giovedì 26 marzo 2009

CNS fungal aspergillosis


T2 weighted intraparenchymal masses in the right temporal lobe and in the right superior frontal gyrus extending across the corpus callosum. There is ependymal enhancement of the right lateral ventricle. There is very minimal enhancement of the masses.

Differential diagnosis:
- CNS leukemia
- CNS aspergillosis
- CNS bacterial infection
- Metastasis
- Septic emboli

Diagnosis: CNS fungal aspergillosis

Key points

Aspergillosis is the 2nd most common fungal CNS infection in an immunocompromised host after cryptococcus.

Risk factors:
- Transplant recipients: renal >liver > heart.
- 1-4 months post transplant.
- Recent transplant rejection +/- retransplantation.
- Leukopenia.
- Associated with CMV infection.
- Reported nosocomial spread in some cases.
- Lung is commonest source then sinuses.


Best finding: Multiple lesions with infarction or hemorrhage in a random distribution due to the angioinvasive nature of the infection. Hemorrhage occurs in approximately 25% of lesions.
Low signal intensity is often seen in the periphery of the lesions on T2-weighted MR images. This finding corresponds at least partially to areas of hemorrhage.
Multiple ring enhancing lesions, although more commonly there is mild/vague enhancement.
Dural enhancement with enhancement in adjacent paranasal sinus.
Mycotic aneurysms may be seen on angiography.
Locations of involvement a felt to be secondary to predilection for the lenticulostriate and thalamoperforator vessels: basal ganglia and thalamus, corpus callosum. The corpus callosum is involved in relatively few other processes (e.g., high-grade astrocytoma, cerebral lymphoma, multiple sclerosis, and Marchiafava-Bignami disease). Metastasis and pyogenic abscess do not commonly involve the corpus callosum.

Differential diagnosis in the immunocompromised patient includes
- Lymphoma
- Metastatic disease
- Septic emboli
- Multiple infarcts

Lack of enhancement may suggest the diagnosis of aspergillosis, since most brain tumors enhance. A prospective diagnosis should be suggested in the setting of early infarction and hemorrhage in the brain of an immunocompromised patient, so that antifungal therapy may be instituted.
Definitive diagnosis obtained with biopsy. Neuropathology shows invasion of blood vessels causing hemorrhagic infarction usually subcortical Meningeal infection usually focal & adjacent to infected cerebral region Angular dichotomously branching septate hyphae infiltrates tissue in centrifugal pattern. Hyphae structure tend to be found on borders of large abscesses.

Prognosis is poor with approximately 35% complete or partial response, although improved from previously 90% mortality. Treatment with Amphotericin B iv (liposomal form avoids nephrotoxicity) +/- 5 fluorocytosine often combined with itraconazole.

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