Colloid cysts of the third ventricle are a benign epithelial lined cyst with characteristic imaging features. Although usually asymptomatic, they can rarely present with acute and profound hydrocephalus.
Classically these cysts are identified as a well-delineated hyperattenuated masses on nonenhanced CT, attached to the anterosuperior portion of the third ventricle. On MRI they usually are hyperintense on T1 and isointense to brain on T2 weighted images. Peripheral rim enhancement may be present in some cases.
In the vast majority of cases, colloid cysts are found incidentally and are asymptomatic. Their position in the roof of the third ventricle immediately adjacent to foramen of Monro can on occasion result in sudden obstructive hydrocephalu and can present with thunderclap headache or unconscious collapse. The headaches tend to be positional, and patients may learn how to relieve symptoms.
They tend to gradually increase in size over time and if resection is required, this can be performed via a transcallosal approach or more recently endoscopically or stereotactically.
When large and or symptomatic the decision to operate is relatively straight forward, as it can be life saving. For small lesions without symptoms attributable to them, the careful discussion between the patient and treating surgeon is required to weigh up the pros and cons of surgical intervention.
The options are open or endoscopic resection or endoscopic or stereotactic aspiration. Aspiration may fail if the content of the cyst is too viscous, which can be predicted by appreciating low signal on T2 weighted sequences.