The Biopathology of Secretory Otitis Media

Abstract

Recent investigations have identified the viscous middle ear effusions in secretory otitis media as being of the same nature as true mucus — the “backbone” of which is glycoproteins. The source of the mucus are mucus producing cells found in the normal middle ear lining and producing excessive amounts of mucus in pathological states. The nature of the pathological state which leads to excessive mucus production is an inflammation associated with deficient ventilation of the middle ear. Ventilation deficiency of the middle ear is a pathophysiological phenomenon which is not associated with hermetic blockage of the Eustachian tube. The “ex-vacuo” theory which assumes the tube to be blocked — the effusion to be a proteinous transudate and the middle ear devoid of mucus secreting elements, is no more tenable. Middle ear effusions can be approached by looking at them as questions of: 1) mucus clearance; 2) excessive mucus production; 3) middle ear ventilation and 4) etiology of middle ear inflammation. Clearance of mucus from the middle ear is governed by the mucociliary system, where the number of cilia and specificity of mucus are known today to be critical for clearance. Excessive amounts of mucus are secondary in the middle ear, as in all other mucosa in the body, to a metaplastic process. Mucosal stem cells can differentiate into mucus cells, ciliated cells, and keratin producing cells. In the presence of inflammation, especially when oxygen tension is low (and CO₂ tension is high) mucosal stem cells differentiate into numerous mucus producing cells which have been shown, in the middle ear, to be responsible for the excessive mucus production. The nature of the mechanism of middle ear ventilation in health and disease is not yet known, though it is in all probability related to the function of the Eustachian tube muscles.