ORIGINAL ARTICLE
Size of the Semicircular Canals Measured by Multidetector Computed Tomography in Different Age Groups Wang Daocai, MD, PhD,* Wang Qing, MD, PhD,† Wang Ximing, MD, PhD,* He Jingzhen, MD, PhD,† Liu Cheng, MD,* and Ma Xiangxing, MD† Purpose: The purpose of the study was to obtain reference values for the sizes of the semicircular canals (SCCs) on multidetector computed tomographic (CT) images in different age groups. Methods: Computed tomographic images of the temporal bone of 210 patients, a total of 420 ears without inner ear pathology, have been evaluated. These patients were divided into 4 groups by age: young children (60 years). The inner diameter, maximum height, and width of the SCCs were measured. Results: There was no significant difference in the size of SCC among the 4 age groups. The inner diameter measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.101 ± 0.016, 0.135 ± 0.033, and 0.124 ± 0.021 cm, respectively. The height measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.535 ± 0.086, 0.349 ± 0.090, and 0.490 ± 0.109 cm, respectively. The width measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.567 ± 0.080, 0.302 ± 0.082, and 0.472 ± 0.099 cm, respectively. Conclusions: The size of SCCs remains constant from children to the elderly people, unlike the other human organs. The reference values provided by multidetector CT can serve as an aid for the interpretation of CT images.
with long-standing severe symptoms associated with the labyrinth is challenging because many anatomical structures have to be assessed and pathological findings may be subtle. In up to 75% of patients, cross-sectional imaging studies may render a “normal” appearance of the labyrinth.8–10 In many cases, the interpreting radiologist may suspect disequilibrium of the sizes of SCCs. However, it is difficult to objectify such findings. Moreover, there may be a lot of variance in the size of SCC in different age groups. In the past, reference values for the size of SCC have been obtained through the measurement of anatomical specimens6–8; however, these specimens had been fixated with formaldehyde before the measurements were performed. Dehydration of the tissue during fixation leads to up to 10% shrinkage of the specimen.11 Consequently, a systematic error is introduced by this technique. Thus, values obtained from anatomical studies cannot be applied for the interpretation of CT images. Accurate knowledge of the dimensions of SCCs is essential for the design of experiments studying the vestibular system and for understanding examination findings during clinical evaluation of patients with vestibular disorders.12 Accordingly, the purpose of the current study was to obtain reference values for SCCs by MDCT in different age groups.
Key Words: multidetector CT, reference values, semicircular canal (J Comput Assist Tomogr 2014;38: 196–199)
T
he bony labyrinth in the petrous part of the temporal bone contains the organs of hearing and balance. The semicircular canals (SCCs) of the vestibular labyrinth encode head rotational velocity and provide input to the vestibulo-ocular reflex, vestibulocollic reflex, vestibulospinal system, vestibuloreticular system, cerebellum, and cortex.1–3 Because the SCCs are confined to the bony otic capsule, the hardest and most compact bone in the skeleton, they are difficult to dissect. This makes it difficult to observe the entire gross anatomy of the SCCs. Most previous anatomical studies of the SCCs have used conventional computed tomography (CT), and a few studies were focused on the morphology of the SCCs themselves.4,5 With the advances of CT technique, high-resolution multidetector CT (MDCT) of the temporal bone has revolutionized imaging of this complex region and allows for the identification and characterization of complex osseous pathologies. Many diseases, such as malformations of the cochlea, otosclerosis, or ossification of the cochlea, can be diagnosed unequivocally.6,7 However, interpretation of the images from patients presenting From the *Department of Radiology, Shandong Medical Imaging Institute of Shandong University, and †Department of Radiology, Qilu Hospital of Shandong University, Jinan, China. Received for publication July 31, 2013; accepted September 30, 2013. Reprints: He Jingzhen, MD, PhD, Department of Radiology, Qilu Hospital of Shandong University, 107 Wenhuaxi Rd, Jinan, 250012, China (e‐mail: [email protected]). Wang Daocai and Wang Qing contribute equally to this study. The authors declare no conflict of interest. Copyright © 2014 by Lippincott Williams & Wilkins
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MATERIALS AND METHODS Patients and CT Protocol The study was performed with the approval of our institutional review board; patient anonymity was maintained. We retrospectively reviewed the electronic medical records of our hospital from January 2010 to June 2012 to identify patients who were referred to the radiology department for thin-section MDCT of the temporal bone without any symptoms related to the inner ear. They underwent CT for the following clinical indications: fractures or trauma (73), acute otitis media (50), peripheral facial nerve palsy (28), otitis externa (26), acute mastoiditis (24), or metastasis or tumors (9). Then, 210 patients with bilateral ears were identified, and a total of 420 ears were evaluated. They were divided into 4 groups by age: young children (60 years) (24 patients: 12 men, 12 women; 60 to 81 years old). All imaging was performed with a 16-slice CT scanner (SOMATOM Sensation Cardiac16; Siemens Medical System). Helical transverse images were acquired with a slice thickness of 0.6 mm and an increment of 0.3 mm (120 kV; 150 mA; pitch, 0.8). The raw data were reconstructed by using a bone algorithm and a display field of view of 12 cm.
