Transcranial magnetic stimulation: normal values of magnetic motor evoked potentials in 84 normal horses and influence of height, weight, age and sex

REASONS FOR PERFORMING STUDY: Cervical spinal cord dysfunction is a common problem in equine medicine and the currently available tests give no objective information about the functionality of the nervous tracts. Therefore, transcranial magnetic stimulation (TMS) was performed in 84 healthy horses of different height in order to have an objective measure for the integrity of the descending motor tracts in normal horses. OBJECTIVES: To obtain reference values for onset latency and peak-to-peak amplitude of magnetic motor evoked potentials (MMEPs) and to evaluate the possible effect of height, age and gender on the neurophysiological measures. METHODS: All horses were sedated and stimulated transcranially by using a magnetic coil placed on the forehead. The stimulator triggered the sweep of an electromyogram machine that recorded MMEPs bilaterally from needle electrodes in the extensor carpi radialis and cranial tibial muscles. In that way, it was possible to measure latency between stimulus and onset of response. RESULTS: A significant difference was found between recordings made in the fore- and hindlimbs; MMEPs recorded in the front legs had a shorter onset latency and higher peak-to-peak amplitude. Mean +/- s.d. normal values for onset latency of 19.32 +/- 2.50 and 30.54 +/- 5.28 msecs and peak-to-peak amplitude values of 9.54 +/- 3.73 and 6.62 +/- 3.62 mV were obtained for extensor carpi radialis and cranial tibial muscles, respectively. The left-to-right difference in onset latency and peak-to-peak amplitude was not significant. In the same horse, differences up to 0.82 and 1.53 msecs for the extensor carpi radialis and cranial tibial muscles, respectively, lie within the 95% confidence limit and are considered normal. In contrast to onset latency, peak-to-peak amplitude showed a very large intra- and interindividual variability, even in the same muscle. To reduce the variability and predict normal values of new individual cases, influence of height, weight, age and sex on the MMEPs were determined. No significant effects of sex were observed on onset latency and peak-to-peak amplitude. The age of the horse had only a small but significant effect on peak-to-peak amplitude, with larger responses in older horses. Height at the withers and weight of the horse, parameters that strongly correlate with the size of the horse, had an important significant influence on onset latency but not on peak-to-peak amplitude. The age of the horse and height at the withers were used to predict peak-to-peak amplitude and onset latency, respectively, in normal horses. CONCLUSIONS AND POTENTIAL RELEVANCE: TMS is an excellent addition to the few tools we have for noninvasive imaging of the equine nervous system. Magnetically evoked potentials are highly reproducible and recent advances suggest that the applications of TMS in horses will continue to grow rapidly.     

Standardization of transcranial magnetic stimulation in the horse

The influence of coil position on the peak-to-peak amplitude and onset latency of transcranial magnetic motor evoked potentials (MMEPs) in the extensor carpi radialis and cranial tibial muscles of horses was evaluated. Seven different stimulating coil positions were obtained by constructing a frame on the forehead. Two stimulation intensities (80% and 100% of maximal stimulator output) and two different coil currents (clockwise and counter-clockwise) were tested. For both recording sites MMEPs with the shortest onset latency and the largest peak-to-peak amplitude were detected when the coil was placed in the median of the forehead. There was no significant difference between left and right side recordings. The direction of the current flow in the coil had no influence on the onset latency of the MMEPs.     

Correlation of motor evoked potentials with magnetic resonance imaging and neurologic findings in Doberman Pinschers with and without signs of cervical spondylomyelopathy

OBJECTIVE: To establish the reference ranges for motor evoked potential (MEP) latency and amplitude in clinically normal Doberman Pinschers, compare the MEPs of Doberman Pinschers with and without clinical signs of cervical spondylomyelopathy (CSM; wobbler syndrome), and determine whether MEP data correlate with neurologic or magnetic resonance imaging (MRI) findings. ANIMALS: 16 clinically normal and 16 CSM-affected Doberman Pinschers. PROCEDURES: Dogs were classified according to their neurologic deficits. After sedation with acepromazine and hydromorphone, transcranial magnetic MEPs were assessed in each dog; latencies and amplitudes were recorded from the extensor carpi radialis and cranial tibial muscles. Magnetic resonance imaging was performed to evaluate the presence and severity of spinal cord compression. RESULTS: Significant differences in cranial tibial muscle MEP latencies and amplitudes were detected between clinically normal and CSM-affected dogs. No differences in the extensor carpi radialis MEP were detected between groups. There was a significant correlation (r = 0.776) between the cranial tibial muscle MEP latencies and neurologic findings. Significant correlations were also found between MRI findings and the cranial tibial muscle MEP latencies (r = 0.757) and amplitudes (r = -0.453). CONCLUSIONS AND CLINICAL RELEVANCE: Results provided a reference range for MEPs in clinically normal Doberman Pinschers and indicated that cranial tibial muscle MEP latencies correlated well with both MRI and neurologic findings. Because of the high correlation between cranial tibial muscle MEP data and neurologic and MRI findings, MEP assessment could be considered as a screening tool in the management of dogs with spinal cord disease.     

