The causes of asymmetry of the mastoid air cell system.

Starting from age 2 up to 7 years, 79 otherwise healthy children underwent nine tympanometric tests. At the age of 7, mastoid X-rays were obtained and the air cell areas measured by planimetry. The mean area was 8.4 cm2, with a left-right mean difference of 1.57 cm2. The children could be divided into three groups: (1) the ears with the smallest cell system associated with abnormal tympanograms (i.e. 'agreement'); (2) the ears with the largest cell system associated with abnormal tympanograms (i.e. 'disagreement'); (3) children with symmetrical cell systems and tympanograms. Significant majority of children showed 'agreement'. The results indicate that the size of the mastoid air cell system is determined by the degree of pathological involvement of the middle ear during childhood.