A 25-year-old presents with hip pain. MRI shows low T1 and T2 signal in the femoral head with a 'double-line sign' on T2 sequences at the subchondral region. Diagnosis and mechanism are:
- A Avascular necrosis of femoral head; ischemic necrosis with granulation tissue formation ✓
- B Transient osteoporosis of hip; reactive bone marrow edema
- C Septic arthritis; hyperemia and joint effusion
- D Pigmented villonodular synovitis; hemosiderin deposition
Correct answer: A. Avascular necrosis of femoral head; ischemic necrosis with granulation tissue formation
Explanation
The 'double-line sign' on T2 MRI is pathognomonic of avascular necrosis (AVN). It consists of an inner band of high T2 signal (representing granulation/vascular tissue at the reactive interface) surrounded by an outer low-signal sclerotic band, bordering the subchondral necrotic segment. This finding represents the histological zone between viable and necrotic bone. Transient osteoporosis shows diffuse marrow edema without a distinct double line. PVNS shows low T1 and T2 signal due to hemosiderin but lacks the double-line pattern and involves synovium primarily.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.