Nasal Meatus

What Is the Nasal Meatus?

The nasal meatus is any of the long, narrow air passages that run from the front to the back of the lateral wall of the nasal cavity, each lying in the space beneath a nasal concha. The word meatus comes from Latin and simply means passage or channel, and anatomists use the plural meatuses (or meatus). Each half of the nose contains three of them, which differ in size and in the openings they hold.

• Superior meatus: the smallest, under the superior concha.
• Middle meatus: the busiest drainage area, under the middle concha.
• Inferior meatus: the largest, under the inferior concha, just above the floor of the nose.

The meatuses cannot be understood without the bony shelves above them. The nasal conchae (turbinates) project from the side wall like curled scrolls, and the meatus is the groove each scroll overhangs. In other words, the concha is the bump and the meatus is the channel underneath it.

Explained simply

Imagine the inside wall of each nostril as a bookshelf with three curved shelves stacked one above the other. The shelves are the conchae, and the tunnels of space under each shelf are the meatuses. Air slides along these tunnels on its way to the throat, and several small drainpipes from the sinuses and the eyes empty into them.

Where Is the Nasal Meatus Located?

The nasal meatuses are located on the lateral wall of each nasal cavity, stacked from top to bottom beneath the superior, middle and inferior conchae, between the nostrils in front and the choanae at the back. They sit on the outer side of each air chamber, facing the nasal septum across the midline.

Borders of the meatus region

• Above: the roof of the nasal cavity and the sphenoethmoidal recess, a small pocket above and behind the superior concha.
• Below: the floor of the nasal cavity, formed by the hard palate, which also forms the roof of the oral cavity.
• Medially: the free curled edges of the conchae and, beyond them, the nasal septum.
• Laterally: the bones of the side wall: the maxilla, the ethmoid labyrinth, the lacrimal bone, the inferior concha, the perpendicular plate of the palatine bone and the medial pterygoid plate.
• Behind: the choanae, the paired openings into the nasopharynx.

Air enters through the nostrils, passes the vestibule and then fans out across the meatuses before it gathers again behind the conchae and flows through the choanae into the throat. Because the maxillary sinus lies just outside the lateral wall and the orbit lies above it, the meatuses are the natural meeting point for sinus and tear drainage.

Nasal Meatus Anatomy: Superior, Middle and Inferior Meatus

Nasal meatus anatomy is built around three main passages, each named after the concha that roofs it, plus two shared spaces called the common meatus and the nasopharyngeal meatus. The three main meatuses grow in size from top to bottom.

What is the superior nasal meatus?

The superior meatus is the smallest and shortest meatus, a narrow slit between the superior concha and the middle concha in the back part of the lateral wall. The posterior ethmoidal air cells open into its front part. Near its back end lies the sphenopalatine foramen, an opening that links the nasal cavity with the pterygopalatine fossa and lets the sphenopalatine artery and the nerves of the nasal mucosa enter. Above and behind the superior concha, the sphenoid sinus drains into the sphenoethmoidal recess rather than into the meatus itself.

What is the middle nasal meatus?

The middle meatus lies beneath the middle concha and above the inferior concha, and it runs along the length of the concha that roofs it. Lifting the middle concha reveals a small landscape of named features:

• Ethmoidal bulla: a rounded bony bulge formed by the middle ethmoidal air cells, which open on or above it.
• Uncinate process: a thin, hook-shaped plate of the ethmoid bone that curves down and back below the bulla.
• Semilunar hiatus (hiatus semilunaris): the half-moon-shaped gap between the bulla and the uncinate process.
• Ethmoidal infundibulum: a funnel-shaped channel lateral to the uncinate process that opens through the hiatus and leads up toward the frontal sinus.

What is the inferior nasal meatus?

The inferior meatus is the largest and longest meatus, lying between the inferior concha and the floor of the nasal cavity and running along almost the whole length of the lateral wall. Its main opening is the lower end of the nasolacrimal duct, found in its front part under the anterior end of the inferior concha. A small fold of mucosa at this opening, often called the valve of Hasner, helps stop air and mucus from being pushed up into the tear duct when we blow the nose.

What is the common nasal meatus?

The common nasal meatus is the narrow, vertical slit between the free edges of the conchae and the nasal septum, which joins all three meatuses on the inner side. Much of the airflow in quiet breathing passes through this central channel. Behind the back ends of the conchae, the space narrows into the nasopharyngeal meatus, which leads through the choanae into the nasopharynx.

What Drains Into Each Nasal Meatus?

Each nasal meatus receives the drainage of specific paranasal sinuses or the tear duct: the posterior ethmoid cells drain into the superior meatus, the frontal, maxillary and anterior and middle ethmoid sinuses drain into the middle meatus, and the nasolacrimal duct opens into the inferior meatus. The sphenoid sinus drains just above them, into the sphenoethmoidal recess.

Middle meatus openings

The middle meatus collects drainage from three of the four paranasal sinuses, which makes it the most important drainage area of the nose. The frontal sinus empties through the frontonasal duct or frontal recess into the front of the ethmoidal infundibulum. The maxillary sinus opens into the back part of the semilunar hiatus, and the anterior ethmoid cells open into the hiatus and infundibulum nearby. Some people also have small accessory openings of the maxillary sinus a little further back in the middle meatus.

