Schwann cell hamartoma as an incidental finding in a colonoscopy

Dear Editor,

We report a case of a 39-year-old male who underwent a colonoscopy after an episode of acute diverticulitis without other relevant medical or family history. In the descending colon an 8 mm sessile polyp (Paris 0-Is, NICE 1) was removed. Histopathological analysis revealed proliferation of spindle cells in the colonic mucosa without atypia (Fig. 1). With immunohistochemistry these cells displayed positivity for S-100 and CD-34, all of it being compatible with a benign mesenchymal polyp with a suggestive Schwann cell hamartoma phenotype (Fig. 1).

Figure 1.

Histological staining showed a colonic polyp with mucosal proliferation of spindle cells without atypia (right side of the figure). The colon biopsy displayed with immunohistochemistry proliferated cells with positivity for S-100 and CD-34 (left side of the figure).

Discussion: In a study based on series of colorectal lesions composed by Schwamm cell proliferation in 2009, a new lesion named Schwann cell hamartoma was described. Schwann cell hamartomas are rare colorectal polyps with a mesenchymal origin.¹ 90% of the gastrointestinal hamartomas are gastric and rarely in the colon.² They consist of pure Schwann cells with S-100 protein immunoreactivity proliferation in the lamina propria.¹ In the majority of cases they are incidental endoscopic findings ranging between 1 and 6 mm in size and they usually occur in women of middle age, in the left colon.³ They are considered benign polyps and have not demonstrated any association with inherited syndromes.³ It is important to differentiate this polyp from other mesenchymal lesions (neurofibromas, ganglioneuromas, perineuromas or schwannomas) that do tend to be associated with inherited syndromes such as Cowden syndrome, multiple endocrine neoplasia 2b (MEN-2b) and neurofibromatosis type 1 as well as from others with malignant potential such as gastrointestinal stromal tumours (GIST).^1,4 Schwann cell hamartomas are a rare entity with an uncertain clinical significance. Further studies are needed in order to increase our knowledge on these lesions, mainly on establishing the appropriate follow up, as well as its possible nature as component of an unknown inherited syndrome. A careful histological assessment is mandatory to avoid mislabelling patients with malignant potential lesions or with inherited syndromes.