Allergic fungal rhinosinusitis

Introduction:

In this condition the colonizing fungi elicits allergic mucosal inflammation without features of invasion. The protein components of fungi elicit IgE mediated allergic mucosal inflammation.

History / physical findings: Presentation of AFRS may range from dramatic to subtle. Dramatic features include: acute visual loss, gross facial dysmorphia or complete nasal obstruction.

Subtle features are more common and include:

1. gradual nasal airway obstruction – may be very gradual that the patient may even be unaware
2. presence of semisolid nasal crusts containing allergic fungal mucin
3. Pain is usually not present, if presence concomitant bacterial rhinosinusitis should be suspected

Physical findings include:

1. Signs of intranasal inflammation
2. Polyposis
3. Gross facial disfigurement
4. Orbital / ocular abnormalities

Diagnostic criteria:

Patients with AFRS demonstrate five characteristics:

1. Gross production of Eosinophilic mucin containing noninvasive fungal hyphae
2. Nasal polyposis
3. Radiological findings
4. Immunocompetence
5. Allergy to fungi

Radiologic features:

Slow accumulation of allergic fungal mucin provides unique characteristics to the disease. Usually allergic fungal mucin is sequestered within involved paranasal sinus cavities. Its accumulation leads to the classic radiologic findings seen in this disease.

1. Even though it is a bilateral condition, there is a certain degree of asymmetry seen in radiographs / CT
2. Bone erosion and extension of the disease into adjacent areas can be seen
3. Expansion, remodeling and thinning of sinus walls are commonly seen – this is due to the expansile nature of accumulating mucin
4. Heterogeneous areas of signal intensities within paranasal sinuses filled with allergic fungal mucin are frequently seen in CT scans – this is due to the accumulation of heavy metals (iron / manganese) and calcium salt precipitation within inspissated allergic fungal mucin.
5. Desiccation of sinus contents contributes to the hyper dense areas seen on CT scans

Coronal CT paranasal sinuses showing features of allergic fungal rhinosinusitis

MRI features: The high protein and low water concentration of allergic fungal mucin coupled with high water content within surrounding oedematous sinus mucosa gives rise to specific MRI characteristics.

T1 – Involved sinus cavities demonstrate varying signal intensities. There is enhancement of periphery of the involved sinuses due to mucosal Oedema

T2 – Hypo intensity of signal within involved sinuses – due to dehydrated state of mucin

Enhancement of periphery of the involved sinus due to mucosal oedema

Investigations:

Estimation of IgE – Total IgE values is elevated in AFRS. A value of more than 1000 IU/ml is an indicator of AFRS activity.

RAST / ELISA Test – Positive for bipolaris specific IgE and IgG antibodies. These patients show positive evidence of fungal allergy.

Histologic characteristics of fungal mucin:

The production of allergic mucin is pathognomonic of AFRS. Grossly allergic mucin is thick, tenacious and viscous in consistency. Its color may vary from brown to dark green. It is only the mucin rather than sinus mucosa that provides the relevant histological evidence necessary to make the diagnosis of AFRS. Examination of nasal mucosa / polypi shows evidence of chronic inflammation. Eosinophils are also seen in abundance. Pathologic examination of these tissues is done to establish that fungal invasion is not present.

Histology of allergic fungal mucin reveals the characteristic ranching non invasive fungal hyphae within sheets of eosinophils and Charcot – Layden crystals. Classically H&E stains accentuate the mucin and cellular components of allergic mucin but fail to stain the fungal hyphae. Silver stains are specifically used to stain fungal hyphae. Silver stains color fungi black / dark brown.

Fungal culture: These tests atmost provide supportive evidence. Diagnosis of AFRS is not based on positive fungal cultures from mucin.

Treatment: Still evolving. Previously it used to be radial surgery. Now a combination of conservative surgery in combination with adjunct medical therapy is becoming popular.

The goal of any surgical procedure is to eradicate all allergic mucin while providing permanent drainage and ventilation for the affected tissues.

Even in the best of hands the incidence of AFRS recidivism is very high when treated with surgery alone. Adjunctive medical therapy should also be tried to get over this problem. Fungal immunotherapy and immunomodulation is becoming popular these days.

Role of steroids is limited only to postpone the surgery.