Bilateral Knee Osteonecrosis in an Adolescent With Leukemia on Prolonged Corticosteroids: Discordant Femoral-Tibial Findings on Bone Scan SPECT-CT.

Osteonecrosis (avascular necrosis, AVN) is a disabling complication of corticosteroid exposure and is well recognized in adolescents treated for hematologic malignancies, including acute lymphoblastic leukemia (ALL). We report a 17-year-old female with ALL and later acute myelogenous leukemia (AML) after hematopoietic stem cell transplantation (HSCT), who received documented post-HSCT prednisolone therapy and presented with progressive bilateral knee pain. MRI demonstrated multifocal osteonecrosis involving both distal femoral condyles and proximal tibiae, with classic serpiginous infarct morphology and a double-line sign. A [99mTc]-MDP three-phase bone scan with hybrid SPECT/CT demonstrated discordant activity: intense uptake and marked sclerosis in the femoral condyles but minimal uptake in the tibial lesions. This pattern may reflect heterogeneous lesion activity or different reparative stages rather than a validated predictor of collapse. The case highlights the potential value of bone scintigraphy/SPECT/CT as an adjunct to MRI for lesion activity mapping and surveillance planning in selected high-risk pediatric oncology patients while emphasizing that its prognostic role requires longitudinal validation.