Measurement of SCC Measurements were performed on a workstation (Volume; Siemens Medical System) using multiplanar reformation (MPR). All images were displayed with a window width of 1600 J Comput Assist Tomogr • Volume 38, Number 2, March/April 2014
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
J Comput Assist Tomogr • Volume 38, Number 2, March/April 2014
Size of the Semicircular Canals Measured by MDCT
FIGURE 1. With MPR, an optimal alignment of image plane with SCCs was confirmed. The entire extent of the anterior (A), posterior (B), and lateral (C) SCCs displayed with uniform disappearance of canal lumen.
Hounsfield unit and a window center of 400 Hounsfield unit. The MPR software system in the workstation allows one to view a CT data set simultaneously using a set of three 2-dimensional images that represent mutually orthogonal “slices” through the data set. We measured an SCC's size by optimally aligning 1 slice plane with the SCC. To optimize placement of the image plane through a canal, we adjusted the other two 2-dimensional images until the entire SCC lumen depicted simultaneously to the greatest extent possible (Fig. 1). he inner diameter, the height, and the width of the 3 SCCs were measured. To render the measurements reproducible, the structures were measured in a standardized way, following the criteria: The average value of 3 measurements obtained from 3 different positions in the apex of the canals was attributed to the inner diameter. The height was defined as the maximal longitudinal extension from the medial walls proximate vestibula to the apex of the canals; the width was the longest distance between the medial walls of the 2 bony crura of each SCC (Fig. 2).
Statistical Analysis Data analysis was performed with Statistical Package for the Social Sciences (SPSS 11.0 for Windows; SPSS, Chicago, Ill). The results were first tested for normal distribution. t Tests for paired data were used to test for significant differences of the left and right sides in each group. A 1-way analysis of variance was applied to test for significant differences of parameters of the 4 different groups. The results are presented as the mean ± the standard error of the mean (SEM). The 90% confidence interval was also provided.
RESULTS The results for each group, including the mean value and the SEM, are summarized in Table 1. There was no statistically significant difference between the left and right sides in each group and there was no significant difference in different age groups for the size of the 3 SCCs, so data were pooled for the
FIGURE 2. The inner diameter, height, and width of the 3 SCCs were measured in the plane with panoramic view of SCCs: 1, 2, and 3 for the inner diameter (A) as well as 1 for height and 2 for width (B) are for ASCC; 1, 2, and 3 for the inner diameter (C) as well as 1 for height and 2 for width (D) are for PSCC; 1, 2, and 3 for the inner diameter (E) as well as 1 for height and 2 for width (F) are for LSCC. Figure 2 can be viewed online in color at www.jcat.org. © 2014 Lippincott Williams & Wilkins
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TABLE 2. The Normal Reference Values of Each Dimension of Corresponding SCCs Within the Range of 90% (in centimeters)
± 0.21; ± 0.13; ± 0.02; ± 0.07; ± 0.10; ± 0.01; ± 0.04; ± 0.01; ± 0.01;
Left Side
0.524 0.565 0.107 0.493 0.470 0.129 0.350 0.301 0.140 0.18 0.11 0.02 0.10 0.11 0.02 0.06 0.02 0.02 ± ± ± ± ± ± ± ± ± 0.20; 0.10; 0.03; 0.16; 0.12; 0.02; 0.12; 0.02; 0.03; ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
Right Side
0.528 0.565 0.101 0.490 0.473 0.125 0.346 0.310 0.138 Height of ASCC Width of ASCC Internal diameter of ASCC Height of PSCC Width of PSCC Internal diameter of PSCC Height of LSCC Width of LSCC internal diameter of LSCC
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Data are given as mean ± SEM (in centimeters). P values are comparison of the 4 age groups. ns indicates standard not significant (right and left side).
