Most people who complain about their sinuses are talking about their "paranasal sinuses." These are air-filled bony cavities that are located adjacent to the nose in the face and skull. They are lined by membranes that are similar to those which line the nose. Each sinus is connected into the nose by a small opening called an ostium. The sinuses begin in babies as small pockets the size of a pea and grow through childhood to adult size -- about the size of a walnut.

There are four sets of paired sinuses, as shown in Figures 1.1 and 1.2.

1. frontal sinuses -- sit in the forehead

2. maxillary sinuses -- sit in the cheek above the teeth and below the eyes

3. ethmoid sinuses -- sit on each side of the nose between the eyes

4. sphenoid sinuses -- sit behind the eyes, and are the most deeply placed

Sometimes the sinuses can differ in size from one side to the other. Some people may be missing one sinus in the pair, but this rarely causes a problem. This asymmetry is most often seen with the frontal sinus.

Despite all we know about the sinuses, there is still some debate regarding their purpose. Some people believe that they lighten your dense skull. Another theory is that they aid in voice resonance, which is one reason physicians often do not want to operate on professional singers' noses: They fear changing their vocal quality. Some feel that the sinuses regulate pressure inside the nose, while others believe that they act as shock absorbers during head trauma. (A medical student once told me that the primary purpose of the sinuses is to provide a living for ear, nose, and throat doctors.)

The partition that separates the right and left sides of the nose is called the septum. It is made up of cartilage in the front and of bone farther back. Often, a person has a deviated septum, which means they have a twist of the septum. If this deviation occurs to a significant degree, it may result in nasal blockage and even affect sinus drainage.

There are bones on the sidewall of the nose called turbinates. There are three turbinates on each side of the nose. The tear duct from the eye (called the nasolacrimal duct) drains underneath the lower, or inferior turbinate. This is why women may see coloring from their eye-lining pencil in their nasal drainage. The middle turbinate is the most important, since it is where the maxillary and anterior ethmoid sinuses drain. The posterior ethmoid and the sphenoid sinus drain under the upper, or superior turbinate, into the nose.

The back of the nose is called the nasopharynx. The eustachian tube runs between the nasopharynx and the ear, equalizing pressures between them. When a person has nasal or sinus problems, this leads to inflammation of the nasopharynx in the back of the nose, eventually causing a feeling of clogged ears. Additionally, tumors of the nasopharynx, which block the eustachian tube opening, prevent adequate ear drainage and ventilation, resulting in fluid behind the eardrum.

The tissue that sits in the nasopharynx is called adenoid tissue. It is made up of lymph tissue, which helps fight infection (this function of adenoid tissue is only important clinically during the first year of life). Adenoid tissue is present in children and tends to shrink during the late teen years and early twenties. Large adenoids can lead to blockage of sinus drainage and sinus disease. In the past, large adenoids were treated by radium, but this has led to increased cancer rates, and so today, large adenoids are surgically removed.

Your nose does a lot more than just fill up the middle of your face. Its primary functions are respiration and smell. While respiration, or breathing, can be carried out via the mouth, it is the nose that is uniquely suited to this function. As air is drawn into the nose for ultimate passage to the lungs, it must be cleaned of the microscopic particles we inhale. These include dust, pollen, and the many pollutants of an industrialized society. The small hairs inside the nose, called cilia, as well as nasal mucus carry out this cleaning process. The nose not only acts as nature's vacuum cleaner, but it is also a humidifier and temperature regulator. Think about when you go outside on a very cold day. If that sub-zero air got through to your lungs, it would cause serious damage. Your nose and respiratory system warm the air to body temperature, protecting the sensitive lining of the lungs and bronchial tubes.

Most people breathe through their nose when they can. When your nose is blocked, you have to switch to breathing through your mouth. This can cause problems:

• When you breathe primarily through your mouth, for instance, when you have a cold, you may end up with a sore throat. This is because the nose humidifies the air you breathe, keeping your throat from getting too dry.
• Sometimes people snore because they are unable to breathe through their nose.
• When mouth breathing persists for a long time (several years), it may lead to a dull facial expression. This is called "adenoid facies" in children when it is due to large adenoids.
• Newborns breathe exclusively through their noses. This becomes important during eating, when the mouth is full. Thus, anything that blocks the nose in a newborn will lead to the inability to breathe during eating, and so must be attended to promptly.

