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Systematic approach by computed tomography and magnetic resonance imaging in cochlear implantation candidates in Suez Canal University Hospital
The Egyptian Journal of Radiology and Nuclear Medicine 48 (2017) 877–884
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Original Article
Systematic approach by computed tomography and magnetic resonance imaging in cochlear implantation candidates in Suez Canal University Hospital Aya S. Al-Rawy a, Mohammad al-Shatouri a,⇑, Mohammed El Tabbakh b, Azza A. Gad a a b
Department of Radiology, Suez Canal University Hospital, Faculty of Medicine, Ismailia, Egypt Department of ENT, Suez Canal University Hospital, Ismailia, Egyptt
a r t i c l e
i n f o
Article history: Received 5 June 2017 Accepted 10 August 2017 Available online 4 January 2018 Keywords: Cochlear implantation Suez Canal area Pre-surgical mapping Sensorineural hearing loss CT MRI
a b s t r a c t Objectives: To create a systematic approach using computed tomography (CT) and magnetic resonance imaging (MRI) findings to facilitate identifying the etiology of hearing loss, evaluating the anatomy for surgery, and predicting complications. Methods: Twenty nine pediatric patients with congenital or acquired sensory-neural hearing loss (SNHL) requiring cochlear implant (CI) were included. They underwent combined CT, 3D DRIVE MRI axial plane and axial T2WIs for the whole brain. The inner ear, cochlear nerve development, temporal bone anatomy, operative window, normal variants and causes of central hearing loss were assessed. Results: CT showed that 100% of the patients are suitable for CI while MRI showed that 96.5% of studied patients are suitable. The examined ears were categorized into 4 groups according the candidacy for operation; 86.2% were suitable for CI, 5.1% were suitable for CI but with expected poor response, 1.7% of examined ears were suitable for CI with modification of surgical procedure and 6.8% were not suitable for CI. Conclusion: In Suez Canal area, the combined CT/MRI approach categorized the majority of patients with SNHL (96.6%) as good candidates for CI. Ó 2017 The Egyptian Society of Radiology and Nuclear Medicine. Production and hosting by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
1. Introduction Hearing loss has a significant impact on the patients and society. Early identification of hearing impairment and differentiation between non progressive (congenital) and progressive types may minimize the loss of development of important skills in speech, language, and social interactions [1].
Abbreviations: CT, computed tomography; MRI, magnetic resonance imaging; CI, cochlear implant; SNHL, sensory neural hearing loss; 3D, three dimensional; IAC, internal auditory canal; T2WIs, T2 weighted images; IP, incomplete partition; LO, labyrinthitis ossificans. Peer review under responsibility of The Egyptian Society of Radiology and Nuclear Medicine. ⇑ Corresponding author at: Radiology Department, Suez Canal University Hospital, Ring Road, 41522 Ismailia, Egypt. Tel.: +20 01001811293. E-mail addresses: [email protected] (A.S. Al-Rawy), [email protected] (M. al-Shatouri), [email protected] (M. El Tabbakh), [email protected] (A.A. Gad).
Cochlear implantation (CI) is a widely available tool for treatment of deafness or severe SNHL in patients who do not show adequate benefits from hearing aids. Imaging plays an important role in the selection of candidates and in the planning of surgery. The preoperative assessment should provide optimal information on the anatomy of the ear, its normal variants, and pathology of the temporal bone and auditory pathway [2]. Cochlear implant is an electronic device used to habilitate or rehabilitate patients with severe hearing impairment. It creates a direct stimulation of the residual spiral ganglion cells of the cochlear nerve by bypassing the destroyed hair cells. Normally, the sound waves coming from the oval window pass to the scala vestibuli up to the helicotrema and then, towards the round window by the scala tympani. The hair cells are excited by the variations of sound waves transmitted to the scala media [3]. The frequency of CI has increased over the last years. Improved speech processing strategies leads recently to improve auditory results [4].
https://doi.org/10.1016/j.ejrnm.2017.08.005 0378-603X/Ó 2017 The Egyptian Society of Radiology and Nuclear Medicine. Production and hosting by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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Both CT and MRI are essential for petrous bone evaluation as it is not amenable to direct clinical examination [5]. They are both used to guide the choice of the cochlear device, the side to implant and the timing of surgery, looking for cochlear patency, round window niche access and degree of mastoid aeration. The main aim of imaging is to determine patients with contraindications for CI as well as choosing the CI type and predicting the outcome [1]. An important advantage of MRI is the direct visualization of the cochlear nerve caliber and integrity of the higher auditory pathway. CT is used selectively to differentiate between cochlear calcification and fibrosis, to define the facial nerve canal in cases of marked inner ear dysplasia, and to detect a cochlear aperture when attempting to differentiate between cochlear nerve hypoplasia and aplasia. It provides important data regarding the feasibility of the posterior tympanotomy surgical approach like decreased mastoid pneumatization, anterior segment sinus, low tegmen mastoideum and small fascial recess. It also provides data about round window anatomy and cochlear orientation [6]. The purpose of this study is to develop a systematic approach in preoperative CT and MRI assessment of CI candidates and to evaluate the suitability of CI for pediatric patients in the Suez Canal and East of Egypt area.
2. Methodology Twenty nine patients with 58 diseased ears were enrolled in the study. Inclusion criteria were as follows: patients aged 2–6 years, suffering from congenital or acquired profound SNHL and showing failure of hearing aids referred for evaluation of the possibility of CI. Exclusion criteria were as follows: general contraindications to surgery and contraindications to MRI as internal defibrillator or pacemaker, some types of clips used for cerebral aneurysms and non-MRI compatible prosthesis. Written consents were obtained from all parents. The study was approved by the local ethical and research committee. All patients underwent light anesthesia using chloral hydrate oral 5 mg/kg. Multidetector CT was performed using Aquilion 16 detector (Toshiba_medical system, Toshiba, Japan). No contrast was used. The scan was obtained in the supine position with no gantry tilt to facilitate free reconstructions of the images. The head position was adjusted so the sections were obtained parallel to the anthropologic line (the plane intersecting the inferior orbital rim and the superior margin of the external auditory canal. Collimation of 0.6 mm was used. The effective mAs; is 200 effective mAs. The kilovolt peak is usually 120 kvp. Helical mode was chosen for better reformate and to avoid the expected motion artifact in this age group. Raw data were transferred to workstation (Vitrea_, Toshiba, medical system, Toshiba, Japan). Additional coronal oblique reformat views 45 degrees in addition to the traditional axial and coronal views were also obtained for evaluation of large vestibular aqueduct, facial nerve, oval window and tegmen tympani dehiscence. Patients were then transferred to the MRI unit (1.5 T, Philips, Healthcare) in the same session. Axial 3D imaging (DRIVE) sequence was taken on the IAC and inner ear using the following parameters: 4000/130/1 (TR/TE/NEX); echo train length, 40; matrix, 256 256; field of view, 13 cm. Reconstruction of oblique sagittal reformat views on the IAC was performed. Threedimensional balanced fast field echo (3D bFFE) sequences were taken on the IAC and inner ear structures. Additional axial T2WI cuts were acquired to evaluate central causes of hearing loss. Image analysis was performed using by two radiologists (a professor and a consultant of radiology) in a non-blinded double reading sessions to minimize the discrepancy. Any disagreement
between the radiologists was solved in consensus. All image post-processing was performed using the Advantage Workstations. CT was used to assess mastoid pneumatization, middle ear aeration and inflammatory conditions, the round window niche, vestibular aqueduct diameter, any vascular anatomical or anomalies of the bony labyrinth. CT also assessed the presence of vascular anatomic variations linked with congenital SNHL as dehiscent jugular fossa, high riding jugular bulb, dehiscent carotid canal. The vestibular aqueduct was measured in the axial images according to the Valvassori method [2]. MRI was used to assess cochlear nerve agenesis, cochlear anomalies, anomalies of the membranous labyrinth, status of the IAC, enlarged endolymphatic duct and sac, and organic brain lesions. 3. Results Twenty nine patients with fifty eight diseased ears were submitted to CI imaging protocol. The mean age is 3.06 years (ranging from 2 to 6 years). The sample included 10 (65.5%) males and 19 (34.5%) females (Table 1). The imaging diagnosis was as follows (Tables 2 and 3): 38 ears were radiologically free and 20 ears showed inner ear abnormalities: 8 ears showed Mondini deformity (cystic appearance of the cochlear apex due to the confluence of the apical and middle turns with dilated vestibule and enlarged vestibular aqueduct) (Fig. 1). One ear was post meningitic and showed ossification of the cochlea and semicircular canals. Four ears had bilaterally absent semicircular canals with dysmorphic vestibule (Figs. 2 and 3). Two of them showed abnormal cochlea (cystic appearance of the cochlear apex due to the confluence of the apical and middle turns denoting incomplete partition deformity II,(IP II) but with intact cochlear nerve bilaterally. The others showed normal cochlea but with absent intrameatal vestibulocochlear nerve bilaterally. One ear showed IAC a horizontal bony septum with undivided vestibulocochlear nerve (Fig. 4). Another one showed absent cochlear nerve. One ear showed complete bony atresia of the IAC with complete aplasia of the vestibulocochlear nerve (Fig. 5). Two ears showed enlarged vestibules with dysplastic semicircular canals. Two ears showed absent posterior semicircular canals (Fig. 6) with dysplastic lateral semicircular canals and enlarged vestibules (Fig. 7). The inner ear showed acquired disease in one patient (3.4%) and congenital anomalies in 10 patients (34.4%). The congenital SNHL cases were syndromic in 2 out of the 10 patients (20%) and non syndromic in 8 patients (80%). The cochlea showed ossification in 1 ear (1.7%), Mondini malformation in 8 ears (13.7%) and IPII in 4 ears (6.8%). The vestibule was normal (mean = 5.9 3.1 mm ± 0.3 by CT & MRI) in 42 ears (72.4%), enlarged in 12 ears (20.7%), and dysmorphic in 4 ears (6.8%). The semicircular canals showed ossifications in 1 ear (1.7%), aplasia in 4 ears (6.9%), dysplasia in 3 ears (5.2%) and combined aplasia with dysplasia in 2 ears (3.4%). The IAC was atretic (<2.8 mm) in 1 ear (1.7%) and duplicated in another ear (1.7%) with a horizontal bony septum detected by CT. Mastoiditis was found
Table 1 Demographic data of the studied patients (N = 29). Variable
No.
