Sinusitis refers to the inflammation of the tissue lining the sinuses.
The inflammation can present with or without infection and is apparent in the mucous membranes in the sinus cavities of the nose, behind the eyes and in the forehead, says Knysna-based ear, nose and throat specialist, Dr Martin Young.
There are between 14 and 16 air-filled sinus cavities in the skull. These are on either side of the nose, behind and between the eyes, in the forehead and even deeper towards the back of the skull. They make the bones lighter, improve voice resonance and absorb some of the impact if you receive a hard blow to the head.
Air reaches the sinuses through tiny openings in the skull. The membrane that lines the sinuses secretes mucus to warm and moisten the inhaled air and the air in the cavities themselves. And therein lies the problem.
Normally the small amount of mucus that is secreted as a filter moves almost like a conveyor belt over the tiny delicate hairs of the nostrils, then down the throat, where it’s swallowed. “But when swelling blocks the tiny air openings in the facial bones, the air can’t penetrate the cavities and the mucus can’t drain,” Dr Young says. “It accumulates and thickens and there’s a good chance that bacteria, viruses or fungi will grow in it.”
Sinusitis affects approximately 30% of the population at some point. Sinusitis can occur in infants and children, but is more common in adults as sinuses are undeveloped in infants and start forming during childhood.
The average adult has 3-4 upper respiratory infections each year, about 1% of which are complicated by sinusitis. In addition to sinusitis associated with viral respiratory infections, many more people suffer inflammation of the sinuses because of seasonal allergic problems.
How sinusitis starts
The paranasal sinuses are air-filled cavities inside the bones of the skull. They are located on either side of the nose, behind and between the eyes, and in the forehead; there is also one further back in the head. They function to reduce skull weight and to enhance vocal resonance. They also have a protective function as they are lined with warm mucus-secreting cells, which allows for moist and filtered air to be breathed in. The air reaches the sinuses through small openings in the bone that connect to the nasal passageways.
The mucus-producing cells have small hair like fibres that beat back and forth to help mucus move out of the sinuses. If these openings become blocked, air can't properly pass into the sinuses and mucus can't drain out. The buildup of mucus in the sinus causes pressure or pain, causing pressure or pain. Also, the mucus is an excellent culture medium for bacteria, and infection can result.
How sinusitis progresses
Typically, early in the development of a sinus infection, the cilia lining the sinuses are lost and mucus becomes increasingly thick, resulting in mucus being retained in the sinus. If the sinus infection lasts long enough, the sinus lining may physically change, causing even thicker mucus to develop. Bacteria become trapped and proliferate. Once this happens, antibiotics will be needed, and possibly surgery.
Types of sinusitis
Sinusitis may be classified based on time span of the problem (acute, sub-acute or chronic), and the type of inflammation (infectious or non-infectious).
“Sinus headache”- typically lasts a few hours until the ostia unblock and allow equalisation of air pressure in the sinus.
Acute sinusitis – typically lasts up to a month.
Sub-acute sinusitis – lasts longer than one month, but less than three months.
Chronic sinusitis – longer than three months.
Infectious sinusitis – usually caused by bacterial growth.
Non-infectious sinusitis – caused by irritants and allergic conditions.
Acute sinusitis is commonly secondary to either allergic rhinitis (hay fever) or viral infection of the nasal passages. Sub-acute and chronic forms of sinusitis usually result from incomplete treatment of acute sinusitis.
The most common complaint is a “sinus headache”. This typically occurs as a result of nasal congestion or sinus mucus which obstructs the ostia, leading to a blockage of air flow and equalisation of air pressure in the sinus and the environment. The air in the sinus is absorbed which causes a negative pressure in the sinus, leading to symptoms of a “sinus headache”.
Once the obstruction is relieved, the pressure equalises and the sinus headache immediately improves. The second most common cause of sinus symptoms is when the sinus starts producing mucus in response to irritation or constant blockage. At this stage an antibiotic is not usually required. Infection of the sinus usually is accompanied by a temperature, which may suggest that an antibiotic is required.
How sinusitis can be treated
What are the causes of sinusitis?
How sinusitis can be treated
Reviewed by Dr Harris Steinman MBChB. (UCT), D.CH (SA), FAAAAI, D.Av.Med.(SAMS), Private specialist at FACTS (Food & Allergy Consulting & Testing Services), February 2015. (Previously updated by Dr H Steinman, June 2007)