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Cochlear implant surgery: Minimally invasive technique
Operative Techniques in Otolaryngology (2005) 16, 74-77
Cochlear implant surgery: Minimally invasive technique Joseph B. Roberson, Jr, MD From the California Ear Institute, E. Palo Alto/San Ramon/Oakland, California; and the Let Them Hear Foundation, Palo Alto, California. KEYWORDS Cochlear implant; Surgical technique; Sensorineural hearing loss; Auditory rehabilitation; Minimally invasive surgery
Minimally invasive cochlear implant surgery has become the mainstay of most experienced centers. Although more difficult for surgeons to perform than traditional techniques, advantages include reduced blood loss and tissue trauma, improved cosmesis, less hair removal, and reduced surgical times. Patient satisfaction with the smaller incision reflects positively on the operative surgeon when compared with traditional techniques. Bilateral implantation and younger age at implantation make the advantages of minimally invasive techniques more appealing. Minimally invasive techniques are being extended to include entrance to the inner ear via cochleostomy as hearing preservation cochlear implant surgery comes into existence. This article gives a detailed description of surgical technique. © 2005 Elsevier Inc. All rights reserved.
Food and Drug Administration approval of cochlear implant devices occurred for adults in 1985 and for children in 1990. Currently, more than 80,000 devices have been implanted in patients with a variety of surgical techniques. As a general trend, incisions have become smaller, procedures shorter, and healing faster because of less surgical trauma created with evolving minimally invasive techniques. Currently, except for patients younger than 10 years, the vast majority of patients are discharged the day of their procedure on an outpatient surgery basis. Clear evidence exists showing the use and improved outcomes associated with implantation at younger ages in congenitally hearing impaired individuals. Current Food and Drug Administration guidelines include cochlear implantation at 12 months of age. Minimized blood loss is a worthy goal in these neonates. Many centers, including our own, are implanting appropriate candidates younger than one year. Guidelines for minimum age of implantation will continue to decrease as they have over the last 14 years. Several other trends make the minimally invasive cochlear implant technique appealing. First, concurrent or sequential bilateral cochlear implantation is proving beneficial in a growing number of patients. On a worldwide basis, more than 3500 recipients are using a cochlear implant in each ear. Second, manufacturers have reduced the Address reprint requests and correspondence: Joseph B. Roberson, Jr, MD, CEO, California Ear Institute, 1900 University Circle, Suite 101, East Palo Alto, CA 94303. E-mail address: [email protected]. 1043-1810/$ -see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.otot.2005.05.005
size of implanted instrumentation with successive generations of their products. Future changes will allow continued reduction in implanted device size, allowing newer adaptations to existing surgical techniques. Third, hearing preservation is possible with insertion of both short and standard electrode length cochlear implants, and early data indicate advantages with both electrical and mechanical stimulation. It is also anticipated that totally implantable cochlear implants will make their entrance during the next several years. These devices will increase in size compared with currently existing cochlear implants. Minimally invasive techniques offer significant advantages for patients, while being technically harder to perform for surgeons. A patient having a small, cosmetically appealing incision and minimal/no hair removal with quick and uncomplicated healing is a goal best achieved with this type of technique. This technique has been practiced with minor modifications since 1994 and is the subject of a previous report we believe to be the first dealing with minimally invasive cochlear implant surgery.1 Surgical time has averaged 56 minutes over our last 50 unilateral implants in adults and children. Concurrent bilateral implantation averages 92 minutes.
