Defining the Limits of Endoscopic Access to Internal Auditory Canal

Abstract

The aim of this study was to quantify the size of the surgical corridor and the anatomical relationships of EETA to IAC using a cadaveric model. Specifics of fundostomy size, access to CPA, and the relationships between surgically relevant landmarks were analyzed Defining the Limits of Endoscopic Access to Internal Auditory Canal OBJECTIVE: To quantify surgical access to the internal auditory canal (IAC) using an exclusively endoscopic transcanal approach (EETA) and investigate surgically relevant relationships with neurovascular and osseous landmarks of the temporal bone. MATERIALS and METHODS:Anatomical dissection of two paired temporal bones and 15 unpaired temporal bones was performed using an exclusively endoscopic approach to IAC. The dissection proceeded until the cerebellopontine angle (CPA) could be accessed. Following dissection, all the specimens were subjected to computed tomography (CT) imaging. Anatomage InVivo5 software was used to analyze the CT scans and record measurements. RESULTS:CPA access and visualization of the labyrinthine segment of the facial nerve were achieved in all specimens. The mean distances from the carotid artery, jugular bulb, and middle fossa to the surgical opening (or fundostomy) of IAC were 4.1±1.5, 6.4±2.5, and 5.5±1.9 mm, respectively. The mean cross-sectional areas of the fundostomy and tympanic ring were 30.8±10.4 and 67.7±11.3 mm2. The mean distances from the osteo-cartilaginous junction and tympanic ring to the porus acusticus were 29±2.6 and 21±2.3 mm, respectively. CONCLUSION:Transcanal access to the entire IAC can be safely achieved using an exclusively endoscopic approach. Generous removal of the cochlear promontory can be accomplished while a safe distance is maintained from key neurovascular structures. EETA to IAC offers a minimally invasive alternative to patients without serviceable hearing for intrameatal and medial IAC tumors. Increased knowledge of crucial anatomical relationships involved in this approach will facilitate acceptance and utilization.

Jugular bulb and skull base pathologies: proposal for a novel classification system for jugular bulb positions and microsurgical implications

“…46 HRJBs can make endoscopic access to the IAC very difficult in certain cases, just like in other skull base approaches to the region. 21,30,34 We feel that the currently proposed classification can offer safer and more efficacious surgical planning to the described region. In Manjila and Semaan classification types 1 and 2, a transpetrous approach to the posterior fossa (translabyrinthine approach) provides adequate exposure given adequate skeletonization of the sigmoid sinus and dome of the jugular bulb is performed.…”

Transcanal Transpromontorial Approach to Lateral Skull Base: Maximal Area of Exposure and Surgical Extensions

“…This could be helpful both during the access to the IAC for the identification of anatomical landmarks to further guide the surgical steps, and after exposure of the IAC and tumor removal, to should be preoperatively assessed to predict the feasibility of the approach and the fundostomy size. 18 The jugular bulb position in the tympanic cavity and its possible dehiscence may influence its management during TTA, as in open approaches, 19 and a highly riding jugular bulb has been reported as a relative contraindication to TTA surgery. 20 Anatomical variants of the ICA have also been described, advocating for routine preoperative evaluation of this arterial segment in relation to the middle ear and the Eustachian tube before a number of surgical procedures.…”