The pyramid-shaped maxillary sinus (or antrum of Highmore) is the largest of the paranasal sinuses, located in the maxilla. It drains into the middle meatus of the nose through the semilunar hiatus. It is located to the side of the nasal cavity, and below the orbit. but may extend into its zygomatic and alveolar processes when large. It is pyramid-shaped, with the apex at the maxillary zygomatic process, and the base represented by the lateral nasal wall.

Relations

The roof of the sinus is also the floor of the orbit. Posterior to the sinus and its wall are the pterygopalatine fossa and the infratemporal fossa. is an additional natural opening in the lateral nasal wall that provides communication between the maxillary sinus and the nasal cavity, apart from the primary or natural maxillary ostium.

Development

Maxillary sinus is the first paranasal sinuses to form. At birth, it is about 6 to 8&nbsp;cm<sup>3</sup> in volume, elongated, as is orientated in antero-posterior direction, located at the next to the medial orbital wall of the eye. The lateral wall of the maxillary sinus goes beneath the medial orbital wall during the first year of life, extends laterally pass the infraorbital groove by the age of four years, and reach the maxilla by the age of nine years. At the final phase of aeration, the floor of maxillary sinus is four to five millimetres below the floor of nasal cavity. However, timing of maxillary sinus growth is variable in different people.

thumb|140px|right|The maxillary sinus can normally be seen above the level of the premolar and molar teeth in the [[maxilla|upper jaw. This dental x-ray film shows how, in the absence of the second premolar and first molar, the sinus became pneumatized and expanded towards the crest of the alveolar process (location at which the bone meets the gum tissue).]]

Clinical significance

Maxillary sinusitis

thumb|CT Brain showing air-fluid level in bilateral maxillary air sinuses post brain trauma. Maxillary sinusitis will also show similar air-fluid collection and should be ruled out from history taking.|130px

Maxillary sinusitis is inflammation of the maxillary sinuses. The symptoms of sinusitis are headache, usually near the involved sinus, and foul-smelling nasal or pharyngeal discharge, possibly with some systemic signs of infection such as fever and weakness. The skin over the involved sinus can be tender, hot, and even reddened due to the inflammatory process in the area. On radiographs, there is opacification (or cloudiness) of the usually translucent sinus due to retained mucus.

Maxillary sinusitis is common due to the close anatomic relation of the frontal sinus, anterior ethmoidal sinus and the maxillary teeth, allowing for easy spread of infection. Differential diagnosis of dental problems needs to be done due to the close proximity to the teeth since the pain from sinusitis can seem to be dentally related.

There are many causes of an OAC. The most common reason is following extraction of a posterior maxillary (upper) premolar or molar tooth. Other causes include trauma, pathology (e.g. tumours or cysts), infection or iatrogenic damage during surgery. Iatrogenic damage during dental treatment accounts for nearly half of the incidence of dental-related maxillary sinusitis. There is always a thin layer of mucous membrane (Schneiderian membrane) and usually bone between the roots of the upper back teeth and the floor of the maxillary sinus. However, the bone can vary in thickness in different individuals, ranging from complete absence to 12mm thick.

An OAC that is smaller than 2mm can heal spontaneously i.e. closure of the opening. Those that are larger than 2mm have a higher chance of developing into oro-antral fistula (OAF).

See also

  • Ohngren's line
  • Zygomatic complex fracture

References

  • (, )
  • Maxillary Sinus: Normal Anatomy & Variants at http://uwmsk.org/sinusanatomy2/Maxillary-Normal.html
  • Cancer in the maxillary sinus, Stanford University at http://cancer.stanford.edu/headneck/sinus/sinus_max.html