Role of transcranial magnetic stimulation in differentiating motor nervous tract disorders from other causes of recumbency in four horses and one donkey

Transcranial magnetic stimulation and measurement of the magnetic motor-evoked potentials (MMEPs) in the thoracic and pelvic limbs of four recumbent horses and one recumbent donkey were used to assess the integrity of the descending motor pathways, in order to confirm or exclude a descending motor tract lesion as the cause of the recumbency. In two of the animals abnormal MMEPs were recorded; in one of the horses a lesion along the cervical spinal cord due to a fracture of the fifth cervical vertebra was diagnosed and confirmed by radiography and postmortem examination; in another horse, damage to the peripheral nerves of the left forelimb was diagnosed and confirmed postmortem when a large abscess was found to have been compressing the peripheral nerves at the level of the last cervical vertebra. In the three other animals, normal MMEPs were recorded, and laminitis, rhabdomyolysis and physitis were diagnosed as the causes of the recumbency.     

Reference values and clinical application of magnetic peripheral nerve stimulation in cats

Magnetic stimulation of radial (RN) and sciatic (SN) nerves was performed bilaterally in 40 healthy cats. Reference values for onset latency and peak-to-peak amplitude of magnetic motor evoked potentials (MMEPs) were obtained and compared with values of electric motor evoked potentials (EMEPs) in 10/40 cats. Onset latencies and peak-to-peak amplitudes of the MMEPs of three cats with polyneuropathy (PNP) were compared to the reference values. Magnetic motor evoked responses were easily recorded in all normal cats. Significant differences were found in onset latencies between MMEPs and EMEPs, but peak-to-peak amplitudes were equal. The MMEPs of three cats with PNP can be seen as outliers in comparison to the reference values. MMEPs from the RN and SN were easily obtained and reproducible in normal cats. The technique could represent a useful adjunct in the assessment of peripheral nerve disorders.     

Comparison of nociceptive withdrawal reflexes and recruitment curves between the forelimbs and hind limbs in conscious horses

OBJECTIVE: To compare nociceptive withdrawal reflexes (NWRs) evoked from the distal aspect of the left forelimb and hind limb in conscious standing horses and to investigate NWR recruitment for graded electrical stimulation intensities. ANIMALS: 20 adult horses. PROCEDURE: Surface electromyographic (EMG) activity evoked by transcutaneous electrical stimulation of the digital palmar (or plantar) nerve was recorded from the common digital extensor and cranial tibial muscles. Stimuli consisted of 25-millisecond train-of-5 constant current pulses. Current intensity was gradually increased until NWR threshold intensity was reached. The EMG signal was analyzed for quantification of the NWR. Behavioral responses accompanying the reflex were scored (scale, 0 to 5). The NWR recruitment curves were determined at 0.9, 1.1, 1.2, and 1.3 times the NWR threshold intensity. RESULTS: The NWR threshold was significantly higher for the hind limb (median value, 6.6 mA; range, 3 to 10 mA) than the forelimb (median, 3 mA; range, 1.7 to 5.5 mA). The NWR of the hind limb had a significantly longer latency (median, 122.8 milliseconds; range, 106 to 172 milliseconds), compared with the forelimb (median, 98 milliseconds; range, 86 to 137 milliseconds), and it was associated with significantly stronger behavioral reactions. Gradual increase of NWR amplitude was evident at increasing stimulation intensities and supported by the behavioral observations. CONCLUSIONS AND CLINICAL RELEVANCE: We documented NWRs evoked from the forelimb and hind limb and their recruitment with stimuli of increasing intensity in horses. These results provide a basis for use of NWRs in studies on nociceptive modulation in horses.     

