History
A 5-month-old Thoroughbred colt was referred to the equine service of the Veterinary Teaching Hospital of the University of Perugia with neck pain and abnormal head-neck posture of 2 days duration following a fall over a fence in the paddock. After the traumatic episode, unilateral epistaxis was initially observed by the breeder, but no treatment was rendered following the trauma. At the time of admission, he was bright and alert. The heart rate was 56 beats/min (reference range [RR], 60 to 80 beats/min), the respiratory rate was 36 breaths/min (RR, 20 to 40 breaths/min), the rectal temperature was 38.1 °C (RR, 37.5 to 38.5 °C), and the mucous membranes were pink. A venous blood sample was collected aseptically for a hemogram and biochemical analyses. Hematology showed a moderate erythrocytosis (16.1 X 109 RBCs/µL; RR, 6.4 X 109 to 10.4 X 109 RBCs/µL), an increased PCV (60.7%; RR, 30% to 47%), and a hemoglobin concentration of 20.6 g/dL (RR, 10.7 to 16.5 g/dL). The biochemical parameters showed slight hypoalbuminemia (2.8 g/dL; RR, 3.0 to 4.0 g/dL), hyperglobulinemia; (4.2 g/dL; RR, 1.8 to 3.6 g/dL), a moderately increased alanine aminotransferase (26 U/L; RR, 0 to 14 U/L), and an elevated serum amylase A (41 U/L; RR, 0 to 10 U/L).
The neurologic evaluation, including the gait analysis, was normal. An overextended collum (neck) posture and a slight right-sided caput (head) tilt were identified, together with a painful swelling over the left regio retromandibularis (pharyngeal region), between the mandible and the ventral margin of the atlas and axis. The colt did not show any difficulties in lowering the head or eating. Based on the findings of the clinical examination, radiographic and ultrasonographic examinations of the head and cranial cervical spine were obtained (Figure 1).
Left to right lateral (LeRtL) radiographic image of the atlanto-occipital (AO) joint and cranial cervical spine (A; cranial is toward the left) and longitudinal ultrasonographic images of the left (B) and right (C) atlanto-occipital joint of a 5-month-old Thoroughbred colt with a history of unilateral epistaxis and abnormal head-neck posture (cranial is toward the left).
Citation: Journal of the American Veterinary Medical Association 262, 3; 10.2460/javma.23.08.0490
Diagnostic Imaging Findings and Interpretation
Left to right lateral (Le–RtL), ventrodorsal (VD) and left 45° dorsal–right ventral oblique (Le45D–RtVO) and right 45° dorsal–left ventral oblique (Rt45D–LeVO) radiographic projections of the atlanto-occipital (AO) joint (articulatio atlantooccipitalis) and cranial cervical spine were obtained with the foal in standing position. The Le–RtL view revealed a small radiolucent defect of 1.4 cm of length, with proximodistal direction, at the middle caudal margin of the occipital condyle, as well as a homogeneous increased soft tissue opacity in the ventral aspect of the guttural pouches, dorsally delineated by a horizontal air/fluid interface (Figure 2). In addition, there was a moderate and homogeneous soft tissue swelling, ventral to the atlas. Ultrasonographic examination was performed to evaluate the occiput (poll) and the cranial neck region including the swelling ventral to the cranial cervical vertebrae. On ultrasonographic examination, severe, bilateral, AO joint distension was noted on longitudinal plane, with presence of anechoic fluid between the cranial rim of the atlas, the occipital condyles (condylus occipitalis) and the surrounding obliquus capitis cranialis muscles within the hyperechogenic joint capsule (Figure 2). The ultrasonographic evaluation of the left pharyngeal swelling revealed a well-defined, smooth marginated, irregular shaped area of heterogeneous echogenicity, lateral and ventral to the atlas, axis, and AO joint, and deep to the longissimus capitis muscle, consistent with acute hematoma; no striated muscle pattern was identified deep to the longissimus capitis muscle. This area was visible also from the right side in a deeper position without clearly defined margins. No other significant abnormalities were identified. The diagnostic imaging findings were consistent with acute, severe synovitis of the AO joints (likely of traumatic origin), hematoma in the left pharyngeal region, and fluid accumulation within the guttural pouches, most likely hemorrhage from acute injury of the rectus capitis ventralis and longus capitis muscles. The radiolucent defect of the caudal margin of the occipital condyle was considered as an incidental finding of developmental orthopedics disease.
