Neurological Disorders: Hydrocephalus

Definition

The term hydrocephalus literally means water in the brain. With this neurological condition there is accumulation of excess cerebrospinal fluid (CSF) within the brain ventricles (the cavities inside the brain tissue) resulting in enlargement of these ventricles. A Neurologist frequently involves in the management of this condition.

More on the anatomy of ventricles & CSF flow

Choroid plexus is a structure present in the inner aspect of the ventricles from which most of the CSF gets secreted. The cells lining the inner surface of ventricles contribute too. In humans there are total 4 ventricles; the two lateral, single third and fourth ventricles. The lateral ventricles are connected to the third and the third with the fourth ventricle. Lateral ventricles communicate with third ventricle via foramen monro, third ventricle communicates with fourth ventricle via cerebral aqueduct of Sylvius, and finally the fourth ventricle communicates with the subarachnoid space (area between the two layers of brain coverings called as arachnoid and pia membranes) through 3 openings; 1 placed centrally (foramen Magendie) and a pair placed laterally (foramena Luschka).

Development of hydrocephalus and its types

This condition may result from one or more of the following mechanisms including;

  • Abnormally excess CSF production
  • Blockage to CSF flow (obstructive)
  • Blockage to CSF absorption (non obstructive)
When CSF production exceeds its absorption back to systemic circulation then it will build up inside the ventricles causing enlarged ventricles. It is an uncommon type and seen with the tumors of choroids plexus which secretes too much of CSF.

Obstructive or non-communicating type means there is a blockage to CSF flow any where within the ventricular system or at the openings linking fourth ventricles with subarachnoid space. Any mass or growth inside or out side & adjacent to the ventricular system can block CSF flow and a resultant enlargement of ventricles. Some examples include;

  • Tumors
  • Cystic lesions (e.g. dermoid cysts)
  • Abscesses (pus collection)
  • Congenital blockage (present at birth) etc
Non-obstructive or communicating type occurs when there is blockage within the subarachnoid space, or for CSF absorption at structures called as the arachnoid granulation, and this is mostly due to scarring of the meninges due to prior irritation. Prior episodes of sub-arachnoid bleeding, meningitis etc are the usual culprits.

NPH (Normal pressure hydrocephalus) is a communicating type with its own characteristic clinical presentation (read below).

How does the patient manifest?

The manifestations generally depend upon whether the hydrocephalus has developed quickly or slowly. With the obstructive hydrocephalus in general the build up of CSF pressure is rapid, and slower with the non obstructive type.

Important to note that there is no much extra space inside the skull cavity, so whenever something additional grows or develops inside the skull it creates extra pressure and this phenomenon is called as “raised intracranial pressure (ICP)”. When the ICP rises it starts suppressing the activity of brain cells. Also the pathologically excessive pressure will try pushing the brain contents out side the skull cavity and towards the only naturally available exit, the spinal canal, and this life threatening situation is called as brain herniation.

The lower part of the brain called as brain stem has vital centers controlling blood pressure, breathing etc. The herniating brain can compress these vital centers and this can be fatal.

Symptoms secondary to raised ICP include:

In the early stages;

    Headache Nausea & vomiting Diminished alertness Irritability, reduced food intake etc in infants & young children Generalized weakness etc
In the advanced stages;
  • Severe drowsiness
  • Large head (mostly in young infants)
  • Coma
  • Respiratory (breathing failure)
  • Certain death if not intervened immediately
The communicating type like NPH usually produces progressive;
  • Dementia
  • Gait unsteadiness
  • Bladder disturbances
Headache in general is not a symptom of NPH however may be seen with other types of communicating hydrocephalus for example when prior episode of subarachnoid hemorrhage as the cause.

Diagnosis

The following tests are generally ordered (case to case basis);

• Brain CT scan
• Brain MRI scan
• CSF (cerebrospinal fluid) analysis including opening pressure estimation

Spinal tap (lumbar puncture) may be contraindicated if certain situations like obstructive hydrocephalus, mass lesion etc are seen or suspected.

Treatment

The treatment depends upon the cause. In NPH large volume CSF tap is done which is also used as a diagnostic test for this condition. Some patients may improve especially with regard to their gait difficulties after the tap and such patients may be candidates for a VP (ventriculoperitoneal) shunt placement.

Structural causes like tumors, abscesses, other growths are treated appropriately.



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