Cephalometry

Lateral cephalometry is a simple and well-standardized technique involving radiographs of the head and neck with focus on bony and soft tissue structures. Several cephalometric studies have been performed in OSA patients and have provided important insights (54-64). Most of these studies have investigated the airway with the subject in the upright position, although comparisons between upright and supine postures have been made (54,55). An upright lateral cephalograph is obtained while the subject is seated with gaze parallel to the floor and teeth together. Investigators have used radiopaque material to enhance the outline of the oropharyngeal structures (56). The cephalometric images are used to study measurements of many set points, planes or distances within the head and neck region. The cepha-lometric technique has highlighted important differences between sleep apneics and normal subjects, sleep apneics and snorers, and obese and nonobese subjects. OSA patients have been shown to have a small posteriorly-placed mandible, a narrow posterior airway space, an enlarged tongue and soft palate, and an inferi-orly located hyoid (58,59,64). All five of the above variables have been shown to be significant determinants of apnea severity. The craniofacial abnormalities in OSA patients are reported more frequently in the subgroup of patients who are not obese (60). OSA patients compared with snorers have been demonstrated to have a longer soft palate in addition to an inferiorly positioned hyoid bone and posteriorly displaced mandible. Interestingly, when subdivided for age or body mass index (BMI), it was found that the significant differences between upper airway dimensions of OSA patients and snorers in the overall population were almost exclusively derived from the younger (age < 52 years) and leaner (BMI < 27 kg/m2) subgroups. The upper airway measurements studied in obese or older OSA patients were not different from obese or older snorers (61). More recent work with supine cephalometry has shown that the transition from upright to supine position in sleep apneics is associated with a significant narrowing of the oropharyngeal sagittal dimension (54,62,63). Cephalometry has also been employed to assess and optimize the efficacy of mandibular advancement oral appliances based on the anatomical changes in supine imaging (62).

Limitations of cephalometry pertain to the two-dimensional nature of the image and to the examination of soft tissue. Cephalometry provides two-dimensional static images in the sagittal plane and therefore cannot provide information about transverse dimensions, cross-sectional shape or volume, or dynamic changes of the airway during sleep. The patient is required to be awake and therefore extrapolation to the sleep state may be inaccurate.

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