Download Utility of Preoperative Computed Tomography and Magnetic

The Laryngoscope
C 2015 The American Laryngological,
V
Rhinological and Otological Society, Inc.
Utility of Preoperative Computed Tomography and Magnetic
Resonance Imaging in Adult and Pediatric Cochlear Implant
Candidates
Matthew Tamplen, MD; Adam Schwalje, BA; Lawrence Lustig, MD;
Aurash S. Alemi, MD; Mia E. Miller, MD
Objectives/Hypothesis: Determine the utility of preoperative imaging in adult and pediatric cochlear implant candidates.
Study Design: Retrospective chart review.
Methods: Medical records of 101 consecutive adult and 20 consecutive pediatric patients who underwent 137 cochlear
implantation (CI) procedures at a single institution were reviewed.
Results: Computed tomography (CT) was obtained preoperatively in 110 (90.9%) patients, preoperative magnetic resonance imaging (MRI) was obtained in 102 (84.3%) patients, and both were obtained in 94 (77.7%) patients. MRI revealed
one acoustic neuroma and two meningiomas, which affected surgical planning for three (2.2%) procedures. MRI identified
enlarged vestibular aqueduct (EVA) in 2.0% of adult patients. CT demonstrated middle ear disease in four (3.3%) patients. CT
was useful in indicating round window and cochlear patency in three (2.2%) patients with cochlear otosclerosis. Twenty
pediatric patients underwent 27 CI procedures. Preoperative CT in the pediatric cohort demonstrated five (25%) dysplastic
cochleae, three (15%) dysplastic vestibules and/or semicircular canals, and three (15%) EVAs. In one patient, CT demonstrated a duplicated right internal auditory canal (IAC) and hypoplastic left IAC; MRI confirmed hypoplastic cochlear nerves.
Conclusions: Preoperative MRI can demonstrate retrocochlear pathology, cochlear patency, and EVA in adults being evaluated for cochlear implantation. CT may provide additional information in patients with chronic otitis media or otosclerosis.
However, in postlingually deafened adults without conductive or asymmetrical hearing loss, imaging is unlikely to affect surgical decision making. Both CT and MRI can identify anomalies in pediatric patients. MRI does not offer substantial benefit over
CT for routine evaluation of pediatric inner ear and temporal bone anatomy.
Key Words: Cochlear implant, radiology, otology, pediatric otology.
Level of Evidence: 4
Laryngoscope, 126:1440–1445, 2016
INTRODUCTION
Preoperative imaging, including computed tomography
(CT) and/or magnetic resonance imaging (MRI), has historically been used in the evaluation of candidates for cochlear
implant (CI). However, the utility of each imaging strategy
has not been clearly defined. Patients often receive CT or
MRI or both, with no clear indication for each independent
From the Department of Otolaryngology–Head and Neck Surgery
(M.T., A.S.A.), University of California–San Francisco, San Francisco,
California; University of California (A.S.), San Francisco School of
Medicine, San Francisco, California; Department of Otolaryngology–
Head and Neck Surgery (L.L.), Columbia University, College of
Physicians & Surgeons, New York, New York; House Clinic (M.M.), Los
Angeles, California, U.S.A.
Editor’s Note: This Manuscript was accepted for publication
August 17, 2015.
Poster presentation at the Triological Society Combined Sections
Meeting, Coronado, California, U.S.A., January 22–24, 2015 (poster #120).
The authors have no funding, financial relationships, or conflicts
of interest to disclose.
Send correspondence to Matthew Tamplen, MD, 3167 California
St., #4c, San Francisco, CA 94115.
E-mail: [email protected]
DOI: 10.1002/lary.25659
Laryngoscope 126: June 2016
1440
imaging study. A blanket approach of routine CT and MRI
imaging in all CI candidates may not be cost-effective. Roberts et al. suggested that in adult patients with symmetric
sensorineural hearing loss (SNHL) without a history of congenital hearing loss, meningitis, or head trauma, preoperative imaging was unlikely to change the surgical plan for
cochlear implantation.1 Schwartz and Chen also suggested
that in postlingually deafened adults, there was limited utility in routine imaging without a concerning clinical history.2
The theoretical utility of preoperative imaging
includes evaluation of round window patency, course of
the facial nerve and location of the jugular bulb and other
important landmarks, identification of cochlear anomalies
including hypoplasia, detection of infection, and evaluation of the vestibular aqueduct system for increased likelihood of a cerebrospinal fluid (CSF) gusher.3,4 However,
the rate of such findings in adult patients is low, and the
rate of any finding on imaging affecting the surgical
approach is even lower.1 There is no consensus on the preferred preoperative imaging strategy for CI candidates.
