Abstract:
Llamas (Lama glama) appear to have predisposing anatomical features for developing
otitis media such as a long and narrow external acoustic meatus and a trabecular
tympanic bulla. However, there is limited information available about the morphology of
the ear in this species. The aim of this study was to evaluate the osseous structures of
external acoustic meatus, tympanic cavity and tympanic bulla using CT, and the soft
tissue surrounding the ear using dissections. Ten heads were collected from healthy
llamas slaughtered for meat production. Using a CT scanner with slices acquired at 1
mm, measurements of the bony structures of the external and middle ear of each head
were obtained. The surrounding soft tissue was examined using dissection, a 6-inch
protractor and a digital caliper. The osseous external acoustic meatus was ventrally
curved with an obtuse angle facing ventrally. Its narrowest portion was located medially
at the level of the tympanic annulus. The conformation of the tympanic bulla was the
most different in appearance compared to other domestic animals. It was divided into
caudo-lateral and caudo-medial processes, body, apex, and stylohyoid fossa to study its
morphometry. The interior of the tympanic bulla had a honeycombed structure with
pneumatized cells similar to the human's mastoid process. The nerves, vessels, muscles
and tendons had the general distribution of those structures in herbivorous domestic
animals. The present study supplied new information about the shape and measurements
of the osseous external and middle ear and surrounding soft tissue in adult llamas. This
study also supplied specific landmarks of the location of these structures in relationship
with each other. Based on our observations and measurements, a new surgical approach
to perform a tympanic bulla osteotomy was suggested to treat otitis media in llamas.
