Colonic Leiomyoma: A Rare Entity Within the GI Tract

Abstract

A 61-year-old male with medical history of hyptertension, hyperlipidemia and diabetes type 2 presented for evaluation of abdominal fullness and constipation for thepast 3 months. Vial signs and physical examination were within normal limits. Laboratory testing including complete blood count, basic metabolic panel, liver function test (including aspartate aminotransferase and alanine aminotransferase), coagulation profile, and urinalysis were all within normal limits. An esophagogastrodudedenoscopy (EGD) was conducted which was remarkable only for mildly erythematous mucosa found in the antrum and body of the stomach suggestive of gastritis and duodenitis. Antral and duodenal biopsies were positive for H. pylori. Colonoscopy revealed a one-centimeter smooth sessile polyp found in the ascending colon that was removed by snare cautery polypectomy. Histologic examination revealed a spindle cell tumor composed of whorls of smooth muscle cells with no mitosis (Figure 1). Tumor cells were positive for smooth muscle actin (Figure 2) and negative for CD117, S100, CD34 and epithelial membrane antigen (EMA). These findings were consistent with a diagnosis of colonic leiomyoma. A leiomyoma is a benign smooth muscle tumor, first noted in the mid 1800s. It is composed of whorls of smooth muscle and has a very low rate of malignant transformation (approx. 0.1%). The benign tumor is mostly seen on the uterus where it causes symptoms related to mass effect. Leiomyomas can also be noted in the GI tract on occasion. In the GI tract, they are mostly seen in the esophagus (65%) and in the stomach (25%). They are noted in the colon (including the rectum) only 3% of the time. Leiomyomas must be distinguished from gastrointestinal stromal tumors (GIST). GIST arises in the smooth muscle interstitial cells of Cajal. These cells are positive in 95% of cases for the c-KIT (CD117) gene and mostly occur in the stomach. Other markers that are commonly tested for are S100 (found in neural crest cells and melanocytes), CD34 protein (found in hematopoietic stem cells) and epithelial membrane antigen (EMA), which is a marker for the presence of epithelial cells. Most colonic leiomyomas that are < 2cm can be successfully resected endosopically. Leions causing symptoms related to mass effect (such as abdominal pain, intestinal obstruction, hemorrhage, or perforation) or having features suggestive of malignant degeneration (such as a high mitotic rate, rapid growth, an ulcer or lesions > 2.5 cm in diameter) should undergo surgical resection.Figure: Microscopic examination reveals whorls of smooth muscle spindle cells with no mitosis (HE x20).Figure: Immunohistochemical stain reveals that tumor cells are positive for smooth muscle actin (X20).