What Are Your Sinuses and How Do They Work?
Anatomy of the Sinuses
We have four pairs of paranasal sinuses. I use the adjective, paranasal, or around the nose, because there are lots of other sinuses in the body. A sinus tract is described in medicine as a pouch in the body filled with air that has a single opening into the inside of a body cavity or to the outside of the body involving the skin.
Each sinus surrounding the nose has an opening to another chamber, to the nose itself or to another sinus chamber.
The four pairs of sinuses are:
- The maxillary sinuses under the cheeks
- The ethmoid sinuses between the eyes
- The frontal sinuses under the forehead
- The sphenoid sinuses behind the nose at the base of the brain.
The maxillary, frontal and sphenoid sinuses are usually single chambers with a single opening, called an ostea, that drains into the nose.
The ethmoid sinus is actually a labyrinth of cells, often from 5 to 15 cells, that each have a separate drainage opening, either into the nose or into another ethmoid cell. These differences will matter when we talk about strategies the treat the sinuses.
All of the sinuses surround important structures including the brain and eye, so sinus problems can affect both. In fact, your nose is connected to most parts of your head and neck anatomy.
It also connects to your ears through the Eustachian tubes – the tubes that can get clogged with increasing elevation, like in an airplane, high elevator or in the mountains. These are the tubes that “pop” when you swallow or chew gum or yawn.
The nose is also above the mouth and oral cavity and connected to them through back of the throat, called the pharynx – in medical terms. Pharynx is pronounced “Fair-inx” like the word “sphinx,” similar to the medical term for the voice box or larynx (“lair-inx”) where the vocal cords are housed.
So diseases in the nose can affect all these areas of the head because they are in close proximity and connected.
At birth and through early infancy (the first year of life) rudimentary ethmoid, maxillary, and occasionally sphenoid sinuses present,
Figures 4 and 5 CT scans of the sinuses and head of a 6 month old.
Understanding Sinus CT Scans
Computed tomography (CT) scans are radiographic exams that basically consist of three colors – white, grey and black. White structures are bone, grey structures are the soft tissues of your body and black is air.
You want your sinuses to be black on CT scan, indicating they are full of air and not fluid or infection. If you look at the two CT scans of the infant above, you can see there are many shades of grey too.
The outline of the eyeballs in the bony orbital socket are evident because there are different shades of grey arising from the fat and muscles of the eye socket. That color differentiation is because our tissues have different consistencies, as indicated in the CTscan of the teenage below to the left and the corresponding cadaveric diagram to the right.
A CT scan or Computerized axial tomography (CAT) scan produces X-rays, like a regular x-ray but more of them in slices. A conventional X-ray image is basically a shadow. A powerful “light” in the form of electromagnetic energy is shined on one side of the body, and a piece of film on the other side registers the silhouette of the bones and the soft tissues, depending on how much energy is given.
These X-ray photons are basically the same thing as visible light photons, but they have much more energy. This higher energy level allows X-ray beams to pass straight through most of the soft material in the human body but the different consistencies or densities of tissue show up differently. In a CT scan machine, the X-ray beam moves all around the patient, scanning from hundreds of different angles. The computer takes all this information and can come up with different angles, slices, and even a 3-D image of the body.
The different position of slices of the head neck and face of a CT scan are in the three standard positions of the x, y and z axis, just like in geometry. There is a coronal slice from the top of the head to the chin such as the the CT scan with the cadaveric comparison above depicts, so it looks like you are looking at the person straight on.
There is an axial slice from the nose to the back of the head, as the second CT scan slice of the infant depicts. To understand this view, picture someone lying on their bed as you are sitting in a chair at the foot of their bed. This view is as if you are looking at them from the vantage point of their feet.
The third orientation is a sagittal slice, which depicts the view as if you are looking at them from the side.
All the paranasal sinuses enlarge over time. The diagram shows the rate that the maxillary and ethmoid develop as the child ages. This rate is an average, and children can develop their own sinuses slower or faster than this average rate.
The next two CT scans show how much bigger the sinuses are at five years of age. The sinuses expand and the teeth are not protruding up into the maxillary sinuses as they were at six months of age.
The maxillary sinuses still sit right over the teeth, so teeth pain is an important symptom of a true infection in the sinuses, compared to allergies or a cold affecting the nasal passages only.
