Morphological classification of crista fenestra of round window corridor during pediatric cochlear implantation.

OBJECTIVES: This study aimed to document the observation of the Crista Fenestra's morphological types (CF) of the round window and to detect its impact during cochlear implant operation. STUDY DESIGN: A prospective descriptive cohort study. SETTINGS: We conducted this study at tertiary referral institutions in Egypt. PATIENTS: This study included 140 children who underwent cochlear implantation. INTERVENTION: We observed the CF's morphological type during the operation according to (Baki-Elzayat) novel classification of CF anatomy, and the need for drilling in each CI operation. MAIN OUTCOME MEASURES: CF has two main types. Type A, in which CF was present at the same level of round window membrane and attached to it. Type B, in which CF was medial to the Round window membrane. RESULTS: Type (A) CF was detected in 125 cases (89.28%), while 25 cases (10.71%) showed type (B) CF. Drilling was needed in 10 cases (7.14%), including CF types A.3 and B2. Drilling was not needed in 130 cases (92.85%), including CF type A.1, A.2, and B.1. There was a statistically significant difference in the need for drilling (P-value <0.001). CONCLUSIONS: According to this prospective study, CF had complicated anatomy. Baki-Elzayat classified the CF into two main types. In type A, CF was at the same level of RWM and attached to it. In type B, CF was medial to RWM. We recommended drilling for partial removal of massive CF types (A.3 and B.2) for atraumatic safe insertion of the electrode without deflection. This classification can offer an easy language system for CI surgeons to describe and register CF during their operations and in the surgical files.

Cadaveric Study of Crista Fenestra: Revisited.

OBJECTIVES: Since there is great confusion in the literature about the anatomy and terms of the crista fenestra (CF) and the crista semilunaris, this paper is confined to the anatomy of the inferior margin of the round window (RW). METHODS: This study was carried out on 20 cadaveric temporal bones. We measured the maximal height of the RW and the maximum height of the inferior bony edge of the RW, (termed CF type A), in this study. The ratio of the maximum height of CF type A to the maximum height of the RW was calculated. After drilling the CF type A, the scala tympani was visualized using a sialendoscope, and any bony projection in the inferior wall of the scala tympani just behind the round window membrane (RWM) was assessed and reported (termed CF B in this study). RESULTS: We identified CF type A in 19/20 of cases (95%), and it was absent in only 1 case (5%). Its height ranged from 0.228 to 1.329 mm with an average of 0.604±0.347 mm. The percentage of CF type A to RW ranged from 19 to 75%, with an average of 42%. CF type B was present in only 2 specimens (10%). CONCLUSION: CF type A occupied a significant part of the RW in most specimens, and therefore its drilling was essential in a large percentage of cases. CF type B (inside the scala tympani) was present in 10% of the temporal bone samples, and curettage had to be done in these cases.