What is hydrocephalus?

Hydrocephalus is a neurological condition characterised by the accumulation of cerebrospinal fluid within the brain. The fluid builds up in empty spaces of the brain, which are called ventricles. Excess fluid inside of the brain can create additional pressure within the brain which may damage the tissue and cause issues with brain function, this includes adverse effects on cognitive abilities. Hydrocephalus is a well-researched and well-understood condition within the scientific field, and it has a good prognosis as long as treatment is obtained.

In almost all cases of hydrocephalus, there is an obstruction to either the circulation or absorption of cerebrospinal fluid.¹ In rare cases, hydrocephalus is caused by excessive production of cerebrospinal fluid (such cases are usually accounted for by tumours of the choroid plexus, which is the site of cerebrospinal fluid production).

Hydrocephalus can be congenital (present from birth) or acquired at any age. However, the condition has a higher prevalence during infancy and among adults who are over the age of 60. The overall global prevalence of hydrocephalus stands at around 85 per 100,000 individuals. However, there are notable differences between age groups: 88 per 100,000 for the pediatric population and 11 per 100,000 in adults.²

What is cerebrospinal fluid?

Cerebrospinal fluid is a clear liquid which surrounds the brain and spinal cord. It supports brain function by:

• Allowing the brain to float within the skull
• Cushioning the brain to prevent injury
• Removing waste products of the brain's metabolism 

Normally, cerebrospinal fluid flows through the brain ventricles, and in moderation, this contributes to a healthy brain for the reasons listed above. Hydrocephalus occurs when there is too much cerebrospinal fluid within the brain.

The importance of cognitive function

The term ‘cognitive function’ describes different mental processes such as memory, language development, intelligence and reasoning which enable us to carry out everyday activities and navigate the world.³ An individual’s cognitive abilities play a big role in determining educational attainment and interpersonal relationships, which can in turn influence their quality of life. As a result, it’s important to understand how hydrocephalus can affect cognitive function and what treatment methods are available.

Pathophysiology of hydrocephalus

Hydrocephalus occurs when there’s an imbalance between the production of cerebrospinal fluid by the tissues of the brain ventricles and how much of the fluid is absorbed into the bloodstream.

Too much cerebrospinal fluid in the ventricles can occur for different reasons, resulting in different types of hydrocephalus. 

• Communicating hydrocephalus: This occurs when the flow of cerebrospinal fluid is impeded after it leaves your ventricles. This may result from a thickening of membranes at the base of your brain called the arachnoid
• Non-communicating hydrocephalus: This is also referred to as ‘obstructive hydrocephalus’. This form of hydrocephalus occurs when the flow of cerebrospinal fluid is blocked along at least one of the narrow passages which connect your ventricles
• Normal pressure hydrocephalus: This happens when the cerebrospinal fluid accumulation causes your ventricles to enlarge (called ventriculomegaly), but the increase in pressure is usually negligible, so the pressure inside your ventricles remains constant. The buildup of cerebrospinal fluid in your ventricles happens gradually, and symptoms occur over a longer timeframe. Normal pressure hydrocephalus has a higher incidence rate among the elderly
• Hydrocephalus ex-vacuo: This is caused by brain damage following a head injury or stroke. In these cases, brain tissue surrounding your ventricles shrinks, and cerebrospinal fluid builds up inside the ventricles to fill the extra space. Your ventricles are enlarged, but the pressure in your head usually remains normal

Cognitive impairments associated with hydrocephalus

Several studies have demonstrated that the cognitive changes associated with hydrocephalus predominantly include inattention, memory complaints, apathy, emotional lability, and disinhibition.⁴ These changes occur due to increased pressure within the brain, damaging structures like the frontal lobe, which are important for cognitive processes. In forms of hydrocephalus where the pressure inside the ventricles remains relatively constant, ventriculomegaly can compress surrounding brain tissues and cause a reduction in the tissue volume, which can also contribute to the following problems:

