Subchondral Cysts in Femoral Head

Overview

This lecture discusses an atypical presentation of subchondral cysts in the femoral head and outlines the differential diagnosis and significance in clinical management.

Case Presentation

• A 38-year-old patient had several years of bilateral hip pain, worsening recently.
• Pain was in the groin, radiating to the greater trochanter, with mild functional discomfort but no nighttime pain.
• Imaging revealed bilateral subchondral cysts in the inferior femoral heads.

Imaging Findings

• Radiographs showed bilateral subchondral cysts in the inferior half of femoral heads.
• MRI: Right side cyst is isointense; left side cyst is inhomogeneous hyperintense (suggesting a chronic component).
• Both cysts had intralesional fine septations and a sclerotic rim, with preserved femoral head sphericity and no collapse.

Differential Diagnosis of Subchondral Cysts

• Subchondral cysts commonly occur in osteoarthritis (OA), less often in rheumatoid arthritis (RA), CPPD, or osteonecrosis (ON).
• OA is suggested by cysts plus joint space narrowing, sclerosis, and osteophytes; these were absent here.
• RA may show cysts but typically has synovial cysts/bursae and inflammatory features, which were absent.
• CPPD is associated with numerous cysts and advanced degeneration, not present in this case.
• Diagnosis favored ON after excluding OA, RA, and CPPD due to absence of degenerative, autoimmune, and inflammatory signs.

Key Learning Points

• Subchondral cysts can be seen in OA, RA, CPPD, or ON.
• Absence of degenerative or inflammatory findings argues against OA, RA, or CPPD.
• Accurate differential diagnosis is critical, as treatment varies among these conditions.

Key Terms & Definitions

• Subchondral cyst — fluid-filled sac beneath the cartilage of a joint.
• Osteoarthritis (OA) — degenerative joint disease with cartilage loss and bone changes.
• Rheumatoid arthritis (RA) — autoimmune disease causing joint inflammation and damage.
• Calcium pyrophosphate dihydrate deposition disease (CPPD) — crystal-induced joint disease with cartilage calcification.
• Osteonecrosis (ON) — bone death due to loss of blood supply.

Action Items / Next Steps

• Follow-up imaging and clinical monitoring to confirm or rule out ON.
• Review differential diagnosis of subchondral cysts and associated imaging features.
• Emphasize importance of a thorough work-up before deciding on management.