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We here summarize the structures of the laryngeal vocal fold as well as its insertion structures at the anterior commissure and at the area of the vocal process and place these findings within the context of biomechanical, functional, and clinical implications.

© 2020 S. Karger AG, Basel

The paired vocal folds are located beneath the false cords in the middle of the laryngeal glottis (transglottic space, glottic space, glottis). The term “vocal cords” in day-to-day clinical use is anatomically incorrect; it should be used only to describe the vocal ligament. The vocal folds, plicae vocales, normally protrude farther into the laryngeal lumen than the false cords, so that they can be evaluated in the context of the laryngeal speculum examination. They comprise, besides the mucous membrane with the vocal ligament and the adjoining conus elasticus, mainly the vocalis muscle and cricoarytenoideus lateralis muscle. Together, the two vocal folds form the glottis, the vocalizing laryngeal element. The length and width of the vocal folds are related to vocal pitch.

The vocal folds delimit the epiglottis (rima glottidis), the central portion of which comprises several layers (Fig. 1):

1Multilayered, unkeratinized squamous cell epithelium (Fig. 1–4)

2Loose connective tissue (subepithelial connective tissue) that is part of “Reinke’s space” (see below) and forms layer 1 = superficial layer (Fig. 1–4)

3Vocal ligament consisting of (Fig. 3–5): (a) Layer 2 = middle layer (dense connective tissue with plentiful elastic fibers) (b) Layer 3 = deep layer (dense connective tissue with plentiful collagen fibers), and

4Vocalis muscle (Fig. 1, 3, 5)

The loose connective tissue extends cranially to the linea arcuata superior and inferiorly to the linea arcuata inferior (Fig. 3, 5, 6). Ventrally, it terminates at the level of the noduli elastici anteriores (see below); dorsal-medial from the processus vocalis. Based on descriptions of “Reinke’s edema” by M. Hajek [1], the anatomist Friedrich Reinke [2] investigated these changes by injecting blue-stained glycerin glue, thus defining “Reinke’s space” as a subepithelial displacement gap of the lamina propria mucosae (layer 1) in the plica vocalis (Fig. 6). This displacement gap contributes essentially to the marginal displacements of the vocal fold epithelium during phonation.

Fig. 1. Frontal section through the central portion of the vocal fold. The epithelium consists of a multilayered, unkeratinized squamous cell epithelium which is underlined by loose connective tissue that is part of “Reinke’s space.” Next follows the vocal ligament, consisting of connective tissue. The vocal ligament is densely connected to the vocalis muscle. HE stain.

Fig. 2. Epithelial and subepithelial layer of the vocal fold. Frontal section through its central portion. a Multilayered, unkeratinized squamous cell epithelium (e) that is underlined by loose connective tissue (lct). b Scanning electron micrograph of the vocal fold’s loose connective tissue layer consisting of loose collagen fibrils. Resorcin-fuchsin-thiazin-red stain.

Fig. 3. Schematic drawing of a frontal section through a larynx after sagittalization (see insert to understand area).

The ventral terminus is in the anterior commissure; dorsally, the pars intercartilaginea transitions into the plica interarytenoidea. The term posterior commissure is anatomically incorrect, since there is no convergence (Lat. committere) of the structures.

The insertion of the vocal ligament in the region of the anterior commissure (ventral vocal cord insertion) involves 2 characteristic structures (Fig. 7): The noduli elastici anteriores, clearly recognizable in the microlaryngological view as yellowish bulges (maculae flavae anteriores), and the vocal cord tendon (Broyles’ tendon; anterior commissure tendon), a dense network of collagen fibrils with intermingled glycosaminoglycans [3].

Fig. 4. Layers of the vocal fold. Frontal section through its central portion. The epithelium is still visible at the upper rim of the picture. Below this, three different layers followed named layers 1–3. Layers 2 and 3 are part of the vocal ligament. At the lower rim of the picture, the muscle fibers of the vocalis muscle can be seen. Combination of Goldner stain and Orcein stain.

The noduli elastici anteriores are elliptical in shape and are anchored with robust reticular fibers in the vocal cord tendon. Connective tissue fibers radiate dorsally from the vocal ligament into the noduli elastici. The medial upper segment of the noduli lies under the free edge of the respective vocal fold; portions of the vocalis muscle are located laterally from this. Anterior sections through the noduli elastici anteriores reveal two segments. In the inferior segment of the noduli elastici, collagen fibrils form, together with elastic and reticular fibers, a scissor grid-like network around embedded cells; in the upper segment, the fibers are arranged in parallel. The vocal cord ligament is connected to the thyroid cartilage or bone by fibrous cartilage. In this region, the perichondrium or periosteum is lacking. The structures of the insertion region (noduli elastici, Broyles’ tendon) perform biomechanical functions related to the oscillation of the plicae vocales by exploiting the different elasticity modules of ligament, cartilage, and bone (so that the oscillation cannot tear the vocal cords from their anchoring structures) [3].