Left Side
0.529 0.565 0.103 0.491 0.476 0.120 0.349 0.307 0.139 0.25 0.09 0.01 0.09 0.08 0.01 0.10 0.02 0.03 ± ± ± ± ± ± ± ± ± 0.534 0.565 0.102 0.491 0.474 0.120 0.339 0.312 0.142 ns ns ns ns ns ns ns ns ns
Right Side
0.567 ± 0.080 0.472 ± 0.099 0.302 ± 0.082
± 0.17; ± 0.08; ± 0.01; ± 0.12; ± 0.09; ± 0.02; ± 0.11; ± 0.02; ± 0.01;
Left Side
0.534 0.565 0.107 0.489 0.477 0.127 0.346 0.311 0.138 0.14 0.17 0.02 0.12 0.19 0.01 0.11 0.02 0.02 ± ± ± ± ± ± ± ± ± 0.534 0.565 0.105 0.478 0.478 0.125 0.351 0.313 0.135 0.531 ± 0.13; ns 0.565 ± 0.18; ns 0.108 ± 0.01; ns 0.481 ± 0.17; ns 0.474 ± 0.19; ns 0.123 ± 0.02; ns 0.346 ± 0.09; ns 0.309 ± 0.01 0.141 ± 0.01; ns
Right Side
Width
0.535 ± 0.086 0.490 ± 0.109 0.349 ± 0.090
DISCUSSION
Anatomical Structure
Left Side
Height
0.101 ± 0.016 0.124 ± 0.021 0.135 ± 0.033
The SCCs are among the most difficult anatomical structures to investigate because of their complicated 3-dimensional shape being embedded inside the dense otic capsule of the petrous bone.13 This has led to conventional CT images being used for measuring SCC dimensions. However, such images are inadequate for measuring SCC dimensions because they were only conducted in a horizontal or coronal orientation unparalleled to the course of any SCC, which makes it difficult to accurately characterize the very complicated 3-dimensional structure of the SCCs.14 Moreover, the slice thicknesses of CT images in the past were all thicker than 1.0 mm and some are even 2.0 mm, which limited the postprocessing of the SCC images for measurement because of its low longitudinal spatial resolution; hence, it is impossible for conventional CT images to precisely measure the very complicated 3-dimensional structure of the SCCs. A recent major advance in CT technology is the introduction of MDCT. Besides providing additional information compared with single-detector row CT, MDCT may also improve the visibility of thin structures. This new type of CT has a submillimeter spatial resolution, which is especially important in the z axis. Multidetector CT offers the potential to overcome the obstacle of single-detector CT because reformatted images have sufficient quality. The high image quality is a result of the thinner section thickness (0.5 mm instead of 1 mm in single-detector row CT) and the smaller reconstruction increment. Furthermore, with MPR, the panoramas of the ASCC, PSCC, and LSCC could be depicted on 1 single plane with similar quality15–17; thus, the dimensions of SCC could be measured quickly and precisely on a single plane. The SCCs and vestibule are involved in balance, with the utricle and saccule responding to linear acceleration and the orientation of the head relative to gravity. Equilibrium dysfunction might be related to subtle morphological changes. On the other hand, there is evidence from current research that changes in the size of anatomical structures might be present in patients
0.12 0.12 0.01 0.12 0.13 0.01 0.10 0.02 0.03
Adults Older Children and Adolescents Young Children
TABLE 1. The Mean Value of the Dimensions of the 3 SCCs
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Internal Diameter
420 labyrinths. The normal reference values for dimensions of each SCC within the range of 90% are shown in Table 2. Our study showed that the dimensions of each SCC were different from others; the biggest inner diameter were the lateral semicircular canals (LSCC) (0.135 ± 0.033 cm) then the posterior semicircular canal (PSCC) (0.124 ± 0.021 cm), and the smallest were the anterior semicircular canals (ASCC) (0.101 ± 0.016 cm); whereas the ASCCs had both the largest height and width (0.535 ± 0.086 and 0.567 ± 0.080 cm, respectively), which was followed by the PSCCs (0.490 ± 0.109 and 0.472 ± 0.099 cm, respectively), and the smallest was the LSCCs (0.349 ± 0.090 and 0.302 ± 0.082 cm, respectively). The 90% normal reference values of the inner diameter, height, and width of the ASCC, PSCC, and LSCC were obtained respectively (unit: cm): 0.101 ± 0.016, 0.535 ± 0.086, 0.567 ± 0.080; 0.124 ± 0.021, 0.490 ± 0.109, 0.472 ± 0.099; 0.135 ± 0.033, 0.349 ± 0.090, 0.302 ± 0.082.