Viad and Vaid outlined the utility of both CT and MRI for
possible anatomic abnormalities that would affect CI operations and recommended both imaging strategies for the
complimentary information they provide.4 Sweeney et al.
Tamplen et al.: Preoperative CT and MRI in CI Candidates
recommended MRI for CI candidates for the diagnosis of
acoustic neuromas, although this was a very rare finding
without concerning clinical history.5
The incidence of anatomic anomalies is different in
different patient populations. Pediatric patients with congenital hearing loss have a 20% rate of anatomic abnormalities, which may make preoperative cross-sectional
imaging much more useful.3 However, the best imaging
strategy for pediatric CI candidates is still debated. The
majority of anatomic abnormalities that would effect the
operation can be diagnosed with either CT or MRI.4 Parry
et al. suggested that MRI is more sensitive for soft tissue
findings that would affect pediatric CI operations than CT
and should be the first choice for imaging in pediatric
patients.6 Historically, the role for MRI has been to visualize a hypoplastic acoustic nerve, but it is unclear how common this finding is without any finding on CT such as a
narrowed internal auditory canal (IAC) or cochlear or vestibular dysplasia. The risk-benefit ratio of each imaging
study always has to be considered in pediatric patients.
MRI often requires sedation in pediatric patients, and
there are potential long-term effects of radiation exposure
from temporal bone CT (Fig. 1).
In adult patients, it appears the cause of deafness
may significantly affect the likelihood of imaging findings that affect the operation. Postlingually deafened
adults without history of meningitis, trauma, or asymmetrical loss may not require any imaging at all.1 Those
with asymmetry or additional clinical history may benefit from an MRI without the need for CT unless there is
a significant conductive component to their hearing
loss.7 The goal of this study was to evaluate the diagnostic yield of both CT and MRI in both children and adults
receiving a CI to help clarify these issues.
MATERIALS AND METHODS
The University of California, San Francisco Committee of
Human Research reviewed and approved this study. We preformed a retrospective chart review of the medical records for 121
consecutive patients (101 adult and 20 pediatric) who underwent
137 cochlear implantation procedures between May 14, 2011 and
July 30, 2014 at a single institution. Seven pediatric and nine
adult patients underwent bilateral cochlear implantation. During
the study period it was institutional practice to obtain routine
preoperative CT and MRI in all CI candidates. Clinical notes,
radiology reports, and operative reports were reviewed for any
complications or planned or unplanned operative changes.
Cost analysis was done using California Medicaid (MediCal) reimbursement rates for 2014. Cost per significant finding
was calculated using the equation: (number of individual scans
3 Medi-Cal reimbursement rate for that type of scan) / number
of significant findings reported by that type of scan. The potential cost savings in the adult cohort if only adult patients with
preoperative indications were scanned was also evaluated. This
was done by subtracting the number of scans from patients
with preoperative indications for that individual scan from the
total number of each scan preformed and multiplying this by
the cost of each scan.
The potential cost savings was also evaluated in the pediatric cohort if all patients had undergone routine CT, and MRI was
only done if there was any abnormal finding on routine CT. The
risks of radiation exposure were estimated by using previously
Laryngoscope 126: June 2016
Fig. 1. Temporal bone computed tomography of an adult with
cochlear otosclerosis. Arrow demonstrates sclerotic cochlea.
[Color figure can be viewed in the online issue, which is available
at www.laryngoscope.com.]
published lifetime attributable risk of solid cancer and lifetime
attributable risk of leukemia per head CT scan and multiplying
this by the number of pediatric head CTs preformed.
RESULTS
CT was obtained preoperatively in 110 (90.9%)
patients, preoperative MRI was obtained in 102 (84.3%)
patients, and both were obtained in 94 (77.7%) patients
(Table I). Significant findings are listed in Table II. MRI
revealed one acoustic neuroma and two meningiomas,
which affected surgical planning for three (2.2%) of the
137 procedures. The patient with the acoustic neuroma
presented with a significant asymmetrical SNHL. Fourteen (13.8%) of the adult patients in this cohort had a
significant asymmetrical SNHL. The majority of patients
received both imaging studies, however, and 37 (22.3%)
patients received only MRI or CT. The retrospective
nature of the current study did not allow for evaluation
of reasoning behind individual imaging decisions.
Twenty pediatric patients underwent 27 CI procedures. Significant findings on preoperative imaging are
listed in Table II. In one patient, CT demonstrated a duplicated right IAC and hypoplastic left IAC; MRI confirmed
hypoplastic cochlear nerves in this patient (Fig. 2). There
were no pediatric patients who underwent both CT and
MRI who had a significant MRI finding with a normal CT
scan (Table III).
