Progressive post traumatic tearing of an arachnoid cyst membrane resulting in intracystic and subdural haemorrhage.

We report the case of a 43-year-old man with a middle cranial fossa arachnoid cyst who presented post trauma with neurological symptoms. The initial CT scan of the brain did not detect acute changes in the arachnoid cyst but subsequent imaging revealed abnormalities which progressed over time. Arachnoid cysts are usually a benign and incidental finding. Rare complications such as intracystic haemorrhage and subdural haemorrhage can occur. It is important to be aware of these complications so that patients with arachnoid cysts are appropriately investigated when presenting with neurological symptoms.