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Definition

Hydrocephalus is a pathological condition characterized by an abnormal accumulation of cerebrospinal fluid (CSF) within brain ventricles.


Epidemiology

  • Estimated prevalence - 1-1,5%;
  • Congenital hydrocephalus incidence - 0,9-1,8/1000 births (the most common surgery condition treated during pediatric age);
  • Acquired hydrocephalus incidence is difficult to estimate due to different kinds of manifestation, either as prevalent clinical condition or complication of many CNS affections.

 

Cerebrospinal fluid physiology

  • CSF surrounds the brain and spinal cord and circulates within the subarachnoid space. It is a colorless fluid with specific gravity of 1.007 and a pH of 7,33-7,35. It has many function such as shock absorber and immunological defense for the CNS;
  • Intracranial CSF is produced by the choroid plexuses located in both lateral ventricles and in fourth one; a small amount may also be produced by the ependymal lining of the ventricles and by interstitial space;
  • Spinal CSF produced in the dura of the nerve root sleeves;
  • Production rate is independent of the intracranial pressure (ICP);
  • CNS is produced at a rate of about 450ml/24hrs which correspond with 3 times every day turn over (if we consider the average total CSF volume is 150 ml);
  • CSF is absorbed by arachnoid villi (Pacchioni’s granulations) located into the dural venous sinus. A small amount may also be absorbed by lymphatics and the choroid plexuses;
  • Absorption rate is pressure dependent (it increases with ICP raising).

 

Pathophysiology

Idrocephalus develops because of an imbalance between CNS reabsorption and production:

  • Subnormal CSF reabsorption - It is the dominant mechanism in most cases and could be functionally divided in two main types;

Obstructive hydrocephalus (non-communicating)

There is a block proximal to arachnoid granulations to CSF discharge leading to mono/bi/tri-ventricular idrocephalus based on blocking level

Communicating hydrocephalus (non-obstructive)

It defects in CSF reabsorption by arachnoid granulations

  • CSF overproduction - It is a rare condition (e.g. choroid plexus papilloma) which could be more tolerated unless a concomitant reabsorption deficit.

 

Etiologies

Congenital hydrocephalus

  • Chiari Type 2 malformation with (29%) or without (38%) myelomeningocele (MM)
  • Chiari Type 1 malformation
  • Primary aqueductal stenosis
  • Secondary aqueductal gliosis due to germinal matrix hemorrhage or intrauterine infection
  • Dandy Walker malformation
  • X-linked inherited disorder

Acquired hydrocephalus post-infectious (the most common cause of communicating HCP)

  • Meningitis
  • Cysticercosis

Acquired hydrocephalus post-hemorrhagic (second most common cause of communicating HCP)

  • Post-SAH (subarachnoid hemorrhage)
  • Post-IVH (intraventricular hemorrhage)
  • Secondary to mass either neoplastic or non neoplastic (e.g. vascular malformation)
  • Post-op: 20% of pediatric patients develop permanent HCP
  • Neurosarcoidosis

Special forms of HP

  • Normal pressure hydrocephalus (also known as Hakim-Adams Syndrome)

Features of Hakim-Adams Syndrome

It is a particular condition described both in adult and child; it is characterized by stable ventriculomegaly at neuroimaging without clinical manifestation of increased ICP. Anyway it is associated with chronic suffering of cerebral tissue due to only apparent normal ICP which can occasionally rise up.
It’s characterized by a suggestive (but not pathognomonic) clinical triad:

  • Gait disturbance which usually precedes other symptoms
  • Dementia with primarily memory impairment
  • Urinary incontinence
  • Arrested hydrocephalus 

Features of Arrested hydrocephalus

It is a sort of compensated HCP which needs no treatment because of the absence of clinical manifestation of increased ICP. However patients should be advised to seek medical attention to cues of possible “involution” of the situation (decompensation).

  • Entrapped fourth ventricle (also known as Isolated fourth ventricle)

Features of Isolated fourth ventricle

It is a condition in which 4th ventricle doesn’t communicate neither with 3rd ventricle nor with basal cisterns. It is usually seen with chronic shunting of the lateral ventricles, especially in those with repeated shunt infections.


Symptoms and Signs

In older children (with rigid cranial vault) and adults

  • Symptoms are those of increased ICP, such as:
  • Papilledema
  • Upward gaze palsy
  • 6th nerve palsy
  • Gait changes

In young children (without rigid cranial vault)

  • Abnormalities in head circumference

Evaluation of the occipital-frontal circumference (OFC)

That’s why the occipital-frontal circumference (OFC) should be followed in every growing child and especially in those with suspected or documented HCP. The OFC of a normal infant should equal the distance from crown to rump.

