Lower skull base: anatomic study with surgical implications.

With advances in the lateral approaches to the skull base and the increasing success of the management of jugular foramen lesions, a thorough knowledge of the anatomy of this region is needed. The purpose of the present work is to study the detailed microsurgical anatomy of the lower skull base and the jugular foramen area as seen through the lateral approaches. Forty preserved skull base specimens and 5 fresh cadavers were dissected. The shape of the jugular bulb and its relationship to nearby structures were recorded. The different venous connections of the bulb were noted. The hypoglossal canal was identified and its contents were observed. The lower cranial nerves were studied at the level of the upper neck, at their exit from the inferior skull base, and in the jugular foramen. The results of the present study showed the complex and variable anatomy of this area. The classic compartments of the jugular foramen were not always present. Cranial nerves IX through XI followed different patterns while passing through the jugular foramen, being separated from the jugular bulb by bone, thick fibrous tissue, or thin connective tissue.