Histological changes in the external ear canal of dogs with otitis externa

Abstract

This study aimed to better characterise the gross anatomy of the normal ear canal, and to compare histological features of the normal ear canal to those affected by chronic otitis externa. In 40 normal ears from 20 dogs, the length of the annular and auricular cartilage was 1.2 +/- 0.2 and 4.1 +/- 0.9 cm, respectively; overall length of the external ear canal was 5.3 +/- 1.0 cm. The maximal internal diameter at the distal end of the external ear canal, the proximal opening of the auricular cartilage and the proximal end of the annular cartilage was 5.8 +/- 1.5, 0.7 +/- 0.2 and 0.5 +/- 0.1 cm, respectively. Body weight correlated positively with the overall length and diameter of the distal end of the ear canal (r = 0.78, P < 0.001; r = 0.42, P < 0.05). Morphometric evaluation was carried in 28 clinically healthy ears of 14 dogs, and 15 otitic ears of 13 dogs. Histological features of this integument revealed that the density and distribution of sebaceous and ceruminous gland tissue exhibits marked variation between individuals. Nevertheless, general patterns were observed; sebaceous tissue increases gradually from the proximal to the distal parts of the ear canal, whilst ceruminous gland tissue by contrast decreases. In otitic canine ears, the distribution of sebaceous and ceruminous glandular tissue was similar to normal ears but the glands became larger and hyperplastic (P < 0.05). Density of hair follicles was not different between healthy and otitic ears (P = 0.16), but the hair follicles became hyperplastic in otitic ears.

Pathogens in otitis externa: diagnostic techniques to identify secondary causes of ear disease

“…Such hyperplasia is particularly seen in cocker spaniels (Angus and others 2002). Stenosis, accompanied by fibrosis and papular to nodular hyperplasia of the walls of the canal, allows further microbial growth that perpetuates disease (Huang and others 2009). …”

Otitis externa und media bei Hund und Katze

“…Auch die Anzahl der Talg-und Schweißdrüsen variiert beim Hund stark. Die meisten Talgdrüsen finden sich am Eingang und im vertikalen Teil des Gehörkanals, während die Schweißdrüsen (Zeruminaldrüsen genannt) am zahlreichsten nahe am Trommelfell vorkommen (47). Vorstellbar ist, dass das feuchtere Sekret tief im Ohr leichter nach außen transportiert wird, während der höhere Fettanteil im Ohreingang einen Schutz vor Wasser und Infektionen darstellt.…”

Comparison of two ear cytological collection techniques in dogs with otitis externa

“…Higher counts of PMNs, but not of other cell types, were detected with the rubber tube compared to the cotton swab technique. The average length of the canine external ear canal is reportedly 5.3 cm . In purulent otitis, exudate may collect deeper in the horizontal canal which could explain the higher counts of PMNs with the rubber tube technique.…”