Presentation
Acute knee pain without trauma.
Patient Data
Displaced fracture of the medial femoral epicondyle with comminution. Probable intra-articular extension. There is a well defined lucent lesion in this region, raising suspicion for a pathological fracture.
Large suprapatellar joint effusion present.
There is large lucent lesion within the distal femoral metaphysis in an eccentric location. It extends into the intercondylar notch. No surrounding sclerotic rim. Small amount of endosteal remodeling. Fracture through the lesion is noted, extending from the medial metaphysis to the intercondylar notch.
A fracture fragment is noted within the dependent portion of the lucent lesion.
Hemarthrosis.
Patient was pregnant (first trimester) so contrast was being withheld.
Hemarthrosis containing multiple fluid- fluid levels.
Pathological fracture through the lesion in the distal femoral metaphysis extending into the epiphysis, but not extending to the articular surface. Lesion is centered eccentrically in the medullary cavity.
Lesion abuts and thins the medial and posterior cortices of the distal femoral metaphysis.
No evidence of cortical destruction. No definite soft tissue tumor component. Extensive medial soft tissue edema extends deep to the vastus medialis to the junction of the middle and distal thirds of the femur.
There is heterogeneous signal within the lesion - predominantly T2 hyperintense, T1 hypointense - but not signal of completely simple fluid. No evidence of osteoid or chondroid matrix.
Fracture line extends through the medial cortex distal femoral metaphysis to the intercondylar notch.
Minimal posterosuperior displacement of the fracture fragment.Minor marrow edema in the medial femoral condyle. Note is made of a horizontal tear of the posterior horn of the medial meniscus.
Conclusion
Pathological fracture through lesion in distal femoral metaphysis.
Heterogeneous material in the lesion may represent acute hemorrhage into fluid in the context of simple bone cyst (note is made of the fallen fragment on CT). A more aggressive lesions such as a metastasis or primary bone sarcoma are less likely. The lesion does not extend to subchondral bone and does not have the signal intensity of a giant cell tumor.
Case Discussion
Histology from CT-guided bone biopsy was of giant cell tumor (GCT). Interestingly, the x-ray and CT favored a GCT, whereas the MRI favored a simple bone cyst.