Cerebral abscess: fungal

Case contributed by RMH Neuropathology

Presentation

Occipital headache blurred vision and unsteady gait. PMHx: heavy smoker; previous PCOM aneurysm coil; immunosuppressed (steroids and methotrexate for RA(?) )

Patient Data

Age: 60 years
Gender: Female
Modality: CT

There is a single ring-enhancing lesion centred on the left occipital lobe, which has a maximum diameter of 13 mm. There is considerable surrounding oedema 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 oedema. 

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

MRI brain

Modality: MRI

A large area of vasogenic oedema 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 centre 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 ischaemic 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 oedema, restricted diffusion and slightly elevated relative cerebral blood volume (CBV) are most in keeping with a malignant tumour. 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.

Modality: Pathology

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  tumour 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 oedematous white matter showing reactive astrocytic gliosis. Scattered PAS and Methenamine Silver positive fungal hyphae and yeast forms are noted. No evidence of tumour is seen.

DIAGNOSIS: 

 Fungal abscess/Mycetoma with morphological features favouring  Aspergillus spp.

Case Discussion

Case prepared by Dr Frank Gaillard (radiology) and Prof Michael Gonzales (pathology). 

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Case Information

rID: 25792
Case created: 8th Nov 2013
Last edited: 7th Sep 2015
Inclusion in quiz mode: Included

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