A Guide to: Colloid Cysts

What is a colloid cyst?

A colloid cyst is a rare, benign (non-cancerous) fluid-filled growth, that develops in an area of the brain called the third ventricle.

Colloid cysts are filled with a gelatinous (gel-like) material, rich in proteins, called colloid. Whilst they do not arise from the brain’s tissues like ‘true’ brain tumours, they are still classified as benign brain tumours.

They typically develop in and around the third ventricle, a fluid-filled sac, located in the centre of brain. The brain contains four fluid-filled ventricles, connected by narrow channels: two lateral ventricles, the third ventricle, and the fourth ventricle. The fluid within the ventricles and channels is called cerebrospinal fluid, or ‘CSF’.

Colloid cysts don’t spread to other parts of the body, but they do grow slowly over time.

If colloid cysts grow large enough, they can cause neurological symptoms. They can also block the normal flow of CSF between the ventricles. This leads to an abnormal build-up of CSF, which increases the pressure in and around the brain. This is called hydrocephalus.

Colloid cysts typically only require treatment If they cause symptoms, hydrocephalus, or the associated symptoms are bothersome enough.

Though colloid cysts can develop at any age, they commonly develop in people aged 30 years and over. They rarely present initially during childhood.

What are the symptoms?

Colloid cysts are commonly asymptomatic (are not associated with any symptoms) in the early stages, as they grow slowly over time.

If symptoms do occur, they tend to develop as a colloid cyst grows larger and/or blocks the CSF pathways in the brain, causing hydrocephalus and raised intracranial pressure (raised pressure in and around the brain). The symptoms of hydrocephalus and raised pressure include:

Headaches
Nausea and vomiting
Visual changes
Issues with memory
Confusion
Dizziness or vertigo
Balance issues
Behavioural changes
Collapse or loss of consciousness

What causes a colloid cyst?

The exact cause of colloid cysts remains unclear.

It is thought that they occur at some point during fetal development, whilst a baby is in the womb. There are no known genetic or environmental risk factors.

How are colloid cysts diagnosed?

A colloid cyst is usually diagnosed incidentally (by accident) on brain imaging, carried out for another reason.

This usually involves either a computed tomography (CT) scan, or magnetic resonance imaging (MRI) scan. Both scans provide detailed picture of inside the brain.

Treatment options for colloid cysts

The size and location of the cyst, the degree of CSF blockage, as well as any associated symptoms will determine whether treatment is required. Treatment options can include a period of observation, or surgery.

Observation or ‘watch and wait’:

If the colloid cyst is causing no symptoms, your surgeon may recommend observation only (also called a ‘watch and wait’ approach). This will usually involve regular MRI scans to monitor the growth of the cyst. This is often the case for small cysts, that are not causing troublesome symptoms, or obstructing the CSF pathways in the brain, causing hydrocephalus.

Surgical treatment:

If the colloid cyst is causing symptoms or hydrocephalus, surgical treatment may be recommended.

Surgical treatment often involves drainage and removal of the cyst using a craniotomy, or an endoscopic craniotomy, which is a minimally invasive procedure.

If hydrocephalus is present, treatment with a CSF shunt may be required. A shunt is a thin plastic tube that sits inside the ventricles. The shunt drains the excess CSF away to another part of the body, such as the abdomen, where it is reabsorbed. This reduces the pressure around the brain. A CSF shunt remains inside the body permanently.