The Human Vocal Fold Layers. Their Delineation Inside Vocal Fold as a Background to Create 3D Digital and Synthetic Glottal Model

Abstract

Objectives: To distinguish the layers of the vocal fold at the submacroscopic level and determine their boundaries, thereby creating a basis for the construction of a digital 3D model of the human vocal folds.

Study design: The submacroscopic delineation of individual layers of fixed vocal ligaments based on their structural differences.

Methods: Following tasks were performed: (1) Submicroscopic dissection of the vocal folds fixed in a solution with a low concentration of fixation substance (in this case, the muscular parts of the vocal folds were removed); (2) Using the CT and micro-MRI methods, we determined the position of the dense parts of the vocal folds; and (3) Using a modified plastination method, we preserved macroscopically natural appearance of all ligamentous and muscular layers.

Results: The vocal ligament is composed of several volumes of connective tissue. It is surrounded by layers of fibrous material permeated by liquid. Individual fibers stretch all the way to the fibrous casing (fascia) of the vocal muscle. The vocal fold layer surrounding the ligament externally has a stratified character.

Conclusions: According to our findings, we infer that this ligament is a complex of several fibrous bundles which are surrounded by a thin layer of connective tissue. Below the surface of epithelium of the vocal fold run several separate bands which are closely adjacent to it. Therefore, we propose using the term ligamentous complex involving closely adjacent structures, instead of the vocal ligament only. We feel that it better reflects the functional and structural character of the whole formation.

Keywords: 3D digital model; Human vocal fold; Lamina propria; Plastinated larynx; Vocal ligamentous complex.