T. S. Mair

The histological features of the immune system of the equine respiratory tract.

The distribution of mucosa-associated lymphoid tissue along the equine respiratory tract was surveyed in light microscopical sections. Intra-epithelial lymphocytes and similar cells scattered in the lamina propria were identified in all sites from the nasal vestibule to bronchioles of 2 to 4 mm diameter. Isolated lymphoid patches, occasionally with nodules, were common in bronchioles, but the density of this bronchiole-associated lymphoid tissue (BRALT) varied between individual horses. Bronchus-associated lymphoid tissue (BALT) was infrequently encountered. In the upper respiratory tract, nodules dispersed within the nasal cavity, nasopharynx and near the auditory tube merit the collective term, nasal-associated lymphoid tissue (NALT). Laryngeal- and tracheal-associated lymphoid tissue (LTALT) was also identified, but this was limited to the epiglottis, arytenoid and rostral trachea. At all sites, the discrete lymphoid masses comprise primary or secondary nodules, a parafollicular and a dome area. The airway lining above was frequently modified into a lympho-epithelium and also showed varied patterns of infolding which might enhance antigen trapping.

Leiomyosarcoma of the Duodenum in two Horses

Two horses affected by chronic, intermittent colic were found, at post-mortem examination, to have localized annular thickening of a segment of the duodenum. Histological examination of the lesion in both cases revealed a tumour composed of bundles of oval or spindle-shaped cells that stained as muscle with van Gieson stain. The histological diagnosis was leiomyosarcoma. The tumour had caused partial bowel obstruction in both horses.

The distribution of mucosal lymphoid nodules in the equine respiratory tract.

Mucosal lymphoid nodules were identified within the equine respiratory tract by an acetic acid fixation technique. Nodules were identified in foetuses from nine months gestational age, and estimates of total and regional nodule populations were made in foetal, neonatal and adult horses. Nodules occurred at specific sites within the tract, which probably relate to areas where inhaled antigens accumulate. The largest populations of nodules occurred in the nasopharynx and larynx, with smaller numbers in the nasal cavity, trachea and bronchi. There was an age-related change in the size of these nodule populations, with an increase in number from late gestation to the neonatal period to early adulthood (up to 5 years of age), followed by a decrease in older adults.

Melanotic hamartoma of the hind brain in a riding horse

A 3 1/2-year-old bay gelding of the cob type showed nervous signs and coughing associated with breaking-in and exercise. At post-mortem examination, heavy melanin pigmentation of the meninges of the hind brain and the medulla was identified and, on histological examination, melanin-containing cells were found within connective tissue extending into the medulla. The lesion was considered to be a melanotic hamartoma.