Quantification approaches for magnetic resonance imaging following intravenous gadolinium injection: A window into brain-wide glymphatic function.

The glymphatic system is a brain-wide network of perivascular pathways along which cerebrospinal fluid and interstitial fluid rapidly exchange, facilitating solute and waste clearance from the brain parenchyma. The characterization of this exchange process in humans has relied primarily upon serial magnetic resonance imaging following intrathecal gadolinium-based contrast agent injection. However, less invasive approaches are needed. Here, we administered a gadolinium-based contrast agent intravenously in eight healthy participants and acquired magnetic resonance imaging scans prior to and 30, 90, 180, and 360 min post contrast injection. Using a region-of-interest approach, we observed that peripheral tissues and blood vessels exhibited high enhancement at 30 min after contrast administration, likely reflecting vascular and peripheral interstitial distribution of the gadolinium-based contrast agent. Ventricular, grey matter and white matter enhancement peaked at 90 min, declining thereafter. Using k-means clustering, we identify distinct distribution volumes reflecting the leptomeningeal perivascular network, superficial grey matter and deep grey/white matter that exhibit a sequential enhancement pattern consistent with parenchymal contrast enhancement via the subarachnoid cerebrospinal fluid compartment. We also outline the importance of correcting for (otherwise automatic) autoscaling of signal intensities, which could potentially lead to misinterpretation of gadolinium-based contrast agent distribution kinetics. In summary, we visualize and quantify delayed tissue enhancement following intravenous administration of gadolinium-based contrast agent in healthy human participants.

Combined GFAP, NFL, Tau, and UCH-L1 panel increases prediction of outcomes in neonatal encephalopathy.

BACKGROUND: Neuroprognostication in neonates with neonatal encephalopathy (NE) may be enhanced by early serial measurement of a panel of four brain-specific biomarkers. METHODS: To evaluate serum biomarkers, 40 NE samples and 37 healthy neonates from a biorepository were analyzed. Blood samples were collected at 0-6, 12, 24, 48, and 96 h of life. MRI provided a short-term measure of injury. Long-term outcomes included death or a Bayley III score at 17-24 months of age. RESULTS: Glial fibrillary acidic protein (GFAP), ubiquitin c-terminal hydrolase-L1 (UCH-L1), and Tau peaked at 0-6 h of life, while neurofilament light chain (NFL) peaked at 96 h of life. These four marker concentrations at 96 h of life differentiated moderate/severe from none/mild brain injury by MRI, while GFAP and Tau showed early discrimination. For long-term outcomes, GFAP, NFL, Tau, and UCH-L1 could differentiate a poor outcome vs good outcome as early as 0-6 h of life, depending on the Bayley domain, and a combination of the four markers enhanced the sensitivity and specificity. Machine learning trajectory analyses identified upward trajectory patients with a high concordance to poor outcomes. CONCLUSION: GFAP, NFL, Tau, and UCH-L1 may be of neuroprognostic significance after NE. IMPACT: Serial measurements of GFAP, NFL, Tau, and UCH-L1 show promise in aiding the bedside clinician in making treatment decisions in neonatal encephalopathy. The panel of four neuroproteins increased the ability to predict neurodevelopmental outcomes. The study utilized a trajectory analysis that enabled predictive modeling. A panel approach provides the bedside clinician with objective data to individualize care. This study provides the foundation to develop a point of care device in the future.

Clinical, electrophysiological, and imaging findings in childhood brachial plexus injury.

