The guttural pouch is an interesting anatomic chamber that is found in only a few species, most of which are odd-toed ungulates. This group includes tapirs, rhinos, and equids. And interestingly enough, these structures are also found in animals that look nothing like the aforementioned ones. Hyraxes (thought to be the closest living relatives of elephants, although superficially resembling rodents) and certain bats also possess this structure. For the purposes of this post, I will be focusing on the guttural pouch in the context of the horse.
The pouch is a separate pouch off the auditory tube, the connection between the nasal cavity and the middle ear. It is normally air filled, but periodically not-so-nice environmental infiltrates can invade this area. For example, fungal species such as Aspergillus, can lodge themselves in the pouch, leading to guttural pouch mycosis, a very real problem. A horse may present with the inability to swallow, and after running an endoscope up its nose and into the pouch, the culprit can be identified. The presence of the mycotic infection not only leads to respiratory problems, but it puts the horse at risk of damage to cranial nerves as well as important blood vessels to the head such as the carotid arteries. During the first-year anatomy course, we learned about Viborg’s Triangle, an area that defines the borders for the surgical approach to this area. These borders are the ramus of the mandible, the tendon of insertion of the sternomandibularis muscle, and the linguofacial vein. Seeing a horse present with guttural pouch mycosis recently gave me the opportunity to revisit these anatomic boundaries and appreciate how first-year anatomy always comes back to make its importance felt.