Internal Auditory Canal and Cerebellopontine Angle

Anatomy of the nerves traversing the internal auditory canal as seen from a retrosigmoid craniotomy perspective. Note the 90-degree rotation of the vestibular and cochlear nerve components of the eighth nerve between inner ear and brainstem entry. C, cochlear nerve; CN, cochlear nerve; IV, inferior vestibular nerve; VN, vestibular nerve; SV, superior vestibular nerve; 7, facial nerve.
At the lateral extremity of the IAC the relationships of the superior vestibular (SV), inferior vestibular (IV), facial (7), and cochlear (C) nerves are highly predictable. In this location, the canal is completely divided in the horizontal plane by the transverse crest (TC) and its upper compartment is partitioned by a vertical bony crest (VC) also known as Bill’s bar (after William F. House, MD). A, anterior; I, inferior; P, posterior; S, superior.
Anatomical relationships of the cerebellopontine as seen through a retrosigmoid posterior fossa craniotomy. JV, jugular vein; JB, jugular bulb; SS, sigmoid sinus; 11s, spinal component of the accessory nerve; 11c, cranial component of the accessory nerve; 10, vagus nerve; 9, glossopharyngeal nerve; Ch, choroid plexus emanating from the lateral recess to the fourth ventricle; Fl, flocculus; BS, brainstem surface (pons); 7, facial nerve; 8, audiovestibular nerve; 5, trigeminal nerve; PA, porus acusticus; IV, inferior vestibular nerve; SV, superior vestibular nerve; ES, endolymphatic sac; VA, vestibular aqueduct; PSCC, posterior semicircular canal; CC, common crus; SSCC, superior semicircular canal; Co, cochlea.
Ventral perspective of the brainstem depicting the root entries and proximal course of cranial nerve entries of V to VIII. Note the seventh nerve enters inferior to the eighth. Most previous illustrations contain errors in the depiction of these anatomical details. (Used with permission from Corrales CE, Jackler RK, Mudry A. Perpetuation of errors in illustrations of cranial nerve anatomy. J Neurosurg 2016;28:1–7.)

 

Dr. Jackler and Ms. Gralapp retain copyright for all of their original illustrations which appear in this online atlas.  We encourage use of our illustrations for educational purposes, but copyright permission should be sought before publication or commercial use. To request permission for publication or commercial use please contact Christine Gralapp ([email protected], https://www.chrisgralapp.com).