Rare co-occurrence of parosteal lipoma and growing osteochondroma: A case report.

Parosteal lipoma is a rare benign tumor originating from the periosteum and composed of mature adipose tissue closely attached to the bone cortex. Occasionally, it may induce reactive osseous or cartilaginous proliferation, forming a lesion resembling osteochondroma or a malignancy. We present a case of a 34-year-old male exhibiting a progressively enlarging mass on the right thigh, accompanied by intermittent pain that radiated down to the leg. Imaging studies indicated a significant lipomatous tumor featuring internal septations and cortical irregularities along the femoral shaft, which initially raised suspicion for sarcoma. However, a CT-guided biopsy revealed mature adipose tissue along with fibrocartilage and bone formation, thereby confirming the diagnosis of a parosteal lipoma with osteochondroma. This case emphasizes the diagnostic challenge involved in distinguishing benign parosteal lipomas with osseous components from malignant surface tumors. Accurate interpretation of imaging and correlation with histopathology are vital for proper management, since complete excision leads to an excellent prognosis with a low rate of recurrence.