Residents Section Pattern of the Month

Residents Section Pattern of the Month Krajewski et al. olonic Dilation Residents Section Pattern of the Month Residents inradiology Katherine Krajewski 1 ettina Siewert Ronald L. Eisenberg Krajewski K, Siewert, Eisenberg RL Keywords: cecum, colon, colonic dilation, ischemia, perforation DOI:10.2214/JR.09.3353 Received July 22, 2009; accepted after revision September 1, 2009. 1 ll authors: Department of Radiology, eth Israel Deaconess Medical enter, Harvard Medical School, 330 rookline ve., oston, M 02215. ddress correspondence to R. L. Eisenberg (rleisenb@bidmc.harvard.edu). WE This is a Web exclusive article. JR 2009; 193:W363 W372 0361 803X/09/1935 W363 merican Roentgen Ray Society olonic Dilation olonic dilation (cecum > 9 cm or transverse colon > 6 cm) can be seen in adult patients presenting with a variety of medical and surgical conditions of the abdomen (Table 1). cute or progressive colonic distention may lead to colonic ischemia or perforation, and an accurate diagnosis of the cause of distention is necessary to initiate appropriate therapy and prevent complications. t times, it can be difficult to differentiate between low colonic obstruction and pseudoobstruction, but certain imaging features and techniques can be helpful in making the distinction. Important observations on radiographs are the distribution of colonic air, the position of the dilated loops, and the presence or absence of air in the rectum. olonic Obstruction Obstructing lesions produce intrinsic or extrinsic mass effect on the colon or rectum. The colon is dilated to an abrupt transition point, and a lesser amount of colonic air, if any, is seen distal to the point of obstruction (i.e., no air in the rectum). ompared with small-bowel obstructions, colonic obstructions tend to be more subacute, with symptoms developing more slowly. The major sites of obstruction in the large bowel are the cecal region, flexures, sigmoid colon, and upper part of the rectum. olonic obstructions occur more frequently on the left side than on the right. They generally produce fewer fluid and electrolyte disturbances than small-bowel obstructions. Fig. 1 ecal volvulus. Thin-walled cecum is markedly distended. ecause ileocecal valve is competent, there is little small-bowel gas. (Reprinted with permission from Eisenberg RL. linical imaging: an atlas of differential diagnosis, 4th ed. Philadelphia, P: Lippincott Williams & Wilkins, 2003) Fig. 2 Torsion of splenic flexure entering traumatic diaphragmatic hernia. ecause of incompetent ileocecal valve, there is diffuse dilation of gas-filled loops of both colon and small bowel, producing radiographic pattern that suggests adynamic ileus. (Reprinted with permission from Eisenberg RL. linical imaging: an atlas of differential diagnosis, 4th ed. Philadelphia, P: Lippincott Williams & Wilkins, 2003) JR:193, November 2009 W363

Krajewski et al. TLE 1: olonic Dilation Obstruction Neoplasm Diverticulitis Inflammatory bowel disease Volvulus Hernia Intussusception Impaction Pseudoobstruction dynamic ileus Ogilvie s syndrome Toxic megacolon The radiographic appearance of colonic obstruction depends on the competency of the ileocecal valve. If the ileocecal valve is competent, obstruction causes a large dilated colon, with a markedly distended thin-walled cecum and little small-bowel gas (Fig. 1). If the ileocecal valve is incompetent, however, there is distention of gas-filled loops of both the colon and small bowel (Fig. 2), often with cecal hypertrophy and thickening of the haustra and colon wall. It is sometimes difficult to distinguish between a low colonic obstruction and colonic ileus. In proximal colonic obstruction, the abnormal distention ends abruptly at the level of the lesion; the colon distal to the lesion is free of gas. This transition is often impossible to detect in low colonic obstructions. In such cases, radiographs should be obtained with the patient in the lateral decubitus position (right side down). This position facilitates the entry of gas into the rectosigmoid and rectum, unless there is a mechanical obstruction at or above this level. Fig. 3 Ogilvie s syndrome., Supine abdominal radiograph shows gaseous distention of descending colon out of proportion to other bowel loops., ontrast-enhanced T image shows dilation of entire colon and mild diffuse rectosigmoid wall thickening to level of rectal tube, without obstructing lesion. W364 JR:193, November 2009

