Schwannomas are usually isolated, well-encapsulated lesions that push axons aside. They are not associated with von Recklinghausen's disease. These tumors have the characteristic histologic patterns of Antoni type A and B type tissues. Neurofibromas, in contrast, are often multiple, nonencapsu-lated deeply infiltrating lesions that incorporate the axon within the substance of the tumor. These tumors are frequently seen in von Recklinghausen's disease.47'48

As with vestibular schwannomas, jugular foarmen schwannomas originate at the transition zone between central and peripheral myelin. Most jugular foramen schwannomas (88%) arise from the glossopharyngeal and vagus nerves.47,49,50 Schwannomas originating from the accessory, hypoglossal, and sympathetic trunk are far less common.

There are three growth patterns of neurogenic tumors of the jugular foramen, depending on their point of origin along the nerve as they pass through the pars nervosa.4,51 The tumors arising in the distal portion of the jugular foramen expand infe-riorly out of the base of the skull, whereas those arising more proximally enlarge into the posterior cranial fossa. Tumors arising from the midregion of the foramen tend to expand primarily into the bone and become bilobed like a "saddlebag."4

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