Chronic subdural hemorrhage into a giant arachnoidal cyst (Galassi classification type III).

The authors present CT and MRI of a patient with an extremely large arachnoidal cyst (Galassi classification type III). The cyst extended from the base of the skull, posterior to the brain stem, on the base of the temporal lobe over the complete convexity of the left hemisphere. The cyst consisted of multiple compartments with intracystic septa and was accompanied by a chronic subdural hemorrhage in the compartments. After contrast agent application, the typical characteristics of chronic subdural membranes were found. Besides bony deformities, a thinning of the inner table was found. The patient underwent craniotomy for evacuation of the hemorrhage and fenestration of the septa while he was free of symptoms. This is a remarkable case proving that chronic local intracranial pressure does not inevitably lead to neurologic symptoms or intellectual disabilities.