Mechanisms of blood-retinal barrier disruption related to intraocular inflammation and malignancy

Blood-retinal barrier (BRB) disruption is a common accompaniment of intermediate, posterior and panuveitis causing leakage into the retina and macular oedema resulting in vision loss. It is much less common in anterior uveitis or in patients with intraocular lymphoma who may have marked signs of intraocular inflammation. New drugs used for chemotherapy (cytarabine, immune checkpoint inhibitors, BRAF inhibitors, EGFR inhibitors, bispecific anti-EGFR inhibitors, MET receptor inhibitors and Bruton tyrosine kinase inhibitors) can also cause different types of uveitis and BRB disruption. As malignant disease itself can cause uveitis, particularly from breast, lung and gastrointestinal tract cancers, it can be clinically difficult to sort out the cause of BRB disruption. Immunosuppression due to malignant disease and/or chemotherapy can lead to infection which can also cause BRB disruption and intraocular infection. In this paper we address the pathophysiology of BRB disruption related to intraocular inflammation and malignancy, methods for estimating the extent and effect of the disruption and examine why some types of intraocular inflammation and malignancy cause BRB disruption and others do not. Understanding this may help sort and manage these patients, as well as devise future therapeutic approaches.

A fluorescein angiography-based computer-aided algorithm for assessing the retinal vasculature in diabetic retinopathy

OBJECTIVE

To present a fluorescein angiography (FA)‒based computer algorithm for quantifying retinal blood flow, perfusion, and permeability, in patients with diabetic retinopathy (DR). Secondary objectives were to quantitatively assess treatment efficacy following panretinal photocoagulation (PRP) and define thresholds for pathology based on a new retinovascular function (RVF) score for quantifying disease severity.

METHODS

FA images of 65 subjects (58 patients and 7 healthy volunteers) were included. Dye intensity kinetics were derived using pixel-wise linear regression as a measure of retinal blood flow, perfusion, and permeability. Maps corresponding to each measure were then generated for each subject and segmented further using an ETDRS grid. Non-parametric statistical analyses were performed between all ETDRS subfields. For 16 patients, the effect of PRP was measured using the same parameters, and an amalgam of RVF was used to create an RVF index. For ten post-treatment patients, the change in FA-derived data was compared to the macular thickness measured using optical coherence tomography.

RESULTS

Compared to healthy controls, patients had significantly lower retinal and regional perfusion and flow, as well as higher retinal permeability (p < 0.05). Moreover, retinal flow was inversely correlated with permeability (R = -0.41; p < 0.0001). PRP significantly reduced retinal permeability (p < 0.05). The earliest marker of DR was reduced retinal blood flow, followed by increased permeability. FA-based RVF index was a more sensitive indicator of treatment efficacy than macular thickness.

CONCLUSIONS

Our algorithm can be used to quantify retinovascular function, providing an earlier diagnosis and an objective characterisation of disease state, disease progression, and response to treatment.

Distorted Optic Nerve Portends Neurological Complications in Infants With External Hydrocephalus

Background: Benign external hydrocephalus (BEH) is defined by rapid increase in head circumference in infancy, with neuroimaging evidence of enlarged cerebrospinal fluid (CSF) spaces. BEH was postulated to predispose to subdural hematoma, neurocognitive impairments, and autism. There is currently no consensus on BEH diagnostic criteria and no biomarkers to predict neurological sequalae. Methods: MRI-based quantitative approach was used for measurement of potential imaging markers related to external hydrocephalus and their association with neurological outcomes. We scanned 23 infants diagnosed with BEH and 11 age-similar controls. Using anatomical measurements from a large sample of healthy infants (n = 150), Z-scores were calculated to classify subject's CSF spaces as enlarged (≥1.96SD of mean values) or normal. Results: Subjects with abnormally enlarged CSF spaces had a significantly wider and longer ON (p = 0.017 and p = 0.020, respectively), and a significantly less tortuous ON (p = 0.006). ON deformity demonstrated a high diagnostic accuracy for abnormally enlarged frontal subarachnoid space (AUC = 0.826) and interhemispheric fissure (AUC = 0.833). No significant association found between enlarged CSF spaces and neurological complications (OR = 0.330, 95%CI 0.070-1.553, p = 0.161). However, cluster analysis identified a distinct subgroup of children (23/34, 67.6%) with enlarged CSF spaces and a wider, longer and less tortuous ON, to have an increased risk for neurological complications (RR = 7.28, 95%CI 1.07-49.40). Discussion: This is the first report on the association between external hydrocephalus, ON deformity and neurological complications. Our findings challenge the current view of external hydrocephalus as a benign condition. ON deformity is a potential auxiliary marker for risk stratification in patients with enlarged CSF spaces.

