A 15-year-old boy has progressive pain around the shoulder. X-ray shows a well-defined lytic lesion in the epiphysis of the proximal humerus with a thin sclerotic margin. Biopsy shows sheets of chondroblasts with abundant eosinophilic cytoplasm, scattered osteoclast-type giant cells, and foci of calcification surrounding individual cells in a lattice pattern. The diagnosis is:
- A Chondrosarcoma
- B Giant cell tumor of bone
- C Chondroblastoma ✓
- D Osteochondroma
Correct answer: C. Chondroblastoma
Explanation
Chondroblastoma occurs in the epiphyses of long bones in skeletally immature patients, a location where GCT is rare. Histology shows chondroblasts with grooved nuclei and the characteristic 'chicken wire' calcification, a lace-like lattice of calcium deposition around individual cells. The mutation H3K36M in the H3F3B gene supports the diagnosis. GCT is excluded by age and the immature skeleton.
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.