Mucosal Schwann Cell Hamartoma Masquerading as a Polyp in the Proximal Colon: A Rare Lesion in an Unusual Location

Abstract

Purpose: Mucosal Schwann cell hamartoma, a rare neural tumor, is rarely found in the colon, yet when seen, it is commonly as a small colorectal polyp, typically on the left side. We report two cases of Schwann cell hamartoma presenting as a polypoid lesion in the proximal colon during routine colonoscopy. Case one: A 78-year-old man with a past medical history of congestive heart failure, hypertension, hyperlipidemia, diabetes mellitus type 2, diverticulosis, and peptic ulcer disease presented with hematochezia. His family history was significant for colorectal cancer in his sister. The patient underwent diagnostic colonoscopy, which revealed scattered diverticula and a 5-mm sessile polyp at the hepatic flexure. Pathology results from the polypectomy specimen revealed colonic mucosa with stromal proliferation of spindle cells with bland nuclear morphology, consistent with Schwann cell hamartoma. Case two: An 84-yearold man with past medical history of hypertension presented for screening colonoscopy. Colonoscopy revealed hemorrhoids and four polyps. Pathology results revealed that a 10-mm sigmoid polyp was a tubular adenoma, a 5-mm hepatic flexure polyp was a tubular adenoma, and a 5-mm splenic flexure polyp was inflammatory. The fourth polyp was a 5-mm polyp in the mid ascending colon. The pathology of this polyp showed colonic mucosa with stromal proliferation of spindle cells with bland nuclear morphology, consistent with Schwann cell hamartoma. Discussion: Neural lesions are relatively rare in the colon, and when found, they present as small colorectal polyps. One type of these polypoid lesions is comprised of a diffuse, uniform proliferation of spindle cells in the lamina propria with a benign cytological appearance and Schwann cell immunophenotype (S100+, CD34-, CD117-, smooth muscle actin- and desmin -). They may occur as multiple lesions associated with inherited syndromes, such as type 1 neurofibromatosis, multiple endocrine neoplasia type 2B, or Cowden syndrome. They may also present as solitary lesions. The term “mucosal Schwann cell hamartomas” has recently been coined in order to distinguish them from other neural lesions, especially those associated with inherited syndromes. These lesions are usually seen in the distal colon, and rarely, they are also observed in the proximal colon as evidenced above, and therefore should be included in the differential of proximal colon polyps. Conclusion: Mucosal Schwann cell hamartoma of the colon is a rare benign lesion, usually presenting as a distal colon polyp, but should also be considered in the differential diagnosis of proximal colon polyps.