Hydrocephalus

Hydrocephalus

• Definition
  • An abnormal increase in the amount of cerebrospinal fluid within the cranial cavity that is accompanied by expansion of the cerebral ventricles and (in infants)enlargement of the skull
  • Can result either from increased production or decreased absorption of CSF, or from blockage of one of the normal outflow pathways of the ventricular system
  • Anatomy of the ventricles
    • Two lateral ventricles (connects to 3rd by foramen of Monro)
    • 3rd ventricle (connects to 4th by Aqueduct of Sylvius)
    • 4th ventricle
  • Most common forms occur in infants
    • Because cranial sutures are not yet fused, head size increases progressively
    • Thus, periodic measurement of the skull’s circumference to detect enlargement is important in neonatal and infant care

• Obstructive
  • Obstruction of CSF drainage from the lateral and third ventricles
  • Most cases of hydrocephalus, resulting from congenital stenosis of the aqueduct of Sylvius (aka, Cerebral aqueduct)
  • Commonly seen with brainstem tumor or a posterior fossa tumor encroaching on the fourth ventricle and obstructing the lateral aperture of Luschka or the median aperture of Magendie
  • In adults, it is also associated with brain tumors that impinge on the ventricular structures

• Communicating
  • There is an interference with the normal rate of absorption
  • This may be seen after intraventricular hemorrhage in premature infants (or in adults due to stroke or infection)
    • The presence of blood breakdown products in the CSF interferes with the normal rate of absorption

• Advanced Infantile Hydrocephalus
  • Scalp veins are distended because venous drainage from the scalp is impaired as a result of elevated intracranial pressure
  • We see a downward deviation of the eyes, referred to as “sunset eyes”
    • Probably results from pressure transmitted to the midbrain by the dilatation of the posterior part of the 3rd ventricles
    • Paralysis of upward gaze is resultant, called Parinaud’s syndrome
  • Affected infants appear emaciated, characterizing the poor feeding and recurrent vomiting that accompanies elevated intracranial pressure

• Normal Pressure Hydrocephalus (NPH)
  • This adult/geriatric syndrome is not associated with an obvious increase in intracranial pressure
  • Initial symptoms are progressive dementia, gait disorders, and urinary incontinence (3 Ws: wet, wacky, and wobbly)
  • The CT scan shows ventricular dilatation, which must be differentiated from ventricular dilatation secondary to brain atrophy
  • Makes up approximately 6% of dementia cases (according to some studies)
  • Reversible dementia with surgery, but less so if the dementia is the most striking feature or has been present for more than two years
    • If the gait abnormality began before or at the same time as dementia, then there is a better chance for successful surgery
    • Alcohol abuse is a poor prognostic indicator
    • Aphasia is a poor prognostic indicator for surgical success
    • Only about 50% of those responding to shunt surgery improve cognitively by the criteria of a significant increase in the test scores in two or more neuropsychological areas (and no decline in another area)
  • 30% of patients experience either major or minor shunt complications

• Shunting
  • A significant number of patients with communicating or obstructive hydrocephalus require shunting
  • For communicating hydrocephalus, the shunt can originate anywhere in the subarachnoid space or ventricular system
  • For obstructive hydrocephalus, the origin of the shunt depends on the location of the obstructing lesion
  • Most shunting operations involve placing a tube or ventricular catheter in the anterior horn of the lateral ventricle
  • The catheter is connected via a subcutaneous tube to either the right atrium of the heart or to the peritoneal cavity