Case Report: Benign colonic schwannoma with restricted diffusion mimicking malignancy.

Introduction: 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. Case presentation: 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. Diagnosis interventions and outcomes: 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. Conclusion: 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.