Uncrossed corticospinal tracts presenting as transient tumor-related symptomatology

Adaptation in the spinal cord after stroke: Implications for restoring cortical control over the final common pathway

Control of voluntary movement is predicated on integration between circuits in the brain and spinal cord. Although damage is often restricted to supraspinal or spinal circuits in cases of neurological injury, both spinal motor neurons and axons linking these cells to the cortical origins of descending motor commands begin showing changes soon after the brain is injured by stroke. The concept of 'transneuronal degeneration' is not new and has been documented in histological, imaging and electrophysiological studies dating back over a century. Taken together, evidence from these studies comports more with a system attempting to survive rather than one passively surrendering to degeneration. There tends to be at least some preservation of fibres at the brainstem origin and along the spinal course of the descending white matter tracts, even in severe cases. Myelin-associated proteins are observed in the spinal cord years after stroke onset. Spinal motor neurons remain morphometrically unaltered. Skeletal muscle fibres once innervated by neurons that lose their source of trophic input receive collaterals from adjacent neurons, causing spinal motor units to consolidate and increase in size. Although some level of excitability within the distributed brain network mediating voluntary movement is needed to facilitate recovery, minimal structural connectivity between cortical and spinal motor neurons can support meaningful distal limb function. Restoring access to the final common pathway via the descending input that remains in the spinal cord therefore represents a viable target for directed plasticity, particularly in light of recent advances in rehabilitation medicine.

A rare case of ispilateral hemiparesis in a patient with uncrossed pyramidal tract shown by tractography

This article presents a unique case of ipsilateral hemiparesis in a 66-year-old individual, contrary to the conventional understanding of supratentorial strokes causing contralateral neurological deficits. The patient exhibited persistent weakness and sensory abnormalities on the left side of the body following a left occipital infarct. Neuroimaging revealed a chronic stroke in the left occipital lobe, with diffusion tensor imaging demonstrating uncrossed pyramidal tracts at the level of the medulla. The discussion encompasses the anatomical basis of corticospinal tract crossing, historical perspectives, and previous documented cases of ipsilateral strokes. The rarity of complete uncrossed corticospinal tracts without underlying congenital abnormalities or genetic disorders is highlighted. The study underscores the importance of considering such atypical presentations in stroke evaluations and the role of advanced imaging techniques in confirming diagnosis and understanding underlying mechanisms.

Syndrome of the third frontal convolution: Léon Ectors´ legacy on paradoxical ipsilateral hemiparesis

Since the crossed control of sensitive-motor body functions by the contralateral cerebral hemispheres was recognized in the early 18th century, clinicians have been baffled by patients developing a motor deficit involving the extremities on the same side as an intracranial lesion. In the first third of the 20th century, three main hypotheses were proposed to explain this so-called ipsilateral or paradoxical hemiparesis: (1) the absence of decussation of the corticospinal tracts; (2) diaschisis, or blocking of the normal input to a brain region anatomically distant from the injured site; and (3) compression of the contralateral cerebral peduncle against the tentorial border, also known as the Kernohan-Woltman notch phenomenon. Here, we deal with the less widely known contributions of the Belgian neurosurgeon Léon Ectors, who included this paradoxical deficit within a neurological syndrome he considered highly specific for an early diagnosis of those meningiomas growing over the third frontal convolution. The present manuscript includes a systematic review of the cases of ipsilateral hemiparesis secondary to intracranial masses reported in ancient and modern scientific medical literature. We also address in-depth the physiopathological theories accounting for this syndrome and contrast them with Léon Ectors' observations.

Beyond uncal herniation: An updated diagnostic reappraisal of ipsilateral hemiparesis and the Kernohan-Woltman notch phenomenon

PURPOSE

This works comprehensively analyses a modern cohort of patients with ipsilateral hemiparesis (IH) and discusses the pathophysiological theories elaborated to explain this paradoxical neurological sign according to the findings from contemporary neuroimaging and neurophysiological techniques.

METHODS

A descriptive analysis of the epidemiological, clinical, neuroradiological, neurophysiological, and outcome data in a series of 102 case reports of IH published on since the introduction of CT/MRI diagnostic methods (years 1977-2021) was performed.

RESULTS

IH mostly developed acutely (75.8%) after traumatic brain injury (50%), as a consequence of the encephalic distortions exerted by an intracranial haemorrhage eventually causing contralateral peduncle compression. Sixty-one patients developed a structural lesion involving the contralateral cerebral peduncle (SLCP) demonstrated by modern imaging tools. This SLCP showed certain variability in its morphology and topography, but it seems pathologically consistent with the lesion originally described in 1929 by Kernohan & Woltman. The study of motor evoked potentials was seldom employed for the diagnosis of IH. Most patients underwent surgical decompression, and a 69.1% experienced some improvement of the motor deficit.

CONCLUSIONS

Modern diagnostic methods support that most cases in the present series developed IH following the KWNP model. The SLCP is presumably the consequence of either compression or contusion of the cerebral peduncle against the tentorial border, although focal arterial ischemia may also play a contributing role. Some improvement of the motor deficit should be expected even in the presence of a SLCP, provided the axons of the CST were not completely severed.

Uncrossed corticospinal tract in health and genetic disorders: Review, case report, and clinical implications

BACKGROUND AND PURPOSE

Crossing pathologies of the corticospinal tract (CST) are rare and often associated with genetic disorders. However, they can be present in healthy humans and lead to ipsilateral motor deficits when a lesion to motor areas occurs. Here, we review historical and current literature of CST crossing pathologies and present a rare case of asymmetric crossing of the CST.

METHODS

Description of the case and systematic review of the literature were based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The PubMed database was searched for peer-reviewed articles in English since 1950. All articles on ipsilateral stroke, uncrossed CST, and associated neurologic disorders were screened. Furthermore, a literature review between the years 1850 and 1980 including articles in other languages, books, opinions, and case studies was conducted.

RESULTS

Only a few descriptions of CST crossing pathologies exist in healthy humans, whereas they seem to be more common in genetic disorders such as horizontal gaze palsy with progressive scoliosis or congenital mirror movements. Our patient presented with aphasia and left-sided hemiparesis. Computed tomographic (CT) scan revealed a perfusion deficit in the left middle cerebral artery territory, which was confirmed by diffusion-weighted magnetic resonance imaging (MRI), so that thrombolysis was administered. Diffusion tensor imaging with fibre tracking revealed an asymmetric CST crossing.

CONCLUSIONS

The knowledge of CST crossing pathologies is essential if a motor deficit occurs ipsilateral to the lesion side. An ipsilateral deficit should not lead to exclusion or delay of therapeutic options in patients with suspected stroke. Here, a combined evaluation of CT perfusion imaging and MRI diffusion imaging may be of advantage.