Endolymphatic Sac and Duct as an Anatomic Repair to Achieve Complete Exposure of the Internal Auditory Canal Through the Retrosigmoid Approach: Anatomic Study

BACKGROUND: The retrosigmoid approach (RSA) is used in a wide variety of diseases in the cerebellopontine angle, and according to the findings, it can preserve hearing function during the resection of vestibular schwannomas. Complete exposure of the fundus of the internal auditory canal (IAC) could jeopardize the integrity of the otic capsule and subsequently cause profound hearing loss and chronic disabling vertigo. Great variability has been described in labyrinthine structures and to date there are no clear data on the distances of these structures to safely expose the IAC fundus. METHODS: A cross-sectional descriptive study was carried out in which complete dissection of the ELSD was performed on 20 preserved human temporal bones, measuring the distances of 9 anatomic structures underlying or closely related to the ELSD. RESULTS: When evaluating the variability between the structures, the distance between the ELSD and the acoustic pore had little variability and remained constant in all specimens. The distance between the acoustic pore and the common crus presented in our study had the lowest coefficient of variation. The distance that had the greatest variability was the measurement of the jugular foramen (JF) both by retrosigmoid and translabyrinthine approaches (RSAetranslabyrinthine approach). The rest of the variables remained stable. CONCLUSIONS: The ELSD is a safe anatomic technique for dissection and exposure of the IAC during RSA in vestibular schwannoma surgery. In our study, the structures evaluated presented little variability, with the exception of the distances between the ELSD and the JF; in some cases, the JF exceeded the lower limit of the ELSD and IAC.