Conf.Dr.

Mohan Dumitru

Hydrocephaly/Hydrocephalus

History
The term “hydrocephaly” comes from the Greek words: “hydro”, meaning “water” and
“cephalus”, meaning encephalon. As it results from the name, hydrocephaly is a pathological
state whose main characteristic is excessive accumulation of liquid at the level of the
encephalon/brain.

Anatomy of the liquidian spaces

The cerebrospinal fluid (CSF) lies in the depths of the encephalon/brain and of the spinal
marrow, filling in the cavities called cerebral ventricles and the spinal canal.
There are four ventricles at the level of the encephalon: two lateral or teleencephalic, the
third ventricle or diencephalic and the fourth ventricle or rhombencephalic.
These ventricles interrelate with each other, with the spinal canal and the subarachnoidian
space surrounding the central nervous system.

The lateral ventricles

The lateral ventricles are two pair cavities situated in the cerebral hemispheres’ white
matter. Their form resembles a horseshoe with a spur, having a downward and a head
orientated opening and the spur orientated backwards. Each ventricle has: a central part
(pars centralis) or the ventricular trigon of Schwalbe and three extensions called horns – the
frontal or anterior horn, the occipital or posterior horn and the temporal (sphenoid) or inferior
horn.
The lateral ventricles are separated by the pellucid septum but they communicate with
the third ventricle through a series of narrower orifices, called the interventricular foramina of
Monro.
The lateral ventricles represent the most voluminous part of the liquidian spaces, their
volume taking up 80-90% of the total ventricular volume. Due to the presence in the central
part (the medial wall) and in the temporal horn (the superior wall) of the choroid plexuses, the
lateral ventricles represent the main location for the cerebrospinal fluid secretion (CSF).

Ventricle III
The third cerebral ventricle (III), situated on the midline, interhemispherically, is a tall slit
saggitally oriented, separating the anatomic formations of the diencephalon. It communicates
in the front side through the interventricular foramina of Monro, measuring 4-5 mm in length
and 3-4 mm in diameter, with the lateral ventricles and in the back side with the aqueduct of
Sylvius.
The Sylvius Aqueduct, the connection between ventricle III and ventricle IV, long of
approx. 2 mm and approx. 1,5 mm in diameter, represent one of the “sensitive” areas of the
ventricular system.

Ventricle IV
Ventricle IV is a rhomboid cavity, displaced between the dorsal faces of the bulb and
bridge, ventrally and the cerebellum dorsally. Enveloped by the ependimus it continues
caudally with the medullar/spinal canal. Ventricle IV communicates rostrally with the cerebral
aqueduct of Sylvius. This ventricle has a great importance in the cerebrospinal fluid

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circulation. At the level of the fourth ventricle the link between the endoneural and the
subarachnoid sectors of the liquidian spaces is realized, through three foramina:

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 The Magendie foramen, punched in the fourth ventricle’s roof. Situated on the midline, it
realizes a large communication between ventricle IV and the cisterna magna, as the main
communication way between the ventricular system and the subarachnoidian space.
 The Luschka foramina situated at the distal end of the fourth ventricle’s lateral recesses,
performs the connection between the fourth ventricle and the pontomedullary cistern. The
Luschka foramina are partially occupied by the choroid plexuses extensions, which thus
slip into the subarachnoidian space.
The 35-38 mm long fourth ventricle has two walls, four margins and four angles.

The Subarachnoidian Space

The subarachnoidian space full of cerebrospinal fluid is contained between the two
membranes of the leptomeninx – pia mater and arachnoid. It is a consequential result of the
different displacement of the two thin sheets. The arachnoid, a thin avascular membrane,
follows the surface of the durra mater and the pia mater is joined to the exterior surface of the
anatomic formations which form the central nervous system, going into all the fissures
(except some of the cerebral hemispheres sulci).

The Choroid Plexuses

The choroid plexuses are anatomic formations resulted from the coalescence of the pia
mater with the ependimus, at the line where the choroidian webs make contact with the
tectorian laminas of ventricles III and IV.
They are disposed in three zones:
 In pars centralis and pars temporalis of the lateral ventricles.
 In the third ventricle, bilateral paramedian,
 In ventricle IV, the choroid rhombencephalic plexuses.
Macroscopically, the choroid plexuses look like some reddish thin chords, with granulous
apparent surface.
Vascularization has its origin in the choroidal arteries: anterior and posterior. These
vessels secure a sanguine debit of approx. 3 ml/min/gram of tissue, twice as much as the
kidneys.
The morphofunctional unity of the choroid plexus is the choroid villum.
The functions of the choroids plexuses are:
 Formation of the cerebrospinal fluid through a mixed process, active secretion and
passive capillary diffusion.
 Some of the substances may be actively conveyed by the choroid plexuses, from the
cerebrospinal fluid into the blood, against a concentration gradient. The association of
the two processes (secretion and absorption) determines, in fact, the composition of
the cerebrospinal fluid.

