Ependymitis granularis sounds far more worrying than it actually is. The term refers to a histological feature that contributes to symmetrical foci of periventricular high T2 and FLAIR signal hyperintensity anterior and lateral to the frontal horns. It is just an anatomical variant, usually small, less than 1 cm, and has a triangular morphology extending laterally from the callosal genu.
Pathologic lesions tend to be larger and demonstrate corresponding low signal intensity in T1WI.
Pathology
Multiple histological features are thought to contribute to the appearance 1:
- focal breakdown of the ependymal lining and astrocytic gliosis (true ependymitis granularis)
- decreased myelin
- loose and random organization of axons
- smaller axons than adjacent white matter
- increased periependymal and extracellular fluid
Despite the name, which suggests an inflammatory cause, and a 1926 article 2 that claimed it as a cause of chronic internal hydrocephalus, it is just an anatomical variant.
Differential diagnosis
-
transependymal edema
- not confined to frontal horns
- ventricle enlarged (for age/for patient)
-
multiple sclerosis
- rarely symmetric, more ovoid, perivenular
-
ears of the lynx sign
- very rare, found in hereditary spastic paraplegia
- similar appearance
-
chronic small vessel ischemia
- usually not symmetric
- often do not abut the ventricles