0.531 0.565 0.104 0.487 0.479 0.128 0.343 0.306 0.143
Right Side
ASCC PSCC LSCC
ns ns ns ns ns ns ns ns ns
Elderly Patients
ns ns ns ns ns ns ns ns ns
P
0.81 0.92 0.75 0.67 0.82 0.98 0.69 0.74 0.99
Daocai et al
© 2014 Lippincott Williams & Wilkins
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J Comput Assist Tomogr • Volume 38, Number 2, March/April 2014
with functional impairment of the inner ear. In a recent study conducted on 15 patients with congenital sensorineuronal hearing loss but have CT images with normal appearance and 15 patients without hearing loss, Purcell et al16 found significantly different values for the height of the cochlea and the “size of the central bony island within the lateral semicircular canal.” These results demonstrate that comparison of the sizes of anatomical structures may reveal valuable information concerning the pathophysiological changes in diseases of the inner ear. In the past, the size of SCC was evaluated through the measurement of anatomical specimens or by CT images in only a small amount of subjects regardless of age difference.14 To our knowledge, there is no record of the size of SCC for different age groups by imaging technology. Reference values for the sizes of SCC of different age groups were obtained in the present study. According to our study, the size of SCC between the left and right sides was similar, which was consistent with former studies by autopsy or CT.14,18 We also found that there was no significant difference in the size of the 3 SCCs in different age groups, which suggested that the SCC did not grow with age. The size of SCC remains constant from the infant stage to the elderly stage, unlike the other human tissues and organs. According to our study, measuring the size of SCCs by the MPR MDCT images of the temporal bone was convenient, time-saving, and allowed various dimensions to be measured directly. Comparison of the values obtained from individual patients with the reference values provided might contribute to objectify suspected disproportions of sizes of SCC. Our study has limitations. First, we purposely performed our measurements in a general patient population and not in patients with 1 specific disease entity. However, our aim was to precisely determine the size of SCCs in different age groups by MDCT. We did not aim to compare these values with those obtained from patients with specific disease but, instead, wanted to obtain normal reference values of SCCs by MDCT. To compare values of SCCs in patients with specific disease entities, focused studies with selected participant populations will be needed to be performed. It would not be feasible to incorporate all different disease categories into a single study design. Second, in this study, the measurements of the inner diameter were limited to the apex of the canals and we did not measure the crus and the ampullae. Because the SCCs are oval-shaped, the inner diameter of the canals proximate to the crura and the ampullae becomes broad; in the apex of the canals, the inner diameter is uniform, which may reflect the actual size of the canals even more.
CONCLUSIONS In summary, the present study has provided the sizes of SCCs by MDCT with MPR. The reference values provided for SCC can serve as an aid for the interpretation of CT images. They may provide a basis for further evaluation of groups of patients with inner ear pathologies and represent very important reference data for otology surgeons.
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Size of the Semicircular Canals Measured by MDCT
REFERENCES 1. Ebata S, Sugiuchi Y, Izawa Y, et al. Vestibular projection to the periarcuate cortex in the monkey. Neurosci Res. 2004;49:55–68. 2. Bohmer A, Straumann D, Suzuki J, et al. Contributions of single semicircular canals to caloric nystagmus as revealed by canal plugging in rhesus monkeys. Acta Otolaryngol. 1996;116:513–520. 3. Spoor F, Zonneveld F. Comparative review of the human bony labyrinth. Am J Phys Anthropol. 1998;27:211–251. 4. Yuan YY, Song YS, Chai CM, et al. Intraoperative CT-guided cochlear implantation in congenital ear deformity. Acta Otolaryngol. 2012;132:951–958. 5. Yamashita K, Yoshiura T, Hiwatashi A, et al. Sensorineural hearing loss: there is no correlation with isolated dysplasia of the lateral semi-circularcanal on temporal bone CT. Acta Radiol. 2011;52:229–233. 6. Yuen HY, Ahuja AT, Wong KT, et al. Computed tomography of common congenital lesions of the temporal bone. Clin Radiol. 2003;58:687–693. 7. Lemmerling MM, Mancuso AA, Antonelli PJ, et al. Normal modiolus: CT appearance in patients with a large vestibular aqueduct. Radiology. 1997;204:213–219. 