The incidence, clinical manifestations, diagnosis and management of common complications of cochlear implant surgery in children are reviewed and summarized by reviewing domestic and international literature, internal communication and clinical case experience, including the latest developments of surgical complications in China and abroad. This article focuses on the complications that are often encountered and difficult to deal with in clinical practice, including flap infection and necrosis, implant silicone rubber allergy, facial nerve injury, facial nerve stimulation and no auditory response after start-up. With careful preoperative diagnosis, refinement of surgical details and improved surgical experience, surgical complications can be avoided and minimized. Cochlear implant is the most effective way to restore hearing to the severely and profoundly deaf. Long-term clinical results have shown that cochlear implantation plays a crucial role in preventing hearing deprivation and promoting language development in childhood, especially in infancy and early childhood. In recent years, with the popularization of cochlear implant technology, more and more hospitals in China have carried out cochlear implant surgery, and most of the surgeries are performed on children. Due to the complexity of the anatomical relationship between the middle and inner ear involved in this surgery, the presence of a significant percentage (>15%) of middle and inner ear malformations in pediatric cases, and the fact that the cochlear implant is a foreign body, the risk of surgical complications is inevitably increased [1]. Early cochlear implant surgery was associated with a high rate of complications. Cohen (1988)[2] investigated 459 cochlear implant surgeries performed by 108 surgeons throughout the United States, and 55 cases had various complications, with an incidence rate of 12%. Of these, 5% were serious complications and 7% were minor complications. Webb (1991)[3] reported 153 cochlear implant surgeries in Germany and 100 in Australia, with surgical complications of 20% (31/153) and 40% (40/100), respectively. In recent years, experience in implantation surgery, improved surgical methods, and newer cochlear implant devices have resulted in a decrease in the rate of surgical complications, but when complications do occur, they can have serious consequences. According to the definition of Cohen (1988)[2] , complications of cochlear implant surgery can be categorized into major and minor complications. Major complications are those that require removal of the cochlear implant or reimplantation, including flap necrosis, severe uncontrolled infection, meningitis, severe facial nerve twitching due to electrical stimulation, and failure of the electrodes to be implanted in the cochlea. Secondary complications are those that can be resolved or alleviated with conservative treatment, such as subcutaneous hematoma, temporary facial paralysis, dizziness and balance disorders, altered sense of taste, and tympanic membrane perforation. In this article, we will discuss several common clinical complications and their diagnosis and management. Flap infection and necrosis Flap necrosis is a common and serious complication of cochlear implant surgery, with an incidence rate of 2% to 5% in the early stage, but due to the improvement of surgical techniques in recent years, the incidence rate has been reduced to 0.5% or less. The incidence is slightly more common in adults than in children abroad, but in China it occurs exclusively in children, as the total number of cochlear implant surgeries performed in children in China is close to 90%. The main reason for the high incidence in children is that the same size cochlear implant is used in both adults and children, but the implant is relatively large and thick for the small skull of infants and young children, and infants and young children have a lack of subcutaneous tissue and muscle, and a thin scalp flap, so that if the flap is not well designed (without taking into account the need to preserve the appropriate area and blood supply), the implant is placed unevenly and protrudes too much, and excessive tension is exerted on the skin during suturing of the incision, all of which can lead to a high incidence of cochlear implantation in children. Ischemic necrosis of the flap can occur if the implant is placed unevenly or protrudes too far, or if the skin is placed under too much tension during suturing of the incision; necrosis can also occur as a result of a severe infection, which can also be secondary to infection. Management of flap necrosis: In the event of flap necrosis, a bacterial culture should be performed, local flushing with antibiotic solution, and systemic antibiotics should be applied. After infection control, the necrotic tissue should be removed, and the defect should be closed by flap transfer technique, making sure that there is no tension on the flap during suturing. If the infection is not effectively controlled and an abscess forms beneath the flap, the implant should be removed promptly if it is surrounded by granulation tissue. In China, there have been many cases of flap necrosis with abscess formation in which the implant was not retained despite prolonged local irrigation and drainage and several transfers of