Communicating Hydrocephalus

What communicating hydrocephalus means

The brain makes about 500 ml (17 fl oz) of CSF a day. It flows through four chambers called ventricles, out into the space around the brain and spinal cord, and is reabsorbed into the veins through small structures called arachnoid granulations.

Hydrocephalus is divided by where the problem lies:

The word "communicating" means the ventricles still communicate freely with the space around the brain. The fluid can get out, but it cannot get back into the blood fast enough, so it builds up. Obstructive hydrocephalus is the opposite situation, and the main hydrocephalus page covers both types by age.

Causes

• Bleeding in or around the brain: blood from a subarachnoid hemorrhage or from bleeding in a premature baby's brain clogs and scars the arachnoid granulations. This is one of the most common causes, and it can appear days to weeks after the bleed.
• Meningitis: inflammation and scarring of the brain coverings after bacterial or tuberculous meningitis.
• Head injury and brain surgery: blood and protein in the CSF impair absorption.
• Normal pressure hydrocephalus (NPH): a form seen mainly after age 60, often with no clear trigger.
• Rare causes: very high CSF protein from spinal tumors, cancer spreading to the brain coverings, a choroid plexus tumor that overproduces CSF, and blockage of the large veins that drain the brain.

Symptoms

Symptoms depend on age and on how quickly pressure rises.

Developing quickly (acute)

When raised pressure inside the skull builds over hours or days, typical signs are:

• headache, often worst in the morning
• nausea and vomiting
• blurred or double vision
• drowsiness that can progress to coma

Developing slowly in adults

Normal pressure hydrocephalus causes a classic trio:

1. A slow, wide, shuffling walk, as if the feet are stuck to the floor
2. Urinary urgency, then incontinence
3. Slowed thinking, apathy and poor attention

In babies

Because the skull bones have not fused, the head grows quickly. Other signs are a tense, bulging soft spot (fontanelle), prominent scalp veins, poor feeding, vomiting, irritability and downward-gazing eyes.

Diagnosis

1. Brain imaging: CT or MRI shows all four ventricles enlarged, which points to a communicating type. MRI can also look for the cause and for flow through the cerebral aqueduct.
2. Cranial ultrasound: used in babies through the open soft spot.
3. Eye examination: swelling of the optic nerve head (papilledema) suggests raised pressure.
4. Lumbar puncture: measures opening pressure. In suspected NPH, removing 30 to 50 ml of fluid (a "tap test") and checking whether walking improves helps predict who will benefit from a shunt. A temporary lumbar drain over several days is a similar test.

Treatment

Shunt surgery

A ventriculoperitoneal (VP) shunt is the standard treatment. A thin tube runs from a ventricle, under the skin, into the abdomen, where the fluid is absorbed. A valve controls the flow, and many modern valves can be adjusted with a magnet from outside the head. Other routes are into the heart (ventriculoatrial) or from the lower spine (lumboperitoneal).

Temporary drainage

After a brain bleed or meningitis, a neurosurgeon may place an external ventricular drain or perform repeated lumbar punctures. Absorption sometimes recovers within days to weeks, so a permanent shunt is not always needed.

Why ETV is less useful here

An endoscopic third ventriculostomy creates a bypass inside the brain. It works well for blockages, but in communicating hydrocephalus the problem is absorption, so a bypass usually does not help.

Complications and outlook

Shunts work well but are not trouble-free. About a third to half need revision within the first few years, mostly in children. The main problems are:

• Blockage (shunt malfunction): symptoms of raised pressure return.
• Infection: most often in the first few months after surgery.
• Over-drainage: headaches that are worse when upright, and sometimes small fluid collections or bleeds over the brain.

The outlook depends on the cause. Hydrocephalus after a bleed or infection often stabilizes once treated. In NPH, walking improves most reliably after a shunt, while memory and bladder control improve less consistently. Untreated, progressive hydrocephalus can cause permanent brain damage.

Frequently asked questions

What is the difference between communicating and non-communicating hydrocephalus?

In communicating hydrocephalus the ventricles are open and connected, but CSF is not absorbed properly, so all four ventricles enlarge. In non-communicating (obstructive) hydrocephalus something blocks the flow inside the brain, so only the ventricles before the blockage enlarge. The difference guides the choice of surgery.

Is normal pressure hydrocephalus a communicating hydrocephalus?

Yes. NPH is a chronic communicating hydrocephalus in older adults. Pressure readings are often normal or only intermittently high, but the enlarged ventricles stretch nerve fibers and cause walking problems, bladder leaking and slowed thinking.

Can communicating hydrocephalus go away on its own?

Sometimes. After a brain bleed or meningitis, the absorption pathways can recover, and a temporary drain may be all that is needed. Hydrocephalus that persists or keeps getting worse usually needs a permanent shunt.

What are the signs of a blocked shunt?

Headache, vomiting, drowsiness, blurred vision and irritability, or a return of the original symptoms such as unsteady walking. In babies, watch for a bulging soft spot and fast head growth. A suspected shunt blockage needs emergency assessment.

Is communicating hydrocephalus hereditary?

Usually not. Most cases follow an acquired event such as bleeding, infection or injury. A small number of inherited forms of hydrocephalus exist, but those are mostly obstructive, such as X-linked aqueductal stenosis.