The occurrence of obstructive vs absorptive hydrocephalus in newborns and infants: relevance to treatment choices

Toward the "Perfect" Shunt: Historical Vignette, Current Efforts, and Future Directions

As a concept, drainage of excess fluid volume in the cranium has been around for more than 1000 years. Starting with the original decompression-trepanation of Abulcasis to modern programmable shunt systems, to other nonshunt-based treatments such as endoscopic third ventriculostomy and choroid plexus cauterization, we have come far as a field. However, there are still fundamental limitations that shunts have yet to overcome: namely posture-induced over- and underdrainage, the continual need for valve opening pressure especially in pediatric cases, and the failure to reinstall physiologic intracranial pressure dynamics. However, there are groups worldwide, in the clinic, in industry, and in academia, that are trying to ameliorate the current state of the technology within hydrocephalus treatment. This chapter aims to provide a historical overview of hydrocephalus, current challenges in shunt design, what members of the community have done and continue to do to address these challenges, and finally, a definition of the "perfect" shunt is provided and how the authors are working toward it.

The ASPECT Hydrocephalus System: a non-hierarchical descriptive system for clinical use

In patients with hydrocephalus, prognosis and intervention are based on multiple factors. This includes, but is not limited to, time of onset, patient age, treatment history, and obstruction of cerebrospinal fluid flow. Consequently, several distinct hydrocephalus classification systems exist. The International Classification of Diseases (ICD) is universally applied, but in ICD-10 and the upcoming ICD-11, hydrocephalus diagnoses incorporate only a few factors, and the hydrocephalus diagnoses of the ICD systems are based on different clinical measures. As a consequence, multiple diagnoses can be applied to individual cases. Therefore, similar patients may be described with different diagnoses, while clinically different patients may be diagnosed identically. This causes unnecessary dispersion in hydrocephalus diagnostics, rendering the ICD classification of little use for research and clinical decision-making. This paper critically reviews the ICD systems for scientific and functional limitations in the classification of hydrocephalus and presents a new descriptive system. We propose describing hydrocephalus by a system consisting of six clinical key factors of hydrocephalus: A (anatomy); S (symptomatology); P (previous interventions); E (etiology); C (complications); T (time-onset and current age). The "ASPECT Hydrocephalus System" is a systematic, nuanced, and applicable description of patients with hydrocephalus, with a potential to resolve the major issues of previous classifications, thus providing new opportunities for standardized treatment and research.

Lysophosphatidic acid as a CSF lipid in posthemorrhagic hydrocephalus that drives CSF accumulation via TRPV4-induced hyperactivation of NKCC1

Background

A range of neurological pathologies may lead to secondary hydrocephalus. Treatment has largely been limited to surgical cerebrospinal fluid (CSF) diversion, as specific and efficient pharmacological options are lacking, partly due to the elusive molecular nature of the CSF secretion apparatus and its regulatory properties in physiology and pathophysiology.

Methods

CSF obtained from patients with subarachnoid hemorrhage (SAH) and rats with experimentally inflicted intraventricular hemorrhage (IVH) was analyzed for lysophosphatidic acid (LPA) by alpha-LISA. We employed the in vivo rat model to determine the effect of LPA on ventricular size and brain water content, and to reveal the effect of activation and inhibition of the transient receptor potential vanilloid 4 (TRPV4) ion channel on intracranial pressure and CSF secretion rate. LPA-mediated modulation of TRPV4 was determined with electrophysiology and an ex vivo radio-isotope assay was employed to determine the effect of these modulators on choroid plexus transport.

Results

Elevated levels of LPA were observed in CSF obtained from patients with subarachnoid hemorrhage (SAH) and from rats with experimentally-inflicted intraventricular hemorrhage (IVH). Intraventricular administration of LPA caused elevated brain water content and ventriculomegaly in experimental rats, via its action as an agonist of the choroidal transient receptor potential vanilloid 4 (TRPV4) channel. TRPV4 was revealed as a novel regulator of ICP in experimental rats via its ability to modulate the CSF secretion rate through its direct activation of the Na⁺/K⁺/2Cl⁻ cotransporter (NKCC1) implicated in CSF secretion.

