10 Subtotal Petrosectomy in Cochlear Implantation In some specific situations in cochlear implant (CI) surgery, a different surgical technique is necessitated. The objective of subtotal petrosectomy (SP) with closure of the external auditory canal and eustachian tube, in combination with obliteration of the cavity with abdominal fat, is to isolate the cavity from the external environment.1,2 An additional reason for using this technique is to obtain easier access to and better visibility of the middle ear and cochlea.3 The decision to perform SP is not taken lightly when normal hearing is still present, but in a cochlear implant candidate this consideration is of importance only if residual hearing is present and electroacoustic stimulation is intended. Subtotal petrosectomy is easy to combine with cochlear implantation in the same procedure and should be among the surgical options in cochlear implant surgery. In general the objectives of subtotal petrosectomy are • To deal with chronic infections of middle ear or cavity • To minimize cerebrospinal fluid (CSF) leakage and/or the risk of meningitis • To reduce the risk of extrusion of the array • To provide better access and visibility Indications for a subtotal petrosectomy combined with cochlear implantation • Chronic otitis media/cholesteatoma/osteoradionecrosis of the temporal bone • Presence of a radical cavity/canal wall down technique • Cochlear ossification/obliteration • Inner ear malformations • Fracture of temporal bone with involvement of the otic capsule • Sometimes in revision surgery • Unfavorable anatomical conditions • Skull base lesions, with preservation of the cochlear nerve and cochlea In certain skull base cases with preservation of the cochlear nerve and cochlea, the last indication mentioned above, cochlear implantation is a possibility for hearing revalidation. The approaches are a combination of the technique of subtotal petrosectomy with obliteration of the cavity in combination with the skull base procedure. These are discussed in Chapters 16 and 17. For all the indications mentioned, the patient follows the same route with the same inclusion criteria for cochlear implantation as used in patients without the need for SP; this includes extensive audiometric testing and evaluation by a multidisciplinary team, which finalizes the decision to implant or not to implant. The most important risks of cochlear implantation in patients with chronic otitis media are represented by returning infection leading either to labyrinthitis or meningitis or to extrusion of the implant. The latter can be either extrusion of the electrode array out of the cochlea or through the tympanic membrane, or breakdown of the retroauricular skin covering the receiver-stimulator.4–6 The fact that the cochlear implant might be introduced through a contaminated field during a single-stage procedure has to be considered. In chronic suppurative otitis media, tympanoplasty or tympanomastoidectomy in the same procedure or in a staged procedure is the alternative option, but still with the risk of recurrence of disease.4–9 In case of recurrence of disease, revision surgery in the presence of a CI is always a challenge accompanied by a serious risk of accidently sacrificing the CI during the procedure. It is difficult, if not impossible, to spare the CI during the revision procedure while at the same time performing radical surgery with removal of all pathology. On the other hand, a staged procedure means postponing the cochlear implantation, which is not always favorable. In patients with cholesteatoma of course this has to be removed meticulously, but they can be operated in a single-stage procedure when the surgeon is convinced of total removal of all disease and matrix. In case of doubt about total removal, a staged procedure, that is, second-look surgery in combination with cochlear implantation after 6–12 months, is recommended. However, in cholesteatoma surgery there is never an absolute guarantee of total removal of disease; residual or recurrent cholesteatoma might return after 12 months or even longer. In both types of pathology (chronic otitis media with/without cholesteatoma) subtotal petrosectomy gives more certainty of removal of all disease.2,10,11 However, radiologic follow-up remains necessary due to the risk of residual cholesteatoma in the obliterated cavity. In addition, the packing of the eustachian tube during SP avoids any connection with the nasopharynx, excluding infections from contact with the middle ear and cochlear implant. An atelectatic middle ear is common in chronic otitis media and may lead to the development of cholesteatoma, one should therefore consider performing an SP in these cases.7 One might also consider SP in patients with a cleft palate or other reasons for impaired eustachian tube function.5 In case of osteoradionecrosis the blood supply to the temporal bone is compromised, with bone necrosis as a result. This pathology can be treated with local débridement, local antibiotics, and hyperbaric