Chondroblastomas but not chondromyxoid fibromas express cytokeratins: an unusual presentation of a chondroblastoma in the metaphyseal cortex of the tibia

chordal cell tumours. The authors have proposed this as evidence that benign notochordal cell tumours may transform into chordomas. The features that best differentiate between chordomas and benign notochordal cell tumours remain those originally described by Mirra and Brien. The importance of clinical and radiological correlation is highlighted, with benign notochordal cell tumours presenting as asymptomatic, often incidentally discovered lesions that are confined to the vertebral body with no evidence of destruction. Bone scans are typically normal. Histologically, the tumours are not lobular and there are no syncytial cords of cells or intercellular myxoid matrix. The trabecular framework of the vertebral body remains intact. The cytology of the tumour cells is bland and there are no mitoses. In contrast, even small chordomas found as incidental lesions consist of cords of cells within a myxoid matrix and have mild nuclear atypia. Although chordomas also have vacuolated and physaliferous cells, they lack the uniform sheets of adipose-like cells seen in benign notochordal cell tumours. In addition, small chordomas may also be traversed by fine fibrous septae, a feature not seen in benign notochordal cell tumours. Immunohistochemistry is non-contributory, with chordomas and benign notochordal cell tumours having the same profile: both positive for S100, cytokeratin 18, epithelial membrane antigen and vimentin. The current recommended management of benign notochordal cell tumours is for ongoing radiological surveillance rather than surgical excision, so recognition of the entity is important to prevent overtreatment. Further investigation into the possible transformation of benign notochordal cell tumours to chordomas is required.