Hydrocephalus
The brain has 4 chambers (called ventricles) containing cerebrospinal fluid (CSF). The two lateral ventricles communicate with the 3rd ventricle through the Monro holes and the 3rd ventricle is connected to the 4th ventricle through the Sylvius aqueduct. When these cavities are excessively dilated, it is called hydrocephalus.

When the dilation is due to cerebral atrophy (age, dementia), it is sometimes referred to as exvacuo hydrocephalus, but the term hydrocephalus is somewhat overused in this case.
Hydrocéphalie: aspect à l'IRM
IRM: différentes séquences pour hydrocéphalie
Hydrocephalus and MRI :

 

The type of sequence used on MRI will drastically change the appearance of the images, but will help estimate the pressure gradient with the brain (transependymal diffusion)

In hydrocephalus, the corpus callosum is stretched by the dilation of the 3rd ventricle and therefore looks thinner. This dilation of the 3rd ventricle can also be the cause of extrapyramidal syndrome (Parkinson's syndrome).
 
This sagittal MRI demonstrates this well. The small size of the aqueduct and the 4th ventricle shows that there is also a relative stenosis of this aqueduct.
IRM sagittale: hydrocéphalie sur sténose de l'aqueduct de Sylvius
Clinical presentation
Adult hydrocephalus:

Adams Triad

 

  • Walking disorders

  • Incontinence

  • Neuropsychological deterioration

Treatment
Adult hydrocephalus:

 

  • Abstention

  • Iterative lumbar punctures

  • Lumbopperitoneal shunt

  • Ventriculoperitoneal shunt

  • Ventriculocardiac shunt

Other hydrocephalus:

 

  • Abstention

  • Ventriculostomy of the floor of the 3rd ventricle

  • Treatment of a possible obstruction (eg tumor)

  • Ventriculoperitoneal shunt

  • Ventriculocardiac shunt

CT-scan: Hydrocéphalie avec drain ventriculaire
The most common treatment for hydrocephalus is the ventriculoperitoneal shunt. A drain is implanted in the lateral ventricles, usually on the right, either in the frontal horn or in the occipital horn. The drain then travels through the subcutaneous tissue to the abdomen where the drain is then implanted through the peritoneum. The peritoneum then absorbs the liquid and this system functions as an "overflow". An intermediate valve is used to regulate the opening pressure of the system or its flow.
Valve pour dérivation ventriculopéritonéale
Valve for ventriculoperitoneal shunt. It is one of the first of the simplest models opening at a given fixed pressure.
There are also adjustable valves without reoperation, constant flow valves, etc.
Radiographie latérale du crâne avec dérivation ventriculocardiaque
Profile x-ray of the skull:
The central part of the valve is radiolucent and gives the false impression of a disconnection from the system.
Frontal skull x-ray:
The central part of the valve is radiolucent and gives the false impression of a disconnection from the system.

The ventricular drain passes the midline, which is not a perfect placement.
Radiographie de face du crâne avec dérivation ventriculocardiaque
Schéma et IRM d'une ventriculostomie du 3ème ventricule
A very special situation of hydrocephalus is the stenosis of the aqueduct of Sylvius.

This can be treated by making a small hole in the floor of the 3rd ventricle to make it communicate with the cisterns of the base.
Endoscope souple pour ventriculostomie
The hole is made under endoscopic control ideally combined with stereotaxic guidance.
The endoscope shown is a flexible endoscope, but many neurosurgeons prefer a rigid endoscope for this procedure
Vue intraventriculaire du foramen de Monro et des corps mamillaires
The endoscope is passed from the lateral ventricle to the 3rd ventricle through the foramen of Monro taking care not to damage the fornix.
 
A hole is then created in the floor of the third ventricle and enlarged with a small balloon.
 
Ventricular shunt: Neuronavigation
Ventricular drains are conventionally implanted "freehand" using the pupillary line and the external auditory canal as landmarks.

Neuronavigation equipment being available in most centers, it is legitimate to wonder whether one should use such machines to implant "a simple drain", especially in very large ventricles.
This example shows poor drain placement in large ventricles. The entry is correct, but the drain is too long and passes Monro's foramen to enter the contralateral thalamus ...
This example is similar to the previous one with narrower ventricles. The drain is again too long and ends up in the contralateral thalamus.

These two examples were performed by very experienced neurosurgeons. This suggests that even in expert hands, a show of hands placement may be inadequate. The use of Neuronavigation techniques therefore seems to provide additional security.