The microsurgical anatomy of the jugular foramen.

The microsurgical anatomy of the jugular foramen was studied in 10 fixed cadavers, each cadaver consisting of the whole head and neck. Five of the cadavers were injected with latex. The jugular foraminal region was exposed using the infratemporal fossa type A approach of Fisch and Pillsbury in five cadavers (10 sides) and the combined cervical dissection-mastoidectomy-suboccipital craniectomy approach in five cadavers (10 sides). The right foramen was larger than the left in seven cases (70%), equal in two cases (20%), and smaller in one case (10%). The dura covering the intracranial portal of the foramen had two perforations, a smaller anteromedial perforation through which passed the ninth cranial nerve (CN IX), and a larger posterolateral perforation, through which passed the 10th and 11th cranial nerves (CNs X and XI) and the distal sigmoid sinus. The perforations were separated by a fibrous septum in 16 specimens (80%). After exiting the posterior fossa, CNs IX, X, and XI all lay anteromedial to the superior jugular bulb (SJB) within the jugular foramen. The inferior petrosal sinus (IPS) entered the foramen between CNs IX and X in most cases; however, in 10% of our cases it entered the foramen between CNs X and XI, and in 10% it entered the foramen caudal to CN XI. The IPS terminated in the SJB in 90% of our cases; in 40%, the IPS termination consisted of multiple channels draining into both the SJB and internal jugular vein. This study shows that the arrangement of the neurovascular structures within the jugular foramen does not conform to the hitherto widely accepted notion of discrete compartmentalization into an anteromedial pars nervosa containing CN IX and the IPS and a posterolateral pars venosa containing the SJB, CNs X and XI, and the posterior meningeal artery.