History
A 2-year-old 450-kg (990-lb) Saddlebred filly was evaluated for head trauma after falling over backward several hours prior to evaluation. At the time of the incident, the horse was unconscious in lateral recumbency with bilateral epistaxis. After administration of anti-inflammatory medications (flunixin meglumine and dexamethasone) and IV administration of fluids, the horse stood but appeared nonvisual and ataxic.
At the time of evaluation, the horse was ambulatory and nervous with evidence of prior epistaxis. A symmetric firm enlargement (8 × 5 cm) was present dorsally in the soft tissues caudal to the occipital protuberance. The right eye had a superficial corneal ulcer (1 × 1 cm). Ataxia was present in the pelvic limbs (grade of 2.5/5; worse on the right) and forelimbs (grade 2/5). Both pupils were mydriatic, and pupillary light reflexes, dazzle reflexes, and menace responses were absent bilaterally. No strabismus or nystagmus was observed. The right palpebral fissure was 70% open in comparison with the left eye, which was normal in appearance. The face was otherwise symmetric and without a head tilt. Tongue symmetry and strength were appropriate, and the horse was able to prehend, masticate, and swallow food. The remaining findings on physical examination were unremarkable.
On endoscopic examination of the upper airway, the following abnormalities were found: blood in the nasopharynx and bruising and hemorrhage in the dorsal and lateral aspects of the right guttural pouch and dorsally in the left guttural pouch. These findings were more severe in the right guttural pouch where air-filled expansion was also present along an intact stylohyoid bone. Radiography of the skull and cranial cervical vertebrae was performed (Figure 1).
Lateral radiographic view of the skull of a 2-year-old 450-kg (990-lb) Saddlebred filly evaluated because of neurologic signs of head trauma, which included lack of vision and ataxia, after falling over backward several hours earlier. Radiographic image is centered over the calvarium.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Lateral radiographic view of the skull of a 2-year-old 450-kg (990-lb) Saddlebred filly evaluated because of neurologic signs of head trauma, which included lack of vision and ataxia, after falling over backward several hours earlier. Radiographic image is centered over the calvarium.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Lateral radiographic view of the skull of a 2-year-old 450-kg (990-lb) Saddlebred filly evaluated because of neurologic signs of head trauma, which included lack of vision and ataxia, after falling over backward several hours earlier. Radiographic image is centered over the calvarium.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
The presphenoid bone is fractured and contains a radiolucent fissure. There is deviation of the ventral cortex of the presphenoid and basisphenoid bones rostral to the rami of the mandibles (Figure 2). The fracture line can be differentiated from the sphenooccipital fissure, as the fissure is visible caudal to the condyloid process. A region of increased radiolucency within the caudodorsal aspect of the calvarium suggests the presence of air within the cranium (ie, pneumocephalus).
Same radiographic image as Figure 1, with an additional high-contrast cropped region of interest as an insert. A faint radiolucent fissure (between arrowheads) and irregular ventral surface to the skull base are identified at the body of the basisphenoid bone. There is a resulting ventral rotation to the rostral aspect of the skull base (rostral to the solid arrow). Radiolucency, as a sign of pneumocephalus, is present in the caudodorsal aspect of the calvarium (dashed arrow).
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Same radiographic image as Figure 1, with an additional high-contrast cropped region of interest as an insert. A faint radiolucent fissure (between arrowheads) and irregular ventral surface to the skull base are identified at the body of the basisphenoid bone. There is a resulting ventral rotation to the rostral aspect of the skull base (rostral to the solid arrow). Radiolucency, as a sign of pneumocephalus, is present in the caudodorsal aspect of the calvarium (dashed arrow).
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Same radiographic image as Figure 1, with an additional high-contrast cropped region of interest as an insert. A faint radiolucent fissure (between arrowheads) and irregular ventral surface to the skull base are identified at the body of the basisphenoid bone. There is a resulting ventral rotation to the rostral aspect of the skull base (rostral to the solid arrow). Radiolucency, as a sign of pneumocephalus, is present in the caudodorsal aspect of the calvarium (dashed arrow).
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
The radiographic findings supported the history of known trauma, with the changes seen within the base of the skull in close proximity to the optic nerve or optic chiasm. However, assessment of the optic nerves was not possible without further advanced imaging (CT or MRI). Advanced imaging was recommended but declined by the owners.
Treatment and Outcome
The horse was hospitalized for stabilization of clinical signs and monitoring. The horse received fluid therapy (IV), an antimicrobial (ie, ceftiofur), and NSAIDs during the first 24 hours of hospitalization. Ophthalmic triple antimicrobial ointment was administered to treat the corneal ulcer. After 24 hours, antimicrobial treatment was changed to trimethoprim-sulfamethoxazole and continued for 5 days. The ataxia and corneal ulcer resolved by day 3 of hospitalization, and the palpebral fissures of the eyes appeared equal.
