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Fungal Sinusitis

Summary

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  • Fungal sinusitis is an infection of the paranasal sinuses caused by various fungal species
  • Clinical presentation ranges from indolent to rapidly progressive, depending on the type and host immune status
  • Imaging findings vary but often include sinus opacification and characteristic hyperdense foci on CT1

Pathophysiology

  • Two main categories: non-invasive and invasive forms
    • Non-invasive:
    • Fungal ball (mycetoma)
    • Allergic fungal sinusitis (AFS)
    • Invasive:
    • Acute invasive fungal sinusitis
    • Chronic invasive fungal sinusitis
    • Granulomatous invasive fungal sinusitis
  • Common causative fungi:
    • Aspergillus species
    • Mucorales (e.g., Rhizopus, Mucor)
    • Dematiaceous fungi (e.g., Bipolaris, Curvularia)

Demographics

  • Non-invasive forms:
    • Fungal ball: more common in older adults, female predominance
    • AFS: typically affects younger adults, history of atopy
  • Invasive forms:
    • Acute: immunocompromised patients (e.g., diabetics, transplant recipients)
    • Chronic: immunocompetent individuals in endemic areas (e.g., Sudan, India)
    • Granulomatous: immunocompetent individuals in tropical and subtropical regions

Diagnosis

  • Clinical presentation:
    • Non-invasive: chronic sinusitis symptoms, nasal polyps (in AFS)
    • Invasive: fever, facial pain, orbital symptoms, neurological deficits
  • Laboratory findings:
    • Elevated serum IgE and eosinophilia in AFS
    • Fungal cultures and histopathology
  • Endoscopic examination:
    • Visualisation of fungal debris or characteristic mucin

Imaging

  • CT findings:
    • Fungal ball:
    • Focal hyperdense material within an opacified sinus
    • Calcifications or metallic densities
    • AFS:
    • Expansile sinus opacification with hyperdense mucin
    • "Double density" sign
    • Bone remodelling and thinning
    • Invasive forms:
    • Aggressive bone destruction
    • Soft tissue invasion
    • Orbital and intracranial extension
  • MRI findings:
    • Fungal ball:
    • T1 and T2 hypointense signal
    • Peripheral enhancement
    • AFS:
    • Characteristically very low (even signal-void) T2 central mucin with a T2-hyperintense peripheral mucosal rim
    • Invasive forms:
    • Variable signal intensity
    • Enhancement of invaded tissues
    • Restricted diffusion in acute invasive fungal sinusitis

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  • A 50-year-old immunocompetent patient presented with right sided proptosis and headache.
  • CT showed hyperostosis secondary to chronic sinusitis.
  • MRI showed enhancing material filling the maxillary sinuses with regions of diffusion restriction.
  • There was intracranial extension of T2-hypointense disease along the dura of the right middle cranial fossa and intraorbital extension.
  • 2 weeks after admission and some clinical response to anti-fungal treatment, the patient developed a left visual field defect and left sided numbness. CTA and DWI showed a right PCA infarct due to an occlusion distal to a mycotic aneurysm.

Treatment

  • Non-invasive disease: surgical removal ± steroids
  • Acute invasive disease is an emergency: urgent debridement, systemic antifungals and reversal of immunosuppression

Differential diagnosis

Differential Diagnosis Differentiating Feature
Nasal Polyps Smooth polypoid mucosal thickening without bone destruction or hyperdense fungal debris
Sinonasal Malignancy Aggressive bone destruction and soft tissue mass with enhancement and diffusion restriction
Mucormycosis Rapid progression with orbital/intracranial extension and devascularised "black turbinate" sign
Aspergilloma Single sinus expansion with hyperdense concretions on CT and markedly low T2 signal
Inverted papilloma Unilateral sinonasal mass with cerebriform T2 pattern and focal hyperostosis at stalk

  1. Raz et al. Fungal Sinusitis. 2015. Neuroimaging clinics of North America - Open in new tab. ↩