[Form and development of the human fetal subarachnoid cistern]

Abstract

The development and form of the human fetal subarachnoid spaces have been elucidated by reconstruction (34 mm CRL fetus) and by plastic casts (several 20-30 cm CRL fetuses). Equivalents of adult cisterns are present in the young fetus. In older fetuses the cisternal shape is of adult type. It is suggested that pressure from the growing brain produces tension in the arachnoid mesenchyme and determines the initial orientation of the endo-ecto-meningeal limiting membrane. The fluid-filled subarachnoid spaces and the fetal brain together form a composite structural unit probably defining the configuration of the fetal head capsule. Prospective sutures develop over the inner ridges of the fetal dura. However, the lambda suture and the associated base of the tentorium eventually separate.