The paranasal sinuses usually consist of four paired air-filled spaces. They have several functions of which reducing the weight of the head is the most important. Other functions are air humidification and aiding in voice resonance. They are named for the facial bones in which they are located:
The paranasal sinuses are subject to marked variation between individuals and between sides in the same individual, regarding size (aeration) and bony septations. Total paranasal sinus agenesis is very rare . Isolated frontal sinus agenesis, on the other hand, is common.