Hypoechoic mesenchymal tumors can be differentiated from lipomas and fibromas, which are usually echo-rich, well demarcated, and located within the submucosal third EUS layer. Another lesion in the submucosa

that can be clearly delineated by EUS is an aberrant pancreas. Cysts in the submucosa have a well-demarcated, echo-free appearance. Carcinoid and lymphoma are also found in the submucosa and can occasionally appear as localized lesions. Varices in the gastric wall have an echo-free appearance; continuity with varices external to the gastric wall establishes the diagnosis.

Organs that have been shown to cause compression of the gastric wall, simulating a submucosal tumor, include spleen, liver, kidney, gallbladder, and vessels around the celiac axis. In addition, tumors of the pancreas, enlarged abnormal lymph nodes due to tumor or inflammation, tumors of the liver, and retroperitoneal tumors can cause an impression on the gastric wall resembling a submucosal tumor. In the esophagus, the bronchus, the thoracic spine, and the aorta can simulate a submucosal tumor. These "tumors" can all be diagnosed with EUS.

Surgical removal of true submucosal tumors may be indicated by suspicious biopsies, location, endoscopic ultrasound findings, or symptoms that suggest malignancy. When benign lesions are small (< 3 cm), observation with EUS is a reasonable approach, especially if negative histology has been obtained. When lesions are smaller than 2 cm and located in the esophagus, biopsies may not be necessary, and lesions can be followed with endoscopic ultrasonography alone, because yield tends to be lower and complication rates higher for biopsies of these small esophageal lesions [28]. Histological confirmation of rectal submucosal lesions is mandatory because more than 50% are malignant [22].

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