paranasal sinus

The paranasal sinuses are air-filled cavities within the bones of the skull that are connected to the nasal cavity. There are four sinuses on each side of the nose: the frontal sinuses above the eye sockets, the maxillary sinuses in the cheekbones, the ethmoidal sinuses between the nasal cavity and eye sockets, and the sphenoidal sinuses located at the base of the skull behind the nose.1

These sinuses are lined with a mucous membrane that produces mucus. This mucus is moved by cilia towards the nasal cavity, where it is either swallowed or expelled. The sinuses are absent or small at birth and grow significantly until puberty. Their exact functions are not fully understood, but theories suggest they may play a role in olfaction, phonation, conserving heat, and lightening the skull. The most common issue affecting the paranasal sinuses is infection, known as sinusitis.1