When you're diagnosed with hydrocephalus, your team may use terms like "communicating" or "obstructive." These describe the type of hydrocephalus, and the distinction is important because it influences which treatment is likely to work. Here's a plain-language guide.
The two core types The most fundamental way to classify hydrocephalus is by where the problem with CSF lies:
Obstructive (non-communicating) hydrocephalus Here, there is a physical blockage within the ventricular system that stops CSF from flowing along its normal path. The ventricles "upstream" of the blockage swell with trapped fluid, while areas downstream may be normal. A classic example is aqueductal stenosis, where the narrow cerebral aqueduct is blocked or narrowed. Because there's a discrete blockage, this type is sometimes treatable by creating a new internal pathway for fluid (an ETV).
Communicating hydrocephalus Here, CSF can flow freely through the ventricles — they still "communicate" with one another — but the fluid isn't absorbed properly once it reaches the surface of the brain, or far more rarely is overproduced. The ventricles enlarge throughout. Because there's no single blockage to bypass, this type is usually treated with a shunt. Normal pressure hydrocephalus (NPH) is a form of communicating hydrocephalus.
Other important terms you may hear Hydrocephalus is also described in other ways that can overlap with the above:
- Congenital vs acquired — whether it was present at/before birth or developed later.
- Normal pressure hydrocephalus (NPH) — a specific communicating form in older adults, with normal or intermittently elevated pressure.
- Hydrocephalus ex vacuo — ventricular enlargement caused by loss of brain tissue (atrophy), rather than a CSF flow or absorption problem. This is a different situation and usually doesn't need shunting (covered in its own article).
Why the distinction matters The type of hydrocephalus shapes treatment:
- Obstructive hydrocephalus from a clear blockage may be well-suited to an ETV, which bypasses the obstruction without leaving an implant.
- Communicating hydrocephalus, where the issue is absorption, generally needs a shunt to divert and absorb the excess fluid elsewhere.
That said, decisions are individualized — your age, the cause, and the specifics of your anatomy all matter, and your neurosurgeon will recommend the approach most likely to help you.
The bottom line "Communicating" and "obstructive" aren't just jargon — they describe two different mechanisms (an absorption problem vs a blockage), and that difference is one of the main factors guiding whether a shunt or an ETV is the better treatment for you.