A 13-year-old boy presents with progressive back pain. Imaging shows an expansile osteolytic lesion in the posterior element of a lumbar vertebra. MRI demonstrates multiple fluid-fluid levels within the lesion. Curettage is planned. Which finding on histopathology would be most important in excluding a telangiectatic osteosarcoma?
- A Absence of atypical stromal cells and malignant osteoid ✓
- B Presence of blood-filled cavernous spaces lined by giant cells
- C Presence of reactive woven bone at the periphery
- D Presence of mitotic figures in spindle cells
Correct answer: A. Absence of atypical stromal cells and malignant osteoid
Explanation
The imaging is typical of aneurysmal bone cyst, whose histology shows blood-filled spaces separated by septa containing fibroblasts, osteoclast-type giant cells and reactive woven bone. Telangiectatic osteosarcoma can mimic it radiologically, so the decisive discriminator on biopsy is the absence of frankly atypical stromal cells and malignant osteoid. Reactive bone and even mitoses occur in benign ABC, so they do not exclude malignancy reliably.
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.