AIM: To assess the prognostic capabilities of various diagnostic modalities for childhood brachial plexus injuries (BPIs) and brachial plexus birth injury (BPBI) and postneonatal BPI. METHOD: In this single-center retrospective cross-sectional study, we examined children with BPIs diagnosed or confirmed by electrodiagnostic studies between 2013 and 2020, and compared the prognostic value of various components of the electrophysiologic findings, magnetic resonance imaging (MRI) data, and the Active Movement Scale (AMS). We developed scoring systems for electrodiagnostic studies and MRI findings, including various components of nerve conduction studies and electromyography (EMG) for electrodiagnostic studies. RESULTS: We identified 21 children (10 females and 11 males) aged 8 days to 21 years (mean 8y 6.95mo) who had a total of 30 electrodiagnostic studies, 14 brachial plexus MRI studies, and 10 surgical procedures. Among the diagnostic modalities assessed, brachial plexus MRI scores, EMG denervation scores, and mean total EMG scores were the most valuable in predicting surgical versus non-surgical outcomes. Correspondingly, a combined MRI/mean total EMG score provided prognostic value. INTERPRETATION: Brachial plexus MRI scores and specific electrodiagnostic scores provide the most accurate prognostic information for children with BPI. Our grading scales can assist a multidisciplinary team in quantifying results of these studies and determining prognosis in this setting. WHAT THIS PAPER ADDS: A new scoring system to quantify results of electrodiagnostic and magnetic resonance imaging (MRI) studies is presented. Severity of denervation has good prognostic value for childhood brachial plexus injuries (BPIs). Composite electromyography scores have good prognostic value for childhood BPIs. Brachial plexus MRI has good prognostic value for childhood BPIs.

Failed caudal block due to physiologic changes associated with a cerebrospinal fluid leak: a case report.

PURPOSE: The sum of the volumes of brain tissue, cerebrospinal fluid (CSF), and intracranial blood remain constant. This tenet of the Monroe-Kellie hypothesis is most often considered in the setting of intracranial hypertension, but it can also be applied in the setting of CSF volume depletion. We used this hypothesis to explain a case of failed caudal block in a patient with an iatrogenic CSF leak. CLINICAL FEATURES: A one-month-old baby (3 kg) born at 35 weeks' gestation presented for right inguinal hernia repair. His past medical history was significant for arthrogryposis (congenital joint contractures in two or more areas of the body) as well as ongoing apneic episodes that required continuous positive airway pressure therapy and neonatal intensive care. An ultrasound confirmed caudal block was completed and within five minutes of the procedure, the patient's heart rate increased, with an accompanying slight increase in T-wave amplitude. Pinch tests revealed anesthesia to the feet bilaterally but insufficient anesthesia to the abdomen. The surgery was delayed but successfully completed under general anesthesia the following week. Magnetic resonance imaging of the brain and spine following the surgery showed a significant CSF leak with engorgement of the epidural venous plexus along the entire spine. These findings were consistent with a CSF leak likely secondary to a prior lumbar puncture (at age 13 days) that was part of the investigation of his respiratory issues. CONCLUSIONS: The possible mechanism of this failed caudal block was high systemic absorption of anesthetic given the epidural venous plexus engorgement thus leaving less anesthetic acting within the CSF and on the exiting spinal nerves. Decreased CSF flow in the thecal sac might also have contributed, as might dilution of the remaining local anesthetic caused by large amounts of leaking CSF within the epidural space.

Intramyelinic edema manifesting as central white matter diffusion restriction associated with brain contusion in pediatric patients.

In traumatic brain injury, white matter diffusion restriction can be an imaging manifestation of non-hemorrhagic axonal injury. In this article, a different pattern of widespread white matter diffusion restriction associated with ipsilateral cortical damage, all noted in pediatric and young adult TBI patients, is presented. Its atypical pattern of distribution and extensive scope on imaging suggest excitotoxicity and intramyelinic edema as possible underlying mechanisms.

MicroRNAs as biomarkers of brain injury in neonatal encephalopathy: an observational cohort study.

