Hydrocephalus: Communicating (aka Non-Obstructive)
Hydrocephalus: Communicating (aka Non-Obstructive)
Hydrocephalus
- Hydrocephalus is an increase in CSF volume with dilatation of either a portion of the ventricular system or the entire system and (depending on the location of the obstruction) divides into:
- Communicating (free flow of CSF into the subarachnoid space.
- Noncommunicating (prevention of CSF flow into the subarachnoid space).
Communicating Hydrocephalus vs Non-communicating hydrocephalus
- Communicating hydrocephalus
- If the cerebrospinal fluid (CSF) flows freely, it's a communicating hydrocephalus.
- Dilatation of ventricles occurs from obstruction of CSF return in the subarachnoid space (eg, from subarachnoid hemorrhage).
- Non-communicating hydrocephalus (aka obstructive hydrocephalus)
- If there is a physical blockage (eg, tumor) it's non-communicating hydrocephalus.
- Obstruction is anywhere from the foramen of Monro (where the lateral ventricles empty into the 3rd ventricle) to the exiting foramina of the 4th ventricle (the foramen of Lushka and Magendie).
Nomenclature
Congenital hydrocephalus
- Present at birth, due to any number of causes.
Acquired hydrocephalus
- Develops later in life
Normal pressure hydrocephalus
- Ventricular enlargement in older adults, out-of-proportion to gyral atrophy. Most importantly, this is a clinical diagnosis, classically of progressive dementia, bladder incontinence and gait ataxia (specifically, magnetic gait).
Compensated hydrocephalus
- Found in adulthood but could have been present since birth.
Common causes
Acquire hydrocephalus
Common causes:
- Tumors (eg, pineal region tumors)
- Structure compression/direct outflow obstruction.
- Meningitis
- Infectious material blocks/plugs the arachnoid villi.
- Subarachnoid hemorrhage
- Blood blocks/plugs the arachnoid villi.
Congenital hydrocephalus
- Aqueductal stenosis (the most common cause)
- Blockage of the outflow between the 3rd and 4th ventricles (the cerebral aqueduct of Sylvius): the brain will be hydrocephalic upstream from the blockage.
- Neural tube defect
- Spina bifida leads to Chiari II malformation, which blocks CSF flow out of the 4th ventricle and causes hydrocephalus.
- Arachnoid cysts
- Often found in the 3rd ventricle in children and can cause upstream hydrocephalus.
- Dandy-Walker syndrome
- 4th ventricle enlargment due to outlet obstruction.
- Chiari malformation
- Can cause outflow obstruction from cerebrellar herniation and upstream hydrocephalus.