Age
Mean ± SD Min–Max
3.07 ± 1.01 2–6
Gender
Male Female
19 10
Percentage
65.5% 34.5%
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A.S. Al-Rawy et al. / The Egyptian Journal of Radiology and Nuclear Medicine 48 (2017) 877–884 Table 2 CT and MRI findings (N = 58). Variable
CT
MRI
No.
Percentage
No.
Percentage
Cochlea
Normal Ossifications Mondini IPII
45 1 8 4
77.5% 1.7% 13.7% 6.8%
45 1 8 4
77.5% 1.7% 13.7% 6.8%
Vestibule
Normal Enlarged Dysmorphic
42 12 4
72.4% 20.7% 6.8%
42 12 4
72.4% 20.7% 6.8%
Semicircular canals
Normal Ossifications Aplasia Dysplasia Aplasia + dysplasia
48 1 4 3 2
82.8% 1.7% 6.9% 5.2% 3.4%
48 1 4 3 2
82.8% 1.7% 6.9% 5.2% 3.4%
IAC
Normal Atretic Duplicated
56 1 1
96.5% 1.7% 1.7%
56 1 1
96.5% 1.7% 1.7%
Inflammatory conditions
Normal Mastoditis Otomastoditis
45 3 10
77.6% 5.2% 17.2%
CT external ear
Normal Stenotic
56 2
96.6% 3.4%
CT Vestibular aqueduct
Normal Enlarged
50 8
86.2% 13.8%
Table 3 MRI findings (N = 58). Variable
No.
Percentage
MRI Vestibulocochlear nerve
Normal Aplasia Dysplasia – divided Dysplasia – absent cochlear nerve
53 3 1 1
91.4% 5.2% 1.7% 1.7%
MRI Facial nerve
Normal Absent
57 1
98.3% 1.7%
MRI Endolymphatic duct and sac
Normal Enlarged
50 8
86.2% 13.8%
MRI Brain findings
Normal Abnormal
28 1
96.6% 3.4%
in 3 ears (5.2%) and otomastoiditis in 10 ears (17.2%). Two stenotic external ears (diameter <4 mm) (3.4%). The vestibular aqueduct was enlarged by CT (diameter >5 mm) in 8 ears (13.8%). The oval window, round window and jugular bulb in the all examined ears showed normal CT appearances with no detected vascular anatomical variations. The MRI showed the following relevant specific findings: vestibulocochlear nerve aplasia in 3 ears (5.2%), undivided in 1 ear (1.7%) and absent cochlear division in 1 ear (1.7%), aplastic fascial nerve in 1 ear (1.7%), enlarged endolymphatic sac in 8 ears (13.8%) and supratentorial hydrocephalus in one patient (3.4%). The examined ears were categorized into four groups according the candidacy for operation (Tables 4 and 5); 86.2% of all examined ears were suitable for CI, 5.1% were suitable for CI but with expected poor response, 1.7% of examined ears were suitable for CI with modification of surgical procedure and 6.8% were not suitable for CI. The CT when compared to the MRI (as the gold standard) in determining candidates (ears) for CI showed 3 false positive cases, 1 false negative case, one true negative case and 54 true positive cases with a calculated sensitivity, specificity, positive predictive value and negative predictive values of 98%, 25%, 94.7% and 50% respectively.
Fig. 1. Mondini deformity, candidate for CI. (a) Axial CT image of the petrous bone showing cystic appearance of the cochlear apex (black arrows) due to the confluence of the apical and middle turns, dilated vestibule (black asterisk, normal = 5.9 3.1 mm ± 0.3, right = 6.7 4mm, left = 6.8 4.1 mm) and enlarged vestibular aqueducts bilaterally (red arrows, normal diameter <1.5 mm, right side = 3.5 mm, left side = 3.2 mm). (b) Axial T2-weighted DRIVE images showing bilateral large endolymphatic ducts and sacs (green arrow). Also cystic cochlear apex (white arrows) and dilated vestibule (black asterisk) is bilaterally noted.
4. Discussion Causes of SNHL include genetic conditions, inflammatory diseases, ischemic events, traumatic sequelae, toxic agents and idiopathic. CI is a well-accepted treatment modality for profound hearing loss or deafness. Preoperative imaging of CI candidates plays a major role treatment planning [2]. Systematic analysis for congenital or obliterative inner ear disease, retrocochlear pathology, and anatomic variants of the middle ear and mastoid provides information on feasibility of the operation, preferred surgical approach including operative side, and type of CI [4].
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Fig. 2. A 2 year old female presented with developmental delay, congenital heart disease (Ebstein anomaly), abnormal auricle shape and characteristic facies, possible CHARGE syndrome. Imaging shows bilateral absence of semicircular canals, candidate for CI. (a) Axial CT image of the petrous bone showing bilaterally absent semicircular canals, cystic appearance of the cochlear apex (red arrow) due to the confluence of the apical and middle turns (IP II deformity) and dysmorphic vestibule (black arrow) bilaterally. Bilateral fluid density within the middle ear and mastoid air cells is also noted (white asterisks). (b) Axial T2-weighted DRIVE images showing bilaterally absent semicircular canals, cystic appearance of the cochlear apex (red arrow) due to the confluence of the apical and middle turns (IP II deformity) and dysmorphic vestibule (white arrow) bilaterally.
This study included 29 patients (11 females and 18 males) with a mean age 3.07 ± 1.01. All patients underwent combined 16 multidetector CT using standard axial and coronal reformat planes. In the same session, 3D DRIVE MRI axial plane reformatted into sagittal plane for the IAC and inner ear as well as axial T2WI for the whole brain. The study aimed to investigate the value of CT and MRI for evaluation and classification of inner ear abnormalities in patients with bilateral profound SNHL who are candidates for CI.
