title: The cochlear-carotid interval: anatomic variation and potential clinical implications.
abstract: OBJECTIVE
  A temporal bone CT study in a patient with episodic mid-tone sensorineural hearing loss and tinnitus demonstrated absence of bone between the petrous internal carotid artery and the basal turn of the cochlea. The potential implications with respect to increasingly popular cochlear implant surgery compelled us to retrospectively analyze a series of temporal bone CT scans to establish typical measurements for this region, which we termed the "cochlear-carotid interval" (CCI).
  
  
  METHODS
  After IRB exemption, 2 observers independently measured the bony interval between the cochlea and the petrous internal carotid artery canal on coronal images from 30 consecutive temporal bone CT studies. The 1-mm thick coronal images were either acquired directly or were reconstructed from an axial dataset acquired at 0.75 or 0.6 mm section thickness. All measurements were performed by using electronic calipers on a Sienet MagicView VE 42 Siemens PACS station. Mixed model analysis of variance was used to evaluate differences between readers and sides with respect to the mean CCI but adjusted for age and accommodating the correlation among observations generated for the same subject.
  
  
  RESULTS
  The patient in our case report had a right CCI of 0.2 mm and left CCI of 0.0 mm. In the other 30 patients, the right CCI ranged from 0.2 to 3.8 mm (mean, 1.2 +/- 0.8 mm; median, 0.9) and the left CCI from 0.2 to 5.0 mm (mean, 1.1 +/- 0.9 mm; median, 0.8). The CCI did not exhibit a significant association with subject age (P = .1336), and there were no significant differences between readers (P = .824) or sides (P = .350) in terms of mean CCI.
  
  
  CONCLUSIONS
  The CCI varies widely between patients and may be as small as zero. Analysis of anatomic relationships suggests a potential relationship between small CCI and mid-tone sensorineural hearing loss, as in our reported patient. Preoperative knowledge of thin or absent bone between the cochlea and petrous carotid canal may help prevent inadvertent penetration of the carotid canal during cochlear implant surgery.
authors.affiliation: Department of Radiology, Division of Neuroradiology, New York University Medical Center, New York, NY, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Young
authors.forename: D R
authors.initials: DR
authors.lastname: Shatzkes
authors.forename: J S
authors.initials: JS
authors.lastname: Babb
authors.forename: A K
authors.initials: AK
authors.lastname: Lalwani
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002343:Carotid Artery, Internal / Q000000981:diagnostic imaging / Q000473:pathology*; D002508:Cephalometry; D002648:Child; D002675:Child, Preschool; D018424:Cholesteatoma, Middle Ear / Q000000981:diagnostic imaging; D003051:Cochlea / Q000000981:diagnostic imaging / Q000473:pathology*; D005260:Female; D005500:Follow-Up Studies; D006319:Hearing Loss, Sensorineural / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007223:Infant; D008297:Male; D008417:Mastoiditis / Q000000981:diagnostic imaging; D008875:Middle Aged; D010579:Petrous Bone / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D013701:Temporal Bone / Q000000981:diagnostic imaging / Q000473:pathology*; D014012:Tinnitus / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D014723:Vestibular Aqueduct / Q000000981:diagnostic imaging