Neonatal Encephalopathy (NE) is a major cause of lifelong disability and neurological complications in affected infants. Identifying novel diagnostic biomarkers in this population may assist in predicting MRI injury and differentiate neonates with NE from those with low-cord pH or healthy neonates and may help clinicians make real-time decisions. To compare the microRNA (miRNA) profiles between neonates with NE, healthy controls, and neonates with low cord pH. Moreover, miRNA concentrations were compared to brain injury severity in neonates with NE. This is a retrospective analysis of miRNA profiles from select samples in the biorepository and data registry at the University of Florida Health Gainesville. The Firefly miRNA assay was used to screen a total of 65 neurological miRNA targets in neonates with NE (n = 36), low cord pH (n = 18) and healthy controls (n = 37). Multivariate statistical techniques, including principal component analysis and orthogonal partial least squares discriminant analysis, and miRNA Enrichment Analysis and Annotation were used to identify miRNA markers and their pathobiological relevance. A set of 10 highly influential miRNAs were identified, which were significantly upregulated in the NE group compared to healthy controls. Of these, miR-323a-3p and mir-30e-5p displayed the highest fold change in expression levels. Moreover, miR-34c-5p, miR-491-5p, and miR-346 were significantly higher in the NE group compared to the low cord pH group. Furthermore, several miRNAs were identified that can differentiate between no/mild and moderate/severe injury in the NE group as measured by MRI. MiRNAs represent promising diagnostic and prognostic tools for improving the management of NE.

A Case of Unilateral Sixth Cranial Nerve (CN VI) Avulsion in the Prepontine Cistern After Severe Head Trauma.

The patient was a 46-year-old woman who presented with right sixth cranial nerve (CN VI) palsy following severe head trauma secondary to a motor vehicle collision one month prior. In this case report, we aim to add to the literature an additional example of unilateral CN VI avulsion as visualized by MRI secondary to head trauma. 3D T2 MRI was used to visualize the CN VI avulsion. CT was also used in the evaluation of head trauma. In our view, the force trajectory of the patient's impact with the vehicle dashboard, as evidenced by the right occipital lobe fracture, explains the etiology of the unilateral right CN VI avulsion. The combination of clinical and imaging findings was central to the analysis of this case.

High-resolution MRI to noninvasively characterize drainage around the carotid artery into the cervical lymph nodes.

BACKGROUND AND PURPOSE: Previous studies have proposed multiple parallel channels for waste clearance from the brain, though many gaps remain in our understanding of these systems. In this study, we examined periarterial fluid drainage around intracranial and extracranial segments of the internal carotid arteries (ICAs) from the brain into the cervical lymph nodes using a noninvasive and clinical-based method. METHODS: Eighty-one subjects (45 females, aged 15-80 years old) with nonlesioned epilepsy underwent high-resolution 3-dimensional T2-weighted fluid-attenuated inversion recovery (FLAIR) MRI. We utilized a noninvasive and clinical-based method with a manual semiautomated approach to characterize the periarterial lymphatic system's maximum thickness and signal intensities along the ICAs using high-resolution 3-dimensional FLAIR imaging. We conducted group comparisons and correlation analyses to investigate sex- and age-based trends. Results were corrected with Bonferroni's test for multiple comparisons, and we performed power analysis for sample size calculations. RESULTS: Using high-resolution FLAIR images, we show evidence that fluid drainage emerges around the ICA petrous segment and joins lymphatic flow from cranial nerves in the upper neck, with this flow ultimately draining into the cervical lymph nodes bilaterally. Lymphatic signal at the petrous segment level was significantly thinner in females compared to males bilaterally (w = 413, p = .0001 on the right, w = 356, p < .0001 on the left). Lymphatic drainage around the petrous segments of the ICAs bilaterally was thicker with age in males but not in females. CONCLUSIONS: We describe the in vivo high-resolution imaging characteristics of periarterial fluid drainage along the vessel walls of ICAs. This represents a potentially major channel for brain waste clearance. We also report interesting sex- and age-based trends in these structures within our cohort.

Imaging features of small vessel disease in cerebral amyloid angiopathy among patients with Alzheimer's disease.

