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Pitfalls in Multi–Detector Row CT Colonography: A Systematic Approach¹

¹ From the Department of Radiology, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received April 25, 2006; revision requested June 12 and received August 9; accepted August 23. All authors have no financial relationships to disclose.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 1a.  Residual stool in a 47-year-old man with a high familial predisposition for colorectal cancer. (a) Three-dimensional endoluminal CT image shows a broad-based, polypoid filling defect (arrow). (b) On a supine contrast material–enhanced CT scan, the pseudolesion (arrow) is unenhanced, has inhomogeneous attenuation, and contains trapped gas.

 

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 1b.  Residual stool in a 47-year-old man with a high familial predisposition for colorectal cancer. (a) Three-dimensional endoluminal CT image shows a broad-based, polypoid filling defect (arrow). (b) On a supine contrast material–enhanced CT scan, the pseudolesion (arrow) is unenhanced, has inhomogeneous attenuation, and contains trapped gas.

 

View larger version (100K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.  Segmental colonic spasm in the descending colon in a 65-year-old man with symptoms of colorectal cancer. (a) Three-dimensional endoluminal CT image shows an irregular, circular narrowing of the colonic lumen (arrow), a finding that simulates a stenosis. (b) Supine coronal contrast-enhanced CT scan shows focal, irregular circular wall thickening with shoulder formation (arrow). The apparent lesion demonstrates enhancement. (c) Prone coronal CT scan shows a normal smooth colonic wall without signs of stenosis or wall thickening (arrow), findings that indicate that the spasm has relaxed.

 

View larger version (180K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.  Segmental colonic spasm in the descending colon in a 65-year-old man with symptoms of colorectal cancer. (a) Three-dimensional endoluminal CT image shows an irregular, circular narrowing of the colonic lumen (arrow), a finding that simulates a stenosis. (b) Supine coronal contrast-enhanced CT scan shows focal, irregular circular wall thickening with shoulder formation (arrow). The apparent lesion demonstrates enhancement. (c) Prone coronal CT scan shows a normal smooth colonic wall without signs of stenosis or wall thickening (arrow), findings that indicate that the spasm has relaxed.

 

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 2c.  Segmental colonic spasm in the descending colon in a 65-year-old man with symptoms of colorectal cancer. (a) Three-dimensional endoluminal CT image shows an irregular, circular narrowing of the colonic lumen (arrow), a finding that simulates a stenosis. (b) Supine coronal contrast-enhanced CT scan shows focal, irregular circular wall thickening with shoulder formation (arrow). The apparent lesion demonstrates enhancement. (c) Prone coronal CT scan shows a normal smooth colonic wall without signs of stenosis or wall thickening (arrow), findings that indicate that the spasm has relaxed.

 

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 3.  Colonic perforation in a 35-year-old woman with acute ulcerative colitis. Supine coronal CT scan shows focal pericolic air formations (arrow) around the transverse colon related to the perforation. Total flattening and disappearance of the haustra is also seen (arrowheads).

 

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  Respiratory artifact in the lower abdomen in a 71-year-old asymptomatic man. (a) Three-dimensional endoluminal CT image shows abrupt wall defects or polypoid structures (arrows) on opposite luminal walls of the colon. (b) Supine coronal CT scan shows linear artifacts of the colonic wall (straight arrows) and wavelike irregularities of the outer abdominal wall (wavy arrow) caused by respiratory motion.

 

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.  Respiratory artifact in the lower abdomen in a 71-year-old asymptomatic man. (a) Three-dimensional endoluminal CT image shows abrupt wall defects or polypoid structures (arrows) on opposite luminal walls of the colon. (b) Supine coronal CT scan shows linear artifacts of the colonic wall (straight arrows) and wavelike irregularities of the outer abdominal wall (wavy arrow) caused by respiratory motion.

 

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 5.  Stair-step artifacts in the rectum in a 58-year-old asymptomatic woman. Three-dimensional endoluminal CT image (3-mm section thickness) shows a series of concentric rings (arrows) around the colonic lumen.

 

View larger version (103K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.  Image noise in a 70-year-old asymptomatic man. (a) Three-dimensional endoluminal CT image (50 mAs) shows a smooth bowel wall with a 10-mm polyp (arrow). (b) Three-dimensional endoluminal CT image (10 mAs) shows the bowel wall with a continuous granular-nodular surface pattern due to increasing noise. Note that the polyp (arrow) is still visible with the decreased dose.

