Auditory  Brainstem  Implanta3on:  What  the  Pediatric  Anesthesiologist  Needs  to  Know  

Eva Waller MD, Kim Blasius MD Department of Anesthesiology, University of North Carolina Children’s Hospital, Chapel Hill, North Carolina

An auditory brainstem implant (ABI) is a prosthetic hearing device that directly stimulates the cochlear nuclei, located on the dorsal surface of the brainstem in the lateral recess of the fourth ventricle (figure 1).

Many factors must be considered during the anesthetic management of ABI placement in the pediatric patient.

1.  Placement of the ABI itself requires craniectomy and exposure of the cochlear nuclei, located on the dorsal surface of the brainstem and accessed via the lateral recess of the fourth ventricle.

2.  Identification of the appropriate position for ABI requires intraoperative monitoring of cranial nerves IX, X, and XI, prohibiting the use of paralytics.

3.  Control of the airway may be compromised due to rotation of the OR table 180 degrees.

4.  Manipulation and/or stimulation of CN X (vagus ne rve ) can cause p ro found bradycardia intraoperatively.

5.  Multiple providers from different specialties are needed for the surgical team, potentially complicating communication in the OR. The team for the case presented consisted of: pediatric otolaryngologist, neurosurgeon, visiting otoneurologist (expert in ABI), pediatric anesthesiologist, audiologist, technicians for both CN monitoring and EABR, and the regular OR nursing staff.

1. Levent S. ABI. Auris Nasus Larynx 2012;39:439-50. 2. Colletti V, et al. ABI: New Frontiers in Adults and Children. Otolaryngology Head Neck Surg 2005;133:126-38. 3. Grayeli AB, et al. ABI to Rehabilitate Profound Hearing Loss with Totally Ossified Cochleae Induced by Pneumococcal Meningitis. Audiol Neurotol 2007;12:27-30. 4. Naidich T, et al. Duvernoy’s Atlas of the Human Brain Stem and Cerebellum. Vienna: Springer; 2009. 5. Lekovic G et al. Auditory Brainstem Implantation. Barrow Quarterly 2004;20,4:40-7.

A 5-year-old female with congenital deafness due to bilateral cochlear nerve deficiencies presented for right ABI placement.

Preoperative course -  Status post bilateral cochlear implantation

(ages 10 and 13 months) with no response -  Non-verbal -  O t h e r w i s e n o r m a l g r o w t h a n d

development

Introduc)on   Case  Report  

References  

Overview  of  procedure   Ø  Patient is positioned lateral with head

secured in Mayfield clamp Ø  Posterior fossa craniectomy via the

retrosigmoid approach is performed Ø  The dura is opened to expose the

foramen magnum and allow access to the inferior pole of the cerebellum

Ø  The cisterna magna is opened and dissection is carried superiorly to i d e n t i f y t h e s t r u c t u r e s o f t h e cerebellopontine angle and the root entry zones of CNs IX, X, XI (figure 3)

Ø  The cerebellum and flocculus are gently retracted to expose the choroid plexus projecting from the foramen of Luschka

Ø  The choroid plexus is retracted to expose the lateral recess of the fourth ventricle, into which the electrode array is placed (figures 2, 3)

Ø  Appropriate placement is confirmed with EABR

Intraoperative course -  Premedicated with PO midazolam -  Inhalaltional induction -  Intubated with size 4.0 cuffed ETT -  Two PIVs and a radial arterial line were placed -  Patient placed in right lateral position and OR table

turned 180° -  GA maintained with propofol infusion and

sevoflurane -  One episode of bradycardia, resolved with cessation

of brainstem manipulation -  Extubated and transferred to PICU postop

Discussion  

It was initially developed for adults with post-lingual deafness due to neurofibromatosis type 2 (NF2). The first use of an ABI in a pre-lingually deaf patient was not reported until 2000, in a 4-year-old male in Italy. In 2013, a phase 1 clinical trial began for ABI placement in patients ages 2-5 years who are not candidates for cochlear implants or demonstrated no benefit from one. As these procedures become more common in the US, the pediatric anesthesiologist must be prepared for the unique challenges ABI placement presents.

Figure  1.  Specimen photograph, median section of the fourth ventricle. 1. Floor of fourth ventricle, 2. Roof, 3. Medulla, 4. Pons, 5. Mesencephalon, 6. Cerebellum, 7. Nodulus, 8. Central canal

Figure  2.  Schematic representation of appropriate placement of the ABI electrode within the lateral recess of the fourth ventricle. 1. Facial nerve, 2. Stump of vestibulocochlear nerve, 3. Cochlear nuclei complex, 4. Electrode paddle in lateral recess, 5. Choroid plexus in foramen of Luschka, 6. Flocculus

Figure  3.  Magnified view of the foramen of Luschka. 1. Facial nerve, 2. Vestibulocochlear nerve, 3. Glossopharyngeal nerve, 4. Vagus nerve, 5. Lateral aperture (of Luschka) and choroid plexus of the fourth ventricle, 6. Flocculus  

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