Your nose also keeps diseases out of your body. Since viruses and bacteria often enter the body through the upper respiratory tract (nose and throat), the nasal lining and mucus that coat the tract act as our first line of defense. In some people, the process of filtering out dust and disease triggers an "allergic reaction."

The other important function of the nose is smell. The medical term for smell is "olfaction". While humans have a less developed sense of smell than some other animals, our ability to smell still accounts for important responses, such as appetite and emotion. Think about all the ways that your sense of smell affects your life:

• When you're an infant, you sense the nearness of your mother, in part, through smell, triggering the sucking response.
• When you smell food, it stimulates your appetite, ensuring that you eat and remain healthy.
• Conversely, foul-smelling items often signal rotten food, which protects you from eating them.
• Pleasant smells, such as perfume, or the absence of unpleasant smells, such as underarm odor, are the basis of multimillion-dollar businesses. Through the centuries, people have known that the sense of smell is a key to attracting the opposite sex.
• Your sense of smell protects you from the dangers of fire and natural gas.
• Your sense of taste is closely linked to your sense of smell. You've probably noticed that when you have a bad cold and your nose is blocked, the taste of food is greatly diminished. Many people who complain about a change in taste are actually experiencing changes in their sense of smell. As people get older, their sense of smell decreases, leading to a decrease in appetite, which can become a medical problem, with significant associated weight loss.

You probably go through most days of your life never thinking about your sense of smell, when, in fact, it is an integral part of many things you do.

Mucus is produced by glands within the lining of the nasal passages and sinus cavities. This mucus "blanket" serves a major role in the nasal defense mechanism by trapping foreign particles and organisms. The mucus contains a number of proteins and enzymes that can render these invaders harmless. Tiny hair cells, called cilia, move the mucus layer toward the back of the nose and throat, where the material is ultimately swallowed, for final deactivation by the stomach acids. The nose produces roughly a quart of mucus a day. Excessive or thickened mucus may result in plugging of the sinus openings with secondary infections. It also accounts for the postnasal drip, the feeling of mucus dripping down the back of the nose into the throat, which is common among sinus patients. I have seen some patients in which increased amounts of swallowed mucus can lead to nausea and vomiting. I even had a patient with colitis (intestinal disease), which only acted up when he had sinus infections.

In the past two decades, doctors have begun to better understand mucus drainage by using telescopes in the nose to follow drainage patterns. The wave of normal mucus production and flow within the sinuses into the nose is called mucociliary flow or mucociliary clearance. This refers to the movement of the mucus blanket on the cilia.

Mucus is directed from the maxillary and frontal sinuses toward an important area called the ostiomeatal complex (nicknamed the OMC). This OMC is primarily composed of ethmoid cells. Problems in the ethmoid sinus and the OMC lead to problems in the other sinuses, such as the frontal and the maxillary. In the past, the emphasis was placed on these secondarily infected frontal and maxillary sinuses. Currently, it is felt that the ethmoid sinuses and the OMC are the key to healthy sinuses, and by correcting drainage patterns here we can improve chronic sinus problems. This will be more fully addressed in Chapter 10, when we discuss the newer techniques of functional sinus surgery which normalize the sinuses to their proper function.

A number of factors keep the sinuses healthy:

1. Sinuses stay healthy when their ostia (openings) are unblocked, allowing them to drain into the nose. If something is in the way of the normal drainage pattern, mucus is blocked which can lead to a sinus infection. Examples of things that can get in the way of normal drainage are swelling resulting from a typical cold or allergy; growths, such as polyps; or anatomic abnormalities, such as a deviated septum.

2. The mucus blanket must have normal contents and be of a normal amount. Part of what makes up the mucus blanket are enzymes that fight infection, and if these are missing, sinus infection may result. If there is an increase in mucus produced, this too can lead to infection.

3. Hair cells move mucus toward the sinus ostia. The interior of the nose is also lined by hair cells, which must be functioning normally to have proper sinus drainage. Anything that impairs the normal motion of hair cells may result in a nasal or sinus infection. For example, hair-cell motility is impaired in cystic fibrosis sufferers. These patients are plagued with chronic sinus infections, as they are unable to normally clear the mucus in their nose and sinuses.

These three factors are interrelated. A problem in one area leads to an abnormal sinus cycle. For example, when a sinus opening is obstructed, sinus mucus stagnates and its contents can be altered, leading to damage of the hair cells, with the result of ultimate abnormal drainage. This can lead to a vicious cycle of sinus infection (see Figure 1.4.)