olonic Dilation Fig. 4 denocarcinoma of colon. and, Supine () and upright () abdominal radiographs show moderate distention and stool in ascending and transverse colon, along with air fluid levels. Descending colon contains air but is not distended, and no rectal air is seen. In setting of abdominal distention and constipation, large-bowel obstruction was suspected., Single-contrast enema using water-soluble contrast agent delineates apple-core lesion of lower descending colon (arrow). Small amount of contrast agent passes through tight and irregular narrowing of lumen. D, ontrast-enhanced T image in different patient shows dilated and stool-filled colon to level of obstructing mass (arrow). Distention of the rectum implies colonic ileus; a collapsed rectum suggests mechanical obstruction. If there is doubt, a barium enema or cross-sectional imaging is required to show the presence of an obstructing lesion or the patency of the colonic lumen (Figs. 3 and 4). The major complication in colonic obstruction is perforation. If the ileocecal valve is competent, the colon behaves like a closed loop, and the increased pressure caused by the obstruction cannot be dissipated. When the colon is massively distended by gas, perforation can occur. In acute colonic obstruction, the possibility of perforation is likely when the cecum distends to more than 10 cm. In intermittent or chronic obstruction, however, the cecal wall may become hypertrophied and the colon diameter may greatly exceed 10 cm without perforation. Massive distention of the colon can compromise the mesenteric vascular supply, leading to strangulation and bowel necrosis. The most common cause of colonic obstruction is a primary colorectal neoplasm, which often results in a characteristic apple-core narrowing of the colonic lumen on a contrast enema examination (Fig. 4). D JR:193, November 2009 W365

Krajewski et al. Fig. 5 ontiguous spread of tumor to colon., Supine abdominal radiograph shows dilated cecum filled with stool and gaseous distention of transverse colon, descending colon, and multiple loops of small bowel., Single-contrast enema shows high-grade obstruction of rectosigmoid junction from extrinsic mass., xial IV contrast-enhanced T image reveals large heterogeneous mass in pelvis, in expected location of cervix, that encased sigmoid colon on contiguous slices. ecum is distended by dense stool, and concern for pneumatosis or ischemia was raised. Small-bowel loops are distended with fluid because of obstruction, and there is small amount of free pelvic fluid. Fig. 6 Diverticulitis. Severe spasm and adjacent walled-off abscess cause marked narrowing of colonic lumen (arrows). (Reprinted with permission from Eisenberg RL. linical imaging: an atlas of differential diagnosis, 4th ed. Philadelphia, P: Lippincott Williams & Wilkins, 2003) Metastases appear as filling defects of the colon or rectum, often with an intact mucosa (Figs. 5 and 5). t times, the colon wall can be involved with contiguous spread of a tumor from an adjacent pelvic malignancy, such as ovarian or cervical carcinoma. ross-sectional imaging is helpful in making this diagnosis (Fig. 5). Diverticulitis is the second most common cause of large-bowel obstruction. Severe spasm, an adjacent walled-off abscess, and fibrous scarring can produce marked narrowing of the colon (Fig. 6). Similar segmental smooth or irregular narrowing can be produced by inflammatory bowel diseases, such as chronic ulcerative colitis or rohn s disease. W366 JR:193, November 2009

olonic Dilation Fig. 7 Sigmoid volvulus., Supine abdominal radiograph shows massively dilated viscus with inverted U-configuration that extends to level of hemidiaphragms. pposition of medial walls of dilated sigmoid produces coffee bean sign. Rectal tube was placed in this patient but did not provide symptomatic relief., Diagnostic single-contrast enema was performed through rectal tube via gravity. Rectal tube traverses persistent twist in sigmoid colon, with torsed mucosal folds outlined by contrast material. Volvulus forms typical beak configuration through which contrast material cannot pass. Fig. 8 ecal volvulus., Oral and IV contrast-enhanced scout (), axial (), and coronal () T images show dilated cecum abnormally positioned in midabdomen, with terminal ileum entering cecum from right (). Mesenteric swirl is seen in right lower quadrant (). JR:193, November 2009 W367