the flap. Therefore, it is recommended that the implant should be removed as soon as possible once there is abscess and granulation tissue formation around the implant, as ineffective treatment will only increase the pain of the child, prolong hospitalization, increase the financial burden of the family, and increase the contradiction between the patient and the doctor. Before removing the implant, the electrode should be cut off outside the round window, preserving the electrode implanted in the cochlea, and reserving the channel for re-implantation of the electrode for re-surgery. Reoperation should be performed six months to one year after infection control. Allergic reactions to the implant are mostly caused by silicone allergy. Cochlear implants made by different manufacturers contain a variety of silicone materials, including silicone wrapped around the receiver/stimulator, silicone for the electrodes, and silicone adhesive, etc. Therefore, cochlear implants that come into contact with human tissues are made of a variety of silicone materials. The problem of implant allergy has recently become a complication of concern to both domestic and international experts. Out of more than 900 cochlear implant cases completed in our hospital, 10 cases with allergy symptoms occurred, with a prevalence of more than 1%. Implant allergy also has a tendency to recur and to run in families. Among the 10 cases in our hospital, 3 cases had multiple episodes, and two siblings of a certain family underwent cochlear implant surgery in our hospital, and both siblings had allergic symptoms successively. Clinical manifestations of implant allergy are: patients feel discomfort, pain or tenderness behind the ear, unclear hearing (the distance between the inner and outer coils is increased); on examination, the skin on the surface of the implant is limitedly swollen, most of the skin is normal in color, and some patients have localized skin congestion; there is a fluctuating sensation when palpation is made, and some patients have localized pressure; the white blood cell counts and classification of the implant are mostly in the normal range; most of the local puncture is clear yellow fluid, and a few are bloody viscous fluid, and some are blood. The local puncture was mostly clear yellow fluid, a few were bloody mucus, and the bacterial culture was negative. The majority of cases resolved within 10 days with antibiotics and antihistamines, and very few cases resolved with immunosuppressive drugs (hormones). The only case of postoperative flap infection and abscess formation occurred in our hospital. Six months later, a cochlear implant was implanted in the contralateral ear, and before the second surgery, we conducted a skin patch test with the implant material provided by the manufacturer, and no allergic reaction was observed; however, the flap redness and swelling appeared at the site of implant 2 months after the surgery, and the symptom disappeared after antiallergic treatment. We considered that this patient was still suffering from an allergic reaction. From the literature review, there are 5 cases of silicone allergy leading to implant removal worldwide: Kronenberg (2001)[8] reported a case of implant removal due to a foreign body reaction to the Nucleus 22 device, and Puri (2005)[9] reported a case of allergic reaction to LSR-30 silicone gel encapsulating an implant in a CI24 Contour device. Puri (2005) [9] reported a case of allergy to LSR-30 silicone encapsulating the implant in a CI24 Contour device, which was changed to an Advanced Bionics device with LSR-70 as the encapsulant, with no recurrence of the allergy. Kunda (2006)[10] summarized three cases of silicone allergy that occurred throughout the United States from 1999 to 2004. The common features were unprovoked localized edema at the implant site months to years after cochlear implant surgery, with purplish-red skin; wound dehiscence shortly afterward, mucus discharge, and negative bacterial cultures. The patient had no other systemic symptoms. After antibiotics, antihistamines, hormones and surgical treatment, the symptoms were relieved, but soon recurred. All three patients underwent skin sensitization tests with implant materials provided by the manufacturer, and two were found to be allergic to the silicone binder RTV, and one was allergic to the MDX-4-4515 silicone gel. The three devices that caused the allergic reactions were removed, and a cochlear implant free of these allergic materials was implanted in the contralateral ear, customized by the manufacturer. The patient was observed for one to several years after the surgery, and no further allergic reactions occurred. The allergic reaction caused by the silicone gel was a T lymphocyte-mediated type IV anaphylactic reaction or delayed-type hypersensitivity reaction, but the type IV reaction usually occurred 2 to 7 days after exposure to the foreign material, while the cochlear implant patients usually had an attack several months or even years after the surgery. Therefore, it is generally believed that the allergic state may be triggered by chronic infection. Most of the allergy cases treated in our hospital were preceded by a high intake of seafood, which may also have contributed to the onset of the allergic reaction. Treatment of anaphylaxis: Once patients are found to have allergic symptoms, they should be treated with antibiotics and antihistamines, and when the symptoms are more severe, hormones and other immunosuppressants can be considered. For cases with severe rejection and need for re-implantation, strict allergy test must be done before re-operation. Test kits are currently available from the 3 major cochlear implant manufacturers (Cochlear, Medel and Advanced Bionics). Allergy testing can be performed by patch, scratch and intradermal methods. It is recommended that the patch method should be performed for more than 72 hours, and if the result is negative, the scratch method should be considered. Based on the test results, the manufacturer will provide the cochlear implant device that is customized for the patient’s needs. The incidence of facial nerve injury from cochlear implant surgery is very low, and the incidence of facial nerve injury is decreasing globally as surgical experience is gained; Cohen reported an incidence of 1.74% in 1988 [2], Hoffman reported 0.73% in 1995 [11], and Fayad reported 0.71% in 2003 [12]. 0.71% reported by Fayad in 2003 [12]. Nevertheless, facial nerve injury is the fourth most common complication after flap necrosis, electrode displacement, and facial nerve irritation. Facial nerve injury consists of permanent paralysis and temporary paralysis of the facial nerve, with permanent paralysis being very rare and temporary paralysis being the majority. Permanent paralysis occurs during surgery and is caused by direct damage to the facial nerve with an electric drill; temporary paralysis occurs after surgery and can be fully recovered in most cases. One of the causes of facial nerve paralysis is due to the large variation in facial nerve anatomy. According to the statistics, in all cochlear implant surgery cases, the facial nerve course variations accounted for 17%, while in the middle ear and inner ear malformation cases, the facial nerve abnormalities as much as 27%. It has been suggested that intraoperative facial paralysis occurs in cases where the angle of the geniculate portion of the facial nerve is sharpened and the vertical segment of the facial nerve is displaced anteriorly below the inferior tympanic cavity [13]. Cochlear implant surgery in children carries greater surgical risk due to the high prevalence of middle and inner ear malformations in congenitally deaf children. In addition, lack of surgical experience is a direct cause of facial paralysis. Mechanisms of facial nerve injury include: direct damage to the nerve by the drill bit during surgery; excessive heat generated by the drill bit or the drill rod to the bone surrounding the facial nerve, resulting in edema of the facial nerve due to thermal injury; viral reactivation and compression of the exposed facial nerve by the electrode in the facial socket, and so on. Facial nerve injury is also categorized into immediate and delayed. Immediate facial paralysis is caused by direct injury from surgery, which occurs during surgery or is detected at the completion of surgery. Even if timely measures are taken, the possibility of full recovery of facial paralysis is very small, and it is a very serious complication. Delayed facial paralysis can occur a few hours to weeks after surgery, mostly due to the heat generated by the drill, viral reactivation and electrode compression, after appropriate treatment, most of them can be fully recovered. Treatment of facial nerve injury: If immediate facial nerve injury occurs during surgery, the degree of facial paralysis should be evaluated first, and if the injury is severe, immediate surgical repair is required. Surgical procedures include facial nerve decompression, direct anastomosis, and cable graft. The latter is often performed using a large auricular nerve graft, but the effect of this procedure is only to maintain the tone and volume of the facial muscles, and rarely to restore their movement. Delayed facial paralysis is usually treated with observation and conservative therapy, such as hormones and antiviral drugs. Surgery should also be considered in severe delayed cases if the degree of facial paralysis is > grade VI or if the degree of neurodegeneration on electrocardiogram is > 95%. Surgery may include facial nerve exploration, decompression, nerve anastomosis, or nerve grafting [14]. No cases of delayed facial paralysis due to compression of the facial nerve by electrodes were found in overseas literature. Two cases were encountered in our hospital, both of which were Mondini inner ear deformity and middle ear deformity, one of which was associated with congenital fusion of the cervical vertebrae. In one case, the facial nerve had to be exposed because of anterior displacement of the facial nerve and stenosis of the facial socket, and in the other case, the vertical segment of the facial nerve had no osseous canal.In both cases, there was a well of cerebrospinal fluid during cochlear opening, and the implantation of the electrodes was uneventful. Both patients developed incomplete peripheral facial paralysis on the second to third day after surgery. Conservative treatment was ineffective, and reoperation was performed on the 21st and 7th day after surgery, respectively. The electrodes were loosened from the saphenous fossa, and connective