BACKGROUND AND PURPOSE: Cerebral small vessel disease biomarkers including white matter hyperintensities (WMH), lacunes, and enlarged perivascular spaces (ePVS) are under investigation to identify those specific to cerebral amyloid angiopathy (CAA). In subjects with Alzheimer's disease (AD), we assessed characteristic features and amounts of WMH, lacunes, and ePVS in four CAA categories (no, mild, moderate and severe CAA) and correlated these with Clinical Dementia Rating sum of boxes (CDRsb) score, ApoE genotype, and neuropathological changes at autopsy. METHODS: The study included patients with a clinical diagnosis of dementia due to AD and neuropathological confirmation of AD and CAA in the National Alzheimer's Coordinating Center (NACC) database. The WMH, lacunes, and ePVS were evaluated using semi-quantitative scales. Statistical analyses compared the WMH, lacunes, and ePVS values in the four CAA groups with vascular risk factors and AD severity treated as covariates, and to correlate the imaging features with CDRsb score, ApoE genotype, and neuropathological findings. RESULTS: The study consisted of 232 patients, of which 222 patients had FLAIR data available and 105 patients had T2-MRI. Occipital predominant WMH were significantly associated with the presence of CAA (p = 0.007). Among the CAA groups, occipital predominant WMH was associated with severe CAA (ß = 1.22, p = 0.0001) compared with no CAA. Occipital predominant WMH were not associated with the CDRsb score performed at baseline (p = 0.68) or at follow-up 2-4 years after the MRI (p = 0.92). There was no significant difference in high grade ePVS in the basal ganglia (p = 0.63) and centrum semiovale (p = 0.95) among the four CAA groups. The WMH and ePVS on imaging did not correlate with the number of ApoE ε4 alleles but the WMH (periventricular and deep) correlated with the presence of infarcts, lacunes and microinfarcts on neuropathology. CONCLUSION: Among patients with AD, occipital predominant WMH is more likely to be found in patients with severe CAA than in those without CAA. The high-grade ePVS in centrum semiovale were common in all AD patients regardless of CAA severity.

Deep cerebral venous abnormalities in premature babies with GMH-IVH: a single-centre retrospective study.

PURPOSE: Germinal matrix haemorrhage/intraventricular haemorrhage (GMH-IVH) is a multifactorial injury with both anatomic and haemodynamic involvement. Normal variants in preterm deep cerebral venous anatomy associated with GMH-IVH have been previously described using MRI susceptibility weighted imaging (SWI). The aims of this study were to use SWI to compare the deep venous systems of a cohort of preterm neonates with various grades of GMH-IVH to a group of age-matched controls without GMH-IVH and to present novel retrospective SWI imaging findings. METHODS: A neuroradiologist retrospectively evaluated 3T MRI SWI and phase imaging of 56 preterm neonates with GMH-IVH (14 of each grade) and 27 controls without GMH-IVH, scoring the venous irregularities according to three variables: decreased venous patency, increased lumen susceptibility and the presence of collaterals. Eight different venous locations, including indicated bilateral components, were evaluated: straight sinus, vein of galen, internal cerebral, direct lateral, thalamostriate, atrial and the anterior septal veins. Variables were analysed for statistical significance. Inter-rater reliability was determined via subset evaluation by a second paediatric radiologist. RESULTS: Deep venous abnormalities were significantly more common in patients with GMH-IVH, with Wilcoxon Rank Sum Test demonstrating significant increase with GMH-IVH for total decreased venous patency (W=0, p<0.0001), increased lumen susceptibility and collateral formation. Venous abnormalities were also positively correlated with an increase in GMH-IVH grade from I to IV (patency, ρ=0.782, p<0.01) (increased lumen susceptibility, ρ=0.739, p<0.01) (collaterals, ρ=0.649, p<0.01), not just GMH-IVH alone. CONCLUSION: Deep venous abnormalities are significantly correlated with GMH-IVH alone and an increase in GMH-IVH grade. Further study is needed to determine cause and effect.

Association of deep white matter hyperintensity with left ventricular hypertrophy in acute ischemic stroke.

