An approximately 11 year old miniature horse mare presented with acute neurologic signs that developed immediately following a dental procedure, during which the mare reared and flipped over backwards. After the incident, the mare was unable to rise and had several seizure-like episodes.
Within a 24-hour period following the traumatic incident, the mare regained the ability to stand and walk but continued to demonstrate severe neurologic deficits and was referred for further care and workup.
On referral examination, the mare was quiet, alert, and responsive, but moderately tachycardic (60 bpm). The mare was severely hypermetric in all four limbs, demonstrated a base-wide stance, and listed to the left when walked in a straight line. Menace response was absent bilaterally. Mild rightward muzzle deviation and slight left head tilt with left ear droop were present. Nasal sensation was absent and ear sensation was present but asymmetric, with reduced sensation on the left. The mare also demonstrated difficulty opening her mouth and had reduced cutaneous sensation along the left side of the neck. Collectively, these resulted in a multifocal neurolocalization including cerebrum, cerebellum, and brainstem abnormalities.
Due to the history of trauma, radiographs of the skull and cervical spine were made with the patient in a standing position.
Moderately to severely increased soft tissue opacity is within the guttural pouch, resulting in ventral displacement of the dorsal margin of the nasopharynx (white arrowheads).
A mildly comminuted, sharply margined fracture is within the basioccipital bone, with mild rightward displacement of the rostral segment that is best seen on the dorsoventral projection (white arrows).
A single small, rectangular fracture fragment with sharp margins is mildly ventrally displaced from the basioccipital bone.
Only seen on the lateral projection of the skull, an additional minimally caudoventrally displaced, small triangular osseous fragment is in the region of the right retroarticular process (black arrow).
Also only seen on the lateral projection, the left temporomandibular joint is widened.
There is superimposition of a jugular venous catheter and neck bandage with the cervical spine. An incidental small spinous process is on the dorsal aspect of the C7 vertebra. The cervical spine is otherwise unremarkable.
Acute traumatic basioccipital bone fracture with avulsion fragment and probable secondary guttural pouch hemorrhage.
Acute traumatic fracture of the right retroarticular process of the temporomandibular joint.
Left temporomandibular joint subluxation, likely traumatic.
Unremarkable cervical spine.
Labelled Images - see imaging reports for detail description
A feeding tube was placed because the patient’s ability to chew was limited, likely secondary to the temporomandibular joint pathologies identified. Anti-inflammatories and neuroprotectants were also included in the treatment plan for pain management and in an attempt to reduce further progression of neurologic signs. Broad-spectrum antibiotics were administered to prevent the development of bacterial meningitis or guttural pouch infection, in light of the concern for intra-cranial involvement and presumed guttural pouch hemorrhage, respectively. The mare improved clinically after several days of hospitalization, including partial resolution of ataxia and return of menace response, and was able to be discharged successfully from the hospital.
Trauma to the skull occurred when the horse reared and flipped backward, resulting in a rare type of fracture that can occur if the horse hits the poll while the ventral neck muscles are in tension. The poll acts as a lever arm, resulting in increased tension on the paired rectus capitis ventralis muscles, which insert on tubercles at the junction between basisphenoid and basioccipital bones. This may result in both local hemorrhage and well as hemorrhage into the guttural pouch, as seen in this patient. Since this area of the skull is also aligned closely with multiple neural structures (cerebrum, cerebellum, brainstem), the cranial nerve deficits and changes in gait in this case can also be explained.
It is presumed that the fracture contributed to multifocal brain trauma, although a concurrent coup contrecoup or other contusive brain injury cannot be excluded. Due to its ability to eliminate superimposition, computed tomography (CT) would allow for better evaluation and characterization of both the skull fractures and temporomandibular joint abnormalities. An additional benefit of CT compared to radiography would be its improved ability to assess the intracranial soft tissue structures and evaluate for the presence or absence of intracranial communication and/or small volume pneumocephalus.
Additionally, MRI could be considered in similar cases to better evaluate the brain and cranial nerves, especially when significant neurologic deficits are present, such as seen in this patient.
At our institution, however, general anesthesia would have been required for both CT and MRI, thereby presenting an increased risk for recovery in an already severely neurologic patient and was not pursued in this case.
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