The glycocalyx is a gel-like layer lining the luminal surface of the endothelium. The glycocalyx exerts an important barrier role because it prevents exposure of plasma components to the endothelial surface. Disruption of the glycocalyx by local inflammation or ischemia results in decreased glycocalyx thickness which is associated with a number of vascular diseases. The cerebrovascular glycocalyx has sparsely been studied, but is of great interest because of its potential role in cerebrovascular disease. In this review, we describe all existing techniques to visualize the glycocalyx and designate techniques that may be suitable for studying the cerebrovascular glycocalyx. A total of seven imaging techniques are discussed thoroughly, including transmission electron microscopy, intravital microscopy, micro-particle image velocimetry, confocal laser scanning microscopy, two-photon laser scanning microscopy, orthogonal polarization spectral imaging and sidestream dark field/oblique imaging. Measurement of serum concentrations of glycocalyx-specific constituents is another method for glycocalyx analysis. Also, we have reviewed the methods of glycocalyx analysis by using these imaging techniques. So far, the cerebrovascular glycocalyx has only been studied in vitro. However, other cerebral microcirculatory properties have been studied in vivo. This suggests that the cerebrovascular glycocalyx can be studied in vivo by using some of the described techniques, when specific software is subjoined to the analysis. In conclusion, we have summarized techniques available for glycocalyx assessment, and explained the significance and technical possibilities regarding cerebrovascular glycocalyx visualization. Cerebrovascular glycocalyx assessment would add valuable information to our understanding of the pathophysiology of cerebrovascular disease. Moreover, as a part of the blood-brain barrier, more knowledge on the cerebrovascular glycocalyx may lead to better understanding of neurodegenerative conditions that are caused by a compromised blood-brain barrier including Alzheimer`s disease, vascular dementia, multiple sclerosis and epilepsy.

IntroductionAdequate functioning of the blood–brain barrier (BBB) is important for brain homoeostasis and normal neuronal function. Disruption of the BBB has been described in several neurological diseases. Recent reports suggest that an increased permeability of the BBB also contributes to increased seizure susceptibility in patients with epilepsy. The endothelial glycocalyx is coating the luminal side of the endothelium and can be considered as the first barrier of the BBB. We hypothesise that an altered glycocalyx thickness plays a role in the aetiology of temporal lobe epilepsy (TLE), the most common type of epilepsy. Here, we propose a protocol that allows intraoperative assessment of the cerebrovascular glycocalyx thickness in patients with TLE and assess whether its thickness is decreased in patients with TLE when compared with controls.Methods and analysisThis protocol is designed as a prospective observational case–control study in patients who undergo resective brain surgery as treatment for TLE. Control subjects are patients without a history of epileptic seizures, who undergo a craniotomy or burr hole surgery for other indications. Intraoperative glycocalyx thickness measurements of sublingual, cortical and hippocampal microcirculation are performed by video microscopy using sidestream dark-field imaging. Demographic details, seizure characteristics, epilepsy risk factors, intraoperative haemodynamic parameters and histopathological evaluation are additionally recorded.Ethics and disseminationThis protocol has been ethically approved by the local medical ethical committee (ID: NL51594.068.14) and complies with the Declaration of Helsinki and principles of Good Clinical Practice. Informed consent is obtained before study enrolment and only coded data will be stored in a secured database, enabling an audit trail. Results will be submitted to international peer-reviewed journals and presented at international conferences.Trial registration numberNTR5568.