Hydrocephalus

Description

• Increased volume of CSF in cranial cavity
• Cerebral atrophy also leads to increased CSF in the cranial vault but CSF pressure is not increased (normal pressure hydrocephalus)
• Obstructive hydrocephalus is the most common form:
  • Obstruction is within ventricular system or in subarachnoid space
• Acute obstructive hydrocephalus may cause rapid rise in intracranial pressure (ICP), rapidly leading to death or permanent cerebral damage
• Nonobstructive hydrocephalus causes subacute symptoms and is a potentially treatable form of dementia
• Also described as “communicating” and “noncommunicating”:
  • Communicating hydrocephalus: Flow of CSF is blocked after it exits the ventricles (ventricles still “communicate”)
  • Noncommunicating hydrocephalus: Flow of CSF blocked along 1 or more of the passages connecting the ventricles (ventricles do not “communicate”)

Etiology

• Obstructive hydrocephalus:
  • Obstruction of:
    • Aqueduct of Sylvius (most common, both lateral ventricles and third ventricle dilated, fourth ventricle is spared)
  • Aqueductal stenosis can be congenital or acquired (tumor, subarachnoid hemorrhage, post meningitis, idiopathic)
    • Foramen of Monro (lateral ventricles dilated, usually both but may be unilateral)
    • Foramina of Luschka and Magendie (fourth ventricle blocked followed by third and lateral ventricles)
    • Subarachnoid space around brainstem (postinfectious or postsubarachnoid hemorrhage [post-SAH] entire system dilated)
  • Acute presentations usually secondary to CSF shunt blockage, SAH, or severe head trauma
• Nonobstructive hydrocephalus:
  • Normal pressure hydrocephalus:
    • Increased intracranial volume of CSF without intracranial hypertension
    • Increased ventricular size on CT (without volume loss as in atrophy)
    • Sometimes called “chronic hydrocephalus”
    • Usually occurs due to inadequate CNS absorption

• Congenital hydrocephalus owing to neonatal hemorrhage, congenital malformations, or acquired postmeningitis secondary to subarachnoid scarring around brainstem