tissue or gelatin sponge was placed between the electrodes and the facial nerve. The facial paralysis recovered significantly on the second to third day after the exploration operation, and fully recovered one week later. Prevention of facial nerve injury: The surgeon should have a thorough understanding of the normal anatomical location of the facial nerve and the characteristics of the deformity; the imaging results should be carefully analyzed and studied before surgery; the facial nerve monitor should be used as much as possible during the surgery, especially in the case of malformation of the middle ear and inner ear; the surface of the facial nerve should be preserved as a thin layer of the bony tube during the surgery, so as to avoid direct contact with the facial nerve with the drill rods or the drill bits; the tympanic nerve can be sacrificed in the case of stenosis of the saphenous fossa if necessary; the tympanic nerve can be removed if necessary; the nerve can be removed by the use of the electrode. In cases of stenosis of the facial recess, the tympanic nerve may be sacrificed if necessary because the taste disturbance caused by tympanic nerve injury is temporary – Bhatia (2004) [15] reported that of 300 cochlear implantations in children, the tympanic nerve was sacrificed in 59 cases (20%) with no adverse effects; in cases where the facial nerve is exposed at the facial recess, the tympanic nerve may be sacrificed to avoid direct contact with the facial nerve. In cases where the facial nerve is exposed in the facial socket, the electrode should be passed close to the underside of the anvil fossa (where there is a relatively large space to keep the electrode away from the facial nerve), and the electrode should be secured appropriately to prevent movement of the electrode to the facial nerve; cochlear implantation in children should be performed by an experienced surgeon. Facial nerve irritation Facial nerve irritation is a phenomenon in which the facial nerve is stimulated by electric current, causing facial muscle twitching while the patient is using the cochlear implant normally. The incidence of facial nerve irritation is high, with Hoffman and Cohen (1995) reporting a rate of 2.71% [11]. Other reports range from 7% to 15%. Facial nerve stimulation is related to the etiology of the patient, the anatomy of the facial nerve, and the design of the electrodes. According to the prevailing view, the mechanism of action is the direct diffusion of electric current through the electrodes implanted in the cochlea and stimulation of the facial nerve, which has a labyrinthine segment that is very close to the cochlear base, and therefore very close to the electrodes in the cochlea. Temporal bone anatomical studies have confirmed that the distance between the facial nerve and the cochlear tympanic process is only (0.33 ± 0.14) mm. When Cochlear’s straight electrodes are implanted into the cochlea, electrodes 12 – 16 are the closest to the facial nerve, and therefore are the electrodes that lead to the symptoms of facial nerve irritation, which has been confirmed in many studies. It has been reported in foreign literature that the incidence of otosclerosis is higher in patients with otosclerosis, even up to 50% to 100%. The reason is that the spongy bone in otosclerosis has a much lower electrical resistance than that of normal bone, which is favorable for the dissemination of electric current. Some scholars believe that the defect of the facial nerve canal is also the cause of facial nerve irritation. Some experts also suggest that the electrode passing through the facial saphenous fossa is close to the facial nerve, which may cause facial nerve irritation when the facial nerve is exposed. Treatment and management of facial nerve irritation: (1) The vast majority of cases are resolved by adjusting the parameters of the stimulation current or turning off the relevant electrodes. The specific method is to find out the electrodes (or electrode groups) that cause facial nerve irritation one by one, and reduce the current intensity of the electrode (or electrode group) or increase the wave width of electrical stimulation; if this method fails to solve the problem, then consider shutting down the electrodes that cause facial nerve irritation, but the prerequisite is to ensure that the patient’s auditory function; (2) For cases of otosclerosis, some people in foreign countries have achieved a certain effect using fluoride treatment; (3) severe cases of facial muscle twitching can be treated by adjusting the parameters of stimulation current or turning off the relevant electrodes. (3) The severe facial twitching can be applied to local injection of botulinum toxin, but the method can only temporarily relieve the symptoms, generally need to repeat the injection once in 3 to 6 months. (4) For cases with severe facial irritation that cannot be solved by adjusting the machine, another surgery can be considered, replacing different types of electrodes. Currently, most of the electrode arrays that cause facial nerve irritation are straight electrodes. Because straight electrodes are implanted close to the outer wall of the cochlea, close to the facial nerve, and the electrode contact points of straight electrodes are ring-shaped, resulting in the outward diffusion of current; the new cochlear electrodes are pre-curved electrodes, which are implanted around the axis of the cochlea, thus increasing the distance from the facial nerve, and the pre-curved electrodes adopt half-ring electrode contact points, which reduces the outward diffusion of current. There is a case of severe facial nerve irritation after cochlear implantation, he used Cochlear CI24M electrode, after a long period of time and repeatedly reduce the current value and turn off multiple electrodes and so on can not be solved, so the listening effect is greatly affected, even so, the patient still have facial twitching when listening to the sound, it is very painful. 