Subtotal Petrosectomy in Cochlear Implant Surgery: Our Experience

Abstract

Aims

Subtotal petrosectomy (SP) with cochlear implant (CI) is required in certain specific situations in the management of patients who are candidates for cochlear implants. To study and review the indications, surgical issues, and complications of this procedure.

Materials and Methods

Retrospective review of all patients who underwent subtotal petrosectomy with cochlear implant during the period January 2010–December 2016 at a tertiary care and referral centre.

Results

19 patients underwent 20 subtotal petrosectomy with cochlear implant during this period. One patient had simultaneous bilateral implantation. The indications were previous mastoid cavity in 7 patients, 5 patients had chronic otitis media, inner ear malformations in 3,ossified cochlea in 3 and unfavourable anatomy in 2 patients. Fat or musculoperiosteal flaps were used to obliterate the cavity. Ninety percent of patients underwent single stage surgery and ten percent underwent two stage procedure.Complications were seen in three patients (15%).

Conclusion

SP helps in isolating the cavity from external environment after removal of disease, improves the exposure and access, reduces risk of infection and cerebrospinal fluid (CSF) leaks and facilitates CI. Meticulous surgical technique will reduce the complications and long term follow up is needed to detect entrapped cholesteatoma. Subtotal petrosectomy with blind sac closure of external ear canal is required in certain specific situations. It is a safe and effective surgery with acceptable rate of complications.

Introduction

Cochlear implantation has now become the standard and established treatment for auditory rehabilitation in severe to profound hearing loss patients with a low and acceptable complication rate [1, 2]. Subtotal petrosectomy (SP) is a surgical procedure that can be employed in difficult cases of cochlear implantation (CI). The technique of SP as first described by Fisch and Mattox involves drilling and eradication of all mastoid cells, removal of middle ear mucosa, tympanic membrane, skin of external auditory canal along with closure of Eustachian tube and external ear canal with obliteration of cavity with fat or muscle [3].

Bendet et al. and Issing et al. for the first time described the role of SP in patients requiring cochlear implantation [4, 5]. SP involves isolation of the surgical cavity from the external environment giving the advantage of low risk of infections, better sealing of cerebrospinal fluid (CSF) leaks reducing the risk of meningitis. Additionally it improves the access and visibility of round window and promontory in difficult situations requiring drill out. We present our data on subtotal petrosectomy with cochlear implantation from a single cochlear implant centre. The aim of this study was to present our data and review the indications for SP with CI, review the surgical issues and complications.

Materials and Methods

This retrospective study was conducted at a tertiary care and CI referral centre, Chennai. All patients between January 2010 and December 2016 who underwent CI along with SP were included in the study. The CI database was used to record the clinical information which included age, gender, aetiology of hearing loss, the indication for subtotal petrosectomy, imaging findings and surgical features. The surgical details recorded included the number of surgical stages, post-operative complications and management. All patients underwent an otological examination, preoperative comprehensive audiological assessment and multidisciplinary team review to determine their suitability for cochlear implantation. High resolution computed tomography (HRCT) of temporal bone and Magnetic resonance imaging (MRI) was done in all patients. The study was approved by the institutional ethical committee.

Surgical Technique

The surgery is performed by the post auricular route. An anteriorly based pedicled flap is raised. The External auditory canal (EAC) is completely transected and the skin is everted to perform a blind sac closure. The subcutaneous tissue and tragal cartilage is used to reinforce the blind sac with a second layer. The skin of EAC is elevated upto annulus and removed along with tympanic membrane, incus and malleus. Canal wall down mastoidectomy is performed to remove as many pneumatised cells as possible. The Eustachian tube is packed with muscle after inverting the mucosa. The bed is drilled for receiver stimulator of implant. The electrode is inserted through round window if present or drill out is done in ossification cases. The cavity is packed with abdominal fat or temporalis muscle flap and the wound is closed in two layers.