Krajewski et al. Fig. 9 Fecal impaction. bdominal radiograph shows obstruction caused by impaction of large amount of stool filling entire colon and rectum. Volvulus of the large bowel is the third most common cause of colonic obstruction. ecause torsion of the bowel usually requires a long, movable mesentery, volvulus of the large bowel most commonly affects the cecum and sigmoid colon; volvulus of the transverse colon occurs infrequently. olonic volvulus typically presents with a massively dilated viscus extending into the upper abdominal quadrants. In sigmoid volvulus, a greatly inflated sigmoid loop appears as an inverted U-shaped shadow that rises out of the pelvis in a vertical or oblique direction, at times even reaching the level of the diaphragm (Fig. 7). On contrast enema examinations, the flow of contrast material ceases at the obstruction, and the rectum becomes distended. The lumen tapers toward the site of stenosis, producing a pathognomonic beak sign (Fig. 7). T findings in sigmoid volvulus include disproportionate sigmoid enlargement, a mesenteric swirl or whirl, and visualization of at least one sigmoid transition point. The finding of two crossing sigmoid transition points at one location has been recently termed the X marks the spot sign, whereas an incomplete sigmoid twist with intervening mesenteric fat is called the split-wall sign. In cecal volvulus, the dilated cecum is displaced upward and to the left and usually has a kidney-bean shape, with the terminal ileum entering the cecum from the patient s right side (Fig. 8). ecal bascule is a variant of cecal volvulus in which the mobile cecum folds anterior or anteromedial to the ascending colon, without a twist. ecal obstruction occurs at the fold, and competence of the ileocecal valve results in a large dilated cecum in the mid abdomen. olocolic intussusceptions result in telescoping colonic loops, often with a leading mass. olonic obstruction also may be caused by hernias, particularly in the left inguinal region, or severe fecal impaction (Fig. 9). olonic Pseudoobstruction olonic dilation may occur in the absence of an obstructing lesion, as in cases of adynamic ileus, Ogilvie s syndrome, and toxic megacolon. In these conditions, colonic dilation may be segmental or diffuse, and gas is generally present within the rectum. Diffuse small- and large-bowel dilation without a point of transition is characteristic of adynamic ileus. mong the numerous causes of this appearance are surgery, peritonitis, and medication (Fig. 10). Ogilvie s syndrome is an acute or chronic pseudoobstruction that is often associated with severe illness, recent surgery, electrolyte imbalance, and medications such as narcotics and anticholinergics. It is thought to be related to altered autonomic control and is characterized by disproportionate colonic distention with relative or intermediate points of transition, often at or near the splenic flexure. However, there is no obstructing lesion or abrupt transition between normal- and abnormal-appearing portions of the colon (Fig. 11). Despite the absence of a mechanical obstruction, perforation can occur. Various modes of treatment include supportive care, medication (parasympathomimetic agents), endoscopy, and surgery. W368 JR:193, November 2009

olonic Dilation Fig. 10 Postoperative adynamic ileus. and, Supine () and upright () radiographs show diffuse gaseous distention of colon with air fluid levels. Note presence of rectal air. Fig. 11 Ogilvie s syndrome. and, Oral contrast-enhanced coronal () and axial () T images show that cecum and ascending colon are markedly distended with stool. There is prominent gaseous dilation of transverse colon to relative transition point at splenic flexure (). Descending and distal colon were normal in caliber, and there is no dilation of small-bowel loops., Repeat abdominal radiograph obtained 2 days after T shows development of free intraperitoneal gas. olon remains distended, and gas is seen on both sides of bowel wall (Rigler sign). Toxic megacolon is a complication of various inflammatory, ischemic, and infectious diseases of the colon, but most often it is associated with ulcerative colitis. lthough the colon may be quite dilated in toxic megacolon, more specific features include marked bowel wall thickening with loss of the haustral pattern in affected segments (Fig. 12). Nodular pseudopolyps may JR:193, November 2009 W369