The Arachnoid Villi or Granulations are some digitiform evaginations of the arachnoid that
open up after crossing the durra mater in the sanguine lacunas of the diploia. As a general
rule they are displaced in systems of parallel tubes, juxtaposed and interconnected. Invisible
with new-born and children, they increase in dimensions progressively, exceeding the limit of
discrete optical detection, towards the age of 7-10 years.
These formations, more visible with ageing, would hyalinise, fibrosise and impregnate
with calcium insoluble salts, called Pacchioni arachnoidian granulations.
These corpuscles, with an incontestable role in the drainage of the cerebrospinal fluid to
the venous system, are placed in large numbers on both sides of the superior longitudinal
sinus which they invade. More rarely, they appear next to the lateral, cavernous and superior
rocky sinuses and in the confluence zone of the sinuses.

The Physiology of the Cerebrospinal Fluid/Liquid (CSF/L)

Generalities
The cerebrospinal liquid is a clear fluid, as clear as “mountain spring” with a specific
density of 1,004 - 1,007 g/cm3, localized inside the cerebral ventricles, the subarachnoidian
space and at the rachidian level. CSF is part of the extracellular space.
The cerebrospinal liquid appears in the third month of the intrauterine life, as a result of
the choroid plexuses activity, formed during the eighth week.
The physiology of the cerebrospinal liquid is determined by the balance between its
formation and its absorption, so that the net exchanged value to be zero. Disturbing this
balance (in the sense of increasing the secretion or decreasing the absorption or the two
mechanisms combined) would result in an increase of the CSF volume, determining implicitly
an increase of the intracranial pressure.

Forming and composition of the cerebrospinal liquid

At this time it has been certified that the medium rate of the cerebrospinal liquid
formation is of 21 ml/hour up to 22 ml/hour or approx. 500 - 550 ml a day. The total volume of
CSF is of approx. 150 ml, with 75 ml in cisterns, 50 ml in the subarachnoidian space and 25
ml in the ventricles. So the quantity of CSF is replaced 3 – 4 times a day. The cerebrospinal
liquid formation rhythm depends on age and the degree of brain development.
The cerebrospinal liquid is secreted through an active process, dependent on a series of
enzymatic mechanisms, from the choroid plexuses (50-60%), from the central nervous
system’s interstitial liquid and directly from the ventricular walls on the nervous system. The
choroid plexuses are the principal locations where the CSF is formed.

The absorption of the cerebrospinal liquid

The CSF absorption is done through the arachnoid villi, by a passive biomechanical
process, dependent on the difference between the hydrostatic and coloidosmotic pressure,
between the CSF and the venous blood (pressure gradient), as well as on the integrity of the
arachnoidian villi. These function as one-way valves, leading the CSF from the
subarachnoidian space into the dural venous sinuses, because, usually, the hydrostatic
pressure of the CSF exceeds the venous one.
Thus, the cerebrospinal liquid forms from the arterial blood and returns to the venous
blood.

Circulation of the cerebrospinal liquid

Harvey Cushing gave an appropriate name to the cerebrospinal liquid, calling it the “third
circulation”, comparable with that of the blood and lymph. Its itinerary is well-known. From the
main CSF formation location, meaning the lateral ventricles, it flows downwards through the
third ventricle, the aqueduct of Sylvius, the forth ventricle and the Magendie and Luschka
foramina, to the perimedullar subarachnoidian spaces and upwards passing by the cerebral
trunk towards the basal and ambient cisterns and finally reaching the lateral and superior
surface of the cerebral hemispheres where it is absorbed, at the greater rate at the level of
the superior saggital sinus.

The function of the cerebrospinal liquid

The basic function of the cerebrospinal liquid seems to be one of mechanical nature: it
has the role of a water mantle at the level of the spinal marrow and the brain, protecting them
from possible blows on the spinal cord and the brain and from drastic changes in the venous
pressure. It also confers the brain the property to “float”. The CSF functions may be
systematized as follows:
1. CSF confers the central nervous system assistance and mechanical protection
against sudden moves and traumatisms.
 2. CSF ensures nutritional and energetic support both for the neurons and for the glial
cells.
3. CSF supplies the absence of the lymphatic system by resorption of the residual
products resulted from the neuronal metabolism.
4. The cerebral extracellular space freely communicating with the CSF allows realization
of a stable ionic composition for the CNS’s cells.
5. The presence of the active biological principles (hormones, neurotransmitters) implies
the role of a conveying system.
6. The CSF composition analysis gives information for diagnostic purposes about the
normal and pathological state of the CNS.
7. Due to its relatively easy approachability, by puncture, the CSF also offers an
anesthetic way of therapeutical goals.

