Laminectomy for relief of atlantoaxial subluxation in four horses

Malalignment of the atlas and axis was seen in 4 horses with an idiopathic form of atlantoaxial subluxation characterized by spinal cord compression on extension. The bone structure and density of the atlas and axis were radiographically normal in 3 of the 4 horses. Clinical signs appeared when the horses were 6 to 30 months old, and 3 of the 4 horses had a history of trauma. Although a congenital anomaly could not be ruled out, the cause was thought to be trauma. The horses were moderately to severely ataxic at the time of examination. Myelography revealed compression of the spinal cord at the atlantoaxial junction on extension. Flexion completely relieved the compression. In each horse, subtotal laminectomy of the caudal two thirds of the dorsal arch of the atlas was used to relieve the spinal cord compression. Two horses recovered fully, one had residual grade-1 neurologic deficits, and a fourth was euthanatized after it fractured a limb 6 weeks after surgery.     

Vertebral malformation, syringomyelia, and ventricular septal defect in a dromedary camel (Camelius dromedarius).

An occipitoatlantoaxial malformation and ventricular septal defect (VSD) were diagnosed in a 36-hour-old female camel. Physical examination revealed a firm protrusion of the dorsal aspect of the atlas and axis, tilting of the head to the left, and a grade V/VI systolic murmur. Neurological examination revealed proprioceptive deficits and ataxia of all 4 limbs. Radiographic examination and necropsy demonstrated malformation, fusion of the atlas to the occiput and hypoplasia of the dens of the axis, and subluxation of the atlantoaxial joint. Dorsoventral laxity of the atlantoaxial joint was also present, with compression of the cervical spinal cord. A 1.5-cm-diameter VSD was observed also. Histopathologic examination of the cervical spinal cord revealed a cavity extending from the level of the first to fourth cervical segment, dorsal to the central canal, 5 cm long and 1-2 mm in diameter. The cells around the cavity were positive for glial fibrillary acidic protein and sporadically positive for vimentin. This cavitary structure was consistent with syringomyelia, which was lined by glial cells, surrounded by edematous white matter with Wallerian-like degeneration and with neuronal necrosis in the adjacent dorsal horns.     

Laminotomy of the Axis for Surgical Access to the Cervical Spinal Cord A Case Report

A cranially hinged laminotomy of vertebra C2 was used to expose the cervical spinal cord of a dog with a meningioma in the region of the atlantoaxial articulation. By preserving the dorsal atlantoaxial ligament, the technique seemed to result in greater and more physiologic stability between the atlas and axis than dorsal laminectomy and prosthetic replacement of the dorsal atlantoaxial ligament. The procedure allowed a dorsal approach, avoiding injury to the vertebral arteries and limited exposure, which are potential problems with hemilaminectomy of C1-C2. Further investigation is needed to evaluate long-term consequences of this procedure.     

COMPUTED TOMOGRAPHY VARIATIONS IN MORPHOLOGY OF THE CANINE ATLAS IN DOGS WITH AND WITHOUT ATLANTOAXIAL SUBLUXATION

Computed tomography images of 120 dogs were reviewed to characterize variations in atlas morphology, and to identify breed‐specific morphologic features. The neural arch of the atlas was thicker in large dogs and male dogs than in small dogs, having a layer of trabecular bone between the inner and outer layers of compact bone. The transverse processes of the atlas were relatively longer in large dogs than in small dogs. Twelve (10%) dogs had incomplete ossification of the atlas. Incomplete ossification of the atlas was associated with gun dogs. Eight dogs had atlantoaxial subluxation. All eight dogs with atlantoaxial subluxation had cervical signs, whereas none of the seven dogs with incomplete ossification of the atlas unaccompanied by atlantoaxial subluxation had clinical signs referable to that area. Of five dogs with both atlantoaxial subluxation and incomplete ossification of the atlas, four had osseous defects affecting both the intercentrum and neural arch, and one had only an osseous defect affecting the neural arch. There was a strong association between incomplete ossification of the atlas and atlantoaxial subluxation (odds ratio 35.0, 95% CI 7.0–175, P=0.00002), which supports the hypothesis that incomplete ossification of the atlas predisposes dogs to atlantoaxial subluxation.     