BACKGROUND AND PURPOSE: White matter hyperintensities (WMHs) are associated with the presence of left ventricular hypertrophy (LVH). It is unclear if periventricular WMH (PV-WMH) and or deep WMH (D-WMH) are associated with LVH. We evaluated the association of PV-WMH and D-WMH with common transthoracic echocardiogram abnormalities, including LVH in acute ischemic stroke. METHODS: PV-WMH and D-WMH were graded on a 0-3 score based on the Fazekas scale. Patients were categorized into clinically significant PV-WMH and D-WMH (score 2-3) and controls (score 0-1). Multivariate logistic regression analysis was performed to determine abnormalities on echocardiogram associated with PV-WMH and D-WMH. RESULTS: Among 272 patients, 137 patients had PV-WMH and 93 patients had D-WMH with a score of 2-3 on Fazekas scale. Compared to controls, patients with PV-WMH (mean age±standard deviation: 60.8±14.4 vs. 73.8±11.2 years) and D-WMH (63.4±14.4 vs. 75.0±11.1 years) were older. Compared to controls, PV-WMH was associated with history of stroke (22 [16%] vs. 37 [27%], p = .03) and valvular calcification (33 [24%] vs. 61 [45%], p = .0005); D-WMH was associated with history of atrial fibrillation (25 [14%] vs. 22 [24%], p = .04), valvular calcification (50 [28%] vs. 44 [47%], p = .001), and LVH (30 [17%] vs. 25 [27%], p = .049). In multivariate analysis, PV-WMH was associated with age (odds ratio [OR] = 1.09; 95% confidence interval [CI] = 1.06-1.12) and stroke history (OR = 2.1; 95% CI = 1.1-4.1), and D-WMH was associated with age (OR = 1.07; 95% CI = 1.05-1.10) and LVH (OR = 2.0; 95% CI = 1.0-4.0). CONCLUSION: LVH is associated with D-WMH but not with PV-WMH. Although valvular calcification is common, it is likely age related than due to WMH.

Streptococcus Intermedius as the cause of sphenoid sinusitis & associated extensive skull base and neck thrombophlebitis & thrombosis.

Acute bacterial sinusitis may be complicated by orbital and intracranial involvement and by thrombophlebitis. Its spread across multiple anatomic compartments is facilitated by the interconnected venous anatomy of the head and neck and the virulence of the primary pathogen. We present a rare case of Streptococcus Intermedius (S. Intermedius) acute bacterial sinusitis complicated by extensive skull base involvement including cavernous sinuses and neck vein thrombophlebitis and thrombosis.

Neurological deterioration and computed tomography perfusion changes with increased time to peak in lacunar stroke.

OBJECTIVES: Lacunar strokes can have fluctuations and progression in the acute period leading to poor outcomes. Our study sought to evaluate if, in lacunar strokes, neurological deterioration (ND) was associated with blood pressure (BP) variations, stroke size, or increased time to peak (TTP) on admission computed tomography perfusion (CTP). METHODS: Patients with lacunar stroke who had magnetic resonance imaging and CTP performed were enrolled in the study. ND was defined as ≥1-point worsening on a modified National Institutes of Health Stroke Scale (NIHSS) score or the Medical Research Council scale compared to baseline assessment. The difference in BP between the day of admission and the day of ND was calculated. Multivariate logistic regression analysis, adjusted for pertinent clinical and imaging covariates, was performed to determine predictors of ND. RESULTS: Among 409 patients screened, 49 were eligible for the study. There was no difference in age, gender, race, medical history, admission BP, and the modified NIHSS score between patients with and without ND. In unadjusted analysis, patients with ND tended to have increased TTP in the stroke area compared to the control (12 [63%] vs. 11 [37%], P = 0.07). On multivariate analysis adjusted for covariates, presence of an increased TTP on CTP was a predictor of ND (odds ratio [95% confidence interval] = 4.80 [1.15-20.10], P = 0.03). CONCLUSION: The presence of an increased TTP on CTP corresponding to the stroke lesion on diffusion-weighted imaging is a predictor of ND in patients with lacunar stroke. Larger studies are needed to confirm our findings.

