Allergic fungal sinusitis is considered to be the most common form of fungal sinusitis. Accurate diagnosis is important because treatment of allergic fungal sinusitis is substantially different from treatment of other types of fungal sinusitis. Mukherji and associates examined computed tomographic (CT) findings in patients with surgically proven allergic fungal sinusitis to further characterize the clinical features of this disease.

The diagnosis of allergic fungal sinusitis in these patients was based on accepted criteria. All of the patients had the characteristic endoscopic finding of allergic mucin and fungal hyphae identified by light microscopy. The presence of allergic mucin, primarily composed of eosinophils, is considered to be highly suggestive of the diagnosis. Of the 45 patients included in the study, 27 were male. Thirty-one patients lived in warm, humid climates, and 14 lived in drier climates. The presenting clinical complaints were nonspecific and consisted of symptoms of chronic sinusitis. Six of the patients had proptosis secondary to extension into the retrobulbar region.

Unenhanced CT scans in each patient revealed increased intrasinus attenuation within the mucosal opacification. Mucosal thickening was visualized in any of the sinuses, but the ethmoid sinus complex was the most commonly involved sinus. At least one ethmoid sinus complex demonstrated infection in 43 (96 percent) of the patients. The next most commonly involved region was the maxillary sinus, which harbored infection in 42 patients (93 percent). Only two patients had disease limited to one sinus.

Unilateral involvement was present in 22 patients (49 percent); the right side was affected in 15 of these patients and the left side in the remaining seven patients. Complete opacification of at least one sinus was found in 44 (98 percent) of the patients. Of these 44 patients, 41 (93 percent) had erosion of a sinus wall. Nine patients (20 percent) had evidence of disease extending into adjacent structures. Each of these nine patients had bony erosion, and three had both intraorbital and intracranial disease extension.

The authors conclude that the CT findings suggestive of a diagnosis of allergic fungal sinusitis included complete unilateral or bilateral opacification of multiple paranasal sinuses, extension beyond the sinus and erosion of a wall of the involved sinus and scattered areas of high attenuation amid mucosal thickening. Bilateral sinus involvement is common in patients with advanced disease. The authors note that the degree of bony erosion and extension beyond a sinus may mimic aggressive sinonasal neoplasms. The presence of increased internal attenuation on unenhanced CT scans may help to distinguish allergic fungal sinusitis from an invasive tumor. The presence of expansion and thinning of the sinus walls may help separate allergic fungal sinusitis from chronic sinusitis of other origins.