Which radiological sign is considered pathognomonic of a simple (unicameral) bone cyst?

• A Soap bubble appearance
• B Onion skin reaction
• C Ground glass appearance
• D Fallen fragment sign ✓

Explanation

When a pathological fracture occurs through a unicameral bone cyst, a piece of cortical bone may settle into the dependent part of the fluid-filled cavity, producing the 'fallen fragment' or 'fallen leaf' sign. This is diagnostic because only a cavity filled with fluid allows free fragments to gravitate. Ground glass appearance indicates fibrous dysplasia and onion skin reaction indicates Ewing sarcoma.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.