Introduction and importance: Retroperitoneal schwannomas are extremely rare, benign tumors originating from Schwann cells in peripheral nerve sheaths, with few reported cases. Their deep location and nonspecific symptoms make preoperative diagnosis challenging, often requiring imaging and surgical resection for confirmation. This case highlights an uncommon presentation of retroperitoneal schwannoma in a young patient, emphasizing its rarity.

Case presentation: An 18-year-old male presented with a progressively enlarging, non-tender mass in the left flank. Imaging revealed an 8 × 7 cm well-circumscribed, encapsulated mass displacing adjacent major vessels without invasion. The patient underwent successful surgical resection, and histopathology confirmed a benign schwannoma. Immunohistochemistry showed strong S100 protein positivity, with no signs of malignancy. Follow-up was uneventful, with no recurrence at six months.

Discussion: Retroperitoneal schwannomas, typically slow-growing and benign, are infrequently encountered. Due to their nonspecific presentation, they often reach considerable size before detection. Imaging may suggest diagnosis but is not definitive, making surgical excision essential for confirmation. Complete resection is generally recommended to reduce recurrence, though partial excision may be appropriate when adjacent critical structures are involved.

Conclusion: Retroperitoneal schwannomas are rare and challenging to diagnose preoperatively. Complete surgical resection remains the primary approach, allowing histological confirmation and reducing recurrence risk. This case underscores the importance of considering retroperitoneal schwannomas in young patients presenting with atypical retroperitoneal masses.

Keywords: Case report; Follow-up; Histology; Retroperitoneal schwannoma; Surgical resection.

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