THE VARIABLE RELATIONSHIP BETWEEN THE LOWER CRANIAL NERVES AND JUGULAR FORAMEN TUMORS - IMPLICATIONS FOR NEURAL PRESERVATION

Tumors involving the jugular foramen (JF) have a variable relationship to the neurovascular structures (jugular vein, cranial nerves IX-XI) that traverse this conduit through the skull base. The surgeon familia r with the site of origin, growth pattern, and geometry of each of the common lesions affecting this region with respect to surrounding nerv es and vessels is at a considerable advantage when undertaking a funct ion-sparing procedure. Anatomically, the JF has two vascular compartme nts that may be affected by tumor: the jugular bulb laterally and a pa ssage for the inferior petrosal sinus medially. Tumors may also penetr ate the JF along the fibro-osseous diaphragm, which divides these two vascular channels. The lower cranial nerves lie on either side of this partition, which is connected to the posterior cranial fossa via a cu rved, funnel-shaped cone of dura. Tumors that arise within or penetrat e the JF lateral to this neural plane displace the nerves medially, a position favorable for their preservation during tumor extirpation. By contrast, medially positioned tumors displace the cranial nerves onto the lateral tumor surface, where they interpose between surgeon and t umor-an unfavorable location. Glomus tumors consistently arise in the lateral aspect of the JF, displacing the lower cranial nerves medially . This positioning accounts for the high rate of neural preservation i n small and medium-size glomus tumors that have not invaded the forame n's central partition. Meningiomas that arise lateral to the JF (e.g., the posterior petrous surface, sigmoid sinus) favorably displace the lower cranial nerves medially. By contrast, tumors that originate medi al to the JF (e.g., clivus, foramen magnum) are unfavorable, laterally displacing the multiple small rootlets that coalesce into cranial ner ves IX-XI into a vulnerable location. Schwannomas arise within the neu ral plane and have a variable geometry that depends, in part, upon the nerve of origin. Theoretically, tumors that arise from the ninth nerv e, which is located on the lateral surface of the neural plane, should be more favorable than those originating from the tenth or eleventh n erves, which lie on its deep surface. The propensity of these three tu mor types toward thrombosis of the jugulosigmoid complex also carries important surgical implications. Because glomus tumors arise from the jugular bulb, the jugulosigmoid complex is nearly always occluded. In both meningiomas and schwannomas, however, the jugular system may occa sionally remain patent. This is important to recognize through angiogr aphy and/or magnetic resonance venography, since sacrifice of a patent , dominant system risks intracerebral venous infarction.