Hemorrhagic cystic subcutaneous schwannoma of the buttock with intracystic reticular septal enhancement: a case report and review of literature

Subcutaneous schwannomas typically appear as solid or cystic-solid soft-tissue masses on magnetic resonance imaging (MRI). The degenerative subtype with marked hemorrhagic cystic change and intracystic reticular septal enhancement represents a diagnostic challenge, as it can mimic a variety of cystic superficial soft-tissue lesions. Herein, we report a case of subcutaneous schwannoma with hemorrhagic cystic degeneration and characteristic intracystic reticular septal enhancement in the left buttock of a 44-year-old male patient. The patient presented with a 12-year history of painless subcutaneous mass in the left buttock, which had progressively enlarged in recent months, accompanied by mild local distending discomfort after prolonged sitting and occasional activity-induced dull pain. Physical examination revealed a soft subcutaneous nodule measuring 4–5 cm in the left buttock with a negative Tinel sign. The lesion was preoperatively misdiagnosed as hemangioma or chronic hematoma based on MRI and ultrasonographic findings. The patient underwent complete surgical resection of the mass. Postoperative histopathological examination confirmed the diagnosis of benign subcutaneous schwannoma with extensive hemorrhagic cystic degeneration. The intracystic reticular septal enhancement on MRI is presumed to mainly represent residual, loosely arranged Schwann-cell septa within Antoni-B regions. The patient achieved an uneventful postoperative recovery, and no local recurrence was detected during the 12-month clinical follow-up. Hemorrhagic cystic subcutaneous schwannoma is a rare degenerative subtype that may demonstrate characteristic intracystic reticular septal enhancement; this lesion may be misdiagnosed preoperatively. Recognition of this potential imaging sign and clarification of its pathological basis may aid preoperative evaluation of atypical subcutaneous schwannoma and inform clinical management.