Histomorphometric Analysis of Collagen and Elastic Fibres in the Cranial and Caudal Fold of the Porcine Glottis

Abstract

The porcine glottis differs from the human glottis in its cranial and caudal vocal folds (CraF, CauF). The fibre apparatus of these folds was studied histomorphometrically in adult minipigs. For object definition and quantification, the colour-selection tools of the Adobe-Photoshop program were used. Another key feature was the subdivision of the cross-sections of the folds into proportional subunits. This allowed a statistical analysis irrespective of differences in thickness of the folds. Both folds had a distinct, dense subepithelial layer equivalent to the basement membrane zone in humans. The subsequent, loose layer was interpreted - in principle - as being equivalent to Reinke's space of the human vocal fold. The next two layers were not clearly separated. Due to this, the concept of a true vocal ligament did not appear applicable to neither CauF nor CraF. Instead, the body-cover model was emphasized by our findings. The missing vocalis muscle in the CraF is substituted by large collagen fibre bundles in a proportional depth corresponding to the position of the muscle of the CauF. The distribution of elastic fibres made the CraF rather than the CauF more similar to the human vocal fold. We suggest that these data are useful for those wishing to use the porcine glottis as a model for studying oscillatory properties during phonation.

The stratigraphical organisation of the microvascular systems of the porcine vocal folds

“…The measured distances between the epithelium and the vascular profiles were correlated with the topographical subunits of the lamina propria which have been reported by Lang et al [17], because these proportional subunits comprised 'Regions of Interest (ROI)' of known widths/diameters [17]. Respecting these numerical (metrical) pre-requisites from the literature, each of the characteristic Zones and Rows, as well as the Avascular Band, and the Avascular Area of the microvascular system of the CraF and the CauF in our study could be allocated to one of these specific layers of the lamina propria: subepithelial, superficial, intermediate, deep layer (SEL, SL, IL, DL; described in the study of Lang et al [17]): In both vocal folds, the Avascular Band was almost congruent with the SEL, which Lang et al [17] had characterised by high amounts of fibres per area.…”

“…Respecting these numerical (metrical) pre-requisites from the literature, each of the characteristic Zones and Rows, as well as the Avascular Band, and the Avascular Area of the microvascular system of the CraF and the CauF in our study could be allocated to one of these specific layers of the lamina propria: subepithelial, superficial, intermediate, deep layer (SEL, SL, IL, DL; described in the study of Lang et al [17]): In both vocal folds, the Avascular Band was almost congruent with the SEL, which Lang et al [17] had characterised by high amounts of fibres per area. Within the underlying SL (a loose region of only few collagen fibres and elastic fibres), the Avascular Area, and Row 1, and Row 2 were located together with the initial lymphatics (all of them components of Zone A).…”

“…blood capillaries and lymphatic capillaries/lymphatic precollectors. The description of their local distribution shall complement the detailed stratigraphical examinations of the minipig's vocal folds [17], whose lamina propria is subdivided into 4 layers: subepithelial, superficial, intermediate, and deep layer. These layers are characterised by different widths, fibre qualities, and fibre densities.…”

“…In particular, band-like or focal regions, which were conspicuous because of their sparse number of fibres [17] and blood vessels, attracted special attention, as they may be related to Reinke's space in the human glottis. In humans, Reinke's space may become frequently affected by pathological conditions, especially by Reinke's oedema [15,32,33,35], which influences the voice [8].…”

“…This is even more relevant because of the species-specific anatomical characteristic of the pig's glottis. A distinction between its phoniatrically relevant cranial and caudal fold (for details see [17]) is mandatory, especially if the minipig is intended to be used as a model for humans.…”