Dr. Barry Eppley, Indianapolis, Indiana
Sunday, October 9th, 2016
Background: The skull is prone to having numerous types of irregularities on its many surfaces. Bumps and indentations are common and can occur from natural development or from later trauma after birth. The fusion of the various skull plates and anterior and posterior fontanelles affords the opportunity for such skull irregularities to occur.
One such well known skull protrusion is that of the occipital knob deformity. This is a distinct midline outcropping of raised bone on the back of the head that is usually circular in shape. It sticks out as a raised knob that is very visible in men that have close cropped hair or shaved heads. It appears to be a gender specific skull protrusion as I have never seen or heard of it in women.
Why the occipital knob skull deformity occurs is not precisely known. It is also known as the occipital bun or occipital horn and is anthropologically associated with Neanderthal skulls. While common in early man it is relatively rare in modern homo sapiens. It has been theorized that it occurs due to enlarged cerebellum or is a remnant of the adaptation to running. It has also been speculated that it occurs more frequently in more narrow skulls. (although I have seen it in both normal as well as more narrow skulls) Regardless of its origins in the man who has a large knob sticking out from the back of their head it is aesthetically undesirable.
Case Study: This 30 year-old male presented with a prominent protrusion on the back of his head. It had been there his entire life and had always bothered him. It was centrally located, firm and at the horizontal level of the middle of his ear.
Under general anesthesia and in the prone position, a 6 cm horizontal skin incision was in a scalp skin crease just below the occipital knob. The thick scalp tissues were elevated off of the bony protrusion where it was reduced down to the level of the surrounding skull using a hand piece and large cutting burr. This left some redundant scalp which was also trimmed and closed.
The occipital knob deformity is caused by an excessive outcropping of bone growth. It is composed of solid bone and is thicker than the surrounding occipital skull bone. It can be safely reduced through an incision that leaves a minimal scalp scar. Most men would prefer this barely detectable scalp scar to have a smooth and rounder back of the head shape.
A Homo erectus skull, and comparison with Neanderthal skull, far right.