**3. Anatomy**

Upper airway obstructions can occur anywhere in the nasopharynx, oropharynx and hypo‐ pharynx. Nasopharyngeal obstruction examples are nasal septum deviation, nasal polyps and rhinosinusitis; they can cause mild OSA [3]. Most common sites of airway collapse occur in the hypopharynx [4]. It extends from the soft palate to the epiglottis; anteriorly it is formed by the base of the tongue and soft palate, while pharyngeal constrictor muscles form the posterior borders. Studies show that tongue volume and lateral walls of the pharynx are independent risks to OSA. There are many craniofacial abnormalities that cause OSA. Even a minimal change in maxillary or mandibular position can lead to upper airway collapse. OSA patients could have one or more of the following anatomical variations:

A retro-position of the mandible or the maxilla, micrognathia, long soft palate, increased thickness of the soft palate, macroglossia (large tongue) and differences in hyoid bone position [5].

The success of surgical treatment is depending on the recognition of the level of obstruction. There is a special surgical procedure for each site of obstruction.