At age five, in the CT scan of the child depicted here, there are no frontal sinuses. The frontal sinus starts as a sinus buds from the superior anterior ethmoid sinuses in children around 6 to 8 years of life. This area of budding of the frontal sinus is called the frontal sinus recess becomes the sinus outflow tract of the frontal sinus as it drains into the nose and anterior part of the ethmoid sinuses.
The frontal sinus expands and aerates in to the frontal bone and seen easily in teenagers
All sinuses continue to expand to the late teens and early 20s.
If you compare the maxillary sinus of this teenage with the CT scans of the two other age groups, you can not only see the expansion, you can now see the maxillary sinuses are lower than the nasal cavity and the bone has thinned out around the teeth. This can cause the symptom of teeth pain to be more significant as the child becomes a young adult
Inside the nose and nasal cavity, the structures look pretty similar in all age groups, even as an infant. Certainly, the structures and space between them will be smaller as an infant, but everything looks pretty similar
These three endoscopic pictures show coronal slices of the nasal cavity from the
This view of the 6 week old infant is fairly similar to the teenage nose below.
The nasal cavity is around two inches long in an infant and three inches long in an adult.
In the back of the nose reside the adenoids. They cannot be seen on routine exam. They can only be seen with an endoscope or with x-rays. A plain film X-ray will show the shadow of the side of the adenoid, and indicate its size.
The adenoids are part of immune system that make antibodies. When you are born, the adenoids are small (see figure of six week old). Their job is to help your immune system mature. They do so by making antibodies to the bacteria and viruses that get into your nasal cavity. Maternal antibodies initially protect you for the first 6 months of life and they gradually leave your system. Your own immune system function kicks in and you start developing your own immunity, in part helped by the adenoids.
Your immune system works hard to get up to speed and by three years of age, your immune system, based on measurement of immunoglobulins, is about 85% of what it should be by three years of age. It continues improvement over the next few years and by five to seven years, your immune system is close to adult maturity.
Methods for Treating Sinus Problems
By performing its function, the adenoids are constantly exposed to bacteria and viruses. At some point they can be overwhelmed and overtaken by these pathogens and begin harboring and actually protecting bacteria. When that happens, bacteria can use the adenoids resembling a fort where they can grow and multiple. Once the numbers are large enough, the bacteria can invade the nose and sinuses and cause infection.
The antibiotics can clear up the infection in the nose, but they do not penetrate into the deep recesses of the adenoid tissue. Studies have been performed where six weeks of antibiotics are given to eradicate the infection, but the infection is still found in the depths of the tissue when the tissue is surgically removed.
This may be in part to that fact that bacteria can form a biofilm that it can hide in as well. Biofilms are polysaccaride homes that can be made by bacteria to protect themselves from the body’s defenses and the medicines we use to fight infection.
Also, when the adenoids enlarge, they can block the flow of mucus in the nose. The flow of mucus from the anterior nasal cavity to the posterior nasal cavity is important in cleansing the nose of bacterial and viruses, pollution and pollen. If that flow is obstructed by large adenoids , it can cause nasal symptoms to occur.
Is It Safe To Have Adenoids Removed?
So sometimes we need to take the adenoids out, when they are causing significant nasal obstruction, or harboring infection. The question is, will the immune system significantly suffer. Basically, the answer is no. The adenoids are only one part of the immune system along with your tonsils and 300 lymph nodes in the back of the nose and neck that are working to help your immune system mature.
Vascularity and Neurology of Noses
Your nose and nasal cavity has a complex system of nerves that have several
Complex system of arteries of the nose.
Just like in all parts of the body, the larger arteries from the heart taper down to smaller arteries, called arterioles, then to the capillaries, where the arteries and veins meet. The flow continues through the post-capillary venules and then the escalating size of veins back to the heart.
The capillaries are fenestrated which allow for the flow of proteins and constituents of the blood to get into the tissue. In the nose lining, which is called the nasal mucosa, there are also large collapsible venous sinusoids which can get filled with blood. When they fill with blood, it causes swelling in the nose and sinus lining and cause nasal congestion.
Complex system of nerves of the nose
There are three components to the nervous system of the nose, the sensory, special sensory and the autonomic nervous system. The sensory system, of course, senses pain from mechanical injury. It can also sense noxious stimuli that include heat and chemicals.