oxygen; sometimes surgical removal of bone sequesters is necessary. Cochlear function often decreases over time due to the irradiation of tonsillar, nasopharyngeal, or parotid tumors12; this can result in bilateral hearing loss with or without bilateral osteoradionecrosis. Management of these cases can be challenging, but an ear without any infection and rehabilitated with a cochlear implant is not an impossible end result.13 Although some suggest obliteration with a muscular flap instead of fat,13 SP in combination with a cochlear implant seems a reasonable solution in these rare cases. Early attempts to insert the CI in a radical cavity/canal wall down procedure resulted in a high rate of complications, mainly extrusion of the array through the very thin epithelial lining of the cavity.1,4,9,14 Also, cavities are in direct contact with the external environment and can easily and repeatedly become infected. These patients usually need cleaning of the cavity once or twice a year, and this outpatient procedure can lead to damage of the epithelial lining with potential risk to the implant. Infections of the cavity involve a higher risk of developing labyrinthitis and meningitis and of implant extrusion. Although there are different techniques for covering the array (using muscle or cartilage) and also a technique with closure of the external ear canal and eustachian tube without abdominal fat obliteration,15 we feel that SP with abdominal fat is the safest and most permanent solution in these cases. Knowledge of this technique and consensus for adopting it in previous canal wall down procedures are growing. More information on cochlear implantation in chronic otitis media or a previous radical cavity can be found in Chapter 14. A partially or totally obliterated cochlea can be present as a result of16–20 • Bacterial meningitis • Autoimmune inner ear disease • Fracture of the labyrinth/intracochlear hemorrhage/persistent perilymphatic fistula • Chronic middle ear or cavity infection • Loss of labyrinthine blood supply (e g, after translabyrinthine surgery) • Otosclerosis In the presence of such pathology, a drill-out procedure of the cochlea would be the first step in hearing revalidation, because it is expected that cochlear implantation will give better outcome than hearing restoration with a possible auditory brainstem implant (ABI). Theoretically, the drill-out procedures may be performed through a posterior tympanotomy approach. However, this may result in a challenging and risky situation, because the narrow approach does not permit control of all landmarks and makes it difficult to perform surgical maneuvers. A dangerous possible complication of a drill-out procedure is damage to the carotid artery, situated in close relationship to the most anterior part of the basal and middle turns.21–24 The canal wall down technique in SP offers an unobstructed view of all middle ear anatomy and, if required, offers the possibility to identify additional structures such as the carotid artery and jugular bulb, making damage less likely. The more open approach offers the opportunity to perform safer maneuvers with better access. Unfortunately, not all attempted drill-out procedures lead to successful implantation as the cochlear lumen cannot always be found. It is therefore advisable to undertake these difficult CI cases in a center where conversion to ABI surgery can be done during the same procedure once the drill-out procedure has failed.25 More information on drill-out procedures can be found in Chapter 11. There are three reasons to perform cochlear implantation using the SP technique in inner ear malformations. First, there is the need to identify the available landmarks; aberrations of middle ear structures such as the round window niche and facial nerve can be present. Second, the possibility of an intraoperative CSF leak/gusher is higher in inner ear malformations.26–31 In the literature, up to 45% of the CI cases with various kinds of malformations resulted in a CSF leakage during surgery.32 The CSF leak/gusher is best controlled by obliteration of the eustachian tube orifice with removal of all peritubal cells, closure of the external ear canal, and obliteration of the cavity. Third, in inner ear malformations the risk of developing meningitis during the patient’s lifetime is higher than in the normal population, even without CI surgery.28 In some inner ear malformations (especially in incomplete partition types I and type III), a cystic structure filled with perilymph/CSF may be present at the oval window niche, with the bony footplate being incomplete.28,32,33 SP is recommended to reduce the lifelong risk of meningitis in these cases, especially for the more severe malformations. With common cavity malformations the introduction of a straight electrode is easiest done via a transmastoid translabyrinthotomy technique; however, in this type of malformation we also advise combination with subtotal petrosectomy because of the risk of postoperative gusher and higher risk of meningitis