Table 1.
Differential diagnosis of PML.
| CT | MRT | |
|---|---|---|
| PML | (i) Nonspecific hypodensities localized in the white matter | (i) Hypointense in T1 and hyperintense in T2, single lesion, round or oval, (majority of cases) lesion or multifocal white matter lesions (ii) Signal at DWI sequences depends on the age and activity of the lesion but is often restricted (iii) Abnormal fractional anisotropy values on DTI (iv) At MRS, lesions are characterized by an increased choline, elevated lactate, variable myoinositol, decrease of N-acetylaspartate, and increased choline/creatine ratio |
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| CNS lymphoma | (i) CT typically shows a high-density (70%) lesion in a central hemispheric location, which often reaches or crosses the midline (ii) Intense and homogeneous CE is the hallmark of primary CNS lymphoma |
(i) Lesion appears at MRI with intermediate-to-low signal intensity on T1-weighted images and either isointense or hypointense signal on T2-weighted images (ii) Diffusion is often restricted (iii) Elevated lipid peaks and high Cho/Cr ratios on MRS (iv) The intense homogeneous enhancement is the hallmark of primary CNS lymphoma |
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| Ischaemic infarct | (i) Usually CT demonstrates a low-density lesion occupying a vascular territory with some swelling | (i) Hyperintense on DWI scans and hypointense on ADC maps (ii) No signs on FLAIR in the first 6 h from onset, with areas of hyperintensity evolving thereafter (iii) Regions of brain tissue that are abnormally perfused on PWI (iv) NAA decrease and Lactate increase on MRS (v) Stenoses, occlusions, and dissections on MRA |
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| ADEM | (i) CT scan is relatively insensitive, but may show scattered low-density areas | (i) T2W and FLAIR images usually show multiple regions of hyperintensity at the gray-white junction, in the brainstem, cerebellum, and basal ganglia (ii) Solid or ring enhancement can be seen (iii) There can be variable diffusion restriction (iv) Spectroscopy can show low NAA |
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| EBV-induced encephalitis | (i) CT results may be negative (ii) Low-density parenchymal lesions (iii) Brain atrophy |
(i) MRI results may be negative (ii) Restricted diffusion on DWI (iii) Presence of an increase in myoinositol together with choline values on MRS |
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| Toxoplasmosis | (i) CT appearance of Toxoplasma encephalitis is not pathognomonic (ii) Ring enhancing may be present on contrast-enhanced CT |
(i) On T1-weighted MRI, the lesions are hypointense relative to brain tissue (ii) On T2-weighted MRI, foci of infections are usually hyperintense (iii) Ring enhancing may be present after Gd administration (iv) Active lesions are often surrounded by edema (v) Elevated lactate and lipid |
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| Early stage brain abscess | (i) Central low-density core (ii) Iso-hyperdense ring (iii) Peripheral low density (edema) (iv) Ring enhancement |
(i) T1: central low intensity, peripheral low intensity (vasogenic edema), ring enhancement after Gd administration (ii) T2/FLAIR: central high intensity, peripheral high intensity (vasogenic oedema) (iii) DWI/ADC: high DWI signal is usually present (iv) Elevation of succinate and acetate is relatively specific |
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| MS relapse | (i) Atrophy (ii) Periventricular or elsewhere white matter hypodensities |
(i) High signal on T2-weighted and FLAIR MRI sequences (ii) When actively inflamed, often enhanced with gadolinium contrast |
| (iii) Areas of abnormal enhancement | (iii) Position abutting ventricles (often perpendicular) (iv) Juxtacortical position (gray-white junction) (v) Involvement of brainstem, cerebellum, or corpus callosum (vi) Decrease in NAA and creatine, and increase of choline on MRS |
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