Structure and Microanatomy - Maxillary sinus is the largest air sinus in the body with a mean volume of about 10 ml. - It is situated within the body of the maxilla and may extend into zygomatic and alveolar processes when large. - The sinus is pyramid-shaped with the apex at the maxillary zygomatic process. - The nasal wall presents a large aperture communicating with the nasal cavity, which is reduced in size by various bones. - The sinus communicates through an opening into the semilunar hiatus. - The medial wall is primarily composed of cartilage, and the posterior wall has alveolar canals transmitting vessels and nerves. - The sinus is lined with mucoperiosteum, and the Schneiderian membrane is a bilaminar membrane with ciliated columnar epithelial cells on the internal side. - The size of the sinuses varies in different skulls and even on the same skull.

Innervation and Relations - The mucous membranes of the maxillary sinus receive mucomotor parasympathetic nerve fibers from the pterygopalatine ganglion. - Sensory innervation is provided by the superior alveolar nerves. - The roof of the sinus is also the floor of the orbit, and posterior to the sinus are the pterygopalatine fossa and infratemporal fossa.

Development and Variation - The maxillary sinus is the first paranasal sinus to form and rapidly increases in size after puberty. - The size of the sinus is variable in adults and may extend into zygomatic and alveolar processes. - The roots of teeth may lie beneath the floor of the sinus or project into the sinus, with the projection more common in advanced age. - The timing of maxillary sinus growth varies in different people.

Clinical Significance Subtopic 4.1: Maxillary sinusitis - Maxillary sinusitis is inflammation of the maxillary sinuses. - Symptoms include headache, foul-smelling discharge, and systemic signs of infection. - The skin over the involved sinus can be tender, hot, and reddened. - Opacification of the sinus on radiographs is due to retained mucus. - The close anatomical relation to the frontal sinus and maxillary teeth allows for easy spread of infection.

Subtopic 4.2: Oro-antral communication (OAC) - OAC is an abnormal communication between the maxillary sinus and mouth. - It is commonly caused by tooth extraction or iatrogenic damage during surgery. - OAC smaller than 2mm can heal spontaneously, while larger OACs require intervention for closure.

Cancer, Age, and History - Carcinoma of the maxillary sinus may invade the palate, block the nasolacrimal duct, cause proptosis, spread to the brain, and spread to the lymph nodes. - With age, the enlarging maxillary sinus may surround the roots of the maxillary posterior teeth and extend into the body of the zygomatic bone. - Loss of maxillary posterior teeth can further expand the maxillary sinus, thinning the bony floor of the alveolar process. - Regular dental care becomes crucial to manage age-related changes in the maxillary sinus. - The maxillary sinus was first discovered and illustrated by Leonardo da Vinci, and Nathaniel Highmore described it in detail in his 1651 treatise. - Leonardo da Vinci's illustrations and Highmore's treatise played important roles in understanding the maxillary sinus.