Three-dimensional conformation of the injected bolus in vocal fold injections in a cadaver model

Objective. To determine the 3-dimensional (3D) conformation of the injected bolus in the larynx in vocal fold injections, to understand how the bolus interacts spatially with elements of the laryngeal framework, and to relate the above to clinical observations in performing vocal fold injections. Study Design. Excised cadaveric larynx study. Setting. Laboratory. Subjects and Methods. Vocal folds of 12 human excised cadaveric larynges were injected with calcium hydroxylapatite. High-resolution computed tomography scans were obtained of the injected larynges. Densities corresponding to the injected bolus and the laryngeal framework were extracted and processed with MATLAB routines to generate selective 3D reconstructions of the injected bolus within the laryngeal framework. Histology analysis was also performed to correlate with observations from the 3D reconstructions. Results. Boluses injected into the lateral aspect of the thyroarytenoid muscle tended to be irregularly shaped, appeared to fill up the paraglottic space, and were associated with significant muscle compression. The vertical thickness of the injected boluses averaged 9.5 mm for lateral boluses and 7.6 mm for medial boluses, which were comparable to the vertical thickness of uninjected vocal folds. Conclusion. Laterally injected boluses are shaped by spatial constraints imposed by elements of the laryngeal framework. Compression of vocal fold muscle may be a mechanism accounting for stiffness from overinjection. The irregular shapes of some boluses may affect the outcome of subsequent medialization attempts. Injections may enhance the vocal fold contact height as a favorable effect beyond simple medialization.