Gliosis is the focal proliferation of glial cells in the CNS in response to insult. By strict definition, gliosis is not synonymous with encephalomalacia which is the end result of liquefactive necrosis of brain parenchyma following an insult. Radiologically they share similar features and the distinction is often only of academic interest. Gliosis and encephalomalacia often coexist during the early and intermediate responses to injury, with gliosis waning with time 1.
- serve as a focus of seizure
Glial cells constitute the non-neuronal component of the CNS, outnumbering the neurones 10:1, and are divided into two main groups: microglia and macroglia 1:
Astrocytes and the microglia are the glial cells predominantly responsible for tissue response to injury. Astrocytosis involves the proliferation and hypertrophy of astrocytes, through complex molecular and cellular pathways. Microgliosis primarily occurs when the insult is infectious (particularly viral), as the microglial cells, which are not of neuroepithelial origin but are likely derived from monocyte or macrophage precursors, function in antigen presentation 1.
Gliosis appears bright on T2 as well as FLAIR unlike encephalomalacia which follows CSF signal on all sequences.