Arthroscopic Approaches and Intraarticular Anatomy of the Equine Elbow

Periarticular anatomy and techniques for arthroscopic access to the equine elbow were studied in six joints from cadavers. Caudomedial and craniolateral approaches were evaluated subsequently in 11 anesthetized horses. The caudomedial approach was made between the flexor carpi radialis and flexor carpi ulnaris muscle bellies. Most of the caudal articular surfaces of the humeral condyles, the caudal perimeter of the radius, and the trochlear notch and portions of the anconeal process of the ulna could be identified. The voluminous caudal joint capsule cul-de-sac proximal to the anconeal process was readily entered. A 70 degree arthroscope allowed examination of more of the joint recesses and articular surfaces of the olecranon fossa than a 25 degree arthroscope. A second portal for intraarticular instrument manipulation was made caudal and slightly proximal to the arthroscope entry. Entry more proximal than the level of the radiohumeral articulation carried significant risk of damage to the ulnar nerve and collateral ulnar artery and vein. For examination of the cranial regions of the elbow, a craniolateral portal was established cranial to the lateral collateral ligament. An instrument portal was made through the muscle bellies of the extensor carpi radialis or common digital extensor muscles. The cranial articular surfaces of the humeral condyles were readily exposed by extension of the elbow. The weight-bearing articular surface of the radius could not be seen. Eight horses were euthanatized without recovery from anesthesia and the elbows were dissected for examination. Three horses were allowed to recover from anesthesia and were euthanatized on days 3, 30, and 60.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of romifidine on the nociceptive withdrawal reflex and temporal summation in conscious horses

OBJECTIVE: To investigate the action of a single IV administration of romifidine on the thresholds of the nociceptive withdrawal reflex (NWR) and temporal summation in conscious horses. ANIMALS: 10 adult horses. PROCEDURE: Single electrical stimulations were applied on the digital nerves to evoke NWR from the left forelimb and hind limb. Repeated electrical stimulations (10 stimuli, 5 Hz) were given to obtain temporal summation. Surface electromyographic reflex activity was recorded from the common digital extensor and cranial tibial muscles. After baseline assessment of NWR and temporal summation thresholds, romifidine (80 microg x kg(-1), IV) was administered. Successive determinations of NWR and temporal summation thresholds were performed 5, 25, and 55 minutes after administration. RESULTS: Romifidine significantly increased the current intensities necessary to evoke NWR and temporal summation in forelimbs and hind limbs of horses. Values were significantly higher than baseline values 55 minutes after romifidine administration. After administration of romifidine, a facilitation of reflex components of tactile origin was observed when repeated stimulations were applied. CONCLUSIONS AND CLINICAL RELEVANCE: Results confirm antinociceptive activity of romifidine and may represent an objective demonstration of the well-known hypersensitivity to tactile stimuli observed in horses receiving alpha2-adrenoreceptor agonists in clinical practice. Romifidine can be included in analgesic and anesthetic protocols to provide additional analgesia in horses.     

Quantitative analysis of computer-averaged electromyographic profiles of intrinsic limb muscles in ponies at the walk.

The function of several intrinsic muscles of the fore-and hind limbs of 5 ponies walking normally was evaluated via surface electromyography. Electromyographic signals were band-pass filtered, rectified, linear enveloped, and standardized to the stride duration. Mean data from the muscles of the left and right limbs that were obtained from at least 30 strides in 2 recording sessions were recorded as electromyographic signals-time curves. The timing of muscle activity was determined from these graphs. On the basis of the major peaks in the electromyographic signal, muscle functions were identified. In the forelimb, the extensor carpi radialis muscle was involved in extension of the carpus at the end of the swing phase of the stride, and it provided support to flexion of the cubital joint at the beginning of the swing phase. The common digital extensor muscle extended the distal joints of the forelimb at the end of the swing phase. The ulnaris lateralis muscle provided support to extension of the cubital joint at the beginning of the stance phase, and the flexor carpi radialis muscle flexed the carpus at the beginning of the swing phase. The flexor carpi ulnaris muscle extended the cubital joint at the end of the swing phase. In the hind limb, the long digital extensor muscle flexed the tarsus at the beginning of the swing phase and extended the digital joints preceding the stance phase. The deep digital flexor muscle prevented overextension of the distal interphalangeal joint during the stance phase and flexion of the digital joints during the swing phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intervertebral disc disease of the cervical and cranial thoracic vertebrae in equidae: eight cases

