Bibliogr. s. 327

BACKGROUND: Arachnoid cysts are congenital, benign and intra-arachnoidal lesions. A great majority of arachnoid cysts are congenital. However, to a lesser extent, they are known to develop after head trauma and brain inflammatory diseases. Arachnoid cysts are mostly asymptomatic and they can develop anywhere in the brain along the arachnoid membrane. CASE REPORT: Arachnoid cysts form 1% of the non-traumatic lesions which occupy a place and it is thought to be a congenital lesion developed as a result of meningeal development abnormalities or a lesion acquired after trauma and infection. There is a male dominance at a rate of 3/1 in arachnoid cysts which locate mostly in the middle fossa. Our patient was a 2-years-old boy. CONCLUSIONS: As a conclusion, spontaneous subdural hygroma is a rare complication of the arachnoid cysts. Surgical intervention could be required in acute cases.