Slow blood-to-brain transport underlies enduring barrier dysfunction in American football players

Repetitive mild traumatic brain injury in American football players has garnered increasing public attention following reports of chronic traumatic encephalopathy, a progressive tauopathy. While the mechanisms underlying repetitive mild traumatic brain injury-induced neurodegeneration are unknown and antemortem diagnostic tests are not available, neuropathology studies suggest a pathogenic role for microvascular injury, specifically blood–brain barrier dysfunction. Thus, our main objective was to demonstrate the effectiveness of a modified dynamic contrast-enhanced MRI approach we have developed to detect impairments in brain microvascular function. To this end, we scanned 42 adult male amateur American football players and a control group comprising 27 athletes practicing a non-contact sport and 26 non-athletes. MRI scans were also performed in 51 patients with brain pathologies involving the blood–brain barrier, namely malignant brain tumours, ischaemic stroke and haemorrhagic traumatic contusion. Based on data from prolonged scans, we generated maps that visualized the permeability value for each brain voxel. Our permeability maps revealed an increase in slow blood-to-brain transport in a subset of amateur American football players, but not in sex- and age-matched controls. The increase in permeability was region specific (white matter, midbrain peduncles, red nucleus, temporal cortex) and correlated with changes in white matter, which were confirmed by diffusion tensor imaging. Additionally, increased permeability persisted for months, as seen in players who were scanned both on- and off-season. Examination of patients with brain pathologies revealed that slow tracer accumulation characterizes areas surrounding the core of injury, which frequently shows fast blood-to-brain transport. Next, we verified our method in two rodent models: rats and mice subjected to repeated mild closed-head impact injury, and rats with vascular injury inflicted by photothrombosis. In both models, slow blood-to-brain transport was observed, which correlated with neuropathological changes. Lastly, computational simulations and direct imaging of the transport of Evans blue-albumin complex in brains of rats subjected to recurrent seizures or focal cerebrovascular injury suggest that increased cellular transport underlies the observed slow blood-to-brain transport. Taken together, our findings suggest dynamic contrast-enhanced-MRI can be used to diagnose specific microvascular pathology after traumatic brain injury and other brain pathologies.

Blood-Brain Barrier Leakage: A New Biomarker in Transient Ischemic Attacks

Background and Purpose- The diagnosis of transient ischemic attack is challenging. Evidence of acute ischemia on MRI diffusion-weighted imaging is highly variable and confirmed in only about one-third of patients. This study investigated the significance of blood-brain barrier dysfunction (BBBD) mapping in patients with transient neurological deficits, as a diagnostic and prognostic biomarker required for risk stratification and stroke prevention. Methods- We used dynamic contrast-enhanced MRI to quantitatively map BBBD in a prospective cohort study of 57 patients diagnosed with transient ischemic attack/minor stroke and 50 healthy controls. Results- Brain volume with BBBD was significantly higher in patients compared with controls ( P=0.002). BBBD localization corresponded with the clinical presentation in 41 patients (72%) and was more extensive in patients with acute infarct on diffusion-weighted imaging ( P=0.05). Patients who developed new stroke during follow-up had a significantly greater BBBD at the initial presentation ( P=0.03) with a risk ratio of 5.35 for recurrent stroke. Conclusions- This is the first description of the extent and localization of BBBD in patients with transient ischemic attack/minor stroke. We propose BBBD mapping as a valuable tool for detection of subtle brain ischemia and a promising predictive biomarker required for risk stratification and stroke prevention.