during the patient’s lifetime.34 More information on the approach for each type of malformation can be found in Chapter 15. In severe trauma leading to a fracture of the otic capsule with loss of sensorineural hearing, a cochlear implantation is a possible solution for hearing revalidation when the cochlear nerve is still intact and the cochlear lumen is patent.35–39 As fractures of the otic capsule heal not with formation of new bone but only by fibrous bonding, a lifelong risk of developing meningitis is present even without cochlear implantation. This risk remains high with a standard CI approach.40 In these cases SP in combination with cochlear implantation is mandatory. Additionally, this procedure will also give better access and overview of the fractured temporal bone. As fractures of the otic capsule can lead to ossification of the cochlea, urgent evaluation for cochlear implantation, including urgent imaging, is necessary in case of bilateral fractures (see Chapter 11). More information on fractures can be found in Chapter 17. Some revision cases in which the previous surgeon was (repeatedly) unable to correctly insert the array might be better treated by means of SP, which allows an unobstructed view of all the middle ear landmarks as well as opportunities for better drill-out. In cases with a very anteriorly positioned sigmoid sinus or other anatomical limitations, a posterior tympanotomy will not be easy to perform; changing to a canal wall down approach will give much easier access in these cases. In the presence of a meningocele or preexistent CSF leakage, SP + CI would also be the preferred treatment.3,41 The absolute contraindication for subtotal petrosectomy is the presence of residual hearing to be spared and utilized by means of electroacoustic stimulation.42 For this technique the speech processor is augmented with an intrameatal (acoustic) hearing aid (see Fig. 9.1). An open external auditory canal is mandatory for the acoustic part of this stimulation; this is no longer available after SP surgery. Relative contraindications can arise in the presence of active purulent infection of middle ear or cavity. Especially in infections with multidrug-resistant microorganisms or tuberculosis, this is of importance. The procedure can be staged when the risks of developing meningitis or failure to control the infection is considered too high. In these cases separate SP with total eradication of the infection under antibiotic coverage has to be performed. After 3 to 6 months, when there is no sign of infection, the obliterated cavity can be reopened and the cochlear implantation can be pursued. In case of bone involvement (osteomyelitis), nuclear scanning can be used to follow up on the infection.43 The use of fat instead of muscle to obliterate the cavity makes landmark identification easier during second-stage surgery, due to the fact that there are fewer adhesions. The same principle applies to cholesteatoma cases when the surgeon is not sure of total removal of the disease. The surgery requires proper positioning, more extensive hair shaving than in normal cochlear implantation, and facial nerve monitoring. The use of antibiotics, the required instruments, monitoring, and other perioperative management is discussed in Chapter 4. Surgical steps in subtotal petrosectomy with cochlear implantation include: • Skin incision • Anterior pedicled flap • Blind-sac closure of the external meatus • Removal of the skin of the lateral portion of the external ear canal • Canal wall down mastoidectomy • Removal of the skin of the medial portion of the external ear canal with annulus, malleus, and incus • Exposure and closure of the eustachian tube • Drill-out of the receiver well • Harvesting of abdominal fat • Exposure of the round window • Insertion of the cochlear electrode • Electrophysiologic testing • Fixation of the implant • Obliteration of the cavity with fat • Closure A wide retroauricular incision along the hairline gives best access; the pinna and subcutaneous tissue should be reflected anteriorly for the work on the blind-sac closure. A broad, anteriorly pedicled periosteal or subcutaneous flap is created, following the classic subtotal petrosectomy approach.44 It is left attached anteriorly and is used for closure of the second layer of the external auditory canal. Cartilage of the tragus can additionally be used as an extra layer. A superiorly or inferiorly pedicled flap can also be used, depending on amount of tissue and the preference of the surgeon. The skin and cartilage of the external auditory canal are transected in the plane beneath the pedicled flap. Anteriorly a clamp can be passed underneath the subcutaneous tissue anterior to the tragal cartilage for protection of the vascular capsule of the parotid gland and branches of the facial nerve. More lateral transection of the skin and cartilage of the external ear canal pose less risk to the parotid capsule and facial nerve branches. The skin of the lateral part of the external canal is elevated from