Presentation
Recurrent sporting injuries and known femoral bone lesion.
Patient Data
Hardly visible lytic lesion with a thin sclerotic margin above the ossified growth plate in the lateral femoral metaphysis projecting just next to the lateral patellar rim.
A well-defined lytic lesion with a narrow zone of transition and chondroid matrix calcification located in the lateral femoral metaphysis just above the ossified growth plate.
The lesion features a chondroid appearance in the calcium-suppressed images and an increased electron density compared to the remaining cancellous bone.
No gross bone destruction, no periosteal reaction, and no soft tissue mass.
Findings
Bone
well-circumscribed lobulated lesion in the lateral femoral metaphysics (~18 x 20 x 15 mm) with internal foci of low signal, 'rings and arcs' characteristics and a narrow transition zone
Intercondylar region
mild amount of fluid
anterior cruciate ligament thin and atrophic with ganglion cyst
normal posterior cruciate ligament
Medial compartment
articular cartilage intact
medial meniscus inconspicuous
medial collateral ligament complex intact
Lateral compartment
articular cartilage intact
lateral meniscus inconspicuous
lateral collateral ligament complex intact
Patellofemoral compartment
articular cartilage intact
distal patellar tendon and quadriceps tendon unremarkable
Impression
inconspicuous chondroid lesion in the lateral femoral metaphysis consistent with an enchondroma
status post anterior cruciate ligament tear with small residual ganglion cyst
Findings
Bone
well-circumscribed lobulated lesion (~14 x 12 x 10 mm) in the lateral femoral metaphysics
Intercondylar region
mild amount of fluid
discontinuity of the elongated anterior cruciate ligament
posterior cruciate ligament intact
Medial compartment
articular cartilage intact
medial meniscus inconspicuous
medial collateral ligament surrounded by fluid, no discontinuity
Lateral compartment
subchondral fracture in the centrolateral zone of the lateral femoral condyle
articular cartilage intact
lateral meniscus inconspicuous
lateral collateral ligament surrounded by fluid, no discontinuity
Patellofemoral compartment
articular cartilage intact
distal patellar tendon and quadriceps tendon unremarkable
Impression
severe anterior cruciate ligament tear with associated low-grade medial collateral ligament injury posterolateral corner injury and small subchondral fracture of the lateral femoral condyle
enchondroma in the lateral femoral metaphysis
Case Discussion
This is an example of an enchondroma with a typical location in the femoral metaphysis. They are typically characterized by the following imaging findings as in this case:
sharply defined margins
narrow transition zone
As visible in this case, they can also grow. The main differential of enchondroma is low-grade chondrosarcoma. The latter usually shows more aggressive features including more severe endosteal scalloping, expansile remodeling, cortical breakthrough, larger size (>5-6 cm) and pain.
This case also displays the natural history after anterior cruciate ligament disruption.
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