Two Types of Congenital Cysts of the Posterior Fossa: A Comparison of Their Clinical and Pathological Characteristics and Their Embryogenesis

Abstract

Two types of cystic lesions can occur in the posterior fossa of infants and children. In one type there is a cystic dilatation of the 4th ventricle known as the Dandy-Walker (D-W) syndrome, and in the second type, a cyst or cysts overlie the cerebellum. This is referred to as a posterior fossa extra-axial cyst (PFEAC). These two entries may be differentiated clincally as will be illustrated by presentation of the findings in 2 infants with PFEAC and 2 with D-W syndrome. The pattern of skull transillumination is distinctive for each entity, although the differences are subtle, and can enable the clinician to suspect the correct diagnosis immediately. Arteriographic and air contrast findings show silmilar abnormalities in the supratentorial region in both conditions but distinctive differernces are present in the infratentorial from that in D-W syndrome. Inferences drawn from a comparsion of the arteriographic and histologic findings in these 4 cases with the appearance of certain brain structures at different stages of human embryogenesis indicate that both conditions are congenital abnormalities occuring before the 3rd fetal month but affecting the leptomeninages in one instance (PFEAC) and the cerebellar anlage in the other (D-W syndrome).