Microcystic reticular schwannoma of the colon.

form the third commonest group of mesenchymal tumors within the gastrointestinal tract. They occur with a frequency of approximately 5%, which compares with 50% for gastrointestinal stromal tumors (GIST) and 30% for smooth-muscle neoplasms [1]. In 2008, Liegl et al. described 10 cases of microcystic reticular schwannoma as a distinct variant with predilection for visceral sites [2]. Herein, we present two additional tumors that were detected upon screening colonoscopy in asymptomatic patients. Tumor A occurred within the sigmoid colon of a 70-year-old woman. The lesion, which measured 0.7 cm at largest diameter, presented as a well circumscribed, yet nonencapsulated submucosal growth with deep muscular extension; it was removed by surgical resection (●" Fig. 1a,b). Tumor B,whichmeasured1.3 cmat largest diameter, presented as a pedunculated lesionwithin the sigmoid colon of a 70-yearold man and was removed by snare polypectomy. This lesion was mainly located in the submucosa but extended into the mucosa causing entrapment of non-neoplastic crypts (●" Fig. 2a,b). Upon histology, a characteristic reticular microcystic growth pattern with intersecting strands of spindle cells arranged around islands of myxoid or collagenous/ hyalinized stroma was observed in both tumors. Tumor A, however, had additional areas indistinguishable from conventional schwannoma. Both tumors showed strong nuclear and cytoplasmic immunoreactivity for S-100 protein (●" Fig. 2c), but were negative for smoothmuscle actin, desmin, CD34, and CD117 (KIT). Microcystic reticular schwannoma represents a newly recognized benign variant of PNST predominantly affecting the gastrointestinal tract, which has to be differentiated from other mesenchymal tumors, such as GISTor smooth-muscle neoplasms [3]. Including our two cases, 15 tumors have been reported to date [1,2,4], six of which arose from the colorectum, three from the small bowel, and one from the stomach, respectively. Polypoid lesions are sufficiently treated by endoscopic resection, whereas local surgical excision is the treatment of choice for intramural tumors. Competing interests: None