Conclusions

Together, our data reveal that a serum lipid present in brain pathologies with hemorrhagic events promotes CSF hypersecretion and ensuing brain water accumulation via its direct action on TRPV4 and its downstream regulation of NKCC1. TRPV4 may therefore be a promising future pharmacological target for pathologies involving brain water accumulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00361-9.

Management and Outcome of Post-Infectious Multiloculated Hydrocephalus: A Case Series

Background and importance:

Infection following ventriculoperitoneal shunt (VPS) placement is a recognized complication, with variable incidence rates worldwide. Development of post-infectious multiloculated hydrocephalus (MLH) is likely if VPS infection is improperly managed, in turn affecting the prognosis. There is a lack of studies from Saudi Arabia regarding patients' functional outcome in relation to different variables.

Objectives:

To study the causative organisms, related variables and patient outcomes in MLH after VPS infection.

Methods:

This case series is a retrospective chart review of pediatric patients diagnosed with hydrocephalus from 2011 to 2019. Patients were included if they were aged <18 years, had confirmed cerebrospinal fluid/blood infection with radiological evidence of MLH, and were regularly followed-up. Functional status score was used to evaluate the outcomes.

Results:

A total of 150 patients underwent VPS insertion during the study period, of which 12 (8%) had postinfection MLH. The mean age at diagnosis and follow-up was 9 and 19 months, respectively. Ten patients developed MLH after their first VPS infection and one each developed MLH following the second and third VPS infections. Cerebrospinal fluid cultures mostly grew only single organisms (6/12), with Staphylococcus species being the most common. All patients underwent navigated endoscopic fenestration; nine patients required VPS placement and three required redo endoscopic fenestration surgery. All patients were developmentally delayed, with the majority (75%) having a functional status score of 6–10.

Conclusion:

Development of MLH after VPS infection is debilitating and requires prompt treatment. Although the overall functional outcome is poor, evolving neuroendoscopic techniques with tailored preoperative planning may play a role in reducing the adverse effect of shunt multiplicity, shunt infections and the higher failure rate among patients with complex hydrocephalus.

Palliative endoscopic third ventriculostomy for pediatric primary brain tumors: a single-institution case series

OBJECTIVE

Children with nonoperative brain tumors, such as diffuse intrinsic pontine gliomas (DIPGs), often have life-threatening hydrocephalus. Palliative shunting is common in such cases but can be complicated by hardware infection and mechanical failure. Endoscopic third ventriculostomy (ETV) is a minimally invasive alternative to treat hydrocephalus without implanted hardware. Herein, the authors report their institutional experience with palliative ETV for primary pediatric brain tumors.

METHODS

The authors conducted a retrospective review of consecutive patients who had undergone palliative ETV for hydrocephalus secondary to nonresectable primary brain tumors over a 10-year period at Rady Children's Hospital. Collected variables included age, sex, tumor type, tumor location, presence of leptomeningeal spread, use of a robot for ETV, complications, ETV Success Score (ETVSS), functional status, length of survival, and follow-up time. A successful outcome was defined as an ETV performed without clinically significant perioperative complications or secondary requirement for a new shunt.

RESULTS

Fifteen patients met the study inclusion criteria (11 males, 4 females; average age 7.9 years, range 0.8-21 years). Thirteen patients underwent manual ETV, and 2 patients underwent robotic ETV. Preoperative symptoms included gaze palsy, nausea/vomiting, headache, lethargy, hemiparesis, and seizures. Tumor types included DIPG (3), intraventricular/thalamic glioblastoma (2), and leptomeningeal spread of medulloblastoma (2), anaplastic oligo-/astrocytoma (2), rhabdoid tumor (2), primitive neuroectodermal tumor (1), ganglioglioma (1), pineoblastoma (1), and embryonal carcinoma (1). The mean preoperative ETVSS was 79 ± 8.8. There was 1 perioperative complication, a wound breakdown consistent with refractory hydrocephalus. The mean follow-up was 4.9 ± 5.5 months overall, and mean survival for the patients who died was 3.2 ± 3.6 months. Two patients remained alive at a mean follow-up of 15.7 months. Palliative ETV was successful in 7 patients (47%) and unsuccessful in 8 (53%). While patients with successful ETV were significantly older (11.9 ± 5.6 vs 4.4 ± 4.1 years, p = 0.010), there were no significant differences in preoperative ETVSS (p = 0.796) or postoperative survival (p = 0.476) between the successful and unsuccessful groups. Overall, functional outcomes were similar between the two groups; there was no significant difference in posttreatment Karnofsky Performance Status scores (68.6 ± 19.5 vs 61.3 ± 16.3, p = 0.454), suggesting that including ETV in the treatment algorithm did not worsen outcomes.

