Intramuscular Myxoma of the Gluteus Maximus: Diagnosis and Management of a Rare Benign Tumor: A Case Report

Abstract: Background: Intramuscular myxoma (IM) is a rare benign soft-tissue tumor, frequently underrecognized due to its subtle clinical presentation and radiological/histopathological overlap with cystic lesions or low-grade myxoid sarcomas. Accurate diagnosis requires multidisciplinary correlation of imaging, histopathology, and clinical context, particularly to exclude associated syndromes such as Mazabraud syndrome. Case presentation: We report the case of a 56-year-old Moroccan woman with no significant family history, who presented with a painless, slowly progressive mass in the right gluteal region evolving over four years. Clinical examination revealed a mobile, non-tender swelling measuring 4 × 5 cm. Ultrasound and MRI identified a 12.7 cm multiloculated solid-cystic lesion within the right gluteus maximus, extending beyond the aponeurosis. Initial surgical biopsy suggested a synovial cyst. Subsequently, a wide monobloc surgical excision was performed. Histopathological examination confirmed benign IM, characterized by a hypocellular myxoid stroma with sparse spindle cells, absence of mitoses or nuclear atypia, and clear resection margins. Systemic skeletal survey excluded fibrous dysplasia. At one-year follow-up, the patient remained asymptomatic with no evidence of recurrence. Conclusion: This case underscores the diagnostic challenges posed by IM, often misinterpreted as a benign cystic lesion. Complete surgical excision, coupled with thorough histopathological analysis, remains the cornerstone of management and ensures an excellent long-term prognosis.