8. Purcell DD, Fischbein N, Lalwani AK. Identification of previously “undetectable” abnormalities of the bony labyrinth with computed tomography measurement. Laryngoscope. 2003;113:1908–1911. 9. Madden C, Halsted M, Benton C, et al. Enlarged vestibular aqueduct syndrome in the pediatric population. Otol Neurotol. 2003;24:625–632. 10. Krombach GA, Schmitz-Rode T, Prescher A, et al. The petromastoid canal on computed tomography. Eur Radiol. 2002;12:2770–2775. 11. Lang J, Hack C. Canal systems in the temporal bone and their right-left differences. Acta Anat (Basel). 1987;130:298–308. 12. Della Santina CC, Potyagaylo V, Migliaccio AA, et al. Orientation of human semicircular canals measured by three-dimensional multiplanar CT reconstruction. J Assoc Res Otolaryngol. 2005;6:191–206. 13. Spoor F, Zonneveld F. Morphometry of the primate bony labyrinth: a new method based on high-resolution computed tomography. J Anat. 1995;186:271–286. 14. Krombach GA, van den Boom M, Di Martino E, et al. Computed tomography of the inner ear: size of anatomical structures in the normal temporal bone and in the temporal bone of patients with Menière's disease. Eur Radiol. 2005;15:1505–1513. 15. Harada T, Ishii S, Tayama N, et al. Computer-aided three dimensional reconstruction of the osseous and membranous labyrinths. Eur Arch Otorhinolaryngol. 1990;247:348–351. 16. Purcell D, Johnson J, Fischbein N, et al. Establishment of normative cochlear and vestibular measurements to aid in the diagnosis of inner ear malformations. Otolaryngol Head Neck Surg. 2003;128:78–87. 17. Vachata P, Petrovicky P, Sames M. An anatomical and radiological study of the high jugular bulb on high-resolution CT scans and alcohol-fixed skulls of adults. J Clin Neurosci. 2010;17:473–478. 18. Lee JY, Shin KJ, Kim JN, et al. A morphometric study of the semicircular canals using micro-CT images in three-dimensional reconstruction. Anat Rec (Hoboken). 2013;296:834–839
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Size of the Semicircular Canals Measured by Multidetector Computed Tomography in Different Age Groups Wang Daocai, MD, PhD,* Wang Qing, MD, PhD,† Wang Ximing, MD, PhD,* He Jingzhen, MD, PhD,† Liu Cheng, MD,* and Ma Xiangxing, MD† Purpose: The purpose of the study was to obtain reference values for the sizes of the semicircular canals (SCCs) on multidetector computed tomographic (CT) images in different age groups. Methods: Computed tomographic images of the temporal bone of 210 patients, a total of 420 ears without inner ear pathology, have been evaluated. These patients were divided into 4 groups by age: young children (60 years). The inner diameter, maximum height, and width of the SCCs were measured. Results: There was no significant difference in the size of SCC among the 4 age groups. The inner diameter measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.101 ± 0.016, 0.135 ± 0.033, and 0.124 ± 0.021 cm, respectively. The height measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.535 ± 0.086, 0.349 ± 0.090, and 0.490 ± 0.109 cm, respectively. The width measurements of the anterior SCC, lateral SCC, and posterior SCC were 0.567 ± 0.080, 0.302 ± 0.082, and 0.472 ± 0.099 cm, respectively. Conclusions: The size of SCCs remains constant from children to the elderly people, unlike the other human organs. The reference values provided by multidetector CT can serve as an aid for the interpretation of CT images.
with long-standing severe symptoms associated with the labyrinth is challenging because many anatomical structures have to be assessed and pathological findings may be subtle. In up to 75% of patients, cross-sectional imaging studies may render a “normal” appearance of the labyrinth.8–10 In many cases, the interpreting radiologist may suspect disequilibrium of the sizes of SCCs. However, it is difficult to objectify such findings. Moreover, there may be a lot of variance in the size of SCC in different age groups. In the past, reference values for the size of SCC have been obtained through the measurement of anatomical specimens6–8; however, these specimens had been fixated with formaldehyde before the measurements were performed. Dehydration of the tissue during fixation leads to up to 10% shrinkage of the specimen.11 Consequently, a systematic error is introduced by this technique. Thus, values obtained from anatomical studies cannot be applied for the interpretation of CT images. Accurate knowledge of the dimensions of SCCs is essential for the design of experiments studying the vestibular system and for understanding examination findings during clinical evaluation of patients with vestibular disorders.12 Accordingly, the purpose of the current study was to obtain reference values for SCCs by MDCT in different age groups.