Same radiographic and ultrasonographic images as in Figure 1 obtained from the colt described in Figure 1. LeRtL radiograph of the cranial cervical spine, centering at the atlantoaxial articulation (A) (cranial is toward the left). Note the small radiolucent defect in proximocaudal direction at the middle caudal margin of the occipital condyle (black arrow), and the homogeneous increased soft tissue opacity in the ventral aspect of the guttural pouches dorsally delineated by a horizontal air/fluid interface (white arrows). There is a moderate and homogeneous soft tissue swelling ventral to the atlas. Ultrasonographic images of the left (B) and right (C; cranial is toward the left) atlanto-occipital (AO) joint showing severe distension of the joints with anechoic synovial fluid (asterisk). 1 = occipital condyle; 2 = cranial rim of atlas; 3 = joint capsule; 4= obliquus capitis cranialis muscle.
Citation: Journal of the American Veterinary Medical Association 262, 3; 10.2460/javma.23.08.0490
Treatment and Outcome
A CT examination of the head and cranial cervical area was recommended, but the owner declined for financial reasons. Endoscopy of the upper respiratory tract, including the guttural pouches, was not considered safe because of the painful and abrupt reaction of the colt when manipulated around the poll, despite sedation. The foal was hospitalized for 5 days for observation. Flunixin meglumine (1.1 mg/kg intravenously one time daily for 5 days) and fluid therapy were administered. The foal was discharged from the hospital with instructions to confine him in a small paddock for 2 months. The colt was admitted again to the Veterinary Teaching Hospital after approximately 2 months following the original traumatic episode to assess possible progression/regression of the injury and prognostication of future career as racehorses. The right-side head tilt was resolved; however, a mild poll extension was still visible with mild sensitivity and reaction to deep palpation of the poll. A radiographic examination of the head and cranial cervical spine was obtained using LeRtL, VD, and Le45V-RtDO and Rt45V-LeDO projections. On the LeRtL radiographic projection, the joint space of the AO articulation was severely narrowed, and the bone margin of the occipital condyles were irregular in their outline with increased surrounding mineral opacity, consistent with sclerosis. On the Le45V-RtDO, a round, focal, well-defined radiolucent contour defect of 1.5 X 0.8 cm with irregular margins was detected on the right lateral expansion of the axis, which was not observed on initial radiographic examination (Figure 3). The repeated ultrasound examination of the right and left AO joints showed mildly increased anechoic synovial fluid within the right AO joint, and increased echogenicity of the cranial part of the joint capsule, suggesting fibrosis, which was ill-defined moving caudally over the occipital condyle; an irregular striated muscle pattern of the right obliquus capitis cranialis muscle was also identified (Figure 4). Ultrasonographic examination of the left AO joint was considered normal. These radiographic and ultrasonographic abnormalities were consistent with severe post-traumatic osteoarthritis of the right AO joint. The colt was discharged from the hospital with a poor to guarded prognosis for the athletic career as a flat racehorse.
At 60 days recheck of the Thoroughbred colt described in Figure 1. The left to right lateral (LeRtL) radiographic image (A) shows an arthritic AO joint, characterized by continuation between the atlas and the occipital condyle without visible joint space, irregular articular margins of the condyles surrounded by increased bone radiopacity of the atlas (ie, sclerosis [black arrows]). Cranial is toward the left. The left 45° ventral-right dorsal oblique (Le45V-RtDO; B) shows a small, well-defined radiolucent area (circled) and contour defect on the right lateral expansion of the axis. Left side is toward the top.
