Hemorrhage into an Arachnoid Cyst

Arachnoid cysts are common, incidentally discovered intracranial masses. They are usually asymptomatic; however, they may occasionally hemorrhage and can be symptomatic if accompanied by increased intracranial pressure. Recognizing this association is essential to making the correct diagnosis, especially in cases with purely intracystic hemorrhage in which blood does not conform to a typical pattern (ie, epidural, subdural, subarachnoid). In addition, surgical intervention may not be required if the patient is asymptomatic.