September 2020
A 54-year-old farmer on extracorporeal membrane oxygenation for respiratory failure; background of ANCA-positive vasculitis on long-term therapy; new symptom of increasing confusion
Ruptured Fusiform Mycotic Basilar Artery Aneurysm
- Case Discussion:
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This case illustrates the temporal evolution of severe intracranial dissemination of Scedosporium apiospermum infection.
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Widespread intraparenchymal abscess formation accompanied by intracranial infective/inflammatory arteritis with development of both proximal (basilar) and peripheral (left parietal) mycotic aneurysms
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Evidence of subsequent rupture with basal cistern and convexity subarachnoid blood
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Basilar perforator ischemia (diffuse brain stem low attenuation) due to dissecting mycotic basilar aneurysm resulted in brain stem death.
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The presence of hemorrhages in a septic patient should prompt the reader to suspect fungal infection and perform angiographic imaging. Early luminal irregularity should prompt careful monitoring for mycotic aneurysm development.
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- Background:
- S. apiospermum is a filamentous fungus found worldwide in contaminated soil, sewage, and polluted waters.
- Disseminated infection enters the CNS by hematogenous spread (often from the lungs), direct inoculation from penetrating trauma, or local extension from the sinuses.
- Proposed pathologic mechanisms of mycotic aneurysm formation include embolic occlusion of the vasa vasorum, direct invasion from the lumen or from adjacent structures, and vascular injury from deposition of immune complexes.
- Clinical Presentation:
- Headache, altered mental status, seizures, vomiting, focal neurologic deficit, fever
- The mortality rate in S. apiospermum CNS infection is high and invariably fatal in the context of mycotic aneurysms.
- This case occurred in the setting of long-term steroid/immunosuppression for ANCA vasculitis and occupational exposure from soil.
- Key Diagnostic Features:
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Fungal cerebral abscesses characteristically have thick irregular/crenulated enhancing walls with T2-hypointense rims. Nonenhancing intracavity projections from the wall are highly specific. Restricted diffusion is often present in the wall and intracavity projections, but the cavity can contain central restricted or free diffusion (the latter has been attributed to coagulative necrosis). Mycotic aneurysms, if present, are often fusiform in shape, involve long segments of the vascular wall, and are within the proximal arteries of the circle of Willis.
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Other CNS manifestations include meningitis, empyema, cerebritis, venous sinus thrombosis, ventriculitis, and infarction.
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- Differential Diagnoses
- Pyogenic bacterial abscesses: These tend to have thin smooth enhancing walls and central low ADC values. Intracavity projections are not a feature. They often cause distal rather than proximal aneurysms.
- High-grade glioma/cerebral metastases: These often have thick irregular walls and central higher ADC values. Spectroscopy in fungal disease is less likely to show high choline and high lipid peaks, although both pathologies can have decreased NAA and high lactate. Mycotic aneurysms are unlikely in neoplastic processes.
- Treatment:
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Surgical evacuation of the abscesses is performed for treatment and to obtain a specimen for culture.
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Surgical or endovascular treatment of intracranial mycotic aneurysms is extremely difficult due to the friability of the affected vascular wall, their fusiform shape, longitudinal extent, and proximal locations.
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S. apiospermum is often resistant to conventional antifungal agents including amphotericin B. Voriconazole may be favorable.
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