|Year : 2017 | Volume
| Issue : 3 | Page : 211-215
Multimodality approach in evaluation of common crus aplasia
Sai Kiran Pendem1, Rajeswaran Rangasami1, S Sanjeev Mohanty2, Prabhu Radhan Radhakrishnan1
1 Department of Radiology and Imaging Sciences, Sri Ramachandra Medical College and Research Institute, Chennai, Tamil Nadu, India
2 Department of ENT, Head and Neck Surgery, Sri Ramachandra Medical College and Research Institute, Chennai, Tamil Nadu, India
|Date of Web Publication||31-Aug-2017|
Sai Kiran Pendem
Department of Radiology and Imaging Sciences, Sri Ramachandra Medical College and Research Institute, Chennai - 600 116, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Common crus aplsia is a rare congenital anomaly caused due to abnormal reabsorption of neuroectodermal tissue of membranous common crus. Three patients came to the Department of Otorhinolaryngology with the complaints of poor response to sound. Audiometry examination revealed bilateral sensorineural hearing loss. They were referred to radiology department for high resolution computed tomography (HRCT) and magnetic resonance imaging (MRI) temporal bone as a part of preoperative cochlear implant work up. In the present study, we discuss the HRCT and MRI findings helpful in the diagnosis of this rare anomaly in three cases.
Keywords: Aplasia, Cochlea, Common crus, Semicircular canals, Vestibule
|How to cite this article:|
Pendem SK, Rangasami R, Mohanty S S, Radhakrishnan PR. Multimodality approach in evaluation of common crus aplasia. Indian J Otol 2017;23:211-5
| Introduction|| |
The posteromedial end of the superior semicircular canal joins with the anteromedial end of the posterior semicircular canal to form common crus. The absence of common crus is a rare congenital anomaly with incidence of 9.68% in children with congenital sensorineural hearing loss (SNHL). It is known that common crus aplasia (CCA) can be associated with lateral semicircular canal (LSCC) dysplasia. Three-dimensional (3D) techniques such as minimum intensity projection (MIP), volume rendering (VR) of high resolution computed tomography (HRCT), and 3D VR of constructive interference in steady state (CISS) in magnetic resonance imaging (MRI) are helpful in improved diagnosis of cochleovestibular anomalies., Few studies have reported CCA with inner ear anomalies. We present a case series of three children with SNHL with CCA and congenital anomalies of inner ear according to the classification proposed by Sennaroglu et al.
| Case Reports|| |
All the three patients presented to the otorhinolaryngology department with a history of poor response to sound since birth. Audiometry examination revealed bilateral SNHL. There were no vestibular disorders noted on clinical examination. There were no associated facial dysmorphism or anomalies in other body parts. They were referred for HRCT and MRI temporal bone for cochlear implant work up.
Protocol and technical details
Parental informed consent was obtained for all three cases. Institutional Ethical Committee approval was obtained.
Computed tomography protocol
Imaging was performed using Philips Brilliance 16-slice Computed tomography (CT) scanner (Brilliance CT, Philips medical systems, OH, Cleveland, USA). The axial sections of temporal bone were acquired at 120 kVp, 250 mA, with thickness of 0.7 mm. and matrix of 512 × 512.
Magnetic resonance imaging protocol
Imaging was performed using Siemens Magnetom Avanto 1.5 tesla MRI scanner (Siemens Health care, Erlangen, Germany). CISS images were acquired using 0.75 mm thickness with no gap and imaging parameters of TR-5.8 ms, TE-2.7 ms, flip angle of 70°, and matrix of 256 × 198.
The VR images of the CISS sequence were done in Siemens work station.
A 4-year-old boy with history as mentioned above HRCT and MRI demonstrated following findings.
