Clinical Technique: Myelography in Rabbits

Spinal disease in rabbits is most often the result of trauma; however, other causes have been reported including congenital defects and degenerative spinal diseases. Diagnosis of spinal disease is based on history, physical and neurologic examination findings, and imaging. Fractures and luxations of the spine are often apparent on plain radiographs; however, myelography is used to determine if the lesion is causing spinal cord compression that may be amenable to surgical decompression. Unless intervertebral discs are mineralized, they are not visible when viewing plain radiographic images; therefore, myelography may be useful to diagnose spinal cord compression from a herniated disc. Myelography can also define lesions that do not result in a disruption of the osseous vertebral architecture such as tumors and granulomas. In rabbits, myelography is performed when the animal is under general anesthesia and in lateral recumbency. A nonionic iodinated contrast agent is injected into the subarachnoid space, usually at the level of the lumbar spine, to outline the spinal cord and identify cord compressive or disruptive lesions.     

犬脊髓造影技术

采用脊髓蛛网膜下腔穿刺将造影剂注入椎管 ,分别对 1 6只不同年龄犬行欧乃派克 ( omnipaque,每毫升含碘 30 0 mg)脊髓造影 ,对 1 1只犬行碘化油 (含碘 4 0 % )脊髓造影。造影后拍摄颈段、胸段、腰荐段正、侧位脊髓造影照片并评定造影结果 ,研究比较水溶性造影剂欧乃派克和脂溶性造影剂碘化油用于不同年龄犬的脊髓造影技术 ,分析了犬正常脊髓造影影像。研究表明 ,每毫升含碘 30 0 mg的欧乃派克可安全地用于犬的脊髓造影 ;不同年龄犬造影剂用量相同 ,每公斤体重 0 .4 5m L时全段脊髓同时清楚显示 ,0 .30 m L时局部 (颈段、胸段或腰荐段 )脊髓显示清楚 ,0 .2 0 m L以下时脊髓显示较模糊。碘化油毒副作用较大 ,不宜再用于犬的脊髓造影     

Thoraco-Lumbar Myelography with Water-Soluble Contrast Medium in Dogs II. Appearance of the Myelogram in Disk Protrusion and its Relation to Functional Disturbances and Patho-anatomic Changes in the Epidural Space

Abstract— Myelography by lumbar injection of a water-soluble contrast medium has been performed in 151 dogs with symptoms of spinal cord compression. In 138 of these animals the contrast medium passed beyond the site of the compression in such an amount that the cranial as well as the caudal borderline of the compression was demonstrated. The myelograms obtained have shown highly satisfactory agreement with the changes in the epidural space (disk protrusion) observed by laminectomy or autopsy.     

Congenital kyphosis secondary to lumbar vertebral hypoplasia causing paraparesis in a Friesian foal

A 5‐day‐old Friesian colt was presented with a history of severe bilateral pelvic limb weakness since birth. Clinical examination revealed a painful dorsal deviation of the spinous processes of the lumbar vertebrae, pelvic limb paraparesis and grade 4/5 ataxia. Radiographic examination revealed kyphosis due to hypoplasia and malformation of the 5 lumbar vertebrae present. At myelography performed immediately after euthanasia, dorsal deviation of the myelographic contrast column was demonstrated at the level of T18–L4 with suspected spinal cord compression noticeable at L1. There was no lateral deviation of the spinal cord or scoliosis of the vertebrae visible.     

Malignant glioma of the spinal cord in a dog

The history, clinical signs, diagnosis and post-mortem findings of a malignant glioma of the spinal cord of a 5-year-old female Borzoi are reported. A discrepancy between the localization of the cord lesion by neurological examination and myelography is described. A myelogram showed a filling defect of the subarachnoid space caudal to the cord lesion. As the site for surgical exploration was based on the myelographic findings the cord tumour was not exposed during surgery. Autopsy confirmed a malignant glioma in the area of the cord suggested by neurological examination.     

