Objective: The purpose of this study was to determine the effectiveness of laryngeal phonation CT for the diagnosis of vocal cord paralysis by examining the physiologic and functional changes in the larynx during vowel phonation in patients with vocal cord paralysis.
Subjects and methods: For the control study, three healthy volunteers underwent laryngeal phonation CT while vocalizing the vowels /hee/, /ih/, and /ah/, and reconstructed coronal images of the larynx were obtained. After the control study, 28 patients with unilateral vocal cord paralysis underwent laryngeal phonation CT during /hee/ phonation, which was chosen as a most appropriate vowel for this purpose. Changes in the paralyzed and normal vocal cords were evaluated quantitatively and qualitatively on coronal reconstruction images.
Results: On the coronal reconstructed images from the healthy volunteers, the normal cords had a shoulder formation appearance, and the cords lay within 1 mm lateral to the midline during phonation. For patients with vocal cord paralysis during /hee/ phonation, the average angle formed by the long axis of the vocal cord and the midline was 71.67 degrees on the affected side and 92.21 degrees on the normal side (p = 0.001). The vocal cord edges lay 1.5 mm lateral to the midline on the affected side and 0.44 mm lateral to the midline on the normal side (p = 0.003). In the qualitative study, the two observers found the coronal reconstructions of the laryngeal phonation CT scans yielded a higher detection rate than did conventional axial CT.
Conclusion: Laryngeal phonation CT proved more useful for evaluating vocal cord paralysis than did conventional CT and can be used as a primary diagnostic tool when vocal cord paralysis is suspected.