Reactive Bursitis secondary to Distal femoral Osteochondroma: MRI features, diagnostic challenges, and surgical correlation: A case report

Abstract

Osteochondroma is the most common benign bone tumor, typically presenting in children and adolescents. It is characterized by a bony outgrowth with a cartilage cap that usually arises in the metaphyseal regions of long bones. These lesions are often asymptomatic but may be complicated by fractures, deformities, neurovascular compression, or bursitis. Imaging, particularly MRI, plays a vital role in identifying these features, and distinguishing benign changes from malignant transformation can occur in adulthood, although metastasis is rare. We report an 18-year-old male presenting with progressive swelling and dull pain in the left distal thigh. Radiographs demonstrated a pedunculated bony lesion originating from the distal femoral metaphysis, with cortical and medullary continuity, consistent with an osteochondroma. MRI revealed a cartilage-capped lesion with an adjacent fluid-filled collection, indicative of secondary reactive bursitis. The lesion was surgically excised, and histopathology confirmed a benign osteochondroma with associated bursal tissue. The postoperative course was uneventful without complications. This case highlights the importance of advanced imaging—especially MRI—for accurately diagnosing osteochondroma and its secondary complications such as reactive bursitis, aiding surgical planning, and distinguishing benign pathology from potential malignant change. MRI also supports postoperative assessment for complete excision and recurrence.