A sinus is a hollow, air-filled cavity. For the purposes of this article, a sinus will referred to those hollow cavities that are in the skull and connected to the nasal airway by a narrow hole in the bone (ostium). Normally all are open to the nasal airway through an ostium. Humans have four pair of these cavities each referred to as the:
- frontal sinus (in forehead),
- maxillary sinus (behind cheeks),
- ethmoid sinus (between the eyes), and
- sphenoid sinus (deep behind the ethmoids).
The four pair of sinuses are often described as a unit and termed the “paranasal sinuses.” The cells of the inner lining of each sinus are mucus-secreting cells, epithelial cells and some cells that are part of the immune system (macrophages, lymphocytes, and eosinophils).
Functions of the sinuses include humidifying and warming inspired air, insulation of surrounding structures (eyes, nerves), increasing voice resonance, and as buffers against facial trauma. The sinuses decrease the weight of the skull.
Sinus Infection Signs & Symptoms
Commonly sinus infection signs and symptoms are headache, facial tenderness, pressure or pain, and fever. However, as few as 25% of patients may have fever associated with acute sinus infection. Other common symptoms include:
- cloudy, discolored nasal drainage,
- a feeling of nasal stuffiness,
- sore throat, and
Some people notice an increased sensitivity or headache when they lean forward because of the additional pressure placed on the sinuses. Others may experience tooth or ear pain, fatigue, or bad breath. Nasal drainage is usually clear or whitish-colored in people with noninfectious sinusitis.