Mucoceles of the paranasal sinuses

Mucoceles are chronic, cystic lesions in the paranasal sinuses. The contents of the mucocele are sterile, and the lesion is known as mucopyocele if it gets infected.

They are the result of obstruction of the sinus ostium, causing the accumulation of secretions into an expanding mass, which lead to remodeling, and erosion of bone, changing the bony architecture.

The symptoms can be facial deformity, abnormal protrusion of the eyeball (proptosis) or abnormal retraction of the eyeball into the socket (enophthalmos), loss of vision or double vision (diplopia). They may also be non-specific, such as facial pain, headache or nasal obstruction.

Lesions include sinonasal polyps and mucous retention cysts. Polyps are inflammatory swelling of the sinonasal mucosa. Mucus retention cyst is a mucinous gland whose duct has become obstructed, causing the accumulation of mucus in the gland.

A mucocele develops when the drainage of a sinus is compromised. The sinus fills with mucus and as more mucus accumulates, the sinus may expand from the pressure. Sinus walls may be remodeled or completely de-ossified and eroded.

Mucoceles can affect any age group, and very often, over a year will elapse between a presumed initiating event and development of a subsequent symptomatic mucocele.

Mucoceles can resemble other expansile processes of the paranasal sinuses, such as neoplasia (new and abnormal growth or formation of tissue) or nasal polyposis.

Ninety percent of mucoceles involve the frontal or the ethmoid sinuses, with the majority being in the frontal sinus.

In a CT, the distinction between a mucocele and a mucous retention cyst can be made on the basis of the presence of air outlining the upper surface of the mass. The distinction becomes less important when the lesion is large, as the treatment is similar for such a large mucous retention cyst as it is for a mucocele.

Mucoceles may extend into adjacent structures by herniation. They may herniate internally, staying within the confines of their sinus of origin or they may herniate externally, extending outside of the sinus into surrounding structures such as the orbit or cranial cavity.

Histopathologic features of the mucoceles are similar in many respects to the appearance of non-specific sinusitis, mucus retention cysts and nasal polyposis.

In recent years, advances in endoscopic sinus surgery have lead to an acceptance of simple drainage procedures, even for some seemingly very complicated mucoceles.