Chapter 30: Fungal Rhinosinusitis

Introduction

• With increased recognition over the past 30 years, fungal rhinosinusitis (FRS) represents a heterogeneous group of disorders whose manifestation depends on host immunologic function and fungus-specific factors.

• The first known case of fungal sinusitis by Plaignaud in 1791 reported a 22-year-old solider with maxillary pain and “fungal tumor.”

• Initial diagnostic focus on the causative organism led to widely used terms: “aspergillosis,” “mucormycosis,” or “zygomycosis.” Modern classification schema relies more on disease characteristics than fungal speciation.

• Detailed understanding of the mycology remains important in the diagnosis and treatment of FRS.

• Modern endoscopy and imaging modalities have allowed for the development of contemporary diagnostic criteria and targeted surgical treatment.

Classification

• FRS is best characterized as invasive or noninvasive—defined by the histopathological presence of fungal invasion into sinonasal soft tissue, more specifically angioinvasion.

• Three noninvasive forms of FRS

  1. Fungal ball

  2. Allergic fungal rhinosinusitis (AFRS)

  3. Saprophytic fungal infestation

• Three invasive forms of FRS

  1. Acute invasive fungal rhinosinusitis (AIFS)

  2. Chronic invasive fungal rhinosinusitis

  3. Granulomatous invasive fungal sinusitis

• Refinement of this classification will evolve with our understanding of the pathophysiologic role of fungi in rhinosinusitis.

Principles of Mycology

With millions of species, fungus is a large, ubiquitous eukaryotic group of organisms that are subclassified into yeasts and molds.

• Characteristics of molds:

  1. Mold is a type of fungus that grows and branches in multicellular filaments called hyphae. Mold colony comprises interwoven hyphae.

  2. Molds reproduce by producing spores, which can be sexual or asexual.

  3. Branching patterns (ie, 45 vs 90 degrees) and presence of septations (ie, septate, pauci-septate, or aseptate/coenocytic) of the hyphae are useful for further classification.

• Characteristics of yeasts:

  1. In contrast, yeasts are unicellular and round fungal organisms.

  2. They most commonly reproduce asexually by fission or budding and less commonly via sexual spores in unfavorable growth conditions.

  3. Multiple attached buds form a pseudohyphae, which appear structurally similar but are distinct from true hyphae.

• Both molds and yeasts have sexual or asexual reproductive cycles and may undergo sporulation. Fungal spores are ubiquitous in the environment and immunologically inert until their germination into yeast or hypha.

• Molds are responsible for most noninvasive and invasive forms of FRS and are further classified into septate, pauci-septate, or aseptate as well as dematiaceous or hyaline.

• Pauci-septate or aseptate molds—largely responsible for invasive disease

  1. Class Zygomycetes

     • Order Mucorales

       • – Genera Rhizopus, Mucor, Rhizomucor, Absidia, Cunninghamella

• Septate molds—largely responsible for noninvasive disease

  1. Dematiaceous molds (dark-colored)

     • Bipolaris, Curvularia, Penicillum, Alternaria, Cladosporium

  2. Hyaline molds (light-colored)

     • Aspergillus, Pseudallescheria, Fusarium

• “Mucormycosis” should not be used interchangeably as AIFS as other molds within the class Zygomycetes as well as Aspergillus are common etiologic organisms as well.

• Fungi are universally found within normal healthy human nose and paranasal sinuses, likely via inhalational spores.

• The pathogenicity of sinonasal fungus depends on the host’s immune system; in immunocompetent hosts, the relationship is most commonly commensal.

Noninvasive Fungal Sinusitis