CONCLUSIONS

Palliative ETV is a safe and potentially efficacious treatment option in selected pediatric patients with hydrocephalus from nonoperative brain tumors. Close follow-up, especially in younger children, is required to ensure that patients with refractory symptoms receive appropriate secondary CSF diversion.

Endoscopic third ventriculostomy in obstructive hydrocephalus: A case report and analysis of operative technique

BACKGROUND

The endoscopic third ventriculostomy (ETV) is a neuroendoscopical procedure that represents a more suitable alternative to the extracranial shunting. It consists of fenestrating the floor of the third ventricle and thus establishing a free flow of the cerebrospinal fluid from the ventricles to the site of resorption in the subarachnoid space. It offers a more physiological solution and a chance at a shunt-free life for children with hydrocephalus. The main indication for the procedure is obstructive hydrocephalus, however, it can also be useful in patients with other forms of hydrocephalus.

CASE SUMMARY

We present a treatment flow of a 9-year-old patient, diagnosed with an obstructive hydrocephalus due to tectal glioma that was successfully treated with an ETV. We review the important factors influencing the success rate such as age, aetiology, shunt history, preoperative planning and visualisation of the basilar artery.

CONCLUSION

Even though the ETV effectively controls obstructive hydrocephalus in more than 75% of all cases, the overall success rate of the procedure varies and could be approved by the correct preoperative patient selection.

MR assessment of pediatric hydrocephalus: a road map

PURPOSE

This study was conducted to design a rational approach to the MR diagnosis of hydrocephalus based on a pathophysiologic reevaluation of its possible mechanisms and to apply it to the different etiological contexts.

METHOD

A review of the literature reports describing new physiologic models of production and absorption and of the hydrodynamics of the CSF was made.

RESULTS

Besides the secretion of CSF by the choroid plexuses, and its passive, pressure-dependent transdural absorption (arachnoid villi, dural clefts, cranial, and spinal nerve sheaths), water transporters, aquaporins, allow water (if not ions and organic molecules) to exchange freely between the brain parenchyma and the CSF spaces across the ependymal and the pial interfaces (including the Virchow-Robin spaces). Consequently, the CSF bulk flow is not necessarily global, and situations of balanced absorption-secretion may occur separately in different CSF compartments such as the ventricular, intracranial, or intraspinal CSF spaces. This means that rather than from a hypothetical pressure gradient from the plexuses to the dural sinuses, the dynamics of the CSF depend on the force provided in those different compartments by the arterial systolic pulsation of the pericerebral (mostly), intracerebral, and intraventricular (choroid plexuses) vascular beds.

CONCLUSION

Using MR imaging, diverse varieties of hydrocephalus may tentatively be explained by applying those concepts to the correspondingly diverse causal diseases. Hopefully, this may have an impact on the choice of the treatment strategies also.

Anesthetic management of labor and delivery in patients with elevated intracranial pressure

The anesthetic management of labor and delivery in patients with elevated intracranial pressure is complex. This review discusses the etiologies of diffuse and focal pathologies which lead to elevated intracranial pressure in pregnancy. The role of neuraxial and general anesthesia in the management of labor and delivery is also examined. Finally, a comprehensive review of strategies to minimize increases in intracranial pressure during general anesthesia for cesarean delivery is presented.

[Hydrocephalus in childhood : causes and imaging patterns]

CLINICAL ISSUE

Causes and imaging patterns of hydrocephalus differ depending on the age of the patient. Traditionally, hydrocephalus was classified into non-communicating and communicating hydrocephalus but more recent classifications also take the site of occlusion and the etiology into account.

DIAGNOSTICS

For the diagnostic work-up computed tomography (CT), sonography and magnetic resonance imaging (MRI) are available and MRI is the method of choice for children and adolescents as it allows determination of the cause and location of a possible obstruction. In the first 12-18 months sonography allows evaluation of the lateral ventricles and the third ventricle and CT is usually only chosen in children in emergency situations and/or if no other modality is available.

