The alteration of craniofacial structures has been associated with obstructive sleep apnea (OSA). We hypothesized that 1) a smaller mandible is a risk factor for OSA; and 2) the previously observed inferiorly positioned hyoid bone in apneics is associated with enlarged tongue volume.This is a case-control study using three-dimensional MRI cephalometry. 55 apneics and 55 controls were matched for age, gender and race. The analysis was stratified by gender and controlled for age, race, height, neck visceral fat, skeletal type and tongue volume.We found that a 1-SD increase in mandibular length and depth were associated with decreased risk of sleep apnea (odds ratio[OR]=0.52, 95% confidence interval[CI]:0.28-0.99, OR=0.46, 95%CI:0.23-0.91, respectively) in men but not in women. Greater hyoid to nasion (OR=2.64, 95%CI:1.19-5.89 in men; OR=5.01, 95%CI:2.00-12.52 in women) and supramentale-to-hyoid (OR=2.39, 95%CI:1.12-5.14 in men; OR=3.38, 95%CI:1.49-7.68 in women) distances were associated with increased risk of OSA. The difference between apneics and controls for hyoid position was lost after controlling for tongue volume.Enlargement of tongue is likely to be the pathogenic factor for inferior-posterior positioning of hyoid. A small and shallow mandible is an independent risk factor for obstructive sleep apnea in men but not in women.
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