Allergic fungal sinusitis

Allergic fungal sinusitis (AFS) is the most common form of fungal sinusitis and is common in warm, humid climates.

Epidemiology

AFS accounts for 5-10% of chronic hypertrophic sinus disease going to surgery and. It is seen in youngeryoung immunocompetent patients at 3^rd decade (mean age ranges aroundrange 23-42 years). In children, M:F ratio = 2:1 and in adults, M:F ratio = 1:1.4.

Clinical presentation

Patients may present with chronic headaches, nasal congestion, chronic sinusitis for years, and past sinus surgery.

Pathology

AFS is an allergic reaction to aerosolized environmental fungi (type 1, IgE-mediated hypersensitivity reaction). Expansion and even erosion (20%) of the sinuses are characteristic. 

Commonly implicated fungi are ¹:

• dematiaceous (pigmented) fungi: Bipolaris, Curvularia, Alternaria
• hyaline molds: Aspergillus, Fusarium

Distribution

AFS usually involves multiple sinuses, and can be unilateral or bilateral (the latter is commoner). There is a frequentfrequently a nasal component. The ethmoid sinus is the most common location, followed by the maxillary, frontal, and sphenoid sinuses. 

Associations

• asthma is associated in in 65% of cases

Radiographic features

CT

The majority sinus showsof sinuses show near complete opacification. On unenhanced CT, the sinuses are typically opacified by centrally (often serpiginous ⁷) hyperdense material with a peripheral rim of hypodense mucosa. 

Approximately 40% of patients may have each of the following features ⁴:

• expansion of an involved sinus
• remodeling and thinning of the bony sinus walls
• erosion of the sinus wall

MRI

Hypointensity on T1WI and T2WI is the most common finding. It can have multiple T1 appearances. Low T2 signal or signal void is due to high concentration of various metals such as iron, magnesium and manganese concentrated by fungal organisms as well as high protein and low free water content in allergic mucin. 

• T1: hypointense inflamed mucosal thickness 
• T2: hyperintense inflamed mucosal thickness 
• T1 C+ (Gd): 
  • an inflamed mucosal lining has contrast enhancement 
  • no enhancement in the centre or majority of the sinus contents (c.f. neoplasms)

Treatment and prognosis

AFS is usually treated by local excision and steroid therapy. Antifungal therapy is also attempted in some cases, but results of this treatment are equivocal. Recurrence after surgery is not uncommon; however, the inclusion of steroid therapy significantly reduces relapse.