12From cause to candidacy
The chapter has walked through the causes one by one; this closing module turns them into a single habit of thought. Every cause, we have seen, leaves a signature in the cochlea and the nerve — and that signature governs three things the implant team cares about: the substrate the electrode will find, the surgery and its timing, and the realistic expectations to set with the family. Read that way, the cause is not a line in the history but the opening move of the work-up. This module makes the translation explicit, gathering the whole chapter into a crosswalk from diagnosis to plan, and hands the reader on to the candidacy and evaluation chapter that follows.
FPulling the thread together
One idea has run through every module: the cause predicts the substrate, and the substrate predicts the implant. A pure cochlear lesion spares the nerve and implants well; a neural lesion damages the target; meningitis threatens the road in; a progressive cause demands watching. None of this is visible on the audiogram — it is carried by the diagnosis. So the cause earns its place not as history but as prognosis and plan.[2001]
TCause → substrate → plan
The crosswalk above is the chapter in one object. Pick a cause and read across: what it leaves behind, what to watch for at surgery, and what to expect. The pattern is consistent — causes that stay upstream of the spiral ganglion are the comfortable ones; causes that reach the ganglion, or that ossify the cochlea, are the ones that change the plan. The same cause-to-substrate logic the temporal bone proved (Module 11) becomes, here, a clinical workflow.[1997]
CWhen the cause sets the clock
For some causes the decisive variable is time. Meningitis is the extreme — implant before the cochlea ossifies — but the principle is broader: long-standing complete deafness lets the spiral ganglion fade whatever the original cause (Chapter 4), and congenital deafness races the sensitive period (Chapter 3). Knowing the cause tells you whether the clock is ticking fast (meningitis, a young child) or slowly (a stable adult loss), and how urgently to move.
CWhen the cause sets expectations
For others the cause mainly shapes counselling. A GJB2 or aminoglycoside loss supports an optimistic conversation; a primary neural lesion or a heavily ossified post-meningitic cochlea calls for a more guarded one; a progressive CMV loss calls for honesty about surveillance and change. Matching expectation to cause is part of doing the operation well — it is how the biology of this chapter reaches the family.
TInto the clinic
With the causes mapped to plans, the natural next step is the formal evaluation that puts them to work: the audiological and medical candidacy assessment, the imaging, and the counselling of the next chapter. The question this chapter adds to that work-up is simple and, by now, second nature — alongside how deaf is this ear?, ask deaf from what?
Which should be prioritised, and on what principle?
What is the chapter's organising workflow from a diagnosis to a plan?
Two children are listed: stable GJB2 deafness and recent meningitis with early basal-turn ossification. Which is the more urgent, and why?