PERFORMANCE

We retrospectively evaluated a population of 785 children and adolescents (426 males aged 0-17 years) referred for MRI between April 2009 and March 2012 due to headaches, somnolence, concentration difficulties or developmental delay. Among these 80 (49 male) met the MRI criteria for hydrocephalus, 75 (46 male) had non-communicating hydrocephalus and 5 (3 male) communicating hydrocephalus. Of the patients 24 (15 male) had posthemorrhagic aqueductal stenosis, 16 (8 male) intracranial tumors, 9 (6 male) Chiari II malformations, 5 (4 male) other congenital malformations including malformations of the Dandy Walker spectrum, 9 (3 male) idiopathic aqueductal stenosis, 7 (5 male) arachnoidal cysts and 10 (8 male) other disorders, such as post-infections, macrocephaly cutis marmorata telangiectatica congenita (M-CMTC) syndrome, mesencephalic arteriovenous malformation (AVM), Langerhans cell histiocystosis.

PRACTICAL RECOMMENDATIONS

It is important to take the age of the patient and the imaging pattern into account and to exclude tumors when reporting MR images of children with hydrocephalus.

Disruption of wave-associated Rac GTPase-activating protein (Wrp) leads to abnormal adult neural progenitor migration associated with hydrocephalus

Hydrocephalus is the most common developmental disability and leading cause of brain surgery for children. Current treatments are limited to surgical intervention, as the factors that contribute to the initiation of hydrocephalus are poorly understood. Here, we describe the development of obstructive hydrocephalus in mice that are null for Wrp (Srgap3). Wrp is highly expressed in the ventricular stem cell niche, and it is a gene required for cytoskeletal organization and is associated with syndromic and psychiatric disorders in humans. During the postnatal period of progenitor cell expansion and ventricular wall remodeling, loss of Wrp results in the abnormal migration of lineage-tagged cells from the ventricular region into the corpus callosum. Within this region, mutant progenitors appear to give rise to abnormal astroglial cells and induce periventricular lesions and hemorrhage that leads to cerebral aqueductal occlusion. These results indicate that periventricular abnormalities arising from abnormal migration from the ventricular niche can be an initiating cause of noncommunicating hydrocephalus.

Benign external hydrocephalus: a review, with emphasis on management

Benign external hydrocephalus in infants, characterized by macrocephaly and typical neuroimaging findings, is considered as a self-limiting condition and is therefore rarely treated. This review concerns all aspects of this condition: etiology, neuroimaging, symptoms and clinical findings, treatment, and outcome, with emphasis on management. The review is based on a systematic search in the Pubmed and Web of Science databases. The search covered various forms of hydrocephalus, extracerebral fluid, and macrocephaly. Studies reporting small children with idiopathic external hydrocephalus were included, mostly focusing on the studies reporting a long-term outcome. A total of 147 studies are included, the majority however with a limited methodological quality. Several theories regarding pathophysiology and various symptoms, signs, and clinical findings underscore the heterogeneity of the condition. Neuroimaging is important in the differentiation between external hydrocephalus and similar conditions. A transient delay of psychomotor development is commonly seen during childhood. A long-term outcome is scarcely reported, and the results are varying. Although most children with external hydrocephalus seem to do well both initially and in the long term, a substantial number of patients show temporary or permanent psychomotor delay. To verify that this truly is a benign condition, we suggest that future research on external hydrocephalus should focus on the long-term effects of surgical treatment as opposed to conservative management.

A consensus on the classification of hydrocephalus: its utility in the assessment of abnormalities of cerebrospinal fluid dynamics

BACKGROUND

Between 2009 and 2011 an attempt has been made to develop a consensus on the classification of hydrocephalus. Clinicians and basic scientists who are recognized internationally for their work in hydrocephalus attended working meetings in which the concepts of classification of hydrocephalus were discussed at length.

PURPOSE

This review attempts to explain the relevance of a classification scheme based on the point of obstruction to the flow of cerebrospinal fluid to basic science research into the pathophysiology and effects of hydrocephalus. The review is designed to give examples of the value of this classification in analyzing research utilizing animal models. The development of hydrocephalus in the absence of a point of obstruction (true communicating hydrocephalus) is analyzed.

