4In the Operating Room: Intraoperative Complications

TThe most feared injury: the facial nerve

The facial nerve runs immediately deep to the posterior tympanotomy (facial recess); the recess is drilled in the triangle bounded by the fossa incudis, the chorda tympani and the descending (mastoid) segment of the nerve. Permanent facial palsy from cochlear implantation is rare (well under 1% in large series); transient weakness from heat or retraction is somewhat more common but usually recovers. Continuous intraoperative facial nerve monitoring (EMG of orbicularis oculi and oris) is standard practice and is strongly advised in malformed ears, where the nerve is aberrant in up to ~16% of cases (higher in severe malformations). Prevention rests on a wide, well-irrigated facial recess, copious cool irrigation while drilling near the nerve, recognising a dehiscent or anomalous course, and never drilling blind into bleeding bone.[1991][2018]

TThe chorda tympani and taste

The chorda tympani crosses the facial recess and carries taste from the anterior two-thirds of the ipsilateral tongue; it is occasionally stretched, cauterised or deliberately sacrificed to widen exposure to the round window. Sacrifice produces ipsilateral loss of taste and sometimes a persistent metallic taste or dysgeusia; many patients adapt and symptoms often (not always) fade over months. Because the deficit is usually well tolerated, opening the recess adequately is generally judged more important than heroic preservation of the chorda — but the trade-off should be a conscious decision and discussed in consent. Bilateral implantation in separate sittings can, in theory, threaten taste on both sides, a point worth noting when counselling sequential bilateral candidates.[1991]

CDura, CSF and the perilymph gusher

In a thin (often paediatric) skull the dura may be exposed or torn while seating the receiver-stimulator; a CSF leak must be sealed (fascia, muscle, glue) because a persistent leak raises meningitis risk. A perilymph/CSF 'gusher' occurs when the cochleostomy or round window is opened in an ear with an abnormal communication between the inner ear and the internal auditory canal subarachnoid space - classically the X-linked (incomplete partition type III) deformity, enlarged vestibular aqueduct, and common-cavity/severe malformations. Gusher management: head-up tilt to lower CSF pressure, optional mannitol, a cochleostomy roughly twice the array diameter so soft tissue can be packed around it, insert the array, then seal with a generous muscle/fascia plug (two-thirds within the lumen) and secure the lead so the plug cannot be dislodged. All implant candidates should be pneumococcal-vaccinated; the malformed-ear gusher patient is at additional meningitis risk independent of the implant itself.[1991]

CBleeding, and catching misplacement on the table

Significant bleeding is uncommon; sources include the sigmoid sinus, emissary veins, dural vessels and bone — meticulous haemostasis over exposed dura also guards against extradural haematoma. Misplacement (tip fold-over, scala vestibuli translocation, partial insertion, or an array straying into the vestibule/IAC in a malformed ear) is best detected before closure, when it is still correctable. Intraoperative tools that flag a wrong position include plain skull/transorbital radiography, intraoperative conebeam/CBCT or O-arm imaging, abnormal electrode impedances, and a reversed or compressed spread-of-excitation profile. The discipline is simple: confirm the array is where it should be while the wound is open, because reinsertion at the same sitting is far easier than a second operation.[2018][2008]