Radiographs display a classic example of the permeative pattern in the left distal femur, ill-defined lucencies simulating a “moth-eathen” appearance with a wide zone of transition.

The differential diagnosis for this pattern:

• Lymphoma
• Ewing’s Sarcoma
• Infection (osteomyelitis)
• Multiple Myeloma
• Eosinophilic Granuloma
• Malignant Fibrous Histiocytoma
• Osteosarcoma
• Metastases

The first three diagnoses (lymphoma, Ewing’s sarcoma, infection) can frequently result in this pattern, whereas the others on the list are either rare or more commonly have a different pattern. The MRI shows an associated soft tissue mass (also visible on the radiographs), which can occur in any of these three entities, though less common in infection.

The permeative pattern has been described with bone marrow predominant processes, with (relative) sparing of the cortex. The Tc99m MDP bone scan demonstrates subtly increased uptake in the left distal femoral physis compared to the contralateral side. This minimal abnormality on the Tc99m bone scan supports a marrow process, as the MDP uptake is a depiction of bone turnover (which is more abundant in cortical bone).

The FDG PET/CT shows multiple abnormalities in this patient:
– Focus of uptake at the pericardium
– Intense FDG activity along the right 9th rib
– Mass-like expansion of the pancreas with intense FDG activity
– FDG-avid periportal, retroperitoneal, left iliac/inguinal lymphadenopathy
– Intensely FDG avid left distal femur mass

Either Ewing’s sarcoma or lymphoma could have this pattern, but the extensive lymphadenopathy and visceral organ (pancreas) involvement suggest the diagnosis.

This patient was diagnosed with B cell lymphoblastic lymphoma/leukemia.