Background: The occipital bone of the skull is the very back part that is shaped like a dish and covers the occipital lobes of the cerebellum. Near the bottom of the visible occipital bone is a series of curved horizontal lines known as the nuchal ridges onto which are attached various ligaments and muscles. In the very center of these lines sits a prominence known as the external occipital prominence.
The highest point of the external occipital prominence is known as the inion. Onto the inion is attached the nuchal ligament and trapezius muscle fibers. It is an enlarged external occipital protuberance that creates the the occipital knob or bun skull deformity. Why it occurs is not known but the fact that it appears to be largely a male skull anomaly suggests it is related to more or stronger muscle attachments onto the bone.
Case Report: This 26 year-old male noticed a hard lump on the back of his head since he began to wear his hair shorter. He always knew he had a bump on the back of his head but it never bothered him until it became visible with shorter hairstyles. It did not cause him any pain but he did not like the big knob that stick out from the back of his head as it made him self conscious.
Under general anesthesia and in the prone position, a 7 cm horizontal skin incision was made in the skin crease just below the bony bump. The occipital knob was exposed and had a 13mm projection above the surrounding occipital skull surface with a distinct horseshoe-shape to it. The bony prominence was burred down to be completely flush with the surrounding skull surface. It was solid cortical bone with few vascular channels.
The occipital knob skull deformity appears to occur exclusively in men, I have never seen it in a female. (It may occur in women it is just I have never seen it yet) It is caused by excessive thickening of the cortices of the bottom of the occipital skull bone. It can reduced completely by a burring bone reduction technique through a fairly small horizontal scalp incision that heals very well. It is a surgery that is performed in an hour with minimal recovery.
Hightlights:
1) The occipital knob or occipital bun skull deformity has become more common as more men shave their heads at even younger ages.
2) It is caused by a central prominence of increased bone thickness which can have various shapes.
3) Occipital knob skull reduction is a very safe and effective skull reshaping surgery that provides a permanent contour flattening effect on the back of the head.
Dr. Barry Eppley
Indianapolis, Indiana