S1733 Schwannoma of the Sigmoid Colon Discovered on Screening Colonoscopy

Abstract

INTRODUCTION: Schwannomas may present anywhere in the body along the peripheral nervous system, but one of colonic origin is very rare. Here we present a case of a colonic schwannoma diagnosed on routine screening colonoscopy. CASE DESCRIPTION/METHODS: A 63-year-old woman with past medical history significant for only hypertension underwent her routine screening colonoscopy. There was no history of any abdominal pain, discomfort, change in bowel movement or any significant change in stool color. During the colonoscopy, four polyps, ranging from 0.3 cm to 0.6 cm in size, were found and removed with via cold snare polypectomy. Post-procedure recovery was uneventful. The microscopic evaluation of the tissue showed proliferating spindle cells arranged in a fascicular palisading pattern. Immunohistochemistry showed that the cells were positive for S-100. Very few cells were positive for Ki-67. The tissues were negative for CD 117, CD 34, desmin and smooth muscle actin. The final diagnosis of Schwannoma of the colon was given. The patient is currently asymptomatic and being managed conservatively. DISCUSSION: Sigmoid colon Schwannomas are rare. Nearly 60% of patients are female and having a median age of 61.5 years. Mesenchymal tumors of the gastrointestinal system such as the slow-growing Schwannoma can be a diagnostic challenge when attempting to differentiate them from their cancerous counterpart, the gastrointestinal stromal tumor. Although Schwannomas tend to be found in the stomach, when they are found in the colon, they have an excellent prognosis, unlike the gastrointestinal stromal tumor which have up to a 30% chance of malignancy. In the colon, they can present as polyps as in our case. These polyps may ulcerate and cause symptoms such as abdominal pain, bleeding and obstruction, though these manifestations are extremely rare. After removal of the suspected tumor, microscopic evaluation and an immunohistochemical panel of the specimen help in the diagnosis. Discovering S-100 protein immune-expression and observing a slow mitotic rate while investigating the proliferative activity using Ki-67 antibodies, provides a definitive diagnosis of Schwannoma. Upon discovery, complete resection of the tumor with adequate free margins is recommended. The chance of malignancy is low and adjuvant chemotherapy is not considered necessary.Figure 1.: colonoscopy finding of sigmoid polyp and after polypectomy.