Pneumatization of the Mastoid

THIS communication purposes to trace the growth and development of the mastoid radiographically; to correlate roentgen findings to anatomic and clinical conceptions, and to elaborate on a recently proposed anatomic classification based on pneumatization. The present classification of mastoids as pneumatic, diploic, or sclerotic is neither sufficiently informative anatomically nor of great assistance otologically. Although several excellent anatomic and histologic studies of the temporal bone and of pneumatization of the mastoid have been made, little has been done to correlate these studies to the actual radiograph of the mastoid, and to correlate the variations of pneumatization, as identified radiographically, to the variations in the clinical manifestations of mastoiditis. Growth The true mastoid process is evolved from the petromastoid part of the temporal bone, which becomes fused with the squamozygomatic portion of the squamous part and the tympanic part to form the entity known as the mastoid. The squamozygomatic portion of the squamous part forms the outer wall and part of the tegmen of the attic and antrum. Radiographically, the squamozygomatic portion is visualized more clearly in the first two years of life than is the petromastoid. The latter, termed the “mastoid mass” by Cheatle (1), is a diploic bone; it offers itself to invasion by air cells which emanate and radiate from the area covered by the squamozygomatic bone. This area is the most important landmark on a mastoid film, and is termed the “peri-antral triangle.” It encompasses the attic, aditus, antrum, and labyrinth, and corresponds to the base of the petrous pyramid; it covers the spaces which represent the center of activity in initiation and promulgation of pneumatization; it is also the first area to show signs of pathologic change. The mastoid grows in three dimensions, its outline expanding from above downward, from before backward, and from within outward. Growth, as such, occurs under any and all conditions and is independent of pneumatization, except that with extensive pneumatization, growth is more expansive than with little or no pneumatization, in which case growth is somewhat limited. Growth begins at birth, accelerates between the ages of two and five, and is practically complete at six years, after which there is little demonstrable increase in the size of the mastoid. Pneumatization Concomitantly with growth, air cells develop in the normal mastoid by a process termed “pneumatization.” This process is governed by vital and anatomic factors, the influence of which causes each mastoid to attain an individual cell pattern which differs from that of its mate and is sufficiently characteristic for actual identification. Pneumatization has been the subject of considerable discussion in which many opinions and various theories have been expressed.