 

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.  Image noise in a 70-year-old asymptomatic man. (a) Three-dimensional endoluminal CT image (50 mAs) shows a smooth bowel wall with a 10-mm polyp (arrow). (b) Three-dimensional endoluminal CT image (10 mAs) shows the bowel wall with a continuous granular-nodular surface pattern due to increasing noise. Note that the polyp (arrow) is still visible with the decreased dose.

 

View larger version (118K): [in this window] [in a new window] [Download PPT slide]   Figure 7.  Metallic artifacts in a 70-year-old woman with bilateral hip prostheses. Prone CT scan shows prominent streaks obscuring large portions of the rectal bowel wall. A 3D endoluminal CT image (inset) demonstrates bizarre luminal artifacts and granular wall irregularity.

 

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.  Effect of varying the window width and level. (a) Supine CT scan (window width, 1500 HU; window level, –200 HU) clearly depicts a thin haustral fold (arrowhead), with loss of differentiation of the fat attenuation of a lipoma (arrow). (b) The same supine CT scan as seen with narrower window settings (width, 400 HU; level, 140 HU) shows better differentiation of the fat attenuation of the lipoma (arrow), but the thin haustral fold (arrowhead) is now displayed incompletely.

 

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.  Effect of varying the window width and level. (a) Supine CT scan (window width, 1500 HU; window level, –200 HU) clearly depicts a thin haustral fold (arrowhead), with loss of differentiation of the fat attenuation of a lipoma (arrow). (b) The same supine CT scan as seen with narrower window settings (width, 400 HU; level, 140 HU) shows better differentiation of the fat attenuation of the lipoma (arrow), but the thin haustral fold (arrowhead) is now displayed incompletely.

 

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 9.  Shine-through artifact of the colonic wall in a 59-year-old asymptomatic woman. Three-dimensional endoluminal CT image obtained with suboptimal reconstruction settings (reduced-perspective SSD threshold) shows pseudodefects of the colonic wall (arrows).

 

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.  Effect of different rendering techniques and evaluation software on lesion conspicuity. (a) Three-dimensional endoluminal CT image of an anthropomorphic colon phantom only faintly shows a small (4-mm), simulated flat lesion (crosshairs). (b) Three-dimensional endoluminal CT image obtained with a more recent version of different software shows improved conspicuity of the simulated lesion (arrow).

 

View larger version (98K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.  Effect of different rendering techniques and evaluation software on lesion conspicuity. (a) Three-dimensional endoluminal CT image of an anthropomorphic colon phantom only faintly shows a small (4-mm), simulated flat lesion (crosshairs). (b) Three-dimensional endoluminal CT image obtained with a more recent version of different software shows improved conspicuity of the simulated lesion (arrow).

 

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.  Underdistention causing perception error in a 65-year-old man with a stenotic sigmoid cancer. (a) Supine coronal CT scan shows collapse of the descending colon (arrow). No lesion is depicted in this segment. (b) Prone coronal CT scan of the distended colonic segment shows a 9-mm synchronous polyp (arrow).

 

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.  Underdistention causing perception error in a 65-year-old man with a stenotic sigmoid cancer. (a) Supine coronal CT scan shows collapse of the descending colon (arrow). No lesion is depicted in this segment. (b) Prone coronal CT scan of the distended colonic segment shows a 9-mm synchronous polyp (arrow).

 

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 12a.  Residual fluid obscuring a polyp in the descending colon in a 67-year-old man. Colonoscopic examination could not be completed because of a suspected stenosis. (a) Prone CT scan shows a fluid level (arrow) in the ventral dependent portion of the descending colon. (b) On a supine CT scan, the fluid level has shifted to the dorsal dependent portion of the colon, revealing a 9-mm polyp (arrow). The polyp was not seen on the prone CT scan because the lesion was submerged in residual fluid.

 

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 12b.  Residual fluid obscuring a polyp in the descending colon in a 67-year-old man. Colonoscopic examination could not be completed because of a suspected stenosis. (a) Prone CT scan shows a fluid level (arrow) in the ventral dependent portion of the descending colon. (b) On a supine CT scan, the fluid level has shifted to the dorsal dependent portion of the colon, revealing a 9-mm polyp (arrow). The polyp was not seen on the prone CT scan because the lesion was submerged in residual fluid.

 

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 13a.  Advantage of performing primary 3D virtual endoscopy in both the antegrade and retrograde directions. The patient was a 49-year-old asymptomatic man. (a) Antegrade 3D endoluminal CT image shows crowded haustral folds (arrowheads) in the hepatic flexure. No lesion is depicted. (b) Retrograde 3D endoluminal CT image of the same region shows a sessile 9-mm polyp (arrow) located behind a haustral fold (arrowhead).

