The maxillary antrum, also known as the maxillary sinus, is the largest of the paranasal sinuses. It is an air-filled cavity located within the maxilla, the bone that forms your upper jaw. It contributes to the overall structure of the midface.
Anatomy and Location
The maxillary antrum is a paired, pyramid-shaped cavity situated within the body of the maxilla, positioned on either side of the nasal cavity and beneath the eye socket. Its base lies along the lateral wall of the nose, while its apex extends towards the cheekbone, specifically the zygomatic process of the maxilla. The floor of this sinus is formed by the alveolar process of the maxilla, which is the part of the jawbone holding the upper teeth.
The roof of the maxillary sinus forms the floor of the orbital cavity. The posterior wall borders the pterygopalatine fossa, a space behind the upper jaw. The maxillary sinus communicates with the nasal cavity through a small opening called the maxillary ostium, which drains into the middle meatus of the nose, facilitating mucus drainage. The roots of the upper premolar and molar teeth can extend close to or even project into the floor of the maxillary sinus, separated by a thin layer of bone or just the sinus membrane.
How It Develops
The development of the maxillary antrum begins early in embryonic life, around the 10th to 12th week of gestation, as an outpouching of the nasal mucosa. At birth, the sinuses are present but are typically filled with fluid, not air. A significant increase in volume occurs during postnatal development.
The most extensive period of growth occurs during the first eight years of life. The sinus expands laterally towards the zygomatic recess and inferiorly towards the developing upper teeth. The growth rate then slows, with full development and maximal volume reached between the ages of 15 and 18 years.
Common Anatomical Variations
Several anatomical variations can occur within or near the maxillary antrum, influencing its function or clinical procedures. Haller cells, also known as infraorbital ethmoidal air cells, are ethmoid air cells located along the inferomedial orbital floor, lateral to the maxillary infundibulum. While often asymptomatic, large Haller cells can narrow the ostiomeatal complex, potentially obstructing drainage from the maxillary sinus.
Concha bullosa refers to an air-filled cavity within a nasal concha, specifically the middle turbinate. This variation is present in up to half the population and is considered a normal anatomical difference. However, a large concha bullosa can obstruct airflow or sinus drainage, leading to symptoms like a stuffy nose, facial pain, or headaches.
Bony septa are thin walls of cortical bone that project from the floor of the maxillary sinus. These septa can divide the sinus into incomplete compartments and vary in size, location, and thickness. Their prevalence ranges widely, from about 10% to 58% in various studies, and they can complicate dental procedures like sinus augmentation by increasing the risk of membrane perforation.
Mucosal thickening is a common finding in the maxillary sinus, where the mucous lining thickens due to inflammation. While thickening up to 4-5mm can be asymptomatic, it often suggests inflammation due to infections, allergies, or irritants. The prevalence of mucosal thickening varies significantly across studies, from about 21% to 66%.
Conditions Affecting the Maxillary Antrum
The maxillary antrum can be affected by various health conditions. Sinusitis is a primary concern, an inflammation or infection of the sinus lining commonly caused by viral, bacterial, or fungal infections. Symptoms include facial pain or pressure, particularly in the cheek area near the upper teeth, nasal congestion, and thick nasal discharge. Allergies and anatomical abnormalities, such as a deviated septum or nasal polyps, can also contribute to the development of sinusitis by obstructing proper drainage.
Dental issues can lead to conditions like odontogenic sinusitis. This type of sinusitis arises from dental infections or procedures, accounting for approximately 10-12% of chronic sinusitis cases. Dental conditions such as tooth decay, gum disease, periapical abscesses, or even dental procedures like tooth extractions, implant placement, or root canal treatments, especially involving the upper posterior teeth, can spread infection to the adjacent maxillary sinus.
The close anatomical relationship facilitates this spread of infection. An oroantral fistula (OAF) is an abnormal communication between the oral cavity and the maxillary sinus, often resulting from tooth extractions, particularly of upper molars or premolars. If not treated promptly, an OAF can lead to chronic sinusitis as oral bacteria enter the sinus cavity.