Neck soft tissue and fat distribution: comparison between normal men and women by magnetic resonance imaging

Background-Obesity and increased neck circumference are risk factors for the obstructive sleep apnoea/hypopnoea syndrome (SAHS). SAHS is more common in men than in women, despite the fact that women have higher rates of obesity and greater overall body fat. One factor in this apparently paradoxical sex distribution may be the differing patterns of fat deposition adjacent to the upper airway in men and women. A study was therefore undertaken to compare neck fat deposition in normal men and women. Methods-Using T1 weighted magnetic resonance imaging, the fat and tissue volumes in the necks of 10 non-obese men and 10 women matched for age (men mean (SE) 36 (3) years, women 37 (3) years, p = 0.7), body mass index (both 25 (0.6) kg/m(2), p>0.9), and Epworth Sleepiness Score (both 5 (1), p = 0.9) were assessed; all denied symptoms of SAHS. Results - Total neck soft tissue volume was greater in men (1295 (62) vs 928 (45) cm(3), p<0.001), but the volume of fat did not differ between the sexes (291 (29) vs 273 (18) cm(3), p = 0.6). The only regions impinging on the pharynx which showed a larger absolute volume of fat in men (3.2 (0.7) vs 1.1 (0.3) cm(3), p = 0.01) and also a greater proportion of neck fat in men (1.3 (0.3)% vs 0.4 (0.1)%, p = 0.03) were the anterior segments inside the mandible at the palatal level. Conclusions-There are differences in neck fat deposition between the sexes which, together with the greater overall soft tissue loading on the airway in men, may be factors in the sex distribution of SAHS.