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Fungal Infections

Last updated on Monday, April 20 2009 by gliageek

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Aspergillus species grow on decaying vegetation and grain products, and are ubiquitous in the environment. Infection typically occurs in immunocompromised, usually neurtropenic,  hosts. Aspergillus may also rarely produce brain abscesses and granulomas in individuals with a normal immune system. Abscesses are the result of hematogenous spread from pulmonary infection, contiguous spread from the sinuses, or direct inoculation due to trauma or surgery. CNS aspergillosis in the immunocompromised host usually presents with fever, confusion, and multifocal neurologic deficits. Common settings are neutropenia and organ transplantation. Aspergillus has a propensity to invade blood vessels, causing ischemic strokes and hemorrhages, as well as multiple abscesses. Pulmonary infiltrates are usually present, reflecting primary Aspergillus pulmonary infection. Diagnosis requires culture of pus from a brain abscess. Treatment involves draining of brain abscesses, and intravenous amphotericin B.

The rhinocerebral Syndrome is a progressive fungal infection of the sinuses, orbits, and brain usually caused by fungi of the order Zygomycetes. Infection begins in the sinuses, and is characterized by nasal congestion and discharge. Fungal hyphae then invade soft tissue and bone. There is often painless necrosis of the palate and nasal septum. Involvement of the orbit causes proptosis, ocular motility disturbance, and blindness. As with aspergillus, zygomycotic species are angioinvasive, often leading to thrombosis of the cavernous sinus and internal carotid artery. The syndrome is most common in diabetics (especially in ketoacidosis), neutropenic patients, organ transplant recipients, and those receiving chelation treatment for hemochromatosis (greater availability of iron speeds fungal growth). Imaging studies can confirm sinusitis, erosion of bone, and vascular involvement. Diagnosis is made by discovery fungal hyphae in necrotic tissue. Treatment involves debridement of infected tissue and intravenous amphotericin B.

Aspergillus (and Mucorales) fungi are angioinvasive. Thus, like toxoplasma, they cause brain damage by occluding cerebral blood vessels. Unlike toxoplasma, however, these fungi cause vascular rupture, with hemorrhagic transformation of the coagulative parenchymal necrosis. While these organisms are large enough to be seen with routine stains, silver (GMS) or PAS stains highlight their morphology, aiding identification.