Pathways Linked to Internuclear Ophthalmoplegia on Diffusion-Tensor Imaging in a Case with Midbrain Infarction

Investigations into the anatomical location, physiological function, clinical implications, and significance of the nucleus of Perlia

BACKGROUND

The article discusses the investigations into the nucleus of Perlia (NP), a spindle-shaped nucleus located in the dorsal aspect of the oculomotor complex. However, there is still debate over its exact location and function, with conflicting findings in nonhuman primates. Therefore, the current study aimed the describe the location, function, clinical and surgical implications of NP.

METHODS

A systematic review was conducted to identify studies related to the following MeSH terms: "perlia nucleus" OR "nucleus of "perlia" OR "convergence nucleus" OR "nucleus of convergence" OR "Perlia's nucleus". The search was conducted until September 2022.

RESULTS

The location of the NP has been consistently reported in various studies, with most describing it as situated ventral to the Edinger-Westphal nucleus (EW) and dorsomedial to the oculomotor complex. The incidence of the NP in humans has been reported to range from 9 to 40%. In primates, it was observed to be absent in 77% of midbrains, while well developed in 9%. It is also noted that the NP is not a single nucleus, but rather a group of nuclei that are interconnected and involved in the coordination of eye movements that contain parasympathetic neurons.

CONCLUSIONS

The study of the NP holds clinical implications for understanding the neural mechanisms underlying the irregularities in the pupillary light reflex, such as anisocoria or abnormal responses to light, diagnosis, and treatment of neurological disorders like Horner's syndrome, and management of eye movement disorders including one-and-a-half syndrome, vertical gaze palsy, skew deviation and ptosis. The current study also highlighted the limitations of previous studies, including variations in the reported prevalence of the NP, limitations of the histological techniques, and inconsistent findings across human and animal studies.

Injury of the Vestibulocerebellar Tract and Signs of Ataxia in Patients with Cerebellar Stroke

BACKGROUND

The vestibulocerebellar tract (VCT) is responsible for maintaining balance, spatial orientation, and coordination. Damage to the vestibular system is accompanied by symptoms of balance disorder or ataxia. This study aimed to compare cerebellar dysfunction according to VCT damage in patients with cerebellar stroke.

METHODS

Six patients with cerebellum injury were recruited. This study measured ataxia and hand function related to visuomotor integration and manual dexterity using the Purdue pegboard test. The primary and bilateral secondary VCTs were reconstructed to investigate the integrity of pathways using diffusion tensor imaging (DTI).

RESULTS

The ataxia sign was positive in five patients (83%) at onset. In the result of the pegboard test, all patients had hand dysfunction in the dominant hand (100%). Likewise, all patients also had non-dominant hand dysfunction (100%). On the DTI tractography, the left and right primary VCTs of the patients demonstrated a 25% injury rate. Furthermore, the injury rates of ipsilateral and contralateral secondary VCTs were 50% and 58%.

CONCLUSIONS

Ataxia is related to secondary VCTs, and hand dysfunction is also related to VCTs. Therefore, we believe that the current study will be helpful in evaluating and providing a clinical intervention strategy for patients with ataxia and hand dysfunction following cerebellar injury.

Isolated Medial Longitudinal Fasciculus Midbrain Infarction Mimicking Medial Rectus Paralysis

INTRODUCTION

Medial longitudinal fasciculus infarction is rare in clinical practice and generally accompanied by brain tissue damage around the medial longitudinal fasciculus. Isolated medial longitudinal fasciculus midbrain infarction was seldom reported.

CASE REPORT

An 81-year-old man with hypertension was admitted to our hospital because of sudden onset diplopia. A neurological examination revealed right adduction paresis without abducting nystagmus in the left eye, whereas the convergence reflex was normal. Diffusion-weighted magnetic resonance imaging demonstrated a small acute lacunar medial longitudinal fasciculus infarction in the right midbrain at the level of the inferior colliculus. Diffusion-tensor imaging showed a reduction of the right medial longitudinal fasciculus. Medial longitudinal fasciculus infarction is rare and occurs most commonly in the pons. The authors report on a case of isolated medial longitudinal fasciculus infarction that was diagnosed because of sudden diplopia and manifested as simple internal rectus paralysis with no abducting nystagmus on the contralateral side of the lesion.

CONCLUSION

Isolated midbrain-medial longitudinal fasciculus infarction without contralateral abducting nystagmus is a rare occurrence. It can be differentiated from partial oculomotor palsy by assessing the convergence reflex, primary gaze, and diffusion-tensor imaging.

Anatomical Location of the Vestibulocerebellar Tract in the Healthy Human Brain: A Diffusion Tensor Imaging Study

The vestibulocerebellar tract (VCT) is regarded as an important pathway of the central vestibular system. We identified the anatomical characteristics of the primary and secondary VCTs in a normal human brain using diffusion tensor imaging (DTI) tractography. Thirty-one healthy adults were recruited. A 1.5 T scanner was used for DTI tractography. A seed region of interest (ROI) was placed on the superior and medial vestibular nuclei at the pons level and a target ROI was placed on the uvula–nodulus of the cerebellum for reconstructing the primary VCT. In the secondary VCTs, the seed ROI was placed on the inferior and medial vestibular nuclei at the medulla oblongata level, and target ROIs were placed on the bilateral uvula–nodulus of the cerebellum. The primary VCT originated from the superior and medial vestibular nuclei at the pons level and terminated at the ipsilateral uvula–nodulus of the cerebellum. The component of the secondary VCTs originated from the inferior and medial vestibular nuclei at the level of the medulla oblongata and terminated at the bilateral uvula–nodulus of the cerebellum. Among them, 70.97% in the contralateral secondary VCT crossed at the vermis of the cerebellum. In addition, the fractional anisotropies (FAs) and mean diffusivity (MD) values of the primary VCT were significantly higher and lower, respectively, compared to those of the secondary VCTs (p < 0.05). The contralateral secondary VCT was significantly higher and lower in the MD and tract volume, respectively (p < 0.05), compared to the ipsilateral VCT. Therefore, we believe that the results will be useful for future studies of the vestibular projection pathway in the human brain injury aspect of central vestibular syndrome.

