A surgical accessory for use in implanting a medical device in a cranial bone of a human patient may serve as a template during a craniectomy for cutting a hole in which a ferrule for a medical device may be situated and then secured. The surgical accessory is dimensioned to allow a surgeon to gauge how far above the outer surface of the cranium the medical device will extend once the ferrule has been secured to the outer bone table and the medical device has been cradled in the ferrule.