Surgical technique Psychologic preparation with a full and complete explanation for adults is even more important for the hearing im-
Roberson
Cochlear Implant Surgery: Minimally Invasive Technique
paired than for most patients. Play therapy is used at our institution before cochlear implantation to communicate to young children the events upcoming. It is our practice to involve other children who have cochlear implants in the “play surgery” within several days of the procedure. In many instances, the practice replaces a feeling of fear with one of expectation and excitement. The night before the procedure, the patient’s hair is washed with antibacterial solution. Pediatric patients receive, 1 hour prior to surgery, premedication in the form of oral midazolam with dosages of 0.5-0.75 mg/kg mixed with liquid acetaminophen. Induction is performed with inhalational anesthetic agents, and an attempt is made to avoid injections and intravenous lines until after the child is asleep. Adults have an intravenous line started in the holding area and are given anxiolytic medications as the anesthesiologist judges necessary. Paralyzing agents are avoided to facilitate facial nerve monitoring. Intravenous antibiotics are given just after induction of anesthesia and intubation before incision. Patients younger than 5 years, older than 70 years, or those with an increased risk of infection (eg, insulin dependent diabetics) are given per os antibiotics for 5 days after the procedure. Patients with a tympanostomy tube in place are also given topical antibacterial drops for the same period. Patients younger than 2-3 years have a towel folded and placed under the shoulders to extend the neck. Most adults are positioned with the head on the table without a head holder. Patients with limited neck mobility and those receiving bilateral implants have the head placed on a gel ring of minimal size to protect the neck from hyperextension. The Medtronic NIM-Response Nerve Integrity Monitoring System (Medtronic, Inc, Minneapolis, MN) is used to perform continuous intraoperative monitoring of facial nerve function in unilateral or bilateral cases. Fixed paired electrodes are placed in the orbicularis oris and orbicularis oculi muscles, with ground wires placed in the upper chest skin. In bilateral implantation cases, special attention is given to allow head mobility after draping. To accomplish this goal, we prepare the entire head and sequester the facial nerve monitoring electrodes, endotracheal tube, and other monitoring connectors in the midline under sterile clear drapes. As mentioned previously, a small head holder is helpful to increase side-to-side range of motion after draping. In pediatric bilateral cases, a calculation of safe ranges of blood loss is made before first incision and tracked for safety throughout the procedure. An incision is planned in the postauricular area that begins just behind the postauricular crease at the inferior end of the external acoustic meats, extending superiorly and slightly curvilinearly posteriorly for 2.5-4.5 cm per surgeon preference (Figure 1). Palpation of the mastoid tip and tympanomastoid suture line/stylomastoid foramen will avoid placing the incision directly over the facial nerve in the youngest of patients. Hair around the incision is shaved for a distance of 1 cm at the superior limb. Long hair is controlled with a rubber band and may be braided to achieve the desired effect. Medium or short hair is best controlled with the draping. Injection of equal parts of 2% lidocaine with 1:100,000 epinephrine and 0.5% bupivacaine plain are mixed, buffered with 1 mL of sodium bicarbonate solution
75
Figure 1
Adult internal device and incision placement.
per 10 mL, and injected into the proposed incision and surrounding surgical field. The proposed incision should be planned, considering several factors. First, the internal device should not be placed in an area where the external coil will be knocked off repeatedly (eg, in a car seat in a young child). Second, no portion of the incision should overlap the internal device. Third, the internal device is placed in such a way that it does not overhang the mastoid cavity. Finally, the internal device needs to be situated far enough away from the ear so that a behind-the-ear processor will not compress skin over the internal instrumentation of the implant. This situation may lead to patient discomfort or worse, skin necrosis and device exposure and explantation. The surgical site and hemicranium, including all hair, is given a vigorous scrub with antibacterial solution. Solution is kept from the external auditory canal only if a tympanostomy tube is in place. A circumferential head drape is placed and pulled superiorly until the surgical site is exposed to assist in hair retraction. The area is squared off with towels and an Ioban (3M, St. Paul, MN) or similar adhesive, and a sterile drape is placed on the towels, and exposed hair and skin to secure the arrangement. Note that the ear should be folded forward and held with the sticky drape. Drying the posterior surface of the pinna allows the drape to stick to the skin, maintaining the pinna in a position out of the surgical field. Ioban is removed carefully over the area of proposed incision. The incision is performed beveling the blade to parallel hair follicles in the superior portions of the wound. Cautery is used to divide the subcutaneous tissues and periosteum over the mastoid cortex, and into the root of the zygoma below the temporalis muscle to a point above the external auditory canal. The mastoid cortex is exposed with
76
Operative Techniques in Otolaryngology, Vol 16, No 2, June 2005
Figure 4
Figure 2
Facial recess approach, hypotympanic perspective.