Evaluation of decision criteria for detection of spinal cord compression based on cervical myelography in horses: 38 cases (1981-2001)

REASONS FOR PERFORMING STUDY: Different criteria have been described based on height reduction of the total myelographic contrast column and components of it as tests for compression of the spinal cord due to cervical stenotic myelopathy (CSM). Fifty percent height reduction of the dorsal myelographic column (DMC), <2 mm empiric height of the DMC and a 40% reduction of the ratio of stenosis calculated based on the height reduction of the entire dural diameter (DD) have been described as decision criteria for considering the test result positive. The reasons for selecting these decision criteria or their accuracies have rarely been reported. OBJECTIVES: To evaluate the accuracy of diagnostic criteria based on reduced height of the total myelographic column and components of it for diagnosing extradural spinal cord compression using different decision criteria, and make recommendations for consistent myelographic interpretation in horses suspected of having CSM. METHODS: Four measurements were obtained by 2 readers in a retrospective sample population of 38 horses in which both cervical myelography and histopathological examination of the cervical spinal cord were performed. The prevalence of CSM in the sample was 50%. At intervertebral sites, the minimum heights of the DD and DMC were measured. At intravertebral sites, the maximum heights of the entire DD and DMC were obtained. Percent height reductions of the DMC and DD were determined as the ratio of minimum intervertebral height to maximum intravertebral height within the next cranial vertebra. Histological examination was used as the gold standard for determining the actual site of spinal cord compression. Sensitivity and specificity for the diagnostic criteria were estimated at each site in neutral and flexed neck positions using several different decision criteria. CONCLUSIONS: At C6-C7, in neutral or flexed neck position and using 20% reduction of DD, the test was highly sensitive and specific for CSM. At other sites, reduced height of the myelographic column generally was not accurate for diagnosing extradural spinal cord compression. Using 20% reduction of DD in neutral position at the mid-cervical sites, the test had only low sensitivity and high specificity. Flexion of the neck appeared to increase detection of spinal cord compression in the mid-cervical region, but also substantially increased the frequency of false-positive diagnoses. POTENTIAL RELEVANCE: By using the reported sensitivity and specificity estimates, readers may decide on a decision criterion for diagnosis of extradural spinal cord compression due to CSM. However, in planning a surgical correction, it is difficult to define a decision criterion that combines acceptable sensitivity and specificity, especially at the mid-cervical sites.     

Ultrasound-Guided Atlanto-Occipital Puncture for Myelography in the Horse

Complications of cervical myelography arising from the puncture of the subarachnoid space to collect the cerebrospinal fluid and to inject the contrast medium have been described in humans and animals. In this study, 2 ultrasound-guided procedures were developed for puncture of the atlanto-occipital subarachnoid space, collection of cerebrospinal fluid, and injection of contrast medium. Myelography was performed on 6 ataxic horses using these procedures. The first attempt to puncture the subarachnoid space was successful in 5 horses and in one horse, a second attempt was necessary. Collection of cerebrospinal fluid and injection of contrast medium were achieved without difficulty. Ultrasound-guided myelography allowed reduction of potential complications associated with blind percutaneous puncture of the subarachnoid space. Methods described in this study should be tried-at least initially in an experimental setting--to collect cerebrospinal fluid from the atlanto-occipital site in standing horses where it may represent an alternative method when lumbosacral cerebrospinal fluid collection has been unsuccessful or contaminated with blood.     

MYELOGRAPHY IN THE CAT

Metrizamide myelographic examinations were performed on five normal cats using sequential cisternal and lumbar injections at weekly intervals to determine the dose of contrast medium required, adverse effects, and quality of the myelographic study. The normal myelographic appearance in the cat is described. All spinal cords were examined histopathologically after the termination of the study, and variable mild lesions were found. Doses of 0.2 ml/kg, 0.35 ml/kg, and 0.4 ml/kg metrizantide, respectively, for lumbar, thoracolumbar, and complete spinal studies are recommended when performing lumbar injection. Recommended doses using cisternal injection for cervical, cervicothoracic, and complete spinal studies are 0.2, 0.45, and 0.5 ml/kg, respectively. Subjectively, lumbar injection produced higher-quality thoracolumbar myelograms and cisternal injection produced higher-quality cervical studies. Clinical complications during the study included one seizure following cisternal myelography and mild neurologic deficits in all cats, which resolved within 36–48 hours.     

A field study of eight ovine vertebral body abscess cases

A vertebral body abscess extending into the epidural space causing spinal cord compression was diagnosed in the cervical spinal cord in four lambs and the thoracic spinal cord in four lambs. The affected lambs were aged between 4 and 10 weeks and clinical signs had been present for 7-21 days before veterinary examination. Treatment with high doses of penicillin did not result in an improvement of the neurological signs and all lambs were destroyed on humane grounds. Collection and analysis of cerebrospinal fluid (CSF) revealed a significant increase in the protein concentration in lumbar compared to cisternal CSF samples. There was a neutrophilic pleocytosis in two lumbar CSF samples. In lambs aged between 4 and 10 weeks with no history of previous locomotor dysfunction, paresis of more than 1 week duration may be suggestive of a vertebral body abscess which has extended into the epidural space causing spinal cord compression. Stagnation of CSF caudal to the lesion results in an increased protein concentration in the lumbar sample.     