Thirty eight percent of study population had inner ear malformation. A former study stated that 20.3% of congenital SNHL is caused by inner ear malformations [7]. MRI is more sensitive and specific in diagnosing soft tissue abnormalities in the inner ear than CT. Also, the abnormalities detected by MRI are more likely to influence the CI process (e.g., asymmetric nerve aplasia, cochlear obstruction) [8]. Standard axial, coronal and sagittal reformat MRI views were enough for identification of these anomalies. The image acquisition requires a high signal from the fluid containing spaces, less susceptibility, pulsation artifacts and short examination time [2]. DRIVE sequence has the effect of reducing flow void artifacts, increasing the brightness of fluids. So it was accurate in identification of internal partitions of the cochlea, minor cochlear hypoplasia and associated cochlear nerve anomalies. Also it can identify thin fibrotic bands that may follow labyrinthitis and attenuate the cochlear lumen. Its reconstruction into sagittal and coronal reformat views allows better identification of the cochlear nerve anomalies [4]. Regarding the inner ear abnormalities, our study included 29 cases with 58 diseased ears. Thirty eight ears were radiologically free. Twenty ears showed inner ear abnormalities. The most common inner ear anomaly was Mondini deformity (8 ears, 13.7%) in which IP II deformity of cochlea associated with dilated vestibule and enlarged vestibular aqueduct. IP II deformity with normal vestibular aqueduct was found in 4 ears (6.8%). Joshi et al. [9] found that IPII deformity is the most common type of cochlear malformation, accounting for more than 50% of all cochlear deformities which is the most common malformation in our study. In the same study, 84% of cases of enlarged vestibular aqueduct were accompanied by other inner ear anomalies and an isolated finding of enlargement of the endolymphatic duct and sac is uncommon which is similar to our study in which all cases of enlarged vestibular aqueduct is associated with IPII deformity. Taha et al. [4] studied 120 cases with 220 diseased ears submitted to CI imaging protocol, 150 ears were radiologically free and
Fig. 3. A 2 year old female presented with developmental delay, congenital heart disease (Ebstein anomaly), abnormal auricle shape, characteristic facies and bilaterally atretic outer ear. Bilateral absence of semicircular canals, possible CHARGE syndrome. Bilateral aplasia of the vestibulocochlear nerve; not candidate for CI. (a), (b) Axial CT image of the petrous bone showing bilaterally absent semicircular canals and dysmorphic vestibule bilaterally with normal cochlea. Fluid density within the middle ear and mastoid air cells is also in the right side and within the left mastoid air cells. (c), (d) Axial T2-weighted DRIVE images showing bilaterally absent semicircular canals, normal cochlea and dysmorphic vestibule bilaterally. (e) Oblique sagittal reformat T2-weighted DRIVE images of the IAC, showing single nerve within the IAC which is the facial nerve (red arrow) with absent vestibulocochlear nerve.
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Fig. 4. Right IAC horizontal bony septum with undivided vestibulocochlear nerve. Bilateral IP II deformity. Absent left cochlear branch; candidate for CI at the Rt. side. (a) Coronal reformat CT image of the petrous bone showing right IAC horizontal bony septum (red arrow) compared to the normal bony canal of the left side (black arrow). (b) Axial T2-weighted DRIVE images showing right abnormal IAC (white arrow). Left side showed cystic appearance of the apex of the cochlea (red arrow) in keeping with IP II deformity. (c) and (d) Oblique sagittal reformat T2-weighted DRIVE images of the IAC. (c) showing 2 nerves (white arrows) within the right IAC (facial nerve and undivided vestibulocochlear nerve). (d) showing absent cochlear division (red arrow) of the left vestibulocochlear nerve.
Fig. 5. Right IAC complete atresia with aplasia of the Rt. vestibulocochlear nerve; candidate for CI at the Lt. side. (a) Axial CT image of the petrous bone showing right IAC complete atresia (black asterisk) compared to the normal bony canal of the left side (white arrow). (b) Axial T2-weighted DRIVE images showing right IAC complete atresia (white asterisk) with non visualized vestibulocochlear and facial nerves compared to the normal canal (white arrow) with intact nerves of the left side.
were requiring implant. Forty ears had congenital malformation in the inner ear: 18 ears showed IP II deformity which is the most common anomaly in our study. One ear (1.7%) was post meningitic and showed ossification of the apex and basal turn of the cochlea as well as semicircular canals. This differs from results of other studies [4] in which 13.6% of examined ears had LO. Dagkiran et al. found two ears with cochlear ossification (1.4% of all examined ears) similar to our study [7]. Ossification is a relative contraindication to CI as it is difficult to achieve safe electrode insertion because of bony obstruction. The electrodes or the inner ear structures can be damaged. Obstructed scala tympani could also limit the number of electrodes that can be
inserted. The efficacy of the electrical stimulation is also questioned, as a higher current will be needed on an ossified cochlea. Also, the neural survival in ossified cochlea is unpredictable [4]. Bilaterally absent semicircular canals with dysmorphic vestibule were found in 4 ears (6.8%). Two of them showed abnormal cochlea (IP II deformity of cochlea) but with intact cochlear nerve bilaterally. The others showed normal cochlea but with absent intrameatal vestibule- cochlear nerve. The patients also showed associated mental and growth retardation, congenital heart disease, characteristic facies and atretic external ear which may suggested possible CHARGE syndrome. Abnormal brain findings were also found in only one patient. IAC horizontal bony septum was found in one ear (1.7%) by CT scan with undivided vestibulocochlear nerve detected by MRI. Absent cochlear nerve was found in one ear (1.7%). Complete bony atresia of the IAC with complete aplasia of vestibulocochlear and facial nerves was found in one ear (1.7%). The IAC may be atretic, or it may have a horizontal bony septum that divides it into two or more separate canals. The narrow duplicated IAC is a very rare malformation. It has been suggested to be associated with congenital SNHL and to be a result of aplasia or hypoplasia of the vestibulocochlear nerve or the cochlear branch [9,10]. Five cases of a narrow IAC with duplication have been reported [11]. The IAC morphologic characteristics and size are not reliable indicators of the integrity of the cochlear nerve; normal size of the IAC and normal inner ear CT anatomy do not exclude a nerve deficiency. The nerve may be absent when the IAC and labyrinth are normal by imaging. Hence, MRI is the modality of choice for assessment of the cochlear nerve [9]. A narrow internal auditory canal is a relative contraindication to CI because it is usually associated with aplasia or hypoplasia of the vestibulocochlear nerve or its cochlear branch [12] which differs from our study in which the partitioned canal associated with undivided vestibulocochlear nerve, in which CI is technically possible. Undivided vestibulocochlear nerve is most frequently associated with severe labyrinth malformations like a common
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Fig. 6. Bilateral absence of posterior semicircular canals, candidate for CI. (a) Axial CT image of the petrous bone showing absent posterior semicircular canals, enlarged vestibule (red arrows, normal = 5.9 3.1 mm ± 0.3, right = 7.7 3.2 mm, left = 7.4 3.2 mm) and dysplastic lateral semicircular canals (green arrows) bilaterally. (b), (c) Corresponding axial T2-weighted DRIVE images showing the absent fluid signal for the posterior semicircular canals bilaterally with enlarged vestibules and dysplastic lateral semicircular canals. (d) Axial T2-weighted DRIVE image showing normal fluid signal for the superior semi circular canals bilaterally (white arrows).
Table 5 CT compared to MRI in determining the cochlear implantation candidates (N = 58). Variable
No.
Percentage
CT
Candidate Not candidate
56 2
96.5% 3.4%
MRI
Candidate Not candidate
54 4
93.1% 6.8%
A = True positive = 54. B = False positive = 3. C = False negative = 1. D = True negative = 1. Sensitivity: A/(A + C) 100 = 54/(54 + 1) 100 = 98%. Specificity: D/(D + B) 100 = 1/(1 + 3) 100 = 25%. Positive predictive value: A/(A + B) 100 = 54/(54 + 3) = 94.7%. Negative predictive value: D/(D + C) 100 = 1/(1 + 1) = 50%.
Fig. 7. Bilateral lateral semicircular Canal—Vestibule Dysplasia, candidate for CI. (a) Axial T2-weighted DRIVE images showing normal MRI appearances of the cochlea. (b) Axial T2-weighted DRIVE images showing the bilateral fluid -filled cystic appearance of the lateral semicircular canals with enlarged vestibules (white arrows). (c) 3D maximum intensity projection image of the inner ear showing abnormal vestibule and lateral semicircular canal appearances (white arrows).
Table 4 Candidacy for operation as decided by CT and MRI (N = 58). Candidacy for CI
No.