2 years later, we implanted Cochlear CI24 Contour electrode in the contralateral ear for the patient. Two years later, we implanted a Cochlear CI24 Contour electrode in the contralateral ear, and he had no facial nerve irritation after the surgery, with a very satisfactory auditory rehabilitation. Battmer (2006)[16] reported four cases of facial nerve irritation, all of which were due to otosclerosis, and all of which were implanted with the Nucleus mini 22 cochlear implant. All four patients had facial nerve irritation of varying degrees after surgery, which was not relieved by repeated adjustments of the machine and switching off of the electrodes. The number of electrodes used was 4, 11, 13, and 15, respectively (compared with the normal 22 electrodes), resulting in a significant decrease in speech recognition. These four patients underwent a reoperation in which the old electrodes (implants) were removed and Nucleus 24 Contour curved electrodes were implanted in the same ear without any difficulty. Since the electrode was encapsulated by scar tissue in the cochlea and formed a sinus tract after the first surgery, postoperative radiographs showed that the trajectory of the newly implanted curved electrode was the same as that of the previously implanted straight electrode. After reimplantation, the symptoms of facial nerve irritation disappeared in all four patients, all 22 electrodes worked normally, and the speech recognition rate of the patients improved significantly. This shows that replacing different types of electrodes is a better way to solve the facial nerve irritation. The main reasons for no or poor auditory response after cochlear implantation are device failure, electrode damage, electrode not implanted in the cochlea and poor function of the auditory nerve, all of which are serious complications that lead to medical disputes. While cochlear implant device malfunctions and unimplanted electrodes can be easily detected by device testing and ear X-rays (CT), it is more difficult to deal with auditory nerve malfunction. There are many causes of auditory nerve and central auditory system malfunction, including severe inner ear malformations, narrowing of the internal auditory canal, cochlear ossification, auditory neuropathy, cerebral palsy, demyelinating disorders, white matter abnormalities, and autism (which has been on the rise recently, and the consequences of which can be quite undesirable). Except in rare cases, these causes are not absolute contraindications, but can lead to serious consequences if not properly diagnosed and managed. The correct diagnosis should include a detailed history, a systematic general examination (especially neurological and pediatric) and psychological and cognitive evaluation, as well as a thorough imaging and audiological evaluation. Cranial MRI should include axial and coronal views to visualize the morphology of the brain tissue; coronal, sagittal, and axial views of the internal auditory canal to visualize the development of the auditory nerve; and thin-layer CT of the temporal bone (1 mm layer thickness) should include axial and coronal views to visualize the morphology and development of the cochlea and the internal auditory canal. Preoperative audiologic evaluation is essential because the presence of residual hearing is critical to the success of the procedure. It is not enough to perform objective audiometry before surgery, but behavioral audiometry is also required, both in the bare ear and with hearing aids. If there is no residual hearing even after amplification with hearing aids, electrical stimulation of the drum capsule should also be performed. While electrical stimulation of the drum cape is relatively easy for adults with postlingual deafness, for children with prelingual deafness, electrical stimulation of the auditory brainstem evoked potentials can be chosen. This method has already become a routine examination in some foreign hospitals, but it is not yet common in China due to the limitation of technical equipment and other conditions. This paper was published in 2007, and is now widely available in China. The majority of cochlear implant surgeries in China are performed on children. The high cost of cochlear implant devices and the high expectations of parents make the surgery risky and stressful, and the consequences of complications are unimaginable. Nevertheless, as long as the preoperative evaluation is done carefully and every detail of the surgery is completed, with the accumulation of surgical experience, complications can be avoided and minimized, and most of them can be corrected with appropriate measures.