Fungal Sinusitis

Allergic Fungal Sinusitis

Overview:
-Most common form of fungal sinusitis
-Particularly common in warm, humid climates such as the southern United States
-Represents a non-infectious, inflammatory process whereby certain inhaled fungal
organisms incite a hypersensitivity reaction
-The inflammatory response is characterized by the accumulation of "allergic mucin"
within the paranasal sinuses. This mucin contains eosinophils, Charcot-Leyden
crystals, and hyphae. The surrounding mucosal tissue contains inflammatory cells but
no hyphae
-Common causative fungi include Alternaria, Aspergillus, Bipolaris, Curvularia,
Fusarium, and Pseudallescheria

Clinical Presentation:

-Tends to be a disease of younger individuals with age ranging from the third to fifth
decades
-Afflicted individuals are immunocompetent
-Involves a type I hypersensitivity reaction
-Frequently associated with a history of atopy including allergic rhinitis and asthma
-Patients complain of chronic headaches, nasal congestion, and chronic sinusitis
-There is often a history of chronic sinusitis and prior sinus surgery.

Imaging:

-There is involvement of multiple sinuses
-Non-contrast CT demonstrates hyperdense allergic mucin within the lumen of the
paranasal sinus which does not enhance in post-contrast studies
-Allergic mucin is usually hyperintense on T1 WI (MRI) with an associated characteristic
signal void on T2 WI
-T2 signal void is attributed to a high concentration of various metals such as iron, mag-
nesium, and manganese concentrated by the fungal organisms. The signal void is also
attributed to the high protein and low free-water content of the allergic mucin
-Inflamed mucosal lining is relatively hypointense on T1 WI, hyperintense on T2 WI, and
demonstrates enhancement upon administration of intravenous gadolinium
-Impacted sinus may resemble a mucocele with expansion and smooth erosion of the
bony walls of the paranasal sinus
-Although not considered invasive, if left untreated the process can erode through the
sinus walls with subsequent nasal, intraorbital, or intracranial extension

Treatment and Prognosis:

-Surgical extirpation of the allergic mucin and restoration of normal sinus drainage
-Frequent postoperative recurrence
-Recurrence is minimized by long term use of topical nasal steroids for suppression of
the abnormal immune response
-Daily sinus lavage to prevent accumulation of mucin
-Local or systemic antifungal medication is not required












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		Allergic Fungal Sinusitis Overview: -Most common form of fungal sinusitis -Particularly common in warm, humid climates such as the southern United States -Represents a non-infectious, inflammatory process whereby certain inhaled fungal organisms incite a hypersensitivity reaction -The inflammatory response is characterized by the accumulation of "allergic mucin" within the paranasal sinuses. This mucin contains eosinophils, Charcot-Leyden crystals, and hyphae. The surrounding mucosal tissue contains inflammatory cells but no hyphae -Common causative fungi include Alternaria, Aspergillus, Bipolaris, Curvularia, Fusarium, and Pseudallescheria Clinical Presentation: -Tends to be a disease of younger individuals with age ranging from the third to fifth decades -Afflicted individuals are immunocompetent -Involves a type I hypersensitivity reaction -Frequently associated with a history of atopy including allergic rhinitis and asthma -Patients complain of chronic headaches, nasal congestion, and chronic sinusitis -There is often a history of chronic sinusitis and prior sinus surgery. Imaging: -There is involvement of multiple sinuses -Non-contrast CT demonstrates hyperdense allergic mucin within the lumen of the paranasal sinus which does not enhance in post-contrast studies -Allergic mucin is usually hyperintense on T1 WI (MRI) with an associated characteristic signal void on T2 WI -T2 signal void is attributed to a high concentration of various metals such as iron, mag- nesium, and manganese concentrated by the fungal organisms. The signal void is also attributed to the high protein and low free-water content of the allergic mucin -Inflamed mucosal lining is relatively hypointense on T1 WI, hyperintense on T2 WI, and demonstrates enhancement upon administration of intravenous gadolinium -Impacted sinus may resemble a mucocele with expansion and smooth erosion of the bony walls of the paranasal sinus -Although not considered invasive, if left untreated the process can erode through the sinus walls with subsequent nasal, intraorbital, or intracranial extension Treatment and Prognosis: -Surgical extirpation of the allergic mucin and restoration of normal sinus drainage -Frequent postoperative recurrence -Recurrence is minimized by long term use of topical nasal steroids for suppression of the abnormal immune response -Daily sinus lavage to prevent accumulation of mucin -Local or systemic antifungal medication is not required