Studies on the area cerebrovasculosa of anencephalic fetuses.

The area cerebrovasculosa has been examined in 35 anencephalic fetuses and coronal sections prepared in 15 cases. A bilaterally symmetrical cystic mass is found covering the anterior and middle cranial fossae. The mass is generally walled with glial tissue, partially lined with ependyma and filled with abnormally vascular choroid plexus. The coverings of the cyst are conspicuously vascular and the overlying squamous epithelium is in continuity with hairy skin at the margins of the lesion. The posterior cranial fossa contains a variable quantity of medulla oblongata which has no connection with the cystic mass. The medulla and cervical cord are more nearly normal in that minority of cases with an intact foramen magnum. The degree of hindbrain development is correlated with previously reported presence of heterotopic glial tissue in the spinal subarachnoid space of some anencephalic fetuses (Bell, Gordon and Maloney, 1981; Bell, 1981, in press). These findings have led us to reject the widely accepted view that the area cerebrovasculosa is totally disorganised, and that anencealy is characterised by absence of the forebrain.