Diffusion Tensor Imaging Tractography Detecting Isolated Oculomotor Paralysis Caused by Pituitary Apoplexy

OBJECTIVES

Pituitary apoplexy (PA)-induced oculomotor palsy, although rare, can be caused by compression on the lateral wall of the cavernous sinus. This study aimed to visualize PA-induced oculomotor nerve damage using diffusion tensor imaging (DTI) tractography.

MATERIALS AND METHODS

We enrolled 5 patients with PA-induced isolated oculomotor palsy (patient group) and 10 healthy participants (control group); all underwent DTI tractography preoperatively. Fractional anisotropy (FA) and mean diffusion (MD) values of the cisternal portion of the bilateral oculomotor nerve were measured. DTI tractography was repeated after the recovery of oculomotor palsy.

RESULTS

While no statistical difference was observed in FA and MD values of the bilateral oculomotor nerve in the control group (P>0.05), the oculomotor nerve on the affected side was disrupted in the patient group, with a statistical difference in FA and MD values of the bilateral oculomotor nerve (P<0.01). After the recovery of oculomotor palsy, the FA value of the oculomotor nerve on the affected side increased, whereas the MD value decreased (P<0.01). Meanwhile, no significant difference was observed in FA and MD values of the bilateral oculomotor nerve (P>0.05). DTI tractography of the oculomotor nerve on the affected side revealed restoration of integrity. Furthermore, the symptoms of oculomotor palsy improved in all patients 7 days postoperatively.

CONCLUSION

DTI tractography could be a helpful adjunct to the standard clinical and paraclinical ophthalmoplegia examinations in patients with PA; thus, this study establishes the feasibility of DTI tractography in this specific clinical setting.

Three-Dimensional Identification of the Medial Longitudinal Fasciculus in the Human Brain: A Diffusion Tensor Imaging Study

Background: The medial longitudinal fasciculus (MLF) interacts with eye movement control circuits involved in the adjustment of horizontal, vertical, and torsional eye movements. In this study, we attempted to identify and investigate the anatomical characteristics of the MLF in human brain, using probabilistic diffusion tensor imaging (DTI) tractography. Methods: We recruited 31 normal healthy adults and used a 1.5-T scanner for DTI. To reconstruct MLFs, a seed region of interest (ROI) was placed on the interstitial nucleus of Cajal at the midbrain level. A target ROI was located on the MLF of the medulla in the reticular formation of the medulla. Mean values of fractional anisotropy, mean diffusivity, and tract volumes of MLFs were measured. Results: The component of the MLF originated from the midbrain MLF, descended through the posterior side of the medial lemniscus (ML) and terminated on the MLF of medulla on the posterior side of the ML in the medulla midline. DTI parameters of right and left MLFs were not significantly different. Conclusion: The tract of the MLF in healthy brain was identified by probabilistic DTI tractography. We believe this study will provide basic data and aid future comparative research on lesion or age-induced MLF changes.

Risk Factors and Outcomes of Early-Onset Peritonitis in Chinese Peritoneal Dialysis Patients

BACKGROUND/AIMS

Studies on the risk factors and outcomes of peritonitis within the first 6 months in peritoneal dialysis patients are sparse. This study aims to investigate the risk factors associated with early-onset peritonitis (EOP) and its influence on patients' technique survival and mortality.

METHODS

This is a retrospective observational cohort study. A total of 483 patients who had at least one episode of peritonitis were enrolled and followed from March 1, 2002, to August 31, 2016, at our center. According to the time to first peritonitis, we divided patients into two groups: EOP (≤ 6 months, n=167) and late-onset peritonitis (LOP, >6 months, n=316). Logistic regression was used to analyze the factors associated with EOP. A Cox proportional hazards model was constructed to examine the influence of EOP on clinical outcomes.

RESULTS

Of the 483 patients, 167 (34.6%) patients developed their first episode of peritonitis within the first 6 months. The EOP patient group had more male patients, a shorter time on peritoneal dialysis (PD), lower serum albumin levels at the time of PD initiation and a higher peritonitis rate (P<0.05). The EOP patient group had fewer infections with Gram-negative organisms (P=0.013) and more culture-negative peritonitis (P=0.014) than the LOP patient group for the first episode of peritonitis. The multivariate logistic regression analysis showed that factors associated with EOP included male gender (odds ratio (OR) 1.920, 95% confidence interval (CI) 1.272-2.897, P=0.002) and a low serum albumin level at the start of PD (OR 0.950, 95% CI 0.914-0.986, P=0.007). In the Cox proportional hazards model, EOP was a significant predictor of all-cause mortality (hazard ratio (HR) 2.766, 95% CI 1.561-4.900, P<0.001). There were no differences between EOP and LOP for technique failure. However, in continuous analyses, a negative correlation was observed between the time to first peritonitis and technique failure (HR 0.988, 95% CI 0.980-0.997, P=0.006). In the Spearman analysis, the time to first peritonitis was negatively correlated with the peritonitis rate (r=-0.573, P<0.001).

CONCLUSION

Male gender and a low serum albumin level before PD were strongly associated with EOP. Additionally, EOP patients had a higher risk of poor clinical outcomes. More importantly, an early peritonitis onset was associated with a high peritonitis rate.