Background: The development is a complex interplay between multiples independently bone plate sites. This combined with the influence of various muscle and facial attachments makes for irregular surfaces around the base of the skull. One such common bony protrusion site is the inion or occipital knob on the back of the head. While everyone has some semblance of an occipital knob, it is bigger in males.
In some men for reasons that are not clear the occipital knob develops more prominently and can create a prominent midline bulge. This bulge on the back of the head is at the horizontal level of the top of the ears. This is the bottom of the skull at the nuchal line before the bone turns inward toward the spine. In the man with short hair or a shaved head, the occipital knob creates an aesthetic deformity.
When considering occipital knob reduction it is important to recognize that this is a skull bone thickening. Inspection of any actual or. anatomic skull models will show that the natural inion is a raised area on the outside which has a corresponding protrusion on the inside of the skull. (called in the inner occipital crest) As a result preoperative imaging, while creating interesting pictures, is not typically needed. The midline occipital protrusion can more than safely be burred down to the level of the surrounding skull outer skull surface.
Case Study: This young male had a classic midline occipital knob skull deformity on the back of his head. Besides its midline location it was a firm rounder structure consistent with the feel of bone. The scalp moved back and forth over it.
Under general anesthesia and in the prone position, a small 3 cm scalp was made in a horizontal orientation over the bony knob. Through this incision and underneath the thick scalp, subperiosteal dissection was done over they whole knob particularly in its inferior extension. (this area of reduction is frequently missed if one is unaware of this extension) The bony protrusion was then burred down to be confluent with the surrounding skull surface. The galea was the closed over the reduced bone surface with skin closure with small dissolvable sutures for the skin.
A minimal incision approach is only needed for most typical occipital knob skull deformities. This leaves a virtually undetectable scar in most cases.
Case Highlights:
1) An overdeveloped occipital knob becomes a prominent bulge in the male with a short hairstyle.
2) The occipital knob represents excessive thickening of the skull on both the intracranial and extracranial surfaces.
3) A minimal incisional approach can be used for most occipital knob skull reductions.
Dr. Barry Eppley
Indianapolis, Indiana