Human primitive meninges in and around the mesencephalic flexure and particularly their topographical relation to cranial nerves

Development of the meninges in and around the plica ventralis encephali has not been well documented A distinct mesenchymal structure the so-called plica ventralis encephali is sandwiched by the fetal mesencephalic flexure We histologically examined paraffin-embedded sections from 18 human embryos and fetuses at 6-12 weeks of gestation In the loose tissues of the plica the first meninx appeared as a narrow membrane along the oculomotor nerve at 7-8 weeks Subsequently the plica ventral's evolved into 3 parts bilateral lateral mesenchymal condensations and a primitive membranous meninx extending between Notably the topographical anatomy of the oculomotor trochlear and trigeminal nerves did not change the oculomotor nerve ran along the rostral aspect of the membranous meninx the trigeminal nerve ran along the caudal side of the lateral mesenchymal condensation and the trochlear nerve remained embedded in the lateral condensation Up to 9-10 weeks the lateral mesenchymal condensations became tongue-like folds i e the primitive form of the tentorium cerebelli while the membranous meninx became the diaphragma sellae The falx cerebri seemed to develop from the tongue-like folds Overall the final tentorium cerebelli corresponded to the regressed plica ventralis while the parasellar area originated from the base of the plica and other tissues along the ventral aspects of the basisphenoid and basioccipital (C) 2010 Elsevier GmbH All rights reserved