Colloid Cyst of the Third Ventricle

A colloid cyst of the third ventricle is a benign, mucin filled cyst lined by epithelium that arises near the foramen of Monro and can cause intermittent or acute obstructive hydrocephalus and sudden death.

It accounts for about 1% of intracranial tumours and is found in about 0.5 to 2 people in 100,000 each year. It presents most often between 20 and 50 years. Most small cysts remain stable.

Pathophysiology. The cyst acts as a ball valve at the foramen of Monro, causing intermittent obstruction of CSF outflow from both lateral ventricles, with paroxysmal rises in intracranial pressure. Rare acute obstruction can cause fatal herniation.

Presentation is positional headache (often relieved by lying down), nausea, vomiting, memory loss, gait disturbance, urinary incontinence, papilloedema and drop attacks. Some patients present with sudden collapse or death. Many are asymptomatic.

Red flags.

• Sudden severe headache, drop attacks or collapse.
• Reduced consciousness, papilloedema or vomiting.
• Progressive memory or gait change with enlarged ventricles.

CT head shows a round, hyperdense lesion at the roof of the third ventricle, with or without hydrocephalus. MRI shows variable signal, depending on cyst contents, and clarifies attachments and ventricular size. Risk markers for symptoms or growth are younger age, larger size (over 10 mm), hyperdense CT appearance, T2 hypointensity and enlarged ventricles.

Differential diagnosis.

• Other third ventricle masses (choroid plexus papilloma, central neurocytoma, ependymoma, subependymal giant cell astrocytoma).
• Craniopharyngioma, neurocysticercosis and aqueduct stenosis.

Acute hydrocephalus. Resuscitate, raise the head to 30 degrees, and place an external ventricular drain urgently if consciousness falls. Do not perform lumbar puncture. Hyperosmolar therapy as a bridge: 3% sodium chloride 250 mL IV over 15 to 20 minutes or mannitol 20% 0.5 to 1 g/kg IV over 15 to 20 minutes.

Definitive treatment. Surgical removal is advised for symptomatic cysts, any hydrocephalus, and cysts with high risk features.

• Endoscopic resection (preferred in most centres).
• Microsurgical transcallosal or transcortical resection.
• Stereotactic aspiration has a high recurrence rate.
• Ventriculoperitoneal shunt for those who cannot have surgery.

Observation. For small (under 10 mm), asymptomatic, low risk cysts: MRI at 6 to 12 months, then at 1 to 2 yearly intervals, with prompt review for new symptoms.

Lifestyle. Avoid situations where sudden collapse is dangerous until treated, with advice about driving from local licensing rules.

Monitoring. Symptoms, ventricular size, and cyst size on imaging.

Referral and escalation. Refer to neurosurgery. Refer as an emergency for any acute symptom.

Special groups. In pregnancy, symptomatic cysts need planned neurosurgical care, since intracranial pressure may rise in labour.