The maxillary sinuses are the largest of the paranasal sinuses, air-filled cavities located within the bones of the face and skull. These paired structures are situated beneath the eyes, residing inside the cheekbones (maxillae) on either side of the nasal cavity. They are the first sinuses to develop, beginning in utero and continuing to grow until early adulthood. Understanding the maxillary sinus involves recognizing its physical layout, its role in the respiratory system, and the common problems that arise when its function is disrupted.
Structure and Function of the Maxillary Sinus
The structure of the maxillary sinus is distinctly pyramidal, with the base adjacent to the side wall of the nasal cavity and the apex pointing toward the cheekbone. The floor of this cavity is formed by the alveolar process of the maxilla, the bone that holds the upper teeth. The roof of the sinus forms the floor of the eye socket, establishing close anatomical relationships with surrounding structures.
The sinus interior is lined with specialized respiratory tissue called pseudostratified ciliated columnar epithelium, which contains hair-like projections (cilia). These cilia constantly sweep a layer of mucus toward the single natural opening, known as the ostium. Located high on the medial wall, the ostium requires mucus to be moved against the pull of gravity to drain into the nasal cavity.
Physiologically, the maxillary sinuses perform several functions. They help to humidify and warm inhaled air before it reaches the lungs. The air-filled spaces also serve to decrease the overall weight of the skull, making the head lighter than if the bone were solid. Finally, the sinuses contribute to the resonance of the voice, affecting its quality and tone.
Understanding Maxillary Sinusitis
Maxillary sinusitis occurs when the lining of the sinus becomes inflamed, typically because the ostium—the drainage pathway—has become blocked. When this opening is obstructed, mucus and air cannot flow freely, leading to a buildup of pressure and creating a favorable environment for infection. The obstruction is often caused by swelling from a common cold, allergies, or other upper respiratory infections.
The symptoms of maxillary sinusitis are often centered on the cheek area due to its location within the cheekbones. Individuals typically experience facial pain or pressure that may worsen when bending over or lying down. Common signs include nasal congestion, a thick, discolored discharge, and post-nasal drip. Inflammation can also lead to a reduced sense of smell and taste.
Sinusitis is classified based on how long the symptoms persist, differentiating between acute and chronic presentations. Acute sinusitis is a short-term condition, usually lasting less than four weeks, and is most frequently caused by viruses. If symptoms continue for 12 weeks or longer, the condition is defined as chronic sinusitis, which may be caused by persistent inflammation, bacterial or fungal infections, or an underlying structural issue. When symptoms improve but then return four or more times in a year, it is classified as recurrent acute sinusitis.
Maxillary Sinus and Dental Health
The maxillary sinus has a close anatomical relationship with the teeth of the upper jaw, particularly the roots of the molars and premolars. In many individuals, only a thin layer of bone, or sometimes only the sinus membrane, separates these tooth roots from the sinus cavity. This proximity means that dental problems can directly affect the sinus, a condition known as odontogenic maxillary sinusitis (OMS).
OMS is an inflammatory condition that results from an infection originating in a tooth, such as an abscess or severe periodontal disease. The infection spreads from the tooth root through the thin bone and into the sinus, causing symptoms like unilateral facial pain, purulent discharge, and congestion. Failure to identify and treat the underlying dental issue often results in sinusitis that is resistant to typical antibiotic treatment.
Another specific risk is the creation of an oral-antral communication (OAC), a direct opening between the mouth and the sinus cavity. This complication occurs most frequently following the extraction of an upper molar or premolar tooth. If this communication is not closed, oral bacteria and debris can contaminate the sinus, leading to chronic infection. Patients may also experience referred pain, where a sinus infection mimics a toothache, or a dental infection causes sinus symptoms.