Key Words: multidetector CT, reference values, semicircular canal (J Comput Assist Tomogr 2014;38: 196–199)
T
he bony labyrinth in the petrous part of the temporal bone contains the organs of hearing and balance. The semicircular canals (SCCs) of the vestibular labyrinth encode head rotational velocity and provide input to the vestibulo-ocular reflex, vestibulocollic reflex, vestibulospinal system, vestibuloreticular system, cerebellum, and cortex.1–3 Because the SCCs are confined to the bony otic capsule, the hardest and most compact bone in the skeleton, they are difficult to dissect. This makes it difficult to observe the entire gross anatomy of the SCCs. Most previous anatomical studies of the SCCs have used conventional computed tomography (CT), and a few studies were focused on the morphology of the SCCs themselves.4,5 With the advances of CT technique, high-resolution multidetector CT (MDCT) of the temporal bone has revolutionized imaging of this complex region and allows for the identification and characterization of complex osseous pathologies. Many diseases, such as malformations of the cochlea, otosclerosis, or ossification of the cochlea, can be diagnosed unequivocally.6,7 However, interpretation of the images from patients presenting From the *Department of Radiology, Shandong Medical Imaging Institute of Shandong University, and †Department of Radiology, Qilu Hospital of Shandong University, Jinan, China. Received for publication July 31, 2013; accepted September 30, 2013. Reprints: He Jingzhen, MD, PhD, Department of Radiology, Qilu Hospital of Shandong University, 107 Wenhuaxi Rd, Jinan, 250012, China (e‐mail: [email protected]). Wang Daocai and Wang Qing contribute equally to this study. The authors declare no conflict of interest. Copyright © 2014 by Lippincott Williams & Wilkins
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MATERIALS AND METHODS Patients and CT Protocol The study was performed with the approval of our institutional review board; patient anonymity was maintained. We retrospectively reviewed the electronic medical records of our hospital from January 2010 to June 2012 to identify patients who were referred to the radiology department for thin-section MDCT of the temporal bone without any symptoms related to the inner ear. They underwent CT for the following clinical indications: fractures or trauma (73), acute otitis media (50), peripheral facial nerve palsy (28), otitis externa (26), acute mastoiditis (24), or metastasis or tumors (9). Then, 210 patients with bilateral ears were identified, and a total of 420 ears were evaluated. They were divided into 4 groups by age: young children (60 years) (24 patients: 12 men, 12 women; 60 to 81 years old). All imaging was performed with a 16-slice CT scanner (SOMATOM Sensation Cardiac16; Siemens Medical System). Helical transverse images were acquired with a slice thickness of 0.6 mm and an increment of 0.3 mm (120 kV; 150 mA; pitch, 0.8). The raw data were reconstructed by using a bone algorithm and a display field of view of 12 cm.
Measurement of SCC Measurements were performed on a workstation (Volume; Siemens Medical System) using multiplanar reformation (MPR). All images were displayed with a window width of 1600 J Comput Assist Tomogr • Volume 38, Number 2, March/April 2014
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
J Comput Assist Tomogr • Volume 38, Number 2, March/April 2014
Size of the Semicircular Canals Measured by MDCT
FIGURE 1. With MPR, an optimal alignment of image plane with SCCs was confirmed. The entire extent of the anterior (A), posterior (B), and lateral (C) SCCs displayed with uniform disappearance of canal lumen.
Hounsfield unit and a window center of 400 Hounsfield unit. The MPR software system in the workstation allows one to view a CT data set simultaneously using a set of three 2-dimensional images that represent mutually orthogonal “slices” through the data set. We measured an SCC's size by optimally aligning 1 slice plane with the SCC. To optimize placement of the image plane through a canal, we adjusted the other two 2-dimensional images until the entire SCC lumen depicted simultaneously to the greatest extent possible (Fig. 1). he inner diameter, the height, and the width of the 3 SCCs were measured. To render the measurements reproducible, the structures were measured in a standardized way, following the criteria: The average value of 3 measurements obtained from 3 different positions in the apex of the canals was attributed to the inner diameter. The height was defined as the maximal longitudinal extension from the medial walls proximate vestibula to the apex of the canals; the width was the longest distance between the medial walls of the 2 bony crura of each SCC (Fig. 2).
Statistical Analysis Data analysis was performed with Statistical Package for the Social Sciences (SPSS 11.0 for Windows; SPSS, Chicago, Ill). The results were first tested for normal distribution. t Tests for paired data were used to test for significant differences of the left and right sides in each group. A 1-way analysis of variance was applied to test for significant differences of parameters of the 4 different groups. The results are presented as the mean ± the standard error of the mean (SEM). The 90% confidence interval was also provided.
