Injury of the corticobulbar tract in patients with dysarthria following cerebral infarct: diffusion tensor tractography study

Reconstructing the somatotopic organization of the corticospinal tract remains a challenge for modern tractography methods

The corticospinal tract (CST) is a critically important white matter fiber tract in the human brain that enables control of voluntary movements of the body. The CST exhibits a somatotopic organization, which means that the motor neurons that control specific body parts are arranged in order within the CST. Diffusion magnetic resonance imaging (MRI) tractography is increasingly used to study the anatomy of the CST. However, despite many advances in tractography algorithms over the past decade, modern, state-of-the-art methods still face challenges. In this study, we compare the performance of six widely used tractography methods for reconstructing the CST and its somatotopic organization. These methods include constrained spherical deconvolution (CSD) based probabilistic (iFOD1) and deterministic (SD-Stream) methods, unscented Kalman filter (UKF) tractography methods including multi-fiber (UKF2T) and single-fiber (UKF1T) models, the generalized q-sampling imaging (GQI) based deterministic tractography method, and the TractSeg method. We investigate CST somatotopy by dividing the CST into four subdivisions per hemisphere that originate in the leg, trunk, hand, and face areas of the primary motor cortex. A quantitative and visual comparison is performed using diffusion MRI data (N = 100 subjects) from the Human Connectome Project. Quantitative evaluations include the reconstruction rate of the eight anatomical subdivisions, the percentage of streamlines in each subdivision, and the coverage of the white matter-gray matter (WM-GM) interface. CST somatotopy is further evaluated by comparing the percentage of streamlines in each subdivision to the cortical volumes for the leg, trunk, hand, and face areas. Overall, UKF2T has the highest reconstruction rate and cortical coverage. It is the only method with a significant positive correlation between the percentage of streamlines in each subdivision and the volume of the corresponding motor cortex. However, our experimental results show that all compared tractography methods are biased toward generating many trunk streamlines (ranging from 35.10% to 71.66% of total streamlines across methods). Furthermore, the coverage of the WM-GM interface in the largest motor area (face) is generally low (under 40%) for all compared tractography methods. Different tractography methods give conflicting results regarding the percentage of streamlines in each subdivision and the volume of the corresponding motor cortex, indicating that there is generally no clear relationship, and that reconstruction of CST somatotopy is still a large challenge. Overall, we conclude that while current tractography methods have made progress toward the well-known challenge of improving the reconstruction of the lateral projections of the CST, the overall problem of performing a comprehensive CST reconstruction, including clinically important projections in the lateral (hand and face areas) and medial portions (leg area), remains an important challenge for diffusion MRI tractography.

Significance of Vertigo, Imbalance, and Other Minor Symptoms in Hyperacute Treatment of Posterior Circulation Stroke

Background

This study aimed to determine the clinical significance of acute vestibular syndrome (AVS)/acute imbalance syndrome (AIS) in posterior circulation stroke (PCS) and how it should be addressed in the thrombolysis code.

Methods

Our institution has recently changed its thrombolysis code from one that is generous to AVS/AIS to one that is exclusive. The subjects in this study were patients with PCS who presented before this transition (May 2016 to April 2018, period 1) and those who presented after (January 2019 to December 2020, period 2) with an onset-to-door time of 4.5 h. Hyperacute stroke treatment was compared between the two periods. The clinical significance of AVS/AIS was evaluated by dichotomizing the patients' clinical severity to minor or major deficits, then evaluating the significance of AVS/AIS in each group. Presenting symptoms of decreased mental alertness, hemiparesis, aphasia (anarthria), or hemianopsia were considered major PCS symptoms, and patients who did not present with these symptoms were considered minor PCS.

Results

In total, 114 patients presented in period 1 and 114 in period 2. Although the code activation rate was significantly lower in period 2 (72.8% vs. 59.7%), p = 0.04, there were no between-group differences in functional outcomes (mRS score at 3 months; 1 [0–3] vs. 0 [0–3], p = 0.18). In 77 patients with PCS and AVS/AIS, the difference in code activation rate was not significant according to changes in thrombolysis code. In minor PCS, AVS/AIS was associated with lower NIHSS scores, lower early neurological deterioration rates, and favorable outcomes. In major PCS, while AVS/AIS was not associated with outcomes, the majority of cases were prodromal AVS/AIS which simple vertigo and imbalance symptoms were followed by a major PCS symptom.

