for decompression 4. Welch J. Bowel obstruction: differential di- the presence of a mass. A contrast en- agnosis and clinical management. Philadel- ema will show extrinsic compression with colonoscopy or surgery (22,80). phia, Pa: Saunders, 1989; 59–95. producing the LBO. The CT findings The presence of pneumatosis in the ce- include large-bowel dilatation from a cum and/or ascending colon indicates 5. Gore RM, Levine MS. Textbook of gastroin- ischemia of the bowel, and if not treat- testinal radiology. 3rd ed. Philadelphia, Pa: soft-tissue mass (Fig 14). Saunders/Elsevier, 2008. ed, the bowel will perforate. Free intra- peritoneal air in ACPO suggests a co- 6. Biondo S, Parés D, Frago R, et al. Large ACPO or Ogilvie Syndrome: An lonic perforation and should prompt bowel obstruction: predictive factors for Important Mimic of LBO immediate surgery (59–61). postoperative mortality. Dis Colon Rectum 2004;47(11):1889–1897. ACPO (Ogilvie syndrome) was first de- Distinguishing between LBO and scribed by Ogilvie in 1948 as a pseudo- pseudo-obstruction is a major diagnos- 7. Sule AZ, Ajibade A. Adult large bowel ob- obstruction secondary to interruption tic challenge. 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