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The paranasal sinuses are eight (four pairs) air-filled spaces, or sinuses, within the bones of the skull and face. These are divided into subgroups that are named according to which bones they lie under;- the maxilliary sinus es, also called the antra, are under the eyes, in the upper jawbone.
- the frontal sinus es, over the eyes, in the bone of the forehead.
- the ethmoid sinus es, between the nose and the eyes, backwards into the skull.
- the sphenoid sinus es, in the centre of the skull base.
The function of the sinuses is not entirely clear, but they may fulfill any or all of the following:
- Decreasing the relative weight of the front of the skull
- Helping to warm and humidify inhaled air before it reaches the lungs
- Increasing resonance of the voice
- Providing a buffer against blows to the face
The paranasal sinuses are joined to the nasal cavity via small orifices called ostia . These become blocked relatively easily by allergic inflammation, or by swelling in the nasal lining which occurs with a cold. If this happens, normal drainage of mucus within the sinuses is disrupted, and sinusitis may occur.
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