What is the diagnostic approach and treatment for fungal sinusitis?

Diagnostic Approach to Fungal Sinusitis

MRI is the optimal imaging technique for diagnosing fungal sinusitis, particularly for suspected invasive forms, while CT scanning is essential for evaluating bony anatomy and preoperative planning. 1, 2

Classification of Fungal Sinusitis

Fungal sinusitis is categorized into two main types:

1. Invasive Fungal Sinusitis

   • Acute invasive
   • Chronic invasive
   • Granulomatous invasive

2. Non-invasive Fungal Sinusitis

   • Allergic fungal sinusitis
   • Fungus ball (mycetoma)

Diagnostic Algorithm

Step 1: Clinical Assessment

• Look for specific risk factors:
  • Immunocompromised status (especially for invasive forms)
  • History of nasal polyps
  • Persistent sinusitis unresponsive to antibiotics
  • Unilateral symptoms
• Key symptoms to evaluate:
  • Facial pain/pressure
  • Nasal congestion/obstruction
  • Purulent nasal discharge
  • Headache
  • Fever (in invasive forms)
  • Orbital symptoms (proptosis, visual changes)
  • Neurological symptoms (in invasive forms with CNS involvement)

Step 2: Nasal Endoscopy

• Perform nasal endoscopy to evaluate for:
  • Mucosal changes
  • Presence of fungal debris
  • Nasal polyps
  • Necrotic tissue (in invasive forms)
• Obtain specimens for:
  • Fungal culture
  • Histopathology 1

Step 3: Imaging Studies

CT Scanning

• Indications:
  • First-line imaging for suspected fungal sinusitis 2
  • Essential for evaluating bony anatomy
  • Preoperative planning for endoscopic surgery
  • Detecting bone erosion/destruction
• Key findings:
  • Hyperattenuation of sinus contents
  • Bone erosion (in invasive forms)
  • Nodular mucoperiosteal thickening
  • Dense intrasinus concretions (in fungal ball) 1

MRI with Contrast

• Indications:
  • Suspected fungal sinusitis (particularly invasive forms)
  • Differentiating between inflammatory disease and malignancy
  • Evaluating orbital or intracranial extension
  • Soft tissue evaluation 1, 2
• Key findings:
  • T2-weighted signal intensity is diagnostic:
    • High signal: bacterial/viral inflammation
    • Intermediate signal: neoplastic processes
    • Very low signal (similar to air): fungal concretions 1

Step 4: Laboratory Testing

• Nasal cytology to evaluate for:
  • Eosinophils (allergic fungal sinusitis)
  • Neutrophils (acute invasive forms)
• Histopathology of biopsy specimens to:
  • Confirm fungal invasion (in invasive forms)
  • Identify fungal elements
  • Rule out malignancy 1

Step 5: Biopsy

• CT-guided transcutaneous needle biopsies have high diagnostic yield when combined with:
  • Mycological examination
  • Molecular testing
  • Histopathological analysis 1
• Tissue should be obtained for:
  • Fungal culture
  • Histopathology
  • PCR testing (specimens should be diluted in isotonic saline) 1

Specific Diagnostic Features by Type

Acute Invasive Fungal Sinusitis

• Most common in immunocompromised patients
• Rapid progression with high mortality
• Imaging: bone destruction, vascular invasion, "black turbinate sign" on MRI
• Histopathology: fungal invasion of tissue and blood vessels 1, 3

Allergic Fungal Sinusitis

• Most common form of fungal sinusitis
• Patients are typically atopic but immunocompetent
• Often presents with nasal polyps
• CT: sinus mucosal hypertrophy with hyperattenuation of contents
• Histopathology: allergic mucin with fungal hyphae and eosinophilic inflammation 4

Fungus Ball (Mycetoma)

• Non-invasive fungal colonization
• Typically unilateral
• CT: focal hyperdense material within sinus
• MRI: signal void on T2-weighted images 5

Diagnostic Pitfalls and Caveats

1. Delayed diagnosis can lead to increased morbidity and mortality, especially in invasive forms. Early imaging is crucial even when symptoms are subtle 6.

2. Ultrasonography has poor sensitivity and specificity (39-61% and 42-53% respectively) and should be avoided except in pregnant women to avoid radiation exposure 1.

3. Standard radiographs have limited utility and may miss progressive lesions including bone erosion 1.

4. Timing of imaging is important - perform imaging more than 2 weeks after an upper respiratory tract infection and more than 4 weeks after acute bacterial sinusitis to avoid false positives 1.

5. Biopsy specimens should be obtained prior to antifungal therapy to isolate and identify causative organisms 7.

By following this diagnostic approach, clinicians can accurately diagnose fungal sinusitis, determine its type, and guide appropriate treatment, ultimately improving patient outcomes and reducing morbidity and mortality.