A Paravermal Trans-Cerebellar Approach to the Posterior Fossa Tumor Causes Hypertrophic Olivary Degeneration by Dentate Nucleus Injury

Vim-PSA Double-Target DBS for the Treatment of Holmes Tremor Secondary to Brainstem Hemorrhage: A Case Report

We report the case of a 53-year-old man who was diagnosed with Holmes tremor and underwent deep brain stimulation of the ventro-intermediate thalamic nucleus and posterior subthalamic area. We assessed the patients' tremor with the Fahn-Tolosa-Marin Tremor Rating Scale at 1, 3, 6, 12 and 24 months after deep brain stimulation. Deep brain stimulation relieved the patient's tremor during the 24-month follow-up period.

National multicentered retrospective review of clinical and intraoperative factors associated with the development of cerebellar mutism after pediatric posterior fossa tumor resection

BACKGROUND

Cerebellar mutism (CM) is characterized by a significant loss of speech in children following posterior fossa (PF) surgery. The biological origin of CM remains unclear and is the subject of ongoing debate. Significant recovery from CM is less likely than previously described despite rigorous multidisciplinary neuro-rehabilitational efforts.

METHODS

A national multi-centered retrospective review of all children undergoing PF resection in four midsized Canadian academic pediatric institutions was undertaken. Patient, tumor and surgical factors associated with the post-operative development of CM were reviewed. Retrospective identification of PF surgery patients including those developing and those that did not (internal control).

RESULTS

The study identified 258 patients across the 4 centers between 2010 and 2020 (mean age 6.73 years; 42.2% female). Overall, CM was experienced in 19.5% of patients (N = 50). Amongst children who developed CM histopathology included medulloblastoma (35.7%), pilocytic astrocytoma (32.6%) and ependymoma (17.1%). Intraoperative impression of adherence to the floor of the 4th ventricle was positive in 36.8%. Intraoperative abrupt changes in blood pressure and/or heart rate were identified in 19.4% and 17.8% of cases. The clinical resolution of CM was rated to be complete, significant resolution, slight improvement, no improvement and deterioration in 56.0%, 8.0%, 20.0%, 14.0% and 2.0%, respectively. In the cohort of children who experienced post-operative CM as compared to their no-CM counterpart, proportionally more tumors were felt to be adherent to the floor of the 4th ventricle (56.0% vs 49.5%), intraoperative extent of resection was a GTR (74% vs 68.8%) and changes in heart rate were noted (≥ 20% from baseline) (26.0% vs 15.9%). However, a multiple regression analysis identified only abrupt changes in HR (OR 5.97, CI (1.53, 23.1), p = 0.01) to be significantly associated with the development of post-operative CM.

CONCLUSION

As a devastating surgical complication after posterior fossa tumor surgery with variable clinical course, identifying and understanding the operative cues and revising intraoperative plans that optimizes the child's neurooncological and clinical outcome are essential.

The Guillain-Mollaret triangle: a key player in motor coordination and control with implications for neurological disorders

The dentato-rubro-olivary pathway, also known as the Guillain-Mollaret triangle (GMT) or myoclonic triangle, consists of the dentate nucleus, the red nucleus, and the inferior olivary nucleus (ION). GMT is important for motor coordination and control, and abnormalities in this network can lead to various neurological disorders. The present study followed a systematic approach in conducting a review on GMT studies. The inclusion criteria were limited to human subjects with primary objectives of characterizing and evaluating GMT syndromes, and the methodology used was not a determining factor for eligibility. The search strategy used MeSH terms and keywords relevant to the study's objective in various databases until August 2022. A total of 76 studies were included in the review after assessing 527 articles for eligibility based on the final inclusion criteria. Most of the studies evaluated the GMT in human subjects, with the majority utilizing magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), or combination of them. The review found that Hypertrophic olivary degeneration (HOD), a common consequence of GMT damage, has diverse underlying causes, including stroke, brainstem cavernous malformations, and structural impairments. Palatal tremor, ocular myoclonus, ataxia, nystagmus, and vertigo were frequently reported symptoms associated with HOD. This systematic review provides comprehensive insights into the association between GMT and various neurological syndromes, shedding light on the diagnostic, etiological, and prognostic aspects of GMT dysfunction. Understanding the role of the GMT and its implications in movement disorders could pave the way for improved treatment options and better management of neurological conditions related to this critical brainstem pathway.

