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Paranasal sinus

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 function of the sinuses is not entirely clear, but they may fulfill any or all of the following:

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.