Definition
Hydrocephaly is defined as an abnormal accumulation of cerebrospinal liquid/fluid
(CSF/L), endocranial and in the specially constituted anatomical spaces, caused by a certain
circulation disorder, resorption or hyperproduction of the same, having as consequence the
appearance of a more or less specific symptomatology.
The incidence of this disease in the general population is of 1-1,5% and for the
congenital hydrocephalies it is of 0,2-3,5/1000 births.

Classification of hydrocephaly
According to the functional criterion, hydrocephaly is classified in two types:
- obstructive
- communicating
Obstructive hydrocephaly defines any action restricting the flux inside or from the
ventricular system. So a blockage anywhere along the ventricular paths (the interventricular
Monro foramen, the Sylvius aqueduct, the Magendie foramina from the fourth ventricle),
produces obstructive hydrocephaly with the enlargement of the ventricles located proximal to
the obstruction.
Any interruption of the liquidian flux after the CSF’s exit from the ventricular system is
called communicating hydrocephaly. It occurs in the case of cisterns obstruction, along the
subarachnoidian space or at the level of the arachnoid villosities.
The old classification grouping hydrocephalies into congenital and acquired is still valid today.
At present, the congenital hydrocephaly may be currently diagnosed by the intrauterine
echography of the fetus. The intracranial pressure is determined by the volume of the
cerebral tissue, the CSF volume, the circulant blood volume as well as by the other
intracranial tissues’ volume. An increase in volume for any of the components leads initially to
the compensating drop of the other’s volume, finally producing a constant growth of the
intracranial pressure.
The braincase content may be divided into three compartments:
- cerebral parenchyma
- vascular tree
- liquidian sector
The vascular system is the only system open to the exterior through the carotid arteries, the
vertebral arteries and the jugular veins. It may be compressed, thus, rapidly changing
volume.
The cerebral parenchyma may also alter its volume, but in the longer term, either through
cellular multiplying during brain development, or by cellular destruction, irrespective of the
mechanism causing it.
The liquidian system is composed of CSF and extracellular liquid. They are interdependent
on either side of the ependimus/ependyma wall and of the perivascular spaces. There are
times when the liquid volume grows abnormally, as it is in the cerebral atrophies and focal
porencephalies; in these cases CSF passively fills up the void created by the destruction of
the cerebral parenchyma. These situations are not consequences of a CSF dynamic
disturbance and do not embody pathological entities that are part of hydrocephaly.

Physiopathology
Hydrocephaly is the result of three mechanisms:
- hyperproduction of CSF
- producing resistance to CSF flowing
- occurrence of a CSF absorption deficit by increase of the venous pressure
The consequence of these mechanisms is increase of CSF pressure in order to maintain the
balance between the secretion and resorption debits. Ventricular dilatation is not the result of
unevenness between secretion and resorption but is secondary to the CSF hydrostatic
pressure growth.
The mechanisms producing dilatation of the ventricular system upstream to the obstacle
placed in the way of the CSF circulation path are several and they occur at different times of
disease progression. Ventricular dilatation is the result of the vascular system compression or
of a modified distribution of CSF and of the extracellular liquid inside the skull.
During a longer period, under the effect of compression, the cerebral parenchyma suffers
cerebral destructions and participates in the ventricles dilatation. With children, the exercise
of an abnormal pressure on the still unossified cranium sutures leads, secondarily, to an
increase of the cranial volume.

Etiopathogeny
Child hydrocephaly has two main causes:
- prenatal
- postnatal
The prenatal causes are responsible for the congenital hydrocephaly but also for the one
appeared postnatal or only belatedly manifested at adolescence. Etiology is usually
malformative, infectious or vascular and sometimes idiopathic.
Malformative causes:
- stenosis of the Sylvius aqueduct
- malformation Chiari type I and II
- malformation Dandy-Walker
- agenesis of the Monro foramina
The most common infectious causes are:
- purulent meningitis
- TBC meningitises
- parasitoses
Vascular causes determine hydrocephaly subsequent to:
- subarachnoidian hemorrhages or
- intraventricular hemorrhages of different etiologies
Postnatal causes for the development of hydrocephaly are the most frequent.
These are:
- tumoral expansive processes which in children represent the cause of over 20% of
hydrocephalies. The disease may be secondary to the evolution of the following tumor
types:
 colloid cyst
 choroid plexus papilloma
 meduloblastoma
 ependymoma
 sellar region tumors with suprasellar extension
 arachnoidian cysts
 - the non-tumoral expansive processes are represented by:
 vascular malformations
 Galen vein aneurysms.

