Mastoid Pneumatization and Normal Curve Distribution

Abstract

The normal variant theory of pneumatization is based on my (1940) findings in groups representative of the population showing a size variation of the mastoid air cell system in adults ranging in an unbroken sequence of sizes from 0 cm² to about 30 cm² and a distribution of the various sizes in fair conformity to a normal curve.

These findings alone, however, although confirmed by several subsequent authors, cannot definitely “prove” that all sizes of the mastoid air cell system are normal variants, i.e. are anatomically caused. The theory could, however, be substantiated by further (1945) investigations showing that hereditary factors play the main part for the growth into final sizes of the mastoid air cell system. If these findings, too, were confirmed by other authors by investigating the importance of heredity for instance in chickens where the pneumatization shows a corresponding variation of size, it would serve as a “close to a final proof” for the normal variant theory.

It is analyzed why the sheer existence in the recordings of: (1) 0 cm² values representing the lowest size value in the range of variation, (2) a slight over-representation of 0 cm² values together with (3) statistically computed negative values in the distribution curve cannot be claimed to be a base for arguments against the normal variant theory and its claim that all sizes recorded, even those in ears with a simultaneously existing otitis media of any type, are in principle anatomically caused.