Blood-brain barrier dysfunction in status epileptics: Mechanisms and role in epileptogenesis

The blood-brain barrier (BBB), a unique anatomical and physiological interface between the central nervous system (CNS) and the peripheral circulation, is essential for the function of neural circuits. Interactions between the BBB, cerebral blood vessels, neurons, astrocytes, microglia, and pericytes form a dynamic functional unit known as the neurovascular unit (NVU). The NVU-BBB crosstalk plays a key role in the regulation of blood flow, response to injury, neuronal firing, and synaptic plasticity. Blood-brain barrier dysfunction (BBBD), a hallmark of brain injury, is a prominent finding in status epilepticus. Blood-brain barrier dysfunction is observed within the first hour of status epilepticus, and in epileptogenic brain regions, may last for months. Blood-brain barrier dysfunction was shown to have a role in astroglial dysfunction, neuroinflammation, increasing neural excitability, reduction of seizure threshold, excitatory synaptogenesis, impaired plasticity, and epileptogenesis. A key signaling pathway associated with BBBD-induced neurovascular dysfunction is the transforming growth factor beta (TGF-β) proinflammatory pathway, activated by the extravasation of serum albumin into the brain when BBB functions are compromised. Specific small molecules blocking TGF-β, and the nonspecific, Food and Drug Administration (FDA) approved blocker and angiotensin antagonist losartan, were shown to reduce BBBD and block epileptogenesis. With these encouraging preclinical data, we have developed imaging approach to quantitatively assess BBBD as a diagnostic, predictive, and pharmacodynamic biomarker after brain injury. Clinical trials in the foreseen future are expected to test the feasibility of BBB-targeted diagnostic coupled therapy in status epileptics and seizure disorders. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

Imaging blood-brain barrier dysfunction as a biomarker for epileptogenesis

A biomarker that will enable the identification of patients at high-risk for developing post-injury epilepsy is critically required. Microvascular pathology and related blood-brain barrier dysfunction and neuroinflammation were shown to be associated with epileptogenesis after injury. Here we used prospective, longitudinal magnetic resonance imaging to quantitatively follow blood-brain barrier pathology in rats following status epilepticus, late electrocorticography to identify epileptic animals and post-mortem immunohistochemistry to confirm blood-brain barrier dysfunction and neuroinflammation. Finally, to test the pharmacodynamic relevance of the proposed biomarker, two anti-epileptogenic interventions were used; isoflurane anaesthesia and losartan. Our results show that early blood-brain barrier pathology in the piriform network is a sensitive and specific predictor (area under the curve of 0.96, P < 0.0001) for epilepsy, while diffused pathology is associated with a lower risk. Early treatments with either isoflurane anaesthesia or losartan prevented early microvascular damage and late epilepsy. We suggest quantitative assessment of blood-brain barrier pathology as a clinically relevant predictive, diagnostic and pharmaco!dynamics biomarker for acquired epilepsy.

Diagnosing necrotic meningioma: a distinctive imaging pattern in diffusion MRI and MR spectroscopy

The differential diagnosis of necrotic meningiomas includes brain abscess and malignant neoplasms. We report and discuss hereby the work-up of two patients diagnosed with necrotic meningioma using diffusion-weighted imaging, magnetic resonance spectroscopy, resective surgery, and histopathology. The purpose of the present article is to add to the scant literature on the use of advanced imaging modalities in the routine investigation of brain lesions and their utility in arriving at the final diagnosis.

Tonsillar contusion associated with benign tonsillar ectopia following minor head trauma

PURPOSE

The relationship between tonsil position and symptomatic cerebellar contusion is unclear. To date, there are no reports of symptomatic traumatic brain injury associated with benign tonsillar ectopia. Reported cases are limited to prominent cerebellar tonsillar displacement by ≥5 mm (i.e., Chiari malformations).