Chemicals that have been studied include
- cigarette smoke
These chemical lead to activating the nerve by what’s called neuronal (nerve) depolarization. The brain interprets these stimuli as sensations ranging from a prickling itch to severe burning pain. Stimulating this system can lead to nasal symptoms.
Special sensory nerves in the nose are the nerves for smell that sit in the top of the nose called the olfactory bulb as seen at the tops of the two diagrams above.
We also have the nerves from the autonomic nervous system that innervate the nose. The autonomic nervous system throughout the body is responsible for regulation of internal organs and glands, by controlling digestion, excretion and the production of tears and saliva.
It also accounts for sexual arousal. The autonomic nervous system includes the sympathetic and parasympathetic nervous system components, which can be complementary or somewhat antagonistic, depending on where they are in the body. The sympathetic nervous system is the quick response. It is the “fight” or “flight” system in which if you get frightened or startled, you get a rush of adrenaline that heightens your awareness of your surroundings and allows you to increase your performance of reacting to an event, like being able to fight back more quickly to an attacker, or being able to run aware more quickly from an attacker. Your heart pumps faster because of the adrenaline.
In the nose, the sympathetic system reacts to the stimulants. It vasoconstricts, or shrinks, the small arteriole blood vessels decreasing the amount of blood and fluid that gets to the venous sinusoids so there is less fluid to cause congestion. This is how Afrin and the other decongestants like Pseudofed work.
The parasympathetic nervous system in the nose is opposite to the sympathetic system. It innervates the glands of the nose and the blood vessels. Stimulation of the parasympathetic nervous system causes secretion of mucous from the glands and cause the veins to dilate, increasing nasal congestion and swelling and stuffiness.
Function of the Nose
So this brings us to the microscopic views of the nasal lining and how the nose works. Any lining of a body area is called epithelium.
Your skin’s epithelium has an outside lining, called the epidermis. Underneath the epidermis is the dermis, then the subcutaneous tissue that has all the fat. Below those layers are your muscles and body organs. If you have ever cut yourself and you see yellow fat, you are through the epidermis and dermis and into the subcutaneous tissue.
The nose lining, or nasal mucosa, also has an outside epithelium. It has components that are similar to your skin as well as extra components specific for the nose. The nose lining is similar to the lining of the tubes that lead to your lungs, the trachea and bronchi.
The lining of the nose, sinuses and lungs is called respiratory epithelium. It is composed of ciliated pseudostratified cells that contain three types: ciliated cells, goblet cells and basal cells.
The ciliated cells are columnar epithelial cells specialized with specialized ciliary modifications.
Cilia help sweep particles, like pollution and microscopic debris in the air, to the back of the nose so you can swallow them. The time it takes to sweep a particle from the front of the inferior turbinate to the back of the nose is called the transit time.
Transit times have been measured with saccharin for 20 to 30 years. Saccharin is placed on the front of the inferior turbinate in the front of the nose. The cilia then sweep it back to the back of the throat where we taste it.
Normal transit time is about 10 minutes. This test is one of the ways scientists study the success of different treatments, especially types of nose sprays. In this normal sweeping mechanism, we swallow a liter of postnasal drainage a day as a way to cleanse the air.
Goblet cells, so named because they are shaped like a wine goblet, are columnar epithelial cells that contain mucous granules and secrete mucus, which helps maintain epithelial moisture and traps particulate material and pathogens moving through the airway.
Often we sweep the contaminated mucous back and swallow it, but sometimes the mucous dries out when the water is reabsorbed into the nasal lining and the particulate matter is left behind in a clump. This is your booger.
The basal cells of the epithelium have some ability to differentiate into other cells types found within the epithelium when need to restore healthy epithelial layer related to injury.
The nose also warms and moistens the air to prepare it for the lungs. Air adjusted to the temperature of the body will be more optimally utilized by the body. Gas exchange in the lungs is easier when the gases (mainly oxygen) are warm, moist and active. The gases diffuse better across the small sacs of the lung – the alveoli.
The very high humidity is essential to provide adequate lubrication to the air. If the air is too dry when it enters the lungs, it interrupts the lining and more crusting of the lung lining occurs, with build up in the bronchial tube and can block the lungs. Humid, moist air is heavier than dry air, therefore it will naturally be prone to be more laminar and less turbulent flow, allowing good airflow pressure through constricted lung cavities.