RESULTS The results for each group, including the mean value and the SEM, are summarized in Table 1. There was no statistically significant difference between the left and right sides in each group and there was no significant difference in different age groups for the size of the 3 SCCs, so data were pooled for the
FIGURE 2. The inner diameter, height, and width of the 3 SCCs were measured in the plane with panoramic view of SCCs: 1, 2, and 3 for the inner diameter (A) as well as 1 for height and 2 for width (B) are for ASCC; 1, 2, and 3 for the inner diameter (C) as well as 1 for height and 2 for width (D) are for PSCC; 1, 2, and 3 for the inner diameter (E) as well as 1 for height and 2 for width (F) are for LSCC. Figure 2 can be viewed online in color at www.jcat.org. © 2014 Lippincott Williams & Wilkins
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TABLE 2. The Normal Reference Values of Each Dimension of Corresponding SCCs Within the Range of 90% (in centimeters)
± 0.21; ± 0.13; ± 0.02; ± 0.07; ± 0.10; ± 0.01; ± 0.04; ± 0.01; ± 0.01;
Left Side
0.524 0.565 0.107 0.493 0.470 0.129 0.350 0.301 0.140 0.18 0.11 0.02 0.10 0.11 0.02 0.06 0.02 0.02 ± ± ± ± ± ± ± ± ± 0.20; 0.10; 0.03; 0.16; 0.12; 0.02; 0.12; 0.02; 0.03; ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
Right Side
0.528 0.565 0.101 0.490 0.473 0.125 0.346 0.310 0.138 Height of ASCC Width of ASCC Internal diameter of ASCC Height of PSCC Width of PSCC Internal diameter of PSCC Height of LSCC Width of LSCC internal diameter of LSCC
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Data are given as mean ± SEM (in centimeters). P values are comparison of the 4 age groups. ns indicates standard not significant (right and left side).
Left Side
0.529 0.565 0.103 0.491 0.476 0.120 0.349 0.307 0.139 0.25 0.09 0.01 0.09 0.08 0.01 0.10 0.02 0.03 ± ± ± ± ± ± ± ± ± 0.534 0.565 0.102 0.491 0.474 0.120 0.339 0.312 0.142 ns ns ns ns ns ns ns ns ns
Right Side
0.567 ± 0.080 0.472 ± 0.099 0.302 ± 0.082
± 0.17; ± 0.08; ± 0.01; ± 0.12; ± 0.09; ± 0.02; ± 0.11; ± 0.02; ± 0.01;
Left Side
0.534 0.565 0.107 0.489 0.477 0.127 0.346 0.311 0.138 0.14 0.17 0.02 0.12 0.19 0.01 0.11 0.02 0.02 ± ± ± ± ± ± ± ± ± 0.534 0.565 0.105 0.478 0.478 0.125 0.351 0.313 0.135 0.531 ± 0.13; ns 0.565 ± 0.18; ns 0.108 ± 0.01; ns 0.481 ± 0.17; ns 0.474 ± 0.19; ns 0.123 ± 0.02; ns 0.346 ± 0.09; ns 0.309 ± 0.01 0.141 ± 0.01; ns
Right Side
Width
0.535 ± 0.086 0.490 ± 0.109 0.349 ± 0.090
DISCUSSION
Anatomical Structure
Left Side
Height
0.101 ± 0.016 0.124 ± 0.021 0.135 ± 0.033
The SCCs are among the most difficult anatomical structures to investigate because of their complicated 3-dimensional shape being embedded inside the dense otic capsule of the petrous bone.13 This has led to conventional CT images being used for measuring SCC dimensions. However, such images are inadequate for measuring SCC dimensions because they were only conducted in a horizontal or coronal orientation unparalleled to the course of any SCC, which makes it difficult to accurately characterize the very complicated 3-dimensional structure of the SCCs.14 Moreover, the slice thicknesses of CT images in the past were all thicker than 1.0 mm and some are even 2.0 mm, which limited the postprocessing of the SCC images for measurement because of its low longitudinal spatial resolution; hence, it is impossible for conventional CT images to precisely measure the very complicated 3-dimensional structure of the SCCs. A recent major advance in CT technology is the introduction of MDCT. Besides providing additional information compared with single-detector row CT, MDCT may also improve the visibility of thin structures. This new type of CT has a submillimeter spatial resolution, which is especially important in the z axis. Multidetector CT offers the potential to overcome the obstacle of single-detector CT because reformatted images have sufficient quality. The high image quality is a result of the thinner section thickness (0.5 mm instead of 1 mm in single-detector row CT) and the smaller reconstruction increment. Furthermore, with MPR, the panoramas of the ASCC, PSCC, and LSCC could be depicted on 1 single plane with similar quality15–17; thus, the dimensions of SCC could be measured quickly and precisely on a single plane. The SCCs and vestibule are involved in balance, with the utricle and saccule responding to linear acceleration and the orientation of the head relative to gravity. Equilibrium dysfunction might be related to subtle morphological changes. On the other hand, there is evidence from current research that changes in the size of anatomical structures might be present in patients
0.12 0.12 0.01 0.12 0.13 0.01 0.10 0.02 0.03
Adults Older Children and Adolescents Young Children
