Ileocecal Region


Ileocecal Region

The ileocecal region comprises the cecum, appendix, ileocecal valve, and terminal ileum. Because of the complex topography of this region, it is sometimes difficult to identify positional anomalies or inflammatory or neoplastic changes. The normal ileocecal valve has a variable appearance on 2D and 3D images.

Detection of flat lesions in the cecum is sometimes difficult, because a cecal mass may be confused with untagged stool or a normal ileocecal valve. Postsurgical findings, such as an inversion ligation appendectomy, which can lead to inversion of the appendiceal stump, are another source of misinterpretation. The ileocecal region is also a predilection site for inflammatory changes, such as appendicitis and terminal ileitis in Crohn disease. These changes require very close inspection of the cecum and its anatomical structures during CT colonography. Especially on bidirectional endoluminal 3D evaluation, the orifice of the appendix and the ileocecal valve should be identified in every patient to ensure that the entire large bowel really has been fully examined.

Postoperative Findings

Among the various postsurgical conditions seen at CT colonography, an inverted appendiceal stump following appendectomy is a common finding and a potential source of misinterpretation.

Inverted Appendiceal Stump

In patients who have previously undergone appendectomy, the inverted appendiceal stump may be seen as a round, smooth, polypoid filling defect at the cecum near the orifice of the appendix, and so can potentially mimic a polyp. An inverted appendiceal stump and an adenomatous polyp both have a sessile polypoid morphology on both 2D and 3D views (Figs. 4.100 and 4.101). On 2D images, both lesions have a homogeneous structure with soft-tissue attenuation. Of course they will not take up any tagging material. After intravenous administration of a contrast agent there may be contrast enhancement. When the patient changes position, neither lesion shows mobility. Hence, it is not always possible to distinguish with certainty between a polyp and an inverted appendix stump on morphological criteria. A history of previous appendectomy (inversion ligation) and absence of the appendix on 2D images can help. If there is uncertainty concerning a polypoid lesion at the cecum, an endoscopic examination should be performed.

Inverted appendiceal stump a The endoluminal 3D view shows a polypoid filling defect at the site of the appendiceal orifice (arrow). This finding is suggestive of an inverted appendiceal stump (check patient history for appendectomy). b The corresponding axial 2D view shows a polypoid lesion with soft-tissue attenuation at the cecum (arrow). Note that CT does not allow sufficient differentiation between an inverted appendix stump and a polyp. c The corresponding coronal 2D view shows a soft-tissue-attenuation polypoid lesion at the typical location below the ileocecal valve. d The corresponding optical colonoscopic view shows a polypoid appendiceal stump at the cecum. e In another patient, a coronal MPR image after fecal tagging shows an inverted appendiceal stump with soft-tissue attenuation and a superficial coating of tagged material (arrow). Immediately above the stump are the ileocecal valve and the air-filled terminal ileum.
Sessile polyp at the cecum. a The endoluminal 3D view shows a slightly lobulated polypoid filling defect (arrow) near the orifice of the appendix (arrowhead). b The corresponding coronal MPR image shows a soft-tissue-attenuation polyp on the cecum (arrow). The appendiceal orifice (arrowhead) and the ileocecal valve (*) are seen medial to the lesion. This rules out the possibility of an inverted appendiceal stump.

Neoplastic Changes


Among the neoplastic lesions of the cecum, the most common are adenomatous polyps, carcinomas, and lymphomas. The CT criteria for identifying these pathologies are identical to the general criteria used for their identification in the remainder of the colon and are described in more detail under their respective headings above. In general, because of the proximity of the cecum to the small bowel, the presence of residual fecal matter is common, complicating the detection and interpretation of lesions.

Untagged stool particles adhering to the bowel wall may either obscure or mimic a flat lesion (Fig. 4.102). Tumorous masses involving the cecum may in some instances be confused with residual stool or with the ileocecal valve. Because of the larger diameter of the cecum and the ascending colon, malignant tumors do not lead to obstruction until they have reached an advanced stage (Fig. 4.103).

Flat villous adenoma in the cecum. a The endoluminal 3D view shows a flat polypoid elevation with a nodular surface in the cecum (arrow). On 3D views, it is not feasible to differentiate further between residual stool and a colonic lesion. b The coronal contrast-enhanced MPR image is useful for differentiation; here it shows a plaque-like, contrast-enhancing, soft-tissue-attenuation lesion which corresponds to a flat polyp (arrow). Histology revealed a villous adenoma.
Cecal carcinoma a The coronal MPR image shows a semiannular enhancing mass at the cecum (arrow). Just above, on the medial wall, is the ileocecal valve, showing a lipomatous internal structure. b The corresponding endoluminal 3D view better shows the saddle-shaped morphology of the semiannual carcinoma (arrow), directly below the ileocecal valve (arrowhead).
Lipoma on the ileocecal valve. a The endoluminal 3D view shows a round polypoid lesion arising from one of the lips of the ileocecal valve (arrow). b The coronal MPR shows homogeneous fat attenuation of the lesion, typical of a lipoma.

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Jun 26, 2020 | Posted by in GASTROENTEROLOGY | Comments Off on Ileocecal Region
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