High resolution [¹⁸F]FDG PET of the inferior colliculi in single-sided deafness.

Introduction: The newest generation of fully digital, clinical PET/CT systems provides an improved spatial resolution that permits identification also of small brainstem nuclei. The present study tested the effect of asymmetric hearing impairment on glucose metabolism of the inferior colliculi as well as primary auditory cortex. Nine patients with asymmetric hearing impairment were scanned with a Philips Vereos PET/CT and [18F]FDG. By volume-of-interest (VOI) analyses of the inferior colliculi and the primary auditory cortex, we investigated differences between ipsi- and contralateral normalized FDG uptake (reference: cerebellum) and associations between duration of hearing impairment and FDG uptake. Consistent with the side of hearing impairment, decreased FDG uptake of the inferior colliculi as well as the primary auditory cortex was observed (p < 0.01 and p < 0.005, respectively). Hypometabolism of the contralateral primary auditory cortex was less pronounced in patients with longer lasting hearing impairment (r = 0,88, p < 0,005). Contralaterally, glucose metabolism of the primary auditory cortex was predicted by that of the inferior colliculus only if adjusted for duration of hearing impairment (t = 2.5, p < 0.05). Fully digital, clinical PET scanners facilitate the investigation of small brainstem nuclei like the inferior colliculi. Neuronal activity contralateral to the side of hearing impairment is reduced in primary auditory cortex as well as in the inferior colliculi. In the primary auditory cortex, this effect is mitigated by the duration of hearing impairment, in line with intermodal cortical plasticity (Rauschecker & Korte, 1993). This observation suggests usefulness of FDG PET for predicition of therapy benefits (e.g., in case of cochlear implantation).