General Medical Information

Fungal Sinusitis

Barbara A. Zeifer

Fungal sinusitis can be categorized into four distinct entities based on the status of the host immune system—invasive fungal sinusitis in an immunosuppressed patient, chronic indolent sinusitis or mycetoma in a patient with normal immune function, and allergic fungal sinusitis in a patient with heightened immune function or atopy. Invasive sinusitis associated with mucormycosis or aspergillosis is an acute, fulminant, destructive disease marked by vascular invasion and necrosis. The patient has nonspecific opacification of the sinus cavities early in the disease and later has bony destruction. Orbital, cavernous sinus, and intracranial extension frequently complicates this disease. Some patients with diabetes have chronic invasive mucormycosis. These patients have a prolonged disease course that responds to surgical débridement and antifungal medication. Imaging studies reflect slowly progressive destruction with eventual formation of a single wide sinonasal cavity.

Chronic indolent fungal sinusitis is rare in the United States. It is a slowly progressive, tissue-invasive infection, typically unilateral and not responsive to antibiotics. Fluid collections are rare in all forms of fungal disease and when present suggest bacterial infection. Mycetoma is a noninvasive fungal ball. It causes complete or near-complete opacification of a sinus cavity and can be associated with thickening of the sinus walls. Mycetoma usually is hyperdense on CT scans and contains calcifications in 25% of cases. Mycetoma is markedly hypointense at MRI regardless of the sequence used to acquire the images.

Allergic fungal sinusitis, a hypersensitivity reaction to fungal antigens, typically occurs among patients with atopy and nasal polyposis. Allergic fungal sinusitis can involve one or many sinus cavities. On CT scans, the involved sinus contains a peripheral rim of low density, edematous mucosa and complete opacification of the central cavity by homogeneous high-attenuation material corresponding to thick allergic mucin. There are often scattered flecks of calcific material. The sinus walls can be surprisingly expanded and destroyed. The high-attenuation contents of a scan that is not contrast enhanced enable the radiologist to exclude neoplasia. On T2-weighted MR images, mucin is extremely hypointense, mimicking an aerated sinus cavity.