TECHNOLOGY AND THE OTOLARYNGOLOGIST
| GAMMA KNIFE SURGERY —Peter C. Weber, MD, Professor and Program Director, Head and Neck Institute, Cleveland
Clinic, Cleveland, OH
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| Gamma Knife (stereotactic) radiotherapy: most often used for small, well-defined (≤4 cm) targets; permits precise
delivery of single radiation fraction; centers 201 beams of radiation on target; gold-standard approach for radiosurgery;
represents important application of radiation therapy for managing patients with brain tumors; effectiveness
confirmed by clinical experience; cobalt 60 source must be replaced every 5 yr (key cost component); compared to linear
accelerator (LINAC), Gamma Knife—provides more accurate conformal administration of radiation; designed specifically
for radiosurgery; more easily used to treat functional disorders; compared to surgery, Gamma Knife—does not require
incision or general anesthesia; can be performed as outpatient procedure; in general, less expensive because
performed on outpatient basis and has low risk for bleeding and infection and relatively quick recovery time
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| Gamma Knife frame: used to make imaging calculations, provide points of reference for targeting, and fix head in position;
careful attachment to patient’s head—prevents skewing of radiation during procedure; allows equipment to move
freely; proper fit ensures stability—loose frame can slip and cause pin injuries to eye or scalp, or lead to radiation damage
of surrounding tissue; tight frame can fracture skull; points—avoid skull defects while placing pins; plan for ease of
postoperative frame removal; during placement, use—diazepam (Valium) for intravenous (IV) sedation; lidocaine with
or without epinephrine as local anesthetic
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| Before performing procedure: merging computed tomography (CT) with magnetic resonance imaging (MRI)—
localizes tumor within bony architecture of skull; locates internal auditory canal (IAC), petrous apex, jugular foramen,
and skull base; may identify “moth eaten” area within bone associated with glomus tumors; to avoid peripheral tissue
damage—plan carefully; administer 12 to 13 Gy to target
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| How Gamma Knife works: when compared to fractionation—administers higher dose of radiation at one time; more
effective at killing targeted disease; radiobiology within central nervous system (CNS)—acute inflammatory phase occurs
when cells die; demyelination phase occurs within 1 to 6 mo; vascular and white matter necrosis occurs at ≈6 mo after
procedure; hypotheses about subsequent tissue damage—vascular (after 6 mo, ischemic changes lead to white matter
necrosis; thickening of walls and oxygen deprivation cause tissue damage); glial (oligodendrite damage occurs); network
(radiation produces cascade of cell death)
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| Gamma Knife surgery: performed by experienced team—coordinates care; enhances treatment quality; avoids practice
variations; improves patient satisfaction; otolaryngologists—can use technology to manage benign brain tumors, eg,
meningiomas, acoustic neuromas, glomus jugulare tumors; probably will not use approach to manage pituitary adenomas,
malignant brain tumors, functional disorders, or arteriovenous malformations (AVMs)
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| Benign tumors: challenging; functional deficits can persist for years; prognosis—if untreated, tumor can grow to produce
significant morbidity or mortality; most patients can expect prolonged survival with treatment; point—for patient
to qualify for stereotactic radiation therapy, anticipated short- and long-term outcomes must be acceptable; lesions—
well-circumscribed without infiltration; possess slow growth rate desirable for high-dose, single-fraction
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| Goals of Gamma Knife therapy: accurately deliver radiation to target; limit radiation exposure outside target area and to
other parts of CNS to minimize risk for visual deficits, cranial neuropathies, and other complications; provide highest potential
for growth control; address hormonal issues when pituitary involved
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| Acoustic neuromas: constitute ≈10% of all intracranial tumors; usually unilateral (bilateral disease pathognomonic for neurofibromatosis
type 2 [NF2]); patient must be educated about—available treatment options, including observation, microsurgery,
radiosurgery, and fractionated radiation therapy (not considered viable option in United States); whether immediate
treatment necessary; treatment goals—long-term control; preservation of cranial nerve function; maintenance of quality of
life; observation—immediate management difficult to justify in patient who presents with hearing loss, small tumor, and no
vestibular symptoms; risks associated with surgery (eg, vestibular nerve damage) and Gamma Knife procedure must be
weighed against merits of monitoring patient
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 | Gamma Knife data show patients receiving 12 to 13 Gy of radiation: probably had optimum radiation dose; achieved—overall
tumor control rate 98.6%; rate of facial nerve function 100%; trigeminal nerve function 95.6%; unchanged hearing 70%; rate
