Background: The occipital bone on the back of the head has a trapezoidal shape that forms the lower and back part of the cranium. It is not a snoot bone and has various ridges and prominences due to the attachment of numerous neck muscles. But there is one often seen and well described bump on the back of the head called the occipital knob or by anatomical terms the inion. This is the tip of the external midline occipital protuberance onto which the ligamentous nuchal and fibers of the trapezius muscle attach.
Most people have an occipital inion although its size is generally bigger in men than women. Having looked at thousands of 3D skull scans for head reshaping surgery I have noticed that all men have an inion, some larger than others, but many women have no evidence of it at all. Presumably the presence is either a genetic origin, created during development by the pull of the neck muscles or both.
While many inions are invisible due to their smaller size and the coverage of a thick scalp, some will enlarge and become visible. While a few enlarged inions are symptomatic in terms of discomfort most are of an aesthetic concern particularly if the patient has short hair. In such cases surgical reduction is the definitive treatment to recontour the prominence to a flatter profile. This can be done using a very small scalp incision and is completely safe as their is no risk of intracranial penetration.
Case Study: This male with short hair was bothered by the central bony prominence on the back of his head. He had no discomfort from it and his concerns were purely aesthetic.
Under general anesthesia and in the prone position a small 2.5cm scalp incision was made over the prominence. Going through thick scalp tissue (2 cms thick) the knob was exposed and reduced by a high speed handpiece and burr. In its reduction the broader base of the bony prominence must be equally reduced as well as its height. Prior to closure redundant galea tissue was also excised.
When seen the next day after head dressing removal, the immediate reduction of the prominence could be seen.
All skull reductions, and an occipital knob reduction is not exception, must be done through the smallest scalp incision as possible. Barring any discomfort from it this is an aesthetic operation so the scar tradeoff must appear better than the appearance of the knob. Through a very small scar incision the entire knob can be completely reduced but it is important to remember that, like an iceberg, the base of the knob is much broader than its visible projection. This knowledge is critical when using a minimal incisional approach as one has to know to continually reduce bone in a wider pattern the more its height is reduced.
Highlights:
- The occipital is one of the more common aesthetic skull prominences and can always be completely reduced.
- The occipital knob prominence appears like a point but has much wider bony base to it than it appears.,
- A minimal overlying scalp incision is all that is needed to achieve an adequate reduction.
Dr. Barry Eppley
World-Renowned Plastic Surgeon