Citation: Journal of the American Veterinary Medical Association 262, 3; 10.2460/javma.23.08.0490
Longitudinal ultrasonographic images of the left (A) and right (B) AO joints of the colt described in Figure 1 after 60 days from injury. The image on the left AO joint (A) demonstrates the joint completely turned to a normal pattern after the injury; however, the ultrasonographic image on the right AO joint (B) shows moderate synovial proliferation, a small amount of anechoic synovial fluid and an ill-defined joint capsule and irregular striated muscle pattern of the obliquus capitis cranialis muscle (asterisk). The amount of visible right occipital condyle is substantially reduced (B) compared to that of the left side (A). Cranial is toward the left. 1 = occipital condyle; 2 = joint capsule; 3 = cranial rim of atlas; 4 = obliquus capitis cranialis muscle.
Citation: Journal of the American Veterinary Medical Association 262, 3; 10.2460/javma.23.08.0490
Comments
Cranial cervical trauma occurs most commonly in foals and young horses due to falling or flipping over backward.1,2 Clinical signs are dependent on the location and the degree of the injury.1 Signs of cranial cervical trauma include the sudden onset of ataxia, reluctance to move, recumbency, and in some cases, epistaxis.1,2 The area most frequently affected in immature foals is the AO region, but the foals might usually improve with time due to the relatively larger spinal canal compared to the cord.
Cervical radiography is an important diagnostic aid and is considered the first imaging technique of choice for identifying and assessing osseous injuries, including cranial cervical trauma and post-traumatic osteoarthritis of the craniovertebral joints.1 Nevertheless, not all cases of vertebral trauma result in radiographic changes, but the horse usually has an extended, stiff, painful neck. In our case, there were clear radiographic findings suggestive of trauma, such as the soft tissue opacity in the guttural pouches dorsally delineated by a horizontal air/fluid interface, consistent with fluid accumulation within the guttural pouches and the increased soft tissue opacity in the pharyngeal region. There are several reasons for fluid accumulation within the guttural pouches2,3; however, in this case, the most likely cause was considered hemorrhage secondary to tear of the rectus capitis ventralis and longus colli muscles. This is supported by the history of trauma and epistaxis, as well as by the ultrasonographic identification of the tear/hematoma, ventral to the atlas and axis. A septic process was considered unlikely based on the absence of signs of infection, such as fever, and absence of significant increase in the white blood cells count or serum amyloid A. Among the differential diagnosis for blood accumulation in the guttural pouches, fracture of the basisphenoid-basioccipital bone and mycosis should be included.2,3 The latter was considered unlike due to the history and the young age of the foal; however, the former should be considered in foals and young horses. In cases of fracture of the basisphenoid-basioccipital bone, the radiographic examination is considered useful when there is displacement of a bone fragment. In our case, no clear displaced fragment/s were detected; the suture line between basisphenoid and basioccipital bone was visible but there were no strong suspicious of fracture pathology, supported by the absence of neurological deficits related to the cranial nerves. Endoscopic examination of the upper respiratory tract including guttural pouches and evaluation of the rectus capitis ventralis and longus colli muscles may aid in the detection of the source of epistaxis to differentiate it from other conditions.3 The authors did not perform an endoscopic examination in this case to avoid damage to the structures within the guttural pouches due to poor patient cooperation and the unlikelihood that the epistaxis was related to mycosis.
