¹ H.Pınar Gunbey, M.D. ¹ Huseyin Aydın, M.D.² Huseyin Cetin, M.D¹ ¹ ¹Ataturk Education and Research Hospital, Ankara, ² Gulkent Hospital, Isparta Turkey

B ackground  The cochlea and the carotid canal are among a number of crucial anatomic structures that extremely close one to another in the petrous pyramid of temporal bone  Anatomic knowledge of these vital structures and relations between them provides an important key to approach this complex region

 This close anatomic course represents possible surgical risk during  petrosectomy apporach to the clivus  brainstem or the middle fossa apporach to the internal acustic meatus or  most recentlly increasingly popular the cohlear implant surgery.  Especially internal carotid artery (ICA) lesion  transoperative bleeding risk  difficult to control  serius results associated with the irrigation of the central nervous system

 In cochlear implant surgery  the risk of potential injury to the carotid artery may be seen during drilling of the basal turn of the cochlea and improper placement of the electrode  The instance between the cochlea and the carotid artery may be also a possible reson for auditory and vestibular symptoms such as tinnitus and hearing loss.

Purpose  investigate the normal range of the this region called ‘‘ cohlear- carotid interval’’ (CCI) in a wide population by 64-slice multi-detector computed tomography (MDCT).

Materials and Method  A retrospective study who had undergone a temporal MDCT between September 2008 and March 2010  1105 patients (510 M and 595 F)  0,5 mm thickness coronal images by 64-slice MDCT  The bony interval for right and left sides confirming from axial and sagittal planes of multiplanar reformat images  Measured independently by 2 observers

 Mann Whitney U test and Sperman correlation test were used to assess differences between readers,sides and gentles

Results All subjects (mm) Female (mm)Male (mm) Right Range0,0-60,0-5,80,0-6 Mean ± SD0,9 ± ± 0.8 Left Range ,1-5,4 Mean ± SD1.0 ± 0.8 Carotid-cochlear interval measures

CCI measured 0.0 mm  unilateraly in 8 patients (0.7%) (Young et al.2006)  bilateraly in 2 patients (0.1%) (Modugno et al.2004)  a score of 10 in total population (0.9%)  CCI scores of total population  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;)

CCI dehisence

3D reconstruction

Bilateral dehisence

 No relation CCI measures and subject gender  Positive correlation Right and left side CCI mesures

Conclusion  The cochlea- carotid interval represents a wide variation independently from gender and the distance can be in microns  The dehisence can be seen unilateraly and more less bilateraly in a large population.  It is a developmental defect like superior semisircular canal dehisence and may be related with defects on maturation stages.

 In preoperative CT imaging special attention to this close relationship may allow the radiologist :  to play a crucial role in alerting the surgeon to prevent the penetration of the carotid canal during cochlear surgery and the cochlear injury during vasculary surgery.  Possible surgical risk may result in unexpected tragic damage