Longitudinal callosal fascicles, or Probst bundles, are aberrant bundles of axons that run in a front-back (antero-posterior) direction rather than a left-right direction between the cerebral hemispheres. They are characteristic of patients with

agenesis of the corpus callosum Agenesis of the corpus callosum (ACC) is a rare birth defect in which there is a complete or partial absence of the corpus callosum. It occurs when the development of the corpus callosum, the band of white matter connecting the two hemispheres ...

and are due to failure of the callosally-projecting neurons (mostly layer 2/3

pyramidal neuron Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cor ...

s) to extend axons across the midline and therefore form the corpus callosum. The inability of these axons to cross the midline results in anomalous

axonal guidance Axon guidance (also called axon pathfinding) is a subfield of neural development concerning the process by which neurons send out axons to reach their correct targets. Axons often follow very precise paths in the nervous system, and how they man ...

and front-to-back projections within each hemisphere, rather than connecting between the hemispheres in the normal corpus callosum. These longitudinal callosal fascicles were originally described by

Moriz Probst Moriz Probst (1 October 1867 in Deutschlandsberg - 21 March 1923 in Vienna) was an Austrian psychiatrist and neuroanatomist. He is best known for first description of so-called Probst bundles, the anomalous brain structures found in dysgenesis ...

in 1901 by gross anatomical observation. More recently, these anomalies are detected by

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

diffusion tensor imaging Diffusion-weighted magnetic resonance imaging (DWI or DW-MRI) is the use of specific MRI sequences as well as software that generates images from the resulting data that uses the diffusion of water molecules to generate contrast in MR images. It ...

References

Central nervous system disorders Corpus callosum {{Neuroanatomy-stub