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Review
. 2022 Jun 30:10:887606.
doi: 10.3389/fped.2022.887606. eCollection 2022.

Secondary Brain Injury Following Neonatal Intraventricular Hemorrhage: The Role of the Ciliated Ependyma

Affiliations
Review

Secondary Brain Injury Following Neonatal Intraventricular Hemorrhage: The Role of the Ciliated Ependyma

William Dawes. Front Pediatr. .

Abstract

Intraventricular hemorrhage is recognized as a leading cause of hydrocephalus in the developed world and a key determinant of neurodevelopmental outcome following premature birth. Even in the absence of haemorrhagic infarction or posthaemorrhagic hydrocephalus, there is increasing evidence of neuropsychiatric and neurodevelopmental sequelae. The pathophysiology underlying this injury is thought to be due to a primary destructive and secondary developmental insult, but the exact mechanisms remain elusive and this has resulted in a paucity of therapeutic interventions. The presence of blood within the cerebrospinal fluid results in the loss of the delicate neurohumoral gradient within the developing brain, adversely impacting on the tightly regulated temporal and spatial control of cell proliferation and migration of the neural stem progenitor cells within the subventricular zone. In addition, haemolysis of the erythrocytes, associated with the release of clotting factors and leucocytes into the cerebrospinal (CSF), results in a toxic and inflammatory CSF microenvironment which is harmful to the periventricular tissues, resulting in damage and denudation of the multiciliated ependymal cells which line the choroid plexus and ventricular system. The ependyma plays a critical role in the developing brain and beyond, acting as both a protector and gatekeeper to the underlying parenchyma, controlling influx and efflux across the CSF to brain interstitial fluid interface. In this review I explore the hypothesis that damage and denudation of the ependymal layer at this critical juncture in the developing brain, seen following IVH, may adversely impact on the brain microenvironment, exposing the underlying periventricular tissues to toxic and inflammatory CSF, further exacerbating disordered activity within the subventricular zone (SVZ). By understanding the impact that intraventricular hemorrhage has on the microenvironment within the CSF, and the consequences that this has on the multiciliated ependymal cells which line the neuraxis, we can begin to develop and test novel therapeutic interventions to mitigate damage and reduce the associated morbidity.

Keywords: cerebrospinal fluid; ependymal cilia; intraventricular hemorrhage; post haemorrhagic hydrocephalus; subventricular zone (SVZ).

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Conflict of interest statement

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Temporizing interventions used for the treatment of neonatal post haemorrhagic hydrocephalus. (A) Ventricular access device – a CSF reservoir is inserted allowing intermittent aspiration of CSF to control intraventricular pressure. (B) Ventricular subgaleal shunt – the potential space between the galea and the periosteal lining of the cranium is surgically opened allowing CSF to drain into the subgaleal space. (C) Neuroendoscopic lavage of the ventricular system with or without septostomy to access the contralateral ventricle. The blood-stained CSF is removed to reduce the potential toxicity to the wall of the lateral ventricle.
Figure 2
Figure 2
Potential mechanisms underlying the secondary brain injury seen following neonatal intraventricular hemorrhage-mechanisms potentially associated with neurodevelopmental outcome are shown in red, whilst mechanisms potentially associated with the development of hydrocephalus are shown in green.
Figure 3
Figure 3
Anatomy of the wall of the lateral ventricle. (A) Anatomy of the E1 ependymal cilia. Multiple motile cilia are shown arising from basal bodies within the apical/ventricular surface of the cell. The basal bodies are shown to be tightly integrated with the actin microfilaments which maintain the structure of the ependymal cell. The motile cilia are asymmetrically distributed across the surface of the cell and found in a tuft of cilia in a downstream position in relation to the flow of CSF. The remainder of the surface is covered in microvilli. Deep to the apical surface the large spherical shaped nucleus is seen surrounded by mitochondria. Connecting the ependymal cells together are three cell to cell junctions: the adherin junction, consisting of n-cadherin and catenins, tight junctions and gap junctions. (B) Cross-sectional anatomy of the wall of the lateral ventricle demonstrating the relationship between the ependymal layer and the underlying neural stem progenitor cells within the subventricular zone. The ependymal layer sits at the interface of the cerebrospinal fluid (CSF) and the brain interstitial fluid (BIF) and acts as a gatekeeper, modulating the brain microenvironment surrounding the NSPC. (C) Enface anatomy of the wall of the lateral ventricle. The tuft of motile cilia are seen to arise from a downstream position in relation to the flow of CSF. The E1 ependymal cells are arranged in a pin-wheel orientation around the cilia of the b-cell.
Figure 4
Figure 4
Impact of denudation of the ependyma within the ventricular and subventricular zones. (1) Subventricular glial nodule bulging into the ventricular lumen. The ependymal surface is discontinuous over the surface of the nodule but islands of ependymal cells remain intact in the surrounding vicinity. (2) Migration and activation of microglia into the subventricular zone. (3) Damage to the neural stem progenitor cells with exposure to bloodstained CSF. (4) Loss of ependymal cells within the lining of the ventricle causes cells to escape into the CSF. (5) Loss of homeostasis at the CSF to BIF border causes periventricular egress of CSF, seen as a band of oedema/hypodensity in the subventricular zone. (6) Ependymal rosettes are seen deep to areas of ependymal denudation within the subventricular zone.

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