Transependymal edema, also known as interstitial cerebral edema or periventricular lucency (PVL), is a type of cerebral edema that occurs with increased pressure within the cerebral ventricles. FLAIR is the most sensitive MRI sequence for detection.
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Pathology
The ventricular ependymal lining is eventually disrupted, allowing for the transependymal migration of cerebrospinal fluid into the brain parenchyma around the cerebral ventricles. This is usually seen surrounding the lateral ventricles in the setting of acute obstructive hydrocephalus.
Radiographic features
CT
low attenuation periventricular changes around the lateral ventricles
effacement of adjacent cerebral sulci may be seen, which is helpful to distinguish the condition from age-related cerebral atrophy with small vessel periventricular ischemic disease
other corresponding features of obstructive hydrocephalus may be noted
MRI
halo of high T2 or FLAIR signal around the lateral ventricles
Practical points
It is important to distinguish interstitial edema from a commonly seen variant of a slight increase in signal anterior to the frontal horns, and posterior to the occipital horns, which is known as ependymitis granularis 3.
