Colloid cyst of the 3rd ventricle as a cause of acute neurological deterioration and sudden death.

A 13 year old girl presented with a 24 h history of headache and vomiting. There were no focal neurological signs. The diagnoses considered were vascular headache, meningitis and subarachnoid haemorrhage. Lumbar puncture revealed clear cerebrospinal fluid under high pressure and subsequent cerebral computed tomography (CT) scan revealed hydrocephalus. Death occurred some hours after the lumbar puncture. Autopsy revealed a colloid cyst of the 3rd ventricle causing the hydrocephalus. Cerebellar tonsillar herniation was present. This case is reported because although 3rd ventricular colloid cysts are a recognized cause of acute neurological deterioration and sudden death, they rarely present in childhood. In this case, it is considered that lumbar puncture may have hastened death by increasing brain-stem compression due to cerebellar tonsillar herniation. It raises the question of whether cerebral CT scan, where readily available, should be performed prior to lumbar puncture. Pathologically, colloid cysts may be easily missed if the brain is examined fresh as the cysts are fragile and have a tendency to be destroyed or fall out.