Intervertebral disc disease in the cervical and cranial thoracic vertebrae is unusual in horses and the majority of documented cases have been associated with infection and resulted in ataxia. The current retrospective study documents the clinical and imaging features, and outcome in eight Equidae with neck stiffness ± forelimb lameness (n = 3) or ataxia (n = 2) assessed during a 10-year period at two clinics. The Equidae (one donkey and seven horses) ranged in age from 1.5 to 12 years (median 5.5 years). The duration of clinical signs ranged from 1 to 6 months (median 1.5 months). The donkey had a depressed demeanour. All Equidae had reduced range of neck movement. The donkey and one horse showed mild and severe ataxia respectively. Two horses showed a propensity to stumble on each forelimb, one of which exhibited forelimb lameness on the lunge or ridden. Two additional horses showed lameness in hand. One horse experienced ‘neck locking’ during grazing. Radiological abnormalities were identified involving the intervertebral symphysis between the sixth cervical vertebra (C6) and C7 in four Equidae; in two horses the articulation between C7 and the first thoracic vertebra (T1) was involved. One horse had abnormalities of the intervertebral symphyses of both C7 and T1, and T1 and T2. In one horse the articulation between C2 and 3 was affected. The donkey was treated with a prolonged course of doxycycline and improved. An advanced dressage horse returned to full-function after surgical fusion of the affected intervertebral symphysis. Intervertebral disc disease is a rare cause of neck stiffness ± lameness or ataxia.     

THE USE OF MAGNETIC RESONANCE IMAGING IN EVALUATING HORSES WITH SPINAL ATAXIA

To determine the accuracy of magnetic resonance imaging for diagnosing cervical stenotic myelopathy in horses, 39 horses with spinal ataxia and 20 control horses underwent clinical and neurologic examinations, cervical radiographs, euthanasia, magnetic resonance (MR) imaging of the cervical spine and necropsy. Twenty‐four horses were diagnosed with cervical stenotic myelopathy, 5 with cervical vertebral stenosis, 7 with idiopathic ataxia, 3 horses had other causes of ataxia, and 20 were controls. The MR images were assessed for spinal cord intensity changes, presence of spinal cord compression, spinal cord compression direction, shape of spinal cord, and the presence of synovial cysts, joint mice, and degenerative joint disease. The height, width, and area of the spinal cord, dural tube and vertebral canal were measured. The identification of spinal cord compression on MR images was significantly different in horses with cervical stenotic myelopathy (P < 0.02), but in the cervical stenotic myelopathy group the identification of spinal cord compression on MR images had poor to slight agreement with histopathologic evidence of compression (κ = 0.05). Horses with cervical stenotic myelopathy were more likely to have a T2 hyperintensity in the spinal cord (P < 0.05). Horses with cervical stenotic myelopathy or cervical vertebral stenosis were more likely to have degenerative joint disease than control horses or horses with other or idiopathic ataxia.     

Effect of protective padding on forelimb intracompartmental muscle pressures in anesthetized horses

Wick catheters were used to measure intracompartmental muscle pressures (ICMP) within the long heads of the triceps brachii and extensor carpi radialis muscles of 8 horses maintained under halothane anesthesia while their breathing was controlled by intermittent positive-pressure ventilation. Blood gas, cardiac output, and blood pressure determinations were monitored to maintain a stable plane of anesthesia. The horses were positioned in left lateral recumbency and were placed sequentially on each of 4 contact surfaces for 1 hour. The 4 surfaces used for each horse were concrete, foam rubber, air dunnage bag, and a water mattress. Hematologic and biochemical determinations were made before and 24 hours after anesthesia. All horses recovered from the anesthesia. One horse had forelimb lameness for 36 hours after anesthesia, which was clinically diagnosed as a myoneuropathy. The ICMP values were markedly elevated in the muscle bellies of the lower limb of all horses. Supporting the horse on a water mattress caused the least dramatic pressure elevation and foam caused the most. The triceps muscle and, to a lesser extent, the extensor carpi radialis muscle of the lower limb are at risk of ischemia in anesthetized horses because the ICMP may exceed the critical closing pressure of 30 mm of Hg required for capillary blood flow.     