Percentage
Candidate Candidate with poor response Candidate with modification of surgical procedure Not candidate
50 3 1 4
86.2% 5.1% 1.7% 6.8%
cavity or cochlear aplasia which differ from our study in which it was associated with IP II deformity of cochlea [2]. Enlarged vestibules with dysplastic semicircular canals (Lateral Semicircular Canal Vestibule Dysplasia) in which a single cavity is formed by the vestibule and lateral semicircular canal were found in 2 ears (3.4%). Posterior semicircular canals aplasia with dysplastic lateral semicircular canals were noted in 2 ears (3.4%). In this study, the lateral semicircular canals are the most frequently malformed canal. Isolated posterior and superior canal
malformations in combination with a normal lateral semicircular canal are uncommonly described in literature because it is the last one to be formed [2]. Dagkiran et al. found 10 ears with posterior semicircular canal (7.3%), 10 ears with lateral semicircular canal (7.4%), 8 ears with superior semicircular canal aplasia/hypopasia (5.9%), and 8 ears with lateral semicircular canal-vestibular dysplasia [7]. In this study, 10 ears (17.2%) showed otomastoiditis. Mastoiditis was noted in 3 ears (5.2%). Inflammation of the middle ear or mastoid cells is associated with high risk of postoperative sepsis and failure [1]. CT is valuable in assessment of mastoiditis and cholesteatomas with a sensitivity approaching 79% [13]. All of examined ears showed normal CT appearances of the oval window and round window. No vascular anatomical variants were detected in our study. The prime requirements for CI are the presence of a cochlea (either normal or malformed) and of a cochlear nerve [14]. Most cochlear abnormalities may be successfully treated with CI but with an increased risk of intraoperative cerebrospinal fluid leakage and postoperative bacterial meningitis. Deficiency of the 8th nerve or brain stem lesions correlates with poor auditory outcomes and affect eligibility for CI [15]. Certain medical conditions that preclude CI surgery (e.g., specific hematologic, pulmonary, and cardiac conditions) also may be contraindications [16]. Two patients (20%) with congenital inner ear malformations in our study were syndromic and 8 patients (80%) were nonsyndromic which is similar to the study in which 20% of the congenital inner ear malformations were syndromic [17]. This study shows that 4 ears will not be suitable for CI (3 ears with absent vestibulocochlear nerve, and one ear with absent
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cochlear nerve). Two of all examined ears will require an implant with expected poor response due to co-morbidities and mental retardation. In these patients, the response is dependent on the type and degree of associated anomalies. One ear will require implant with expected poor response due to undivided vestibulocochlear nerve. Twelve ears showed inner ear anomalies with no contraindication to surgery (vestibular and semicircular canals dysplasia). One ear showed LO of the basal turn and semicircular canals which may require modification of surgical technique (Fig. 8). Thirty eight ears were completely normal with no contraindication for surgery. Most inner ear malformation could be detected in CT and MRI however some anomalies are detected only in MRI such as cochlear nerve aplasia/hypoplasia, minor cochlear hypoplasia, fibrous LO, and associated cerebral congenital or post inflammatory anomalies. Also, some abnormalities are detected only in the CT as calcified lumen of inner ear structures in LO, and totally ossified cochlea that is difficult to differentiate from cochlear aplasia in MRI [4]. DRIVE sequence in the standard MRI temporal bone protocol is important for evaluation of the cochlear nerve hypoplasia, aplasia
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or post meningitic atrophy, as well as assessment of cochlear lumen patency, and minor hypoplasia. T2WI of the brain helps in identifying central causes of SNHL [2]. In this study, while the CT scan found that all of the studied patients are suitable for CI in both sides or in one side only (as in the case of unilateral complete atresia of the IAC). MRI found that 28 patients (96.5%) are suitable for CI and only one patient (3.4%) will not gain benefit from CI due to bilaterally absent vestibulocochlear nerve. When CT was compared to MRI (as a gold standard) in determining candidates for CI in our study, the sensitivity of CT was 98%, specificity was 25%, positive predictive value was 94.7% and negative predictive value was 50%. CT may be better at defining some abnormalities but MRI appears to be able to detect all abnormalities that are critical to patient management. Most candidates for CI should therefore be assessed by MRI initially. CT is most likely to be helpful in those with a history of severe middle ear disease, meningitis or dysmorphic syndromes who should undergo both CT and MRI.
Fig. 8. A 5 year old female with history of meningitis at the age of 9 month. LO of the Lt. cochlea, candidate for CI at the Lt. side. (a), (b) and (c) Axial CT image of the petrous bone showing abnormal bone formation within the apex (green arrow) and the basal turn of the left cochlea (red arrow) compared to the normal right one. (d), (e) Corresponding axial T2-weighted DRIVE images showing signal loss at the apex (green arrow) and part of the basal turn of the left cochlea (red arrow).
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One of the drawbacks of our study is limited number of cases. CT/MRI protocol is recommended to be generalized for pediatric SNHL cases for proper preoperative evaluation to reach the best results particularly in complex cases of SNHL. Correlation with the surgical data is also valuable in confirming the imaging findings. In conclusion, for the work-up of CI candidates, MRI is the main tool to determine the accessibility of the cochlea, the presence of a normally sized cochlear nerve branch, the absence of lesions at the level the auditory pathways or the auditory cortex. CT is helpful in those with a history of severe middle ear disease, meningitis or dysmorphic syndromes who should undergo both CT and MRI. The results of this study are unique as it is the first study to be published internationally regarding the suitability for cochlear implants in pediatric patients in the Suez Canal area and the east of Egypt as well as the imaging findings in patients located in this area. In the Suez Canal area and the east of Egypt, the majority of patients with profound SNHL (96.6%) are good candidates for CI; the race and ethnic variations in ear malformation are appreciated in multiple studies [18]. Conflict of interest The authors declared that there is no conflict of interest. References [1] Marsot-Dupuch K, Meyer B. Cochlear implant assessment: imaging issues. Eur J Radiol 2001;40(2):119–32. [2] Lemmerling M, Foer B. Temporal bone imaging. Berlin Heidelberg: SpringerVerlag; 2015. p. 237–48. [3] Yousem D, Grossman R. Neuroradiology: the requisites. Philadelphia, PA: Mosby/Elsevier; 2010. p. 385–413.
[4] Taha T, Wahba H, Ibrahim A, AbdElazim Y. Cochlear implant tailored imaging protocol: what clinicians need to know. Egypt J Radiol Nucl Med 2015;46 (1):33–43. [5] Razek AA, Huang BY. Lesions of the petrous apex: classification and findings at CT and MR imaging. Radiographics 2012;32(1):151–73. [6] Connor SEJ. Contemporary imaging of auditory implants. Clin Radiol 2017. doi: https://doi.org/10.1016/j.crad.2017.03.002 (Article in press). [7] Dagkiran M, Dagkiran N, Surmelioglu O, Balli T, Tuncer U, Akgul E, et al. Radiological imaging findings of patients with congenital totally hearing loss. J Int Adv Otol 2016;12(1):43–8. [8] Mackeith S, Joy R, Robinson P, Hajioff D. Pre-operative imaging for cochlear implantation: magnetic resonance imaging, computed tomography, or both? Cochlear Implants Int 2012;13(3):133–6. [9] Joshi VM, Navlekar SK, Kishore GR, Reddy KJ, Kumar EC. CT and MR imaging of the inner ear and brain in children with congenital sensorineural hearing loss. Radiographics 2012;32(3):683–98. [10] Lee SY, Cha SH, Jeon MH, Bae IH, Han GS, Kim SJ, et al. Narrow duplicated or triplicated internal auditory canal (3 cases and review of literature) can we regard the separated narrow internal auditory canal as the presence of vestibulocochlear nerve fibers? J Comput Assist Tomogr 2009;33(4):565–70. [11] Baik HW, Yu H, Kim KS, Kim GH. A narrow internal auditory canal with duplication in a patient with congenital sensorineural hearing loss. Korean J Radiol 2008;9(Suppl.):S22–5. [12] Vincenti V, Ormitti F, Ventura E. Partitioned versus duplicated internal auditory canal: when appropriate terminology matters. Otol Neurotol 2014;35(7):1140–4. [13] Razek AA, Ghonim MR, Ashraf B. Computed tomography staging of middle ear cholesteatoma. Polish J Radiol 2015;80:328–33. [14] Witte RJ, Lane JI, Driscoll CL, Lundy LB, Bernstein MA, Kotsenas AL, et al. Pediatric and adult cochlear implantation. Radiographics 2003;23 (5):1185–200. [15] Young JY, Ryan ME, Young NM. Preoperative imaging of sensorineural hearing loss in pediatric candidates for cochlear implantation. Radiographics 2014;34 (5):E133–49. [16] Wendling P. Cochlear implant revision surgery beneficial. Pediatric News 2006;40(2):40. [17] Huang BY, Zdanski C, Castillo M. Pediatric sensorineural hearing loss, part 2: syndromic and acquired causes. AJNR Am J Neuroradiol 2012;33(3):399–406. [18] Källén B. Severe ear malformations. In: Epidemiology of human congenital malformations. Springer, Cham; 2014. p. 45–48.
