What causes acorn cyst in the hip on imaging?
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Answer:
Acorn cyst: Small, rounded subchondral or juxta-articular cyst at the femoral head-neck junction, seen in early osteoarthritis or femoroacetabular impingement due to synovial fluid intrusion under pressure into weakened subchondral bone.
Why is it called so?:
Named for its small, rounded shape resembling an acorn located at the femoral head-neck junction.
Pathophysiology:
Repetitive abutment from cam-type femoroacetabular impingement or early osteoarthritis causes microfractures in subchondral bone at the head-neck junction; elevated intra-articular pressure forces synovial fluid into these defects, forming a geode-like cyst.
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