Hydrocephalus

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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


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