In cases of previous cavity, meticulous elevation of cavity lining should be done to avoid leaving any remnant debris which would leave a potential risk of cholesteatoma in a obliterated cavity. In patients with cholesteatoma, complete removal of disease should be done before inserting the implant.

Results

During the period between Jan 2010 and Dec 2016, 19 patients underwent subtotal petrosectomy with cochlear implantation and 20 SP with CI were performed. One patient had simultaneous bilateral implantation. The youngest patient was 1 year old and oldest was 59 years. Out of 19, 8 (42.1%) patients were male and 11 (57.9%) were females. The patient demographics are outlined in Table 1. The cochlear implant was placed in right ear in 11 (55%) patients and in 9(45%) patients in left ear. Follow up range was 12–84 months. Two patients with cholesteatoma underwent two stage surgery, rest all other patients were operated in single stage in this cohort (Table 1).

Table 1.

Demographic data (n = 19)

Age (Mean)	16.8 years
Sex
Male: Female (n)	0.73:1.00
Follow up (mean)	37.2 months

07 (35%) patients who underwent SP with CI had previous mastoid cavity, the most common indication in our study (Table 2). Chronic otitis media was the second most common indication for performing the procedure in 5 patients (25%).Out of these, 2 patients had cholesteatoma, 1 patient had Tympanic membrane(TM) perforation and 2 patients had atelectatic TM. In 15% patients, ossification of cochlea was present with etiology as meningitis in 2 cases and third patient had advanced otosclerosis. One patient underwent middle turn cochleostomy because of complete basal turn ossification (Fig. 1).

Table 2.

Indications of 20 SPs with CI in 19 patients

Indication for subtotal petrosectomy	No
Previous mastoid cavity	7
Chronic Otitis media	5
Cholesteatoma	2
Atelectatic TM	2
TM perforation	1
Inner ear malformations	3
Cochlear ossification	3
Unfavourable anatomy	2

TM tympanic membrane, SPs subtotal petrosectomies, CI cochlear implant

Fig. 1.

Middle turn cochleostomy with electrode insertion in one patient

Inner ear malformations were the reason for SP with CI in 15% patients. Two patients had Incomplete partition 2(IP2) and one hypoplastic cochlea. Two (10%) patients with unfavourable anatomic conditions like contracted sclerotic mastoid with anteriorly placed sigmoid sinus were converted to SP to give a better access for cochlear implantation (Fig. 2 and Table 2).

Fig. 2.

Subtotal petrosectomy with cochlear implant in a patient with contracted sclerotic mastoid and anteriorly placed sigmoid sinus

Obliteration of cavity was performed with fat in six ears and with vascularised musculoperiosteal flaps in fourteen ears. (Fig. 3) Out of these 20 procedures, 3 (15%) patients had complications (Table 3). One patient had device failure for which explantation and reimplantation was done. One patient had breakdown of EAC blind sac closure who was explanted and reimplanted after six months and third had wound infection with exposed implant receiver stimulator which was repositioned after wound debridement (Table 3).

Fig. 3.

Temporalis muscle flap for obliteration and covering the electrode array

Table 3.

Clinical data, complications and follow up of 19 patients who underwent subtotal petrosectomy with cochlear implant surgery

Case No.	Age (Years)	Sex	Surgical stages	Fat or muscle flap	Complication	Management	Follow up (months)
1	12	M	1	Fat			84
2	2	F	1	Muscle Flap	Post operative infection with partial exposed receiver	Wound debridement and repositioning of receiver	24
3	5	F	1	Muscle Flap			60
4	14	M	2	Muscle flap			13
5	33	F	1	Fat			24
6	3	F	1	Muscle flap			76
7	42	M	1	Fat			80
8	36	M	1	Fat			84
9	8	F	2	Muscle Flap			72
10	5	F	1	Muscle flap	Blind sac closure breakdown and exposed electrode	Explant and reimplant after 6 months	48
11	7	F	1	Muscle flap			36
12a	42	M	1	Fat	Device failure	Explant and reimplant	24
13	59	M	1	Fat			22
14	5	F	1	Muscle flap			28
15	1	F	1	Muscle flap			18
16	2	M	1	Muscle flap			18
17	4	M	1	Muscle flap			16
18	5	F	1	Muscle flap			14
19	35	F	1	Fat			16