Traumatic communication of the extensor carpi radialis tendon sheath and antebrachiocarpal joint in two horses

Two horses were examined due to lacerations at the level of the craniodistal antebrachii. Further evaluation of the lacerations revealed communication with the extensor carpi radialis tendon sheath and potentially the antebrachiocarpal joint. Positive contrast arthrography performed via the palmarolateral pouch of the antebrachiocarpal joint was used to diagnose communication with the extensor carpi radialis tendon sheath. Both the joints and tendon sheaths were treated aggressively with surgical debridement and lavage, followed by post operative medical management and rehabilitation. Both horses made a full recovery and are performing in their intended level of use with acceptable cosmetic results. Traumatic communication with the carpal joints should be considered when evaluating lacerations involving the forelimb extensor tendon sheaths.     

Cervical intervertebral disc protrusion in two horses

Two horses with ataxia of all four limbs were found to have cervical intervertebral disc protrusion. Severe pelvic limb ataxia, proprioceptive deficits and spasticity were present in both horses with similar but less severe signs in the thoracic limbs. Cerebrospinal fluid analysis was within normal limits. Metrizamide myelography allowed definitive diagnosis in one case when a compression of the spinal cord was demonstrated at the level of the second intervertebral space. In the second case, an intervertebral disc protrusion between cervical vertebrae 6 and 7 was found at necropsy. Fiber degeneration with poor myelin staining characterized the spinal cords histologically.     

Quantitative assessment of nociception in horses by use of the nociceptive withdrawal reflex evoked by transcutaneous electrical stimulation

OBJECTIVES: To evoke and measure the nociceptive withdrawal reflex (NWR) by use of electromyographic recordings and to score the behavioral nociceptive responses to electrical pulses in standing nonsedated horses. ANIMALS: 10 adult horses. PROCEDURE: The lateral palmar digital nerve of the forelimb was transcutaneously stimulated, and surface electromyographic responses were recorded from the ulnaris lateralis, extensor carpi radialis, and common digital extensor muscles. Stimuli consisted of a 25-millisecond train of 5 constant-current pulses delivered by a computer-controlled stimulator. The 80- to 250-milliseconds poststimulation interval was analyzed to detect the NWR. The current intensity was increased in steps of 0.5 mA until the NWR threshold intensity (lt) was reached. The stimulus at It was repeated twice. Latency and amplitude of the NWR, together with the behavioral reaction of horses, were analyzed. The latter was scored according to a scale from 0 (no reaction) to 5 (vigorous reaction). Finally, 3 suprathreshold stimuli at 1.2 X It were analyzed. RESULTS: The median It to elicit NWR was 2.5 mA. Median onset latency of the NWR was 96.0 milliseconds at It and 89.6 milliseconds for suprathreshold stimuli. The amplitude of the reflexes was higher for suprathreshold stimulations, and behavioral reactions were slightly stronger when stimulus intensity increased. CONCLUSIONS AND CLINICAL RELEVANCE: Results of our study indicate that it is possible to record NWR in conscious standing horses, to define a reflex threshold, and to measure reflexes in response to increasing stimulus intensity.     

Correlation between severity of clinical signs and motor evoked potentials after transcranial magnetic stimulation in large-breed dogs with cervical spinal cord disease

OBJECTIVE: To evaluate use of transcranial magnetic motor evoked potentials for assessment of the functional integrity of the cervical spinal cord in large-breed dogs with cervical spinal cord disease. DESIGN: Randomized, controlled, masked study. ANIMALS: 10 healthy large-breed control dogs and 25 large-breed dogs with cervical spinal cord diseases. PROCEDURE: Affected dogs were allocated to 3 groups on the basis of neurologic status: signs of neck pain alone, ambulatory with ataxia in all limbs, or nonambulatory. Transcranial magnetic stimulation was performed on each dog with the same standard technique. Motor evoked potentials (MEP) were recorded from electrodes inserted in the tibialis cranialis muscle. Following the procedure, each dog was anesthetized and cervical radiography, CSF analysis, and cervical myelography were performed. The MEP latencies and amplitudes were correlated with neurologic status of the dogs after correction for neuronal path length. RESULTS: Mean MEP latencies and amplitudes were significantly different between control dogs and dogs in each of the 3 neurologic categories, but were not significantly different among dogs in the 3 neurologic categories. A linear association was evident between MEP latencies and amplitudes and severity of neurologic deficits; the more severe the neurologic deficits, the more prolonged the latencies and the more decreased the amplitudes. CONCLUSIONS AND CLINICAL RELEVANCE: Transcranial magnetic MEP are useful to assess severity of cervical spinal cord disease in large-breed dogs. Impairment of the functional integrity of the cervical spinal cord was found even in dogs with neck pain alone.     

