Abstract
The identification of the internal auditory canal (IAC) has relied on visualization
of the arcuate eminence (AE). However, it is not uncommon that the topographic markers
on the middle cranial base are featureless and difficult to identify, including the
AE. “Point T”, the intersection of the posterior border of the trigeminal ganglion
(TG) and the superior petrosal sinus (SPS) has been presented as a marker to localize
the IAC. Thirty-four sides from 17 dry skulls and five formalin-fixed latex-injected
cadaver heads were studied. In the dry skull, the imaginary line of the IAC was defined
by connecting the uppermost point of the rim of the external auditory canal and the
uppermost point of the porus acousticus on the petrosal ridge. Point T was defined
as the posterior margin of the trigeminal impression on the petrosal ridge. For cadaver
heads, a standard middle fossa approach was performed, and the line of the IAC was
defined by joining the tip of Bill’s Bar and the midpoint of the dura on the porus
acousticus. Point T was expressed as the intersection of the posterior border of the
TG and the SPS. The distance between point T and the medial end of the IAC was termed
“segment TI”, and the angle spanning from segment TI to the IAC was “angle theta (θ)”.
In dry skulls, segment TI (mean ± standard deviation [SD]) measured 9.74 ± 0.71 mm and angle θ was 135.56 ± 3.21°; in cadaver heads, segment TI measured 10.25 ± 0.58 mm and angle θ measured 133.43 ± 2.00°. An alternative for localization of the IAC is proposed when the AE is difficult
to identify in the middle cranial fossa. As a mnemonic, the IAC can be located by
identifying point T first, and then tracing 1 cm posteriorly along the SPS and turning laterally 90° plus half of 90° (135° total).
Keywords
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Article info
Publication history
Accepted:
February 17,
2009
Received:
October 23,
2008
Identification
Copyright
© 2009 Published by Elsevier Inc. All rights reserved.
