Craniofacial and upper airway morphology in adult obstructive sleep apnea patients: A systematic review and meta-analysis of cephalometric studies

Summary

Obstructive sleep apnea (OSA) is one of the common sleep breathing disorders in adults, characterised by frequent episodes of upper airway collapse during sleep. Craniofacial disharmony is an important risk factor for OSA. Overnight polysomnography (PSG) study is considered to be the most reliable confirmatory investigation for OSA diagnosis, whereas the precise localization of site of obstruction to the airflow cannot be detected. Identifying the cause of OSA in a particular ethnic population/individual subject helps to understand the etiological factors and effective management of OSA. The objective of the meta-analysis is to elucidate altered craniofacial anatomy on lateral cephalograms in adult subjects with established OSA. Significant weighted mean difference with insignificant heterogeneity was found for the following parameters: anterior lower facial height (ALFH: 2.48 mm), position of hyoid bone (Go-H: 5.45 mm, S–H: 6.89 mm, GoGn-H: 11.84°, GoGn-H: 7.22 mm, N–S–H: 2.14°), and pharyngeal airway space (PNS-Phw: −1.55 mm, pharyngeal space: −495.74 mm² and oro-pharyngeal area: −151.15 mm²). Significant weighted mean difference with significant heterogeneity was found for the following parameters: cranial base (SN: −2.25 mm, S–N–Ba: −1.45°), position and length of mandible (SNB: −1.49° and Go-Me: −5.66 mm) respectively, maxillary length (ANS-PNS: −1.76 mm), tongue area (T: 366.51 mm²), soft palate area (UV: 125.02 mm²), and upper airway length (UAL: 5.39 mm). This meta-analysis supports the relationship between craniofacial disharmony and obstructive sleep apnea. There is a strong evidence for reduced pharyngeal airway space, inferiorly placed hyoid bone and increased anterior facial heights in adult OSA patients compared to control subjects. The cephalometric analysis provides insight into anatomical basis of the etiology of OSA that can influence making a choice of appropriate therapy.

Introduction

Obstructive sleep apnea (OSA) is being recognized as an important public health problem worldwide, with the a prevalence of 9% of middle aged men and 4% of women adult population [1]. Signs and symptoms of OSA are snoring, frequent episodes of sleep interruption, excessive daytime sleepiness, hypoxemia, hypercapnia, swings in the intra-thoracic pressure and increased sympathetic activity [2], [3]. It leads to significant impairment in quality of life of affected subjects and is associated with a number of potential negative health consequences [1], [4]. The pathophysiology of OSA is not thoroughly understood and multifactorial origin is suggested [3]. The potential risk factors of OSA are increasing age, male sex, obesity, anatomical abnormalities of the craniofacial region and upper airway [1].

Craniofacial disharmony is an important predisposing factor in development of OSA [5], [6], [7]. In OSA subjects, the pharyngeal airway gets blocked partially or completely, leading to obstructive apnea/hypopnea episodes and arousal [2]. The anatomical relationship of craniofacial skeletal and soft tissue structures of the upper airway determines its patency. Most commonly associated craniofacial abnormalities with OSA are mandibular deficiency, maxillary hypoplasia, inferior position of hyoid bone, a narrowed posterior air space, a greater flexion of the cranial base, and elongation of the soft palate [8], [9]. Major obstructive sites observed in OSA patients are nasal cavity, maxilla, oral cavity, tongue, soft palate, mandible, hyoid bone and pharynx.

Diagnosis of OSA is still a challenging task despite advances in newer diagnostic modalities and imaging technologies. Overnight polysomnography (PSG) study in a sleep laboratory is considered to be the most reliable confirmatory investigation for OSA. It comprises assessment of electroencephalogram (EEG), electrocardiogram, electrooculogram, airflow, chin electromyogram, oxygen saturation and heart rate. Recently smart phone applications have also been launched for screening of OSA [10], [11]. Though PSG is considered as a gold standard test for OSA diagnosis [12], the precise localization of site of obstruction to the airflow cannot be detected by this investigation. Nasal endoscopy is a useful tool for the assessment of level, degree and shape of upper airway obstruction [13] and usually performed in operating room. Imaging modalities such as X-ray cephalometry, sleep videofluoroscopy, computed tomography (CT) scanning and magnetic resonance imaging (MRI) have been used to detect the obstruction site and other structural abnormalities [14]. Recently dynamic imaging modalities like cine MRI, ultrafast CT and functional imaging have been introduced, for upper airway analysis [14], [15].

Lateral cephalogram is one of the widely used modalities for 2D analysis to quantify craniofacial skeletal abnormalities and analyse oro-pharyngeal space [16]. This simple inexpensive investigation provides a host of reliable information on craniofacial pattern, with much less radiation compared to MDCT (multi-detector computed tomography). Common cephalometric variables associated with OSA are: sagittal position of maxilla (SNA) and mandible (SNB) in relation to cranial base, posterior airway space (PAS), length of soft palate, and hyoid bone to the mandibular plane distance (MP-H) ∗[17], [18].

Literature is available on systematic reviews with meta-analysis related to craniofacial abnormalities in pediatric OSA ∗[19], [20], consequences of untreated OSA [21] and upper airway analysis ∗[22], [23], [24]. For this reason, the present study was designed to assess the craniofacial morphology in adult OSA patients using lateral cephalograms, on which a systematic review with meta-analysis was subsequently performed. This would aid to supplement diagnosis and management of adult OSA cases.