Agenesis of arachnoid granulations and its relationship to communicating hydrocephalus

Posthemorrhagic hydrocephalus development after germinal matrix hemorrhage: Established mechanisms and proposed pathways

In addition to being the leading cause of morbidity and mortality in premature infants, germinal matrix hemorrhage (GMH) is also the leading cause of acquired infantile hydrocephalus. The pathophysiology of posthemorrhagic hydrocephalus (PHH) development after GMH is complex and vaguely understood, although evidence suggests fibrosis and gliosis in the periventricular and subarachnoid spaces disrupts normal cerebrospinal fluid (CSF) dynamics. Theories explaining general hydrocephalus etiology have substantially evolved from the original bulk flow theory developed by Dr. Dandy over a century ago. Current clinical and experimental evidence supports a new hydrodynamic theory for hydrocephalus development involving redistribution of vascular pulsations and disruption of Starling forces in the brain microcirculation. In this review, we discuss CSF flow dynamics, history and development of theoretical hydrocephalus pathophysiology, and GMH epidemiology and etiology as it relates to PHH development. We highlight known mechanisms and propose new avenues that will further elucidate GMH pathophysiology, specifically related to hydrocephalus.

Cerebrospinal Fluid Absorption Revisited: Do Extracranial Lymphatics Play a Role?

It would seem heretical to suggest that extracranial lymphatic vessels play a major role in the volumetric clearance of cerebrospinal fluid (CSF) from the cranial vault. It is well established that there are no lymphatics within the brain parenchyma, and it has been assumed that the drainage of CSF into the venous system occurs predominantly through the arachnoid villi and granulations. Nonetheless, a physiological association between extracellular fluid in the brain and extracranial lymph has been appreciated for more than 100 years. More important, recent studies in adult experimental animals have demonstrated that on average, one-half of the total volume of CSF absorbed from the cranial compartment was removed by extracranial lymphatics. Our objective in writing this review is to outline the experimental data that support the hypothesis that extracranial lymphatic vessels play an important role in CSF transport in the adult. Additionally, we will develop the hypothesis that lymphatic vessels may provide the primary route through which CSF is cleared from the cranial subarachnoid space in the fetus. With this new conceptual framework, we will reassess hydrocephalus from a lymphatic perspective to determine if impaired CSF transport through extracranial lymphatics might contribute to the development of this disease.

The intracranial arachnoid mater : a comprehensive review of its history, anatomy, imaging, and pathology

INTRODUCTION

The arachnoid mater is a delicate and avascular layer that lies in direct contact with the dura and is separated from the pia mater by the cerebrospinal fluid-filled subarachnoid space. The subarachnoid space is divided into cisterns named according to surrounding brain structures.

METHODS

The medical literature on this meningeal layer was reviewed in regard to historical aspects, etymology, embryology, histology, and anatomy with special emphasis on the arachnoid cisterns. Cerebrospinal fluid dynamics are discussed along with a section devoted to arachnoid cysts.

CONCLUSION

Knowledge on the arachnoid mater and cerebrospinal fluid dynamics has evolved over time and is of great significance to the neurosurgeon in clinical practice.

The function and structure of the cerebrospinal fluid outflow system

This review traces the development of our understanding of the anatomy and physiological properties of the two systems responsible for the drainage of cerebrospinal fluid (CSF) into the systemic circulation. The roles of the cranial and spinal arachnoid villi (AV) and the lymphatic outflow systems are evaluated as to the dominance of one over the other in various species and degree of animal maturation. The functional capabilities of the total CSF drainage system are presented, with evidence that the duality of the system is supported by the changes in fluid outflow dynamics in human and sub-human primates in hydrocephalus. The review also reconciles the relative importance and alterations of each of the outflow systems in a variety of clinical pathological conditions.

Usefulness of spinal drainage for post-traumatic external hydrocephalus: report of two cases

An 8-year-old girl presented with symptoms of increased intracranial pressure on the 18th day after removal of an occipital epidural haematoma. A 69-year-old woman exhibited the same symptoms on the 6th day after the removal of a left frontal subdural haematoma. Computed tomography (CT) revealed that both patients were suffering from external hydrocephalus. Spinal drainage, maintained for 18 days in the former case and for 7 days in the latter, not only relieved those symptoms but also cured the external hydrocephalus. Recurrence of external hydrocephalus has not been observed in either case for several years since discontinuation of spinal drainage. Usefulness of spinal drainage for post-traumatic external hydrocephalus is discussed.