The ostiomeatal complex

Surgeons and radiologists group the uncinate process, ethmoidal infundibulum, semilunar hiatus, ethmoidal bulla, maxillary sinus opening and frontal recess into one functional unit, the ostiomeatal complex (also spelled osteomeatal). Because so many sinuses share this narrow corridor, a small swelling here can block several sinuses at once. On a coronal CT scan of the sinuses, the standard view for nasal meatus anatomy in radiology, this corridor is one of the first areas checked.

Why the sinuses drain where they do

The drainage pattern is a leftover from development. Before birth, the lateral nasal wall forms a series of ridges, the future conchae, separated by grooves, the future meatuses. The paranasal sinuses grow as small pouches of lining that bud outward from these grooves into the surrounding bones, so each sinus keeps its opening in the meatus it grew from.

What Is the Function of the Nasal Meatus?

The function of the nasal meatus is to guide inhaled air over a large, moist, warm surface so it is filtered, warmed and humidified, and to give the sinuses and the tear duct a path to drain into the nose. These jobs make the meatuses a small but busy part of the airway described in our overview of respiratory system functions.

Nasal meatus function in the respiratory system

• Air conditioning: together with the conchae, the meatuses greatly increase the area of mucosa that air touches. Warm blood flowing just under the lining heats the air, and moisture from the mucus humidifies it before it reaches the pharynx and lungs.
• Filtering: the curved channels make airflow swirl, so dust, pollen and microbes are thrown against the sticky mucus and trapped.
• Mucus clearance: cilia on the lining beat toward the back of the nose, carrying the mucus blanket out of the meatuses to the nasopharynx, where it is swallowed.
• Sinus drainage: mucus made inside the sinuses is swept through their small openings into the meatuses and joins the same stream.
• Tear drainage: tears from the surface of the eye drain through the nasolacrimal duct into the inferior meatus.

Superior, middle and inferior nasal meatus function

The superior meatus drains the posterior ethmoid cells and lies close to the olfactory area at the roof of the nose, so air reaching it brings odor molecules near the smell receptors. The middle meatus is the main drainage gateway for the frontal, maxillary and anterior ethmoid sinuses. The inferior meatus carries a large share of the airflow along the floor of the nose and receives the tear duct.

Lining, blood supply and nerves

All the meatuses are lined by respiratory mucosa: pseudostratified ciliated columnar epithelium with mucus-making goblet cells over a layer of glands and blood vessels. Blood arrives mainly from branches of the sphenopalatine artery, a branch of the maxillary artery, with help from the anterior and posterior ethmoidal arteries. Sensation is carried by small nasal branches of the maxillary nerve and by the anterior ethmoidal nerve, both parts of the trigeminal nerve.

Nasal Meatus vs Conchae: How Do They Work Together?

The nasal conchae are the curled bony shelves on the side wall of the nose, while the nasal meatuses are the air channels underneath them, so the two always work as a pair. Turbinate is simply another name for a concha, so nasal meatus vs turbinate is the same comparison: one is a channel and the other is the projection that forms its roof.

How the conchae shape the meatuses

The superior and middle conchae are thin plates of the ethmoid bone, while the inferior concha is a separate bone of its own. Over each concha lies thick mucosa packed with venous spaces, a kind of erectile tissue that can fill with blood and swell. When the mucosa swells, the meatus below it narrows; when it shrinks, the meatus widens.

The nasal cycle

In most people the lining of one side of the nose swells while the other side shrinks, then the two sides swap every few hours, a rhythm called the nasal cycle. During the congested phase, the meatuses on that side narrow and less air passes through them. People rarely notice the cycle unless one side is already narrowed for another reason.

How the meatuses change with age

In a newborn the nasal cavity is short and low, the conchae fill much of it, and the meatuses are small slits, which is one reason babies breathe mainly through the nose and are easily stuffed up. The meatuses lengthen and deepen as the face grows and the maxillary sinus expands. In older adults the mucosa often becomes thinner and drier.

Common Conditions That Affect the Nasal Meatus

Conditions of the nasal meatus usually involve narrowing or blockage of one of its channels or openings, which can trap mucus in the sinuses or tears in the eye. Our respiratory diseases section covers airway conditions in more depth, and anyone with lasting nasal symptoms should see a doctor.

• Sinusitis: inflammation of the sinus lining. Swelling around the ostiomeatal complex in the middle meatus can block drainage from the frontal, maxillary and anterior ethmoid sinuses at the same time.
• Nasal polyps: soft, noncancerous growths of inflamed lining, which often arise around the ethmoid sinuses and the middle meatus and can fill the channel.
• Turbinate hypertrophy: long-term enlargement of a concha, most often the inferior one, which narrows the meatus beneath it and the common meatus beside it.
• Concha bullosa: an air cell inside the middle concha that enlarges it and may crowd the middle meatus.
• Deviated nasal septum: a septum bent toward one side narrows the common meatus on that side.
• Nasolacrimal duct obstruction: a blocked tear duct, often at its opening in the inferior meatus, causing a watery eye. In newborns a thin membrane at this opening is a common cause.