Acoustic neuromas do not cause trigeminal signs and symptoms until there is actual mechanical pressure on the nerve trunk in the cerebellopontine angle. The fifth nerve emerges from the pons, superior and slightly anterior to the exit of the seventh nerve. As the acoustic tumor expands from the internal auditory canal into the cerebellopontine angle, it is bounded anteriorly by the seventh nerve which is somewhat stretched as the tumor grows.2 When the tumor has grown medially enough to contact the pons, it begins to cause pressure against this structure. The tumor will, therefore, involve the fifth nerve as it exits from the pons. During surgery, we have actually seen the point of pressure against the fifth nerve in a number of cases. In these cases, it has been possible to separate the tumor from the surface of the fifth nerve as well as from the surface of the
PULEC JL, HOUSE WF. Trigeminal Nerve Testing in Acoustic Tumors. Arch Otolaryngol. 1964;80(6):681–684. doi:10.1001/archotol.1964.00750040697008
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