Ethmoiditis refers to inflammation of the ethmoid sinuses.
Within the facial skeleton are mucus-lined, air-filled cavities called paranasal sinuses. These are formed by the facial bones around the nose. There are 4 pairs of paranasal sinuses, including the ethmoid sinuses. These are honeycomb-like spaces between the eye sockets and nasal cavity. Each space is about the size of a matchbox. They contain small openings that drain into the nose. When the mucous membrane of the sinus becomes inflamed, it starts to swell. This leads to nasal blockage and mucus buildup.
The most common cause of ethmoiditis is an upper respiratory infection. Invading viruses attack the lining of the nose and sinuses. Other causes include allergies, structural abnormalities, and long-term bacterial infections. Fungal infections can occur in a person with a weak immune system.