There was a documented change in surgical plan
based on imaging findings for eight (7.9%) of the adult
patients and 13 (65%) of the pediatric patients (Table III).
The eight adult patients with documented change in surgical plan consisted of three intracranial neoplasms that
changed side and/or type of implant, three cases of
restricted cochlear patency that changed the side of
implantation, and two enlarged vestibular aqueducts that
Tamplen et al.: Preoperative CT and MRI in CI Candidates
1441
TABLE I.
Patient Characteristics.
Age, yr, mean, range (SD)
Adult (101)
Pediatric (20)
Total (121)
58, 18–90 (16.9)
5.4, 1–15 (5.1)
49.3, 1–90 (25.4)
Preoperative CT, n (%)
Preoperative MRI, n (%)
91 (90.1%)
85 (84.1%)
19 (95%)
17 (85%)
110 (90.1%)
102 (84.3%)
Preoperative MRI and CT, n (%)
78 (77.2%)
16 (80%)
94 (77.7%)
CT 5 computed tomography; MRI 5 magnetic resonance imaging, SD 5 standard deviation.
changed the side of implantation. The 13 pediatric patients
with documented change in surgical plan consisted of eight
dysplastic cochlea, three enlarged vestibular aqueducts,
and two hypoplastic cochlear nerves, all changing the side
of implantation.
The surgical plan was changed based on findings
considered exclusive to CT (or documented only on the
CT report) for three (3%) adult patients and 12 (60%)
pediatric patients. The surgical plan was changed by
findings considered exclusive to MRI (or documented
only on the MRI report) for three (3%) adult patients
and zero (0%) pediatric patients (Table III). No patients
in this study had a history of meningitis.
Based on Medi-Cal reimbursement rates for MRI
and CT, it cost $36,062 to find a single significant finding on routine preoperative MRI for our adult cohort. In
our pediatric cohort, it cost $310 to find one significant
finding on routine preoperative CT. All CTs preformed
lead to an estimated 0.0053 lifetime risk for solid tumor
or leukemia based on previously published data on radiation risks of head CTs in children.
DISCUSSION
The utility of routine
candidates is still debated
clinical history. In patients
ing loss, imaging is used to
preoperative imaging for CI
and is highly dependent on
who have a congenital hearscreen for the approximately
TABLE II.
Imaging Findings.
Adult
CT
91
Pediatric
19
Total
110
20% who have malformations of the inner ear, some of
which may impact surgical planning; however, there is
still debate regarding the optimal imaging study.3,5–7 In
adult patients with postlingual hearing loss, preoperative
imaging has historically been standard, although there is
no consensus on the type of scan or the utility of imaging
without consideration of pertinent clinical history.1,2
Recent studies have shown limited utility of preoperative imaging in postlingually deafened adults. In a retrospective chart review of 118 adults with progressive
sensorineural hearing loss, Roberts et al. found that preoperative imaging led to no mandatory changes in surgical
management, even when an abnormality was found. Notably, six of these patients had intraoperative findings,
including round window ossification, multiple insertion
attempts, or CSF leak, which were not predicted by preoperative scans.1 This led the authors to recommend imaging
only for cases where there was another clinical indication
for imaging such as a history of head trauma, history of
meningitis, significant asymmetry on audiogram, or significant conductive hearing loss.
Schwartz and Chen also found limited utility of routine preoperative imaging in postlingually deafened
adults. In 109 postlingually deafened adult CI candidates without concerning features on history or physical
exam, they found imaging results were unlikely to affect
surgical management. In two of these patients (1.8%),
an incidental cerebellopontine angle (CPA) tumor was
found; however, both patients presented with asymmetrical hearing loss.2 These findings are similar to the
findings in the current study, in which only eight (7.9%)
adult patients had their operation affected by preoperative imaging, three (3.0%) intracranial neoplasms
Chronic middle ear
disease, n (%)
4 (4.4%)
0 (0%)
4 (3.6%)
Restricted cochlear
patency, n (%)
3 (3.3%)
0 (0%)
3 (2.7%)
Dysplastic cochlea/
vestibule, n (%)
EVA, n (%)
0 (0%)
8 (44.8%)
8 (7.3%)
0 (0%)
3 (15.8%)
3 (2.7%)
Abnormal CT, n (%)
7 (6.9%)
13 (65%)
20 (16.5%)
Abnormal MRI, n (%)
Surgical plan changed
by imaging, n (%)
5 (5.0%)
8 (7.9%)
3 (15%)
13 (65%)
8 (6.6%)
23 (19%)
Surgical plan changed
by finding exclusive to
or read best on CT, n (%)
3 (3.0%)
12 (60%)
15 (12.4%)
Surgical plan changed
by finding exclusive to
or read best on MRI, n (%)
3 (3.0%)
0 (0%)
3 (2.5%)
Hypoplastic IAC, n (%)
MRI
Acoustic neuroma/
meningioma, n (%)
EVA, n (%)
Hypoplastic cochlear
nerve, n (%)
0 (0%)
2 (10.5%)
2 (1.8%)
85
3 (3.3%)
17
0 (0%)
102
3 (2.7%)
2 (2.4%)
0 (0%)
2 (1.8%)
0 (0%)
2 (10.5%)
2 (1.8%)
CT 5 computed tomography; EVA 5 enlarged vestibular aqueduct;
IAC 5 internal auditory canal; MRI 5 magnetic resonance imaging.
