Changes over time

N.B.

Calcification of an ischemic infarction may occur months to years after the event; however, this is very rare.

Brain classification is most commonly seen with certain neoplasms (e.g, oligodendroglioma), infections (eg. neurocysticercosis), and vascular malformations.

Nerve Injuries

Nerve Degeneration

Wallerian degeneration is a process that results when a nerve fiber is cut or crushed, in which the part of the axon separated from the neuron's cell body degenerates distal to the site of injury. This is also known as anterograde or orthograde degeneration

Degeneration of the axon usually begins within a few days after lesion onset.

PNS vs CNS

In the PNS, Schwann cells sense the axonal degeneration and begin to degrade their myelin and secrete cytokines and chemokines that recruit macrophages => clear myelin debris which, along with trophic factor secretion by Schwann cells, stimulates formation of a growth cone from the stump of the proximal axon and facilitates nerve regeneration.

In the CNS, phagocytic macrophages/microglia are recruited more slowly because of BBB. Myelin-producing oligodendrocytes also become inactive or undergo apoptosis and do not assist with phagocytosis.

This slows removal of the myelin debris, which can persist for years in the degenerating tracts and suppress axonal growth via myelin-associated inhibitory factors.

Astrocytes also release inhibitory molecules and proliferate in the weeks to months following injury, forming a glial scar that acts as a barrier to axon regeneration.