Asymptomatic Huge Congenital Arachnoid Cyst Successfully Treated by Endoscopic Surgery

A female neonate was the first child of a 30-year-old mother, with unremarkable medical history. Prenatal ultrasonography performed at 36 weeks of gestation suggested intracranial mass lesion. The baby was delivered by cesarean section at 41 weeks of gestation because of bradycardia and asphyxia. The birth weight, height, and head circumference were within the normal ranges with soft fontanels. Congenital anomaly was not observed with normal neurological findings. She was referred to our department at age 5 months. Physical examination revealed normal developmental milestones and intact endocrinological function without macrocephaly. Cerebral magnetic resonance (MR) imaging revealed a unilocular huge cyst appearing as homogeneously hypointense on T_1- and hyperintense on T_2-weighted images, and extending into the basal, suprasellar, ambient, quadrigeminal, interpeduncular, prepontine, right cerebellopontine angle, and premedullary cisterns. The pituitary stalk was markedly stretched and displaced ventrally, and the brainstem was displaced dorsally by the cyst. No other brain anomalies, dysgenesis of the corpus callosum, or ventriculomegaly were recognized. Neuroendoscopic cystocisternostomy was performed to form a communication between the cyst cavity and premedullary cistern. Pressurized watery fluid was released on puncturing the cyst wall which consisted of transparent membrane. Surveillance MR imaging at 2 and 9 months after the surgery revealed remarkable regression without regrowth of the cyst. She remained in good condition and showed normal development during the follow up for 1 year 9 months. Less invasive prophylactic surgery using the neuroendoscope may be beneficial for carefully selected cases of asymptomatic neonatal arachnoid cysts.