Conclusions

This study failed to show differences in outcome in patients with PCS according to how AVS/AIS is addressed in the stroke thrombolysis code. In patients with minor PCS, AVS/AIS was associated with a benign clinical course. Prompt identification of prodromal AVS/AIS is essential.

Dysphagia prognosis prediction via corticobulbar tract assessment in lateral medullary infarction: a diffusion tensor tractography study

We investigated the capacity for dysphagia prognosis prediction using diffusion tensor tractography (DTT) to assess the state of the corticobulbar tract (CBT) during the initial period following lateral medullary infarction (LMI). Twenty patients with LMI and 20 control subjects were recruited for this study. The patients were classified into two subgroups: subgroup A (16 patients with nasogastric tube required for six months or less after LMI onset) and subgroup B (4 patients with nasogastric tube required for more than six months after onset). DTT was used to reconstruct the CBTs of each patient and control subject, and the fractional anisotropy (FA) and tract volume (TV) measurements were obtained. In the affected hemisphere, the FA value of the CBT was significantly lower in subgroup B than in subgroup A and the control group (p < 0.05), with no significant difference between subgroup A and the control group. In the affected and unaffected hemispheres, the TV values of CBT in subgroups A and B were lower than those of the control group (p < 0.05), with no significant difference between subgroups A and B. In addition, among the four patients of subgroup B, reconstruction of the CBT was not possible in three patients, and the remaining patients exhibited on old lesion in the corona radiate involving descending pathway of the CBT in the affected hemisphere. We found that the injury severity of the CBT in the affected hemisphere appeared to be related to a poor dysphagia prognosis following LMI. Our results suggest that evaluation of the CBT state during the early post-LMI could be useful for dysphagia prognosis prediction.

Prognostic Prediction of Dysphagia by Analyzing the Corticobulbar Tract in the Early Stage of Intracerebral Hemorrhage

We investigated the predictive value of the corticobulbar tract (CBT) for dysphagia using diffusion tensor tractography in the early stage of intracerebral hemorrhage (ICH) for dysphagia. Forty-two patients with spontaneous ICH ± intraventricular hemorrhage (IVH) and 22 control subjects were recruited. The patients were classified into three groups: group A-could remove nasogastric tube (NGT) in the acute stage of ICH, group B-could remove NGT within 6 months after onset, and group C-could not remove NGT until 6 months after onset. The CBT were reconstructed, and fractional anisotropy (FA) and tract volume (TV) values were determined. The FA of the CBT in the affected hemisphere in group A was lower than in the control group (p < 0.05). The FA and TV of the CBT in the affected hemisphere in group B were lower than those in the control group (p < 0.05). In group C, the FA and TV in the affected hemisphere and unaffected hemispheres were lower than in the control group (p < 0.05). The TV of the CBT in the affected hemisphere in group B showed a moderate negative correlation with the length of time until NGT removal (r = 0.430, p < 0.05). We found that patients with CBT injuries in both hemispheres were not able to remove the NGT until 6 months after onset, whereas patients who were injured only in the affected hemisphere were able to remove NGT within 6 months of onset. The severity of injury to the CBT in the affected hemisphere appeared to be related to the length of time until NGT removal.

The Relationship Between Leukoaraiosis Involving Contralateral Corticobulbar Tract and Dysphagia in Patients with Acute Unilateral Corona Radiata Infarction with Corticobulbar Tract Involvement

This study investigated the impact of leukoaraiosis (LA) involving the contralateral corticobulbar tract (CBT) on dysphagia in patients with unilateral corona radiata (CR) infarction with CBT involvement. Patients admitted to the Department of Neurology (September 2011-August 2014) were evaluated; those with a first episode of acute unilateral CR infarction involving the CBT and with LA were included. The 'Case' group comprised patients with LA involving the contralateral CBT; the 'Control' group comprised patients with LA not involving the contralateral CBT. The primary outcome was the feeding method at discharge; secondary outcomes were the feeding method at admission and results of the bedside swallowing test, videofluoroscopic swallowing study (VFSS), videofluoroscopic dysphagia scale, penetration-aspiration scale, American Speech-Language-Hearing Association National Outcome Measurement System Swallowing Scale (ASHA NOMS), oral transit time, and pharyngeal transit time. Infarct size was measured using brain magnetic resonance imaging; LA severity was rated using the Fazekas scale. Eighty-one patients were included (mean age 64.6 ± 11.5 years; 64% male; Case group: 20, 5 underwent VFSS; Control group: 67, 11 underwent VFSS). The Case group was older and had higher total Fazekas scale score than the Control group. The feeding method at discharge and ASHA NOMS score were significantly worse in the Case group than in the Control group. Multivariate analysis revealed that LA involving the contralateral CBT independently predicted the feeding method at discharge and ASHA NOMS score. In conclusion, LA involving the contralateral CBT is associated with dysphagia in patients with unilateral CR infarction involving the CBT.

