Cerebral abscess: fungal

There is a single ring-enhancing lesion centered on the left occipital lobe, which has a maximum diameter of 13 mm. There is considerable surrounding edema within the left occipital and parietal lobes, resulting in effacement of the sulci. There is no midline shift and no effacement of the left lateral ventricle.

No other parenchymal lesions are identified. The brainstem and posterior fossa have normal appearances. The ventricular system is unremarkable and the basal cisterns remain patent. The cranial vault and skull base are unremarkable.

CONCLUSION:

13 mm left occipital ring-enhancing lesion, with significant surrounding cerebral edema. 

This most likely represents a neoplastic lesion (either primary or secondary) although the differential diagnosis includes an infective lesion.

A large area of vasogenic edema within the left occipital lobe surrounds an irregularly rounded lesion of intermediate signal intensity, measuring approximately 17 mm in diameter. T2-weighted scans indicate that the central lesion has a rim of reduced magnetic susceptibility within it, in the center of which diffusion is markedly restricted. Contrast enhancement is vivid with some loculation and several "fingers" of enhancement extending into the adjacent tissue. Relative cerebral blood volume (CBV) is increased in the peripheral enhancing portion of the lesion. Spectroscopic imaging shows large lactate/lipid peaks indicative of necrosis. Choline peaks are not prominent. Elsewhere, scattered foci of white matter abnormal signal probably indicate chronic small vessel ischemic disease. A small lateral occipital cortical signal abnormality may represent an old cortical infarct. Magnetic susceptibility effect from coils noted in relation to the terminal portion of the right internal carotid artery with the suggestion of residual aneurysmal cavity.

Conclusion:

The vivid contrast enhancement, extensive edema, restricted diffusion and slightly elevated relative cerebral blood volume (CBV) are most in keeping with a malignant tumor. Glioblastoma multiforme and metastasis could both produce such an appearance. The restricted diffusion and lack of prominent choline peaks means abscess cannot be entirely discarded as the diagnosis, despite the relative thickness of the enhancing walls, which can be a feature of atypical organisms in immunocompromised patients.

MACROSCOPIC DESCRIPTION:

One piece of pale tan soft tissue 14x10x8mm. Sectioning reveals a cavity 5x4x3mm.

MICROSCOPIC DESCRIPTION:

1. Sections show inflamed granulation tissue in which there are numerous PAS and Methenamine Silver (Grocott) positive fungal spores and acutely branching septate hyphae. Fragments of necrotic inflammatopry debris are also included. No evidence of  tumor is seen. 

2.  The sections show an abscess containing necrotic iflammatory debris. The abscess wall is composed of inflamed granulation tissue which, in turn, is surrounded by a mantle of edematous white matter showing reactive astrocytic gliosis. Scattered PAS and Methenamine Silver positive fungal hyphae and yeast forms are noted. No evidence of tumor is seen.

DIAGNOSIS: 

 Fungal abscess/Mycetoma with morphological features favoring  Aspergillus spp.