Aberrant pyramidal tract in medial lemniscus of brainstem in the human brain.

The aberrant pyramidal tract (APT) refers to the collateral pathway of the pyramidal tract through the medial lemniscus in the brainstem. We showed the presence of an APT in the normal human brain using diffusion tensor tractography. Diffusion tensor tractography showed that the motor tracts of the 28 hemispheres in 14 healthy normal individuals originated from the primary sensori-motor cortex and descended through the known pathway of the pyramidal tract. However, in five (17.9%) of the 28 hemispheres, we observed that the APT descended through the medial lemniscus from the midbrain to the pons, and then entered into the pyramidal tract at the upper medulla, after which it descended through the pyramidal tract to the lower medulla.