History
An adult female bald eagle (Haliaeetus leucocephalus) was evaluated after being found down in a field with apparent paralysis of both hind limbs. On physical examination, the eagle was sternally recumbent, appeared unable to grasp a perch, had vertical nystagmus of both eyes, and had dull mentation; the wings appeared normal. No other abnormalities were found on physical examination. A CBC revealed marked leukocytosis (37,000 cells/μL; reference range, 8,000 to 17,600 cells/μL). Because a mercury spill had occurred in the area approximately 2 weeks prior, blood mercury concentration was measured; concentration was 0.49 μg/mL (reference range for piscivorous birds, 0 to 0.4 μg/mL). Right lateral and ventrodorsal radiographs of the celomic cavity were obtained while the bird was under general anesthesia (Figure 1).
Right lateral (A) and ventrodorsal (B) views of the celomic cavity of an adult bald eagle (Haliaeetus leucocephalus) with pelvic limb paralysis.
Citation: Journal of the American Veterinary Medical Association 246, 6; 10.2460/javma.246.6.605
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
No abnormalities of the celomic viscera were identified. On the right lateral radiograph, a focal area of mild increase in bone opacity of the midbody to caudal end plate of the last thoracic vertebra, just cranial to the synsacrum, was observed, with mild, smooth bone remodeling ventrally at the same level and without evidence of vertebral displacement or fracture fragments (Figure 2); these findings were not evident on the ventrodorsal view, likely as the result of superimposed structures. Differential diagnoses for this mild abnormality included spondylosis, trauma, or less likely (given the absence of lysis) infection or osseous neoplasia (which is rare in birds).
Because of the inability to confirm spinal cord trauma, dimercaptosuccinic acid (30 mg/kg [13.6 mg/lb], PO, q 24 h) and calcium EDTA (30 mg/kg, SC, q 24 h) were administered for 5 days to treat the acute mercury toxicosis. The eagle's mentation improved markedly, but posterior paralysis remained unchanged. Five days later, the eagle was anesthetized and CT was performed with a 40-row multidetector scanner,a including pre- and postcontrast scans (iohexol [240 mg of I/mL]; 2.2 mL/kg [1 mL/lb]). On transverse images of the celomic cavity, a comminuted fracture of the last thoracic vertebra was visible (Figure 3). This vertebra was mildly shortened, and there was minimal displacement of the comminution fragments, with none of the fragments impinging into the vertebral canal. Gas was identified in this vertebra and in the nearby subcutaneous tissues, but no skin wound was identified near the fracture site. Golden eagles (Aquila chrysaetos) and other birds have been shown to have pneumatized vertebrae,1 which likely explains the presence of gas near the fractured vertebra. Soft tissue–attenuating material was also identified within and around the vertebra; some of this material had mild contrast enhancement, likely representing a combination of hemorrhage and early callus formation. No evidence of lysis of the end plates of contiguous vertebrae was found. On the basis of CT findings, a diagnosis of comminuted compression fracture of the last (free) thoracic vertebra was made.
Same lateral radiograph as Figure 1. A focal area of increased mineral opacity is seen at the level of the last thoracic vertebra, cranial to the synsacrum (arrow).
Citation: Journal of the American Veterinary Medical Association 246, 6; 10.2460/javma.246.6.605
Transverse CT image of the eagle in Figure 1 obtained at the level of the last (free) thoracic vertebra (A) and sagittal (B) and dorsal (C) maximum intensity projection reconstructions. The CT scan was obtained with a 40-row multidetector scanner at submillimeter slice collimation and edge-enhancing algorithm; all images are displayed in a bone window. Notice the increased soft tissue–attenuating material within and around the normally air-filled vertebral body, the overall preserved alignment of the vertebral canal, and the shortened appearance of the free vertebra (asterisk). Multiple small osseous fragments arising from the vertebral body are displaced laterally and ventrally (arrows), and a large fragment is seen on the left side of the fractured vertebra (open arrow). Notice the soft tissue–attenuating material around the fractured vertebra (arrowhead). Multiple small areas of gas attenuation are visible in the vertebrae (a normal finding) and in the dorsal subcutaneous tissues, suggesting disruption of the spinous process. The diameter of the vertebral canal is not reduced.