Stabilization of atlantoaxial subluxation secondary to atlantooccipital malformation in a Devon calf

Atlantoaxial subluxation secondary to atlantooccipital malformation in a 14-day-old female Devon calf was corrected by alignment and stabilization of the atlantoaxial joint. Stabilization was achieved by the ventral placement of pins and screws, and the dorsal placement of a figure 8 tension band wire. At 2 and 14 days post operatively, adequate alignment of the atlantoaxial joint was confirmed radiographically. Following surgery the calf improved clinically, but was terminated 14 days following the surgery due to a pneumonia. At necropsy the fixation was stable and spinal cord decompression had been achieved. It was concluded that this technique could be utilized to allow decompression, anatomical alignment, and stabilization of an atlantoaxial subluxation secondary to atlantooccipital malformation in a calf. At necropsy, there was gross and histologic evidence of congenital fusion of the basioccipital bone to the malformed atlas.     

Congenital occipitoatlantoaxial malformations in the horse

From a clinical, radiological and morphological study of 9 horses with congenital malformations of the occiput, atlas and axis, and from a study of 2 reported cases, 3 diseases were defined: A. Familial occipitalisation of the atlas with atlantalisation of the axis in Arabian horses (7 cases in this report and the case reported by Leipold, et al., 1974). These horses had congenital atlantooccipital fusion, hypoplasia of the atlas and dens, malformation of the axis and modification of the atlantoaxial joint. B. Congenital asymmetrical occipitoatlantoaxial malformation (2 cases in this report). A Standardbred and a Morgan horse had atlantooccipital fusion, a wedge shaped vertebral piece attached to the caudal end of the axis and sigmoid scoliosis of the cervical vertebrae. C. Asymmetrical atlantooccipital fusion (the case reported by Schmaltz, 1915). This horse of an unknown breed had asymmetrical fusion between the atlas and occiput and cervical scoliosis. The clinical syndromes shown by horses with these malformations were variable but were broadly classified as: 1. Foal dead at birth, seen in one foal with A. 2. Tetraparesis at birth, seen in 5 foals with A. These foals were born with signs varying from tetraparesis to tetraplegia. 3. Progressive ataxia, seen in 2 foals with A. Clinical signs were due to a progressive focal cervical compressive myelopathy. 4. Congenital cervical scoliosis/deviated head, seen in the 2 horses with B and the horse with C. These horses had no signs of spinal cord or brain disease. The diagnoses were made clinically by palpation of the occipitoatlantoaxial region and were confirmed radiographically and/or by post mortem examination in all except one case. Pedigree analysis showed the familial nature of the particular occipitoatlantoaxial malformation seen in horses of only the Arabian breed.     

Cervical Vertebral Osteomyelitis With Secondary Septic Arthritis of the Atlantoaxial Joint in a Foal: A Case Report

A 36-day-old, 100-kg Thoroughbred colt was presented with a sudden onset of abnormal head carriage and pyrexia. Radiography revealed an osteomyelitis of the vertebral body of the second cervical vertebra. Ultrasonography revealed abscessation in the region of the atlantoaxial articulation on the left side, and fluid aspirated from the abscess confirmed suppurative inflammation. Surgical management was not feasible on economic grounds, and therefore this case was managed with aggressive medical therapy based on the most likely pathogens involved. To provide prolonged antibiotic therapy within the client’s budget, the antibiotic flucloxacillin (Staphlex, 500 mg) was used at a dose of 10 mg/kg by mouth, three times daily. Thirty-eight days after first presentation, the foal was euthanized because of chronic pain and deterioration in neurologic signs. A diagnosis of chronic osteomyelitis of the body of the second cervical vertebra (axis) was made with concurrent septic arthritis of the atlantoaxial joint involving the articular surface of the first cervical vertebra (atlas) and cervical myelopathy of the spinal cord within the first two vertebrae. No pathogens were isolated post mortem. This is the first report to describe the use of flucloxacillin in a foal. Although the outcome was fatal, the medical therapy provided could be considered successful at sterilizing the bony lesion.     

Atlantoaxial cartilaginous exostosis causing spinal cord compression in a mature Bernese mountain dog

Cartilaginous exostosis developed in the atlantoaxial region of a three-and-a-half-year-old Bernese mountain dog. The dog exhibited ataxia in the hindlimbs and flailing movements in the forelimbs. On survey radiographs of the cervical spine there was a focal calcified mass between the dorsal arch of the atlas and the spinous process of the axis. Lumbar myelography revealed severe dorsal spinal cord compression. The mass was removed surgically and the dog made a complete recovery. Histopathology of the excised mass was consistent with a diagnosis of cartilaginous exostosis.     

Surgical decompression for traumatic atlantoaxial subluxation in a weanling filly.

A filly with ataxia and splinting and crepitation in the neck was found to have atlantoaxial subluxation. Radiographic diagnosis was based on the same criteria as those used in other species, ie, increased distance between the atlas and spine of the axis and increased distance between the dens and floor of the atlas. Extensive hemilaminectomy was performed to decompress the spinal cord. Stabilization was not attempted. Immediate postoperative response was encouraging, but the untimely death of the filly prevented further evaluation of the procedure.     

