Background The endoscopic endonasal approach to the jugular foramen has been previously described and it usually requires resection/transposition of the eustachian tube or complementary endoscopic transoral exposure. The division of the eustachian tube may carry tubal dysfunction and conductive hearing loss. The objective is to describe the surgical anatomy of the area between the vidian canal and the eustachian tube and the feasibility, safety, and limitations when approaching the jugular foramen through this area.
Methods Sixteen sides of eight formalin-fixed specimens were used for dissections. Endoscopic endonasal sphenoidotomy, ethmoidectomy, ipsilateral maxillary antrostomy, and posterior septectomy were performed. The transpterygoid approach and exposure of the vidian nerve were performed to have an anatomical reference of the lateral aspect of the petrous carotid artery around the foramen lacerum. The pterygoid base was drilled inferior to the vidian canal and the soft fibrous tissue between the foramen lacerum and torus tubarius was carefully removed. The clivus was drilled up to the foramen magnum inferiorly and laterally up to the medial aspect of the jugular foramen. At the end of the procedure, the dura mater was opened to describe and confirm the presence of the lower cranial nerves at the lateral limit of the exposure. Twenty sides of 10 dry skulls were examined and several measurements of interest were performed with a digital caliper.
Results In all the specimens, the pars nervosa of the jugular foramen was exposed through this window. It was also possible to expose the medial aspect of the hypoglossal canal inferiorly without transposing or resecting the eustachian tube. This approach is limited in accessing the area between the jugular foramen and hypoglossal canal in the craniocaudal dimension and in this case, resection of the torus tubarius should be performed. The medial aspect of the foramen lacerum is on average 10 mm lateral to midline, the hypoglossal canal is 16 mm, the jugular foramen is 22 mm, and the opening of the carotid canal are 24 mm lateral to midline, respectively. The distance from the medial aspect of the hypoglossal canal to the medial aspect of the jugular foramen is 6.4 mm on average. The dura mater curves posteriorly in its deepest angle lateral to the hypoglossal canal and this anatomical feature helps in working behind the eustachian tube in the last portion of the approach. Care must be taken not to injure the carotid artery when working below the foramen lacerum as well as with anatomical variations of the cervical carotid artery that may involve a more medial trajectory at this level. This characteristic must be assessed with preoperative studies and intraoperative Doppler.
Conclusion The medial aspect of the pars nervosa of the jugular foramen and the medial aspect of the hypoglossal canal can be safely approached endonasally without resecting or transposing the eustachian tube. The extent of the pathology and individual anatomy will dictate if this step is necessary, knowledge of the important vascular and neural relationships is essential to perform safe surgeries in this area.
