Abstract
Purpose
The study aimed to identify age-related changes in the hyoepiglottic ligament associated with function of the epiglottis during swallowing and respiration.
Materials and Methods
Normal postmortem laryngeal tissue samples were obtained at autopsy from 20 individuals with no history of laryngeal disease. The subjects were divided into 2 groups: those aged 81–91 years (elderly group, n = 11) and those aged 31–48 years (non-elderly group, n = 9). Specimens were subjected to Elastica van Gieson and hematoxylin-eosin staining, and characteristics of the hyoepiglottic ligament were compared between groups.
Results
The hyoepiglottic ligament extended from the epiglottis to both lingual muscles and the hyoid bone ( pars lingualis and pars hyoideus ). The numbers of muscle fibers ( P < .001), collagenous fibers ( P < .01), and elastic fibers ( P < .001) were significantly decreased in the elderly group in comparison to those in the non-elderly group.
Conclusion
Age-related changes in the hyoepiglottic ligament appear to be associated with aspiration, obstructive sleep apnea syndrome, and acquired laryngomalacia in the elderly.
1
Introduction
The epiglottis plays an important role in protecting the lower airway during the pharyngeal stage of swallowing . Epiglottic dysfunction leads to aspiration and other airway troubles . The epiglottis is connected to the hyoid bone by the hyoepiglottic ligament ( ligamentum hyoepiglotticum ), which is a connective tissue structure that serves as the roof of the paraglottic space and the preepiglottic space. Anatomically, the hyoepiglottic ligament separates the supraglottic larynx from the base of the tongue . Some clinical studies have shown that this ligament inhibits the spread and invasion of carcinoma . A previous study revealed the following relation between the hyoepiglottic ligament and epiglottic fold closure during swallowing. The hyoepiglottic ligament is elongated by approximation of the thyroid to the hyoid during swallowing. Tension on the ligament results in a “snap” retroversion of the epiglottis. Thus, the folded epiglottis represents a state of higher energy than that represented by the unfolded epiglottis; relaxation of the tension on the hyoepiglottic ligament releases the cartilage to automatically return to its normal resting position .
However, relations between mobility of the epiglottis and the hyoepiglottic ligament are not fully understood . The purpose of this study was to clarify whether age-related changes in the hyoepiglottic ligament are associated with function of the epiglottis during swallowing and respiration.
2
Materials and methods
2.1
Specimens
Normal postmortem laryngeal tissue samples were obtained at autopsy from 20 individuals with no history of laryngeal disease. All procedures in this article were approved by the Saga Medical School Research Committee of Anatomy and Pathology. The subjects were divided 2 groups according to age: an elderly group and a non-elderly group. In the elderly group (n = 11), average age was 84 years (range, 80–91 years). In the non-elderly group (n = 9), average age was 39 years (range, 31–48 years).
2.2
Histologic examination
The specimens generally consisted of the base of the tongue, hyoid bone, and larynx with associated pharyngeal musculature. Hematoxylin-eosin staining and Elastica van Gieson staining were performed and fixed in 10% formalin and embedded in paraffin. The morphologic structures of the median hyoepiglottic ligament ( ligamentum hyoepiglotticum ) were compared between the elderly group and the non-elderly group. Histologic examination of the median hyoepiglottic ligament was performed in sagittal sections.
2.3
Analysis of staining patterns
The distribution of collagen, elastic, and muscle fibers in the hyoepiglottic ligament was classified as dense, moderate, or sparse according to staining intensity in a ×200 microscopic field (0.723 mm 2 per field), as reported previously . The distribution of these was compared between the elderly group and the non-elderly group.
2.4
Image analysis
As shown in Fig. 1 , a diagonal line was drawn from the bottom of the valleculae to the upper border of the body of the hyoid bone, and a square was drawn on this diagonal. The area of the square was measured. The percentage of muscle fiber (ie, the ratio between the area of muscle fibers and the area of the square) was measured with an image analysis system (Image J 1.34S). The percentage of muscle fiber in the hyoepiglottic ligament was compared between the elderly group and the non-elderly group.
2.5
Statistical analysis
Differences between groups in fiber density patterns were analyzed by Mann-Whitney U test. A P value of less than .01 was considered statistically significant.
2
Materials and methods
2.1
Specimens
Normal postmortem laryngeal tissue samples were obtained at autopsy from 20 individuals with no history of laryngeal disease. All procedures in this article were approved by the Saga Medical School Research Committee of Anatomy and Pathology. The subjects were divided 2 groups according to age: an elderly group and a non-elderly group. In the elderly group (n = 11), average age was 84 years (range, 80–91 years). In the non-elderly group (n = 9), average age was 39 years (range, 31–48 years).
2.2
Histologic examination
The specimens generally consisted of the base of the tongue, hyoid bone, and larynx with associated pharyngeal musculature. Hematoxylin-eosin staining and Elastica van Gieson staining were performed and fixed in 10% formalin and embedded in paraffin. The morphologic structures of the median hyoepiglottic ligament ( ligamentum hyoepiglotticum ) were compared between the elderly group and the non-elderly group. Histologic examination of the median hyoepiglottic ligament was performed in sagittal sections.
2.3
Analysis of staining patterns
The distribution of collagen, elastic, and muscle fibers in the hyoepiglottic ligament was classified as dense, moderate, or sparse according to staining intensity in a ×200 microscopic field (0.723 mm 2 per field), as reported previously . The distribution of these was compared between the elderly group and the non-elderly group.
2.4
Image analysis
As shown in Fig. 1 , a diagonal line was drawn from the bottom of the valleculae to the upper border of the body of the hyoid bone, and a square was drawn on this diagonal. The area of the square was measured. The percentage of muscle fiber (ie, the ratio between the area of muscle fibers and the area of the square) was measured with an image analysis system (Image J 1.34S). The percentage of muscle fiber in the hyoepiglottic ligament was compared between the elderly group and the non-elderly group.
2.5
Statistical analysis
Differences between groups in fiber density patterns were analyzed by Mann-Whitney U test. A P value of less than .01 was considered statistically significant.
3
Results
3.1
Hyoepiglottic ligament consists of 2 parts
All hyoepiglottic ligaments were composed of muscle tissue, elastic fibers, and collagenous fibers. The fibers forming the hyopiglottic ligament extended to 2 parts, from the epiglottis to both lingual muscles and to the hyoid bone, in 17 of the 20 cases ( Figs. 1 and 2 , Tables 1 and 2 ). We classified components of the hyoepiglottic ligament into 2 parts, the pars lingualis and the pars hyoideus ( Figs. 1 and 2 ). The pars lingualis extended from the anterior surface of the epiglottis to the root of the tongue (suggestive of the genioglossus muscle). The pars hyoideus extended from the anterior surface of the epiglottis to the upper border of the hyoid bone. All hyoepiglottic ligaments in the non-elderly consisted of the pars lingualis and the pars hyoideus ( Table 1 ). Only 8 of the 11 hyoepiglottic ligaments in the elderly group consisted of 2 parts (the pars lingualis and pars hyoideus , Table 2 ). There was no pars lingualis in the other 3 ligaments in this group.
