1. Study of agreement between
radiological and cadaveric
dissection findings of cochlear
carotid interval of human temporal
bone
Dr. R S Lakhawat, Dr. Mohnish Grover, Dr. Man Prakash Sharma, Dr.
Sunita Agarwal, Dr. Sunil Samdani.
Dept. of Otorhinolaryngology, SMS Medical College and Hospital,
Jaipur, Rajasthan
2. INTRODUCTION
Cochlear carotid interval is minimum distance between petrous
segment of internal carotid artery and basal turn of cochlea. This
very small distance leads to potential surgical hazard during
cochlear implantation and a possible source of auditory and
vestibular symptoms such as tinnitus and hearing loss.
The carotid canal is a potential space that may give tactile sensation
similar to cochlea and may mislead the CI surgeon. Preoperative
knowledge of thin or absent bone between cochlea and petrous
carotid canal may help prevent inadvertent penetration of carotid
canal during cochlear implant surgery.
3. This distance is also critical in a cochlear drill out procedure in case
of labyrinthitis ossificans.
Less than 10% of tinnitus patients suffer from pulsatile tinnitus.
It is possible that the energy transmitted from the petrous carotid
artery to the basal turn of cochlea may result in fluid pressure
changes and the direct stimulation of hair cells on basilar
membrane1.
4. In recent years the cochlear implantation surgery is getting
popularised, so this cochlear carotid interval is getting more and
more attention from CI surgeons. Inadvertent electrode insertion in
the carotid canal has also been reported2.
Our study is aimed to calculate this very distance in cadaveric human
temporal bones radiologically and on dissection.
5. Material and Methods
The present study was conducted at Department of
Otorhinolaryngology, Department of Anatomy and Department of
Radiology in SMS Medical College and Hospital, Jaipur.
40 cadaveric Human temporal bones were acquired from
department of anatomy through proper channel.
6. All specimens were initially undergone high-resolution CT scanning.
The specimens then dissected under microscope.
The carotid cochlear interval was the minimum distance between
basal turn of cochlea and the internal carotid artery. It was
measured on HRCT Temporal bone with help of DICOM viewer
software
CCI then measured on dissection by placing millimetre graph paper
in dissection field and ImageJ software was used to convert pixel to
millimetre.
8. CCI on HRCT CCI on Dissection
Mean 2.08 mm 2.19 mm
SD 0.89 mm 0.85 mm
Range 0.48 - 4.25 mm 0.85 - 4.12 mm
9. DISCUSSION
Our results were similar to Young R. J. and et al (2006) who did a study
on 59 temporal bones with help of HRCT Temporal bone and find in
their study that CCI was in right side measured with range of 0.4-3.7
mm and Mean ± SD =1.2±0.8 mm and in left side range = 0.4-4.9
mm and Mean ±SD =1.1±0.9 mm and concluded that the CCI varies
widely between patients1.
Gunbey et al (2011) in a study on 1105 patients found that the CCI
showed a range of 0.0 to 6 mm for the right side (mean 0.9 ± 0.8;)
and 0.0 to 5.9 mm for the left side (mean 1.0 ± 0.8;). They found
dehisence of the CCI 0.0 mm unilaterally in eight patients (0.7%) and
bilaterally in two (0.1%) with a score of 10 in the total population
(0.9%)3.
10. The bone thickness between otic capsule and carotid canal varies
from 0.5 to 10 mm with mean distance 1.3 to 1.5 mm.
We found in our study that the distances measured by CT and on
dissection were similar, the small differences were due to measuring
technique limitations and limited access available during dissection.
The similarity between both results indicate towards importance of
pre op HRCT, and proves the importance of the same. Pre op HRCT
TB gives an idea to the surgeon about the anatomical roadmap of the
important neurovascular structures of the temporal bone.
11. The temporal bone contains important structures in a relatively
smaller area. Hence, anatomical abnormalities and even variation in
bone thickness separating its contents become important when
surgical intervention is required. Familiar variants include facial nerve
canal dehiscent, high and or dehiscent jugular bulb.
Cochlear implant is a breakthrough in medical engineering and its
implantation surgery is increasing rapidly in popularity. The
implantation is quite safe but number of complications have been
reported , including inadvertent penetration of the electrode array in
petrous carotid canal.
So, CCI becomes important and close attention should be given to
this distance during pre op imaging.
12. CONCLUSION
The cochlea carotid interval varies widely between cadaveric
temporal bones. Attention to this area when examining pre
operative CT scan may help prevent inadvertent carotid canal
penetration during Cochlear implant surgery.
13. REFERENCES
1. Young RJ, Shatzkes DR, Babs JS, et al. The cochlear-carotid interval: anatomic
variation and potential clinical implications. Am J Neuroradiol. 2006; 27 (7): 1486-
1490.
2. Gastman B, Hirsch B, Sando I, et al. The potential risk of carotid injury in cochlear
implant surgery. Laryngoscope 2002;112:262–66.
3. Gunbey HP, Aydın H, Cetin H, Gunbey E, Karaoglanoglu M, Cay N, Alhan A. MDCT
Assessment of the Cochlear-Carotid Interval. Neuroradiol J. 2011 Jun 30;24(3):439-
43.
