Application of dynamic CT scan in the three-dimensional dynamic morphology changes of laryngeal soft tissue in unilateral vocal fold paralysis patients

Abstract

Objective: To explore the dynamic changes of three-dimensional morphology of laryngeal soft tissue and its clinical value in the unilateral vocal fold paralysis (UVFP) patients through dynamic CT scanning during the process from inspiration to phonation. Methods: From October 2017 to July 2019, a retrospective study was performed in 18 patients with UVFP (10 males and 8 females with the range of age from 29 to 75 years old) and 10 normal subjects (5 males and 5 females with the range of age from 25 to 58 years old) in Department of Voice-Otolaryngology Head and Neck Surgery, Section Two, Zhongshan Hospital Xiamen University. The laryngeal dynamic computed tomography (CT) of cine mode was performed. Ten dynamic sequence images of vocal folds movements were obtained during the process from inspiration to phonation. Based on the dynamic changes of glottic area and the displacement of cricoid cartilage. The above dynamic sequence images were divided into inspiratory phase and phonation phase as well as open phase and closed phase. The soft tissue parameters were measured respectively, including vocal folds length, width, thickness and subglottal convergence angle. Independent-sample t test was used to analyze between UVFP group and control group. Results: During the process from inspiration to phonation, the morphology of vocal folds in control group was relatively stable at inspiratory phase and closed phase in phonation. When open phase and closed phase of phonation were switching, the morphology of vocal folds changed obviously. The length of vocal folds became longer (1.19±0.10) mm, the width became wider (2.19±0.17) mm, the thickness became thinner (2.66±0.56) mm, and the subglottal convergence angle decreased (31.45±4.78)°. Compared with the controll group, in the open phase, the thickness and width of the vocal fold on affected side in the UVFP group were thinner (t=10.25, P<0.001) and wider (t=5.25, P<0.001).While in the closed phase, the subglottal convergence angle was larger (t=4.41, P=0.001).The width of the healthy side vocal fold in the UVFP was wider (t=2.54, P=0.026) than that in the control group. The differences in other parameters were not statistically significant. Conclusions: Dynamic laryngeal CT scanning provides a simple and non-invasive method for the objective and quantitative measurement of the dynamic changes of laryngeal morphology from inspiration to phonation. Compared with the control group, the characteristic dynamic changes among UVFP were observed during this particular process, which included changes of subglottal convergence angle and thickness of vocal muscle due to denervation. In addition, in UVFP group, the width of the vocal fold healthy side in the closed phase may be used to assess its compensatory function.