CI Atlas · Preoperative Imaging · Module 13

13Paediatric imaging & radiation safety

Imaging a child carries extra weight in both directions. On one side, it must not miss a cochlear-nerve deficiency that a normal CT would conceal, which is why high-resolution MRI is non-negotiable in a child with profound loss — even at the cost of a general anaesthetic. On the other, the developing lens is exquisitely radiosensitive, so temporal-bone CT is held to ALARA, sparing the eyes by careful positioning. Two further paediatric questions recur: does the implant outgrow the child, and is the small, still-pneumatising temporal bone ready for surgery? Reassuringly, serial studies show the intracochlear electrode does not migrate as the skull grows, though excess lead is coiled in the mastoid to allow for it. This module covers imaging the youngest candidates.

Imaging note

Representative CT and MRI images for this chapter are being added soon. The interactive figures here are original schematic teaching diagrams; to respect copyright we do not reproduce third-party radiographs.

TMRI, not CT alone

For young children imaging carries extra weight: all children with profound loss should have high-resolution MRI (not CT alone) to detect the cochlear-nerve deficiency that a normal IAC on CT would miss (Module 8). MRI in young children frequently needs general anaesthesia— a cost weighed against CT's radiation and lower nerve sensitivity.[2006]

CLens dose & ALARA

The lens is the most radiosensitive deterministic target in temporal-bone CT; the ICRP lowered the cataract threshold to 0.5 Gy. In-beam lens dose is ~0.03–0.06 Gy, falling to ~0.003 Gy when positioning keeps the lens out of the beam — ALARA via positioning, leaded glass and a small field of view.[2022]

CHead growth & migration

Head-growth planning: the promontory-to-mastoid-cortex distance and array geometry increase about 1.7 cm birth-to-adult (half in the first two years), so excess lead is coiled in the air-containing mastoid. Reassuringly, serial radiographs with computer-graphic analysis showed the intracochlear electrode position does NOT migrate with skull growth.

Implanting a baby raises a natural worry: will the array pull out as the skull grows? The geometry does change — the promontory-to-mastoid-cortex distance increases about 1.7 cm from birth to adulthood (half of it in the first two years) — which is why a length of excess lead is left coiled in the air-containing mastoid. But serial radiographs with computer-graphic analysis showed the intracochlear electrode position does NOT migrate with growth — reassurance for early paediatric implantation. Schematic.

CThe developing temporal bone

The developing mastoid and facial-recess anatomy are explicitly assessed — pneumatisation may be incomplete in the very young. And an imaging-detected malformation, ossification or nerve aplasia steers device choice, surgical approach and family counselling (Candidacy and Surgery chapters).

Case 12.13 · CT or MRI for the infant?

An infant with profound loss needs imaging. A clinician proposes CT alone to avoid a general anaesthetic.

What is the correct approach?

Self-assessment — Module 122 questions

Question 1 · Foundation

Why do children with profound loss need MRI, not CT alone?

Question 2 · Clinician

Does the intracochlear electrode migrate as the child's skull grows?

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