Mucosal Schwann cell hamartoma of the gastroesophageal junction: A series of 6 cases and comparison with colorectal counterpart.

Mucosal Schwann cell hamartoma (MSCH) is an uncommon neural lesion characterized by an ill-defined proliferation of S100-positive Schwann cells in the lamina propria, with reported cases exclusively occurring in the colorectum. Here we describe the first series of MSCHs arising in the gastroesophageal junction (GEJ) and discuss their clinicopathologic features in comparison with their colorectal counterparts. We searched the UCLA pathology database from 01/2014 to 12/2018 to identify cases carrying the diagnosis of MSCH. A total of 48 cases (45 in-house, 3 consults) of colorectal MSCHs and 6 cases (1 in-house, 5 consults) of GEJ MSCHs were identified. For GEJ MSCHs, there were 4 males and 2 females with an average age of 70.2 years (range: 57-76 years). Clinical indications for endoscopy included history of gastroesophageal reflux disease (n = 2), heartburn (n = 2), dysphagia (n = 1), and iron deficiency anemia (n = 1). Endoscopic findings at the GEJ were available for 5 patients including irregular Z-line (n = 3), mild nodular carditis (n = 1), and normal (n = 1). None of them showed a polyp or nodule. The mean size of the lesion was 2.8 mm (range: 2-4 mm) microscopically. None of the colorectal or GEJ MSCH cases had an association with inherited syndromes. In conclusion, MSCH of the gastrointestinal tract is predominantly seen in the colorectum, but also infrequently seen in the GEJ. GEJ MSCH shares histologic and immunohistochemical features with its colorectal counterpart, but is usually an incidental finding with no endoscopically visible lesion. As there is no syndromic association with MSCH, additional treatment, work-up and follow-up are unnecessary.

Mucosal Schwann Cell Hamartoma of the Rectosigmoid Junction: A Rare Lesion Mimicking Mucosal Prolapse Syndrome and Other Neural Lesions.

In this article, we report the case of a 40-year-old woman with a sessile polyp of the rectosigmoid junction that underwent endoscopic resection. The resected specimen showed spindle cell proliferation with eosinophilic cytoplasm between mucosal crypts, mimicking mucosal prolapse syndrome. However, these were immunohistochemically positive for S-100, indicating neural cell origin. As neural polypoid lesion of the rectum, neurofibroma, perineurioma, schwannoma, and mucosal Schwann cell hamartoma were in the differential diagnosis. Histology and additional immunohistochemistry confirmed mucosal Schwann cell hamartoma. Mucosal Schwann cell hamartoma of the rectosigmoid junction or rectum can be a histological mimic of mucosal prolapse syndrome and other S-100 positive neural cell lesions; however, the lesion in the present case was correctly diagnosed with histology and immunohistochemistry.