 

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 13b.  Advantage of performing primary 3D virtual endoscopy in both the antegrade and retrograde directions. The patient was a 49-year-old asymptomatic man. (a) Antegrade 3D endoluminal CT image shows crowded haustral folds (arrowheads) in the hepatic flexure. No lesion is depicted. (b) Retrograde 3D endoluminal CT image of the same region shows a sessile 9-mm polyp (arrow) located behind a haustral fold (arrowhead).

 

View larger version (111K): [in this window] [in a new window] [Download PPT slide]   Figure 14a.  Polypoid stool simulating a filling defect in a 73-year-old woman. Colonoscopic examination could not be completed because of diverticulosis. (a) Supine 3D endoluminal CT image shows a round, well-circumscribed, polypoid "filling defect" (arrow) in the splenic flexure of the colon. (b) Supine CT scan shows a collection of gas inside the lesion (arrow), which is located on the dorsal dependent wall. (c) Prone 3D endoluminal CT scan shows that the lesion (arrow) has moved to the ventral dependent wall, a finding that is indicative of lesion mobility.

 

View larger version (140K): [in this window] [in a new window] [Download PPT slide]   Figure 14b.  Polypoid stool simulating a filling defect in a 73-year-old woman. Colonoscopic examination could not be completed because of diverticulosis. (a) Supine 3D endoluminal CT image shows a round, well-circumscribed, polypoid "filling defect" (arrow) in the splenic flexure of the colon. (b) Supine CT scan shows a collection of gas inside the lesion (arrow), which is located on the dorsal dependent wall. (c) Prone 3D endoluminal CT scan shows that the lesion (arrow) has moved to the ventral dependent wall, a finding that is indicative of lesion mobility.

 

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 14c.  Polypoid stool simulating a filling defect in a 73-year-old woman. Colonoscopic examination could not be completed because of diverticulosis. (a) Supine 3D endoluminal CT image shows a round, well-circumscribed, polypoid "filling defect" (arrow) in the splenic flexure of the colon. (b) Supine CT scan shows a collection of gas inside the lesion (arrow), which is located on the dorsal dependent wall. (c) Prone 3D endoluminal CT scan shows that the lesion (arrow) has moved to the ventral dependent wall, a finding that is indicative of lesion mobility.

 

View larger version (88K): [in this window] [in a new window] [Download PPT slide]   Figure 15a.  Solid collections of retained barium simulating a polypoid lesion in a 77-year-old patient with diverticulosis. (a) Prone 3D endoluminal CT image shows a round, well-circumscribed, polypoid filling defect in the sigmoid colon (arrow). (b) Prone coronal CT scan shows the filling defect with homogeneous high attenuation (arrow), a finding that represents barium-tagged fecal material.

 

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   Figure 15b.  Solid collections of retained barium simulating a polypoid lesion in a 77-year-old patient with diverticulosis. (a) Prone 3D endoluminal CT image shows a round, well-circumscribed, polypoid filling defect in the sigmoid colon (arrow). (b) Prone coronal CT scan shows the filling defect with homogeneous high attenuation (arrow), a finding that represents barium-tagged fecal material.

 

View larger version (56K): [in this window] [in a new window] [Download PPT slide]   Figure 16a.  Gas bubble on an intraluminal fluid level simulating a polypoid lesion in a 64-year-old asymptomatic man. (a) Drawings illustrate how a gas bubble (top) appears at CT (bottom). (b) Prone 3D endoluminal CT image shows a round, "polypoid" abnormality (arrow) in a horizontal fluid level in the colon. (c) Prone CT scan shows the abnormality to be a round, depressed structure caused by a gas bubble (arrow). Note that the bubble layer cannot be visualized at CT.

 

View larger version (77K): [in this window] [in a new window] [Download PPT slide]   Figure 16b.  Gas bubble on an intraluminal fluid level simulating a polypoid lesion in a 64-year-old asymptomatic man. (a) Drawings illustrate how a gas bubble (top) appears at CT (bottom). (b) Prone 3D endoluminal CT image shows a round, "polypoid" abnormality (arrow) in a horizontal fluid level in the colon. (c) Prone CT scan shows the abnormality to be a round, depressed structure caused by a gas bubble (arrow). Note that the bubble layer cannot be visualized at CT.

 

View larger version (84K): [in this window] [in a new window] [Download PPT slide]   Figure 16c.  Gas bubble on an intraluminal fluid level simulating a polypoid lesion in a 64-year-old asymptomatic man. (a) Drawings illustrate how a gas bubble (top) appears at CT (bottom). (b) Prone 3D endoluminal CT image shows a round, "polypoid" abnormality (arrow) in a horizontal fluid level in the colon. (c) Prone CT scan shows the abnormality to be a round, depressed structure caused by a gas bubble (arrow). Note that the bubble layer cannot be visualized at CT.

