A case of retroperitoneal malignant schwannoma in a young male: a case report

Malignant peripheral nerve sheath tumors (MPNSTs) are uncommon soft-tissue sarcomas, and primary retroperitoneal presentation in young adults is rare. Because imaging features may overlap with benign schwannoma, diagnosis and risk stratification rely on histopathology and proliferative indices.

A 27-year-old Arab male presented with a progressively enlarging abdominal mass associated with early satiety and heaviness. Abdominal ultrasonography and contrast-enhanced computed tomography (CT) demonstrated a well-circumscribed retroperitoneal mass measuring approximately 15 cm, located beneath the liver and posterior to the pancreatic head, closely related to the anterior surface of the right kidney and in proximity to the inferior vena cava, with heterogeneous predominantly hypoattenuating components and internal low-attenuation areas consistent with cystic/degenerative change. No lymphadenopathy or distant metastases were identified. The patient underwent exploratory laparotomy with complete excision; estimated blood loss was 250 mL and no transfusion or en bloc organ resection was required. Histopathology showed a spindle cell neoplasm with mild cytologic atypia and mitotic activity quantified as 6 mitoses per 10 high-power fields, without necrosis; margins were free of tumor. Immunohistochemistry demonstrated diffuse strong S100 positivity, negative Actin/CD117/CD34, and a Ki-67 index of 10-15%, supporting a low-grade MPNST. At 6 months postoperatively, the patient remained clinically well with no radiologic evidence of recurrence.

This case underscores that a large, well-circumscribed retroperitoneal peripheral nerve sheath tumor in a young adult may still be malignant. Pathology-driven risk stratification with quantified mitotic activity and Ki-67 is essential for accurate classification and for planning structured post-resection surveillance.