^aOne patient had bilateral simultaneous implantation, M male, F female

Discussion

Indications of CI have expanded tremendously over the last few years both from an audiological and clinical point of view, since the first CI in 1960 [6]. In the early years, middle ear diseases and anatomical variations were the limiting factor for successful cochlear implant surgery [7]. For the first time Parnes et al. used SP with CI to rehabilitate patients who were not considered as candidates for CI [8].

SP with CI in a previous canal wall down cavity helps to isolate the cavity and diminish the risk of infections and extrusions. In a previous cavity, a strong protective cover layer is needed to protect the implant from infection and extrusion. Various authors have advocated different techniques like reconstruction of posterior canal wall or partial obliteration of cavity to protect the electrode using various flaps [9–11]. However, insertion of CI in a radical cavity/canal wall down procedure has led to complications like infection and extrusion of implant array through the very thin lining of cavity [5, 12, 13]. SP is the safest and most permanent solution to prevent these complications. Seven patients in our study had open cavities for which SP with CI was done. Two patients also had complete ossification of basal turn so middle turn cochleostomy was done in these patients for electrode insertion. One patient had device failure who underwent explant and reimplantation.

Cochlear implantation in patients of chronic middle ear disease is complicated and challenging. The main aim of CI surgery in these patients is eradication of disease, and creating a closed and sterile cavity [12]. This will help in sealing off the cochlear implant from the external environment and reducing chances of infection and extrusion [14]. The debate whether patient with chronic middle ear disease should undergo single or two stage continues.Many authors have advocated two stage procedure in the presence of infection [5, 13, 15]. Some groups have advocated performing CI after 3 or 6 months of myringoplasty or tympanoplasty with the aim of achieving a stable and dry middle ear status for the CI [10, 15]. However, many issues need to be considered before staging the procedure like recurrence of disease, revision surgery with CI insitu which is a challenge and threat to the safety of CI. Staging the disease also delays the implantation which is not desirable. Similarly in cases with cholesteatoma patient will have to wait for 6–12 months for CI and may still have residual cholesteatoma after 6 to 12 months and recurrent cholesteatoma even later [14]. SP provides better exposure which helps in better clearance of disease with aggressive drilling and many authors have recommended performing SP with CI in a single stage [4, 14]. Having said that if there is any doubt regarding complete eradication and removal of cholesteatoma, procedure should be staged. In our series of patients, 2 patients had cholesteatoma and CI was performed in two stages with a gap of 6 months without any complications.

An Atelectatic TM is always a serious threat in the development of cholesteatoma over many years, performing a SP with CI must be considered in them [12]. We had 3 patients of Atelectatic TM,one was already implanted and had a device failure. During reimplantation the TM was found to be completely atelectatic and adherent to the electrode,leading to perforation in TM while separation. All patients were implanted in single stage without any complications.

Inner ear malformations (IEM) are associated with an abnormally positioned facial nerve, or cerebrospinal fluid (CSF) or perilymph ‘gusher’ [16]. Easy identification and better exposure of anatomical landmarks like facial nerve trajectory, high chances of CSF or perilymph gusher, sealing off Eustachian tube and isolating cavity to reduce the possibility of CSF leak and meningitis are the reasons to consider SP with CI in patients with inner ear malformations [14]. In our series of 3 patients with IEM, two patients had intaoperative CSF gusher. One patient with hypoplastic cochlea also had abnormal facial nerve course with sclerotic mastoid and anteriorly placed sigmoid sinus making the access for posterior tympanotomy difficult. No patient had any episode of meningitis in the follow up.