The insertion structures on the thyroid cartilage play an important role in the spread of vocal fold carcinomas. For the most part, glottic carcinomas grow caudally and penetrate the lig. cricothyreoideum. They may also extend along the connective tissue fibers [4] or the ventriculus larynges [5, 6], which reaches to within a few millimeters of the thyroid cartilage above the insertion structures up to the thyroid cartilage skeleton. In contrast to the presentations of Kirchner and Carter [7], the insertion structures do not present a barrier to tumors. The lack of periosteum, and connective tissue fibers radiating into the skeleton, facilitate tumor growth in the ventral direction. Additional factors relevant to tumor invasion into the thyroid cartilage skeleton include osteogenesis and the associated vascularization of these segments. Numerous investigations have shown that vessels from the plica vocalis grow into the bony cartilaginous skeleton in the region of the anterior commissure, where they become associated with extralaryngeal vessels [8–10]. Werner et al. [11] also described potential lymphogenic metastasis via lymphatic vessels that emerge from the anterior commissure region through the lig. cricothyreoideum and drain into the prelaryngeal lymph nodes. The lack of periosteum, as well as the connective tissue fibers radiating into the skeleton, facilitate the tumorous invasion.

Fig. 5. Frontal section through the vocal fold in its central portion. The histological section shows all structures from the superior arcuate line to the inferior arcuate line. Orcein-picroindigocarmine stain.

In the area of the dorsal vocal cord insertion, the lig. vocale inserts into the processus vocalis of the arytenoid cartilage with 3 structures (Fig. 8): (1) the nodulus elasticus posterior (macula flava posterior), which transitions into (2) elastic cartilage at the tip of the processus vocalis, and (3) the hyaline cartilage in the base of the arytenoid cartilage [12]. The elastic and hyaline cartilage of the arytenoid cartilage also transition continuously into one another. In the dorsal insertion region as well, the insertion structures serve to mediate the different elasticity modules in the vocal fold oscillation process. At the same time, the arrangement of the insertion structures facilitates their deflection during the movements of the arytenoid cartilage in different phonation configurations such as whispering, speaking, shouting, different pitches, etc. [12]. No perichondrium is present in the insertion region. The perichondrium (or periosteum) ends at the transition from the processus vocalis to the nodulus elasticus posterior. Following endotracheal intubation and long-term intubation, so-called intubation granulomas can form in this area. The assumed pathomechanism is a perichondritis of the processus vocalis. Intubation granulomas are, however, not limited to this nexus, but also occur in the dorsal segment of the lig. vocale. However, the absence of perichondrium along the nodulus elasticus posterior makes the development of intubation granulomas due to perichondritis unlikely [12].

Fig. 6. Frontal section through the vocal fold in its central portion. Same section as Figure 5 with marked Reinke’s space (orange).

Fig. 7. Insertion structures at the anterior commissure. a Horizontal section of the larynx (male, age 56 years) at the level of the plicae vocales. Noduli elastici anteriores (ne) and vocal ligament tendon (vlt) are visible in the anterior commissure. The vocal ligament tendon runs directly into the already ossified thyroid cartilage (bone, black arrows). Toluidine blue stain. b Sagittal section through an anterior nodulus elasticus. In the upper part, fibers have a parallel orientation (pc), whereas in the lower part fibers intermingle each other (sc). a, anterior; p, posterior. Elastica stain. c Fibers from a meshwork around embedded fibroblast-like cells. Toluidine blue stain. d Transmission electron microscopy of two fibroblast up to chondroblast-like cells (c) surrounded by elastic fibers (arrowheads) and collagen fibrils (arrows).

Fig. 8. Structures at the vocal process of the arytenoid cartilage. a Inside the insertion zone of the vocal ligament at the vocal process, three structures are distinguishable: hyaline cartilage at the base of arytenoid cartilage, elastic cartilage at its apex, and the posterior elastic nodule in front of them. b Horizontal section through the insertion zone of the vocal ligament at a right vocal process. Compare to a: hc, hyaline cartilage; ec, elastic cartilage; ne, posterior nodulus elasticus. Left rim of the picture shows the lumen of the larynx; on the right, one can see the attachment of the vocalis muscle and the thyroarytenoid muscle at the artenoid cartilage. Orcein-picroindigocarmine stain. c Elastica stain revealing all the elastic tissue (red) in the posterior elastic nodulus (ne) and the elastic cartilage (ec) at the vocal process. White area on the right indicates lumen of the larynx. d Frontal section through the posterior elastic nodule (ne). The elastic nodule looks like a triangle. The base of the triangle borders vocalis muscle (lower part of the picture). Elastica stain. e Scissor-like orientation of elastic fibers (red) inside the posterior elastic nodule. The fibers surround integrated cells. Collagen fibrils are green. f Section through the tip of the vocal process revealing elastic cartilage. Elastic fibers in red; collagen fibrils in green, pale areas indicate chondrocytes. g Section through the tip of the vocal process revealing hyaline cartilage. Elastic fibers in red; collagen fibrils in green, pale areas indicate chondrocytes. e–g Goldner-elastica stain.