COVID-19-Related Rhino-Orbito-Cerebral Mucormycosis Complicated by the Optic Nerve and Optic Tract Ischemia With Ischemic Neuropathy.

Mucormycosis is a life-threatening invasive fungal infection usually seen in immunocompromised patients and patients with poorly controlled diabetes mellitus with or without diabetic ketoacidosis. We present a rhino-orbito-cerebral mucormycosis (ROCM) case in a coronavirus disease 2019 (COVID-19) patient complicated by the optic nerve and optic tract ischemia with ischemic neuropathy. Both CT and MRI played an essential role in diagnosing ROCM and the accompanying complications in our patient. CT showed sinonasal sinusitis and MRI showed the sinusitis and its progression to ROCM. MRI also showed necrosis involving the bilateral orbits, basal ganglia, thalamus, internal capsule, hypothalamus, optic chiasm, optic nerves, olfactory bulbs, and skull base. ROCM associated with optic nerve ischemia is a rare but life-threatening complication of COVID-19, especially in patients with underlying diabetes and/or those treated with corticosteroids. Physicians should be aware of this complication as early diagnosis may improve the chances of survival in such patients.

Visualization of the perivenous glymphatic efflux in human brain after laser interstitial thermal therapy.

Recent studies have revealed that there is existence of a specific waste clearance pathway in the brain, coined the glymphatic system. This case report demonstrates supportive finding of drainage of Gadolinium and waste products released after Laser Interstitial Thermal Therapy via perivenous routes and a paradural lymphatic system. These findings provide further evidence of interstitial fluid drainage along the perivenous spaces in accordance with a glymphatic system theory.

Non-invasive MR imaging of human brain lymphatic networks with connections to cervical lymph nodes.

Meningeal lymphatic vessels have been described in animal studies, but limited comparable data is available in human studies. Here we show dural lymphatic structures along the dural venous sinuses in dorsal regions and along cranial nerves in the ventral regions in the human brain. 3D T2-Fluid Attenuated Inversion Recovery magnetic resonance imaging relies on internal signals of protein rich lymphatic fluid rather than contrast media and is used in the present study to visualize the major human dural lymphatic structures. Moreover we detect direct connections between lymphatic fluid channels along the cranial nerves and vascular structures and the cervical lymph nodes. We also identify age-related cervical lymph node atrophy and thickening of lymphatics channels in both dorsal and ventral regions, findings which reflect the reduced lymphatic output of the aged brain.

Neuronal exosome proteins: novel biomarkers for predicting neonatal response to therapeutic hypothermia.

OBJECTIVE: Central nervous system (CNS) derived exosomes can be purified from peripheral blood and have been used widely in adult neurological disease. Application to neonatal neurological disease deserves investigation in the setting of hypoxic-ischaemic encephalopathy (HIE). DESIGN: Observational cohort. SETTING: Level III neonatal intensive care unit. PARTICIPANTS: Term/near-term neonates undergoing therapeutic hypothermia (TH) for HIE. INTERVENTIONS: Blood samples were collected at 0-6, 12, 24, 48 and 96 hours of life. MAIN OUTCOMES AND MEASURES: CNS exosomes were purified from serum using previously described methods. Biomarker protein levels were quantified using standard ELISA methods and normalised to exosome marker CD-81. The slope of change for biomarker levels was calculated for each time interval. Our primary outcome was MRI basal ganglia/watershed score of ≥3. RESULTS: 26 subjects were included (umbilical artery pH range 6.6-7.29; 35% seizures). An increasing MRI injury score was significantly associated with decreasing levels of synaptopodin between 0-6 and 12 hours (p=0.03) and increasing levels of lipocalin-2 (NGAL) between 12 and 48 hours (p<0.0001). Neuronal pentraxin was not significant. The negative predictive values for increasing synaptopodin and decreasing NGAL was 70.0% and 90.9%, respectively. CONCLUSIONS AND RELEVANCE: Our results indicate that CNS exosome cargo has the potential to act as biomarkers of the severity of brain injury and response to TH as well as quantify pharmacological response to neuroactive therapeutic/adjuvant agents. Rigorous prospective trials are critical to evaluate potential clinical use of exosome biomarkers.