Parasagittal Arachnoid Markings on the Inner Skull on Three-Dimensional CT: Relation between Hydrocephalus and Arachnoid Granules

The purpose of the study was to evaluate the number and size of arachnoid markings on the inner plate of the skull on 3D-CT. The subjects included 16 hydrocephalus and 26 non-hydrocephalus cases. We evaluated the correlation between age and both the number and sizes of the arachnoid markings, and compared them between hydrocephalus and non-hydrocephalus cases. We also evaluated cases exhibiting a “smooth cranium” that had no arachnoid markings at all on the inner plate. There was a positive correlation between age and the number of the arachnoid markings. There were no statistically significant differences in arachnoid markings between hydrocephalus and non-hydrocephalus cases, while, there were statistically significant differences in the frequency of “smooth cranium” findings in the population under ten years old. The “smooth cranium” can only be seen in hydrocephalus cases. These findings may be a clue to the morphological or functional changes of the arachnoid villi in hydrocephalus cases.

[The meninges, an anatomical point of view]

The meninges correspond to an anatomical concept. For the morphologist, the microscopic organization, the hypothetical presence of a subdural space, the nature of the interface between the deep meningeal layer and the nervous parenchyma in the perivascular spaces are the central issues. For the clinician, dynamic aspects of cerebrospinal fluid flow, secretion, and resorption are essential factors with practical consequences in terms of disease and patient management. Comparative anatomy, embryology, and organogenesis provide an interesting perspective for the descriptive and functional anatomy of the meninges. Usually considered as protective membranes, the meninges play a prominent role in the development and maintenance of the central nervous system. The meninges are in constant evolution, from their formation to senescence. The meninges present three layers in children and adults: the dura mater, the arachnoid and the pia mater. The cerebrospinal fluid is secreted by the choroid plexuses, flows through the ventricles and the subarachnoid space, and is absorbed by arachnoid granulations. Other sites of secretion and resorption are suggested by comparative anatomy and human embryology and organogenesis.

Cranial venous outflow obstruction and pseudotumor Cerebri syndrome

The pathophysiology of PTS including idiopathic intracranial hypertension or 'BIH', remains controversial. The older literature frequently referred to pathology in the cerebral venous drainage but more modern imaging techniques (CT and early MR) failed to reveal gross venous pathology. The role of impaired cranial venous outflow has recently been re-examined in the light of new methods of investigation (advanced MR venography and direct microcatheter venography with manometry) and of treatment (venous sinus stenting). Venous sinus obstruction in PTS is a more common factor in the pathogenesis of the condition than previously recognised. Venous obstruction may be primary, that is, it is the underlying aetiological factor in PTS. Venous sinus obstruction may also be secondary to raised CSF pressure which may exacerbate problems with intracranial compliance and raised CSF pressure. Early experience with venous stenting suggests that it may be a helpful treatment for patients with PTS but more experience and longer follow-up is required to define the subgroups of patients for whom it is most appropriate.

Pediatric neurosurgical disease

The most common, primary referrals to a pediatric neurosurgeon's office are the evaluation and management of the child with a large head (to rule out hydrocephalus and other space occupying lesions) a mishappen head (to rule out various forms of craniosynostosis), or some form of congenital spinal abnormality (spinal dysraphism). The authors discuss the pathogenesis and clinical features of these disorders, provide a framework for diagnostic evaluation and referral, and discuss the various treatment options available for each.

Hydrocephalus--revision of its definition and classification with special reference to "intractable infantile hydrocephalus"

With the advent of computed tomography (CT) scan, much information has been obtained about the pathophysiology of hydrocephalus. It is now clear that hydrocephalus is not a disease entity but rather a syndrome or sign resulting from disturbances in the dynamics of cerebralspinal fluid (CSF) caused by various diseases. Consequently, it has become necessary to revise its definition and classification. In this paper, a contemporary definition and classification of hydrocephalus are presented. Also, a classification of "intractable hydrocephalus"--with its diagnostic criteria--which is a clinically unsolved problem, is attempted, bearing in mind its place in the clinical management and future investigation of the pathophysiology of hydrocephalus.

