paranasal sinuses

Paranasal sinuses are air-filled spaces, communicating with the nasal cavity, within the bones of the skull and face.

These 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.