Case Report: Schwannoma of the sigmoid colon: a case report of a rare colonic neoplasm and review of literature

Abstract

Background: Schwannomas are tumors originating in Schwann cells of the peripheral nerve system and uncommonly develop in the gastrointestinal tract. Sigmoid colon schwannomas are very rare and only 28 cases have been reported. This study aims to report a case of a sigmoid colon schwannoma and present a literature review. Case report: We report a case of a 66-year-old female with asymptomatic sigmoid colon schwannoma. The patient underwent a screening colonoscopy and about 4cm sized submucosal tumor was identified at the sigmoid colon. A colonoscopic biopsy was performed and the microscopic exam revealed an ulcerated lesion with a proliferation of fibroblast-like spindle cells beneath ulcer, which was insufficient for diagnosis. Abdominopelvic computerized tomography (CT) scan showed a well-defined, well-enhancing, round shaped and slightly heterogenous mass at the sigmoid colon. No distant metastasis was identified in abdominopelvic CT and chest CT scans. Carcinoembryonic antigen level was within a normal range (1.33ng/mL). The patient underwent laparoscopic anterior resection. Immunohistochemical staining of the resected specimen showed positivity for S-100 protein in tumor cells and schwannoma was diagnosed post-surgically. Surgical resection margins were free from tumor and no regional lymph node metastasis was reported. Conclusion: Colon schwannomas are rare diseases. Most cases of colon schwannomas are accidentally identified during screening colonoscopy. The tumors usually present as submucosal masses and colonoscopic biopsies are mostly non-diagnostic. Surgical resection is required, and definitive diagnosis is made by confirming S-100 positive tumor cells in immunohistochemical analysis. Most cases are benign; a few cases have been reported to be malignant. Surgical resection with free negative margins is the treatment of choice.

Keywords: Colon; colectomy; colonic neoplasms; schwannoma.

Figure 1.. Colonoscopy.

About 4cm sized submucosal tumor was identified at the sigmoid colon.

Figure 2.. Abdominopelvic computerized tomography (CT).

A well-circumscribed, well-enhanced, round-shaped mass was identified at the sigmoid colon. ( A) Coronal view. ( B) Axial view.

Figure 3.. Gross findings of the resected specimen.

( A) 4.5 × 4.0cm sized round, protruding mass was observed on the surface of the serosa. ( B) The photo was taken from the mucosal side.

Figure 4.. Cut section after fixation.

Relatively well-demarcated yellowish mass without encapsulation is shown.

Figure 5.. Hematoxylin and eosin (H&E) stain.

( A) The tumor cells are composed of spindle cells with low nuclear atypia. ( B) Nuclear palisading growth pattern is shown. ( C) Lymphoid cuffing surrounding tumor cells is shown.

Figure 6.. Immunohistochemical stain.

( A) S-100 is diffuse, strong positive in tumor cells. ( B) C-KIT is negative in tumor cells. ( C) CD34 is negative in tumor cell, but normal vessel structures were stained. ( D) SMA is negative in tumor cells, but normal smooth muscle in the proper muscle layer is stained.