Verminous (Strongylus vulgaris) myelitis in a donkey

A fifth stage Strongylus vulgaris migrated through the spinal cord of a 2-year-old, male donkey resulting in progressive paraparesis and then tetraplegia. A profound neutrophilic pleocytosis was detected on analysis of cerebrospinal fluid. The parasite appeared to have entered the mid-lumbar spinal cord, migrated to the cranial thoracic segments, exited, then re-entered the spinal cord a few segments craniad. It then traveled further cranially and was found in the third cervical spinal cord segment. Some parts of the lesion were remarkably free from tissue necrosis, hemorrhage and inflammation. Severe granulomatous myelitis with hemorrhage and necrosis were seen at other sites. The latter were quite similar to lesions seen in equine protozoal myeloencephalitis.     

Gross anatomic organization of the capybara's (Hydrochaeris hydrochaeris) brachial plexus

The innervation of the capybara thoracic limb was characterized. The following nerves were observed constituting the right and left brachial plexus: n. dorsalis scapulae (C4 and C5; C4, C5 and C6) which innervates the m. serratus ventralis cervicis and m. rhomboideus; n. suprascapularis (C4, C5 and C6; C5, C6 and C7) supplying the m. supraspinatus and the m. infraspinatus; cranial and caudal nn. subscapulares (C5 and C6; C5, C6 and C7) innervating the m. subscapularis; n. axillaris (C5 and C6; C6, C7 and C8) which supplies the m. triceps brachii (caput mediale); n. radialis (C6, C7, C8 and T1; C6, C7 and C8) which innervates the m. triceps brachii (caput longum and caput mediale) and the m. extensor carpi radialis, m. extensor digitorum communis, m. extensor digitorum lateralis; n. medianus joined to the n. musculocutaneus (C6, C7, C8 and T1; C6, C7 and C8) supplying the m. biceps brachii, m. flexor carpi radialis and m. coracobrachialis; n. ulnaris (C6, C7, C8 and T1; C6, C7 and C8) leading to the m. flexor carpi radialis, the m. flexor carpi ulnaris and the m. flexor digitorum superficialis; n. thoracodorsalis (C6, C7, C8 and T1; C6, C7 and C8) supplying the m. latissimus dorsi; n. thoracicus lateralis (C8, T1; C7, C8, T1) which innervates m. pectoralis profundus (caudal portion); n. thoracicus longus (C6, C7; C7, C8) which is distributed to the m. serratus ventralis thoracis. A communication between the n. radialis and n. ulnaris was observed at the left brachial plexus.     

Spinal ataxia in a 2-year-old colt caused by a compressive primary vertebral osteosarcoma

Neoplasia is a rare cause of ataxia in horses. This report describes a 2-year-old colt presented with sudden-onset ataxia in which a cervical vertebral osteosarcoma causing severe compression of the spinal cord was diagnosed. Radiological changes included a large osteolytic lesion in the vertebral body, the vertebral arch, the right cranial articular process and the right transverse process of C4, interrupting the borders of the vertebral foramen and the right transverse foramen. Myelography revealed a marked spinal cord compression. Necropsy confirmed the presence of a well-demarcated, invasive and firm mass protruding from the fourth cervical vertebral body that led to severe compression of the spinal cord. In spite of its strongly pleomorphic nature, the detection of osteoid confirmed the diagnosis of a central osteosarcoma of the combined type. To the best of our knowledge, a primary single vertebral osteosarcoma causing ataxia in a juvenile horse has not previously been reported, and findings of this case report could help in the diagnostic work-up of similar cases.     

SPINAL CORD COMPRESSION CAUSED BY A METASTATIC LESION FROM AN AORTIC BODY TUMOUR

An aortic body tumour in a 7-year-old wire-haired fox terrier with hind limb ataxia is described. A metastatic lesion in the dorsal arch of the eighth thoracic vertebra caused compression of the spinal cord. Radiographic techniques are discussed that enabled the position and extent of the primary tumour and its metastasis to be defined and allowed a provisional diagnosis of chemodectoma.