elevators until the spine of Henle is identified at the margin of the external auditory canal. The tissues of the canal are elevated several millimeters beyond the spine of Henle, maintaining intact skin of the canal. A pocket is created for the internal device that is just larger than the device itself, up and behind the ear. In most patients the correct plane is between the pericranium and the bone of the skull. In the occasional patient, it will be necessary to remove muscle and connective tissue over the area of the future seat of the device. Attention is turned to the mastoid drilling, where a mastoidotomy is created anteriorly while thinning the posterior bony external auditory canal to allow the correct angle to enter the middle ear via the facial recess. The facial recess is dissected, leaving bone over the facial nerve and preserving the chorda tympani nerve. Removal of bone anterior and medial to the facial nerve is possible and preferable to expose fully the round window niche (Figure 2). A Silastic (Dow Corning, Corp, Midland, MI) model of the internal device is placed in the prepared pocket. Adjustments to the pocket are made as needed for final positioning. The seat of the device is then drilled to allow maximal flush seating of the device. Dura is exposed if needed without consequence. Diamond burrs are used to avoid dural laceration. Self-retaining retractors are removed during this step, the table is rotated toward the surgeon, and an assistant is enlisted to hold the skin with a hand-held retractor as needed. The surgeon provides most of the retraction needed with a fenestrated suction irrigator in the nondrill hand. The drilled seat is then connected to the mastoidotomy with a
Figure 3 Securing suture placement. (A and C) Adult. (B and D) Pediatric.
(A and B) Pediatric retention suture placement.
small burr to allow electrode passage after device placement. Suture retention holes are created because it is our belief a device not anchored has a higher chance of migrating postoperatively. In those patients with thicker skulls, partial depth holes are drilled and connected with cross drilling so that suture may be passed through the bony tunnel to secure the implant. In children with thin skulls, holes are created through to dura and suture placed posteriorly with a doublearmed suture from inside out (Figures 3 and 4). Hemostasis is achieved, and all bone dust is removed in preparation for final placement steps. A 0.5-1.0 mm diamond burr is selected for cochleostomy placement. Care is taken not to heat or damage the facial nerve with the rotating shaft of the burr while drilling bone away at the inferior edge of the round window membrane at the crista fenestra, thereby avoiding the insertion of the lateral basilar membrane in the cochlear hook area (Figure 5).2,3 Every attempt is made to preserve the endosteum intact to minimize intracochlear trauma. The endosteum is opened, and a saline soaked resorbable sponge is placed to prevent perilymph egress. Suction at the cochleostomy is to be avoided as it would be in a stapedotomy case. The internal cochlear implant instrumentation is then placed in the seat and pocket. The previously placed suture is then passed through the anterior suture holes and tied off the top of the device with a buried knot. (We use a 2-0 polyester suture.) The electrode is then passed via the cochleostomy in such a way as to minimize trauma to the membranous cochlea. Hearing preservation will not be possible if the basilar membrane is perforated. Different strat-
Figure 5 Facial recess surgical view. Cochleostomy placement with basilar membrane avoidance. RW, round window.
Roberson
Cochlear Implant Surgery: Minimally Invasive Technique
egies and instrumentation are available from different manufacturers designed to minimize intracochlear damage. A free connective tissue graft is taken and used to seal the cochleostomy around the electrode. Ground electrodes are placed deep to the temporalis muscle if the selected device has such an attachment. In pediatric patients, a “reserve” of electrode wire is placed in the mastoid to allow for growth. Most young patients will reconstitute the mastoid cortex with healing. This process should be considered also, so that future growth does not remove an electrode from the cochlea. Wound closure is effected with interrupted resorbable 3-0 suture, and Steri-Strip adhesive (3M) or resorbable subcuticular monofilament is used to close the skin. An
77
overnight mastoid pressure dressing is placed. Skin tapes are removed one week after the procedure.
