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The origin of cranial epidermoid cysts (EC) remains controversial, and although generally considered to be congenital, acquired origin has been reported. EC represent 0.2 to 1.8% of all brain tumours, and only one fourth are intradiploic in location. We report of a 44-year-old woman with a giant intradiploic EC of the occipital bone with intracranial extension confirmed on brain MRI. Three years previously, in the same location, she underwent resection of an intradermal melanocytic naevus of the skin under local anaesthesia with lidocaine infiltration of skin and periosteum. Brain CT scan performed at the time of naevus surgery because of associated headache did not show a lesion of the cranial vault. Iatrogenic epidermoid tumours are extremely rare, and although seeding of epidermal cells has been classically described only after lumbar puncture, the same mechanism may be involved after head injury, cranial surgery or cranial periosteal iatrogenic puncture.

Optic chiasm location provides useful information to predict the percentage of resection in both prefixed and postfixed chiasm patients but not in the normal optic chiasm location group. Optic nerve length was proven to provide a more accurate way to predict the percentage of resection than the optic chiasm location in the normal optic chiasm location group.