Standardization of CT Depiction of Cochlear Implant Insertion Depth

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Fig 1.
Oblique reformations along the plane of quadrant I. Axial CT, right temporal bone, through the first cochlear turn, quadrant I, showing the slab thickness for oblique reformations.
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Fig 2.
Drawing of the cochlea with quadrants numbered. Drawing of all cochlear turns, with the quadrants numbered I–X. Use of this approach in reporting the CI tip will standardize discussion of implant tip location. Courtesy of Eric Jablonowski, medical illustrator.
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Fig 3.
A 7-year-old boy with a left-sided cochlear implant. Single oblique reformation shows the CI tip in quadrant IV.

Table 1:

Agreement about quadrant of cochlear implant depth in 36 ears (33 patients)

Agreement of Concern	Expression of Agreement
Agreement of Concern	Spearman r	Same Quadrant	1-Quadrant Difference	2-Quadrant Difference	3-Quadrant Difference
Rdr 1: axial-coronal vs reformatted images	.90, P <.001	21	13	2	0
Rdr 2: axial-coronal vs reformatted images	.89, P <.001	20	15	1	0
Rdr 1 vs 2: axial-coronal images	.88, P <.001	16	18	2	0
Rdr 1 vs 2: reformatted images	.90, P <.001	16	16	4	0

Table 2:

Examples from dictations by neuroradiologists interpreting temporal bone CT obtained for CI position

Examples
“Enters the cochlea at the basal turn via the cochlear promontory and extends to the apical half turn.”
“Left cochlear implant in place.”
“Implant lead then enters the round window, passes into the cochlea and terminates near the apical half turn.”
“Electrode intact and normal in course.”
“Electrode continues to the cochlea where it has appropriate turns.”
“Enters the basal turn of the cochlea, looping within the cochlea, and terminating near the apex.”
“It extends to, but does not go through, the aperture.”
“Through the round window and filling the basal and middle turns of the cochlea.”