CONCLUSION

Contemporary neuroimaging techniques are now available that can identify the actual point of obstruction to the flow of CSF, if any, which results in the development of hydrocephalus. Such identification may lead to improved ability to analyze animal models used in hydrocephalus research as well as deciding among various treatment options.

Endoscopic third ventriculostomy in obstructive infantile hydrocephalus: remarks about the so-called 'unsuccessful cases'

BACKGROUND

The failure rate following endoscopic third ventriculostomy (ETV) in infants younger than 2 years of age has been reported to be higher compared with that of older children, and it is unclear whether ETV might be superior to shunt placement in this age group.

METHODS

Between 2003 and 2009, 23 patients younger than 6 months and without a previous history of shunting underwent ETV in our institution. A review of the literature was performed on the basis of publications presenting detailed data on age and etiology in every single patient.

RESULTS

In our own patients, total success rate was 39.1%. In the successful cases, median age was 140 days, whereas in the unsuccessful cases it was 47 days. The difference between the two groups was statistically significant (p = 0.01). The median ages of both successful and unsuccessful groups corresponded to data gained from an analysis of the literature (p = 0.04). At a median follow-up of 47 months, 2 out of 14 patients shunted after a failed ETV were revised for ventriculoperitoneal shunt malfunction.

CONCLUSION

The impact of age on ETV failure in infants is clear and becomes crucial during the first 2 months of life, even when excluding etiological factors. Nevertheless, age cannot be considered the only parameter of the decision-making process, especially in these very young patients. Probably, the definition of 'unsuccessful ETV' should be reevaluated in light of decreased risk of shunt malfunction observed after a failed ETV.

Is all "communicating" hydrocephalus really communicating? Prospective study on the value of 3D-constructive interference in steady state sequence at 3T

BACKGROUND AND PURPOSE

3D-constructive interference in steady state (3D-CISS) sequence has been used to assess the CSF pathways. The aim of this study was to investigate the additive value of 3D-CISS compared with conventional sequences in the diagnosis of obstructive membranes in hydrocephalus.

MATERIALS AND METHODS

A total of 134 patients with hydrocephalus underwent MR imaging examination with a 3T unit consisting of turbo spin-echo, 3D-CISS, and cine phase-contrast (cine PC) sequences. 3D-CISS was used to assess obstructive membranes in CSF pathways compared with other sequences. Cine PC, follow-up imaging, and surgical findings were used to confirm obstructive membranes.

RESULTS

Comparing the number of noncommunicating cases by using the conventional and 3D-CISS images, we found 26 new cases (19.4%) of 134 cases that were previously misdiagnosed as communicating hydrocephalus by conventional images. 3D-CISS sequence identified obstructive membranes invisible in other sequences, which facilitated selection of neuroendoscopy in the treatment of 31 patients (23.1%) in total who would have been otherwise treated with shunt insertion. These patients included 26 newly diagnosed noncommunicating cases after demonstration of intraventricular and/or fourth ventricular outlet membranes and 5 cases of communicating hydrocephalus with obstructing cisternal membranes. There were obstructions of the foramina of Luschka in 22 of 26 newly found noncommunicating cases.

CONCLUSIONS

Conventional sequences are insensitive to obstructive membranes in CSF pathways, especially in the fourth ventricular exit foramina and the basal cisterns. 3D-CISS sequence, revealing these obstructive membranes, can alter patient treatment and prognosis.

Complex hydrocephalus (combination of communicating and obstructive type): an important cause of failed endoscopic third ventriculostomy

Background

Hydrocephalus can be classified as purely obstructive, purely communicating or due to combinations of pathologies (obstruction in addition to defective absorption). Endoscopic third ventriculostomy (ETV) as an alternative to shunt procedures is an established treatment for obstructive hydrocephalus. However, patients who have combination of pathologies (complex hydrocephalus) could result in failure of ETV in spite of a patent stoma. The aim of this study was to prospectively evaluate the incidence of complex hydrocephalus in patients with obstructive hydrocephalus who failed an endoscopic third ventriculostomy.

