Colloid cysts are relatively unusual (1.5% neurosurgically treated tumours) benign intracranial masses located in the rostral aspect of the IIIrd ventricle. As they grow they obstruct the foramen of Munro producing hydrocephalus of the lateral ventricles.¹ This can be acute and catastrophic because of the pedunculated nature of the tumour resulting in brain herniation and death.² Both computed tomography (CT) and magnetic resonance imaging (MRI) will usually show the lesion and its effects on the ventricular …