Ophthalmologic consultation on the first day after hospital admission confirmed the corneal ulcer in the right eye and bilateral blindness but did not reveal any pathological changes on fundic evaluation. Repeated consultation 2 weeks later did not reveal any return of vision or changes to the fundus, and a poor prognosis for return to vision was given. Because of the horse's poor behavioral adjustment to complete blindness, euthanasia was performed at 2 weeks after hospitalization.
Computed tomography and MRI of the skull were performed immediately after euthanasia and following decapitation. On CT, a severe comminuted fracture of the presphenoid bone is evident (Figure 3) with a small bony fragment within the optic chiasm (Figure 4). Complete obliteration of the right rostral alar foramen, orbital fissure, and optic foramen was present. The comminuted fractures extended caudally from the level of the pterygoid bone to the presphenoid bone (Figure 5). On MRI, the optic nerves appeared intact rostral to the optic chiasm, which was not supportive of optic nerve shearing as the cause of blindness. Disruption of the skull margin supported the radiographic findings of a fracture. These imaging findings accounted for the cause of the horse's blindness. However, with the damage present at the foramina and the severe comminution of the fracture, it was surprising there were no other cranial nerve deficits observed.
Same radiographic image as Figure 1 with an overlay of a median sagittal slice CT image (obtained immediately after euthanasia of the horse), which further highlights the fracture to the skull base (arrow). Notice the rotation of the rostral aspect of the skull base.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Same radiographic image as Figure 1 with an overlay of a median sagittal slice CT image (obtained immediately after euthanasia of the horse), which further highlights the fracture to the skull base (arrow). Notice the rotation of the rostral aspect of the skull base.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Same radiographic image as Figure 1 with an overlay of a median sagittal slice CT image (obtained immediately after euthanasia of the horse), which further highlights the fracture to the skull base (arrow). Notice the rotation of the rostral aspect of the skull base.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Transverse CT image at the level of the optic chiasm, displayed in a bone window (slice thickness, 0.625 mm; window width, 2,000 Hounsfield units; window level, 800 Hounsfield units), of the horse in Figure 1 after euthanasia. Notice the comminuted fracture of the entire basisphenoid bone, and large penetrating fracture fragment (arrow) within the sulcus chiasmatis, which encases the optic chiasm. The gas pockets seen throughout the calvarium and soft tissues are postmortem artifacts.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Transverse CT image at the level of the optic chiasm, displayed in a bone window (slice thickness, 0.625 mm; window width, 2,000 Hounsfield units; window level, 800 Hounsfield units), of the horse in Figure 1 after euthanasia. Notice the comminuted fracture of the entire basisphenoid bone, and large penetrating fracture fragment (arrow) within the sulcus chiasmatis, which encases the optic chiasm. The gas pockets seen throughout the calvarium and soft tissues are postmortem artifacts.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Transverse CT image at the level of the optic chiasm, displayed in a bone window (slice thickness, 0.625 mm; window width, 2,000 Hounsfield units; window level, 800 Hounsfield units), of the horse in Figure 1 after euthanasia. Notice the comminuted fracture of the entire basisphenoid bone, and large penetrating fracture fragment (arrow) within the sulcus chiasmatis, which encases the optic chiasm. The gas pockets seen throughout the calvarium and soft tissues are postmortem artifacts.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Three-dimensional volume rendered image of the ventral surface of the skull base (with parts of the mandible and hyoid apparatus digitally removed) of the horse in Figure 1 after euthanasia. The image highlights a transverse fracture at the level of the optic chiasm (solid black arrows); a sagittal fracture of the palatine bone (dotted black arrows); and bilateral comminuted fractures of the pterygoid processes (white arrows). The ventral angulation of the rostral aspect of the skull base seen in Figures 2 and 3 is explained by this combined comminuted fracture plane across the region of the pterygoid processes and rostral aspect of the skull base. In this image, rostral is toward the top and the right side is toward the left.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Three-dimensional volume rendered image of the ventral surface of the skull base (with parts of the mandible and hyoid apparatus digitally removed) of the horse in Figure 1 after euthanasia. The image highlights a transverse fracture at the level of the optic chiasm (solid black arrows); a sagittal fracture of the palatine bone (dotted black arrows); and bilateral comminuted fractures of the pterygoid processes (white arrows). The ventral angulation of the rostral aspect of the skull base seen in Figures 2 and 3 is explained by this combined comminuted fracture plane across the region of the pterygoid processes and rostral aspect of the skull base. In this image, rostral is toward the top and the right side is toward the left.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Three-dimensional volume rendered image of the ventral surface of the skull base (with parts of the mandible and hyoid apparatus digitally removed) of the horse in Figure 1 after euthanasia. The image highlights a transverse fracture at the level of the optic chiasm (solid black arrows); a sagittal fracture of the palatine bone (dotted black arrows); and bilateral comminuted fractures of the pterygoid processes (white arrows). The ventral angulation of the rostral aspect of the skull base seen in Figures 2 and 3 is explained by this combined comminuted fracture plane across the region of the pterygoid processes and rostral aspect of the skull base. In this image, rostral is toward the top and the right side is toward the left.