Occipitoatlantoaxial malformation in two non-Arabian horses

Occipitoatlantoaxial malformation was diagnosed in a 19-month-old mare of Appaloosa breeding and in a 3-year-old Quarter Horse gelding. Both horses had abnormal head and neck carriage since birth, but neurologic deficits did not become evident clinically until the horses reached 2 and 3 years of age, respectively. Palpation and manipulation of the base of the skull and cervical area proved to be useful diagnostically. Movement could not be elicited at the atlantooccipital joint but, in comparison with clinically normal horses, the range of dorsoventral motion at the atlantoaxial joint was increased. Alternate subluxation and relocation of this joint generated audible clicking sounds. Radiography revealed symmetric atlantooccipital fusion, with modification of the atlas, atlantoaxial joint, and axis. These findings were confirmed at necropsy.     

Congenital occipitoatlantoaxial malformation in a Warmblood mare

A 3-year-old Warmblood mare was presented with spinal ataxia of 3 months’ duration. Clinically, reduced mobility of the neck and a prominent atlas were identified. Neurological evaluation revealed hypermetria, circumduction and reduced proprioception, predominantly in the hindlimbs. Occipitoatlantoaxial malformation (OAAM) was diagnosed based on radiography and computed tomography, and confirmed on post-mortem magnetic resonance imaging and pathological examination. Both the atlas and axis were hypoplastic and dysplastic, and a fusion of the atlanto-occipital joint was found. A dynamic compression of the spinal cord was present at the first and second cervical vertebrae. Histologically, the spinal cord was degenerated due to compression. Furthermore, there were muscular malformations including a fibrotic obliquus capitis cranialis muscle, aplasia of parts of the rectus capitis muscles and presence of additional abnormal muscle. Such muscular abnormalities associated with OAAM have not been reported yet and this is the first report of a case of OAAM in a Warmblood horse.     

ATLANTO-AXIAL MALARTICULATION IN ANGORA GOATS

SUMMARY Two male Angora goats presented with ataxia and weakness of the hind limbs. Both tired easily when exercised and often stumbled and fell. In both cases, post-mortem examination revealed focal areas of gliosis and diffuse Wallerian degeneration in the spinal cord at the level of the atlanto-axial joint. There were also two areas of myelomalacia in one of the goats. In the other, the caudal articular surfaces of the atlas were unusually convex and the odontoid process of the axis was laterally compressed. It is suggested that these vertebral anomalies resulted in excessive mobility of the joint leading to the development of a compressive myelopathy.     

Atlanto-axial approach for cervical myelography in a Thoroughbred horse with complete fusion of the atlanto-occipital bones

A 2-year-old Thoroughbred gelding with clinical signs localized to the first 6 spinal cord segments (C1 to C6) had complete fusion of the atlanto-occipital bones which precluded performing a routine myelogram. An ultrasound-assisted myelogram at the intervertebral space between the atlas and axis was successfully done and identified a marked extradural compressive myelopathy at the level of the atlas and axis, and axis and third cervical vertebrae.     

Cervical fibrotic stenosis in a young Rottweiler.

An 18-month-old neutered male Rottweiler was examined because of slowly progressive spastic tetraparesis and ataxia. Signalment and clinical signs were suggestive of 2 neuronal degenerative diseases presumed to be inherited in young Rottweilers: leukoencephalomyelopathy and neuroaxonal dystrophy. Myelography revealed an extradural compression at the articulation of the second and third cervical vertebrae. At surgery, focal hypertrophy of the yellow ligament was observed to compress the spinal cord ventrally at that site.     

INCOMPLETE OSSIFICATION OF THE ATLAS IN DOGS WITH CERVICAL SIGNS

Osseous defects affecting the atlas were identified in computed tomography and magnetic resonance images of five dogs with cervical signs including pain, ataxia, tetraparesis, or tetraplegia. Osseous defects corresponded to normal positions of sutures between the halves of the neural arch and the intercentrum, and were compatible with incomplete ossification. Alignment between the portions of the atlas appeared relatively normal in four dogs. In these dogs the bone edges were smooth and rounded with a superficial layer of relatively compact cortical bone. Displacement compatible with unstable fracture was evident in one dog. Concurrent atlantoaxial subluxation, with dorsal displacement of the axis relative to the atlas, was evident in four dogs. Three dogs received surgical treatment and two dogs were treated conservatively. All dogs improved clinically. Incomplete ossification of the atlas, which may be associated with atlantoaxial subluxation, should be considered in the differential diagnosis of dogs with clinical signs localized to the cranial cervical region.     

