The skull has many normal raised areas particularly around its lower base. One of these is the mastoid process which is located behind the ear. The derivation of the mastoid name comes from the Greek word for breast with refers to its shape. This conical bony process is on the lower end of the temporal bone located behind the external auditory canal. Its raised outer surface is where numerous muscles attach including the sternocleidomastoid muscle. Its inner surface is filled with open spaces known as the mastoid air cells which connect to the inner ear. The size of these irregular air cells varies greatly and their contribution to the size of the external mastoid prominence is highly variable.
The mastoid process is larger in males not only due to their typically bigger skull size but also due to a stronger pull from the larger sternocleidomastoid muscle. In men with short cropped hair or a shaved head the prominence of the mastoid process may be an aesthetic distraction. Like any portion of the skull it can be reduced by burring but the two considerations are an acceptable scar location to do so and to make sure that the mastoid air cells are not encountered or exposed as a result of the cortical bone reduction.
The only way to determine how much of the mastoid process can be safely reduced is by a CT scan with coronal slicing. This allows to assess how thick the cortical bone is and the location of the air cells underneath it.
The incision location for mastoid process skull reduction is directly over it along the edge of the hairline. This incision location is right behind the ear and typically falls within the shadow of the outer helix of the ear. The incision length does not need to be greater than 2.5cms.
Direct direction requires removing some of the fibers of the sternocleidomastoid muscle on top of the mastoid process. Using a high speed handpiece the bony prominence is reduced until it is flat. Attention is paid to ensuring that the bone removal does not result in air cell exposure. But this is usually assured by the preoperative CT scan.
During closure the deeper layers should not be closed to allow some soft tissue thinning as well to help the flattening effect. It is always impressive how thick the overlying soft tissues are.
Mastoid process skull reduction can be safely performed through small scalp incision that will typically heal well.
Dr. Barry Eppley