Anatomical Location and Histology of the Tonsilla Paraepiglottica in Sheep

Abstract

The location, size and histological structure of the ovine paraepiglottic tonsils were determined in 20 sheep. Macroscopic examination of the pharyngeal tonsils was performed in 10 sheep of 9 months of age, of which the heads were fixed in acetic acid 2% for 24 h, and in non‐fixed heads of five sheep aged between 6 and 9 months. The paraepiglottic tonsil is located lateral to the epiglottis in the ventromedial segment of the pharyngeal sidewall, i. e. at the floor of the piriform recess. The tonsil appears as a cluster of small nodular elevations, which are white after fixation in acetic acid and are called hereafter tonsillar nodules. The number of these nodules per tonsil ranged from 1 through 8. The length of the tonsil varied from 5 till 14 mm, and the width ranged from 2 till 5 mm. The tonsils of 5 sheep aged between 6 and 9 months and of five sheep aged between 9 and 12 months were excised and fixed in 3.5% formaldehyde. The blocks were processed routinely for histology and embedded in paraffin wax. Serial sections (8 μm thick) were stained with eosin and haematoxylin. Histology revealed that each tonsillar nodule consisted of several lymphoid follicles (noduli lymphatici) surrounded by parafollicular tissue. Most lymphoid follicles were secondary follicles consisting of a germinal centre, a dark zone and a mantle zone. Primary follicles devoid of germinal centres were most obvious at the periphery of the tonsillar nodules. The stratified squamous pharyngeal epithelium covering the lymphoid tissue was frequently infiltrated by numerous lymphocytes, forming a follicle‐associated epithelium. Crypts were absent, but in some cases the pharyngeal epithelium was slightly infolded into the lymphoid tissue. The tonsillar nodules were almost completely encapsulated by dense connective tissue from which septa extended into the larger nodules.Acknowledgement: This study was supported by BOF Grant of Ghent University Project #011B4101).