of preservation of serviceable hearing 78.6%; had small amount of tissue growth 6 to 12 mo after procedure—usually
caused by inflammation and scar formation during first 12 mo postsurgery; in 73% of patients, marked reduction in tumor
volume occurred over time (10-15 yr)
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| Safety, satisfaction, and effectiveness: Gamma Knife considered relatively safe, surgeon-dependent modality; when
compared to microsurgery, Gamma Knife achieves—lower rate of complications, eg, meningitis, cerebrospinal fluid
(CSF) leaks, cerebrovascular accidents (CVAs), requirement for shunts, and mortality; similar good tumor control rates; better
facial nerve function, especially for larger tumors (results comparable to microsurgery for small intracanalicular tumors);
better hearing preservation rate for large tumors initially; superior rate of patient satisfaction; produced no new balance
problems (78% of patients undergoing microsurgery developed balance problems); reduced risk for tinnitus by not pressing
on or dissecting tumor off of auditory portion of eighth nerve (tinnitus rate increased among microsurgery group)
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| Nonvestibular schwannomas (malignant schwannoma, NF2, or trigeminal nerve problems): management
requires higher radiation dose; Gamma Knife achieves control rate of 96%; some eustachian tube dysfunction may
occur with treatment of hypoglossal lesions; treatment of trigeminal nerve involvement—may lead to development of
more facial pain (≈30% of patients); does not cause hearing loss, facial weakness, or swallowing problems
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| Glomus tumors: rare; radiosensitive; highly vascularized; small percentage may be malignant; grow slowly; locally aggressive;
can infiltrate bone, CNS space, and blood vessels; surgery—requires time, technical expertise, anatomic
knowledge, and team approach; has higher rate of morbidity than radiosurgery, but can immediately eliminate tumor;
radiosurgery—appears to achieve ≈95% “no-growth” rate over 10 yr
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| Lesions not managed by Gamma Knife: dural AVM—can cause pulsatile tinnitus; must be treated by neurosurgeon,
ie, lateral position and risk for postoperative bleeding preclude use of Gamma Knife; meningiomas—usually
treated by neurosurgeon; lesions located in cerebellopontine (CP) angle and petrous or cavernous regions may be treatable
by neurotologist; NF2—Gamma Knife avoided because of inability to restore hearing with implantable device and
questionable radiosensitivity of lesion
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| Billing code number 61793: key to compensation; includes frame placement, and calculating and delivering dosage;
does not cover involvement of assistants or cosurgeons; requires otolaryngologist be present when radiation delivered;
permits 1 reimbursement in 90-day period
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| THE BONE ANCHORED HEARING AID (BAHA) FOR SINGLE-SIDED DEAFNESS —Robert A. Battista, MD, Assistant
Clinical Professor of Otolaryngology, Northwestern University Medical School, Chicago, IL
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| Bone anchored hearing aid (BAHA; bone anchored cochlear stimulator): percutaneous system—bypasses
skin and soft tissue of skull; provides direct bone conduction stimulus; avoids sound attenuation associated with bone conduction
devices; converts acoustic energy to electromechanical energy that vibrates skull bone and stimulates cochlea; clinical
indications for BAHA include—conductive and mixed hearing loss; profound unilateral hearing loss; audiologic
criteria for using BAHA to manage single-sided deafness—1 ear with profound sensorineural hearing loss (SNHL) and
pure tone average >90 dB; word recognition score <20%; normal hearing in contralateral ear; however, patients with mild to
moderate hearing loss in contralateral ear do well with BAHA; implantation (outpatient procedure that requires 35 to 40
min)—mark skin ≈55 mm posterosuperior from external meatus; create skin graft (remove subcutaneous tissue to eliminate
potential for sound attenuation once device activated); open periosteum to accommodate titanium fixture; use slow-speed
drill to attach titanium fixture to bone; reapproximate skin graft without subcutaneous tissue; before loading implant with
sound processor, wait 3 mo for osteointegration of fixture to occur
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| Bone conduction sound: inertia of cochlear fluids key source of bone conduction sound in most patients; bone conduction
sound—differs depending on frequency of sound; travels at almost same speed as sound conducted by air; for
BAHA, depends on output of sound processor, implant location, head volume, and frequency of vibratory energy; 0.2
msec—time difference between cochleas for bone conduction sound at frequencies of >0.8 kHz; minimum interaural
time difference needed to localize sound from 1 side to other
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| How patients hear with BAHA device implanted behind deaf ear: processor converts acoustic energy to electromechanical
energy; vibration of skull bone transmits sound to contralateral cochlea (hearing ear); patient perceives
sound as coming from deaf ear; hearing ear remains free of occlusion, unlike air-conduction contralateral routing of offside