  • Cranium enlargement
  • Fontanelle full and bulging
  • Splaying of cranial sutures (be seen on plain skull x-ray)
  • Enlargement and engorgement of scalp veins
  • Macewen’s sign: cracked pot sound on percussing over dilated ventricles
  • Setting sun sign due to upward gaze palsy
  • 6th nerve palsy (the most sensitive to pressure nerve due to its long intracranial course)
  • Irritability
  • Hyperactive reflexes
  • Irregular respiration with apneic spells

Symptoms of increased ICP

In addition, headache, vomiting, visus, respiratory and consciousness disorder could be sudden or progressive depending on the acute or chronic development of HCP, respectively

 

Complications

Blindness is a rare complication most likely resulting from:

  • Occipital lobe infarctions due to posterior cerebral arteries occlusion caused by downward trans tentorial herniation or in alternative by upward cerebellar herniation (cortical or post-geniculate blindness);
  • Chromic papilledema causing injury to optic nerve at the optic disc (pre-geniculate blindness);
  • Dilatation of the 3rd ventricle causing compression of optic chiasm (pre-geniculate blindness).

 

Diagnosis

TC and MRI represent the gold standard to demonstrate HCP.

Ratio for the evaluation

Many features suggest HCP, such as:

  • Both temporal horns size >= 2mm in width with sylvian and interhemispheric fissures and cerebral sulci not visible;
  • Both temporal horns size >= 2mm in width with ratio FH/ID > 0.5 (FH stands for the largest width of the frontal horns, ID stands for the internal diameter from inner-table to inner-table).

Trans fontanelle US represents a very important exam to demonstrate HCP in the infant (under 2 years old) with open fontanelle; it is very useful thanks to its safety (no radiation exposure) and accuracy. Moreover, its useful during post-operative follow-up.

 

Differential diagnosis

HCP must be distinguished from:

  • “Hydrocephalus ex vacuo” which is characterized by an enlargement of the ventricles due to loss of cerebral tissue (cerebral atrophy) which could be as a part of normal aging but also as a result of certain CNS disease (e.g. Alzheimer disease);
  • Developmental anomalies where the ventricles or their portions appear enlarged (e.g. hydranencephaly, agenesis of corpus callosum):

 

Treatment

It could be subdivided in non surgical and surgical one. The former approach consists of medical treatment with drugs (e.g. acetazolamide) that reduce production of CSF but their aim is only palliative. The latter consists of several surgical methods such as:

Ventriculoperitoneal shunt

It has been the most common technique used until the development of endoscopic 3rd ventricolostomy. It consists in drainaging of CSF from the ventricle to peritoneal cavity with the application of a catheter.

Endoscopic 3rd ventriculostomy

It has been the elective method since nearly twenty years. It is a sort of bypass; it consists in introducing of an endoscopic in lateral ventricle from which can be reached 3rd one passing through Monroe foramen. Once arrived at the third ventricle its wall is pierced to make it communicating with basal cisterns.

 

 

References

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Lorenzo AV, Page LK, Wlaters GV. Relationship Between Cerebrospinal Fluid Formation, Absorption, and Pressure in Human Hydrocephalus. Brain. 1970; 93:679–692

Gri th HB, Jamjoom AB. The Treatment of Childhood Hydrocephalus by Choroid Plexus Coagulation and Artificial Cerebrospinal Fluid Perfusion. Br J Neurosurg. 1990; 4:95–100

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Parker T. Never Trust a Calm Dog: And Other Rules ofThumb. NewYork:HarperPerennial;1990 


Joynt RJ, Honch GW, Rubin AJ, Trudell RG, Frederiks JAM. In: Occipital Lobe Syndromes. Handbook of Clinical Neurology. Holland: Elsevier Science Pub- lishers; 1985:49–62 


Hoyt WF. Vascular Lesions of the Visual Cortex with Brain Herniation Through the Tentorial Incisura. ArchOphthalm.1960;64:44–57 


Rinaldi I, Botton JE, Troland CE. Cortical Visual Dis- turbances Following Ventriculography and/or Ventricular Decompression. JNeurosurg. 1962; 19:568– 576 


LeMay M, Hochberg FH. Ventricular Differences 
Between Hydrostatic Hydrocephalus and Hydrocephalus Ex Vacuo by CT. Neuroradiology. 1979; 17:191–195 


Sutton LN. Current Management of Hydrocephalus in Children. Contemp Neurosurg.1997; 19:1–7

Pang D, Zwienenberg-Lee M, Smith M, Zovickian J. Progressive cranial nerve palsy following shunt placement in an isolated fourth ventricle: case report. J Neurosurg. 2005; 102:326–331

Hakim S, Adams RD. The Special Clinical Problem of Symptomatic Hydrocephalus with Normal CSF Pres- sure. J Neurol Sci. 1965; 2:307–327
Mark S. Greenberg, Handbook of Neurosurgery, Thieme.

Guido Staffa, Elementi di Neurochirurgia, Timeo Editore.

Renzo Dionigi, Chirurgia Specialistica, Edra.

 

Authors

 

Fabio Paio, MS

Medical Student
University of Verona (Italy)


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