Fungal sinusitis cases can be classified into three main categories: Allergic Fungal Sinusitis, Fungus ball, and Invasive form. Invasive Fungal Sinusitis is further subdivided into three categories: Acute/fulminant, Chronic, and Granulomatous. Dematiaceous fungi are common causes of both Chronic Invasive Sinusitis and Allergic Fungal Sinusitis(AFS). They are also may cause sinus fungus balls.

Allergic Fungal Sinusitis

It is estimated to cause approximately 7% of chronic sinusitis cases for which surgery is required. Diagnosis requires operative specimens to be processed appropriately for histologic examination and fungal culture. Historical and laboratory evidence of type I hypersensitivity is suggestive of this diagnosis. Histopathologic examination is particularly important, because it allows for the fungal cause to be established and is the basis for distinguishing AFS from Chronic Fungal Sinusitis. AFS is characterized by the presence of Allergic mucin and by the absence of tissue invasion. The most commonly implicated Dematiaceous organisms include: Bipolaris, Curvularia, Exserohilum, Alternaria, and Cladosporium species.

Chronic Fungal Sinusitis

The same organisms that have been implicated in AFS can also cause a slowly progressive but invasive form of sinusitis. The diagnostic approach is similar to that for AFS. The presence of fungal elements in the mucosal tissue or bone by definition indicate invasive chronic sinusitis, and rules out AFS.

Sinus Fungus Balls

Histopathologic findings reveal densely packed hyphae adjacent to the mucosa, but there is no invasion of mucosa, vessels, or bone. Allergic mucin is not seen.