• 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”)


  • 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

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

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