Cervical vertebral canal endoscopy in a horse with cervical vertebral stenotic myelopathy

A 3-year-old Thoroughbred gelding presented with a history of neurological signs, including incoordination in his hindlimbs, of about 7 months' duration. On initial examination, the horse exhibited ataxia and paresis in all limbs with more severe deficits in the hindlimbs. Cervical radiographs displayed severe osteoarthritis of the articular processes between C5 and C6. On subsequent cervical myelography the dorsal contrast column was reduced by 90% at the level of the intervertebral space between C5 and C6. Cervical vertebral canal endoscopy, including epidural (epiduroscopy) and subarachnoid endoscopy (myeloscopy), was performed under general anaesthesia. A substantial narrowing of the subarachnoid space at the level between C6 and C7 was seen during myeloscopy, while no compression was apparent between C5 and C6. Epiduroscopy showed no abnormalities. After completion of the procedure, the horse was subjected to euthanasia and the cervical spinal cord submitted for histopathological examination. Severe myelin and axon degeneration of the white matter was diagnosed at the level of the intervertebral space between C6 and C7, with Wallerian degeneration cranially and caudally, indicating chronic spinal cord compression at this site. Myeloscopy was successfully used to identify the site of spinal cord compression in a horse with cervical vertebral stenotic myelopathy, while myelography results were misleading.     

Subdural injection of contrast medium as a complication of myelography

In a retrospective evaluation of 654 canine and feline myelograms, 58 were found to have been complicated by injection of the contrast medium into the subdural space. The medium was present predominantly dorsal to the spinal cord, with a sharp dorsal border and an undulating ventral border. Confirmation that this myelographic appearance was due to subdural localisation was achieved using fresh cadavers injected with contrast medium labelled with Indian ink. It was further showed that the dorsal accumulation of contrast medium was due to the denticulate ligaments which restricted the ventral extension of the contrast medium.     

Segmental Spinal Cord Hypoplasia in a Holstein Friesian Calf

An 8‐day‐old female Holstein Friesian calf was examined because of congenital spastic paresis of the hind limbs. Myelography revealed deviation and thinning of subarachnoid contrast medium columns in the lumbar segment. Upon magnetic resonance imaging, the ‘hour‐glass’ subdural compression appeared as a T1‐hypointense, T2‐hyperintense ovoidal area suggestive of cerebral spinal fluid collection, compatible with hydrosyringomyelia. The calf was euthanized and the necropsy confirmed the diagnosis of segmental spinal cord hypoplasia of the lumbar tract associated to hydromyelic and syringomyelic cavities.     

Lumbosacral myelography in dogs--a safer technique

In search of a safer myelographic technique, we performed myelography via the lumbosacral intervertebral space. Eight dogs, in which the backflow of cerebrospinal fluid was observed, received contrast media via the lumbosacral intervertebral space. The subarachnoid contrast columns were successfully observed in 6 dogs. During and after examination, no physiological changes or neurological signs were observed. We recommend that the lumbosacral intervertebral space be selected first before implementing the conventional lumbar myelography.     

Spinal cord astrocytoma in a cat

A nine-year-old neutered male domestic shorthaired cat with a history of spinal pain and progressive hindlimb dysfunction was presented to the Norwegian School of Veterinary Science. Following neurological and myelographic examination, an intramedullary mass affecting several lumbar spinal cord segments was diagnosed. A neoplastic lesion was suspected and a poor prognosis was given. On postmortem examination, the spinal cord was found to be dorsally flattened from the 12th thoracic vertebra to the fifth lumbar vertebra and severely thickened with a dorsal cleft from the fifth to the seventh lumbar vertebra. Histologically, the tumour was diagnosed as an anaplastic astrocytoma.     

