Gastrointestinal and Genitourinary Smooth-Muscle Tumors
Margaret T. Betts ; Eugene J. Huo ; Frank H. Miller

1 Department of Radiology, Northwestern University Medical School, Ste. 800, 676 N St. Clair, Chicago, IL 60611. Received December 2, 2002; accepted after revision March 3, 2003.

Leiomyomas are benign tumors of smooth muscle. They occur most commonly in the uterus but may be found wherever there is smooth muscle. Differentiation from their malignant counterpart, leiomyosarcomas, is difficult on both imaging studies and histology. The presence of metastases is the only definitive sign of malignancy. The terminology used for tumors arising from smooth muscle of the gastrointestinal tract was recently reassessed. A previously used term “gastrointestinal stromal tumor” or “GIST” was used to denote any tumor arising in the stroma of the gastrointestinal tract including leiomyoma or leiomyosarcoma. This term should no longer be used as such. Because of recent advances in immunohistochemistry and genetic markers, the term “GIST” should be reserved for only those tumors expressing c-kit protooncogene and the CD34 antigen. The smooth-muscle terminology of leiomyoma or leiomyosarcoma is still used in the intestinal tract if there is clear evidence of this differentiation—for example, in esophageal tumors [1]. The purpose of this pictorial essay is to review the imaging appearance of smooth-muscle tumors of the gastrointestinal and genitourinary tracts and highlight the features that are most helpful for diagnosis.