THE COCHLEAR AQUEDUCT - AN IMPORTANT LANDMARK IN LATERAL SKULL BASE SURGERY

The cochlear aqueduct (CA) is used as a landmark in lateral skull base surgery. In this study anatomic relationships between the CA and adja cent neurovascular structures were examined by dissecting 32 temporal bones, Observations of the relationship of the external opening (EO) o f the CA with the ninth, tenth, and eleventh cranial:nerves, inferior petrosal sinus (IFS), and intrapetrous carotid artery (ICA) were noted . In addition to the distance of the EO of the CA to the vertical port ion of the ICA, the entire length of the CA and the width of the EO we re also measured, The ninth nerve was the only structure lodged at the EO of the CA in 34.4% of bones. However, in 40.6% of bones only the I FS crossed the EO of the CA, although the ninth nerve was situated jus t anteroinferiorly in the vicinity of the EO, In 15.6% of bones it was possible to observe both the ninth nerve and the IFS crossing the EO, In 9.4% of bones the EO of the CA was found to be occupied by the ten th and eleventh nerves, It was also observed that the ICA was located anteriorly on the same sagittal plane with the EO in 15.6% of bones, I t was concluded that although in 90% of cases the EO of the CA was in close relation with the ninth nerve, other structures such as the IFS, the tenth and eleventh cranial nerves, and the ICA were also at risk during drilling in this area because of their intimate relationships w ith the EO of the CA.