References 1. Roberson JB Jr, Stidham KR, Scott KM, et al: Cochlear implantation: Minimal hair removal technique. Otolaryngol Head Neck Surg 122:625629, 2000 2. Stidham KR, Roberson JB Jr: Cochlear hook anatomy: Evaluation of spatial relationship of the basal cochlear duct to middle ear landmarks. Acta Otolaryngol 119:773-777, 1999 3. Briggs RSJ, Tykocinski M, Stidham KR, et al: Cochleostomy site: Implications for electrode placement and hearing preservation. 2005 (in press)
Cochlear implant surgery: Minimally invasive technique Joseph B. Roberson, Jr, MD From the California Ear Institute, E. Palo Alto/San Ramon/Oakland, California; and the Let Them Hear Foundation, Palo Alto, California. KEYWORDS Cochlear implant; Surgical technique; Sensorineural hearing loss; Auditory rehabilitation; Minimally invasive surgery
Minimally invasive cochlear implant surgery has become the mainstay of most experienced centers. Although more difficult for surgeons to perform than traditional techniques, advantages include reduced blood loss and tissue trauma, improved cosmesis, less hair removal, and reduced surgical times. Patient satisfaction with the smaller incision reflects positively on the operative surgeon when compared with traditional techniques. Bilateral implantation and younger age at implantation make the advantages of minimally invasive techniques more appealing. Minimally invasive techniques are being extended to include entrance to the inner ear via cochleostomy as hearing preservation cochlear implant surgery comes into existence. This article gives a detailed description of surgical technique. © 2005 Elsevier Inc. All rights reserved.
Food and Drug Administration approval of cochlear implant devices occurred for adults in 1985 and for children in 1990. Currently, more than 80,000 devices have been implanted in patients with a variety of surgical techniques. As a general trend, incisions have become smaller, procedures shorter, and healing faster because of less surgical trauma created with evolving minimally invasive techniques. Currently, except for patients younger than 10 years, the vast majority of patients are discharged the day of their procedure on an outpatient surgery basis. Clear evidence exists showing the use and improved outcomes associated with implantation at younger ages in congenitally hearing impaired individuals. Current Food and Drug Administration guidelines include cochlear implantation at 12 months of age. Minimized blood loss is a worthy goal in these neonates. Many centers, including our own, are implanting appropriate candidates younger than one year. Guidelines for minimum age of implantation will continue to decrease as they have over the last 14 years. Several other trends make the minimally invasive cochlear implant technique appealing. First, concurrent or sequential bilateral cochlear implantation is proving beneficial in a growing number of patients. On a worldwide basis, more than 3500 recipients are using a cochlear implant in each ear. Second, manufacturers have reduced the Address reprint requests and correspondence: Joseph B. Roberson, Jr, MD, CEO, California Ear Institute, 1900 University Circle, Suite 101, East Palo Alto, CA 94303. E-mail address: [email protected]. 1043-1810/$ -see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.otot.2005.05.005
size of implanted instrumentation with successive generations of their products. Future changes will allow continued reduction in implanted device size, allowing newer adaptations to existing surgical techniques. Third, hearing preservation is possible with insertion of both short and standard electrode length cochlear implants, and early data indicate advantages with both electrical and mechanical stimulation. It is also anticipated that totally implantable cochlear implants will make their entrance during the next several years. These devices will increase in size compared with currently existing cochlear implants. Minimally invasive techniques offer significant advantages for patients, while being technically harder to perform for surgeons. A patient having a small, cosmetically appealing incision and minimal/no hair removal with quick and uncomplicated healing is a goal best achieved with this type of technique. This technique has been practiced with minor modifications since 1994 and is the subject of a previous report we believe to be the first dealing with minimally invasive cochlear implant surgery.1 Surgical time has averaged 56 minutes over our last 50 unilateral implants in adults and children. Concurrent bilateral implantation averages 92 minutes.
