The Nervus Intermedius in Children with Cochlear Nerve Deficiency Submitted to Auditory Brainstem Implantation

Abstract

Objectives: Anatomical distortions of the neural structures surrounding the foramen of Luschka (FL) characterize children with cochlear nerve deficiency (CND). Our goal was to investigate the anatomical features of the nervus intermedius (NI) and cranial nerve 7 (CN) VII in children with CND and verify if the NI can provide an additional landmark during auditory brainstem implantation (ABI) surgery, preventing intraoperative injuries of the nearby vessels and nerves. Methods: Sixty-four CND children ranging in age from 8 months to 16 years (2.92 ± 1.54) were video-recorded during retrosigmoid surgery for fitting the ABI and retrospectively examined with particular reference to the number and variety of NI bundles, the associated malformations of CN VII, the relationship with CN VII, and the possibility that NI might represent a landmark for ABI insertion. Results: Absence of CNs VI, VII, and VIII was observed respectively in 3, 8, and all children. Eighteen children showed several abnormalities of CN VII in the cerebellopontine angle. The identification of CN VII and of the bundles comprising NI was possible anatomically in 46 children. In 12 the identification was obtained with the assistance of intraoperative monitoring. The number of bundles comprising the NI varied from 1 to 6. The NI and CN IX were useful landmarks for identifying the FL of the lateral recess. Conclusions: NI provides an additional landmark during ABI microsurgery. Knowledge of NI anatomy and its topographical relationship with the neurovascular structures around the FL may prevent iatrogenic injuries and ABI electrical stimulation of the surrounding cranial nerves.