What is the pathophysiology of allergic fungal sinusitis (AFS)?

Updated: Mar 16, 2018
  • Author: John E McClay, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Currently, the pathophysiology of allergic fungal sinusitis (AFS) is postulated to be similar to that of allergic bronchopulmonary fungal disease (a term replacing bronchopulmonary aspergillosis). Manning and colleagues have suggested that several interrelated factors and events lead to the development and perpetuation of allergic fungal sinusitis (AFS). First, an atopic host is exposed to fungi, theoretically via normal nasal respiration, which provides the initial antigenic stimulus. An initial inflammatory response ensues as the result of both a Gell and Coombs type I (IgE-mediated) and type III (immune complex–mediated) reaction, causing subsequent tissue edema. The resulting obstruction of sinus ostia, which may be accentuated by anatomic factors such as septal deviation or turbinate hypertrophy, results in stasis within the sinuses. This creates an ideal environment for further proliferation of the fungus, thus increasing the antigenic exposure to which the host is allergic.

At some point, the cycle becomes self-perpetuating, resulting in the eventual product of this process, allergic mucin, the material that fills the involved sinuses of patients with allergic fungal sinusitis (AFS). Accumulation of this debris obstructs the involved sinuses and propagates the process.

The production of this allergic mucin and its eventual clinical, histologic, and radiographic characteristics are unique to allergic fungal sinusitis (AFS) and serve as a hallmark of the disease. Grossly, allergic fungal mucin is thick, tenacious, and highly viscous. Its color may vary from light tan to brown or dark green, as depicted in the images below. Its characteristic gross appearance has resulted in the use of such descriptive terms as peanut butter and axle grease when referring to allergic fungal mucin.

Left middle meatus with suctioning of thick allerg Left middle meatus with suctioning of thick allergic mucin from the ethmoid bulla in the center of the picture; the end of the suction is in the inferior portion of the picture.
The viscosity of a thick allergic mucin being suct The viscosity of a thick allergic mucin being suctioned from the nasal cavity and vestibule in a patient with allergic fungal sinusitis.

In a study of 74 patients, White et al indicated that in cases of allergic fungal sinusitis, younger patients and African Americans are more likely to suffer bony erosion, suggesting that these individuals have a more severe inflammatory response in the disease. [14]


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