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The Egyptian Journal of Radiology and Nuclear Medicine journal homepage: www.sciencedirect.com/locate/ejrnm
Original Article
Systematic approach by computed tomography and magnetic resonance imaging in cochlear implantation candidates in Suez Canal University Hospital Aya S. Al-Rawy a, Mohammad al-Shatouri a,⇑, Mohammed El Tabbakh b, Azza A. Gad a a b
Department of Radiology, Suez Canal University Hospital, Faculty of Medicine, Ismailia, Egypt Department of ENT, Suez Canal University Hospital, Ismailia, Egyptt
a r t i c l e
i n f o
Article history: Received 5 June 2017 Accepted 10 August 2017 Available online 4 January 2018 Keywords: Cochlear implantation Suez Canal area Pre-surgical mapping Sensorineural hearing loss CT MRI
a b s t r a c t Objectives: To create a systematic approach using computed tomography (CT) and magnetic resonance imaging (MRI) findings to facilitate identifying the etiology of hearing loss, evaluating the anatomy for surgery, and predicting complications. Methods: Twenty nine pediatric patients with congenital or acquired sensory-neural hearing loss (SNHL) requiring cochlear implant (CI) were included. They underwent combined CT, 3D DRIVE MRI axial plane and axial T2WIs for the whole brain. The inner ear, cochlear nerve development, temporal bone anatomy, operative window, normal variants and causes of central hearing loss were assessed. Results: CT showed that 100% of the patients are suitable for CI while MRI showed that 96.5% of studied patients are suitable. The examined ears were categorized into 4 groups according the candidacy for operation; 86.2% were suitable for CI, 5.1% were suitable for CI but with expected poor response, 1.7% of examined ears were suitable for CI with modification of surgical procedure and 6.8% were not suitable for CI. Conclusion: In Suez Canal area, the combined CT/MRI approach categorized the majority of patients with SNHL (96.6%) as good candidates for CI. Ó 2017 The Egyptian Society of Radiology and Nuclear Medicine. Production and hosting by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
1. Introduction Hearing loss has a significant impact on the patients and society. Early identification of hearing impairment and differentiation between non progressive (congenital) and progressive types may minimize the loss of development of important skills in speech, language, and social interactions [1].
Abbreviations: CT, computed tomography; MRI, magnetic resonance imaging; CI, cochlear implant; SNHL, sensory neural hearing loss; 3D, three dimensional; IAC, internal auditory canal; T2WIs, T2 weighted images; IP, incomplete partition; LO, labyrinthitis ossificans. Peer review under responsibility of The Egyptian Society of Radiology and Nuclear Medicine. ⇑ Corresponding author at: Radiology Department, Suez Canal University Hospital, Ring Road, 41522 Ismailia, Egypt. Tel.: +20 01001811293. E-mail addresses: [email protected] (A.S. Al-Rawy), [email protected] (M. al-Shatouri), [email protected] (M. El Tabbakh), [email protected] (A.A. Gad).
Cochlear implantation (CI) is a widely available tool for treatment of deafness or severe SNHL in patients who do not show adequate benefits from hearing aids. Imaging plays an important role in the selection of candidates and in the planning of surgery. The preoperative assessment should provide optimal information on the anatomy of the ear, its normal variants, and pathology of the temporal bone and auditory pathway [2]. Cochlear implant is an electronic device used to habilitate or rehabilitate patients with severe hearing impairment. It creates a direct stimulation of the residual spiral ganglion cells of the cochlear nerve by bypassing the destroyed hair cells. Normally, the sound waves coming from the oval window pass to the scala vestibuli up to the helicotrema and then, towards the round window by the scala tympani. The hair cells are excited by the variations of sound waves transmitted to the scala media [3]. The frequency of CI has increased over the last years. Improved speech processing strategies leads recently to improve auditory results [4].
https://doi.org/10.1016/j.ejrnm.2017.08.005 0378-603X/Ó 2017 The Egyptian Society of Radiology and Nuclear Medicine. Production and hosting by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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Both CT and MRI are essential for petrous bone evaluation as it is not amenable to direct clinical examination [5]. They are both used to guide the choice of the cochlear device, the side to implant and the timing of surgery, looking for cochlear patency, round window niche access and degree of mastoid aeration. The main aim of imaging is to determine patients with contraindications for CI as well as choosing the CI type and predicting the outcome [1]. An important advantage of MRI is the direct visualization of the cochlear nerve caliber and integrity of the higher auditory pathway. CT is used selectively to differentiate between cochlear calcification and fibrosis, to define the facial nerve canal in cases of marked inner ear dysplasia, and to detect a cochlear aperture when attempting to differentiate between cochlear nerve hypoplasia and aplasia. It provides important data regarding the feasibility of the posterior tympanotomy surgical approach like decreased mastoid pneumatization, anterior segment sinus, low tegmen mastoideum and small fascial recess. It also provides data about round window anatomy and cochlear orientation [6]. The purpose of this study is to develop a systematic approach in preoperative CT and MRI assessment of CI candidates and to evaluate the suitability of CI for pediatric patients in the Suez Canal and East of Egypt area.
2. Methodology Twenty nine patients with 58 diseased ears were enrolled in the study. Inclusion criteria were as follows: patients aged 2–6 years, suffering from congenital or acquired profound SNHL and showing failure of hearing aids referred for evaluation of the possibility of CI. Exclusion criteria were as follows: general contraindications to surgery and contraindications to MRI as internal defibrillator or pacemaker, some types of clips used for cerebral aneurysms and non-MRI compatible prosthesis. Written consents were obtained from all parents. The study was approved by the local ethical and research committee. All patients underwent light anesthesia using chloral hydrate oral 5 mg/kg. Multidetector CT was performed using Aquilion 16 detector (Toshiba_medical system, Toshiba, Japan). No contrast was used. The scan was obtained in the supine position with no gantry tilt to facilitate free reconstructions of the images. The head position was adjusted so the sections were obtained parallel to the anthropologic line (the plane intersecting the inferior orbital rim and the superior margin of the external auditory canal. Collimation of 0.6 mm was used. The effective mAs; is 200 effective mAs. The kilovolt peak is usually 120 kvp. Helical mode was chosen for better reformate and to avoid the expected motion artifact in this age group. Raw data were transferred to workstation (Vitrea_, Toshiba, medical system, Toshiba, Japan). Additional coronal oblique reformat views 45 degrees in addition to the traditional axial and coronal views were also obtained for evaluation of large vestibular aqueduct, facial nerve, oval window and tegmen tympani dehiscence. Patients were then transferred to the MRI unit (1.5 T, Philips, Healthcare) in the same session. Axial 3D imaging (DRIVE) sequence was taken on the IAC and inner ear using the following parameters: 4000/130/1 (TR/TE/NEX); echo train length, 40; matrix, 256 256; field of view, 13 cm. Reconstruction of oblique sagittal reformat views on the IAC was performed. Threedimensional balanced fast field echo (3D bFFE) sequences were taken on the IAC and inner ear structures. Additional axial T2WI cuts were acquired to evaluate central causes of hearing loss. Image analysis was performed using by two radiologists (a professor and a consultant of radiology) in a non-blinded double reading sessions to minimize the discrepancy. Any disagreement
between the radiologists was solved in consensus. All image post-processing was performed using the Advantage Workstations. CT was used to assess mastoid pneumatization, middle ear aeration and inflammatory conditions, the round window niche, vestibular aqueduct diameter, any vascular anatomical or anomalies of the bony labyrinth. CT also assessed the presence of vascular anatomic variations linked with congenital SNHL as dehiscent jugular fossa, high riding jugular bulb, dehiscent carotid canal. The vestibular aqueduct was measured in the axial images according to the Valvassori method [2]. MRI was used to assess cochlear nerve agenesis, cochlear anomalies, anomalies of the membranous labyrinth, status of the IAC, enlarged endolymphatic duct and sac, and organic brain lesions. 3. Results Twenty nine patients with fifty eight diseased ears were submitted to CI imaging protocol. The mean age is 3.06 years (ranging from 2 to 6 years). The sample included 10 (65.5%) males and 19 (34.5%) females (Table 1). The imaging diagnosis was as follows (Tables 2 and 3): 38 ears were radiologically free and 20 ears showed inner ear abnormalities: 8 ears showed Mondini deformity (cystic appearance of the cochlear apex due to the confluence of the apical and middle turns with dilated vestibule and enlarged vestibular aqueduct) (Fig. 1). One ear was post meningitic and showed ossification of the cochlea and semicircular canals. Four ears had bilaterally absent semicircular canals with dysmorphic vestibule (Figs. 2 and 3). Two of them showed abnormal cochlea (cystic appearance of the cochlear apex due to the confluence of the apical and middle turns denoting incomplete partition deformity II,(IP II) but with intact cochlear nerve bilaterally. The others showed normal cochlea but with absent intrameatal vestibulocochlear nerve bilaterally. One ear showed IAC a horizontal bony septum with undivided vestibulocochlear nerve (Fig. 4). Another one showed absent cochlear nerve. One ear showed complete bony atresia of the IAC with complete aplasia of the vestibulocochlear nerve (Fig. 5). Two ears showed enlarged vestibules with dysplastic semicircular canals. Two ears showed absent posterior semicircular canals (Fig. 6) with dysplastic lateral semicircular canals and enlarged vestibules (Fig. 7). The inner ear showed acquired disease in one patient (3.4%) and congenital anomalies in 10 patients (34.4%). The congenital SNHL cases were syndromic in 2 out of the 10 patients (20%) and non syndromic in 8 patients (80%). The cochlea showed ossification in 1 ear (1.7%), Mondini malformation in 8 ears (13.7%) and IPII in 4 ears (6.8%). The vestibule was normal (mean = 5.9 3.1 mm ± 0.3 by CT & MRI) in 42 ears (72.4%), enlarged in 12 ears (20.7%), and dysmorphic in 4 ears (6.8%). The semicircular canals showed ossifications in 1 ear (1.7%), aplasia in 4 ears (6.9%), dysplasia in 3 ears (5.2%) and combined aplasia with dysplasia in 2 ears (3.4%). The IAC was atretic (<2.8 mm) in 1 ear (1.7%) and duplicated in another ear (1.7%) with a horizontal bony septum detected by CT. Mastoiditis was found
Table 1 Demographic data of the studied patients (N = 29). Variable
No.
