Surgical anatomy of round window and its implications for cochlear implantation

Abstract

The objective of this work was to study the morphometry and morphology of the round window (RW) and its relationships with the internal carotid artery, jugular bulb (JB), facial nerve and oval window (OW). Fifty cadaveric temporal bones were microdissected to expose the medial wall of the middle ear. The areas around the RW were cleared and its shape, height and width were noted. Its distances from the carotid canal (CC), jugular fossa (JF), facial canal (FC), and OW were measured. Oval, round, triangular, comma, quadrangular, and pear shapes of RW were observed. The average height and width of the RW were 1.62 ± 0.77 mm and 1.15 ± 0.39 mm, respectively. There was a statistically significant correlation (r = 0.4, P < 0.01) between the height and width. The distances between the RW and the CC, JF, FC, and OW were in the ranges 4.39-11.05 mm, 0.38-8.65 mm, 2.99-6.3 mm, and 1.39-3.57 mm, respectively. In 8% of cases, the distance between the RW and the JF was <1 mm. There were no statistically significant differences with regard to age group, gender, or side. Electrode insertion can be challenging in cases where the height and width of the RW are <1 mm. The thin bone separating the roof of the JF from the RW (<1 mm in 8%) highlights a potential risk of injury to the JB during cochleostomy placement. This information could be useful for selecting cochlear implant electrodes in order to avoid potential risks to vital neurovascular structures during implant surgery.

Links Between Surgical Landmarks of the Temporal Bone and Cochlear Implant Approaches

“…The distances measured in our study showed a large variability and a large area of dispersion for the values, similar to the real life [11][12][13][14][15].…”

Surgical anatomy of the round window—Implications for cochlear implantation

“…The mean minimum distance between the RW and jugular bulb is 2.85 mm. However, in about one‐third of the cases, the distance is <2 mm and in 8% <1 mm . The mean distance between the RW and oval window is about 1.50 mm (range 1.11‐2.24 mm) .…”

“…There is substantial variability in size of the RWM itself. Its horizontal and vertical axis differ in lengths, and hence, the membrane has more an elliptical shape . In some studies, the minimal diameter was shown to be less than 1 mm, but it is not always clear, which reference points were used for these measurements.…”

Time‐saving and fail‐safe dissection method for vestibulocochlear organs in gross anatomy classes

“…The difficulty in observing the vestibulocochlear organs is attributable to their anatomical features and the fact they are covered by the petrous part of the temporal bone. These osseous structures are themselves components of the vestibulocochlear organs (Berkovitz et al, ; Singla et al, ). The above method is effective for taking these anatomical features into account.…”

“…The vestibulocochlear organs are very small and have a unique morphology. They are embedded in the petrous part of the temporal bone (Berkovitz et al, ; Rask‐Andersen et al, ) with some variations (Miller and Pensak, ; Nikolaidis et al, ; Singla et al, ). They cannot be seen from the temporal bone surface.…”