Table 1

Basic MRI features of infectious and non-infectious adverse events during multiple sclerosis (MS) therapies

LocationShape/appearanceMRI sequences
JCV

PML
  • Juxtacortical WM, infiltrating adjacent GM

  • Extending in deep WM

  • Can start in cortical or deep GM

  • Infratentorial in 10%

  • Unifocal or multifocal, later diffuse/confluent

  • Spreading via WM tracts

  • Punctate lesions with perivascular distribution

  • Microcystic appearance on T2

  • Later: development of PML-IRIS: patchy/punctuate contrast enhancement lesion border and swelling

  • T2/FLAIR hyperintense

  • T1 isointense or hypointense (especially later as demyelinisation progresses)

  • Contrast enhancement in 30%

GCN
  • Cerebellum

  • Sometimes concomitant PML lesions (infratentorial and/or supratentorial)

  • Cerebellar atrophy

  • Sometimes ‘hot cross bun sign’

  • T1 and T2 shows atrophy

  • T2 and FLAIR show ‘hot cross bun sign’

  • T2 and FLAIR show PML lesions

Herpesviruses
HSE
  • Temporal lobe(s)/insular in 80%

  • Extratemporal in 55%: brainstem, cerebellum, cortical or a combination

  • Starting in cortex, spreading along limbic pathways

  • Later spreading parietal, occipital, brainstem

  • T2/FLAIR hyperintense and T1 hypointense

VZV
  • Meninges

  • Cortex/parenchyma

  • Spinal cord

  • Large and small intracranial vessels

  • or a combination of the above

  • Meningitis

  • Cortical/parenchymal lesions (encephalitis)

  • Myelitis

  • Irregularities and dilation (vasculopathy) of large vessels, and ischaemic lesions

  • Meningeal contrast enhancement

  • T2/FLAIR hyperintense cortex/parenchyma

  • MRA vasculopathy, DWI/ADC map ischemia

 Cryptococcus
  • Meninges

  • Parenchymal gelatinous pseudocysts

  • Parenchymal cryptococcomas in mesencephalon and basal ganglia

  • Meningitis in 69%

  • Dilated perivascular spaces

  • Hydrocephalus

  • Gelatinous pseudocysts: ‘soap bubble’ appearance

  • Single or multiple round cryptococcoma masses

  • Meningeal contrast enhancement

  • Cryptococcomas and pseudocysts T2 and FLAIR hyperintense and T1 hypointense

  • Cryptococcomas homogeneous or ring enhancement

 Listeriosis
  • Brainststem, cerebellum and/or thalamus

  • Subcortical abscesses in the thalamus, pons and medulla

  • Cerebritis

  • T2/FLAIR hyperintense

  • T1 hypointense or isointense

  • DWI hyperintense

  • ADC map hypointense

  • Ring enhancement and/or cranial nerve enhancement

 Nocardiosis
  • Brain parenchyma

  • Meninges

  • Parenchymal brain abscess (often multiple)

  • Meningitis

  • T1 with rim enhancement

  • Diffusion restriction (including low ADC)

  • Meningeal contrast enhancement

 RCVS
  • Infarcts and haemorrhage typically in watershed areas

  • Infarcts usually bilateral and symmetrical

  • Oedema in posterior regions

  • Cerebral infarction (39%)

  • Convexity SAH (34%)

  • Lobar haemorrhage (20%)

  • Oedema resembling PRES

  • Fitting ischaemia, SAH or lobar haemorrhage

  • ‘String of beads’ on vascular imaging; bilateral narrowing of all intracerebral arteries

 PRES
  • Bilateral parieto-occipital region in 70%

  • Also frequently superior frontal sulcus or watershed pattern

  • Vasogenic oedema

  • T2/FLAIR hyperintense

  • ADC hyperintense

  • Contrast enhancement in 20%

 PCNSL
  • Cerebral hemispheres (38%)

  • Basal ganglia and thalamus (16%)

  • Corpus callosum (14%)

  • Mostly a single lesion (65%)

  • Often near CSF

  • Moderate perifocal oedema

  • Often contrast enhancement

  • T2/FLAIR often isointense but shows perifocal oedema

 TDL
  • Mostly supratentorial in frontal and parietal lobes

  • Large lesions

  • Mass effect (45%)

  • Oedema (77%)

  • T2/FLAIR hyperintense

  • T2 hypodense ring surrounding lesion

  • Almost always contrast enhancement (eg, open-ring enhancement)

  • Cerebrovascular events (in patients treated with alemtuzumab) are not included in this table due to the diversity of reported events in patients treated with alemtuzumab, which on its own are radiologically similar to those seen in patients with a primarily cardiovascular cause for the event.

  • ADC, apparent diffusion coefficient; CSF, cerebral spinal fluid; DWI, diffusion weighted imaging; FLAIR, fluid attenuation inversion recovery; GCN, granule cell neuronopathy; GM, grey matter; IRIS, immune reconstitution inflammatory syndrome; JCV, JC virus; MRA, magnetic resonance angiography; PCNSL, primary central nervous system lymphoma; PML, progressive multifocal leukoencephalopathy; PRES, posterior reversible encephalopathy syndrome; RCVS, reversible cerebral vasoconstriction syndrome; SAH, subarachnoidal haemorrhage; TDL, tumefactive demyelinating lesion; WM, white matter.