Age
Mean ± SD Min–Max
3.07 ± 1.01 2–6
Gender
Male Female
19 10
Percentage
65.5% 34.5%
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A.S. Al-Rawy et al. / The Egyptian Journal of Radiology and Nuclear Medicine 48 (2017) 877–884 Table 2 CT and MRI findings (N = 58). Variable
CT
MRI
No.
Percentage
No.
Percentage
Cochlea
Normal Ossifications Mondini IPII
45 1 8 4
77.5% 1.7% 13.7% 6.8%
45 1 8 4
77.5% 1.7% 13.7% 6.8%
Vestibule
Normal Enlarged Dysmorphic
42 12 4
72.4% 20.7% 6.8%
42 12 4
72.4% 20.7% 6.8%
Semicircular canals
Normal Ossifications Aplasia Dysplasia Aplasia + dysplasia
48 1 4 3 2
82.8% 1.7% 6.9% 5.2% 3.4%
48 1 4 3 2
82.8% 1.7% 6.9% 5.2% 3.4%
IAC
Normal Atretic Duplicated
56 1 1
96.5% 1.7% 1.7%
56 1 1
96.5% 1.7% 1.7%
Inflammatory conditions
Normal Mastoditis Otomastoditis
45 3 10
77.6% 5.2% 17.2%
CT external ear
Normal Stenotic
56 2
96.6% 3.4%
CT Vestibular aqueduct
Normal Enlarged
50 8
86.2% 13.8%
Table 3 MRI findings (N = 58). Variable
No.
Percentage
MRI Vestibulocochlear nerve
Normal Aplasia Dysplasia – divided Dysplasia – absent cochlear nerve
53 3 1 1
91.4% 5.2% 1.7% 1.7%
MRI Facial nerve
Normal Absent
57 1
98.3% 1.7%
MRI Endolymphatic duct and sac
Normal Enlarged
50 8
86.2% 13.8%
MRI Brain findings
Normal Abnormal
28 1
96.6% 3.4%
in 3 ears (5.2%) and otomastoiditis in 10 ears (17.2%). Two stenotic external ears (diameter <4 mm) (3.4%). The vestibular aqueduct was enlarged by CT (diameter >5 mm) in 8 ears (13.8%). The oval window, round window and jugular bulb in the all examined ears showed normal CT appearances with no detected vascular anatomical variations. The MRI showed the following relevant specific findings: vestibulocochlear nerve aplasia in 3 ears (5.2%), undivided in 1 ear (1.7%) and absent cochlear division in 1 ear (1.7%), aplastic fascial nerve in 1 ear (1.7%), enlarged endolymphatic sac in 8 ears (13.8%) and supratentorial hydrocephalus in one patient (3.4%). The examined ears were categorized into four groups according the candidacy for operation (Tables 4 and 5); 86.2% of all examined ears were suitable for CI, 5.1% were suitable for CI but with expected poor response, 1.7% of examined ears were suitable for CI with modification of surgical procedure and 6.8% were not suitable for CI. The CT when compared to the MRI (as the gold standard) in determining candidates (ears) for CI showed 3 false positive cases, 1 false negative case, one true negative case and 54 true positive cases with a calculated sensitivity, specificity, positive predictive value and negative predictive values of 98%, 25%, 94.7% and 50% respectively.
Fig. 1. Mondini deformity, candidate for CI. (a) Axial CT image of the petrous bone showing cystic appearance of the cochlear apex (black arrows) due to the confluence of the apical and middle turns, dilated vestibule (black asterisk, normal = 5.9 3.1 mm ± 0.3, right = 6.7 4mm, left = 6.8 4.1 mm) and enlarged vestibular aqueducts bilaterally (red arrows, normal diameter <1.5 mm, right side = 3.5 mm, left side = 3.2 mm). (b) Axial T2-weighted DRIVE images showing bilateral large endolymphatic ducts and sacs (green arrow). Also cystic cochlear apex (white arrows) and dilated vestibule (black asterisk) is bilaterally noted.
4. Discussion Causes of SNHL include genetic conditions, inflammatory diseases, ischemic events, traumatic sequelae, toxic agents and idiopathic. CI is a well-accepted treatment modality for profound hearing loss or deafness. Preoperative imaging of CI candidates plays a major role treatment planning [2]. Systematic analysis for congenital or obliterative inner ear disease, retrocochlear pathology, and anatomic variants of the middle ear and mastoid provides information on feasibility of the operation, preferred surgical approach including operative side, and type of CI [4].
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Fig. 2. A 2 year old female presented with developmental delay, congenital heart disease (Ebstein anomaly), abnormal auricle shape and characteristic facies, possible CHARGE syndrome. Imaging shows bilateral absence of semicircular canals, candidate for CI. (a) Axial CT image of the petrous bone showing bilaterally absent semicircular canals, cystic appearance of the cochlear apex (red arrow) due to the confluence of the apical and middle turns (IP II deformity) and dysmorphic vestibule (black arrow) bilaterally. Bilateral fluid density within the middle ear and mastoid air cells is also noted (white asterisks). (b) Axial T2-weighted DRIVE images showing bilaterally absent semicircular canals, cystic appearance of the cochlear apex (red arrow) due to the confluence of the apical and middle turns (IP II deformity) and dysmorphic vestibule (white arrow) bilaterally.
This study included 29 patients (11 females and 18 males) with a mean age 3.07 ± 1.01. All patients underwent combined 16 multidetector CT using standard axial and coronal reformat planes. In the same session, 3D DRIVE MRI axial plane reformatted into sagittal plane for the IAC and inner ear as well as axial T2WI for the whole brain. The study aimed to investigate the value of CT and MRI for evaluation and classification of inner ear abnormalities in patients with bilateral profound SNHL who are candidates for CI.
