A 30-year-old man presents with anterior tibial bowing and a painless diaphyseal mass. X-ray shows a well-defined intracortical lytic lesion with sclerotic margins in the anterior tibial cortex. Biopsy shows nests of epithelial cells within a fibrous stroma with immunohistochemical positivity for cytokeratin. Which is the diagnosis?
- A Non-ossifying fibroma
- B Osteofibrous dysplasia
- C Adamantinoma ✓
- D Fibrous dysplasia
Correct answer: C. Adamantinoma
Explanation
Adamantinoma is a rare low-grade malignant biphasic tumor classically arising in the tibial diaphysis. The hallmark is nests of epithelial cells within a fibrous stroma, with cytokeratin positivity on immunohistochemistry confirming epithelial differentiation. Osteofibrous dysplasia occurs in younger children and lacks the epithelial nests with keratin positivity. Non-ossifying fibroma is purely lytic without epithelial elements.
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.