Schwannomas are rare tumors originating from the Schwann cells, which form the neural sheath. These tumors occur most frequently in the head, neck, arms and limbs. Primary schwannomas of the colon and rectum are extremely rare; they are usually benign, but in extremely rare cases (2%), they can present with malignant degeneration if not surgically removed. The current study presents the case of a 65-year-old male with blood in the feces who underwent a colonoscopy that revealed an oval-shaped mass covered by ulcerated mucosa. A standard biopsy examination indicated a gelatinous carcinoma, and the patient consequently underwent a laparoscopic resection of the left colon. Histological examination revealed a schwannoma. Immunohistochemistry showed the tumor to be positive for S100 and vimentin, but negative for cluster of differentiation (CD)117, cytokeratin (CK)7, CK20, chromogranin, actin and synaptophysin, with a Ki-67 proliferative index of 3%. Lymph nodes were not involved. Overall, pre-operative biopsy examinations may be difficult for schwannomas, and immunohistochemistry is necessary for the correct diagnosis of this condition. In contrast to gastrointestinal stromal tumors, schwannomas are negative for CD117 and positive for S100 protein and vimentin. A Ki-67 index of ≥5% is strictly correlated with greater tumor aggressiveness. Therefore, the gold standard treatment for schwannomas is oncological radical surgical resection.
Keywords: colon; immunohistochemistry; schwannoma; surgery; tumor.