Thirty eight percent of study population had inner ear malformation. A former study stated that 20.3% of congenital SNHL is caused by inner ear malformations [7]. MRI is more sensitive and specific in diagnosing soft tissue abnormalities in the inner ear than CT. Also, the abnormalities detected by MRI are more likely to influence the CI process (e.g., asymmetric nerve aplasia, cochlear obstruction) [8]. Standard axial, coronal and sagittal reformat MRI views were enough for identification of these anomalies. The image acquisition requires a high signal from the fluid containing spaces, less susceptibility, pulsation artifacts and short examination time [2]. DRIVE sequence has the effect of reducing flow void artifacts, increasing the brightness of fluids. So it was accurate in identification of internal partitions of the cochlea, minor cochlear hypoplasia and associated cochlear nerve anomalies. Also it can identify thin fibrotic bands that may follow labyrinthitis and attenuate the cochlear lumen. Its reconstruction into sagittal and coronal reformat views allows better identification of the cochlear nerve anomalies [4]. Regarding the inner ear abnormalities, our study included 29 cases with 58 diseased ears. Thirty eight ears were radiologically free. Twenty ears showed inner ear abnormalities. The most common inner ear anomaly was Mondini deformity (8 ears, 13.7%) in which IP II deformity of cochlea associated with dilated vestibule and enlarged vestibular aqueduct. IP II deformity with normal vestibular aqueduct was found in 4 ears (6.8%). Joshi et al. [9] found that IPII deformity is the most common type of cochlear malformation, accounting for more than 50% of all cochlear deformities which is the most common malformation in our study. In the same study, 84% of cases of enlarged vestibular aqueduct were accompanied by other inner ear anomalies and an isolated finding of enlargement of the endolymphatic duct and sac is uncommon which is similar to our study in which all cases of enlarged vestibular aqueduct is associated with IPII deformity. Taha et al. [4] studied 120 cases with 220 diseased ears submitted to CI imaging protocol, 150 ears were radiologically free and
Fig. 3. A 2 year old female presented with developmental delay, congenital heart disease (Ebstein anomaly), abnormal auricle shape, characteristic facies and bilaterally atretic outer ear. Bilateral absence of semicircular canals, possible CHARGE syndrome. Bilateral aplasia of the vestibulocochlear nerve; not candidate for CI. (a), (b) Axial CT image of the petrous bone showing bilaterally absent semicircular canals and dysmorphic vestibule bilaterally with normal cochlea. Fluid density within the middle ear and mastoid air cells is also in the right side and within the left mastoid air cells. (c), (d) Axial T2-weighted DRIVE images showing bilaterally absent semicircular canals, normal cochlea and dysmorphic vestibule bilaterally. (e) Oblique sagittal reformat T2-weighted DRIVE images of the IAC, showing single nerve within the IAC which is the facial nerve (red arrow) with absent vestibulocochlear nerve.
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Fig. 4. Right IAC horizontal bony septum with undivided vestibulocochlear nerve. Bilateral IP II deformity. Absent left cochlear branch; candidate for CI at the Rt. side. (a) Coronal reformat CT image of the petrous bone showing right IAC horizontal bony septum (red arrow) compared to the normal bony canal of the left side (black arrow). (b) Axial T2-weighted DRIVE images showing right abnormal IAC (white arrow). Left side showed cystic appearance of the apex of the cochlea (red arrow) in keeping with IP II deformity. (c) and (d) Oblique sagittal reformat T2-weighted DRIVE images of the IAC. (c) showing 2 nerves (white arrows) within the right IAC (facial nerve and undivided vestibulocochlear nerve). (d) showing absent cochlear division (red arrow) of the left vestibulocochlear nerve.
Fig. 5. Right IAC complete atresia with aplasia of the Rt. vestibulocochlear nerve; candidate for CI at the Lt. side. (a) Axial CT image of the petrous bone showing right IAC complete atresia (black asterisk) compared to the normal bony canal of the left side (white arrow). (b) Axial T2-weighted DRIVE images showing right IAC complete atresia (white asterisk) with non visualized vestibulocochlear and facial nerves compared to the normal canal (white arrow) with intact nerves of the left side.
were requiring implant. Forty ears had congenital malformation in the inner ear: 18 ears showed IP II deformity which is the most common anomaly in our study. One ear (1.7%) was post meningitic and showed ossification of the apex and basal turn of the cochlea as well as semicircular canals. This differs from results of other studies [4] in which 13.6% of examined ears had LO. Dagkiran et al. found two ears with cochlear ossification (1.4% of all examined ears) similar to our study [7]. Ossification is a relative contraindication to CI as it is difficult to achieve safe electrode insertion because of bony obstruction. The electrodes or the inner ear structures can be damaged. Obstructed scala tympani could also limit the number of electrodes that can be
inserted. The efficacy of the electrical stimulation is also questioned, as a higher current will be needed on an ossified cochlea. Also, the neural survival in ossified cochlea is unpredictable [4]. Bilaterally absent semicircular canals with dysmorphic vestibule were found in 4 ears (6.8%). Two of them showed abnormal cochlea (IP II deformity of cochlea) but with intact cochlear nerve bilaterally. The others showed normal cochlea but with absent intrameatal vestibule- cochlear nerve. The patients also showed associated mental and growth retardation, congenital heart disease, characteristic facies and atretic external ear which may suggested possible CHARGE syndrome. Abnormal brain findings were also found in only one patient. IAC horizontal bony septum was found in one ear (1.7%) by CT scan with undivided vestibulocochlear nerve detected by MRI. Absent cochlear nerve was found in one ear (1.7%). Complete bony atresia of the IAC with complete aplasia of vestibulocochlear and facial nerves was found in one ear (1.7%). The IAC may be atretic, or it may have a horizontal bony septum that divides it into two or more separate canals. The narrow duplicated IAC is a very rare malformation. It has been suggested to be associated with congenital SNHL and to be a result of aplasia or hypoplasia of the vestibulocochlear nerve or the cochlear branch [9,10]. Five cases of a narrow IAC with duplication have been reported [11]. The IAC morphologic characteristics and size are not reliable indicators of the integrity of the cochlear nerve; normal size of the IAC and normal inner ear CT anatomy do not exclude a nerve deficiency. The nerve may be absent when the IAC and labyrinth are normal by imaging. Hence, MRI is the modality of choice for assessment of the cochlear nerve [9]. A narrow internal auditory canal is a relative contraindication to CI because it is usually associated with aplasia or hypoplasia of the vestibulocochlear nerve or its cochlear branch [12] which differs from our study in which the partitioned canal associated with undivided vestibulocochlear nerve, in which CI is technically possible. Undivided vestibulocochlear nerve is most frequently associated with severe labyrinth malformations like a common
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Fig. 6. Bilateral absence of posterior semicircular canals, candidate for CI. (a) Axial CT image of the petrous bone showing absent posterior semicircular canals, enlarged vestibule (red arrows, normal = 5.9 3.1 mm ± 0.3, right = 7.7 3.2 mm, left = 7.4 3.2 mm) and dysplastic lateral semicircular canals (green arrows) bilaterally. (b), (c) Corresponding axial T2-weighted DRIVE images showing the absent fluid signal for the posterior semicircular canals bilaterally with enlarged vestibules and dysplastic lateral semicircular canals. (d) Axial T2-weighted DRIVE image showing normal fluid signal for the superior semi circular canals bilaterally (white arrows).
Table 5 CT compared to MRI in determining the cochlear implantation candidates (N = 58). Variable
No.
Percentage
CT
Candidate Not candidate
56 2
96.5% 3.4%
MRI
Candidate Not candidate
54 4
93.1% 6.8%
A = True positive = 54. B = False positive = 3. C = False negative = 1. D = True negative = 1. Sensitivity: A/(A + C) 100 = 54/(54 + 1) 100 = 98%. Specificity: D/(D + B) 100 = 1/(1 + 3) 100 = 25%. Positive predictive value: A/(A + B) 100 = 54/(54 + 3) = 94.7%. Negative predictive value: D/(D + C) 100 = 1/(1 + 1) = 50%.
Fig. 7. Bilateral lateral semicircular Canal—Vestibule Dysplasia, candidate for CI. (a) Axial T2-weighted DRIVE images showing normal MRI appearances of the cochlea. (b) Axial T2-weighted DRIVE images showing the bilateral fluid -filled cystic appearance of the lateral semicircular canals with enlarged vestibules (white arrows). (c) 3D maximum intensity projection image of the inner ear showing abnormal vestibule and lateral semicircular canal appearances (white arrows).
Table 4 Candidacy for operation as decided by CT and MRI (N = 58). Candidacy for CI
No.