signal (CROS) hearing aid, which requires placement of device in good ear
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| Patients with single-sided deafness: have difficulty understanding speech in noise; cannot localize sounds; can become
isolated, depressed, and develop poor job performance; point—one third of children with unilateral problem must
repeat 1 school grade because of deafness
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| Predicting efficacy of BAHA for single-sided deafness
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| Transcranial attenuation of skull: varies with patient; with sound delivered—to front, individuals with low attenuation do
fairly well with BAHA in midfrequency range where majority of speech sounds occur; from behind ear, better sound
awareness occurs in patients with low attenuation; to BAHA-equipped side, even patients with mid-to-low level attenuation
hear fairly well; to side with good hearing ear, BAHA of no benefit
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| Office evaluation: equipping patient with headband and BAHA provides quick means of determining device efficacy
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| Data assessing efficacy of BAHA: multi-institutional data show BAHA—superior to CROS device for ease of communication,
reverberation, background noise, and aversiveness of sound; achieved average patient satisfaction score of
80%; when compared to individuals with unaided hearing or using air-conduction CROS device, patients with
BAHA—did better when noise and speech presented from front; also did better when noise came from non-BAHA side
and speech from front; did worse when noise came from BAHA side and speech came from front
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| Sound localization for single-sided deafness: objective measures of sound localization for BAHA disappointing;
ability of BAHA to improve sound localization observed in some subjective evaluations; people with normal hearing—
localize sound by differences in time, intensity, and spectra of sound; time and intensity important for sound in horizontal
plane; time important for sound <1000 Hz; intensity important for sound >1000 Hz; spectra of sound important for sounds in
vertical plane; basic sound localization—binaural process in individuals with 2 normal-hearing ears (individual’s brain localizes
sound by interpreting differences in sound encoded in superior olivary complex of brainstem); theoretically, sound
localization in patients with BAHA may differ based on artificial head shadow and sound attenuation due to bone conduction
of skull and frequency of sound patient tries to localize
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| Risks and complications of BAHA: intraoperative complications—dural tear; sigmoid sinus bleeding; postoperative
complications—skin overgrowth (most common problem); infections ranging from small and localized with granulation
tissue around abutment to deeper infections, eg, osteomyelitis; brain abscess; loose abutment; bone exposure;
fixture loss; key point—speaker’s data show duration of hearing loss does not reduce effectiveness of BAHA
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| BAHA for single-sided hearing loss: approved by Food and Drug Administration (FDA); considered safe and effective;
provides expanded sound field relative to unaided or air-conduction CROS device; improves speech understanding
in noise; promotes sound localization in some patients; achieves high patient satisfaction rate
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| THE CORRELATION BETWEEN SENSORINEURAL HEARING LOSS (SNHL) AND AMINOGLYCOSIDE EXPOSURE
IN PATIENTS WITH CYSTIC FIBROSIS (CF)—D.J. Trigg, MD, Pediatric Otolaryngology, University of California,
San Francisco, School of Medicine
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| Aminoglycoside ototoxicity: most common form of acquired SNHL; contributing factors—high incidence of gram-
negative, eg, pseudomonal, infections among patients with CF leads to high lifetime exposure to aminoglycosides and increased
risk for SNHL; mitochondrial RNA mutation A1555G (thought to diminish ability to repair cochlear damage;
people with mutation can develop SNHL after single dose of aminoglycoside)
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| Study assessing correlation between CF and aminoglycoside ototoxicity: reviewed charts of patients with CF
to assess audiometric results, aminoglycoside exposure, and risk factors for hearing loss; obtained blood samples for genetic
analysis; points—free radicals form from aminoglycoside that infiltrates endolymph and hair cells; must be scavenged to
avoid cell destruction; CF patients require almost double standard 6 mg/kg per day dose of tobramycin to compensate for
faster excretion rates and higher volumes of distribution; observations—patients undergoing aminoglycoside therapy require
early and periodic hearing assessment; mitochondrial mutation undetected in study population
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Educational Objectives
| The goal of this program is to educate the listener about the pros and cons of some current otolaryngologic technology. After
hearing and assimilating this program, the clinician will be better able to:
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| 1. Assess the technical aspects of performing successful Gamma Knife surgery.
