Submucosal Tumors of the GI Tract

EUS is the only imaging technique that can delineate the histological layers of the GI tract wall. Therefore, evaluation of submucosal tumors becomes one of the main indications for EUS because it can accurately define the origin, extent, and depth of invasion of submucosal tumors. CT does not further characterize these lesions unless they are quite large.

Although submucosal tumors of the GI tract are most often found on barium radiological examination or endoscopy, standard endoscopic biopsies usually do not demonstrate any abnormality because the lesion is under the mucosa. In addition, it is often impossible to determine whether a mass below the mucosal surface is an extrinsic or intrinsic tumor, a vascular structure, or compression from an adjacent organ. EUS can make this differentiation very accurately (98%), compared with barium radiographs (75%), endoscopy with biopsy (67%), or CT (53%) [15]. EUS will detect a submucosal tumor in nearly 100% of patients as compared with 92% for barium radiographs and 67% for CT. Failure to demonstrate a submucosal tumor with EUS in up to 5% of patients occurs mainly for technical reasons; placement of the transducer on the tumor may be difficult when the location of the tumor is on the lesser curvature or in the cardia.

If a tumor is found, an EUS-directed submucosal deep-needle biopsy or aspiration can be performed to make a histological diagnosis [26-291]. This type of biopsy is essential because sonographic features to differentiate benign from malignant tumors overlap. Tumor destruction of the wall architecture appears to be the most specific sign of malignancy, particularly for primary or metastatic submucosal carcinomas. Biopsy with EUS distinguishes these types of tumor from mesenchymal tumors [28].

Mesenchymal tumors less than 3 cm are almost never malignant; those larger than 4 cm have a higher probability of malignancy [76]. When the lesion is in the fourth EUS layer (i.e., the muscularis propria), differentiation between a leiomyoma, a leiomyoblastoma, and a leiomyosarcoma is very difficult without the presence of a disrupted wall architecture or abnormal lymph nodes. Some leiomyomas arise from the second deep mucosal EUS layer. Defining this superficial location with EUS (Fig 6) may allow endoscopic removal of certain mesenchymal tumors with new endoscopic tools.

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