Cochlear ossification which requires drill out procedures may be performed through standard posterior tympanotomy approach in combination with or without transcanal approach [17]. Some authors have advocated SP in most of these cases to avoid the damage to critical structures and landmarks like facial nerve, jugular bulb and internal carotid artery [14]. We had 3 cases of cochlear ossification,two as a result of meningitis and one advanced otosclerosis. One patient needed a middle turn cochleostomy as the whole basal turn was ossified.

Two patients without any prior history of middle ear disease in our study had very sclerotic,contracted mastoid which was assessed on the pre-operative CT scan. Along with that they also had an anteriorly placed sigmoid sinus which made the access to the round window via a posterior tympanotomy approach difficult and converting these patients to subtotal petrosectomy improved access and facilitated safe cochlear implantation. Wide exposure of the promontory in these unfavourable anatomical situations has been supported by other groups [4, 12].

SP with CI has also been proposed for fractures of temporal bone with intact cochlear nerve [14], as fractures of otic capsule heal just by fibrous union rather than new bone formation, which carries a lifelong risk of meningitis with or without CI [18]. There was no patient with fractures of temporal bone needing SP with CI in this study.

The only absolute contraindication for SP with CI is the presence of residual hearing and used by means of electroacoustic stimulation as closure of the EAC hinders the acoustic stimulation through the canal [19]. Relative contraindications are active infection of middle ear or cavity, where staging can be done. Similarly, in cholesteatoma if there is any doubt regarding complete excision of matrix, CI can be performed in two stages.

Obliteration of cavity has been described by both vascularised musculoperiosteal flaps [20] and abdominal fat [14], and one does not seem to confer a particular advantage over the other. In our series, both were used without any specific issues or complications.

Fat infection, blind sac closure breakdown and entrapped cholesteatoma are risks associated with SP. Also, abdominal wound haematoma and infection are additional risks. We had one patient of blind sac closure breakdown which got infected and finally explanted. One important consideration must be given to the risk of entrapped cholesteatoma in a obliterated cavity. Long-term follow up of these patients is recommended, as late complications can occur. However, the detection of recurrent cholesteatoma is limited clinically and radiologically by the blind sac closure of the external auditory canal and the artefact caused by the cochlear implant making MRI redundant. Soft tissue expansion or bony erosion in sequential CT scanning has been advocated as an indicator of recurrent cholesteatoma [21].

Distinguishing between soft tissue and cholesteatoma reliably is very difficult. Studies with long term follow up using radiological investigation has failed to detect cholesteatoma postoperatively [21, 22]. We followed up our patients and high resolution CT scanning was performed only when they presented with suspicious signs or symptoms. So far, we have not had any case of residual cholesteatoma after SP with CI.

In this study, out of 20 SPs with CI, 3 patients had complications. One patient had device failure for which explantation and reimplantation was done. Surgery related complication was found in two (10%) patients, one had breakdown of EAC blind sac closure and other had wound infection with exposed implant for which revision surgery with repositioning was done. Another study showed a complication rate of 6% in 32 patients of SP with CI [14]. Issing et al. had a complication rate of 21% in their study with three patients having temporary facial palsy, a retroauricular fistula and inflammation requiring explantation [5]. Considering the procedure related complication rate of 10% in our study with a mean follow up of 37.2 months, SP can be considered to be a safe and effective surgery in these difficult situations with a meticulous surgical technique.

Conclusion

Subtotal petrosectomy with blind sac closure of external ear canal is required in certain specific situations. Meticulous surgery with removal of all disease, complete sealing off the external ear canal and covering the implant to prevent extrusion is key to a successful surgery. In addition, excellent exposure and access in difficult anatomy and sealing of cavity to reduce risk of meningitis and CSF leaks makes it a suitable alternative which has allowed CI in patients considered ineligible earlier. It is a safe and effective surgery with an acceptable rate of complications. Long term follow up is recommended in view of late complications.

Compliance with Ethical Standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethics Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study formal consent is not required.

Human/Animal Rights Statement

This article does not contain any studies with animals performed by any of the authors.