Adult hydrocephaly has a really varied etiology, congenital or acquired. The most frequent
causes are:
- meningeal hemorrhages
- meningitis
- cranial traumatisms
- neurosurgical interventions with opening of the ventricular system
- intracranial tumors (colloid cysts, craniopharyngiomas, hypophyseal adenomas,
epidermoid cysts, pineal region tumors, tumors of the posterior cerebral fossa, tumors
of the meninx developed on the tentorial incisure)
- intrarachidian tumors
Other rare causes with adults are:
- non-tumoral stenosis of the Sylvius aqueduct
- Dandy-Walker and Chiari malformations
- Sarcoidosis
- Paget’s disease (creates bony origin venous compressions), etc.

The clinical picture differs according to the patient’s age.

In infants, there occurs the macrocephaly, irritability, bulging of fontanelles, accentuation of
the scalp’s vascular drawing, abducens paresis, Parinaud syndrome, disorders of the
respiratory rhythm and apnea crises and the cranial sutures dehiscence.
The grown child and the adult develop the following:
- Syndromes of evolutive intracranial hypertension
- Abducens nerve paresis
- Psychic disturbances
- Ophthalmologic disturbances
A separate category of adult hydrocephaly is the normal pressure chronic hydrocephaly,
characterized by a triad of signs described by Hakim and Adams in 1965, consisting in:
- walking disorders (ataxy)
- psycho-intellectual disturbances
- sphyncterian disorders (gatism)

Paraclinical explorations
Invention and spreading of CT-scan and of the nuclear magnetic resonance imaging have
revolutionized the diagnosis and post-operational follow-up of hydrocephalies.
The CT-scan exam is the first step of the diagnosing process. Besides the fact that it reveals
a possible cause of the hydrocephaly, it allows to appreciate the ventricular dilatation and the
aspect of other subarachnoidian spaces.
The MRI exam completes the CT-scan allowing the precise description of a alleged
obstructive lesion. The typical exam is to highlight the Sylvius aqueduct stenosis impossible
to assess by a CT-scan. Besides the very detailed morphological aspects the MRI exam
allows a dynamic exploration of the CSF flux.

The treatment of hydrocephaly

Hydrocephaly is treated surgically and it is called for when there is an association of the
symptoms and the signs of an intracranial pressure increase, with the dilatation of the
ventricular system (radiologically observed). The surgical treatment consist in extracranial
drainages, performing a by-pass of the obstruction through a tubular system in the body, that
realizes the connection between the ventricular system and a compartment where the
cerebrospinal liquid is absorbed to or eliminated. At present there are two routine methods
used: ventriculoperitoneostomy and ventriculoatriostomy.
The goals of the neurosurgical treatment are:
 Removal of the causes of hydrocephaly (when possible)
 Stopping the evolution of hydrocephaly
 Securing a favorable functional prognosis
The relative contraindications to the neurosurgical treatment are:
 albuminorachia over 1g0/00; an increased albuminorachia over this value may
cause valve blockage;
 too advanced stages of hydrocephaly when the cerebral mantle has a thickness
under 1 cm;
 an altered general state;
 stable hydrocephaly, with no visible symptoms.
The only absolute contraindication to the neurosurgical treatment is the infectious diseases
(septicemy, meningoencephalitis, pyodermitis).
A classical shunt system is formed of four components: a ventricular catheter, a reservoir,
one valve and a distal catheter. All these have different dimensions for adaptation to the
patient’s age and size.
A very important part of the shunts is represented by interposing in the system a
unidirectional valve that would open only when the intraventricular pressure reaches a certain
level, for reason to avoid the continuous drainage of the cerebrospinal liquid that could lead
to a too low intracranial pressure or even to a ventricular collapse syndrome.
The valves used today are pressure valves with preestablished opening pressure (low,
medium and high), modular opening valves and programmable valves of variable resistance.
The CSF intrathecal derivations consist in endoscopic ventriculostomy in the third ventricle’s
floor, desiring to reestablish a communication between the intraventricular liquidian system
and the subarachnoidian one.

The medical treatment aims at stopping the evolution of hydrocephaly, reducing the CSF
production by administration of carbon anhidrasis inhibitors (acetazolamid) and diuretics
(furosemid), or by monitoring the resorption increase by administration of izosorbide-dinitrate.
The medical treatment indications are: infections of the shunts that require ablation,
monitoring the hydrocephaly until the next intervention of derivation; the medical treatment is
also useful in the symptomatic treatment of hydrocephaly subsequent to subarachnoidian
hemorrhages; to postpone the surgical intervention for a proper moment.
A timely treatment of an acute hydrocephaly with intracranial hypertension syndrome is
always successful, overlooking, of course, the cause of the disease. The hydrocephalies
treatment prognosis is directly dependant on the frequency and the severeness of the shunt’s
possible complications, meaning:
- mechanical complications (tubulature obstructions, tubulature detachment or
migration, etc.)
- infectious complications
- complications caused by excessive drainage of the CSF (subdural hematomas).