Posterior cranial fossa crowdedness is related to age and sex: an magnetic resonance volumetric study

PURPOSE: To measure 3-dimensional (3D) posterior cranial fossa (PCF) crowdedness and to evaluate the effect of age, sex, and body height on PCF. MATERIAL AND METHODS: Fifty-two healthy volunteers (24 M and 28 F; mean age 55.4 +/- 17.2 years; range 24-82 years) were recruited. Using a semi-automated magnetic resonance technique, we calculated a PCF crowdedness index (CI) as the ratio of hindbrain (HB) volume to PCF volume x 100% and correlated this index with age, sex, body height, and other crowdedness parameters. RESULTS: The mean PCF CI was 93.7 +/- 2.7%. Women had a more crowded PCF than men (95.0+1.7% versus 92.1 +/- 2.7%; P<0.001). PCF CI declined with age for both men (r = -0.61; P=0.002) and women (r = -0.68; P<0.001). The association with age--but not HB volume was maintained after we controlled for sex and body height. On multiple regression, both age and sex accounted for 57.5% of the PCF CI variance. CONCLUSION: Our study shows that PCF CI is associated with age and sex, and can therefore be used as a surrogate to assess hindbrain atrophy in a cross-sectional sample. Moreover, sex- and age-specific normal ranges may be needed to evaluate the PCF CI in clinical practice.