General Medical Information

Maxillary Sinus

Ronald G. Amedee
Andrew J. Miller

The maxillary sinus (antrum of Highmore) occupies the body of the maxilla in adults and is the largest of the paranasal sinuses. It is generally pyramidal in shape, the base being formed by the lateral wall of the nasal cavity and the apex directed laterally toward the zygomatic process. The roof, which also functions as the floor of the orbit, is composed of thin bone crossed in the central portion by the infraorbital nerve. This nerve is dehiscent in 14% of the population and can be damaged during manipulation in this area. A Haller cell, which is a pneumatization of the ethmoid complex into the roof of the maxillary sinus, sometimes can be identified. This is important because this cell can grow to occlude the maxillary sinus or the ethmoid infundibulum. The anterior wall corresponds to the canine fossa and separates the sinus from the cheek skin. The posterior wall separates the sinus from the contents of the infratemporal and pterygomaxillary fossae.

The floor of the sinus, which is half as wide as the roof, is formed by the alveolar process of the maxilla. Although it lies 4 mm above the floor of the nasal cavity in children, it ultimately lies 4 to 5 mm below the floor of the nasal cavity in adults. The first and second molars are the two most commonly dehiscent teeth in the maxillary sinus at 2.2% and 2.0% of persons, respectively. With extensive pneumatization, the third molar, bicuspids, and canine teeth can be exposed in the maxillary sinus. Exposure of the tooth roots places the neurovascular bundle of the teeth in danger during curettage of the sinus. Infection of dehiscent tooth roots and subsequent removal of the tooth can cause an oral-antral fistula.

The medial wall of the maxillary sinus is the lateral wall of the nose, and it contains the main sinus ostium by which the maxillary sinus communicates with the ethmoid infundibulum. The ostium is located in the superior aspect of the medial wall, usually in the posterior half of the infundibulum an average of 9 mm posterior to the nasolacrimal duct. The posterior edge of the ostium is continuous with the lamina papyracea of the ethmoid bone, allowing this edge of the ostium to be a reliable lateral limit in intranasal dissection. In 15% to 40% of cases, an accessory ostia is present, which is a hole in the mucous membrane covering a bony dehiscence, also called a fontanelle. The accessory ostia, which are uncommon in children, can be inferior and anterior to the uncinate process or more commonly superior and posterior to the uncinate process above the insertion of the inferior turbinate.