Imaging evaluation of incomplete partition type Ⅲ cochlea malformation before cochlear implantation operation / 中华放射学杂志

ABSTRACT

Objective:To investigate the imaging findings of incomplete partition type Ⅲ (IP-Ⅲ) cochlea malformation using high-resolution CT (HRCT) and MRI, and to measure the key anatomical structures, providing the accurate qualitative and quantitative data for cochlear implantation (CI).Methods:Totally 14 patients (28 ears) with IP-Ⅲ cochlea malformation who underwent cochlear implantation at Beijing Tongren Hospital, Capital Medical University from February 2012 to March 2019 were retrospectively collected. All the patients were male, aged 7 months to 27 years old, with the median age as 3 years old. All the 14 patients underwent preoperative HRCT and 9 of them underwent preoperative MRI. The development of inner ear structure, including cochlea, vestibule, semicircular canals, vestibular aqueduct and internal auditory canal (IAC) was reviewed and analyzed. The travel route and position of labyrinthine, tympanic and mastoid segment of facial nerve canal were evaluated; the width of labyrinthine segment of facial nerve canal and superior vestibular nerve canal, as well as the angle between first and second parts of the facial nerve canal were measured on HRCT. The shape of stapes and the development of cochlear nerve were analyzed on MRI.Results:All the 14 cases (28 ears) showed nearly normal shape of the cochlea, with the bony interscalar septa presenting while the modiolus completely absent. The lateral portion of the IAC was dilated, and the septum was absent between the base of the cochlea and the IAC, appearing as a"gourd-like"shape. A small saclike protrusion was formed in the vestibule and protruded into the upper semicircular canal in 10 cases (20 ears) (71.4%, 20/28). The beginning of the vestibular aqueduct enlarged in 12 cases (24 ears) (85.7%, 24/28). All the 14 cases (28 ears) showed that labyrinthine segment of facial nerve canal was located almost above the cochlea and showing stiffly. The labyrinthine segment of facial nerve canal widened in 7 cases (14 ears) (50.0%, 14/28) and the superior vestibular canal widened in 13 cases (26 ears) (92.9%, 26/28). The width of labyrinthine segment of facial nerve canal and the superior vestibular canal were (1.14±0.37) mm and (1.66±0.35) mm, respectively. The angle between the first and second parts of the facial nerve canal was 96.83°±15.63°. Eleven cases (22 ears) (78.6%, 22/28) showed thickened footplate of stapes and poor oval window, but the round window was clear. Nine cases (18 ears) showed normal development of the cochlear nerve on MRI.Conclusion:IP-Ⅲ cochlea malformation has the characteristic imaging features. Preoperation accurate assessment of the shape and location of important anatomical structures such as cochlea, internal auditory canal and facial nerve can provide valuable information for CI.