Objectives/hypothesis: This study used computed tomography (CT) to identify anatomic features of the awake upper respiratory tract (URT) that correlate with severity of obstructive sleep apnea (OSA).
Study design: An IRB approved radiographic study of 80 patients with OSA and 56 patients from the general population.
Methods: Awake, noncontrast CT was performed from the skull base to the thoracic inlet in patients with OSA. Cross-sectional measurements of the retropalatal and retrolingual airways were made along with the size of the cervicomandibular ring and the percentage neck fat. The mandibular plane to hyoid distance, neck length, and laryngeal descent were also recorded. The posterior tongue fat content was estimated using the Hounsfield unit for radiodensity. The radiographic data were then compared with clinical information, including apnea-hypopnea index (AHI), body mass index, and neck circumference using linear regression.
Results: AHI increases with smaller retrolingual cross-sectional airway (P = .0026) and increasing mandibular plane to hyoid distance (P = .0003) but not retropalatal airway or laryngeal descent. The posterior tongue is hypodense with higher fat content than other muscles of the head and neck.
Conclusions: This study describes anatomic findings of the retrolingual airway in patients that correlate with OSA and can be measured on an upper airway CT. Patients with severe OSA (AHI > or = 40) tend to have retrolingual airways less than 4% of the cross-sectional area of the cervicomandibular ring. The retrolingual airspace is the major site of obstruction in severe OSA and should be carefully evaluated before surgical treatment is considered.