RADIOGRAPHIC AND MYELOGRAPHIC EXAMINATION OF THE CERVICAL VERTEBRAL COLUMN IN 306 ATAXIC HORSES

This study consists of a review of 306 ataxic horses subjected to survey radiography and myelography of the cervical vertebral column. Fifty-eight percent of horses had evidence of compressive spinal cord lesion on myelography. Sixty-six percent of horses were less than 3 years old. Age had no effect on the distribution of spinal cord compressive lesions. No conclusion could be drawn from sex and breed distribution. The most common sites of cord compression on myelography in order of decreasing frequency were C_3–4, C_6–7, C_5–6, and C_4–5. Twenty-nine percent of horses with myelographic evidence of cord compression had multiple compressive sites. Survey radiographs were not reliable to diagnose compressive spinal cord lesions. Myelography was a safe and more accurate procedure. Several factors may result in misinterpretation of the myelographic examination.     

IOHEXOL MYELOGRAPHY IN THE DOG

Myelography with iohexol (180 mg iodine/ml, 0.25 ml/kg), a new nonionic radiologic contrast medium, was performed in 100 dogs of 33 different breeds. In 96 of the dogs the iohexol mixed evenly with the cerebrospinal fluid, providing an homogeneous, continuous column of contrast medium within the subarachnoid space, and a radiologic diagnosis of a normal myelogram or disease involving the spinal cord was made. Pooling of iohexol in the dorsal part of the subarachnoid space occurred in four dogs; whether this was related to poor mixing of contrast medium with cerebrospinal fluid or disease of the spinal cord and meninges requires further study. Postmyelographic signs of central nervous system irritation (fasciculations of the temporal muscles and three episodes of seizure activity) were observed in only one dog and were controlled with diazepam. The presenting neurologic signs were aggravated after myelography in four other dogs, two of which were eventually killed. This study provided further evidence of the increased safety of iohexol compared with metrizamide, the first of the nonionic media, as a contrast medium for myelography in the dog.     

INTRAOPERATIVE SPINAL ULTRASONOGRAPHY IN DOGS: NORMAL FINDINGS AND CASE-HISTORY REPORTS

Intraoperative spinal ultrasonography was performed in cervical and lumbar spine of 2 and 5 normal dogs, respectively, following ventral slot technique or dorsal or hemilamenectomy. The dura was hyperechoic, while the parenchyma was hypoechoic. The subarachnoid space was anechoic. An echogenic line was present in the center of the spinal cord, as seen in human. Pulsation of the spinal cord was noted during M-mode imaging. Clinical findings of one dog with thoracolumbar disk herniation and one with thoracic vertebral fracture/subluxation confirmed the usefulness of intraoperative spinal ultrasonography for real time evaluation of spinal canal spatial abnormalities (mass lesion and degree of spinal cord compression on scanning planes) and spinal cord motion. Follow-up ultrasound examinations were possible from 6 days postoperatively.     

SPINAL SUBARACHNOID CYST IN A CAT

A 7-year-old neutered female domestic short hair cat was presented with hind limb ataxia. A subarachnoid cyst in the T10-T11 spinal cord region was identified by myelography as a collection of contrast medium in the subarachnoid space.     

Myelographic localization of spinal cord compression in dogs. A comparison between cisternal and lumbar injections of metrizamide "Amipaque" in diagnosing and locating spinal cord compression.

Metrizamide is a new water-soluble contrast medium possessing unique properties, one of which is that even in an isotonic solution it has a radiographic density sufficient for a diagnostic myelogram. Whereas in the past myelography with water-soluble preparations invariably entailed lumbar injections, which are technically difficult in dogs, the fact that isotonic metrizamide causes so little tissue irritation has made it possible to inject the contrast solution into the cisterna magna. The author has compared metrizamide myelograms obtained with both cisternal and lumbar injections. Myelography with a cisternal injection is preferable for demonstrating cervical cord compressions and also in cases in which it is desirable to obtain myelographic information on both the cervical and the thoraco-lumbar areas. If, on the other hand, it is necessary to determine exactly the extent of a thoraco-lumbar compression before decompressive laminectomy, the contrast should be injected in the lumbar region in such an amount and at a pressure high enough to ensure that the contrast is forced past the site of the compression. The safety of metrizamide will probably enable a better prognosis following surgery than was previously possible.     

Odontoid process dysplasia in a dog

A six-and-a-half year old spayed female Sheltie was referred to The Animal Medical Center with upper motor neurone signs to the four limbs. Radiographic and myelographic examinations were not significant. Postmortem examination revealed that dysplasia of the dens caused compression of the spinal cord.