목적: New slim modiolar electrode is pre-curved and the electrode is wrapped in a straight sheath that acts as an insertion guide. The problem is the insertion of the sheath; since the sheath is thicker and stiffer than the intracochlear electrode, sometimes it is necessary to open the RW with a further extension, so-called extended RW approach, to place the sheath in the optimal position. The authors found that a bony spicule existing between the RW and the basal turn is important to predict the necessity of the extended RW approach. 방법:We reviewed 17 patients who received cochlear implantation using Nucleus® CI632. The use of the extended RW approach has been identified through their surgical records. The presence of the bony spicule was recognized in preoperative high-resolution temporal bone computed tomography (TBCT). We modeled a transcochlear view from axial and coronal CT images using OTOPLAN developed by CAScination, reconstructing the RW and the basal turn of a patient into a single plane. 결과:Extended RW approaches were performed on 7 subjects (41.2%). In axial TBCT, bony spicule suspicious findings were observed in 10 patients. Extended RW approach was performed in 5 subjects (50.0%) of them. In the reconstruction images, the bony spicules were identified in 8 subjects; finally, 6 of them (75.0%) underwent the extended RW approach. In 2 subjects, although bony spicules were suspected on axial TBCT, these spicules were not seen on the reconstructed images. 결론:If the sheath insertion is not working well due to the bony spicule, a surgeon may repeatedly attempt to reinsert it by changing the insertion direction or do unplanned extended RW approach, which may cause surgical trauma in the cochlea. Rather, the implementation of planned extended RW approach can reduce the surgical trauma. Thoroughly investigating preoperative TBCT and detecting the bony spicule, it would be better to consider the extended RW approach for the insertion of the slim modiolar hugging type electrode.