From external to internal auditory canal: surgical anatomy by an exclusive endoscopic approach

Abstract

Surgical approaches to the inner ear and internal auditory canal (IAC) are well known and well documented. The objective of this study is to analyze the morphology, and surgical and anatomic findings of an exclusive endoscopic transcanal approach (EETA) to the IAC. Cadaveric dissections were performed on 11 temporal bones, approaching the internal auditory meatus directly through the external ear canal and avoiding mastoidectomy. In all cases, it was possible to dissect the internal carotid artery and jugular bulb with a 0° endoscope, and with good control of these two structures. The medial wall of the bony labyrinth guaranteed good landmarks for IAC dissection, such as the spherical recess, and the labyrinthine tract of the facial nerve. The IAC can be thoroughly visualized in the cadaver using EETA, avoiding mastoidectomy, extensive temporal bone tissue removal and external incisions. Clinically based reports will be required in future to strengthen our preliminary results.

Defining the Limits of Endoscopic Access to Internal Auditory Canal

“…The expansion of this technique to IAC and the lateral skull base, however, remains a relatively novel concept with limited published data. The present study supports prior data and suggests that EETA is a viable and safe route of access to the lateral skull base in select cases [5][6][7]9] . The facial nerve was structurally preserved in this study despite the fact that the labyrinthine segment of the facial nerve lies adjacent to the fundostomy created into IAC.…”

“…This distance indicates that caution should be taken when widening the entry point to IAC anteriorly. Our results underscore those of Marchioni et al and others who suggest that visualization of the carotid canal in the protympanum is recommended to maximize safety when using this approach [6][7][8][9]14] .…”

“…Other studies have shown that ample hypotympanic space may permit a corridor to IAC that preserves the cochlea, possibly for drug delivery or brachytherapy [14] . Access can be gained to the petrous apex in the same manner to drain cholesterol granuloma [6] .…”

“…Recently, Marchioni et al [6][7][8][9] have described an exclusively endoscopic transcanal approach (EETA) to IAC. It differs from traditional approaches as it offers a direct route through the ear canal, a natural orifice of the temporal bone.…”

Anatomy of the fundus of the internal acoustic meatus — micro-computed tomography study

“…Knowledge on the detailed anatomy and topography of the singular quadrants of the FIAM and bony canals emerging from them is necessary during evaluation the temporal bone trauma and congenital anomalies affecting the individual nerves as well as during neurootologic surgical procedures [6,9]. For instance, the singular foramen is used as a landmark for certain surgical procedures on the internal acoustic meatus and labyrinth, such as retrosigmoid acoustic neuroma surgery and transcochlear cochleovestibular neurectomy [11].…”