Impact of Cerebral Revascularization on Pial Collateral Flow in Patients With Unilateral Moyamoya Disease Using Quantitative Magnetic Resonance Angiography.

BACKGROUND AND OBJECTIVES: Moyamoya disease (MMD) is a chronic steno-occlusive disease of the intracranial circulation that depends on neoangiogenesis of collateral vessels to maintain cerebral perfusion and is primarily managed with cerebral revascularization surgery. A quantitative assessment of preoperative and postoperative collateral flow using quantitative magnetic resonance angiography with noninvasive optimal vessel analysis (NOVA) was used to illustrate the impact of revascularization on cerebral flow distribution. METHODS: A retrospective review of patients with unilateral MMD who underwent direct, indirect, or combined direct/indirect cerebral revascularization surgery was conducted between 2011 and 2020. Using NOVA, flow was measured at the anterior cerebral artery (ACA), ACA distal to the anterior communicating artery (A2), middle cerebral artery (MCA), posterior cerebral artery (PCA), and PCA distal to the posterior communicating artery (P2). Pial flow (A2 + P2) and collateral flow (ipsilateral [A2 + P2])-(contralateral [A2 + P2]) were measured and compared before and after revascularization surgery. Total hemispheric flow (MCA + A2 + P2) with the addition of the bypass graft flow postoperatively was likewise measured. RESULTS: Thirty-four patients with unilateral MMD underwent cerebral revascularization. Median collateral flow significantly decreased from 68 to 39.5 mL/min (P = .007) after bypass. Hemispheres with maintained measurable bypass signal on postoperative NOVA demonstrated significant reduction in median collateral flow after bypass (P = .002). Median total hemispheric flow significantly increased from 227 mL/min to 247 mL/min (P = .007) after bypass. Only one patient suffered an ipsilateral ischemic stroke, and no patients suffered a hemorrhage during follow-up. CONCLUSION: NOVA measurements demonstrate a reduction in pial collateral flow and an increase in total hemispheric flow after bypass for MMD, likely representing a decrease in leptomeningeal collateral stress on the distal ACA and PCA territories. Further studies with these measures in larger cohorts may elucidate a role for NOVA in predicting the risk of ischemic and hemorrhagic events in MMD.

Direct Wave Intraoperative Neuromonitoring for Spinal Tumor Resection: A Focused Review.

At present, surgical resection of primary intramedullary spinal cord tumors is the mainstay of treatment. However, given the dimensional constraints of the narrow spinal canal and dense organization of the ascending and descending tracts, intramedullary spinal cord tumor resection carries a significant risk of iatrogenic neurological injury. Intraoperative neurophysiological monitoring (IONM) and mapping techniques have been developed to evaluate the functional integrity of the essential neural pathways and optimize the surgical strategies. IONM can also inform on impending harm to at-risk structures and can correlate with postoperative functional recovery if damage has occurred. Direct waves (D-waves) will provide immediate feedback on the integrity of the lateral corticospinal tract. In the present review, we have provided an update on the utility of D-waves for spinal cord tumor resection. We have highlighted the neuroanatomical and neurophysiological insights from the use of D-wave monitoring, the technical considerations and limitations of the D-wave technique, and multimodal co-monitoring with motor-evoked potentials and somatosensory-evoked potentials. Together with motor-evoked potentials, D-waves can help to guide the extent of tumor resection and provide intraoperative warning signs and alarm criteria to direct the surgical strategy. D-waves can also serve as prognostic biomarkers for long-term recovery of postoperative motor function. We propose that the use of D-wave IONM can contribute key findings for clinical decision-making during spinal cord tumor resection.

Multifocal lumbar myxopapillary ependymoma presenting with drop metastasis: a case report and review of the literature.

INTRODUCTION: Spinal myxopapillary ependymomas (SME) are rare WHO grade II neoplasms of the spinal cord. Despite their good prognosis, they have a high propensity for metastasis and recurrence, although the presentation of SME as multifocal is uncommon. CASE PRESENTATION: Here we describe a rare case of a 34-year-old man who presented with painful bilateral radiculopathy with sexual dysfunction and altered sensation with defecation. The patient also reported worsening weakness of bilateral lower extremities when climbing stairs. Biopsy results revealed multifocal SME in the lumbar and sacral spine that was treated with staged surgical resection and post-operative focal radiation therapy. DISCUSSION: We discuss and evaluate surgical resection and the role of postoperative radiotherapy for SME. We also review the literature surrounding multifocal SME presenting in adults.

Utility of quantitative magnetic resonance angiography and non-invasive optimal vessel analysis for identification of complications and long-term hemodynamic changes in post-pipeline embolization patients.