Cerebrospinal fluid physiology and the management of increased intracranial pressure

Increased intracranial pressure can result in irreversible injury to the central nervous system. Among the many functions of the cerebrospinal fluid, it provides protection against acute changes in venous and arterial blood pressure or impact pressure. Nevertheless, trauma, tumors, infections, neurosurgical procedures, and other factors can cause increased intracranial pressure. Both surgical and nonsurgical therapeutic modalities can be used in the management of increased intracranial pressure attributable to traumatic and nontraumatic causes. In patients with cerebral injury and increased intracranial pressure, monitoring of the intracranial pressure can provide an objective measure of the response to therapy and the pressure dynamics. Intraventricular, intraparenchymal, subarachnoid, and epidural sites can be used for monitoring, and the advantages and disadvantages of the various devices available are discussed. With the proper understanding of the physiologic features of the cerebrospinal fluid, the physician can apply the management principles reviewed herein to minimize damage from intracranial hypertension.

Neurosonography of hydrocephalus in infants

Transfontanel cranial ultrasonography reliably delineates ventricular size and anatomy in small infants. In these children, it is an excellent primary imaging technique for evaluation of the many clinical problems related to ventricular dilatation. Sonography can be useful for: detecting ventriculomegaly, differentiating nonobstructive ventricular dilatation from obstructive enlargement (hydrocephalus), determining the cause of hydrocephalus; aiding in the temporary management of patients with hydrocephalus; and aiding in the management of patients with permanent ventricular shunts.

Giant cell arteritis and normal pressure hydrocephalus. A case report

The first known case of association of giant cell arteritis and normal pressure hydrocephalus is described. The arteritis was cured with corticosteroid therapy while hydrocephalus required ventriculo-peritoneal shunt. The high protein content of cerebrospinal fluid of this patient is probably the pathogenetic mechanism of cerebrospinal fluid block, leading to occult obstructive hydrocephalus.

Recent research into the nature of cerebrospinal fluid formation and absorption

Recent information regarding the nature of bulk cerebrospinal fluid formation and absorption is reviewed, integrated with previous knowledge, and applied to the clinical setting.

Congenital myopathy and communicating hydrocephalus--a possible pathogenetic combination

A 5 1/2-year-old boy with congenital myopathy associated with communicating hydrocephalus is described. Motor milestones were delayed with generalized nonprogressive muscular weakness and moderately elevated serum CK. Muscle biopsy revealed multifocal areas of decreased oxidative enzyme activity which were characterized ultrastructurally by myofibrillar disorganization and Z-band streaming with decrease or absence of mitochondria in this area. The head circumference measured more than 98 percentile at 14 months. The CT scan disclosed moderately dilated ventricles and enlarged cortical sulci. Radioisotope cisternograms showed early ventricular reflux and persistence of radioactivity especially in the parasaggital region even after 72 hours. Some common pathogenetic mechanism may have been involved in the development of both the myopathy and the hydrocephalus.

Acquired hydrocephalus. I. A clinical analysis of 160 patients studied for hydrocephalus

A total of 160 patients suspected of having acquired hydrocephalus were studied either by quantitative isotope ventriculography (QIV) or by lumbar isotope cisternography (LIC). Of these patients, 56 had hydrocephalus. Mental deterioration, gait disturbances, ataxia, spasticity, and incontinence were most frequently present in the hydrocephalic patients, but none of the signs or combinations thereof are pathognomonic of acquired hydrocephalus. These signs are independent of the intracranial pressure (ICP) and the type of hydrocephalus. Surgical shunt procedures were in most cases followed by the disappearance of mental deterioration, gait disturbances, ataxia, and spasticity.

Acquired hydrocephalus. III. A pathophysiological study correlated with neuropathological findings and clinical manifestations

On the basis of the laws of Pascal and Laplace, it is shown that the ventricular dilatation in acquired hydrocephalus is due to a primary increase in the intraventricular pressure (IVP), and that a new steady state can be reached, whether the IVP is increased or normal. The pressure increase is due to a disproportion between the production and reabsorption of cerebrospinal fluid (CSF). As water and salts pass freely across the ependyma and the choroid plexus in hydrocephalus, the pressure increase is caused by an increased protein concentration in the ventricular CSF, leading to increased fluid contents according to the Gibbs-Donnan equilibrium. During the ventricular dilatation, the ependyma is destroyed, and the protein molecules penetrate into the subependymal part of the white matter. This results in a reduction in the colloid osmotic pressure of the ventricular CSF, and a new steady state can be reached, with a normal protein concentration in an increased volume. The attendant microscopic changes in the ventricular wall were demonstrated in a patient with acquired hydrocephalus, and the observations made were in conformity with the results of a number of animal experiments. The symptomatology of acquired hydrocephalus is in agreement with a primary affection of the axons running in the juxtaventricular part of the white matter.