This case demonstrates a chondroblastoma ("Codman tumor") in a very unusual localization.

Temporal bone chondroblastomas are rare benign osseous tumors with very low prevalence (1-2%). They can be commonly found in all bones with endochondral ossification, but mostly in the epiphysis and/or metaphysis of long bones in young patients (2nd decade). The growth pattern of chondroblastoma differs from other entities affecting the temporal bone and should be differentiated from other temporal bone lesions. The patients usually complain of pain in the area, swelling and neurological symptoms such as facial nerve palsy. Common imaging modalities are CT and MRI. Microscopic and immunohistochemical analysis complete the diagnosis.

Differential diagnoses are clear cell chondrosarcoma, chondromyxoid fibroma and giant cell tumor. Furthermore eosinophilic granuloma (Langerhans cell histiocytosis) and enchondroma. Specific for the temporal bone lesions are: confluent apical petrositis, cholesterol granuloma, plasmocytoma and temporal bone rhabdomyosarcoma.

The treatment approach differs depending on the location of the tumor and on the grade of the expansive/destructive pattern.