A 10-year-old child presents with thigh pain. X-ray shows an eccentric, expansile, lytic 'blown-out' lesion in the proximal tibial metaphysis with a thin cortical shell. MRI shows multiple fluid-fluid levels. Biopsy shows blood-filled cystic spaces lined by fibrous septa containing osteoclast-type giant cells. Which is the diagnosis?

• A Aneurysmal bone cyst ✓
• B Giant cell tumor
• C Telangiectatic osteosarcoma
• D Brown tumor of hyperparathyroidism

Explanation

Aneurysmal bone cyst characteristically shows blood-filled cystic spaces lined by fibrous septa with osteoclast-type giant cells and reactive woven bone. Fluid-fluid levels on MRI are classic. Telangiectatic osteosarcoma is malignant with pleomorphic cells. GCT has solid sheets of giant cells without blood-filled spaces. Brown tumor shows fibrosis and hemosiderin but no cystic blood-filled spaces.

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.