Narrow band imaging accentuates differences in contrast between cartilage and perichondrium in the elevation of the muco-perichondrium flap during septoplasty and open septorhinoplasty

Abstract

Objective: In the elevation of the muco-perichondrium flap during septoplasty and septorhinoplasty, it is important to elevate the subperichondrial layer. When performing subperichondrial elevation of the flap, the surgeon uses differences in color tone to distinguish the perichondrium from cartilage; however, it is relatively difficult to understand these differences and to share them with assistants. Furthermore, the perichondrium at the caudal end adheres tightly to the cartilage, making it difficult to detach accurately the subperichondrial layer. Narrow band imaging (NBI) is an optical technology that facilitates detailed observation of microvessels in the mucosal surface layer. In this study, we investigated whether NBI is better than white light (WL) in accentuating differences in contrast between cartilage and perichondrium in the elevation of the muco-perichondrium flap during septoplasty and septorhinoplasty.

Methods: Twenty-six sides of 15 patients (the modified Killian approach was used in two patients, the hemitransfixion approach was used in seven patients, and open septorhinoplasty was used in six patients) with elevated muco-perichondrium flaps were studied under WL endoscopy and NBI. The brightness of the perichondrium and cartilage and the differences between the two tissues were compared between WL and NBI using ImageJ 1.53a. Next, the WL and NBI endoscopic images used for cartilage identification were divided into the three separate primary color channels of red, green, and blue, and the brightness of the perichondrium and cartilage were measured separately for each channel.

Results: Under WL, the perichondrium appeared reddish-white and the cartilage appeared white, whereas under NBI the perichondrium appeared greenish-gray, differentiating it from the white cartilage. The difference in brightness between the cartilage and perichondrium was significantly higher on NBI (grayscale difference 80.8 (SD 42.4)) than on WL imaging (grayscale difference 35.6 (SD 31.1)) (p<0.001). In the red channel, the difference in image intensity between cartilage and perichondrium was significantly higher on NBI than on WL imaging (Red WL grayscale difference -1.5 (SD 33.7), Red NBI grayscale difference 90.0 (SD 56.7); p<0.001).

Conclusions: NBI is better than WL at accentuating the difference in contrast between cartilage and the perichondrium during the elevation of the muco-perichondrium flap during septoplasty and septorhinoplasty. The difference in the processing of red light between WL and NBI provides the largest contribution to the differentiation of cartilage from the perichondrium under WL and NBI. We believe that NBI can be usefully applied during septoplasty and septorhinoplasty to distinguish cartilage from the perichondrium with precision.

Keywords: Muco-perichondrium flap; Narrow band imaging; Open septorhinoplasty; Septoplasty; Subperichondrium.