Qualitative and quantitative detectability of hypertrophic olivary degeneration in T2, FLAIR, PD, and DTI: A prospective MRI study

Purpose:

Hypertrophic olivary degeneration (HOD) is a pathology of the inferior olivary nucleus (ION) that occurs after injuries to the Guillain-Mollaret triangle (GMT). Lacking a diagnostic gold standard, diagnosis is usually based on T2 or FLAIR imaging and expert rating. To facilitate precise HOD diagnosis in future studies, we assessed the reliability of this rater-based approach and explored alternative, quantitative analysis.

Methods

Patients who had suffered strokes in the GMT and a matched control group prospectively underwent an MRI examination including T2, FLAIR, and proton density (PD). Diffusion tensor imaging (DTI) was additionally performed in the patient group. The presence of HOD was assessed on FLAIR, T2, and PD separately by 3 blinded reviewers. Employing an easily reproducible segmentation approach, relative differences in intensity, fractional anisotropy (FA), and mean diffusivity (MD) between both IONs were calculated.

Results

In total, 15 patients were included in this study. The interrater reliability was best for FLAIR, followed by T2 and PD (Fleiss κ = 0.87 / 0.77 / 0.65). The 3 raters diagnosed HOD in 38–46% (FLAIR), 40–47% (T2), and 53–67% (PD) of patients. False-positive findings in the control group were less frequent in T2 than in PD and FLAIR (2.2% / 8.9% / 6.7%). In 53% of patients, the intensity difference between both IONs on PD was significantly increased in comparison with the control group. These patients also showed significantly decreased FA and increased MD.

Conclusion

While the rater-based approach yielded the best performance on T2 imaging, a quantitative, more sensitive HOD diagnosis based on ION intensities in PD and DTI imaging seems possible.

Hypertrophic Olivary Degeneration Postoperatively Following Pilocytic Astrocytoma Resection

A 25-year-old male presented with headaches 3 weeks after a car accident. His MRI images showed a hemorrhagic vermis mass with 4^th ventricle effacement. One month later, he underwent suboccipital craniotomy for removal of a pilocytic astrocytoma. A 3-month postoperative scan demonstrated a new area of medullary hyperintensity in the inferior olive also present 7-months postoperatively consistent with hypertrophic olivary degeneration (HOD). This condition is caused by disruption to the dento-rubro-olivary pathway with MRI enlargement of the inferior olivary nucleus and increased T2 signal. HOD should be considered after cerebellar surgery and should not be mistaken for tumor recurrence.

Multicenter Prospective Analysis of Hypertrophic Olivary Degeneration Following Infratentorial Stroke (HOD-IS): Evaluation of Disease Epidemiology, Clinical Presentation, and MR-Imaging Aspects

Introduction: Ischemic and hemorrhagic strokes in the brainstem and cerebellum with injury to the functional loop of the Guillain-Mollaret triangle (GMT) can trigger a series of events that result in secondary trans-synaptic neurodegeneration of the inferior olivary nucleus. In an unknown percentage of patients, this leads to a condition called hypertrophic olivary degeneration (HOD). Characteristic clinical symptoms of HOD progress slowly over months and consist of a rhythmic palatal tremor, vertical pendular nystagmus, and Holmes tremor of the upper limbs. Diffusion Tensor Imaging (DTI) with tractography is a promising method to identify functional pathway lesions along the cerebello-thalamo-cortical connectivity and to generate a deeper understanding of the HOD pathophysiology. The incidence of HOD development following stroke and the timeline of clinical symptoms have not yet been determined in prospective studies—a prerequisite for the surveillance of patients at risk.

Methods and Analysis: Patients with ischemic and hemorrhagic strokes in the brainstem and cerebellum with a topo-anatomical relation to the GMT are recruited within certified stroke units of the Interdisciplinary Neurovascular Network of the Rhine-Main. Matching lesions are identified using a predefined MRI template. Eligible patients are prospectively followed up and present at 4 and 8 months after the index event. During study visits, a clinical neurological examination and brain MRI, including high-resolution T2-, proton-density-weighted imaging, and DTI tractography, are performed. Fiberoptic endoscopic evaluation of swallowing is optional if palatal tremor is encountered.

Study Outcomes: The primary endpoint of this prospective clinical multicenter study is to determine the frequency of radiological HOD development in patients with a posterior fossa stroke affecting the GMT at 8 months after the index event. Secondary endpoints are identification of (1) the timeline and relevance of clinical symptoms, (2) lesion localizations more prone to HOD occurrence, and (3) the best MR-imaging regimen for HOD identification. Additionally, (4) DTI tractography data are used to analyze individual pathway lesions. The aim is to contribute to the epidemiological and pathophysiological understanding of HOD and hereby facilitate future research on therapeutic and prophylactic measures.

Clinical Trial Registration: HOD-IS is a registered trial at https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00020549.