Citation: Journal of the American Veterinary Medical Association 250, 2; 10.2460/javma.250.2.161
Comments
Equine skull fractures are common sequelae of traumatic incidents in young horses, typically secondary to rearing and falling over backward, as in the horse of the present report. Because of the complex anatomy and vulnerability of the involved structures, clinical signs can be highly variable and the extent of structural damage can be difficult to determine. The base of the skull is frequently damaged as a result of the sudden extreme forces placed on the rectus capitis ventralis muscles as the horse's head is forcibly extended by contact between the occipital protuberance and the ground.1 The stretching of these muscles can result in muscle rupture, tearing of vasculature, avulsion of attachments, and displacement or fracture of basilar bones (basioccipital or basisphenoid bones). This can result in epistaxis and variable neurologic signs, depending on the site of damage. Optic nerve stretching has been implicated as a cause of acute blindness after head trauma, as has damage to the nerve itself.2 Bilateral mydriasis has also been reported as a sign of severe midbrain injury; therefore, it is an indicator of a poor prognosis.3
Radiography can provide prompt imaging of the equine skull after head trauma, but the superimposition of structures and the complex anatomy can obscure lesions, such as in the horse of the present report.4 The lateral view is considered most useful for evaluation of the base of the skull in standing horses.4 In the horse of the present report, pneumocephalus was appreciated on the lateral radiograph; this finding should raise suspicion of a communicating wound with a sinus or penetrating wound, allowing air within the calvarium.1,5 Dorsoventral or oblique views of the equine skull may offer little additional information and may require general anesthesia in patients with neurologic disorders.4 Evaluation with CT or MRI can provide substantial benefits over radiography for the examination of minimally displaced or superimposed skull fractures and associated lesions in the brain.1,4,5 Computed tomography is considered more sensitive, compared with MRI, for detection of bony abnormalities and gas and allows for 3-D reconstruction, which can assist in viewing bone fragments and fractures. Magnetic resonance imaging provides superior neural tissue contrast and the ability to image in any plane; it may be advantageous in instances where brain edema or infarcts are suspected.1 The risks of general anesthesia should be considered prior to pursuing CT or MRI, particularly in patients with neurologic signs.5
In the horse of the present report, the damage to the optic chiasm was not detected by use of radiography but was readily appreciated with CT imaging. Although MRI provided additional neuroanatomic detail regarding optic nerve integrity rostral to the optic chiasm, its usefulness was primarily in the support of findings on CT. Disruption of the nerve fibers by the fragment was the likely reason for the acute and persistent bilateral mydriasis and loss of vision. The findings of epistaxis, guttural pouch hemorrhage and air-filled expansion along the stylohyoid bone, and sphenopalatine sinus hemorrhage are all consistent with acute trauma to the rectus capitis muscles and the base of the skull.1 The initial ataxia may have been the result of concurrent brainstem inflammation or trauma, compounded by the sudden loss of vision.
Treatment of acute head trauma in patients with neurologic signs includes supportive care and administration of anti-inflammatory drugs and antimicrobials (as prevention for meningitis).1 Prognosis is dependent on clinical signs and progression, but is worse for horses with basilar skull fractures.3 Therefore, accurate imaging and diagnosis are helpful in providing recommendations to owners of affected horses. Advanced imaging, such as CT or MRI, should be helpful in instances where radiographic findings are inconclusive or do not match the severity of clinical signs.
Acknowledgments
The authors thank Sue Hartman for technical assistance with the CT and MRI.
References
1. MacKay RJ. Brain injury after head trauma: pathophysiology, diagnosis, and treatment. Vet Clin North Am Equine Pract 2004; 20: 199–216.
2. Martin L, Kaswan R, Chapman W. Four cases of traumatic optic nerve blindness in the horse. Equine Vet J 1986; 18: 133–137.
3. Feary DJ, Magdesian KG, Aleman MA, et al. Traumatic brain injury in horses: 34 cases (1994–2004). J Am Vet Med Assoc 2007; 231: 259–266.
4. Ramirez O III, Jorgensen JS, Thrall DE. Imaging basilar skull fractures in the horse: a review. Vet Radiol Ultrasound 1998; 39: 391–395.
5. Beccati F, Angeli G, Secco I, et al. Comminuted basilar skull fracture in a colt: use of computed tomography to aid the diagnosis. Equine Vet Educ 2011; 23: 327–332.