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| 2. Explain the clinical role of Gamma Knife surgery in otolaryngology.
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| 3. Describe how the bone anchored hearing aid (BAHA) helps patients with single-sided deafness achieve bilateral hearing
function.
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| 4. Summarize the risks and intraoperative and postoperative complications of the BAHA .
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| 5. Discuss the correlation between sensorineural hearing loss and aminoglycoside exposure in patients with cystic fibrosis.
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Discussed on This Program
Ceftazidime [Ceptaz, Fortaz, Tazicef, Tazidime
Diazepam [Diastat, Diazepam Intensol, Valium]
Gentamicin sulfate (everal trade names and preparations)
Lidocaine HCl (several trade names and preparations)
Lidocaine HCl with epinephrine [Octocaine, Xylocaine, Xylocaine MPF]
Piperacillin sodium and tazobactam sodium [Zosyn]
Tobramycin sulfate (several trade names and preparations)
Suggested Reading
Goodyear PW et al: The Bradford bone-anchored hearing aid programme: impact of the multidisciplinary team. J
Laryngol Otol 120:543, 2006; Hol MK et al: The bone-anchored hearing aid: quality-of-life assessment. Arch Otolaryngol
Head Neck Surg 130:394, 2004; Hol MK et al: Long-term results of bone-anchored hearing aid recipients who had
previously used air-conduction hearing aids. Arch Otolaryngol Head Neck Surg 131:321, 2005; Mulheran M et al: Occurrence
and risk of cochleotoxicity in cystic fibrosis patients receiving repeated high-dose aminoglycoside therapy. Antimicrob
Agents Chemother 45:2502, 2001; Shirazi MA et al: Perioperative complications with the bone-anchored
hearing aid. Otolaryngol Head Neck Surg 134:236, 2006; Snik AF et al: Consensus statements on the BAHA system:
where do we stand at present? Ann Otol Rhinol Laryngol Suppl 195:2, 2005; Weber PC: Medical and surgical considerations
for implantable hearing prosthetic devices. Am J Audiol 11, 134, 2002.
Faculty Disclosure
In adherence to ACCME guidelines, the Audio-Digest Foundation requests all lecturers to disclose any significant financial
relationship with the manufacturer or provider of any commercial product or service discussed. For this issue, the faculty
reported nothing to disclose.
Dr. Battista gave his scientific presentation at the Chicago Laryngological and Otological Society (CLOS) program held
February 6, 2006, in Chicago, IL; Dr. Trigg gave his scientific presentation at the annual Combined Otolaryngology Spring
Meetings (COSM) conference of the American Society of Pediatric Otolaryngology (ASPO) held May 20 to 22, 2006, in
Chicago, IL; Dr. Weber gave his scientific presentation at the CLOS program held November 7, 2005, in Chicago, IL. The
Audio-Digest Foundation thanks the speakers and the sponsors for their cooperation in the production of this program.
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