Intestinal perineuriomas: clinicopathologic definition of a new anatomic subset in a series of 10 cases.

Benign peripheral nerve sheath tumors are uncommon in the gastrointestinal tract, and perineuriomas have not previously been reported to occur at this anatomic location. In this study, we analyzed the clinicopathologic and immunohistochemical features of 10 perineuriomas arising in the intestine. Eight patients were female and 2 male (median age, 51 years; range, 35-72 years). Eight of the lesions were intramucosal perineuriomas presenting as small sessile polyps detected during colonoscopy; 6 of these 8 patients were asymptomatic and undergoing colorectal cancer screening. The remaining 2 cases were submucosal masses, one each located in the colon and jejunum. Of the mucosal polyps, six were located in the rectosigmoid or sigmoid colon and one each was detected in the descending colon and transverse colon. The polyps ranged from 0.2 to 0.6 cm (median, 0.4 cm) in greatest dimension. The colonic and jejunal masses measured 3 cm and 4.5 cm, respectively. Histologically, the intramucosal perineuriomas were composed of uniform bland spindle cells having ovoid to elongated nuclei and pale indistinct cytoplasm, with no cytologic atypia, pleomorphism, or mitotic activity. The lesions had a fine collagenous stroma, demonstrated irregular borders with the adjacent lamina propria, and entrapped colonic crypts. Five cases exhibited hyperplastic changes in the adjacent or entrapped epithelium. The colonic submucosal tumor was microscopically well circumscribed, whereas the jejunal perineurioma showed focal infiltration through the muscularis propria into the subserosa. The stroma was collagenous in the colonic tumor and predominantly myxoid in the jejunal tumor. The spindle cells in the submucosal perineuriomas demonstrated tapered nuclei and elongated bipolar cytoplasmic processes. All tumors except one were positive for epithelial membrane antigen (EMA); 4 of 10 expressed claudin-1 and 2 of 10 expressed CD34. All tumors were negative for S-100 protein, glial fibrillary acidic protein, neurofilament protein, smooth muscle actin, desmin, caldesmon, KIT, and pan-keratin. Electron microscopy was performed on the tumor lacking EMA expression, revealing typical features of perineurioma, namely, spindle cells with long bipolar cytoplasmic processes and prominent pinocytotic vesicles, surrounded by discontinuous basal lamina. Clinical follow-up was available for 4 patients (median, 34 months; range, 8-53 months). No tumor recurred. In summary, perineuriomas may arise in the intestine, most often as intramucosal lesions detected as colorectal polyps with distinctive histologic features including entrapment of colonic crypts. Distinguishing perineuriomas from other spindle cell neoplasms of the gastrointestinal tract can be facilitated by immunostaining for EMA and claudin-1.