Radiographic morphology of the cranial portion of the cervical vertebral column in Cavalier King Charles Spaniels and its relationship to syringomyelia

OBJECTIVE: To compare radiographic morphology of the atlantoaxial region between Cavalier King Charles Spaniels (CKCSs) and dogs of other breeds and determine whether there was an association between radiographic morphology of the atlantoaxial region and syringomyelia in CKCSs. ANIMALS: 65 CKCSs and 72 dogs of other breeds. PROCEDURES: The amount that the spinous process of the axis overlapped the dorsal arch of the atlas, the relative size of the spinous process of the axis, and the amount of widening of the atlantoaxial joint that occurred when the neck was moved from a neutral to a flexed position were measured on lateral radiographic projections of the atlantoaxial region. Magnetic resonance images were reviewed to identify CKCSs with syringomyelia. RESULTS: The amount of overlap of the atlas and axis and the relative size of the spinous process of the axis were significantly smaller in CKCSs than in dogs of other breeds. However, the amount of widening of the atlantoaxial joint that occurred when the neck was moved from a neutral to a flexed position was not significantly different between groups, and no association was detected between syringomyelia and excessive atlantoaxial joint space widening or between syringomyelia and an excessively small axial spinous process. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that radiographic morphology of the atlantoaxial region in CKCSs differs from morphology of that region in dogs of other breeds, but that these differences do not account for why some CKCSs develop syringomyelia and others do not.     

Association of spinal cord compression seen on magnetic resonance imaging with clinical outcome in 67 dogs with thoracolumbar intervertebral disc extrusion

OBJECTIVES: To determine whether there is an association between the degree of transverse spinal cord compression detected by magnetic resonance imaging following thoracolumbar Hansen type 1 intervertebral disc disease in dogs and their presenting and postsurgical neurological status. METHODS: Medical records of 67 dogs with surgically confirmed Hansen type 1 intervertebral disc disease (2000 to 2004) were reviewed to obtain the rate of onset of disease, duration of clinical signs and presurgical and postsurgical neurological grade. Percentage of spinal cord compression was determined on transverse T2-weighted magnetic resonance images. Linear regression was used to examine the association between spinal cord compression and each of the above variables. Chi-squared tests were used to examine associations among postsurgical outcome and presurgical variables. RESULTS: Eighty-five per cent (57 of 67) of dogs were chondrodystrophoid. Mean spinal cord compression was 53 per cent (sd=219.7, range 14.3 to 84.9 per cent). There was no association between the degree of spinal cord compression and the neurological grade at presentation, rate of onset of disease, duration of clinical signs or postsurgical outcome, with no difference between chondrodystrophoid and non-chondrodystrophoid dogs. CLINICAL SIGNIFICANCE: The degree of spinal cord compression documented with magnetic resonance imaging in dogs with thoracolumbar Hansen type 1 intervertebral disc disease was not associated with the severity of neurological signs and was not a prognostic indicator in this study.     

Atlantoaxial malformation in a half-Arabian colt

A 1-year-old half-Arabian colt was referred for evaluation of a cranial cervical abnormality. Physical examination revealed the left wing of the atlas to be more ventral than the right wing. A head tilt, with the pole deviated to the left, was present because of the malpositioned atlas. Neurologic examination identified symmetrical weakness, ataxia, and proprioceptive deficits in all four limbs. Radiographs of the cranial cervical region revealed fusion of the atlas and axis, and deviation of the atlantoaxial joint to the left of the median plane. Euthanasia was elected. Necropsy confirmed the radiographic findings. The atlas was rotated 20 degrees counterclockwise when viewed from the caudal aspect. Multifocal myelomalacia was present in the first and second cervical spinal cord segments. The malformation was believed to be due to a degenerative process or abnormal embryological development.     

Postanesthetic hemorrhagic myelopathy in a horse

Acute hemorrhagic myelopathy developed in the sixth cervical to the eighth thoracic spinal cord segments of a 1-year-old Quarter Horse colt that was castrated under general anesthesia while in dorsal recumbency. Clinical signs were consistent with severe transverse myelopathy caudal to the brachial enlargement and cranial to the lumbosacral enlargement of the spinal cord. Histologic examination of the spinal cord revealed hemorrhage in the gray matter, with multiple blood-filled clefts in otherwise normal neuropil. Hemodynamic changes in the spinal cord associated with anesthesia and dorsal recumbency may have led to hypoxic vessel damage, with massive hemorrhage after surgery, when the horse was returned to lateral recumbency. Postanesthetic hemorrhagic myelopathy is a possible complication of positioning in dorsal recumbency, during anesthesia, in rapidly growing, young horses.