METHODS

The authors describe a case of symptomatic concussion in a toddler with unusual computerized tomography (CT) presentation and incidental finding of benign tonsillar ectopia, hemorrhagic contusion of the tonsils, blood-brain barrier (BBB) disruption and delayed atrophy shown using magnetic resonance imaging (MRI) studies. The radiological presentation and the clinical challenges are discussed through a review of the literature.

CONCLUSION

This case suggests that damage to cerebellar structures is not limited only to overt tonsillar herniation. Benign tonsillar ectopia may predispose to cerebellar contusion even after minor concussion and thus has a clinical significance. The current paradigm viewing only noticeable tonsillar herniation as a risk factor for hindbrain injury should be revisited.

Anatomy and physiology of the blood-brain barrier

Essential requisite for the preservation of normal brain activity is to maintain a narrow and stable homeostatic control in the neuronal environment of the CNS. Blood flow alterations and altered vessel permeability are considered key determinants in the pathophysiology of brain injuries. We will review the present-day literature on the anatomy, development and physiological mechanisms of the blood-brain barrier, a distinctive and tightly regulated interface between the CNS and the peripheral circulation, playing a crucial role in the maintenance of the strict environment required for normal brain function.

Should losartan be administered following brain injury?

Brain injury is a major health concern and associated with delayed neurological complications, including post-injury epilepsy, cognitive and emotional disabilities. Currently, there is no strategy to prevent post-injury delayed complications. We recently showed that dysfunction of the blood-brain barrier, often reported in brain injuries, can lead to epilepsy and neurodegeneration via activation of inflammatory TGF-β signaling in astrocytes. We further showed that the FDA approved angiotensin II type 1 receptor antagonist, losartan, blocks brain TGF-β signaling and prevents epilepsy in the albumin or blood-brain barrier breakdown models of epileptogenesis. Here we discuss the potential of losartan as an anti-epileptogenic and a neuroprotective drug, the rationale of its use following brain injury and the challenges of designing clinical trials. We highlight the urgent need to develop reliable biomarkers for epileptogenesis (and other complications) after brain injury as a pre-requisite to challenge neuroprotective therapies.

Stimulation of the sphenopalatine ganglion induces reperfusion and blood-brain barrier protection in the photothrombotic stroke model

Purpose

The treatment of stroke remains a challenge. Animal studies showing that electrical stimulation of the sphenopalatine ganglion (SPG) exerts beneficial effects in the treatment of stroke have led to the initiation of clinical studies. However, the detailed effects of SPG stimulation on the injured brain are not known.

Methods

The effect of acute SPG stimulation was studied by direct vascular imaging, fluorescent angiography and laser Doppler flowmetry in the sensory motor cortex of the anaesthetized rat. Focal cerebral ischemia was induced by the rose bengal (RB) photothrombosis method. In chronic experiments, SPG stimulation, starting 15 min or 24 h after photothrombosis, was given for 3 h per day on four consecutive days. Structural damage was assessed using histological and immunohistochemical methods. Cortical functions were assessed by quantitative analysis of epidural electro-corticographic (ECoG) activity continuously recorded in behaving animals.

Results

Stimulation induced intensity- and duration-dependent vasodilation and increased cerebral blood flow in both healthy and photothrombotic brains. In SPG-stimulated rats both blood brain-barrier (BBB) opening, pathological brain activity and lesion volume were attenuated compared to untreated stroke animals, with no apparent difference in the glial response surrounding the necrotic lesion.

Conclusion

SPG-stimulation in rats induces vasodilation of cortical arterioles, partial reperfusion of the ischemic lesion, and normalization of brain functions with reduced BBB dysfunction and stroke volume. These findings support the potential therapeutic effect of SPG stimulation in focal cerebral ischemia even when applied 24 h after stroke onset and thus may extend the therapeutic window of currently administered stroke medications.