[Image analysis of the contour of paralyzed vocal cord during phonation]

The development of digital radiography (DR) has made it possible to analyze the contour of the laryngeal soft tissue structures in more detail than the conventional screen-film method. We analyzed the contour of the paralyzed vocal cord during phonation using motion subtraction technique. Forty four patients with unilateral recurrent nerve palsy were examined. The images were obtained by means of frontal tomography of the larynx during quiet inspiration and normal (expiratory) phonation. Tomography during inspiratory phonation was also examined in ten patients who can perform it. The thickness of the slices was 5.0 mm. The authors found that the free margin of the paralyzed vocal cord shifted by the aerodynamic power along the direction of the air flow, i.e. it shifted to the cranial direction during normal phonation and to the caudal during inspiratory phonation. The displacement phenomenon of the paralyzed vocal cord was significantly correlated with the degree of vocal cord atrophy (p less than 0.01). The result would indicate that the aerodynamic power during phonation is one of the factors eliciting the higher position of the paralyzed vocal cord during phonation, in addition to its anatomical displacement due to abduction of the paralyzed arytenoid. This notion should be taken into consideration in selecting the surgical approach for the treatment of unilateral recurrent nerve palsy.