Sinus Infection (Sinusitis)

What is a sinus?

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:

  1. frontal sinus (in forehead),
  2. maxillary sinus (behind cheeks),
  3. ethmoid sinuses (between the eyes), and
  4. 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. If the inflammation hinders the clearance of mucous or blocks the natural ostuim, the inflammation may progress into a bacterial infection.

Reviewed on 7/14/2014