Presentation
Headache, convulsions, left sided weakness and loss of consciousness since 10 days.
Patient Data
A right temporo-parietal fairly defined lobulated marginally enhancing cystic mass lesion is seen, it measures about 4.3 X 3.7 X 2.6 cm in its maximal TS, AP and cranio-caudal dimensions.
The core of the lesion shows T1 hypointense and T2 hyperintense signal intensity and demonstrating evident restricted diffusion with high DWI and low ADC / high exponential ADC signals. The margin of the lesion shows hyperintense T1 and hypointense T2 signal with intense post-contrast enhancement.
The lesion is surrounded by moderate vasogenic brain edema with compression of the right lateral ventricle and contra-lateral mid-line shift as well as mild dilatation of the 3rd ventricle with slight dilatation of the left lateral ventricle and mild periventricular T2/FLAIR hyperintensity. The lesion is effacing the related cortical sulci as well.
MR spectroscopy of the lesion shows:
- increased amino-acid peak (valine, leucine, and isoleucine) (0.9 ppm) and a small alanine peak (1.48 ppm) as well as increased acetate peak (1.92 ppm), and increased succinate peak (2.4 ppm). A small aspartate peak (2.6 ppm) is noted as well. All these metabolites are fairly specific for brain abscess
- mild to moderate elevation of the lipid/lactate peak (1.33 ppm); predominantly within the central necrotic portion of the lesion
- marked depression and almost total nullification of the neural markers: N-acetyl aspartate (NAA) (2.03ppm) and creatine (Cr) (3.02 ppm & 3.94 ppm)
- depression of the choline (Cho) peak (3.22 ppm)
Case Discussion
This case shows typical brain abscess with characteristic conventional MRI and MR spectroscopy criteria.
The main differential diagnosis of a brain abscess is cystic glioma (GBM) and cystic metastasis.
Although restricted diffusion is highly suggestive of brain abscess, cystic metastasis of squamous cell carcinoma and post-irradiation necrosis can show restricted diffusion.
The main MRS findings in brain tumors are :
- decreased NAA and decreased Cr as well as decreased NAA / Cr ratio. The degree of the neuronal markers, as well as the Myo-inositol reduction, correlates with the high grade of the brain tumor
- increased choline (Cho)
- increased lipid/lactate is noted in both tumors and abscess. BUT only abscess spectrum shows amino acids, acetate, aspartate, and succinate peaks
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