Magnetic resonance imaging assessment of posterior airway space (PAS) after maxillomandibular advancement in patients with obstructive sleep apnea

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Obstructive sleep apnea (OSA) is a common disorder and is associated with hypertension, cardiovascular disease, a diminished quality of life and an increased rate of motorvehicle accidents, thus making it a significant public health concern1. To effectively treat OSA, it is important to detect the severity and site of obstruction of the airway. Maxillomandibular advancement surgery (MMA) has been described as the most effective surgical treatment for OSA2. The assessment of the retrolingual (RL) pharynx is important in patients with OSA. However, the clinical and cephalometric evaluations are performed with the patient standing or sitting, not reproducing faithfully the morphology of pharynx when the patient is in supine position, as occurs during sleep. The aim of this study was to evaluate, using Magnetic Resonance Imaging (MRI) with the patient in supine position, the changes that have occurred in posterior airway space (PAS) of the retrolingual pharynx, in patients with OSA after MMA. This prospective study was conducted on 12 patients (7 males and 5 females), with a polysonographic diagnosis of OSA submitted to MMA. The mean apnea-hypopnea index (AHI) was 29,35 events per hour of sleep. The research protocol was approved by the Research Ethics Committee of the Institution and all patients gave written informed consent to participate. All patients were submitted to image acquisition by magnetic resonance (MRI) performed during wakefulness. Polysonography and MRI were performed preoperatively and six months after MMA. The MRI protocol included a set of sagittal and axial high resolution T1-weighted (T1-w) and T2-weighted images for anatomical analysis. For this study, were used two sequences with the same location, on the sagittal plane in the midline of the pharynx, with a slice each, preoperatively and after the surgery. The images acquired in DICOM-3 format were transferred to an auxiliary workstation. The measurements were carried out using the software Display, developed by McGill University, in Montreal, Canada. Linear distance measurements (mm) were performed between the base of the tongue and the posterior wall of the pharynx at the level of the inferior border of the second vertebra (C2). This pharyngeal space is related to retrolingual airway space, being named PAS. Before MMA, the patients studied presented reduction in PAS (an average of 8,74 mm), increasing to 12,52 mm after surgery. Preoperatively, the patients had average AHI of 29.76 events per hour of sleep, and postoperatively there was a reduction of the average AHI for 12.78 events per hour of sleep. All patients treated with MMA for OSA in this study had an improved (decreased) AHI. In conclusion, MMA increased airway dimensions by increasing the distance from the base of the tongue to posterior wall of the pharynx (PAS), evidenced by the images of MR, which resulted in reduction in the apnea-hypopnea index (IAH) and improvement in sleep apnea. These findings justify the great index of success that this surgery has achieved on the treatment of OSA patients.