Presentation
Painful swollen leg and constitutional symptoms for 4 months.
Patient Data
A large proximal fibular osteolytic aggressive lesion with soft tissue swelling and bone destruction and a wide zone of transition. Proximal lateral tibia metaphysis lucency. No periosteal reaction.
Well-defined multi-lobulated mass replaces the proximal fibula and invades the cortex of the lateral tibial plateau with extension into the lateral knee joint space. The mass demonstrates heterogeneous signal intensity which is predominantly isointense to muscle on T1W and hyperintense on T2W imaging. The mass displaces and abuts the popliteal artery which has an irregular outline. The peroneal nerve is displaced and encased laterally.
The patient had a surgical biopsy.
Histology
Macroscopy: The specimen consists of multiple tissue fragments, the largest measure 3 mm in greatest dimension.
Microscopy: Sections show multiple fragments of tissue with infiltrates of atypical spindled cells with hyperchromatic nuclei, small nucleoli and frequent mitoses. Intracytoplasmic PAS-positive accumulations are noted. Extensive coagulative necrosis but no osteoid production is seen. No evidence of lymphovascular invasion.
Immunohistochemistry negative for desmin, S100, AE1/AE3, SMA, BCL2, CD34 and EMA. CD99 is positive
Pathological diagnosis favors Ewing sarcoma.
Case Discussion
Pathologically proven Ewing sarcoma of the left fibula. The main differential on imaging would include osteosarcoma. Ewing sarcoma is an aggressive lesion that typically presents with an onion skin appearance periosteal reaction, which is absent in this case.