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1442
TABLE III.
Surgical Plan Changed by Imaging.
Adult (101) Pediatric (20)
Total (121)
CT 5 computed tomography; MRI 5 magnetic resonance imaging.
Tamplen et al.: Preoperative CT and MRI in CI Candidates
Fig. 2. Fiesta magnetic resonance imaging of a pediatric patient
with a hypoplastic cochlear nerve and dysplastic cochlea. Arrow
demonstrates dysplastic cochlea. [Color figure can be viewed in
the online issue, which is available at www.laryngoscope.com.]
affecting the side and type of implant (due to anticipated
MRI artifact or implant-specific MRI compatibility), three
(3.0%) cases of restricted cochlear patency in patients with
otosclerosis affecting the side of implantation, and two
(2.0%) cases of enlarged vestibular aqueduct affecting the
side of implantation.
In the current study, the single patient with a CPA
neoplasm met institutional criteria of MRI imaging for
asymmetrical hearing loss with either >10 dB asymmetry
across three consecutive frequencies, 15 dB in two consecutive frequencies, or 20 dB in one frequency and/or
marked differences in speech discrimination between the
two ears. Thirteen other adult patients also met these criteria for asymmetric hearing loss; each of which had an
MRI scan that was read as normal. The findings of an
intracranial neoplasm led to operative changes in both
side and device choice. In total, three intracranial neoplasms were found in this study. A single 9-mm vestibular
schwannoma was managed with serial MRIs for observation. The patient had the side and type of implant changed
by this preoperative finding. There were two meningiomas. One has been undergoing observation with serial
MRIs and one underwent radiotherapy. Both had the type
of implant changed by the preoperative finding to ensure
MRI compatibility. Although some studies have shown
that MRI with CI in situ is safe for all CI manufacturers,8
MED-EL is the only device that is Food and Drug
Administration-approved with head wrap at 1.5 T (and
more recently 3 T), and the others currently recommend
magnet removal. Also, due to artifact from the CI, the side
contralateral to the tumor is often preferred.
Cochlear otosclerosis was a rare finding in this cohort,
which was found in only three (2.2%) adult patients. All
patients with otosclerosis, and thus possible round window
Laryngoscope 126: June 2016
obliteration, had a significant conductive hearing loss with
a >20 dB air-bone gap preoperatively. Four (3.3%) patients
had a CT scan that confirmed middle ear disease. All of
these patients with CT evidence of middle ear disease were
noted to have concern for middle ear disease on preoperative clinical examination. There was no documented
change in surgical plan based on the imaging findings for
the patients with noted middle ear disease; however, CT
may have assisted is confirming the diagnosis or evaluating the extent of middle ear disease. Thus, the current
study is in agreement with others in that CT is most useful
when there is a clinical or audiometric concern for otosclerosis or middle ear/mastoid disease.
Pediatric patients have been found to have a much
higher rate of abnormal findings on preoperative imaging
that may affect surgical planning.3 The current study corroborates this finding, as 13 (65%) pediatric patients had
their operation affected by imaging findings (Table III).
There is often a debate regarding the preferred imaging
study, as MRI has been shown to be superior for soft tissue
abnormities and the absence of a cochlear nerve. However,
it is very rare for an MRI to show a significant abnormality
if the CT was read as normal. On review of the literature,
there is not a single case of a cochlear implant candidate
with a completely normal CT scan and a hypoplastic or
aplastic cochlear nerve on MRI.9–13 Often a narrow IAC is
found if there is significant dysplasia of the cochlear nerve.