 

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 17a.  Bulbous haustral fold simulating a sessile polyp in a 60-year-old asymptomatic woman. (a) Coronal CT scan shows a polypoid filling defect with soft-tissue attenuation in the cecum (arrow). (b) Three-dimensional endoluminal CT image shows the filling defect (arrow) with linear morphologic features, a finding that is indicative of a haustral fold.

 

View larger version (98K): [in this window] [in a new window] [Download PPT slide]   Figure 17b.  Bulbous haustral fold simulating a sessile polyp in a 60-year-old asymptomatic woman. (a) Coronal CT scan shows a polypoid filling defect with soft-tissue attenuation in the cecum (arrow). (b) Three-dimensional endoluminal CT image shows the filling defect (arrow) with linear morphologic features, a finding that is indicative of a haustral fold.

 

View larger version (168K): [in this window] [in a new window] [Download PPT slide]   Figure 18a.  Collapsed colonic segments in two patients with suspected colorectal cancer. (a) Supine sagittal contrast-enhanced CT scan obtained in a 72-year-old man shows a collapsed rectum (arrow) with only mild pseudothickening of the colonic wall, no shoulder formations, and normal pericolic fat tissue. (b) Supine sagittal contrast-enhanced CT scan obtained in a 61-year-old man shows a collapsed rectum (arrow) with circumferential wall thickening, stranding of the pericolic fat, and contrast enhancement, findings that are indicative of malignancy. Histologic analysis revealed a rectal cancer.

 

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 18b.  Collapsed colonic segments in two patients with suspected colorectal cancer. (a) Supine sagittal contrast-enhanced CT scan obtained in a 72-year-old man shows a collapsed rectum (arrow) with only mild pseudothickening of the colonic wall, no shoulder formations, and normal pericolic fat tissue. (b) Supine sagittal contrast-enhanced CT scan obtained in a 61-year-old man shows a collapsed rectum (arrow) with circumferential wall thickening, stranding of the pericolic fat, and contrast enhancement, findings that are indicative of malignancy. Histologic analysis revealed a rectal cancer.

 

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 19a.  Mobile pedunculated polyp in the descending colon in a 49-year-old asymptomatic man. (a) Supine sagittal CT scan shows a large, polypoid intraluminal lesion with homogeneous soft-tissue attenuation (arrow) adjacent to the dorsal bowel wall. Note that the lesion has a stalk (arrowhead), a finding that is indicative of a pedunculated polyp. (b) On a prone sagittal CT scan, the polypoid lesion (arrow) has moved to the ventral dependent bowel wall. Arrowhead indicates the stalk.

 

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 19b.  Mobile pedunculated polyp in the descending colon in a 49-year-old asymptomatic man. (a) Supine sagittal CT scan shows a large, polypoid intraluminal lesion with homogeneous soft-tissue attenuation (arrow) adjacent to the dorsal bowel wall. Note that the lesion has a stalk (arrowhead), a finding that is indicative of a pedunculated polyp. (b) On a prone sagittal CT scan, the polypoid lesion (arrow) has moved to the ventral dependent bowel wall. Arrowhead indicates the stalk.

 

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 20a.  Sessile polyp in a mobile colonic segment in a 74-year-old woman with a history of colorectal cancer. (a) Prone CT scan shows a lesion (arrow) on the ventral dependent wall of the sigmoid colon. (b) On a supine contrast-enhanced CT scan, the lesion (arrow) demonstrates enhancement and has moved to the dorsal dependent wall of the sigmoid colon. Note that the sigmoid colon moves on its mesentery.

 

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   Figure 20b.  Sessile polyp in a mobile colonic segment in a 74-year-old woman with a history of colorectal cancer. (a) Prone CT scan shows a lesion (arrow) on the ventral dependent wall of the sigmoid colon. (b) On a supine contrast-enhanced CT scan, the lesion (arrow) demonstrates enhancement and has moved to the dorsal dependent wall of the sigmoid colon. Note that the sigmoid colon moves on its mesentery.

 

View larger version (105K): [in this window] [in a new window] [Download PPT slide]   Figure 21a.  Polyp versus diverticulum. (a) Three-dimensional endoluminal CT image shows a complete dark ring (arrow), a finding that is typical for a diverticulum. (b) Three-dimensional endoluminal CT image shows incomplete ring shadowing (arrow), a finding that is typical for a polyp.

