Quantitative analysis of laryngeal structures during phonation in patients with unilateral vocal fold paralysis

We devised a method to scan the whole larynx within five seconds period with the aid of multislice helical computed tomography (MSHCT). This method allows us to quantitatively evaluate the three-dimensional movement of the arytenoid cartilage muscular process of the in vivo human larynx during inspiration and phonation. The distances involved in the arytenoid cartilage muscular process and several other points were measured in patients with unilateral vocal fold paralysis (UVFP). The purposes of the present study were to determine accuracy of the measurements and to compare the measurements taken during phonation with those observed during inspiration. Utilizing an excised human larynx, two examiners independently measured the two distances between the muscular process and the most lateral superior point of the cricoid, and between the muscular process and the posterior inferior point at the midline of the posterior cricoid lamina. They measured these two distances 10 times with the aid of MSHCT and then directly measured with fine-scale. The subjects included 17 men and 16 women with UVFP. Points were set to simulate the points where each intrinsic laryngeal muscle starts. The reliability and the accuracy of the measurements of the two examiners were confirmed. Distances simulating the thyroarytenoid and lateral cricoarytenoid muscles became shorter during phonation than those during inspiration on the healthy side while those on the paralyzed side became longer during phonation. These changes were statistically significant. In conclusion, MSHCT was quite useful in assessing the functional movements of laryngeal structures in patients with UVFP.