CASE PRESENTATION
We report the case of a 4-year-old boy who had received a simultaneous bilateral cochlear implant (CI), because of a progressive profound bilateral sensorineural congenital hearing loss of genetic origin. His medical history is remarkable because, in January 2020, 1 year after CI surgery, he developed a post-viral acute disseminated encephalomyelitis (ADEM). At that time, the surgical removal of the magnet bilaterally was done to confirm ADEM by brain and spine magnetic resonance imaging (MRI); the magnets were replaced, uneventfully two months later.
Two years after CI, the boy incurred in a head trauma in the left temporal region on the receiver–stimulator (R/S) area of the left CI, which caused the dislodgment of the magnet and the rupture of the silicone sheath of the magnet encasement.
Immediately after the trauma (October 2020), the left CI speech processor could not be linked to the internal R/S. A CT scan excluded fractures of the left temporal bone but identified the dislocation of the magnet. (Figure 1) The CI team discussed with the parents the options of explanting and re-implanting the left CI: however, considering the correct position of the intracochlear array, the previous normal intraoperative impedances and neural telemetry testing and the very good speech perception performances, a conservative surgical approach was considered mandatory. The risk of a subsequent relapse of the magnet dislocation caused by the possible weakening or even rupture of the thin silicone ring around the magnet well was likely. The literature was not helpful in this respect: as far as we know, no similar cases were reported in the literature, neither surgical options different from explantation, were offered. PDLLA was identified by our Maxillo-Facial Surgery consultant as a possible means to reduce the risk of recurrent dislodgment. After thorough discussion and informed consent by the parents, 2 weeks after the head trauma, the boy underwent a surgical revision. A small skin incision over the R/S was performed and 1 cm of the cortical bone around it for was expose. (Figure 2) The dislodged magnet was replaced with a new sterile one, and a tiny fissure of the silicon ring was observed. In order to reinforce the damaged silicone case a PDLLA mesh was prepared: first it was heated in hot water, then it was shaped in order to correctly cover the recess, and finally it was screwed to the bone using 5 dedicated Sonic Pins®, inserted in pre-drilled holes, by means of the SonicWeld® system. The insertion was done with a “sonotrode”, a dedicated ultrasonic tool that liquifies and expands the pins after the insertion, allowing a tight bond with the mesh and anchoring them securely to the holes in the bone. (Figure 2) No complications were noticed immediately after the surgery. Figure 3 shows the surgical site without inflammation, edema, hematoma, or infection at 1 month after surgery; the area above the R/S was thickened but no coupling troubles were reported at the time of CI reactivation. Immediate restoration of optimal auditory performances at the pre-trauma levels was achieved. At the latest check-up (18 months), no complications have been observed, the CI is working regularly, and the child has no complaint.