Evaluation of submucosal lesions of the large intestine: part 1. Neoplasms.

At luminal evaluation of the large intestine, any masslike protrusion that is covered by normal mucosa, whether the underlying process is intramural or extramural in origin, may be reported as a submucosal lesion. The full characterization of submucosal lesions may be difficult with optical colonoscopy alone, and endoscopic biopsy is often nondiagnostic. Cross-sectional radiologic imaging studies allow evaluation of the entire thickness of the bowel wall and surrounding tissues and often provide additional information with regard to lesion origin, internal composition, and extent of disease. Likewise, it may be difficult to distinguish submucosal lesions from mucosal polyps on radiologic images, and optical colonoscopy may provide complementary information about superficial submucosal soft-tissue lesions that are detected at computed tomographic (CT) colonography or barium imaging. Depending on the specific clinical situation, colonoscopy, CT colonography, transrectal ultrasonography, and magnetic resonance imaging all may play an important role in the diagnostic evaluation of submucosal lesions of the large intestine. It is important that radiologists be familiar with the multimodality imaging appearances of such entities so that neoplasms--especially those that are malignant--can be accurately identified and characterized and effectively managed.

Evaluation of submucosal lesions of the large intestine: part 2. Nonneoplastic causes.

Various nonneoplastic entities may manifest as submucosal abnormalities at colorectal evaluation, and it may be difficult to distinguish between those with an intramural origin and those with an extramural origin on the basis of optical colonoscopy alone. Cross-sectional radiologic imaging, which allows evaluation of the entire bowel wall and the surrounding tissues, plays an important role in the localization and characterization of these abnormalities. However, some superficial submucosal lesions that are initially detected at computed tomographic colonography or barium enema studies may be better characterized with colonoscopy; thus, it is important to recognize the complementary uses of these diagnostic tests. In addition, modalities such as transrectal ultrasonography and magnetic resonance imaging may be useful for the identification and characterization of some abnormalities. For timely and effective management, it is especially important that submucosal neoplasms of the large intestine be accurately distinguished from nonneoplastic entities such as lymphoid polyps, vascular lesions, and cystic lesions, as well as from extracolonic abnormalities (eg, endometriosis, uterine fibroids) and normal extracolonic structures (eg, uterus, vasculature).