Hydrocephalus syndrome. Obstruction of the foramina of the fourth ventricle.

In 1914, Dandy and Blackfan6described an entity consisting of hydrocephalus associated with cystic dilatation of the fourth ventricle and absence of the posterior cerebellar vermis. In a subsequent report, Dandy5noted that the foramina of Luschka and Magendie were absent, with resultant lack of communication between the ventricular system and the subarachnoid space. Taggart and Walker13contributed an excellent review of the pathology, pathogenesis, and surgical therapy of the syndrome. They considered the cystic dilatation of the fourth ventricle to be due to failure of the foramina of Luschka and Magendie to open in the period of gestation before the third or fourth month. Dilatation of the fourth ventricle, occurring before the end of the fourth month, would prevent a fusion of the lateral cerebellar commissures to form the posterior vermis. (Gibson,7however, feels that all parts of the inferior vermis are present, although they