INTRODUCTION: Quantitative magnetic resonance angiography and non-invasive optimal vessel analysis serve as powerful tools to collect and analyze hemodynamic data from pipeline embolization patients. At our institution, patients receive post-embolization quantitative magnetic resonance angiography within 24 h of treatment and within 6 months for follow-up to evaluate pipeline patency. Here, we aim to elucidate the long-term hemodynamic changes following pipeline embolization device placement and report two cases in which in-stent stenosis was detected. METHODS: Medical records of patients who underwent pipeline embolization device placement for an internal carotid artery aneurysm between 2017 and 2019 were reviewed. Patients who received post-procedure NOVA and follow-up NOVA were included in the study (n = 32). Location and size of aneurysm, number of pipeline embolization device deployed, and complications were collected along with the non-invasive optimal vessel analysis report (flow volume rate (ml/min), mean, systolic, and diastolic flow velocities (cm/s), and vessel diameter (mm)). Internal carotid artery vessel flow rate was measured proximal to the pipeline embolization device. Derivations of hemodynamic parameters (pulsatility index, Lindegaard ratio, and wall shear stress) were calculated. RESULTS: The middle cerebral artery mean and diastolic flow velocities were significantly lower on the follow-up NOVA compared to the post-procedure NOVA. Moreover, follow-up NOVA demonstrated lower middle cerebral artery wall shear stress on the side with flow diversion compared to the post-procedure NOVA. In-stent stenosis, requiring intervention, was detected in two patients on follow-up NOVA. One patient had a successful balloon angioplasty of the stented internal carotid artery that resolved her stenosis. However, the second patient developed progressive stenosis and expired despite intervention. CONCLUSION: Long-term hemodynamic adaptations post-pipeline embolization device demonstrate decreased wall shear stress and decreased mean and diastolic flow velocities in the distal middle cerebral artery, which suggest decreasing velocity of blood flow with endothelialization of the device. Furthermore, follow-up NOVA is a useful tool for detecting potential flow-related complications such as in-stent stenosis.

Quantitative magnetic resonance angiography to assess post embolization hemodynamics following pipeline embolization.

INTRODUCTION: Delayed intraparenchymal hemorrhage is a known complication of the Pipeline Embolization device (PED); however, its etiology is unclear and some have suggested it is a flow related phenomenon. Quantitative magnetic resonance angiography (QMRA) serves as a powerful tool to collect and analyze hemodynamic data. We report a detailed characterization of short-term hemodynamics after PED placement. METHODS: Patients who underwent PED placement for a distal internal carotid artery (ICA) aneurysm between 2017 to 2019 with post embolization QMRA were reviewed. Aneurysm characteristics, flow volume rate (ml/min), mean, systolic, and diastolic flow velocities (cm/s), vessel diameter (mm), pulsatility index, Lindegaard ratio, and wall shear stress (WSS) were collected. RESULTS: A total of 67 patients were included. Post-procedure patients were found to have a significantly lower ICA flow on the side with flow diversion when compared to the side without flow diversion (218 vs. 236.3; P < 0.05). Average ICA flow after flow diversion for aneurysms >2 cm was significantly lower when compared to the untreated side (187.7 vs. 240.4; P < 0.05). There was no difference in MCA or ACA flow or velocity. WSS was significantly lower in the treated ICA (8.2 vs. 9.0; P < 0.05). Lindegaard ratio was not different in the treated vs. contralateral untreated sides. CONCLUSION: PED placement for distal ICA aneurysms results in lower flow, mean velocity, and WSS when compared to the contralateral untreated ICA. This is not demonstrated distal to the Pipeline device in the ACA or MCA territories. Ultimately these findings suggest hemodynamic changes are not a cause of PED complications.

Erosion of the sella turcica and pituitary expansion secondary to polymicrobial brain abscesses: a case report.

INTRODUCTION: Brain abscesses can lead to a diverse array of complications, especially when they are polymicrobial in nature. Multiple underlying pathogens may present with a unique set of clinical symptoms which require an early identification and treatment. Skull base osteomyelitis with sellar floor erosion and pituitary involvement with SIADH are such rare complications of brain abscesses which have never been reported previously in the literature. CASE PRESENTATION: We report the case of an immunocompetent 38-year-old male with altered mental sensorium and left hemiparesis due to polymicrobial brain abscess which required surgical evacuation. The post-operative recovery was complicated by severe hyponatremia secondary to SIADH which was treated uneventfully. Radiological imaging demonstrated pituitary enlargement with herniation through an eroded sella turcica without active CSF leak. Patient responded well to the antibiotic therapy based on microbiological susceptibility testing with a complete resolution of the pituitary enlargement on radiological follow-up. CONCLUSION: Conservative treatment with targeted antibiotics can lead to the resolution of pituitary enlargement secondary to a brain abscess. However, a close clinical follow-up is required to look for a CSF leak considering the sellar floor erosion due to osteomyelitis.

Chronic loss of inhibition in piriform cortex following brief, daily optogenetic stimulation.

It is well established that seizures beget seizures, yet the cellular processes that underlie progressive epileptogenesis remain unclear. Here, we use optogenetics to briefly activate targeted populations of mouse piriform cortex (PCx) principal neurons in vivo. After just 3 or 4 days of stimulation, previously subconvulsive stimuli trigger massive, generalized seizures. Highly recurrent allocortices are especially prone to "optokindling." Optokindling upsets the balance of recurrent excitation and feedback inhibition. To understand how this balance is disrupted, we then selectively reactivate the same neurons in vitro. Surprisingly, we find no evidence of heterosynaptic potentiation; instead, we observe a marked, pathway-specific decrease in feedback inhibition. We find no loss of inhibitory interneurons; rather, decreased GABA synthesis in feedback inhibitory neurons appears to underlie weakened inhibition. Optokindling will allow precise identification of the molecular processes by which brain activity patterns can progressively and pathologically disrupt the balance of cortical excitation and inhibition.