Cholesterol ester crystals in polarized light show pathways in the human brain.

It is well known that crystals of cholesterol esters exhibit birefringence. In the central nervous system such crystals are formed in the course of myelin degeneration following axonal interruption. Thus, anterogradely degenerated tracts assume birefringence. In the human brain, where modern tracing techniques commonly used in animals cannot be applied, anterogradely degenerated fiber systems can be visualized in formalin-fixed frozen tissue by simple polarizing microscopy. Using this phenomenon, tracing cerebral connections may permit one to interpret neuropsychological symptoms unique to man (aphasia, amnesia, neglect). Also, it should be a useful addition to routine neuropathology for it shows the long-distance effects of a brain lesion; it would facilitate the study of peripheral nerve pathology; and it would yield information about the age of a lesion.