Nontraumatic Subdural Hematoma and Intracystic Hemorrhage Associated with a Middle Fossa Arachnoid Cyst.

Intracranial arachnoid cysts (ACs) are relatively common findings that can be seen in up to 2% of patients. They are generally found incidentally with a benign clinical course and can be usually managed by observation. We report an unusual case of a middle fossa AC presenting with spontaneous intracystic hemorrhage along with subdural hematoma (SDH) causing significant mass effect and midline shift requiring surgical treatment. Even though the risk of hemorrhage in patients with AC is very low, the presence of AC is a known risk factor for SDH. Fortunately, the clinical outcome of patients who present with hemorrhage associated with AC is generally favorable with early recognition and prompt surgical treatment. Our case highlights the fact that both intracystic hemorrhage and SDH can occur in association with AC even in the absence of trauma and should be kept in mind when counseling patients with incidental AC about the natural history of these lesions.