Krajewski et al. Fig. 12 Toxic megacolon. D, In patient with medically refractory ulcerative colitis, oral and IV contrast-enhanced scout (), axial (), coronal (), and sagittal (D) T images show that ascending and transverse portions of colon are dilated and contain both air and oral contrast material. Nodular pseudopolyps protrude into air-filled lumen (). ircumferential wall thickening extends from descending colon through rectum. Distention of ascending and transverse colon continued to increase despite treatment, and patient ultimately required total colectomy. D W370 JR:193, November 2009

olonic Dilation E Fig. 13 Invasive bladder cancer. and, Supine () and upright () radiographs show distention of colon with fluid and multiple air fluid levels. One year after treatment with chemotherapy, cystoprostatectomy, and ileal conduit formation, patient presented with 1 month of constipation. He underwent colonoscopy preparation without any passage of stool., Water-soluble contrast enema reveals that smooth-walled rectum has very small caliber, much less than that of sigmoid colon. D and E, Sagittal (D) and axial (E) T2-weighted images with rectally administered negative contrast administration show marked diffuse, circumferential thickening of walls of rectum and anus. F, ontrast-enhanced T1-weighted image shows diffuse enhancement of thickened anorectal wall with transmural extension of enhancement (arrow). iopsy revealed poorly differentiated adenocarcinoma with signet-cell-type infiltration, consistent with recurrent disease in anorectum. D F JR:193, November 2009 W371

Krajewski et al. protrude into the bowel lumen with intervening gas-filled ulcerations. rohn s colitis, ischemia, amebic colitis, and pseudomembranous colitis may also produce a toxic megacolon pattern. t times, it may be difficult to reliably differentiate between obstruction and pseudoobstruction on radiographs. In these cases, a contrast enema may be helpful to exclude an obstructing lesion if contrast material clearly passes the perceived transition point. This technique may have the additional benefit of some therapeutic effect. It is critical to remember, however, that in patients with suspected toxic megacolon, an enema of any kind (even using water-soluble contrast material) is contraindicated because of the high risk of perforation. ross-sectional imaging (primarily T and MRI) can provide additional information regarding the site, degree, and cause of colonic obstruction (Fig. 13). These techniques show the mechanism and site from multiple perspectives, particularly when multiplanar and reformatted images are obtained. The obstructing lesion and its organ of origin may be better delineated, particularly in cases of extrinsic disease. ross-sectional imaging may permit staging of malignancies and allow cases of pseudoobstruction to be diagnosed with improved confidence. Suggested Reading 1. dler YT, Draths KG, Markey WS. Pseudoobstruction in the geriatric population. RadioGraphics 1986; 6:995 1005 2. ufort S, harra L, Lesnik, et al. Multidetector T of bowel obstruction: value of post processing. Eur Radiol 2005; 15:2323 2329 3. hoi JS, Lim JS, Kim H, et al. olonic pseudoobstruction: T findings. JR 2008; 190:1521 1526 4. Eisenberg RL. Gastrointestinal radiology: a pattern approach, 4th ed. Philadelphia, P: Lippincott Williams & Wilkins, 2006 5. Horton KM, orl FM, Fishman EK. T evaluation of the colon: inflammatory disease. RadioGraphics 2000; 20:399 418 6. Levsky JM, Den EI, Durow R, et al. T findings of sigmoid volvulus. JR 2010 (in press) W372 JR:193, November 2009