Introduction 1 2 ® Production of 3DCT 3 6 Scans were made when the glottis was closed (with phonation) and open. Each patient was scanned for about 2 s. The speed of the scan enables scanning of patients with unilateral vocal fold paralysis during a brief phonation and minimizes motion artifact. Before scanning, doctors (the authors) were consulting the patient about the timing between phonation and the scan. ® ® 1 Fig. 1 ® ®  7 Stereoscopic location of the arytenoid cartilage in unilateral vocal fold paralysis 2 Fig. 2 yellow red  During inspiration, the arytenoid cartilage on the healthy side was located in the lateral part of the cricoarytenoid joint. Simultaneously, the vocal process was located outside and above the joint. In comparison, the arytenoid cartilage on the paralyzed side was located in the dorsocranial part of the cricoarytenoid joint, while the paralyzed vocal process was located inferiorly and the arytenoid cartilage dropped forward. This position on the paralyzed side was the result of posterior cricoarytenoid muscle paralysis. During phonation, the healthy side rocked and moved to the ventromediocaudal part of the cricoarytenoid joint to adduct the vocal cord, and the vocal process moved inward and downward. Conversely, the paralyzed side glided dorsocranially in comparison with its position during inspiration. Therefore, the arytenoid cartilage showed a rocking movement on the healthy side, and a gliding movement on the paralyzed side. This gliding movement on the paralyzed side was a passive movement. the paralyzed arytenoid underwent passive movement caused by contact with the mobile side during phonation. The vocal fold blown up may affect this passive movement. We call such arytenoids “flaccid arytenoids.” The position of the paralyzed arytenoid depends on the severity of paralysis. Surgical simulation This section describes type I thyroplasty. It is important to determine the level of the vocal folds in this procedure. Note that the arytenoid cartilage on the paralyzed side glides dorsocranially, as mentioned above. The paralyzed vocal fold becomes higher than the vocal fold on the healthy side during phonation. The type I thyroplasty window should be based on the vocal cord level on the healthy side during phonation. Therefore, the vocal fold level of the healthy side must be projected onto the thyroid cartilage of the paralyzed side. 3 8 9 10 Fig. 3 red dotted line black dotted line  Postoperative evaluation Case 1 4 Fig. 4 a b c d double-headed arrow  Case 2 5 ® Fig. 5 a ® b  Case 3 6 10 11 Fig. 6 a b c  Case 4 7 7 7 Fig. 7 a b c  Conclusions Laryngeal 3DCT is useful for determining the stereoscopic configuration of the arytenoid cartilage. In addition, 3DCT enables observation of the laryngeal framework from every angle, and is also useful for surgical simulation and feedback after surgery.