![]() Internal auditory canal Meningioma Posterior fossa Retrosigmoid approach Translabyrinthine approach Vestibular schwannoma.Ĭopyright © 2020 by the Congress of Neurological Surgeons. The retrosigmoid approach is less affected with IAC variability in position and angle. MRI provides excellent assessment of the IAC and the bony changes occurring in the canal walls, and it provides excellent demonstration of the content of the canal. Specifically, a horizontally oriented IAC with a small IAA may have significant impact on visualization of the facial nerve within its cisternal segment with the translabyrinthine approach. Magnetic resonance imaging (MRI) is presently the study of choice for assessment of the internal auditory canal (IAC). IAC variability can have a substantial effect on the surgical exposure of the IAC and facial and vestibulocochlear nerves. Bill bar ( TA: crista verticalis) also known as the vertical crest, is a bony anatomical landmark that divides the superior compartment of the internal acoustic meatus into an anterior and posterior compartment. Disease processes in the pontine angle and in the internal acoustic meatus are not discussed. MRI is more useful for diseases of the inner ear. The results quantitatively demonstrate tremendous variability of the position and orientation of the IAC in the petrous temporal bone. CT is the imaging modality of choice for most of the pathologic conditions of the temporal bone, especially for those of the middle ear. Measurements, including the anterior (APD) and posterior (PPD) petrous distances, the anterior (APA) and posterior (PPA) petro-auditory angles, and the internal auditory angle (IAA), were obtained to quantify the position and orientation of the IAC within the petrous temporal bone. The authors retrospectively reviewed magnetic resonance imaging studies of 50 randomly selected patients with pathologically confirmed vestibular schwannomas. It measures 15 to 20 mm in length and has a diameter as small as 2 mm and as wide as 12 mm (1,2). To test the hypothesis that IAC position and orientation affects the surgical exposure of the IAC and facial nerve, especially when performing the translabyrinthine approach. ANATOMY The internal auditory canal (IAC) extends from its opening in the posteromedial surface of the petrous pyramid to the cribriform plate, which closes the canal laterally and separates the canal from the vestibule. There is significant variability in the position and orientation of the IAC radiographically, and the authors have noted differences in surgical exposure depending on the individual anatomy of the IAC. The internal auditory canal (IAC) is an important landmark during surgery for lesions of the cerebellopontine angle.
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