Surgical technique Psychologic preparation with a full and complete explanation for adults is even more important for the hearing im-
Roberson
Cochlear Implant Surgery: Minimally Invasive Technique
paired than for most patients. Play therapy is used at our institution before cochlear implantation to communicate to young children the events upcoming. It is our practice to involve other children who have cochlear implants in the “play surgery” within several days of the procedure. In many instances, the practice replaces a feeling of fear with one of expectation and excitement. The night before the procedure, the patient’s hair is washed with antibacterial solution. Pediatric patients receive, 1 hour prior to surgery, premedication in the form of oral midazolam with dosages of 0.5-0.75 mg/kg mixed with liquid acetaminophen. Induction is performed with inhalational anesthetic agents, and an attempt is made to avoid injections and intravenous lines until after the child is asleep. Adults have an intravenous line started in the holding area and are given anxiolytic medications as the anesthesiologist judges necessary. Paralyzing agents are avoided to facilitate facial nerve monitoring. Intravenous antibiotics are given just after induction of anesthesia and intubation before incision. Patients younger than 5 years, older than 70 years, or those with an increased risk of infection (eg, insulin dependent diabetics) are given per os antibiotics for 5 days after the procedure. Patients with a tympanostomy tube in place are also given topical antibacterial drops for the same period. Patients younger than 2-3 years have a towel folded and placed under the shoulders to extend the neck. Most adults are positioned with the head on the table without a head holder. Patients with limited neck mobility and those receiving bilateral implants have the head placed on a gel ring of minimal size to protect the neck from hyperextension. The Medtronic NIM-Response Nerve Integrity Monitoring System (Medtronic, Inc, Minneapolis, MN) is used to perform continuous intraoperative monitoring of facial nerve function in unilateral or bilateral cases. Fixed paired electrodes are placed in the orbicularis oris and orbicularis oculi muscles, with ground wires placed in the upper chest skin. In bilateral implantation cases, special attention is given to allow head mobility after draping. To accomplish this goal, we prepare the entire head and sequester the facial nerve monitoring electrodes, endotracheal tube, and other monitoring connectors in the midline under sterile clear drapes. As mentioned previously, a small head holder is helpful to increase side-to-side range of motion after draping. In pediatric bilateral cases, a calculation of safe ranges of blood loss is made before first incision and tracked for safety throughout the procedure. An incision is planned in the postauricular area that begins just behind the postauricular crease at the inferior end of the external acoustic meats, extending superiorly and slightly curvilinearly posteriorly for 2.5-4.5 cm per surgeon preference (Figure 1). Palpation of the mastoid tip and tympanomastoid suture line/stylomastoid foramen will avoid placing the incision directly over the facial nerve in the youngest of patients. Hair around the incision is shaved for a distance of 1 cm at the superior limb. Long hair is controlled with a rubber band and may be braided to achieve the desired effect. Medium or short hair is best controlled with the draping. Injection of equal parts of 2% lidocaine with 1:100,000 epinephrine and 0.5% bupivacaine plain are mixed, buffered with 1 mL of sodium bicarbonate solution
75
Figure 1
Adult internal device and incision placement.
per 10 mL, and injected into the proposed incision and surrounding surgical field. The proposed incision should be planned, considering several factors. First, the internal device should not be placed in an area where the external coil will be knocked off repeatedly (eg, in a car seat in a young child). Second, no portion of the incision should overlap the internal device. Third, the internal device is placed in such a way that it does not overhang the mastoid cavity. Finally, the internal device needs to be situated far enough away from the ear so that a behind-the-ear processor will not compress skin over the internal instrumentation of the implant. This situation may lead to patient discomfort or worse, skin necrosis and device exposure and explantation. The surgical site and hemicranium, including all hair, is given a vigorous scrub with antibacterial solution. Solution is kept from the external auditory canal only if a tympanostomy tube is in place. A circumferential head drape is placed and pulled superiorly until the surgical site is exposed to assist in hair retraction. The area is squared off with towels and an Ioban (3M, St. Paul, MN) or similar adhesive, and a sterile drape is placed on the towels, and exposed hair and skin to secure the arrangement. Note that the ear should be folded forward and held with the sticky drape. Drying the posterior surface of the pinna allows the drape to stick to the skin, maintaining the pinna in a position out of the surgical field. Ioban is removed carefully over the area of proposed incision. The incision is performed beveling the blade to parallel hair follicles in the superior portions of the wound. Cautery is used to divide the subcutaneous tissues and periosteum over the mastoid cortex, and into the root of the zygoma below the temporalis muscle to a point above the external auditory canal. The mastoid cortex is exposed with
76
Operative Techniques in Otolaryngology, Vol 16, No 2, June 2005
Figure 4
Figure 2
Facial recess approach, hypotympanic perspective.
