Role of MR imaging in the diagnosis of complicated arachnoid cyst

Background. Arachnoid cysts are intra-arachnoidal cerebrospinal fluid collections that are usually asymptomatic, however, they may become acutely symptomatic due to enlargement of the cyst or the presence of hemorrhage. Materials and methods. We report a case of a child presenting with a 3-week history of headaches, nausea, and vision problems. There was no history of trauma. MRI clearly demonstrated a left middle cranial fossa arachnoid cyst with associated subacute intracystic and subdural hematoma that was causing mass effect and required surgery. Results. This lesion was isodense to the brain on CT. Conclusion. We focus on the importance of MR imaging in the differentiation of these subacute/early chronic hemorrhagic collections that may be overlooked with CT.