BONE - Dermoid cyst

This shows part of the vault of the skull, expanded by essentially necrotic, but outwardly smooth, cystic lesion.
This man presented at the age of 30 with an 18-month history of a large swelling in the left occipital region. X-rays showed a large erosive lesion, with flat sclerosis around it. This was removed and was found to extend into the mastoid process on the left.