Acute invasive fungal sinusitis

Acute invasive fungal sinusitis is the most aggressive form of fungal sinusitis. It is seen particularly in immunocompromised patients and is the source of significant morbidity and mortality. It should be distinguished from the other two forms of invasive fungal sinusitis: chronic invasive fungal sinusitis and chronic granulomatous invasive sinusitis, which are discussed separately.

Epidemiology

Acute invasive fungal sinusitis is seen in patients who are immunocompromised, and thus the demographics will match those of the underlying immunosuppressing condition. Common causes of underlying immunosuppression include ^1-3: 

• diabetes mellitus: especially those with ketoacidosis
• neutropaenic patients
  • haematologic malignancies
  • solid organ transplants
  • bone marrow transplantation
  • chemotherapy-induced neutropaenia
• advanced AIDS

Clinical presentation

Clinical presentation is variable, but often dramatic with a rapid development of fever, facial pain, nasal congestion and epistaxis. Extension into the orbit, cavernous sinus or intracranial compartment is frequent resulting in deterioration in vision, proptosis and neurological deficits respectively ^1-2.

The disease progresses over a few days or at most a few weeks, and often results in vascular invasion and systemic dissemination ^2,5.

Pathology

Infection is believed to originate in the nasal cavity (most often the middle turbinate) with subsequent spread to the paranasal sinuses ³. Some fungal agents are implicated, including ^1-2:

• Aspergillus spp: typically neutropaenic patients
• Zygomycetes: usually in diabetic patients
  • Rhizopus spp
  • Mucor spp
  • Rhizomucor spp
  • Absidia spp

Radiographic features

CT

Unlike chronic invasive fungal sinusitis, acute infection generally does not demonstrate hyperdense material within the sinus on non-contrast CT. CT is particularly effective at assessing bony change. Findings include ²:

• mucosal thickening: hypoattenuating
• opacification of the sinus: soft tissue attenuation
• bone destruction
  • may be extensive
  • may be very subtle or inapparent (extension through intact bone via vascular invasion)
• stranding of fat on the outside of the sinus
  • intraorbital fat
  • masticator space
  • pterygopalatine fossa

Features of potential complications should also be sought (see below).

MRI

MRI is the modality of choice to assess soft tissue extension. The findings within the sinus itself are variable, and range from mucosal thickening, to complete opacification of the sinus.

• T1: intermediate low signal
• T2
  • fungal mass is of intermediate to low signal
  • often associated with fluid or blood elsewhere in the paranasal sinuses
• T1 C+ (Gd): absent sinus mucosal enhancement which suggests necrosis, when there is invasion outside the sinus there is increased enhancement

Particular attention should be paid to assessment of invasion beyond the sinuses. In some cases, a complication may be obvious (see below). Early invasion should be sought, and findings that are particularly important include ²: 

• stranding of the periantral fat (T1 and STIR or Fat Sat T2)
  • intraorbital fat
  • masticator space
  • pterygopalatine fossa
• subtle enhancement (T1 C+ Fat Sat)
• leptomeningeal enhancement
• intracranial granulomas: low on both T1 and T2

Treatment and prognosis

The key to successful management is early and aggressive medical and surgical treatment and correction of neutropaenia. Systemic antifungal (e.g. amphotericin B) should be administered and diabetic ketoacidosis or neutropaenia should be corrected. 

Aggressive surgical débridement is usually required.

Complications include ²:

• intraorbital extension
• intracranial extension
  • leptomeningeal enhancement
  • intracranial granulomas
  • epidural abscess and empyema
• vascular invasion
  • cavernous sinus thrombosis or dural venous sinus thrombosis
  • mycotic aneurysm formation
  • cerebral infarction or cerebral haemorrhage
  • systemic dissemination

Despite modern management, mortality remains high (50-80%), and is especially high in patients whose neutropenia cannot be corrected, and in general higher in diabetic patients (often due to later presentation) ^2-4. Reduced mortality has been reported in patients who are at risk and receive close active surveillance, down to as low as 18% ⁴.

Differential diagnosis

• chronic invasive fungal sinusitis
  • longer clinical history (usually more than 12 weeks) ⁵
  • hyperdense material within the sinus is more common
  • sclerotic changes in the bony walls of the affected sinuses representing chronicity of disease
• complicated acute sinusitis
  • Pott puffy tumour 
• sinonasal carcinoma
• sinonasal non-Hodgkin lymphoma
• mucocoele