The pyramid-shaped maxillary sinus (or antrum of Highmore) is the largest of the paranasal sinuses, and drains into the middle meatus of the nose through the osteomeatal complex.  It is the largest air sinus in the body. Found in the body of the maxilla, this sinus has three recesses: an alveolar recess pointed inferiorly, bounded by the alveolar process of the maxilla; a zygomatic recess pointed laterally, bounded by the zygomatic bone; and an infraorbital recess pointed superiorly, bounded by the inferior orbital surface of the maxilla. The medial wall is composed primarily of cartilage. The ostia for drainage are located high on the medial wall and open into the semilunar hiatus of the lateral nasal cavity; because of the position of the ostia, gravity cannot drain the maxillary sinus contents when the head is erect (see pathology). The ostium of the maxillary sinus is high up on the medial wall and on average is 2.4 mm in diameter; with a mean volume of about 10 ml. The sinus is lined with mucoperiosteum, with cilia that beat toward the ostia. This membranous lining is also referred to as the Schneiderian membrane, which is histologically a bilaminar membrane with pseudostratified ciliated columnar epithelial cells on the internal (or cavernous) side and periosteum on the osseous side. The size of the sinuses varies in different skulls, and even on the two sides of the same skull. The infraorbital canal usually projects into the cavity as a well-marked ridge extending from the roof to the anterior wall; additional ridges are sometimes seen in the posterior wall of the cavity and are caused by the alveolar canals. The mucous membranes receive their postganglionic parasympathetic nerve fibres for mucous secretion from the pterygopalatine ganglion. The preganglionic parasympathetic fibres are coming to this ganglion through the greater petrosal nerve (a branch of the facial nerve) and the nerve of the pterygoid canal. The superior alveolar (anterior, middle, and posterior) nerves, branches of the maxillary nerve provide sensory innervation.[citation needed] The nasal wall of the maxillary sinus, or base, presents, in the disarticulated bone, a large, irregular aperture, communicating with the nasal cavity.[citation needed] In the articulated skull this aperture is much reduced in size by the following bones: The uncinate process of the ethmoid above, the ethmoidal process of the inferior nasal concha below, the vertical part of the palatine behind, and a small part of the lacrimal above and in front. The sinus communicates through an opening into the semilunar hiatus on the lateral nasal wall. On the posterior wall are the alveolar canals, transmitting the posterior superior alveolar vessels and nerves to the molar teeth. Maxillary sinus is the first paranasal sinuses to form. At birth, it is about 6 to 8 cm3 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. After the first permanent tooth erupted at the age of six to seven, aeration of maxillary sinus is the main growth feature. At the final phase of aeration, the floor of maxillary sinus is four to five milimetres below the floor of nasal cavity. However, timing of maxillary sinus growth is variable in different people.

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Catherine
Journal Co-Ordinator
Journal of Orthodontics and Endodontics