Recovery of an injured corticobulbar tract in a patient with stroke: A case report

RATIONALE

The corticobulbar tract (CBT) is known to be involved in the motor function of the non-oculomotor cranial nuclei and controls the muscles of the face, head, and neck. Several studies have reported injury of the CBT in patients with brain injury, however, little is known about recovery of the injured CBT.

PATIENT CONCERNS

A 59-year-old right-handed male underwent decompressive craniectomy for management of brain swelling and intracerebral hemorrhage following an infarction in the left middle cerebral artery territory. Initially, the patient had showed severe dysphagia and had to be fed using a Levin tube. Five weeks after the onset of stroke, the patient was transferred to the rehabilitation department and underwent comprehensive rehabilitative therapy. Cranioplasty was performed eight weeks after the onset. The patient was completely recovered from dysphagia and the Levine tube was removed nine weeks after the onset.

INTERVENTIONS

Diffusion tensor imaging was performed twice; at five weeks and nine weeks from the onset.

OUTCOME

On five-week diffusion tensor tractography (DTT), the right CBT was discontinued at the subcortical white matter and showed severe narrowing and the left CBT was not reconstructed. By contrast, on nine-week DTT, the right CBT was extended to the cerebral cortex and thickened while the left CBT remained not reconstructed in DTT.

LESSONS

This case demonstrates the association of the recovery of injured CBT with the recovery of dysphagia using DTT.

Localization of orofacial representation in the corona radiata, internal capsule and cerebral peduncle in Macaca mulatta

Subcortical white matter injury is often accompanied by orofacial motor dysfunction, but little is known about the structural substrates accounting for these common neurological deficits. We studied the trajectory of the corticobulbar projection from the orofacial region of the primary (M1), ventrolateral (LPMCv), supplementary (M2), rostral cingulate (M3) and caudal cingulate (M4) motor regions through the corona radiata (CR), internal capsule (IC) and crus cerebri of the cerebral peduncle (ccCP). In the CR each pathway was segregated. Medial motor area fibers (M2/M3/M4) arched over the caudate and lateral motor area fibers (M1/LPMCv) curved over the putamen. At superior IC levels, the pathways were widespread, involving the anterior limb, genu and posterior limb with the M3 projection located anteriorly, followed posteriorly by projections from M2, LPMCv, M4 and M1, respectively. Inferiorly, all pathways maintained this orientation but shifted posteriorly, with adjacent fiber bundles overlapping minimally. In the ccCP, M3 fibers were located medially and M1 fibers centromedially, with M2, LPMCv, and M4 pathways overlapping in between. Finally, at inferior ccCP levels, all pathways overlapped. Following CR and superior IC lesions, the dispersed pathway distribution may correlate with acute orofacial dysfunction with spared pathways contributing to orofacial motor recovery. In contrast, the gradually commixed nature of pathway representation inferiorly may enhance fiber vulnerability and correlate with severe, prolonged deficits following lower subcortical and midbrain injury. Additionally, in humans these findings may assist in interpreting orofacial movements evoked during deep brain stimulation, and neuroimaging tractography efforts to localize descending orofacial motor pathways.

Oropharyngeal dysphagia in secondary normal pressure hydrocephalus due to corticobulbar tract compression: cases series and review of literature

The association and mechanism involved in swallowing disturbance and normal pressure hydrocephalus (NPH) needs to be established. We report a case report where a patient who showed progressive swallowing dysfunction was diagnosed with secondary NPH. Tractography analysis showed corticobulbar tract compression by ventricular dilation. Drainage operation led to the recovery of tract volume with an improvement of swallowing function. We also report ten case series in which secondary NPH was associated with a swallowing disturbance. In these cases, dysphagia also showed improvement after shunt operation. We review the literature regarding the corticobulbar tract and its association with swallowing disturbance and the possible underlying pathophysiological mechanism in secondary NPH. This report highlights that swallowing disturbance may manifest in those with secondary NPH due to corticobulbar tract involvement. Our findings suggest that involvement of the corticobulbar tract may be a possible cause of dysphagia in secondary NPH that may be reversible after shunt operation.