What is sinusitis? Cause, Symptoms and Signs

What are sinuses?

Sinuses are air-filled bony cavities located in our bony skull.  Usually we all have 4 pairs of sinuses which develop to different degrees of sizes. They are collectively called the para-nasal sinuses as they all surround, and drain into, the central nasal air cavity. Our para-nasal sinuses are made up by the frontal sinuses (above the eyes), the ethmoid sinuses (between the eyes), the maxillary sinusses (below the eyes) and the sphenoid sinuses (in the middle of the skull below our brain).  Our sinuses start to develop from age 2 years, at different rates until we are teenagers.

No one knows for sure what our sinuses are for, and many theories exist. Some anthropologists say, as mankind evolved from fish, sinuses were to reduce the total weight of the skull and allow the head to float in water. However most human biologists believe it is to increase the surface area of our nasal lining so humidification and warming of the air we breathe is more efficient and effective for oxygen respiration, preparing the air before it reaches our lung.

Each of these sinuses communicates with the nasal cavity through its own bony opening or sinus ostium. These ostia are very narrow, usually 2-5 mm in diameter, depending on the sinus. Mucous from the sinus, will only drain out only through its own natural ostium, even though another hole is made into the sinus e.g. by surgery.

So what is sinusitis and what can cause it?

The word sinus-itis mean inflammation of the sinuses. Our sinuses become inflamed when their openings are blocked.  A nasal allergy, say to house dust mite extracts, pollen and /or pollution, is probably the commonest cause of sinusitis. It causes the nasal lining to become swollen and this may block the sinus openings. Also infections with viruses, bacteria and fungus, are other common cause of sinusitis. Surgery for the nose or accidental trauma to the face and nose, are other causes.

When these sinus openings are blocked, the air pressure in the sinus starts to drop as the oxygen in the sinus air is continually absorbed by the body. The person can experience heaviness of the head as well as pain above, below and behind the eyes when this happens. Our sinuses respond to this insult by secreting more mucous so a runny nose may ensue. This mucous can accumulate in our sinuses if the opening remains blocked. Our sinus now becomes like a “warm bowl of soup”. If relief does not come soon to re-open the sinus drainage opening, this “warm bowl of soup” becomes a perfect growing ground for bacteria, and pus then is formed, transforming the inflammation into a full-blown bacterial sinusitis. As the sinus become inflamed with pus, the patient may also complained of a bad smell whilst others around him do not. This is usually from the collection of pus in his nose and sinus.

With the pus accumulation, now the symptoms change. The increasing pus creates a positive pressure inside the sinus, which becomes painful from the distension whilst the bacteria cause the body to respond with a fever. In uncontrolled bacterial sinusitis, the infection may cause the skin and soft tissue outside the sinus to become red, swollen and painful to the touch. As the brain and the eyes are vital neighboring structures, they are therefore at risk of becoming infected too. Thankfully and usually, by now the patient would have seen a doctor for treatment which would include antibiotics, pain relief & fever medication and decongestant. If not, then a brain infection, epileptic seizures, meningitis, double vision and loss of eyesight, may occur. Equally thankfully, it should be remembered that these brain and eye complications are very uncommon complications of sinusitis. By and large, the acute sinus infection subsides completely especially when the pus eventually drains though the sinus opening.

Can sinusitis recur or become long-standing and chronic?

Usually an acute sinusitis attack resolves. However sometimes it can become chronic, which is to say, that the infection remains long term. It is always partially draining (so pain is not a significant symptom) but never draining completely. This occurs as the opening of the sinus has been scarred by infection previously and has become even narrower, limiting the drainage of the pus. A bad smell, recurrent running postnasal drip, vague sinus pressure or pain is usually the symptom at this stage of the disease. Complete healing would usually not occur without some surgery to drain the sinus at this stage of the condition. Also in 30% of cases with maxillary sinusitis, where there is pain and swelling below the eye, the cause is usually the infected root of the premolar tooth on the upper jaw. This root may sit in the floor of this sinus, and will require additional dental treatment before the sinusitis can be cured. Often an X-ray of the sinuses will identify this as the problem.

Sinusitis is a common infection. But sinusitis requiring medical attention and sometimes surgery is uncommon. Facial discomfort with postnasal discharge, odd smell with or without a fever, might suggest an early and ensuing sinusitis. If this progresses, an endoscopic examination of the sinus openings +/- X-ray of the sinuses will usually confirm the diagnosis.

The Chinese version of this article was published in Hong Kong Economic Journal on July 4, 2013.