 

View larger version (98K): [in this window] [in a new window] [Download PPT slide]   Figure 21b.  Polyp versus diverticulum. (a) Three-dimensional endoluminal CT image shows a complete dark ring (arrow), a finding that is typical for a diverticulum. (b) Three-dimensional endoluminal CT image shows incomplete ring shadowing (arrow), a finding that is typical for a polyp.

 

View larger version (86K): [in this window] [in a new window] [Download PPT slide]   Figure 22a.  Stool-impacted diverticulum simulating a polyp in a 66-year-old woman with diverticulosis. (a) Three-dimensional endoluminal CT image shows a polypoid intraluminal lesion (arrow) adjacent to a haustral fold. (b) Unenhanced CT scan shows a filling defect (arrow) projecting beyond the colonic wall into the pericolic tissue and filled with hyperattenuating material, findings that are typical for an impacted diverticulum.

 

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   Figure 22b.  Stool-impacted diverticulum simulating a polyp in a 66-year-old woman with diverticulosis. (a) Three-dimensional endoluminal CT image shows a polypoid intraluminal lesion (arrow) adjacent to a haustral fold. (b) Unenhanced CT scan shows a filling defect (arrow) projecting beyond the colonic wall into the pericolic tissue and filled with hyperattenuating material, findings that are typical for an impacted diverticulum.

 

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 23a.  Inverted appendiceal stump versus cecal polyp. (a) Three-dimensional endoluminal CT image obtained in a 46-year-old woman with a history of prior inversion-ligation appendectomy shows a sessile, smooth polypoid lesion (arrow) on the cecal base. Note that morphologic differentiation from a polyp is not possible. (b) Three-dimensional endoluminal CT image obtained in a 67-year-old man shows a sessile, slightly lobulated polypoid lesion (arrow) on the cecal base. Arrowhead indicates the appendiceal orifice.

 

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 23b.  Inverted appendiceal stump versus cecal polyp. (a) Three-dimensional endoluminal CT image obtained in a 46-year-old woman with a history of prior inversion-ligation appendectomy shows a sessile, smooth polypoid lesion (arrow) on the cecal base. Note that morphologic differentiation from a polyp is not possible. (b) Three-dimensional endoluminal CT image obtained in a 67-year-old man shows a sessile, slightly lobulated polypoid lesion (arrow) on the cecal base. Arrowhead indicates the appendiceal orifice.

 

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 24.  Lipomatous ileocecal valve in a 63-year-old woman with rectal cancer. CT scan shows a polypoid filling defect (arrow) on the medial aspect of the cecum. The defect primarily demonstrates fat attenuation.

 

View larger version (117K): [in this window] [in a new window] [Download PPT slide]   Figure 25a.  Villous adenoma on the ileocecal valve in a 62-year-old man with a family history of colon cancer. (a) Three-dimensional endoluminal CT image shows a large, irregular lobulated lesion (arrow) on the ileocecal valve. (b) On a coronal CT scan, the lesion (arrow) demonstrates homogeneous soft-tissue attenuation rather than fat attenuation, a finding that suggests a mass. Histologic analysis revealed a villous adenoma on the ileocecal valve.

 

View larger version (169K): [in this window] [in a new window] [Download PPT slide]   Figure 25b.  Villous adenoma on the ileocecal valve in a 62-year-old man with a family history of colon cancer. (a) Three-dimensional endoluminal CT image shows a large, irregular lobulated lesion (arrow) on the ileocecal valve. (b) On a coronal CT scan, the lesion (arrow) demonstrates homogeneous soft-tissue attenuation rather than fat attenuation, a finding that suggests a mass. Histologic analysis revealed a villous adenoma on the ileocecal valve.

 

View larger version (103K): [in this window] [in a new window] [Download PPT slide]   Figure 26a.  Extrinsic compression simulating a colonic lesion in a 47-year-old woman with hereditary, nonpolypoid colorectal cancer syndrome. (a) Three-dimensional endoluminal CT image shows a broad-based, smooth filling defect in the sigmoid colon (arrow). (b) CT scan shows a uterine fibroid (arrow) causing focal compression of the sigmoid colon and thereby simulating an endoluminal mass.

 

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 26b.  Extrinsic compression simulating a colonic lesion in a 47-year-old woman with hereditary, nonpolypoid colorectal cancer syndrome. (a) Three-dimensional endoluminal CT image shows a broad-based, smooth filling defect in the sigmoid colon (arrow). (b) CT scan shows a uterine fibroid (arrow) causing focal compression of the sigmoid colon and thereby simulating an endoluminal mass.

 

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