• Inattention: An inability to maintain sustained focus on a task
• Memory: You may experience deficits in memory, including working memory, which plays an important role in multitasking 
• Apathy: You may not feel as emotionally invested in people or events that would normally mean a lot to you
• Emotional lability: This is the tendency to shift between different emotional states rather rapidly and seemingly without cause
• Disinhibition: A reduction in the ability to control your impulses and think actions through carefully

Variability in cognitive outcomes

Even though there are multiple causes for both congenital and acquired variants of hydrocephalus, the cognitive impairments experienced paint a relatively consistent picture across individuals.⁵ However, cognitive outcomes may vary slightly depending on:

• Type of hydrocephalus
• Age at onset
• Severity and duration before treatment
• Location of fluid accumulation

Diagnosing hydrocephalus

Your healthcare provider can diagnose hydrocephalus through various means, including the use of CT and MRI scans of the brain. These techniques show the build-up of fluid in the brain and any change in pressure, as well as highlighting possible structural defects that could be causing the problem. Sometimes, congenital hydrocephalus is detected before birth, in an ultrasound during pregnancy.² 

Furthermore, in the case of acquired hydrocephalus, the cognitive impairments experienced can overlap with the characteristics of Alzheimer’s disease and other conditions, meaning that your healthcare provider will try to differentiate between whether you have hydrocephalus or, for example, Alzheimer’s disease. This is important because the prognosis for hydrocephalus is much better than that of Alzheimer’s disease. Hydrocephalus is more likely to be diagnosed, as opposed to Alzheimer’s disease, if you present with difficulty walking, mental and bladder problems, and cerebrospinal fluid levels that are higher than usual, although you may not have all these symptoms. 

Treatment options

Without treatment, hydrocephalus results in various complications, which may include learning disabilities or developmental and physical disabilities. Complications of hydrocephalus can be severe and result in death. In cases where hydrocephalus is mild and receives prompt treatment, there are likely to be few, if any, serious complications.^6,7 

Surgical treatments

Shunt

Shunts are the most common treatment for hydrocephalus that is in use. Shunts serve as a drainage system for the cerebrospinal fluid. A shunt is a tube that is inserted into the brain ventricles at one end and then leads either to the heart or stomach so that the excess fluid can be absorbed more efficiently. 

This treatment method is usually permanent and requires regular monitoring. There can be problems with shunt systems, such as poorly regulated drainage due to mechanical malfunctions, a blockage or infections. However, shunts are typically an effective solution to hydrocephalus

Endoscopic third ventriculostomy

This is a neurosurgical technique where a surgeon creates an opening in the bottom of a brain ventricle to create a drainage pathway for excess cerebrospinal fluid to flow out of the brain, alleviating some pressure. Possible complications of ventriculostomy include bleeding and infections, which should be discussed with your healthcare provider

Lumbar drainage

• You will be given a local anaesthetic, and a tube will be inserted between the bones in your spine (which are called the vertebrae) to drain a significant amount of cerebrospinal fluid. This is done over a few days to see whether your symptoms improve 

Supportive therapy

• Developmental therapist: A developmental therapist with specialist knowledge of hydrocephalus can help with the normal development of age-appropriate behaviours and interpersonal skills
• Social worker: Social workers can help your family access the necessary services, such as educational support for children affected by hydrocephalus or occupational therapists for adults

Summary

• Hydrocephalus is caused by the buildup of cerebrospinal fluid within the ventricles of the brain
• Hydrocephalus can cause cognitive problems, including inattention, emotional lability, apathy, memory issues and disinhibition. These issues can all translate to problems with educational attainment and problems in the workplace
• Hydrocephalus can be present from birth or acquired later in life
• Hydrocephalus is usually diagnosed through CT or MRI scans
• Hydrocephalus can be fatal if left untreated, however, the treatment options available include shunts and an endoscopic third ventriculostomy, which are both effective at managing the condition