Findings

Seventy one patients of obstructive hydrocephalus who underwent ETV in our institution were included in this study. Aetiology of hydrocephalus included congenital aqueductal stenosis in 42 and tubercular meningitis (TBM) in 29 patients. Failure of ETV was seen in 15 (21%) patients. These 15 patients included 6 (14.3%) from the congenital group and 9 (31.0%) patients from the TBM group. Iohexol CT ventriculography confirmed a patent stoma (suggesting a complex hydrocephalus) in 10 (66.7%) out of the 15 failed ETV cases. The incidence of complex hydrocephalus was more common in TBM group (8/29 patients, 27.60%) compared to congenital group (2/42 patients, 4.8%). The complex hydrocephalus patients with a patent ETV stoma were successfully managed by a lumbar peritoneal (LP) shunt.

Conclusion

Ten out of the 71 patients (14%) with obstructive hydrocephalus who underwent an ETV had a complex hydrocephalus, which was the major (66.7%) cause for failure of ETV. Improving methods to detect the exact type of hydrocephalus pre-operatively could increase success rate of ETV and avoid an unnecessary operative procedure (ETV).

On the changing epidemiology of hydrocephalus

PURPOSE

The purpose of this study is to evaluate the changing epidemiology of paediatric hydrocephalus over the past three decades in a single institution.

METHODS

All children treated for newly diagnosed hydrocephalus during the 1985-1990 (group A) and the 2000-2005 periods (group B) were enrolled and classified according to the associated cause of hydrocephalus.

RESULTS

A significant 8.8% decrease of the incidence of hydrocephalus was noticed between the two time periods, resulting from the reduction of hydrocephalus associated to myelomeningocele, aqueduct stenosis (p = 0.04), CNS infection (p = 0.03), cranio-cerebral malformation and head injuries; post-haemorrhagic hydrocephalus remained stable, while the tumour-associated one increased (p < 0.0001). No consistent differences in terms of rate of adjunctive surgery (30.3% versus 23.9%) and number revision procedures (200 versus 104) were recorded.

CONCLUSIONS

The present study confirmed data from the literature about the declined incidence of paediatric hydrocephalus, which mainly results from the decrease of congenital malformations. In spite of the recent advances in neuroendoscopy and in the shunting valve design, the impact of hydrocephalus in the paediatric neurosurgical practice remains high.

A contemporary definition and classification of hydrocephalus

This review focuses on the problems related to defining hydrocephalus and on the development of a consensus on the classification of this common problem. Such a consensus is needed so that diverse research efforts and plans of treatment can be understood in the same context. The literature was searched to determine the definition of hydrocephalus and to identify previously proposed classification schemes. The historic perspective, purpose, and result of these classifications are reviewed and analyzed. The concept of the hydrodynamics of cerebrospinal fluid (CSF) as a hydraulic circuit is presented to serve as a template for a contemporary classification scheme. Finally, a definition and classification that include all clinical causes and forms of hydrocephalus are suggested. The currently accepted classification of hydrocephalus into "communicating" and "noncommunicating" varieties is almost 90 years old and has not been modified despite major advances in neuroimaging, neurosciences, and treatment outcomes. Despite a thorough search of the literature using computerized search engines and bibliographies from review articles and book chapters, I identified only 6 previous attempts to define and classify different forms of hydrocephalus. This review proposes the following definition for hydrocephalus: hydrocephalus is an active distension of the ventricular system of the brain related to inadequate passage of CSF from its point of production within the ventricular system to its point of absorption into the systemic circulation. Based on this definition (potential points of flow restriction) and on the view of the CSF system as a hydraulic circuit, a classification system is proposed. The acceptance of this proposed definition and classification schema would allow clinicians and basic scientists to communicate effectively, to share information and results, and to develop testable hypotheses.

Endoscopic management of hydrocephalus in pediatric patients: a review of indications, techniques, and outcomes

Although ventriculoperitoneal shunting remains the treatment of choice for many children with hydrocephalus, advances in endoscopic technology have greatly expanded the treatment options for these patients. For selected patients with obstructive hydrocephalus, endoscopic third ventriculostomy and other endoscopic techniques offer substantial advantages over shunting. As with any surgical procedure, appropriate patient selection is critical to successful outcomes. This article reviews modern endoscopic techniques available to treat hydrocephalus, with a focus on selection criteria and outcomes.

