Page 786 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Gastrointestinal system: 4.1 The upper gastrointestinal tr act 761

VetBooks.ir these bones are often open and communicate with Differential diagnosis
The condition must be differentiated from other
the oral cavity. These are covered in Chapter 1.6
causes of dysphagia including botulism, tetanus,
(The head).
equine grass sickness, dental lesions, guttural pouch
DISEASES OF THE HYOID APPARATUS mycosis, jaw fractures and temporomandibular
luxations.
Definition
The hyoid apparatus is the trapeze-like arrange- Diagnosis
ment of bones that suspend the larynx and tongue Endoscopic examination may reveal gross deformity
from the base of the skull. The bones comprise of the stylohyoid bones, particularly at the articu-
paired ketarohyoid, epihyoid, stylohyoid and thy- lation with the petrous temporal bone. In some
rohyoid bones joined by a single basihyoid and the cases changes are not endoscopically visible. Lateral
linguohyoid, into which the base of the tongue radiographs, obliqued in a rostrocaudal direction
inserts. Injuries affecting the hyoid apparatus to separate the radiographic superimposition of the
include fracture of the hyoid apparatus and tem- stylohyoid bones, may reveal lysis or proliferative
porohyoid osteopathy, in which periosteal reaction changes to the margins of the stylohyoid bones.
around the temporohyoid articulation can result in Since the advent of CT three-dimensional recon-
enlargement of the hyoid bones and ankylosis of struction is possible, which gives a much more
this articulation. detailed appraisal of this area and is the technique
of choice (Fig. 4.82).
Aetiology/pathogenesis
Primary fractures of the hyoid apparatus are
extremely rare. They are reported to arise occa- 4.82
sionally following severe trauma from the ventral
aspect of the head, although the physical protec-
tion accorded by the skull and mandibles renders
such precise trauma extremely unusual. Basihyoid
bone fracture has been reported after laryngeal tie-
forward surgery. Pathological fracture of the stylo-
hyoid bones is suspected in cases with temporohyoid
osteopathy in which ankylosis of the articulation has
occurred. This obscure disease has been described
as a chronic sequela to eustachian tube and guttural
pouch inflammation associated with guttural pouch
mycosis or empyaema. The strain put on the stylo-
hyoid during swallowing is suspected to be sufficient
to cause fracture of the weakened bone where the
articulation is fused.

Clinical presentation
Signs may include nasal discharge and neurological
disease if secondary to guttural pouch empyaema or
mycosis. Swelling in the parotid region may be pal-
pated. Slow eating or difficulty with swallowing may Fig. 4.82 CT image of a case of temporohyoid
be detectable on the affected side. Palpation of the osteopathy with an enlarged and very abnormal joint
larynx and manipulation of the larynx or tongue is and surrounding periarticular periosteal reaction
resented when the condition is painful. (arrow).