Semicircular canals: LSCC was dilated and fused with dilated vestibule suggesting LSCC and vestibular dysplasia. Bony Island of LSCC measured on axial HRCT image was 0.5–0.8 mm (normal: 2.0–2.5 mm) [Figure 1]a superior semicircular canal (SSCC) was hypoplastic. Common crus was absent. Posterior semicircular canal (PSCC) was normal [Figure 1]c
|Figure 1: A 4-year-old boy with history of bilateral sensorineural hearing loss. (a) Axial high resolution computed tomography image show dysplastic lateral semicircular canal on both sides (white arrows). Internal auditory canal is widened (asterisks). Vestibular aqueduct is dilated on right side and is normal on left side (arrow heads). (b) Axial high resolution computed tomography image show incomplete partition-I on both sides (black arrows). (c and d) Volume rendering image of right (purple colour) and left (dark brown colour) sides show dysplastic lateral semicircular canals (asteriks). Common crus is absent on both sides (open white arrows). Superior semicircular canal is hypoplastic on right side (white arrow head)|
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Cochlea appeared cystic were fused with the absence of modiolus and were seen to be separate from vestibule suggesting incomplete partition (IP) Type I [Figure 1]b. Vestibular aqueduct (VA) was minimally dilated. Internal auditory meatus was widened [Figure 1]a.
Semicircular canals: LSCC was dilated and fused with dilated vestibule suggesting LSCC and vestibular dysplasia. Bony Island of LSCC measured on axial HRCT image was 1.1–1.3 mm [Figure 1]a. Common crus was absent. Both Posterior and superior semicircular canals showed focal stenosis just below the junction [Figure 1]d.
Cochlea appeared cystic with absence of modiolus and was seen to be separate from vestibule suggesting IP Type I [Figure 1]b. VA was normal. Internal auditory canal (IAC) was widened [Figure 1]a.
A 6-year-old boy with history as mentioned above HRCT and MRI demonstrated following findings.
Semicircular canals: LSCC was dilated and fused with dilated vestibule suggesting LSCC and vestibular dysplasia. Bony island of LSCC measured on HRCT axial image was 1.1–1.3 mm [Figure 2]a Common crus was present. Posterior and superior semicircular canals were normal [Figure 3]a.
|Figure 2: A 6-year-old boy with history of bilateral sensorineural hearing loss. (a) Axial high resolution computed tomography image shows reduced bony island of the lateral semicircular canal on right side (white arrow); the bony island of the lateral semicircular canal is absent on left side (white arrow head). Internal auditory canal is narrowed on both sides (asterisks). (b) Axial high resolution computed tomography image shows hypoplastic cochlea on right side (black arrow); the cochlea is cystic and fused with vestibule on left side (black arrow head)|
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|Figure 3: A 6-year-old boy with history of bilateral sensorineural hearing loss.(a) Volume rendering image of right side (purple colour) show dysplastic lateral semicircular canal (asterik). Common crus is present (white arrow). (b) Volume rendering image of left side shows dysplastic lateral semicircular canal (asterik). Common crus is absent (white arrow head). (c) Oblique sagittal magnetic resonance image of constructive interference in steady state sequence of right side show absence of cochlear nerve (open arrow) (d) Oblique sagittal magnetic resonance image of constructive interference in steady state sequence of left side show absence of cochlear nerve (open arrow) and single vestibular nerve|
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Cochlea appeared hypoplastic [Figure 2]b. Cochlear nerve was not visualized [Figure 3]c. IAC was narrowed. VA was normal.
LSCC and vestibular dysplasia was seen. Bony island of LSCC was absent [Figure 2]a. Common crus was absent. Posterior and superior semicircular canals were normal [Figure 3]b.
Cochlea appeared cystic with absence of modiolus and was fused with vestibule suggesting Common cavity deformity [Figure 2]b. IAC was narrowed. Cochlear nerve was not visualized. Vestibular nerve was appeared as single [Figure 3]d. VA was normal.
A 9-year-old boy with history as mentioned above HRCT and MRI demonstrated following findings.
Bilateral LSCC s were dilated and fused with vestibule. CCA was noted on both sides. Posterior and superior semicircular canals were seen [Figure 4]a and [Figure 4]b.
|Figure 4: A 9-year-old boy with history of bilateral sensorineural hearing loss. (a and b) Volume rendering images of right and left sides shows dysplastic lateral semicircular canal (asterisks). Common crus is absent (white arrows). (c and d) Axial high resolution computed tomography images of the right and left ears shows normal cochlea (black arrows) on both sides|
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Cochlea was normal on both sides. IAC was normal. VA was normal [Figure 4]c and [Figure 4]d.
