Question:medium
Where will be the placement location for an Auditory Brainstem Implant (ABI)?
Where will be the placement location for an Auditory Brainstem Implant (ABI)?
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The ABI skips the cochlear nerve and stimulates the cochlear nucleus, whose surface lies in the lateral recess of the 4th ventricle.
Updated On: Jun 23, 2026
- Scala tympani
- Recess of 4th ventricle
- Internal auditory canal (IAC)
- Back of ear
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The Correct Option is B
Solution and Explanation
Step 1: Decide what the ABI is meant to stimulate. Unlike a cochlear implant, which needs a working cochlear (auditory) nerve, the ABI is chosen precisely when that nerve is gone - classically after bilateral vestibular schwannoma removal in NF2, or in congenital nerve aplasia. The only remaining place to inject the signal is the first central relay, the cochlear nucleus.
Step 2: Locate the cochlear nucleus anatomically. It sits on the dorsolateral brainstem at the pontomedullary junction, and its surface landmark opens into the lateral recess of the fourth ventricle. The surgeon therefore lays the paddle electrode into the lateral recess of the 4th ventricle, typically through a retrosigmoid or translabyrinthine approach at the time of tumour resection.
Step 3: Eliminate the others. Scala tympani is the cochlear-implant target and requires an intact nerve, so it fails the basic premise. The IAC is just the bony channel for the nerve, and the back of the ear holds only the external processor. None of these stimulate the nucleus.
\[\boxed{\text{Recess of 4th ventricle}}\]
Step 2: Locate the cochlear nucleus anatomically. It sits on the dorsolateral brainstem at the pontomedullary junction, and its surface landmark opens into the lateral recess of the fourth ventricle. The surgeon therefore lays the paddle electrode into the lateral recess of the 4th ventricle, typically through a retrosigmoid or translabyrinthine approach at the time of tumour resection.
Step 3: Eliminate the others. Scala tympani is the cochlear-implant target and requires an intact nerve, so it fails the basic premise. The IAC is just the bony channel for the nerve, and the back of the ear holds only the external processor. None of these stimulate the nucleus.
\[\boxed{\text{Recess of 4th ventricle}}\]
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