Relation of the Vocal Cord to the Thyroid Cartilage

The radiotherapist is frequently called upon to treat a carcinoma of the larynx limited to the vocal cord. These small lesions should be treated with the smallest possible field consistent with adequate coverage of the tumor volume. Because of the small size, accurate localization is critical and localization films should always be obtained. If necessary, instillation of contrast material into the larynx may be used to better outline the cords. Even with good localization films available, every treatment requires careful positioning of the patient by the radiotherapist himself. Daily verification of the accuracy of the portal is needed, and palpation can afford an additional safeguard. This can be reliable, provided it can be demonstrated that the relation of the cord to the easily palpable thyroid cartilage is reasonably constant in the age group of the cancer patient. Material and Methods In the course of another study, to be published at a later date, the larynges of 50 consecutive patients who died of conditions unrelated to the larynx were obtained immediately after autopsy from the Department of Pathology. The soft tissues, including the muscles of the larynx, were removed down to and including the perichondrium of the laryngeal cartilages. The vocal cords were left in place. The epiglottic cartilage was completely excised so that the notch in the superior border of the thyroid cartilage and its relation to the anterior commissure were clearly exposed. The distance between the lowest point in the notch and the superior surface of the cords at the anterior commissure was measured in each case. From radiographs of the specimens in the lateral view, the angle between the anterior surface of the cords and the anterior surface of the thyroid cartilage was measured (Fig. 1). Results The distance between the superior surface of the cords at the anterior commissure and the lowest portion of the thyroid cartilage notch averaged 7 mm; the maximum was 11 and the minimum 5 mm. The angle between the cords and the thyroid cartilage averaged 60 degrees in males and 65 in females. This slight difference, however, has no statistical significance in view of the small number of cases. The maximum value for this angle was 75 degrees and the minimum 50. Incidentally, these values happened to be in a female and a male, respectively. Discussion These average measurements should be helpful in locating the approximate position of the cords in an individual case. The superior thyroid notch is formed by the border of the two wings of the thyroid cartilage. The point where the two borders seem to fuse into one is easily identified. This point should be palpated from the front, not from above (Fig. 2). In the average adult the superior surface of the anterior commissure of the vocal cords lies 7 mm below this point.