How is fungal sinusitis classified?

Fungal Sinusitis Classification

Fungal sinusitis is classified into two major categories: invasive and non-invasive forms, with distinct subtypes in each category based on pathophysiology, clinical presentation, and treatment approaches. 1

Primary Classification

1. Invasive Fungal Sinusitis

Invasive fungal sinusitis is defined by the presence of fungal hyphae within the mucosal tissue, submucosa, blood vessels, or bone of the paranasal sinuses 1. This category includes:

• Acute Invasive Fungal Sinusitis

  • Rapidly progressive (less than 4 weeks)
  • Primarily affects immunocompromised patients
  • Most lethal form with mortality rates of 50-80% 1
  • Common pathogens: Zygomycetes (Rhizopus, Mucor, Rhizomucor) and Aspergillus species 1
  • Characterized by angioinvasion causing thrombosis and tissue necrosis 1
  • Clinical presentation: facial pain, swelling, nasal obstruction, fever, and potentially facial numbness, ophthalmoplegia, and cerebral involvement 1

• Chronic Invasive Fungal Sinusitis

  • Slower progression (greater than 4 weeks)
  • Affects immunocompromised patients, though less severely than acute form 1
  • Similar pathophysiology to acute form but with slower progression

• Chronic Granulomatous Invasive Fungal Sinusitis

  • Low-grade submucosal granulomatous inflammation with diffuse fibrosis
  • Limited fungal elements
  • Can occur in immunocompetent hosts, particularly reported in India 1
  • More prevalent in older patients 1

2. Non-Invasive Fungal Sinusitis

Non-invasive forms show absence of fungal hyphae within the mucosal tissue 2:

• Allergic Fungal Sinusitis

  • Occurs in immunocompetent patients with atopic disease
  • Often presents with nasal polyps and chronic nasal congestion 1
  • Characterized by "peanut butter-like" mucin containing fungal elements 1
  • Immunologically mediated reaction to fungal spores
  • Common pathogens: Bipolaris, Curvularia, Aspergillus, and Dreschlera species 1
  • More aggressive in children with increased fungal load and higher incidence of proptosis 1

• Fungus Ball (Fungal Mycetoma)

  • Typically unilateral, often affecting maxillary or sphenoid sinuses 1
  • Chronic symptoms
  • No tissue invasion
  • Most commonly caused by Aspergillus species 3
  • Treatment primarily involves surgical removal 4

Diagnostic Criteria

The two most important diagnostic criteria for invasive fungal disease are 1:

1. Rhinosinusitis confirmed by radiological imaging (may show tissue destruction)
2. Histopathological evidence of hyphal forms within sinus mucosa, submucosa, blood vessels, or bone

Risk Factors for Invasive Disease

• Diabetes (50% of cases)
• Hematologic malignancy (40% of cases)
• HIV/AIDS
• Iron overload
• Protein-energy malnutrition
• Transplant patients on azole prophylaxis 1

Treatment Approaches

• Acute Invasive Fungal Sinusitis: Requires prompt antifungal therapy and extensive surgical debridement 4
• Chronic Invasive Fungal Sinusitis: Combination of surgical debridement and antifungal agents 4
• Fungus Ball: Usually treated with surgical extirpation without need for antifungal therapy 4
• Allergic Fungal Sinusitis: Management typically involves surgical debridement combined with corticosteroid therapy rather than antifungal agents 4; complete surgical exenteration with mucosal preservation and steroid therapy is recommended 1

Clinical Pearls

• Endoscopic appearance of tissue necrosis is a hallmark sign of invasive disease 1
• Loss of contrast enhancement on MRI is more sensitive (86%) than CT (69%) in detecting invasive fungal disease 1
• Allergic fungal sinusitis is more common in the southern, southwestern, and western regions of the United States 1
• Serum analysis via PCR and/or galactomannan can be useful for diagnosing invasive aspergillosis 1
• When both PCR and galactomannan for aspergillus are negative, the negative predictive value is 100%; when both are positive, the positive predictive value is 88% 1

Pitfalls to Avoid

• Delayed diagnosis of invasive fungal sinusitis can lead to significant morbidity and mortality
• Allergic fungal sinusitis in children is less responsive to treatment with increased recurrence rates compared to adults 1
• Isolated sphenoid sinusitis, though rare in children (1-3% of sinonasal diseases), has high mortality if diagnosis is delayed 1
• Painless nasal septal necrosis is a classical presentation of acute invasive fungal sinusitis and requires immediate attention 1

Understanding the classification of fungal sinusitis is essential for appropriate diagnosis, management, and prognosis, as each subtype requires a different treatment approach.