TABLE 1. The Mean Value of the Dimensions of the 3 SCCs
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Internal Diameter
420 labyrinths. The normal reference values for dimensions of each SCC within the range of 90% are shown in Table 2. Our study showed that the dimensions of each SCC were different from others; the biggest inner diameter were the lateral semicircular canals (LSCC) (0.135 ± 0.033 cm) then the posterior semicircular canal (PSCC) (0.124 ± 0.021 cm), and the smallest were the anterior semicircular canals (ASCC) (0.101 ± 0.016 cm); whereas the ASCCs had both the largest height and width (0.535 ± 0.086 and 0.567 ± 0.080 cm, respectively), which was followed by the PSCCs (0.490 ± 0.109 and 0.472 ± 0.099 cm, respectively), and the smallest was the LSCCs (0.349 ± 0.090 and 0.302 ± 0.082 cm, respectively). The 90% normal reference values of the inner diameter, height, and width of the ASCC, PSCC, and LSCC were obtained respectively (unit: cm): 0.101 ± 0.016, 0.535 ± 0.086, 0.567 ± 0.080; 0.124 ± 0.021, 0.490 ± 0.109, 0.472 ± 0.099; 0.135 ± 0.033, 0.349 ± 0.090, 0.302 ± 0.082.
0.531 0.565 0.104 0.487 0.479 0.128 0.343 0.306 0.143
Right Side
ASCC PSCC LSCC
ns ns ns ns ns ns ns ns ns
Elderly Patients
ns ns ns ns ns ns ns ns ns
P
0.81 0.92 0.75 0.67 0.82 0.98 0.69 0.74 0.99
Daocai et al
© 2014 Lippincott Williams & Wilkins
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
J Comput Assist Tomogr • Volume 38, Number 2, March/April 2014
with functional impairment of the inner ear. In a recent study conducted on 15 patients with congenital sensorineuronal hearing loss but have CT images with normal appearance and 15 patients without hearing loss, Purcell et al16 found significantly different values for the height of the cochlea and the “size of the central bony island within the lateral semicircular canal.” These results demonstrate that comparison of the sizes of anatomical structures may reveal valuable information concerning the pathophysiological changes in diseases of the inner ear. In the past, the size of SCC was evaluated through the measurement of anatomical specimens or by CT images in only a small amount of subjects regardless of age difference.14 To our knowledge, there is no record of the size of SCC for different age groups by imaging technology. Reference values for the sizes of SCC of different age groups were obtained in the present study. According to our study, the size of SCC between the left and right sides was similar, which was consistent with former studies by autopsy or CT.14,18 We also found that there was no significant difference in the size of the 3 SCCs in different age groups, which suggested that the SCC did not grow with age. The size of SCC remains constant from the infant stage to the elderly stage, unlike the other human tissues and organs. According to our study, measuring the size of SCCs by the MPR MDCT images of the temporal bone was convenient, time-saving, and allowed various dimensions to be measured directly. Comparison of the values obtained from individual patients with the reference values provided might contribute to objectify suspected disproportions of sizes of SCC. Our study has limitations. First, we purposely performed our measurements in a general patient population and not in patients with 1 specific disease entity. However, our aim was to precisely determine the size of SCCs in different age groups by MDCT. We did not aim to compare these values with those obtained from patients with specific disease but, instead, wanted to obtain normal reference values of SCCs by MDCT. To compare values of SCCs in patients with specific disease entities, focused studies with selected participant populations will be needed to be performed. It would not be feasible to incorporate all different disease categories into a single study design. Second, in this study, the measurements of the inner diameter were limited to the apex of the canals and we did not measure the crus and the ampullae. Because the SCCs are oval-shaped, the inner diameter of the canals proximate to the crura and the ampullae becomes broad; in the apex of the canals, the inner diameter is uniform, which may reflect the actual size of the canals even more.
CONCLUSIONS In summary, the present study has provided the sizes of SCCs by MDCT with MPR. The reference values provided for SCC can serve as an aid for the interpretation of CT images. They may provide a basis for further evaluation of groups of patients with inner ear pathologies and represent very important reference data for otology surgeons.
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Size of the Semicircular Canals Measured by MDCT
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