54 years old male with pain in the lower thigh with radiolucent medullary lesion on X-ray shows on MRI : large complex lobulated heterogenously altered signal intensity central medullary lesion is suggested in the lower femoral metadiaphyseal location with peripheral satellite foci within the proximity of the old epiphyseal plate with no expansion or pathological fracture or cortical abnormality or soft tissue involvement, representing possibly enchondroma.
Teaching points by Dr.M.G.K.Murthy, Mr.Abdul Hamed, Mr.Maniyam:
Incidental enchondroma of the femur is seen in 3% of the routine MR knee examination ( 10 times higher than autopsy series). The other common side are proximal tibia and proximal fibula. The incidence of higher prevalence of enchondroma on imaging as compared to autopsy series is due to increase sensitivity of MRI.
The average size is approx 2 cm. Proximity ( within 1.5 cm ) to the physeal plate is explained as the cartilage rests from the physeal plate produce this enchondromas. Only 30% are more than 1.5 cm away from the physeal plate.
No signs of radiological aggression including peritumoral edema or pathological fracture are seen. Deep endosteal scalloping greater than 2/3rd of the normal cortical thickness also helps in differentiating from chondrosarcoma.
Most of the lesions are asymptomatic. The other differentials including intraosseous contusion , subchondral cyst , intraosseous ganglion and metastasis are differentiated by their individual patterns.