Normal pressure hydrocephalus

Definitions & Key takeaways

Normal pressure hydrocephalus is a condition characterized by ventricular enlargement, without an increase in cerebrospinal fluid pressure on lumbar puncture. Cerebrospinal fluid (CSF) accumulates slowly and gradually in the ventricles, causing them to dilate. Ventricular dilation restores the CSF pressure to the normal level, hence the normal findings on lumbar puncture.

People with normal pressure hydrocephalus present with urinary incontinence, gait disturbances, and dementia. The excess amount of CSF can be temporarily drained through a lumbar puncture, but the long-term management is a surgical procedure called a ventriculoperitoneal shunt, in which a tube is inserted into one of the ventricles of the brain and directed to the abdomen, where the excess CSF can be absorbed.

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Introduction0:00–0:27

In normal pressure hydrocephalus, hydrocephalus can be broken down into “hydro” which means water and “cephalus” which means head.
Hydrocephalus, which is also termed as “water on the brain”, is an excessive buildup of cerebrospinal fluid within the brain.
Even though the pressure on lumbar puncture is expected to be increased, in this case, it’s normal, which is why it’s termed as “normal pressure” hydrocephalus.

Physiology0:27–2:06

Let's start with some relevant anatomy. The brain has four interconnected cavities in the brain called ventricles, and each one contains a structure called a choroid plexus.
The choroid plexus is made up of ependymal cells which produces cerebrospinal fluid - a fluid that helps provide buoyancy and protection, as well as metabolic fuel for the brain.
Highest up, are two C-shaped lateral ventricles that lie deep in each cerebral hemisphere. The two lateral ventricles drain their cerebrospinal fluid into the third ventricle, which is a narrow, funnel-shaped, cavity at the center of the brain.
The third ventricle makes a bit more cerebrospinal fluid and then sends all of the cerebrospinal fluid to the fourth ventricle via the cerebral aqueduct.
The fourth ventricle is a tent-shaped cavity located between the brainstem and the cerebellum. After the fourth ventricle, the cerebrospinal fluid enters the subarachnoid space, which is the space between the two inner linings of the brain - the arachnoid and pia mater.
Now, the arachnoid mater protrudes into the outermost covering, called dura mater, at various points. It looks a bit like little fingers poking through, and these protrusions are called arachnoid granulations.
Cerebrospinal fluid makes its way through these arachnoid granulations and gets into the dural sinus which is filled with venous blood and is on the other side of the arachnoid granulation.
The pressure within the subarachnoid space is higher than the pressure in the dural sinus, so CSF flows through the arachnoid granulations is only in one direction.

Causes2:06–2:52

Normal pressure hydrocephalus develops when cerebrospinal fluid is unable to get through those arachnoid granulations normally.
This process develops gradually and most commonly affects the elderly. There are two types of normal pressure hydrocephalus.
The first type is an primary normal pressure hydrocephalus, where the cause is idiopathic or unknown. The second type is secondary normal pressure hydrocephalus, where the cause is damage to the arachnoid villi which disrupts CSF reabsorption.
Some known causes of arachnoid villi damage are a subarachnoid hemorrhage and meningitis, both of which cause a tremendous amount of inflammation to the protective layers of the brain.

Pathology2:52–3:55

Regardless of the cause, when cerebrospinal fluid doesn’t get completely reabsorbed, over time, it leads to an slow buildup of CSF within the ventricles of the brain.
This causes increased pressure in the ventricles, and since it develops gradually, the ventricles begin to slowly dilate.
The increased ventricular volume does restore CSF pressure back to a normal level. But the expanding ventricles compress nearby brain tissue, in particular, the enlarged lateral ventricles compress the corona radiata - the part of the brain that has fibers that relay sensory and motor information between the body and the cerebral cortex.
Fiber that carry motor information for the muscles of the legs and bladder are most commonly affected, leading to gait disturbance and urinary incontinence.
As the enlargement of the ventricles continues, it leads to a distortion of the periventricular limbic system, which is a part of the cerebrum that controls emotions, memory, and behavior.
So when this region is affected, it leads to dementia. So the three hallmark symptoms of normal pressure hydrocephalus are urinary incontinence, gait disturbance, and dementia.

Symptoms3:55–4:37

They can be remembered as the three “W’s” - wet, referring to incontinence, wobbly, referring to gait disturbance, and wacky, for dementia.
People with normal pressure hydrocephalus, have a wide based gait, meaning that their feet are wide apart, and they take small, slow steps.
Sometimes, their steps look “magnetic” because it’s difficult for them to lift their feet off the ground to initiate a step.
Symptoms of dementia include slow thought processes, reduced concentration, memory problems, and other behavior changes.

Diagnosis4:37–5:01

Diagnosis of normal pressure hydrocephalus is based on an imaging studies like a CT or MRI which can help identify the enlarged ventricles.
If a lumbar puncture is done, the CSF opening pressure is usually normal - about 100-180 mm of H2O or 8-15 mm Hg. The short term treatment of normal pressure hydrocephalus is a lumbar puncture, which is when a needle is placed into the spinal canal to remove cerebrospinal fluid.

Treatment5:01–5:34

Long-term treatment typically involves the placement of a shunt, like a ventriculoperitoneal shunt, which connects the ventricular system to the peritoneal cavity in order to allow fluid to drain out and get reabsorbed by the cells lining the peritoneal pleura.
This helps to drain off the excess cerebrospinal fluid and reduce the need for the ventricles to dilate. All right, as a quick recap.

Review5:34–6:06

Normal pressure hydrocephalus is the condition of ventricular enlargement in the absence of an increased cerebrospinal fluid pressure on lumbar puncture.
It’s represented by the symptom triad which includes the three “W’s” - wet, referring to incontinence, wobbly, referring to gait disturbance, and wacky, for dementia.
Normal pressure hydrocephalus is diagnosed by imaging methods such as CT and MRI and it’s treated by insertion of shunts.