POU3F4 X-linked Stapes Gusher (DFNX2)

A 6-year-old boy presents with bilateral hearing loss since infancy. Audiometry shows a mixed pattern with a 20 dB air-bone gap predominantly at low frequencies. CT temporal bones reveal the abnormality marked **A** in the diagram: dilated internal auditory canals, absent modiolus, and a thin bony separation between the IAC and basal cochlear turn. The child's mother is a known carrier. Which of the following is the MOST IMPORTANT consideration before any middle-ear surgical intervention in this patient?