Citation: Journal of the American Veterinary Medical Association 246, 6; 10.2460/javma.246.6.605
Treatment and Outcome
Because of the apparent preservation of vertebral alignment and lack of spinal cord compression by fracture fragments, supportive treatment was elected. This included strict cage rest for 3 months. The eagle received SC administration of fluids for 4 days and meloxicam (0.30 mg/kg [0.136 mg/lb], PO, q 24 h) for 14 days. The eagle's neurologic status progressively improved during the following months, and 3 months later, the bird was able to walk and fly. Follow-up CT was performed to evaluate healing before planned release back into the wild and showed development of smooth bone proliferation on the left and ventral aspect of the fracture with preserved diameter of the vertebral canal and no spinal cord compression.
Unfortunately, the eagle died of a seizure 2 days after the second CT scan. Necropsy revealed irregular thickening of the thoracic fifth, sixth, and seventh vertebral bodies. Histopathologic findings included osseous and cartilaginous proliferation and remodeling consistent with callus formation at the sixth and seventh thoracic vertebrae and segmental chronic active myelomalacia in the spinal cord at the level of the bony proliferation. Multiple scattered 50- to 200-μm protozoal organisms in the epaxial muscle fibers were consistent with a Sarcocystis sp. The cause of the seizure was not determined. Death in bald eagles associated with natural infection by Sarcocystis neurona with resultant neurologic signs has been documented.2 Although the eagle had no complications after the first CT scan, the possibility of a reaction to contrast medium or anesthetic complications cannot be excluded. No evidence of chronic metal toxicosis was found on necropsy.
Comments
Hind limb paralysis is a common finding in wild eagles. Trauma and acute heavy metal toxicosis are the most common causes, and an accurate diagnosis is critical for appropriate treatment.3 In the case described in the present report, the eagle had both acute mercury toxicosis and a vertebral fracture. Radiography is typically used to detect spinal cord trauma in birds, but recent evidence suggests that radiography may be unreliable for the diagnosis of spinal cord trauma in raptors.3,4 In a series of 3 bald eagles with hind limb paralysis, radiography revealed no abnormalities, whereas MRI revealed substantial vertebral fractures.3 In human patients with acute spinal cord trauma, CT or MRI is the preferred diagnostic imaging modality, because of the higher sensitivity and specificity, compared with conventional radiography.3,5
The vertebral bodies of eagles are fused in multiple locations to form sections of the vertebral column termed the notarium (thoracic vertebrae), the synsacrum (lumbosacral vertebrae), and the pygostyle (caudal vertebrae). A free thoracic vertebral body is located between the notarium and synsacrum and is a common location for fractures and luxations caused by trauma.3 In the eagle of the present report, the inability to conclusively diagnose the vertebral fracture on survey radiographs delayed the diagnosis of spinal cord trauma; CT allowed for accurate determination of the extent and severity of the fracture, thereby guiding choice of treatment. Conservative treatment of nondisplaced vertebral fracture in eagles can result in successful return to function, potentially allowing rerelease into the wild.
Philips DS Brilliance 40 mCT, Philips Healthcare, Andover, Mass.
References
1. Orosz SE, Toal RL. Tomographic anatomy of the golden eagle (Aquila chrysaetos). J Zoo Wildl Med 1992; 23: 39–46.
2. Olson EJ, Wunschmann A, Dubey JP. Sarcocystis sp.–associated meningoencephalitis in a bald eagle (Haliaeetus leucocephalus). J Vet Diagn Invest 2007; 19: 564–568.
3. Stauber E, Holmes S, DeGhetto DL, et al. Magnetic resonance imaging is superior to radiography in evaluating spinal cord trauma in 3 bald eagles (Haliaeetus leucocephalus). J Avian Med Surg 2007; 21: 196–200.
4. Grioni A. Tibiotarsal fracture and neurologic problems of a black-eared kite (Milvus migrans). Vet Clin North Am Exot Anim Pract 2006; 9: 533–538.
5. Berry GE, Adams S, Harris MB, et al. Are plain radiographs of the spine necessary during evaluation after blunt trauma? Accuracy of screening torso computed tomography in thoracic/lumbar spine fracture diagnosis. J Trauma 2005; 59: 1410–1413.
