Background: The occipital knob is a visible prominence of bone that is situated in the center of the back of the head at the bottom of the occiput. While it is a feature of a normal occipital skull, known as the inion, it is unknown why it grows excessively and becomes a visible bulge. While it likely occurs in both men and women, I have seen men present for treatment undoubtably due its exposure with shorter hairstyles. Patients tell similar stories about when they observed its presence and it was always long after puberty. They were not born with it nor was it seen in their childhood or early teenage years.
The occipital knob is often confused with the occipital bun which is a much larger protrusion of the entire lower central occiput and is not just the knob proper. The bun may be associate with nuchal line protrusions which radiate out from the central bony protrusion. This is not a feature of the occipital knob
Occipital knobs can present in a variety of sizes. Some are small and fairly discrete while others can get quite large. The larger the bony protrusion the more likely there will be an excess of overlying scalp skin once it is reduced. This may require some excision of the superior scalp excess to ensure a smooth external contour.
Case Study: This young male had an occipital knob that become noticeable and an aesthetic distraction once he joined the military. Since he was going to maintain a shot hairstyle he wanted it removed.
Under general anesthesia and in the bone position a 3.5 cm long scalp incision was made in the skin crease just below it. Once exposed the knob measured 11mms thick as was evident with an initial bone cut down through its middle. The sides of the knob was then burred down to be equal to the center and confluent with the surrounding skull surface. Once it was removed a small scalp skin fold was evident and it was removed and the scalp tucked in multiple layers for closure.
The scalp is incredibly thick particularly at the bottom of the occipital skull where it blends into the posterior neck. While thick tissues can have a great propensity to contract down and achieve a smooth surface, it is not always predictable. Thus, when in doubt about any scalp excess after an occipital knob reduction, a scalp excision and tuck should be performed.
1) The occipital knob skull deformity is a central projection of bone that sticks it at the bottom of the occiput.
2) In some cases the occipital knob is associated with an excess of scalp tissue that should be concurrently removed. (scalp tuck)
3) A smooth occipital contour in side profile is the goal of occipital knob skull reduction.
Dr. Barry Eppley