Case Report: Benign colonic schwannoma with restricted diffusion mimicking malignancy

Colonic schwannoma is a rare gastrointestinal mesenchymal tumor that is usually benign but may be difficult to distinguish from malignancy before surgery. This case is notable because a benign colonic schwannoma showed both pronounced restricted diffusion on MRI and prominent mesocolic lymphadenopathy, creating a strong radiologic impression of malignancy.

A 43-year-old woman presented with a 2-day history of abdominal pain accompanied by altered bowel habits. Colonoscopy revealed a large spherical submucosal mass in the transverse colon. Biopsy suggested a neurogenic tumor favoring schwannoma, but malignancy could not be excluded because of limited sampling. Contrast-enhanced CT showed a large colonic mass with heterogeneous internal density, focal cystic change, irregular serosal appearance, and multiple enlarged mesocolic lymph nodes. MRI demonstrated marked restricted diffusion, with hyperintensity on diffusion-weighted imaging and hypointensity on ADC maps.

The lesion was clinically suspected to be a malignant colonic tumor. The patient underwent laparoscopic adhesiolysis and left hemicolectomy. Postoperative histopathology unexpectedly confirmed a benign gastrointestinal schwannoma. All 34 harvested mesocolic lymph nodes showed reactive hyperplasia without metastasis. The patient recovered after surgery and was discharged following supportive treatment.

Benign colonic schwannoma can closely mimic malignancy when restricted diffusion and prominent regional lymphadenopathy are present. This single case underscores that such features are not specific for malignancy; because imaging and biopsy could not exclude a malignant tumor, oncologic resection remained appropriate, and the definitive diagnosis still depended on histopathology and immunohistochemistry.