Magnetic resonance imaging enhances the diagnosis of intra-articular osteochondroma in normal plain radiography

Abstract

Osteochondroma accounts for 10%–15% of primary bone tumors and typically develops extra-articularly from the metaphysis of long bones. However, its intra-articular occurrence presents substantial diagnostic challenges, particularly in radiologic evaluation. This report describes a 27-year-old man with a six-month history of left knee pain without prior trauma. Physical examination revealed no abnormalities, and laboratory parameters were within normal limits. Plain radiographs showed no detectable abnormalities and were interpreted as normal. In contrast, magnetic resonance imaging (MRI) demonstrated a distinct intra-articular lesion in the distal femoral intercondylar fossa, characterized by low signal intensity on T1-weighted images, high signal intensity on T2-weighted images, continuity with the epiphyseal bone, and preservation of a stalk, findings consistent with osteochondroma. Evidence of anterior cruciate ligament (ACL) impingement was also noted, but no features suggestive of malignant transformation were identified. The final diagnosis confirmed the presence of an intra-articular osteochondroma of the knee, verified by arthroscopic evaluation and histopathological examination. This case highlights the limitations of plain radiography for diagnosing intra-articular osteochondroma and emphasizes the essential role of MRI in establishing an accurate diagnosis and guiding appropriate management.