Background: The shape of the skull frequently has various lumps and bumps of bone that stick up from an otherwise smooth surface. Many such bony protuberances have no specific reason for being in their location and are aesthetic nuisances that merely represent the way the skull formed and are present at a very early age. Other skull lumps are actually benign bony tumors, known as osteomas, that form for either no known reason or the result of trauma and calcification of a bone bleeding site. They occur later in life and are very discrete round elevations of bone which very commonly occur on the forehead and may be associated with very slow ongoing growth.
One very unique skull lump is the occipital knob. Occurring on the back of the skull at the junction of the bottom edge of the skull and the neck muscles, this is a skull bony protrusion that exists at the midline and can stick out just like a knob. Unlike developmental bumps or osteomas, the occipital knob occurs as an external occipital protuberance and is the result of a well known skull deformity. It usually occurs in patients who have a very narrow skull and reflects a mild manifestation of sagittal craniosynostosis. Premature closure of the posterior portion of the sagittal suture causes bone to heap up and develop an abnormal bony protrusion. The occipital bone becomes the site of compensatory overgrowth because it is located distal and perpendicular to the fused suture.
Sticking out like a knob, this skull protrusion can be very noticeable in men. Short hair cuts and shaved heads can reveal this abnormal skull protrusion. Like all skull lumps and osteomas, occipital knobs can be reduced to a normal skull contour. Because the occipital knob represents an abnormal thickening of skull bone, there is no risk of intracranial penetration or making the bone too thin in its reduction.
Case Study: This 45 year-old male had been bothered by a large protrusion on the back of his head since he was a child. It has been present as long as he could remember and had never changed in size. As he wore his hair shorter as he got older, it became more bothersome. He finally decided to have it reduced.
Under general anesthesia, he was placed into the prone position. Through a 6cm horizontal incision in the low occipital hairline, the very thick scalp tissue was elevated to expose it. A large bony bump was exposed that measured 3.5 x 3.5cm in diameters and was 2cms in height. A handpiece and burr was used to reduce the bony protrusion down to the level of the surrounding bone. The outer cortical bone was so thick that even in bringing it down to the surrounding skull contour the internal diploic space was not encountered and no bone bleeding was seen. The overlying incision was then closed after excising some excess scalp skin and underlying soft tissues. No drain was used.
A circumferential pressure dressing was used for the first 24 hours after surgery and then removed. He took no pain medications and said he felt no discomfort whatsoever.When seen at one week after surgery, a small fluid collection (8ccs) was removed by needle aspiration to remove some slight fullness and return the scalp contour back to completely flat. He was thrilled to have solved his lifelong occipital knob concern so completely and easily.
Even at just one week after surgery, the occipital hairline scar was barely noticeable.
Case Highlights:
1) An occipital knob is a midline protrusion of hypertrophic bone that sticks out at the base of the skull.
2) Occipital knobs can be reduced through a small horizontal hairline incision to make for a smooth contour at the base of the occipital skull.
3) For the bald, shaved or short hair styled men, a smooth skull contour is a desired aesthetic feature and can be achieved by a minor skull reshaping procedures for the occipital knob deformity.
Dr. Barry Eppley
Indianapolis, Indiana