the cartilage for a length of 1 cm and is subsequently everted. Use of a microscope or ocular loupes will make this easier. The skin edges, now on the outside, are sutured with resorbable 4–0 sutures. The second layer consisting of subcutaneous tissue or tragal cartilage is now folded back and sutured to the anterior rim of the remaining cartilage. The skin of the external ear canal is elevated up to the level of the annulus. The lateral part of the skin is removed. The more medial part is removed in a later stage together with the tympanic membrane, annulus, and ossicles. After mobilizing the subcutaneous tissue and temporal muscle, now the canal wall down mastoidectomy can be drilled, removing as many pneumatized cells as possible. Some surgeons also remove the mastoid tip. The medial remnant of the skin of the external ear canal with the annulus is now elevated. The incudostapedial joint is separated. Skin, annulus, and tympanic membrane with malleus and incus can now be removed en bloc to reduce the risk of leaving some skin behind. Bone around the eustachian tube orifice can be removed. Peritubal cells should also be eradicated because they can form the route for CSF to the nasopharynx bypassing the closed eustachian tube. The mucosal lining of the eustachian tube entrance is mobilized and folded back into the eustachian tube. The mucosa can be cauterized with bipolar coagulation, after which the orifice is filled with muscle, cartilage, and bone wax to close it off from the tympanic cavity. A layer of fascia can be used as a second layer. Additionally, all mucosa is removed from the tympanic cavity; this might give better adhesion of the fat to the bone and also prevents mucosal cysts. Depending on the type of implant a receiver well is drilled or just a pocket underneath the temporal muscle is created. Abdominal fat is harvested just below and medial to the level of the spina iliaca anterior using a horizontal incision of ~2 cm. Preferably the fat is harvested on the left side to avoid confusion with an appendectomy incision in future. Hemostasis is important, as many small vessels run in the fat, and is performed using bipolar coagulation or sutures. The abdominal wound is closed in two layers. Similarly to normal cochlear implantation, the round window niche is widened by removing the superior and anterior inferior overhangs by drilling. Either the round window is inserted comparably to standard cochlear implantation, or drill-out of the cochlea is undertaken, depending on the pathology. The techniques of drill-out surgery can be found in Chapter 11. Impedances, stapedial reflexes, and neural response telemetry (NRT) are measured. More information on eletrophysiologic testing can be found in Chapter 4. The electrode array is fixated with a small piece of fascia in the round window niche. The receiver stimulator is fixated with a nonresorbable suture, through two drilled bony canals, or by screws depending on the type of implant. The temporal muscle covers and protects the receiver-stimulator and remains at its anatomical location. The cavity is then filled with the abdominal fat, which is cut in small pieces. Fibrin glue can be used. The wound is closed in two or three layers using non-resorbable sutures. The periost flaps and superiorly the temporal muscle, which remains in its anatomical position to cover and protect the receiver stimulator, cover the fat. A head bandage is carried for at least 48 hours. Fig. 10.1.1 After the wide retroauricular incision that extends superior and inferior more anteriorly for better access and possibly to reflect the pinna, the skin and cartilage of the external ear canal (EAC) are transected. Transection should not be performed too medially as the skin is thinner here, making dissection of the lateral part more difficult.
10.1 Indications
10.1.1 Chronic Otitis Media/Cholesteatoma/Osteoradionecrosis of the Temporal Bone
10.1.2 Presence of a Radical Cavity/Canal Wall Down Technique
10.1.3 Cochlear Ossification/Obliteration
10.1.4 Inner Ear Malformations
10.1.5 Fracture of the Temporal Bone with Otic Capsule Involvement
10.1.6 Revision Cases
10.1.7 Unfavorable Anatomical Conditions for Posterior Tympanotomy
10.2 Contraindications
10.3 Surgical Procedure
10.3.1 Skin Incision
10.3.2 Anterior Pedicled Flap
10.3.3 Blind-sac Closure of the External Meatus
10.3.4 Removal of the Skin of the Lateral Portion of the External Ear Canal
10.3.5 Canal Wall Down Mastoidectomy
10.3.6 Removal of the Skin of the Medial Portion of the External Ear Canal with Annulus, Malleus, and Incus
10.3.7 Exposure and Closure of Eustachian Tube
10.3.8 Drill-out of the Receiver Well
10.3.9 Harvesting of Abdominal Fat
10.3.10 Exposure of the Round Window
10.3.11 Insertion of the Cochlear Electrode
10.3.12 Electrophysiologic Testing
10.3.13 Fixation of the Implant
10.3.14 Obliteration of Cavity with Fat
10.3.15 Closure
Case 10.1 Surgical Steps
Subtotal Petrosectomy with Cochlear Implantation (Fig. 10.1.1–Fig. 10.1.38)
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