Rectal Granular Cell Tumors are Rare and Difficult to Diagnose Preoperatively

Granular cell tumors (GCTs), likely derived from Schwann cells can occur in any organ, including the gastrointestinal tract. Among gastrointestinal GCTs, esophageal GCTs are the most common; however, GCTs can also occur in the large intestine, especially the right-sided colon. Rectal GCTs are extremely rare. Here, we describe a case of rectal GCT detected incidentally during a colonoscopy. A submucosal tumor (SMT) with a smooth, yellow surface, approximately 5 mm in diameter, was observed in the rectum. Endoscopic ultrasonography showed a well-demarcated, homogenous hypoechoic mass in the third layer. Although a rectal neuroendocrine tumor (NET) was suspected, histopathological examination of multiple endoscopic biopsies of the lesion did not successfully reveal the tumor type. Therefore, we performed an endoscopic mucosal resection with ligand (EMRL).Based on histopathological analysis and immunohistochemical studies, this SMT was diagnosed as a GCT. The endoscopic features of colorectal GCTs closely resemble those of colorectal NETs. Colorectal GCTs have a reported diagnosis rate of only 50% on endoscopic biopsy and are difficult to diagnose preoperatively. When endoscopic biopsy does not provide a reliable diagnosis, GCTs should be included within the differential diagnosis; without malignant signs, endoscopic resection for diagnosis and treatment may be recommended.

Keywords: Colonoscopy; Endoscopic Ultrasonography; Granular Cell Tumor of Rectum; Neuroendocrine Tumor of Rectum; Submucosal Tumor.