Sinus of maxilla

The sinus of maxilla (or the maxillary sinus), a large pyramidal cavity within the maxilla, is the earliest to develop among all paranasal air sinuses. Its size varies across different skulls and even between the two sides of the same skull.

The sinus’s apex points laterally towards the zygomatic process of the maxilla, while its base, or the nasal wall, faces medially towards the lateral wall of the nose.

The walls of the maxillary sinus are thin and correlate to the nasal, orbital, anterior, and infratemporal surfaces of the maxillary bone. The nasal wall features a significant, irregular aperture that connects the sinus with the nasal cavity. This aperture is framed by several bones: the uncinate process of the ethmoid and the descending part of lacrimal bone above, the ethmoidal process of the inferior nasal concha below, and the vertical or perpendicular part of the palatine bone from behind, which together reduce its size. Typically, the sinus communicates with the nose’s middle meatus via two small apertures, though in the fresh state, usually only one opening exists, the other being closed by the mucous membrane.

The posterior wall houses the alveolar canals, carrying posterior superior alveolar vessels and nerves to the molar teeth. The floor, lying below the nose’s floor level, is formed by the maxilla’s alveolar process and often projects conical processes into the antrum, corresponding to the roots of the molar and premolar teeth, sometimes even breaching the floor to lie underneath the mucous lining.

Lastly, the roof of sinus of maxilla is formed by the floor of the orbit, traversed by the infraorbital canal.