Subacute Posterior Inferior Cerebellar Artery Stroke Radiographically Mimicking Lhermitte-Duclos Disease.

Lhermitte-Duclos disease (LDD) is a rare cerebellar lesion characterized by a hamartomatous lesion of the cerebellum. Mainly diagnosed by MRI, the clinical presentation is usually made of neurological symptoms. Modern neuroimaging techniques such as MRI have led to accurate diagnosis of this disease in both its pre- and post-operative periods. We present the case of a 68-year-old male with a past medical history of cardiac stenting and coronary artery disease who originally presented to the emergency department as a transfer for evaluation of possible obstructing hydrocephalus and left posterior inferior cerebellar artery (PICA) infarct. Based on the clinical presentation and imaging, the favored diagnosis of his left cerebellar abnormality was LDD rather than an unusual acute/subacute infarct or a metastatic lesion. The rapid progression of symptoms with rapidly progressive cytotoxic edema on serial CTs helped exclude LDD, which is nearly always more of a chronic process. The classic neuroimaging findings and clinical presentation of LDD are also discussed.

Gadolinium in tears: Evidence for an alternative cerebrospinal fluid absorption pathway in the setting of ischemia-induced blood brain barrier disruption.

Cerebral ischemia results in disruption of the blood-brain barrier (BBB) allowing leakage of gadolinium-based contrast media (GBCM) into cerebrospinal fluid (CSF) within the craniospinal and perineural subarachnoid spaces (SAS). This phenomenon is well visualized with fluid-attenuated inversion recovery MRI techniques and allows for visualization of CSF flow dynamics. We present a case of ischemia-induced BBB disruption resulting in accumulation of GBCM in the SAS and ocular chambers as well as within the precorneal tear film and nasolacrimal duct. We present imaging evidence for a hypothetical alternate CSF absorption pathway through the ocular structures in keeping with prior experimental evidence.

Detailed imaging of abducens nerve anatomy using contrast-enhanced 3D-TOF MR angiography.

PURPOSE: Cranial nerves (CNs), particularly CN IV and VI are difficult to visualize with conventional MRI techniques, particularly within the cavernous sinus region. The aim of this study was to evaluate the capacity of high-resolution contrast enhanced 3D time-of-flight (TOF) MR angiography using new generation 3 T imaging technology to provide detailed visualization of CN VI anatomy, particularly within the cavernous sinus and petroclival regions. METHODS: Two neuroradiologists conducted bilateral evaluation of CN VI visibility in 23 patients for nerve segments located in the petroclival segment (dural cave and Dorello's canal), and three divisions of the cavernous sinus. All images were collected using contrast enhanced TOF MR angiography using a new generation 3 T machine. RESULTS: Of the CN VI segments assessed, average visibility of CN VI was best achieved in Dorello's canal. Overall visibility of CN VI within the regions inspected was best achieved in the axial view, with the exception of the dural cave, which was best assessed using the coronal view. We also identified strong agreement in assessment of nerve visibility between the two reviewers. We also identified a putative CN6 duplication and a small schwannoma, highlighting the fidelity of our approach. CONCLUSION: Contrast enhanced 3D TOF MR angiography can visualize CN VI anatomy, particularly within the petrocavernosal region and cavernous sinus with simultaneous visualization of arterial and venous structures. This cannot be easily achieved using traditional MRI techniques. This imaging technique might be used with new generation machines to evaluate CN VI anatomy and pathologies within the petrocavernosal region and cavernous sinus, especially relating to vascular pathologies.