Dystopic myelination with hypertrophy of pyramidal tract.

In a case of hypertrophy of the pyramidal tract the cross section of the hypertrophic pyramids was 174% of controls with an increase (148%) in the total population of myelinated fibers. However, there was no commensurate increase in the density of Betz cells. Confined to the hypertrophic tract there was a peculiar anomaly consisting of tubes of thick myelin sheaths that encompassed columns of glial nuclei instead of axons. This type of change, along with the clinical data, may indicate that the lesion originated in the perinatal period when myelin formation is in progress and is susceptible to derangement.