Anatomical definition of the subglottic region.
Due to laryngeal neoplasia, as well as infectious and autoimmune diseases, the subglottic region is of great clinical relevance. However, descriptions of the subglottic structures are inconsistent. The aim of our study was to present a precise analysis of the subglottic region and derive functional and clinical conclusions. Histological, histochemical and immunohistochemical investigations as well as scanning electron microscopy were performed and combined with injection techniques applied to the subglottic region of the larynges of 33 body donors. The three-dimensional extensions of the subglottic region were newly defined: the inferior arcuate line of the vocal cord was defined as the cranial border. The lower margin of the cricoid is the caudal border. Craniolaterally, the elastic cone and, further caudally, the cricoid form the border. Therefore, the definition presented comprises heretofore unnamed ventral and dorsal parts of the lower larynx. The subglottic region can be described as cylindrical, becoming smaller in the cranial direction, following the elastic cone. The ventral boundary is formed by the median part of the cricothyroid ligament (ligamentum conicum), the dorsal part by the cricoid cartilage. The walls of the subglottis are divided into three or four layers composed of collagenous and elastic fibres in which seromucous glands are embedded. Subglottic blood vessels including a tight subepithelial capillary plexus were delineated. The new definition of the subglottic extensions presented is helpful and essential for precise laryngeal tumour classification. The results indicate that the boundaries are unlikely to counteract tumour progression in the subglottis. Furthermore, the findings suggest that these structures contribute to temperature regulation of breath, protection against inflammation as well as breath frequency and depth-dependent mucus secretion.