Longitudinal callosal fascicle

Longitudinal callosal fascicles (or Probst bundles) are abnormal collections of brain cells characteristic of patients with agenesis of the corpus callosum. Failure of the callosally-projecting neurons (mostly layer 2/3 pyramidal neurons) to extend axons across the midline and therefore form the corpus callosum results in anomalous collection of these axonal projections in both hemispheres. Longitudinal callosal fascicles were originally described by Moriz Probst in 1901 by gross anatomical observation. More recently, these anomalies are detected by Magnetic Resonance Imaging or Diffusion Tensor Imaging.