Although the vast majority of gastrointestinal (GI) masses are epithelial neoplasms, a variety of subepithelial masses are infrequently encountered during endoscopic or radiologic examination. A subepithelial mass, which was previously called a submucosal mass, is defined as a mass covered with normal-appearing mucosa, whether the underlying process is intramural or extramural in origin. At contrast material-enhanced computed tomography (CT), hypervascular subepithelial masses are usually detected more easily than isoattenuating or hypovascular masses. Entities that appear as intramural hypervascular subepithelial lesions include neuroendocrine tumors, GI stromal tumor, glomus tumor, hemangioma, angiosarcoma, Kaposi sarcoma, nerve sheath tumors, hypervascular metastases, heterotopic tissues, and vascular structures. Entities that appear as extramural hypervascular subepithelial lesions include Castleman disease, solitary fibrous tumor, inflammatory myofibroblastic tumor, and actinomycosis. Some rare gastric cancers resemble subepithelial tumors. In comparison with endoscopic ultrasonography, CT is of limited value in differentiating the layers of the GI wall and determining the origin of mass lesions. However, recent advances in multidetector CT with multiplanar reformation allow one to determine whether a GI mass is of epithelial, intramural subepithelial, or extramural subepithelial origin. Furthermore, the full extent of tumors can be delineated, and local invasion and distant metastases can be identified. Familiarity with the characteristic CT appearances of hypervascular subepithelial masses of the GI tract will help radiologists make a more confident diagnosis.
© RSNA, 2010.