elevators until the spine of Henle is identified at the margin of the external auditory canal. The tissues of the canal are elevated several millimeters beyond the spine of Henle, maintaining intact skin of the canal. A pocket is created for the internal device that is just larger than the device itself, up and behind the ear. In most patients the correct plane is between the pericranium and the bone of the skull. In the occasional patient, it will be necessary to remove muscle and connective tissue over the area of the future seat of the device. Attention is turned to the mastoid drilling, where a mastoidotomy is created anteriorly while thinning the posterior bony external auditory canal to allow the correct angle to enter the middle ear via the facial recess. The facial recess is dissected, leaving bone over the facial nerve and preserving the chorda tympani nerve. Removal of bone anterior and medial to the facial nerve is possible and preferable to expose fully the round window niche (Figure 2). A Silastic (Dow Corning, Corp, Midland, MI) model of the internal device is placed in the prepared pocket. Adjustments to the pocket are made as needed for final positioning. The seat of the device is then drilled to allow maximal flush seating of the device. Dura is exposed if needed without consequence. Diamond burrs are used to avoid dural laceration. Self-retaining retractors are removed during this step, the table is rotated toward the surgeon, and an assistant is enlisted to hold the skin with a hand-held retractor as needed. The surgeon provides most of the retraction needed with a fenestrated suction irrigator in the nondrill hand. The drilled seat is then connected to the mastoidotomy with a
Figure 3 Securing suture placement. (A and C) Adult. (B and D) Pediatric.
(A and B) Pediatric retention suture placement.
small burr to allow electrode passage after device placement. Suture retention holes are created because it is our belief a device not anchored has a higher chance of migrating postoperatively. In those patients with thicker skulls, partial depth holes are drilled and connected with cross drilling so that suture may be passed through the bony tunnel to secure the implant. In children with thin skulls, holes are created through to dura and suture placed posteriorly with a doublearmed suture from inside out (Figures 3 and 4). Hemostasis is achieved, and all bone dust is removed in preparation for final placement steps. A 0.5-1.0 mm diamond burr is selected for cochleostomy placement. Care is taken not to heat or damage the facial nerve with the rotating shaft of the burr while drilling bone away at the inferior edge of the round window membrane at the crista fenestra, thereby avoiding the insertion of the lateral basilar membrane in the cochlear hook area (Figure 5).2,3 Every attempt is made to preserve the endosteum intact to minimize intracochlear trauma. The endosteum is opened, and a saline soaked resorbable sponge is placed to prevent perilymph egress. Suction at the cochleostomy is to be avoided as it would be in a stapedotomy case. The internal cochlear implant instrumentation is then placed in the seat and pocket. The previously placed suture is then passed through the anterior suture holes and tied off the top of the device with a buried knot. (We use a 2-0 polyester suture.) The electrode is then passed via the cochleostomy in such a way as to minimize trauma to the membranous cochlea. Hearing preservation will not be possible if the basilar membrane is perforated. Different strat-
Figure 5 Facial recess surgical view. Cochleostomy placement with basilar membrane avoidance. RW, round window.
Roberson
Cochlear Implant Surgery: Minimally Invasive Technique
egies and instrumentation are available from different manufacturers designed to minimize intracochlear damage. A free connective tissue graft is taken and used to seal the cochleostomy around the electrode. Ground electrodes are placed deep to the temporalis muscle if the selected device has such an attachment. In pediatric patients, a “reserve” of electrode wire is placed in the mastoid to allow for growth. Most young patients will reconstitute the mastoid cortex with healing. This process should be considered also, so that future growth does not remove an electrode from the cochlea. Wound closure is effected with interrupted resorbable 3-0 suture, and Steri-Strip adhesive (3M) or resorbable subcuticular monofilament is used to close the skin. An
77
overnight mastoid pressure dressing is placed. Skin tapes are removed one week after the procedure.
References 1. Roberson JB Jr, Stidham KR, Scott KM, et al: Cochlear implantation: Minimal hair removal technique. Otolaryngol Head Neck Surg 122:625629, 2000 2. Stidham KR, Roberson JB Jr: Cochlear hook anatomy: Evaluation of spatial relationship of the basal cochlear duct to middle ear landmarks. Acta Otolaryngol 119:773-777, 1999 3. Briggs RSJ, Tykocinski M, Stidham KR, et al: Cochleostomy site: Implications for electrode placement and hearing preservation. 2005 (in press)