Motor recovery via aberrant pyramidal tract in a patient with traumatic brain injury A diffusion tensor tractography study

The aberrant pyramidal tract is the collateral pathway of the pyramidal tract through the medial lemniscus in the brainstem. A 21-year-old man presented with right hemiparesis due to a traumatic intracerebral hemorrhage in the left corona radiata. His motor function recovered almost to the normal state at 10 months after onset. Through diffusion tensor tractography, the pyramidal tract in the affected （left） hemisphere showed discontinuation at the pontine level at 13 months after onset. An aberrant pyramidal tract was observed, which originated from the primary motor cortex and the supplementary motor area and descended through the corona radiata, then through the posterior limb of the internal capsule and the medial lemniscus pathway from the midbrain to the pons, finally entered into the pyramidal tract area at the pontomedullary junction, it suggests that the motor functions of the right extremities in this patient had recovered by this aberrant pyramidal tract.

Aberrant pyramidal tract in a patient with corona radiata infarct A diffusion tensor tractography study

The aberrant pyramidal tract refers to the collateral pathway of the pyramidal tract through the medial lemniscus in the brainstem. A 63-year-old male patient presented with severe paralysis of the left extremities due to a right corona radiata infarct. He was able to extend the affected fingers against resistance at 2 months after stroke onset. At 6 months after stroke onset, he was able to perform some fine motor activities, as well as to walk with a nearly normal gait. Functional MRI, which was performed at 6 months after onset, showed that the contralateral primary sensorimotor cortex was activated during affected （left） hand movements. Diffusion tensor tractography results showed that at 2 weeks after stroke onset, pyramidal tracts of the affected hemisphere originated from the primary motor cortex and descended along the known pathway of the pyramidal tract with an aberrant pyramidal tract, which was bypassed through the medial lemniscus from the midbrain to the lower pons. However, the pyramidal tract from midbrain to pons in the affected hemisphere could not be depicted by diffusion tensor tractography at 6 months after stroke onset; instead, only the aberrant pyramidal tract existed for the course of the disappeared pyramidal tract. Results from this study indicate that the main motor functions of the affected extremities appeared to be controlled via the aberrant pyramidal tract with degeneration of the pyramidal tract in the brainstem of the affected hemisphere.

Motor recovery via aberrant pyramidal tract in a patient with a cerebral peduncle infarct

The presence of the aberrant pyramidal tract has been demonstrated by several studies; however, little is known about its role in motor recovery in stroke patients. In the present study, we reported a 69-year-old right-handed female patient with an infarct in the mid to lateral portion of the left cerebra peduncle, who showed an aberrant pyramidal tract by diffusion tensor tractography. The patient presented with severe weakness of the right extremities at stroke onset. The patient showed progressive motor recovery as much as being able to extend the affected extremities against some resistance at 6 months after onset. At 20 months after stroke onset, motor function of the left extremities had recovered to a nearly normal state. Diffusion tensor tractography results showed that the PT was disrupted at the lower midbrain of the affected （left） hemisphere at 3 weeks after stroke onset and this disruption was not changed at 20 months. An aberrant pyramidal tract in the left hemisphere was also observed, which originated from the primary motor cortex and descended through the corona radiata, posterior limb of the internal capsule, thalamus, the medial lemniscus pathway from the midbrain to the pons, and then entered into the pyramidal tract area at the pontomedullary junction. Transcranial magnetic stimulation did not elicit motor evoked potential from the affected hand muscle at 3 weeks, but it elicited motor evoked potential with mildly delayed latency and low amplitude in the affected hand muscle at 20 months. The main motor functions of the affected extremities in this patient appeared to be recovered via this aberrant pyramidal tract.