The value of CT measurement of normal human mandible, hyoid and the airway area at the hyoid level

Objective: To determine the normal value and clinical significance of the lengths and angles of both mandible and hyoid, and their relationship with cervical vertebra as well as the transverse area of the airway at the hyoid level using CT. Methods: Several lines and angles on the CT images were measured in 68 normal subjects. Line A was the length between both free ends of the mandible; line B was the distance from the body of the mandible to line A; Line C was the distance from line A to the anterior aspect of the cervical vertebra. α1 was the angle between the middle of mandible body and its two free ends. Line a was the distance between two free ends of greater horn of hyoid bone. Line b was the distance from hyoid to line a. Line c was the distance from line a to the cervical vertebra. α2 was the angle between the middle of hyoid body and its two free ends. S stood for the area of the airway at the hyoid level. SPSS 11.5 statistical analysis package was used to analyze the results. Results: The average and median distance/angle of various measurements were as follows: line A was (89.28±5.90) mm and 88.70 mm, line B was (62.61±5.78) mm and 62.50 mm, line C was (9.29±3.29) mm and 4.20 mm, α1 was (71.25±6.77) degree and 71.05 degree, line a was (38.69 ± 6.07) mm and 39.90 mm, line b was (28.79 ± 4.37) mm and 28.50 mm, line c was (1.91 ± 3.03) mm and 1.75 mm, α2 was (68.47 ± 15.71) degree and 66.95 degree. The average S was (436.14 ± 160.37) mm2 and median was 431.75 mm2. Conclusion: It is easy to measure the three lines and the two angles of mandible and hyoid. The measurement is of vital importance in the diagnosis and treatment for obstructive sleep apnea syndrome