Avascular Necrosis of the Femoral Head on Bone Scan
CC BY 3.0 · Jarraya et al. / Wikimedia Commons · source file
Question
A bone scan is performed in a patient with acute hip pain and sickle cell disease. The study shows a 'cold' (photopenic) area in the right femoral head. This finding on bone scan is most consistent with:
- ANormal physiologic variation in the femoral head
- BAvascular necrosis (AVN) — early ischemic phase with absent blood flow to the femoral head
- CStress fracture of the femoral neck
- DSeptic arthritis of the hip joint
Show the answer and explanation
B. Avascular necrosis (AVN) — early ischemic phase with absent blood flow to the femoral head
Avascular necrosis (AVN) of the femoral head in its EARLY ischemic phase presents as a photopenic (cold) area on bone scan, reflecting absent blood flow and no osteoblastic activity. This cold phase is the classic early finding. Later, as the body attempts repair (creeping substitution), the scan shows increased uptake ('hot' phase) surrounding the cold defect — or a mixed pattern. In sickle cell disease, AVN results from vascular occlusion by sickled erythrocytes. MRI is more sensitive and specific for AVN than bone scan.
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