[Table 1] shows the summary of findings demonstrated on HRCT and MRI for the three cases.
|Table 1: Summary of findings demonstrated in high resolution computed tomography and magnetic resonance imaging|
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| Discussion|| |
HRCT and MRI temporal bone have become routine part of preoperative cochlear implant work up for diagnosing congenital anomalies of inner ear in children with SNHL.
Embryology of inner ear
At the 3rd week of gestation, otic placode develops from the ectodermal layer on either side of the rhombencephalon. By the 4th week, the otic placode invaginates into the connective tissue adjacent to the rhombencephalon to form the otic cyst or otic vesicle. Otocyst starts to differentiate by the 5th week. At around 6th week, the cochlea and semicircular canals were identified. The cochlear duct achieves the full 2.5 turns at 9–11 weeks. The development of the cochlea is completed between 22nd and 25th weeks. Thus, the human labyrinth achieves adult size at birth and does not grow further.,,
Jackler et al. proposed the classification of inner ear abnormalities, based on a linear developmental model towards normal anatomy and most likely time at which developmental arrest occurs during embryogenesis. Sennaroglu and Saatci  further modified this classification. They stated five groups of malformations; which include cochlear, vestibular, semicircular canal, IAC, vestibular, and cochlear duct malformations.
The classification of Cochleo-vestibular malformations according to Sennaroglu et al. was shown in [Table 2].
|Table 2: Classification of cochlear anomalies according to Sennaroglu et al.|
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Semicircular canal anomalies
They can be either completely absent/hypoplastic or enlarged. The most common anomaly is short LSCC being confluent with vestibule known as LSCC-vestibular dysplasia.
Large vestibular aqueduct syndrome
It is the most common inner ear anomaly occurring in children with congenital SNHL. Usually presents bilaterally. It is defined as having a width of more than 1.5 mm measured at the mid-point between common crus and external aperture.
Benton and Bellet  proposed that occurrence of CCA is not related to developmental arrest of otic placode. It is caused due to abnormal reabsorption of neuro-ectodermal tissue of membranous crus which results in insufficient stimulation for the surrounding mesenchyme to get differentiated in to cartilage and finally to bone.
Manfré et al. reported a case with unilateral CCA associated with Goldenhar syndrome (Occuloauriculo vertebral dysplasia). On CT and MRI imaging they have identified CCA on the right side with LSCC-vestibular dysplasia. There were no cochlear anomalies.
Kim et al. retrospectively studied the findings of 3D volume rendered images obtained from CISS sequence in six cochlear implant candidates who had been diagnosed with CCA. They stated that 3D VR images can help in better comprehension of CCA compared to two-dimensional axial sections and MIP techniques. The six cases with CCA were found to be associated with cochlear anomalies such as cochlear hypoplasia and IP.
Emmrich et al. have described the usefulness of 3D CT VR technique in evaluation of CCA. They stated that it is difficult to identify the CCA on axial and coronal sections on CT scan and would require 3D reconstructed VR images for better visualization of this anomaly.
In our study, unilateral aplasia was found in the second case. Kim et al. have also reported a case with unilateral aplasia. It is difficult to understand the occurrence of unilateral aplasia as the development of inner ear occurs simultaneously on both sides.
All the three cases showed lateral semicircular-vestibular dysplasia which is in accordance with the known fact that it is associated with CCA. As LSCC is the last to be formed any developmental malformations happened during development of posterior and LSCC will also affect the LSCC which is evident from our study.
In our study, we have used combined HRCT and MRI findings to diagnose these malformations. Volume rendered MRI obtained from CISS sequence was extremely useful to confirm the CT diagnosis. Further, they could show area of stenosis in the semicircular canals. The oblique sagittal magnetic resonance sections obtained perpendicular to the vestibulo-cochlear and facial nerves would help in better understanding of the hypoplasia/agenesis of the nerves. The accurate diagnosis of inner anomalies associated with CCA and in evaluating status of nerves would be helpful for ENT surgeon in determining the implantation side and choosing the length of the electrode array.
| Conclusion|| |
Our study shows that HRCT and MRI imaging with advanced rendering techniques such as VR techniques were quiet useful for radiologists in studying the complex anatomy of cochleo-vestibular structures and improve the confidence in accurate diagnosis and classification of cochlea-vestibular anomalies. These findings would help the surgeon in making choice of implantation side and determining the length of cochlear implant according to the cochlear duct length in cochlear anomalies.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]