Incidentally discovered large ancient retroperitoneal schwannoma: a rare case report and literature review.

Ancient schwannoma is a rare retroperitoneal tumor that often remains asymptomatic and is frequently misdiagnosed. We present a case of a 16-year-old male with acute appendicitis, where a contrast-enhanced computed tomography scan incidentally revealed a well-defined cystic retroperitoneal lesion. The patient underwent appendectomy and enucleation of the mass. Histopathological analysis confirmed ancient schwannoma, showing Antoni A and B areas, degenerative changes, and positive S100 staining. Postoperative recovery was uneventful, with no recurrence at 6 months. This case underscores the importance of thorough imaging evaluations, even when assessing unrelated conditions, as incidental findings like ancient schwannoma can significantly impact patient management. Early diagnosis and complete surgical excision offer favorable outcomes.