The paranasal sinuses are air cavities that help circulate the air that is breathed in and out of the respiratory system. They are situated around the nasal cavity and they are all paired and sometimes symmetrical, while always being bilateral. There are four different pairs of sinuses and they are called the:
- maxillary sinuses
- frontal sinuses
- sphenoidal sinuses
- ethmoidal sinuses
The Maxillary Sinuses
The maxillary sinuses are the largest of the all the paranasal sinuses. They have thin walls which are often penetrated by the long roots of the posterior maxillary teeth. The superior border of this sinus is the bony orbit, the inferior is the maxillary alveolar bone and corresponding tooth roots, the medial border is made up of the nasal cavity and the lateral and anterior border is limited by the cheekbones. Posteriorly, two anatomical spaces known as the pterygopalatine fossa and the infratemporal fossa exist. The submandibular lymph nodes are the main destination during lymphatic drainage. The blood supply includes a contribution from the anterior superior alveolar artery, the middle superior artery and the posterior superior alveolar artery. Innervation occurs through nerve of the same names as the arteries.
The Frontal Sinuses
Anteriorly, the frontal sinuses are contained by the forehead and the superciliary arches, superiorly and posteriorly by the anterior cranial fossa and inferiorly by the bony orbit, the anterior ethmoidal sinuses and the nasal cavity. Medially the sinuses face one another, separated by the midline. This pair of sinuses are irregular in shape when compared to one another and is underdeveloped at birth. They reach their full size and shape around seven to eight years of age. They drain primarily into the ethmoidal infundibulum and the corresponding lymph drainage occurs via the submandibular lymph nodes. It is innervated by the ophthalmic nerve, including the supraorbital and supratrochlear branches and supplied by the anterior ethmoidal artery, the supraorbital artery and the supratrochlear artery.
The Sphenoidal Sinuses
The most posterior of all the sinuses in the head, the sphenoidal sinuses are large and irregular, just like their septum, which is made by the sphenoid bone. Laterally, a cavernous sinus exists which is part of the middle cranial fossa and also the carotid artery and cranial nerves III, IV, V/I, V/II and VI can be found. The anterior wall separates this pair of sinuses from the nasal cavity, as does the hypophyseal fossa, the pituitary gland and the optic chiasm superiorly and the nasopharynx and pterygoid canal inferiorly. The lymphatic drainage occurs in the same way as the posterior ethmoid sinus. The posterior ethmoid artery and the posterior lateral nasal branches supply the sphenoidal sinuses and the posterior ethmoid nerve and the orbital branch of the pterygopalatine ganglion innervate them.
The Ethmoidal Sinuses
Superior to the ethmoidal sinus is the anterior cranial fossa and the frontal bone, laterally the orbit can be found and medially the nasal cavity. The ethmoid sinuses are unique because they are the only paranasal sinuses that are more complex than just a single cavity. On each side of the midline anywhere from three to eighteen ethmoidal air cells may be grouped together. These air cells are smaller individual sinuses grouped together to form one large one which encompass the anterior, middle and posterior nasal meatuses. The anterior and middle ethmoid sinuses send their lymphatic drainage to the submandibular lymph nodes while the posterior ethmoid sinus sends its own to the retropharyngeal lymph nodes. The anterior and posterior ethmoid artery as well as the posterior lateral nasal branches provide an ample blood supply to this region, meanwhile the anterior and posterior ethmoid nerves and the posterior lateral superior and inferior nasal nerves help innervate it.
Sinusitis is an extremely common outpatient case which presents as an inflammation of the epithelia of the sinuses. The causes can be a viral or bacterial infection or an allergic reaction. The inflammation can be acute or chronic and the maxillary sinuses are the most frequently affected. Antivirals, antibiotics and antihistamines are prescribed in persistent cases.