Sharp margins & lentiform, follow CSF on all sequences

May be associated with gliosis in elderly (FLAIR hyperintense rim)

Solitary enlarged PVS unusual, smaller characteristic lesions often seen elsewhere in the brain

Usually in lentiform nuclei, rarely in thalamus

Usually in basal ganglia (BG), thalamus, internal capsules, less commonly in periventricular WM

Mildly irregular, but sharp margins, T2 hyperintense rim, ± GRE hypointense hemosiderin rim

Often associated with more confluent WM arteriolosclerotic or hypertensive changes

Usually multiple & confluent, but can be solitary early in the disease

Usually in deep & periventricular WM

Associated with lacunar infarcts

Corpus callosum (CC) & peri 4th ventricular involvement in a young adult

Acute tumefactive lesions large with hypointense T2 ring that enhances, usually with little mass effect

Solitary lesion commonly in deep or peripheral WM & at the onset of typical disease or with tumefactive lesions

Enhancement may be ring-like or “U” shaped in the subcortical fibers

May be punctate to massive, with variable surrounding edema, mass effect

Hemorrhagic in renal cell, melanoma, choriocarcinoma

Hyperintensity, edema, & mass effect less prominent in posterior fossa, but risks higher

Solitary at presentation in 45-50%

Usually multifocal WM lesions, but can be solitary

Range from punctate to flocculent, with enhancement, faint & fuzzy early, ring-like later

Usually 10-14 days following infection or vaccination

Often occurs in children 3-5 years, but can occur at any age

Gliosis is T2 hyperintense without mass effect & often associated with focal atrophy (encephalomalacia)

FLAIR helpful in separating microcystic encephalomalacia & gliosis (hyperintense) from macrocystic changes (hypointense)

Brain’s only response to insult: Infectious, stroke, trauma

Irregular WM mass with ring enhancement, hemorrhage

Mass effect, heterogeneous signal typical

Often involves, extends across CC

Most non-herpes encephalitides involve BG, thalamus, midbrain, & WM

Poorly marginated, mild mass effect

Usually multiple, but may be solitary in midbrain, or with solitary cerebritis

Variable enhancement of the parenchyma or meninges

Peripheral lesion, often with significant cortical involvement

Frontal & temporal lobes, often with skull changes due to slow growth

Calcification common, enhancement from none to intense

Often peripheral, but occurs in any lobe & brainstem

Poorly marginated, cortical involvement less common

Usually no enhancement, hemorrhage, or calcification

WM tumor midrange between GBM & low grade with significant overlap

Typically more enhancement & mass effect than low grade astrocytoma

Similar to low grade or anaplastic astrocytoma in appearance

May arise from a lower grade oligodendroglioma or astrocytoma

Lesions usually solitary when isolated cortical venous

Dural sinus: Multiple lesions

Deep venous: Bilateral thalamic

T2 hyperintensity without diffusion restriction unless infarct has developed

Usually subcortical WM, sparing the cortex, often hemorrhagic

Look for the thrombosed cortical vein which may be hyperintense on T1 or FLAIR, hypointense on GRE

Central pontine myelinolysis: Pontine hyperintensity sparing the periphery & cortical spinal tract, round or trident-shaped, usually solitary

Extra-pontine myelinolysis: BG & WM lesions usually bilateral, but may be solitary