Kutz et al. demonstrated 86% of patients with a hypoplastic or aplastic cochlear nerve had an IAC <1.4 mm in diameter.10 McClay et al. demonstrated that out of 170 pediatric
patients with SNHL, 18% had a hypoplastic or aplastic
cochlear nerve on MRI, and of these 82% had narrow IAC
and 76% had additional cochlear abnormalities.11 Bamiou
et al. reported 93% of patients with cochlear nerve hypoplasia had a narrow IAC.13 There is consistently reported to
be a high rate of associated inner ear abnormalities and
narrow IAC in pediatric patients with clinically significant
hypoplasia of the cochlear nerve. In our cohort of 32 pediatric temporal bones that underwent both imaging modalities, there was no significant MRI finding with a normal
CT scan. This may provide clinical utility, as pediatric
patients often require sedation for MRI imaging, and CT
may be more available and cost-effective for routine
screening.
When deciding the preferred imaging strategy for
pediatric CI screening, one must consider the cost of each
imaging modality and the potential risks associated with
each imaging modality. Medi-Cal reimbursement rates for
2014 are $212 for a CT temporal bone, $953 for an MRI of
the IAC, and an estimated additional $250 for sedation during the exam. The lifetime risk of solid tumor and leukemia
attributable to a single CT scan was estimated by Miglioretti et al., who found the number of solid tumors or leukemia associated to one head CT in children <5 years of age
to be 0.00144 and 0.000288 in children >5 years of age.14
Pediatric MRIs often require sedation due to the length of
the exam. Although the risks of pediatric sedation outside
the operating room are often debated, Cravero et al., from a
voluntary database of 35,000 pediatric sedation encounters, reported that there were no deaths reported and only
one cardiac emergency. There was a single aspiration
Tamplen et al.: Preoperative CT and MRI in CI Candidates
1443
Fig. 3. Flowchart indicating proposed imaging algorithm for cochlear implantation candidates. CI 5 cochlear implantation; CT 5 computed
tomography; MRI 5 magnetic resonance imaging.
episode reported, but one in 400 procedures was associated
with stridor, laryngospasm, wheezing, or apnea. One in
every 200 sedation encounters required airway interventions ranging from bag-mask ventilation to oral airway
placement to emergency intubation.15 Long-term affects of
early anesthesia are still debated; however, several studies
have suggested early pediatric anesthesia is a significant
risk factor for learning disabilities, and this must be considered when ordering procedural sedation for any pediatric
patient.16,17
In our adult patient cohort, it cost $36,062 to find a
single significant finding on routine preoperative MRI. In
our pediatric cohort it cost $310 to find one significant finding on routine preoperative CT scan, with a total attributable lifetime risk for solid cancer or leukemia of 0.0053
(0.00028 3 19) for all scans performed. The findings of the
current study suggest that routine imaging may not be
cost-effective for postlingually deafened adults without a
clinical history of asymmetrical hearing loss or a conductive hearing loss. These findings also suggest the routine
CT scan is cost-effective in the pediatric cohort and may be
a preferred imaging strategy in pediatric CI candidates
where an MRI can be performed if CT scan reveals any
abnormal finding. Following this algorithm (Fig. 3) in the
current adult cohort would have led to only 14 MRIs and
seven CT scans. This would have saved 71 MRI scans and
84 CT scans, for a total savings of $85,471 or $846 per adult
patient. Following this algorithm in the pediatric cohort
would have lead to 13 MRI scans and 20 CT scans. This
would have saved four MRI scans and added one CT scan,
for a total savings of $3,600 or $180 per pediatric patient.
This study has several limitations. It is retrospective and includes a limited number of subjects. In particLaryngoscope 126: June 2016
1444
ular, 40 pediatric temporal bones may be too few to
derive a reliable conclusion regarding the preferred
imaging strategy for pediatric patients in general. Several studies have demonstrated that routine MRI screening of children during the CI evaluation may detect
cytomegalovirus-related changes or subtle brain developmental malformations important for developing appropriate expectations for parents.18–20 However, the
current study does suggest that CT is useful in this
cohort, and may be an acceptable routine imaging strategy for the surgical planning of pediatric cochlear
implant candidates.
CONCLUSION
Preoperative MRI can demonstrate retrocochlear
pathology, cochlear patency, and an enlarged vestibular
aqueduct in adults being evaluated for cochlear implantation, and CT may provide additional information in
patients with chronic otitis media or otosclerosis. However, routine preoperative imaging in adults may not be
cost-effective unless patients have an asymmetric or conductive hearing loss. Both CT and MRI can identify
inner ear anomalies in pediatric patients. Routine MRI
scanning in children does not offer substantial diagnostic
benefit over CT for routine evaluation of pediatric inner
ear and temporal bone anatomy for surgical planning
and may not be cost-effective for routine CI screening.
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