Colloid Cyst

A colloid cyst is a benign tumour located usually in the fluid-filled spaces of the brain (ventricles), most commonly in the third ventricle. It consists of a fibrous wall containing mucoid substances.


The cause of colloid cysts is unknown. They are typical in location and presentation and are extremely slow growing.

Signs and Symptoms

Due to its position in the ventricles, it can cause symptoms by:

  • Raised intracranial pressure from intermittent blockage of CSF flow or,
  • Neurological deficits

Raised intracranial pressure

Intermittent and chronic obstructive hydrocephalus may result in headaches, nausea/vomiting or other neurological symptoms (eg blurred vision, seizures). Even with removal of the colloid cyst, chronic enlargement and scarring of the ventricles may be present resulting in persistent symptoms of raised intracranial pressure.

Neurological deficits

Pressure on surrounding tissue may result in neurological deficits. This may include weakness, numbness or personality changes. Memory and attention span may be unduly affected.

Reports of sudden death has been reported with colloid cysts although the mechanism of how this occurs is not fully understood. Theories include sudden increases in intracranial pressure due to obstructive hydrocephalus or venous obstruction have not been confirmed.


  • Blood tests - there are no specific blood tests to diagnose a colloid cyst. Routine FBE, electrolytes and clotting profiles will be performed prior to operative removal of a colloid cyst
  • Radiological tests
  • CT head – there is a classical appearance of the rounded cyst in the region of the third ventricle. Associated hydrocephalus is also seen well with a CT head.
  • MRI head – this gives a better definition and allows confident delineation of the cyst from surrounding structures.

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