Percentage
Candidate Candidate with poor response Candidate with modification of surgical procedure Not candidate
50 3 1 4
86.2% 5.1% 1.7% 6.8%
cavity or cochlear aplasia which differ from our study in which it was associated with IP II deformity of cochlea [2]. Enlarged vestibules with dysplastic semicircular canals (Lateral Semicircular Canal Vestibule Dysplasia) in which a single cavity is formed by the vestibule and lateral semicircular canal were found in 2 ears (3.4%). Posterior semicircular canals aplasia with dysplastic lateral semicircular canals were noted in 2 ears (3.4%). In this study, the lateral semicircular canals are the most frequently malformed canal. Isolated posterior and superior canal
malformations in combination with a normal lateral semicircular canal are uncommonly described in literature because it is the last one to be formed [2]. Dagkiran et al. found 10 ears with posterior semicircular canal (7.3%), 10 ears with lateral semicircular canal (7.4%), 8 ears with superior semicircular canal aplasia/hypopasia (5.9%), and 8 ears with lateral semicircular canal-vestibular dysplasia [7]. In this study, 10 ears (17.2%) showed otomastoiditis. Mastoiditis was noted in 3 ears (5.2%). Inflammation of the middle ear or mastoid cells is associated with high risk of postoperative sepsis and failure [1]. CT is valuable in assessment of mastoiditis and cholesteatomas with a sensitivity approaching 79% [13]. All of examined ears showed normal CT appearances of the oval window and round window. No vascular anatomical variants were detected in our study. The prime requirements for CI are the presence of a cochlea (either normal or malformed) and of a cochlear nerve [14]. Most cochlear abnormalities may be successfully treated with CI but with an increased risk of intraoperative cerebrospinal fluid leakage and postoperative bacterial meningitis. Deficiency of the 8th nerve or brain stem lesions correlates with poor auditory outcomes and affect eligibility for CI [15]. Certain medical conditions that preclude CI surgery (e.g., specific hematologic, pulmonary, and cardiac conditions) also may be contraindications [16]. Two patients (20%) with congenital inner ear malformations in our study were syndromic and 8 patients (80%) were nonsyndromic which is similar to the study in which 20% of the congenital inner ear malformations were syndromic [17]. This study shows that 4 ears will not be suitable for CI (3 ears with absent vestibulocochlear nerve, and one ear with absent
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cochlear nerve). Two of all examined ears will require an implant with expected poor response due to co-morbidities and mental retardation. In these patients, the response is dependent on the type and degree of associated anomalies. One ear will require implant with expected poor response due to undivided vestibulocochlear nerve. Twelve ears showed inner ear anomalies with no contraindication to surgery (vestibular and semicircular canals dysplasia). One ear showed LO of the basal turn and semicircular canals which may require modification of surgical technique (Fig. 8). Thirty eight ears were completely normal with no contraindication for surgery. Most inner ear malformation could be detected in CT and MRI however some anomalies are detected only in MRI such as cochlear nerve aplasia/hypoplasia, minor cochlear hypoplasia, fibrous LO, and associated cerebral congenital or post inflammatory anomalies. Also, some abnormalities are detected only in the CT as calcified lumen of inner ear structures in LO, and totally ossified cochlea that is difficult to differentiate from cochlear aplasia in MRI [4]. DRIVE sequence in the standard MRI temporal bone protocol is important for evaluation of the cochlear nerve hypoplasia, aplasia
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or post meningitic atrophy, as well as assessment of cochlear lumen patency, and minor hypoplasia. T2WI of the brain helps in identifying central causes of SNHL [2]. In this study, while the CT scan found that all of the studied patients are suitable for CI in both sides or in one side only (as in the case of unilateral complete atresia of the IAC). MRI found that 28 patients (96.5%) are suitable for CI and only one patient (3.4%) will not gain benefit from CI due to bilaterally absent vestibulocochlear nerve. When CT was compared to MRI (as a gold standard) in determining candidates for CI in our study, the sensitivity of CT was 98%, specificity was 25%, positive predictive value was 94.7% and negative predictive value was 50%. CT may be better at defining some abnormalities but MRI appears to be able to detect all abnormalities that are critical to patient management. Most candidates for CI should therefore be assessed by MRI initially. CT is most likely to be helpful in those with a history of severe middle ear disease, meningitis or dysmorphic syndromes who should undergo both CT and MRI.
Fig. 8. A 5 year old female with history of meningitis at the age of 9 month. LO of the Lt. cochlea, candidate for CI at the Lt. side. (a), (b) and (c) Axial CT image of the petrous bone showing abnormal bone formation within the apex (green arrow) and the basal turn of the left cochlea (red arrow) compared to the normal right one. (d), (e) Corresponding axial T2-weighted DRIVE images showing signal loss at the apex (green arrow) and part of the basal turn of the left cochlea (red arrow).
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One of the drawbacks of our study is limited number of cases. CT/MRI protocol is recommended to be generalized for pediatric SNHL cases for proper preoperative evaluation to reach the best results particularly in complex cases of SNHL. Correlation with the surgical data is also valuable in confirming the imaging findings. In conclusion, for the work-up of CI candidates, MRI is the main tool to determine the accessibility of the cochlea, the presence of a normally sized cochlear nerve branch, the absence of lesions at the level the auditory pathways or the auditory cortex. CT is helpful in those with a history of severe middle ear disease, meningitis or dysmorphic syndromes who should undergo both CT and MRI. The results of this study are unique as it is the first study to be published internationally regarding the suitability for cochlear implants in pediatric patients in the Suez Canal area and the east of Egypt as well as the imaging findings in patients located in this area. In the Suez Canal area and the east of Egypt, the majority of patients with profound SNHL (96.6%) are good candidates for CI; the race and ethnic variations in ear malformation are appreciated in multiple studies [18]. Conflict of interest The authors declared that there is no conflict of interest. References [1] Marsot-Dupuch K, Meyer B. Cochlear implant assessment: imaging issues. Eur J Radiol 2001;40(2):119–32. [2] Lemmerling M, Foer B. Temporal bone imaging. Berlin Heidelberg: SpringerVerlag; 2015. p. 237–48. [3] Yousem D, Grossman R. Neuroradiology: the requisites. Philadelphia, PA: Mosby/Elsevier; 2010. p. 385–413.
[4] Taha T, Wahba H, Ibrahim A, AbdElazim Y. Cochlear implant tailored imaging protocol: what clinicians need to know. Egypt J Radiol Nucl Med 2015;46 (1):33–43. [5] Razek AA, Huang BY. Lesions of the petrous apex: classification and findings at CT and MR imaging. Radiographics 2012;32(1):151–73. [6] Connor SEJ. Contemporary imaging of auditory implants. Clin Radiol 2017. doi: https://doi.org/10.1016/j.crad.2017.03.002 (Article in press). [7] Dagkiran M, Dagkiran N, Surmelioglu O, Balli T, Tuncer U, Akgul E, et al. Radiological imaging findings of patients with congenital totally hearing loss. J Int Adv Otol 2016;12(1):43–8. [8] Mackeith S, Joy R, Robinson P, Hajioff D. Pre-operative imaging for cochlear implantation: magnetic resonance imaging, computed tomography, or both? Cochlear Implants Int 2012;13(3):133–6. [9] Joshi VM, Navlekar SK, Kishore GR, Reddy KJ, Kumar EC. CT and MR imaging of the inner ear and brain in children with congenital sensorineural hearing loss. Radiographics 2012;32(3):683–98. [10] Lee SY, Cha SH, Jeon MH, Bae IH, Han GS, Kim SJ, et al. Narrow duplicated or triplicated internal auditory canal (3 cases and review of literature) can we regard the separated narrow internal auditory canal as the presence of vestibulocochlear nerve fibers? J Comput Assist Tomogr 2009;33(4):565–70. [11] Baik HW, Yu H, Kim KS, Kim GH. A narrow internal auditory canal with duplication in a patient with congenital sensorineural hearing loss. Korean J Radiol 2008;9(Suppl.):S22–5. [12] Vincenti V, Ormitti F, Ventura E. Partitioned versus duplicated internal auditory canal: when appropriate terminology matters. Otol Neurotol 2014;35(7):1140–4. [13] Razek AA, Ghonim MR, Ashraf B. Computed tomography staging of middle ear cholesteatoma. Polish J Radiol 2015;80:328–33. [14] Witte RJ, Lane JI, Driscoll CL, Lundy LB, Bernstein MA, Kotsenas AL, et al. Pediatric and adult cochlear implantation. Radiographics 2003;23 (5):1185–200. [15] Young JY, Ryan ME, Young NM. Preoperative imaging of sensorineural hearing loss in pediatric candidates for cochlear implantation. Radiographics 2014;34 (5):E133–49. [16] Wendling P. Cochlear implant revision surgery beneficial. Pediatric News 2006;40(2):40. [17] Huang BY, Zdanski C, Castillo M. Pediatric sensorineural hearing loss, part 2: syndromic and acquired causes. AJNR Am J Neuroradiol 2012;33(3):399–406. [18] Källén B. Severe ear malformations. In: Epidemiology of human congenital malformations. Springer, Cham; 2014. p. 45–48.