The pyramidal tract is the major neuronal pathway that mediates voluntary movements. Several studies have reported that the pyramidal tract has a collateral pathway in the human brain, which separates from the original pyramidal tract at the midbrain, and the pons descends through the medial lemniscus in what is referred to as the aberrant pyramidal tract (APT).1 Although the existence of this pathway has been demonstrated by several pathological, electrophysiological and radiological studies, its detailed course and function have not yet been elucidated.2^–4

Recent advances in diffusion tensor tractography (DTT) have allowed us to visualise and localise the PT at the brainstem in three dimensions. Conversely, functional MRI (fMRI) is capable of precisely identifying cortical activation sites at the cortex and can provide additional information regarding the characteristics of the pyramidal tract.

In this study, we describe a patient with pontine infarct who showed an APT in the medial lemniscus of the brainstem on both DTT and fMRI.

Case report

A 70-year-old right-handed woman was referred to our hospital for motor-function evaluation. T2-weighted MR images showed an infarct in the left pons (fig 1A). The Motricity index was used to determine motor function. The patient presented with severe weakness of the right extremities at the onset …