Prenatal Diagnosis of Ambient Cistern Cyst

Ambient cistern is an expansion of the subarachnoid space of the brain located between the posterior end of the corpus callosum, thalamus and the superior surface of the cerebellum. It represents the extension of the superior cistern to the midbrain, connecting it to the interpeduncular cistern. Ambient cistern cyst accounts for 20 % of all congenital arachnoid cysts (Sinha S, Brown JI. Childs Nerv Syst 2004 ; 20: 100 – 103). It is rarely detected prenatally, mostly during the third trimester of gestation.