Aberrant Pyramidal Tract in the Medial Lemniscus of the Human Brainstem:Normal Distribution and PathologicalChanges

Abstract

We examined the consistency of the so-called aberrant pyramidal tract (APT) in 150 consecutive autopsied human brains using the modified Bielschowsky stain for axons. We were able to identify the APT in all brains except for one with holoprosencephaly. The APT left the pyramidal tract within the crus cerebri and passed in the medial lemniscus of the pons through the upper medulla oblongata. In 13 of the 63 brains with cerebrovascular diseases, wallerian degeneration was found in the APT on the ipsilateral side of the cerebral lesions. Further, the APT showed depletion of small-sized fibers in 2 of the 5 brains with multiple-system atrophy. These findings confirmed that the APT is a normal descending fiber tract and a part of the pyramidal tract.

Characteristics of the aberrant pyramidal tract in comparison with the pyramidal tract in the human brain

“…In 2011, two patients were reported with midbrain infarct or corona radiata, respectively, that showed motor recovery via APT [13,14]. As for the incidence of APT existence, our results coincide with those of Hong's DTT study and the course of the APT was similar with that of all previous studies [3,6,11,12]. …”

“…Like this study, several other studies have reported on the incidence and courses of the APT [3,6,11,12]. In 2001, using the modified Bielschowsky stain, Yamashita and Yamamoto [6] investigated the incidence and details of the course of the APT in 150 consecutive autopsied human brains.…”

“…In 2001, using the modified Bielschowsky stain, Yamashita and Yamamoto [6] investigated the incidence and details of the course of the APT in 150 consecutive autopsied human brains. They found that all of the 150 brains examined, with the exception of one brain with holoprosencephaly, showed the APT, and reported that the course of the APT left the PT within the cerebral peduncle and then passed into the medial lemniscus of the pons through the upper medulla.…”

“…The aberrant pyramidal tract (APT) indicates the collateral pathway of the PT, which separates from the original PT at the level of the midbrain and the pons, and descends through the medial lemniscus [3-6]. Existence of the APT has been demonstrated by various methods, including pathological, electrophysiological, and radiological studies [3,6-10]. In addition, recently, the APT has been suggested as a motor recovery mechanism in stroke [11-14].…”

Motor Recovery Mechanisms in Patients with Middle Cerebral Artery Infarct: A Mini-Review

“…These results seemed to suggest that the alternate motor fibers in the posterior pons could contribute to motor recovery in patients with MCA infarct. Although they did not declare the exact pathway of the alternate motor fibers in their study, the alternate motor fibers appeared to be the aberrant pyramidal tract which separates from the original pyramidal tract at the level of the midbrain and the pons and descends through the medial lemniscus [50,51,52,53]. It is well known that the pyramidal tract has collateral pathways [54,55].…”