The nose and paranasal sinuses: basic anatomy and physiology

This page provides a brief overview of the anatomy and physiology of the nose and sinuses. A basic understanding of these topics is necessary to define nasal and sinus disorders.

The nose and sinuses are a part of the upper respiratory tract. The three-dimensional anatomy of this area is complex. The external nose consists of a cartilaginous framework, as well as a bony framework including the nasal bones, nasal process of the frontal bone, and frontal process of the maxilla. The nostrils, or anterior nares, form the external opening to the nose. The nasal septum is a midline internal structure that separates the left and right nasal cavities. It is composed of septal cartilage, as well as bones including the vomer, perpendicular plate of the ethmoid, maxillary crest and premaxilla. A deviated nasal septum can cause nasal obstruction. Internally, the nasal cavity connects to the nasopharynx and aerodigestive tract via the posterior nares, also known as the choanae. The adenoids, lymphoid tissue that can enlarge and cause nasal obstruction, especially in children, are located in the nasopharynx.

The lateral nasal wall internally contains the three turbinate bones. These scroll-like structures are covered in a mucous membrane that contains vascular channels which can swell under certain conditions, such as allergy or inflammation. The lower or inferior turbinate is a large structure that is associated with the inferior meatus. This opening is where the nasolacrimal tear duct drains. Blockage of this duct from injury or disease causes excess watering of the eye, or epiphora. The middle turbinate, a projection of the ethmoid bone, is associated with the middle meatus. The uncinate process is a thin projection of the ethmoid bone that separates the middle meatus from the nasal cavity. This key region (the ostiomeatal unit) is a pathway for drainage from the maxillary (cheek) sinus, frontal (forehead) sinus, and the anterior ethmoid sinus, which is located near the orbit. The superior turbinate is a small structure located high in the nose.

The superior meatus provides an opening for the posterior ethmoid sinus. Behind this area in the back or posterior region is an opening to the sphenoid sinus, located centrally. The pituitary gland is located directly behind the sphenoid sinus and is accessed surgically by a trans-sphenoidal route.

The surrounding anatomy closely associated with the nose and sinuses contains critically important structures. Extension of nasal and sinus disease to involve nearby structures can have serious consequences. The eye is separated from the ethmoid sinus by a paper thin bone, the lamina papyracea. The roof of the sinuses is the skull base or floor of the anterior cranial fossa, and is often very thin medially. The sphenoid sinus is bordered by the internal carotid artery (the major blood supply to the brain) as well as the optic nerve, cavernous venous sinus, and third, fourth, fifth, and sixth cranial nerves. Infection, inflammation, or neoplasm expanding to involve the eye or intracranial structures are complications of nasal or sinus disease requiring urgent care.

The sensory systems of the nose contain fibers of the trigeminal nerve, which senses noxious stimuli. Also, the olfactory nerves project from a sensory epithelium lining the superior region of the nose through the thin cribriform plate of the ethmoid bone to enter the brain. These nerves interact with inspired odors to mediate the sense of smell. Also, most of the flavor qualities of food and beverages are sensed by the olfactory nerve. Disease processes blocking the ability of air to reach the olfactory area of the nose or directly damaging the olfactory nerve pathways can cause an olfactory loss, termed anosmias.