Moreover, no significant abnormalities were seen radiographically at the first admission of the foal at the level of the AO joints; but radiography remained inadequate to clearly identify an injury of the AO joint because of the complexity of the area as a consequence of the superimposition of the anatomic structures. The radiographic examination performed 60 days after the first admission revealed an extensive and severe osteoarthritis of the AO joint suggesting severe trauma to the articulation. Articular fracture involving the condyle of the occiput and/or the cranial articular surface of the atlas cannot be excluded and, in this case, advanced diagnostic imaging as CT could have been performed for a complete understanding of the case; unfortunately, it was declined by the owner for financial reasons. The defect on the middle caudal margin of the occipital condyle was considered an incidental finding; this irregular shape is common in young foal under 5.1 months of age.4 Similarly, the irregular area on the right lateral expansion of the axis, which was cartilaginous at the first presentation, might be related to incomplete ossification1 or to lesion at the insertion of cervical juxtavertebral muscles sustained at the time of the trauma. Osteomyelitis was considered unlike for the reasons previously reported.
These mentioned areas cannot be visualized using the ultrasound examination5; however, in our case, ultrasonography of the poll was able to give additional and important information not seen on radiographic projections, allowing a safe approach to the AO joint, well-tolerated by the patient. It has been previously reported how ultrasonographic imaging represents an easy and non-invasive diagnostic technique that facilitates the evaluation of some articular and periarticular structures of the AO articulation in the horse.5
Diagnostic ultrasound can be used as an essential diagnostic tool in the identification of changes in the cranial vertebral joints components and the soft tissue of the cranial cervical region because radiologic diagnosis of the inflammatory process has a high false-negative result in the detection of noticeable structural (destructive) abnormality of the joints of the cervical spine involved (AO and atlantoaxial joints).1,5 In normal AO joint, no fluid distension is detected,5 and in our case there was a severe synovitis, which is an uncommon ultrasonographic finding of this articulation. At the time of second admission, synovitis of the left AO joint was no longer visible and showed the normal appearance as reference images.5 In contrast, the right AO joint showed substantial changes probably related to remodeling of the articulation following the trauma; the normal appearance of the right occipital condyle was impossible to identified during real time examination resulting in only partial visualization, likely due to collapse of the joint space. In addition, the uniform echogenic thickness of the joint capsule was not detected, and a more echogenic round area was visualized at the most cranial margin of the condyle. In the authors’ opinion, this area might represent a fibrotic capsule; however, fibrosis in the surrounded muscles cannot be excluded. Furthermore, ultrasound allowed visualization of muscle tear/hematoma formation responsible for the pharyngeal swelling suggesting trauma of the muscle located ventrally and laterally to the atlas and axis as cause of hemorrhage in the guttural pouch and epistaxis.
Finally, as previously suggested, alternative imaging modalities can be used to evaluate this highly complex anatomic region on a case-by-case basis with specific benefits.3 CT can reveal abnormalities that conventional procedures cannot; nevertheless, this comes at a high expense and frequently necessitates the use of a general anesthetic, especially in foals.
In conclusion, the authors would like to suggest that ultrasonography of the cranial cervical vertebrae is a useful additional technique, representing an easy and safe method to evaluate the articular components of the AO joints, which are difficult to image with radiography because of superimposition of the occipital condyles and the atlas. This method also has the advantage of evaluating soft tissues of the pharyngeal area.
Acknowledgments
None reported.
Disclosures
The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.
Funding
The authors have nothing to disclose.
References
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Thomas I, Dixon JJ, Fraser B. Longus capitis and rectus capitis ventralis minor rupture in a horse following general anaesthesia for a laryngeal tie-forward procedure. Vet Rec Case Rep. 2020;8(4):e000962. doi:10.1136/vetreccr-2019-000962
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Sage SE, Olive J, Lavoie J-P. Occipital condyle defects assessed by radiography or CT can be a normal finding in foals. Vet Radiol Ultrasound. 2021;62:218-224. doi:10.1111/vru.12940
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Gollob E, Edinger H, Stanek C, Wurnig C. Ultrasonographic investigation of the atlanto-occipital articulation in the horse. Equine Vet J. 2002;34(1):44-50. doi:10.2746/042516402776181196
