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Sinus - Types, Functions, and Clinical Aspects

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Paranasal sinuses are air-filled cavities in the bones of the skull between the eyes, behind cheekbones, and on the forehead. There are four on each side.

Written by

Dr. Ruchika Raj

Medically reviewed by

Dr. Akshay. B. K.

Published At August 25, 2022
Reviewed AtJanuary 4, 2024


All these paranasal (present laterally to the nose) sinuses are outward growth from the nose. A membrane lines these sinuses; any inflammation and infection of these membranes are called sinusitis. Sinusitis disturbs the normal functions of the sinus, like mucus drainage, and causes fluid to clog within the sinus spaces, resulting in complete blockage of the sinus.

How Many Sinuses Are There?

There are four pairs of paranasal sinuses. It is connected to the nose from the medial side.

  1. Maxillary Sinus: It is a pyramid-shaped sinus located within the maxillary bone. It is present above the roots of the first and second maxillary premolars, extending backward to the roots of the first and second maxillary molars. It drains its contents into the middle meatus of the nose.

  2. Frontal Sinus: It is a triangular-shaped sinus present within the forehead bone. It drains its contents into the middle meatus of the nose.

  3. Ethmoid Sinus: These are small air sacs (3-8 in number) present between the nose and orbit.

  4. Sphenoidal Sinus: It is present within the sphenoid bone at the back of the head.

What Are the Functions of Paranasal Sinuses?

The sinuses have a variety of functions in our body:

  • They add resonance to speech.

  • Lightens skull weight.

  • Warms and moistens inhaled air.

  • It acts as a cushion for the skull bones (especially in case of trauma).

  • It contributes to the growth of skull bones.

  • Evenly distributes the inspired air.

The most common infection related to the sinus is inflammation or swelling of the tissue that lines the sinus and is termed sinusitis or rhinosinusitis (as it involves the nose).

What Are the Types of Sinusitis?

  • Acute Sinusitis:Sinusitis that ends within three to four weeks is known as acute sinusitis. This is usually caused by the common cold, which causes a blocked nose and sinus, preventing mucus drainage.

  • Sub-Acute Sinusitis: Sinusitis that lasts 10-12 weeks.

  • Chronic Sinusitis: It continues for months or years.

  • Recurrent Sinusitis: If a person gets affected several times with sinusitis within a year, it is recurrent sinusitis.

What Are the Causes of Sinusitis?

  • Common cold or flu.

  • Allergies.

  • Bacterial infections.

  • Viral infections.

  • Dental infections.

  • Abnormal nasal growth.

  • Deviated nasal bone.

  • Smoking.

  • Trauma to sinuses (mostly during intubation).

  • Compromised immune system.

  • Systemic diseases like asthma.

What Are the Signs and Symptoms of Sinusitis?

  • Difficulty in breathing due to a stuffy nose.

  • Runny nose.

  • Headache.

  • Mucus is present in the throat (post nasal drip).

  • Cough.

  • Bad breath.

  • Head heaviness.

  • Sore throat.

  • Reduced smell sensation.

  • Fever.

  • Weakness.

  • Fatigue.

  • Facial pain and pressure.

How Is Sinusitis Diagnosed?

Sinusitis is diagnosed based on:

  • Medical History: A complete history of signs and symptoms is recorded.

  • Clinical Examination: A small instrument with light is used by an ENT specialist to check the nose.

  • X-Ray of Paranasal Sinuses (Townes View): A simple investigation that can detect fluid or inflammation in sinuses.

  • Computed Tomography (CT) Scan: It is a definitive tool for the diagnosis of sinusitis. It shows any abnormal changes in the sinus like:

  1. Opaque areas in the sinuses.

  2. Displacement or rupture in the lining of the sinus.

  3. Thickening of the sinus lining of more than 0.197 inch.

  • Culture Test: The doctor uses a small cotton swab to collect the secretion from the nose and send it to the laboratory to identify the causative organism and type of infection.

  • Ciliary Function Test: A nasal brush biopsy is done to collect the sample to check for any abnormalities in the cilia.

How Is Sinusitis Treated?

  • Drink plenty of fluids to thin the mucus drainage.

  • Warm water compression on the forehead to relieve sinus pressure.

  • Taking hot water steam two to three times a day helps to relieve sinus pressure.

  • Nasal wash with warm water or saline.

Sinus medication:

Antibiotics cannot help to treat sinus infections as they are caused by viruses. Even if, in some cases, bacteria cause sinusitis, it subsides without any treatment in a few days. If the sinus infection does not improve, doctors may suggest antibiotics. The whole course of sinus medication needs to be taken even if the symptoms improve faster.

  • Over-the-counter pain medications (Paracetamol is the drug of choice for children less than six months).

  • Antibiotics like Amoxicillin or Amoxicillin-Clavulanate are the drug of choice.

  • Oral or topical steroids are given to decrease nasal swelling or edema, keeping in mind the patient at risk.

  • Intranasal sprays for reducing nasal congestion.

  • Antihistamines are prescribed for allergy-related sinusitis.

  • Second and third-generation Cephalosporins.

  • Metronidazole drug against anaerobic infections if the patient does not show improvement in five to seven days.

  • Surgical treatment is preferred when all drug therapy fails for the patient.

When Is Surgical Treatment Indicated in Sinusitis?

  • When all medicinal therapy fails for the patient.

  • Functional endoscopic sinus surgery (FESS) is one of the current surgical approaches to draining the sinus completely and restoring normal ventilation and function to the sinuses.

  • Using endoscopic sinus surgery, all the adhesions or soft tissue mass are removed to clear the nasal obstruction.

  • Balloon sinus ostial dilation (BSOD) is one of the latest treatments to enlarge the sinus to clear the nasal blockage.

  • The type of surgery that needs to be done is decided by an ENT specialist based on the severity of the disease.

Sinus infection without mucus occurs when there are persistent sinus symptoms despite treatment for allergies and headaches. It is very important to find the cause of sinus infection without mucus because if a sinus patient is under migraine treatment or vice versa, the symptoms will not get cured; instead, they will become worse.

What Are the Warning Signs of Sinusitis for Immediate Concern?

  • Double vision.

  • Blurred vision.

  • Loss of sensation in any area of the face.

  • Eye swelling.

  • Cranial involvement is diagnosed in a computed tomography (CT) scan.

  • Increase eye pressure.Stiffness in the neck.

What Are the Complications of Sinusitis?

If sinusitis is left untreated or treatment is delayed much, it can result in:

  • Blindness due to compression of the optic nerve.

  • Osteomyelitis in advanced cases.

  • Meningitis if infections spread to the cranium.

  • Sinus thrombosis (formation of a mass of tissue).

  • Subdural or epidural empyema (collection of pus between the layer of the cranium).

How Is Sinusitis Prevented?

  • Avoid allergic substances.

  • Get vaccinations on time.

  • Avoid smoking.

  • Maintain hygiene - frequent hand washing (especially before meals).

  • Immediate treatment in case of cough and cold.

  • Avoid contact with people who have the flu or cold.


Sinusitis is a very common infection that can infect anyone at any point in time. Immediate diagnosis and treatment by an ENT specialist are key to getting rid of it completely without any severe complications. If left untreated for longer, it can spread to vital structures such as the brain, eyes, and lungs, making the treatment difficult.

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Dr. Akshay. B. K.
Dr. Akshay. B. K.

Otolaryngology (E.N.T)


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