Loss of Fyn tyrosine kinase on the C57BL/6 genetic background causes hydrocephalus with defects in oligodendrocyte development

The supportive functions of oligodendrocytes are required for the survival and development of axons, ensuring the organization of highly specialized neuronal networks in brain. Although the molecules that regulate oligodendrocyte differentiation in vitro have been identified, their roles in vivo are largely uncertain. Here we report that fyn deficiency on the C57BL/6 genetic background resulted in premature death, showing severe hydrocephalus with neonatal onset. One week after birth, fyn-deficient mice showed enlarged lateral ventricles with thinner cerebral cortices and degenerating axons in the corpus callosum. In addition, before the onset of myelination, the number of oligodendrocytes was reduced and their morphogenesis was impaired in the cerebral cortex. These results demonstrate that Fyn is essential for normal brain development and suggest that defects in oligodendrocyte development cause degeneration of cortical axons and subsequent hydrocephalus in fyn-deficient mice.

The definition and classification of hydrocephalus: a personal recommendation to stimulate debate

The aim of this review is to refine the definition and classification of hydrocephalus as a preview to developing an international consensus on the nomenclature of this complex condition. This proposed definition and classification is based on my own work in this area and is intended to promote a debate on the concepts presented.

A literature review of contemporary definitions and classifications of hydrocephalus, and of the historic context in which these concepts developed, is presented. Based on new technology and understanding of hydrocephalus, the rationale for nomenclature is also discussed.

Currently, there is no recognized definition of hydrocephalus. The failure to agree on a working definition impedes progress in understanding the pathophysiology and treatment of hydrocephalus. There are many proposed classifications, each with its own starting point in terms of the definition of the condition. This author recommends that the following definition be used as a starting point to develop a consensus statement defining hydrocephalus: "Hydrocephalus is an active distension of the ventricular system of the brain resulting from inadequate passage of cerebrospinal fluid from its point of production within the cerebral ventricles to its point of absorption into the systemic circulation." Such a definition can be used to develop a rational classification consistent with observations from contemporary neuroimaging and can lead to testable hypotheses. It is concluded that hydrocephalus is a complicated neurologic disorder with many causes and methods of treatment. Clinicians and basic scientists must agree on a working definition of the condition to be able to interpret results from different investigators. Reaching a consensus on a working definition and functional classification should be a high priority for researchers in this field.

Cyclophosphamide-induced agenesis of cerebral aqueduct resulting in hydrocephalus in mice

The present work was undertaken to reveal the mechanism of cerebral aqueduct agenesis found to result in hydrocephalus following intrauterine exposure to model teratogen, cyclophosphamide, in murine fetuses. A single dose of 10-mg/kg body weight cyclophosphamide was injected intaperitoneally to pregnant mice on day 10, 11 or 12 of gestation. Fetuses were collected through abdominal incision on day 18 and studied for various malformations of brain and cranium including hydrocephalus. Incomplete development and failure of canalization of the cerebral aqueduct were detected when serial sections of brain in coronal and transverse planes were studied under the microscope. Biotechnological investigations such as % DNA fragmentation, % viable cell count and cell proliferation assay were carried out on brain cells for further studies. Agenesis and non-canalization of the cerebral aqueduct resulted in increased pressure of CSF, which led to rupture of the aqueduct complicated by leakage and accumulation of CSF in brain substance forming a cavity containing CSF parallel and lateral to the unopened part of the cerebral aqueduct. Incomplete development along with non-canalization of the cerebral aqueduct resulted in blockage of CSF flow through the ventricles that manifest as internal hydrocephalus. External hydrocephalus on the other hand was detected where the CSF accumulated in the cavity formed inside the brain substance and established communication with the CSF in the subarachnoid space. Cyclophosphamide induced inhibition of mitosis and cell differentiation of ependymal cells reflecting a decreased % viable cell count and cell proliferation assay along with augmentation of apoptosis of brain cells quantified as increased % DNA fragmentation count, which were identified as the contributing factors underlying the agenesis and incomplete development of the cerebral aqueduct. The study also suggests that cell survival, proliferation, migration or differentiation of ependymal cells might have been affected, and we speculate that CSF may have an inducing role in the development and canalization of the cerebral aqueduct.