Leiomyomatosis of the colon.

Excluding the rectum, smooth muscle cell tumors of the large bowel are extremely rare lesions. A unique case is reported of an infiltrating multinodular myomatous growth of semi-constrictive type affecting the ascending and transverse colon along its entire circumference and over a length of 35 cm. In the mesocolon near the colonic wall two tumor foci were present. Contrary to expectations from the growth behavior, histological examination revealed well differentiated smooth muscle cells with distinct myofilaments and absence of nuclear abnormalities and mitotic figures. No clinical evidence of malignancy was found and no recurrence was detected during a 39-month follow-up period which included a second-look operation. The contrasting fidings are discussed and it is concluded that the tumor should be considered a benign multicentric lesion, for which the term "leiomyomatosis of the colon" is suggested.