COMPLICATIONS OF METRIZAMIDE MYELOGRAPHY IN THE DOG: A SUMMARY OF 107 CLINICAL CASE HISTORIES

The case histories of 107 dogs undergoing metrizamide myelography at two veterinary hospitals were reviewed. Twenty-three variables, including body weight, injection site, dose of contrast medium, and medical complications during and after recovery from anesthesia, were submitted to statistical analysis by computer. Partial or generalized seizures were the most common medical complications, occurring in 54 percent of the dogs weighing more than 29 kg. Other less frequent medical complications were exacerbation of neurologic signs the day following myelography (11 percent), transient apnea during contrast medium injection (9 percent), vomiting (5 percent), hyperesthesia (3 percent), pyrexia (1 percent), and death (1 percent). The incidence of medical complications associated with metrizamide myelography in this study is higher than in previous reports. The most likely variables associated with seizures were high injection volumes and metrizamide injection at the cisterna magna. The preanesthetic administration of intramuscular pentobarbital did not significantly reduce seizure incidence. Seizures were controlled by anticonvulsant medication.     

EXPERIMENTAL ARACHNOID FIBROSIS PRODUCED BY METRIZAMIDE IN THE DOG*

The short-term neurologic and long-term leptomeningeal effects of repeated subarachnoid administration of metrizamide at concentrations of 170 mg I/ml and 300 mg I/ml were investigated in dogs. After two months, arachnoid fibrosis of varying degrees was present in all dogs that had received metrizamide at the higher concentration. The higher concentration of met-rizamide was more epileptogenic than the concentration of 170 mg I/ml. The presence of subarachnoid hemorrhage was not considered to play a role in the development of the arachnoid fibrosis. Veterinary Radiology Vol. 21, No. 2, 1980; pp 78–81.     

A COMPARISON OF IOPAMIDOL AND METRIZAMIDE FOR CERVICAL MYELOGRAPHY IN THE DOG

Cervical myelography using iopamidol, a new nonionic contrast medium, was studied in nine dogs. Postmyelographic seizure activity, motor evoked potentials, and rectal temperatures were monitored, and myelographic quality was subjectively evaluated. The results were compared with data from eight dogs that had metrizamide myelography. The iopamidol group had fewer seizures ( p < 0.01) but exhibited no difference in motor evoked potential or rectal temperature recordings. Myelographic quality was similar for iopamidol and metrizamide. The study suggests that iopamidol was less neurotoxic than metrizamide for canine cervical myelography.     

METRIZAMIDE MYELOGRAPHY OF THE EQUINE CERVICAL SPINE

Case histories of 14 horses with pelvic limb ataxia requiring myelography were reviewed. Because differential diagnosis requires radiography, comparisons of lesion location, radiographic techniques, and lesion patterns were studied. Survey radiography and myelography were performed under general anesthesia, with recumbent-lateral and flexed-lateral views of the carnial and caudal cervical spine. Metrizamide was the myelographic contrast medium. Assessment of radiography as a diagnostic aid for cervical vertebral instability and cervical stenotic myelopathy was made through the comparison of survey radiographs and myleograms, in nonflexed and flexed positions, using these criteria: width of dorsal and ventral columns of contrast medium, compression of intervertebral disc spaces, presence or absence of bone proliferation at articular facets, remodeling secondary to vertebral instability. Radiography was an adequate diagnostic aid for cervical vertebral instability and cervical stenotic myelopathy. Distribution of lesions showed C_3–4 most common, with C_2–3 and C_4–5 following.     

HEMATOMYELIA SECONDARY TO LUMBAR CEREBROSPINAL FLUID ACQUISITION IN A DOG

A 2-year-old male (Hungarian Vizsla) was evaluated for progressive discomfort of possible spinal origin. A minimum data base, thoracolumbar magnetic resonance (MR) imaging examination and electrophysiologic investigation were all normal. Cerebellomedullary and lumbar cerebrospinal fluid (CSF) was collected. The fluid was unremarkable except for elevated total protein. Shortly, thereafter, the dog had progressive neurologic deterioration referable to a caudal lumbar spinal cord lesion. In a repeated MR examination there was a well-circumscribed intramedullary lesion at the site where lumbar CSF was collected. The signal characteristics of the lesion were compatible with subacute hemorrhage, which was confirmed to be hematomyelia at the time of successful decompressive surgery.     

EFFECTS OF POSTMYELOGRAPHIC REMOVAL OF METRIZAMIDE IN DOGS

Using a paired crossover trial, the effects of postmyelographic removal of metrizamide injected via the cerebellomedullary cistern were studied in 16 normal dogs. Each animal received a routine and a withdrawal myelogram. Seizure activity, changes in spinal evoked motor potentials and body temperature were measured following each myelogram. The amount of metrizamide removed was determined by densitometrically analyzing radiographs of cerebrospinal fluid/metrizamide aliquots recovered during the withdrawal procedure. There was a significant decrease in the number of seizures for withdrawal versus nonwithdrawal myelography (p < 0.01). The mean amount of metrizamide withdrawn per dog was 29% of the total injected.     

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.     

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.     

CEREBROSPINAL FLUID SIGNAL-VOID SIGN IN DOGS

The cerebrospinal fluid signal-void sign is an observable signal loss from cerebrospinal fluid (CSF), especially on T2-weighted magnetic resonance (MR) images. In people, this sign is attributed to rapid CSF flow or turbulence from arterial pulsations and occurs more frequently with reduced intracranial compliance. The purposes of this study were to describe the CSF signal-void sign, document whether a similar sign occurs in dogs and investigate associations between it and other conditions. The sample population consisted of 327 dogs admitted for neurocranium evaluation using a 0.2 T system. Review of the medical records and MR images was performed to characterize the presence and location of a CSF signal-void sign, ventricular size, syringomyelia, and other lesions. A CSF signal-void sign was detected in at least the mesencephalic aqueduct in 59/327 (18.0%) dogs, including some with no morphologic brain abnormality. The majority of these dogs (45/59% or 76%) weighed <15 kg. In two other dogs, a CSF signal-void sign was detected only in a cervical syrinx. In dogs weighing >15 kg, a CSF signal-void sign was seen with various conditions. In 137/327 (41.9%) dogs weighing <15 kg, the presence of a CSF signal-void sign in the aqueduct (45 dogs) was associated with syringomyelia ( P =0.0468) and increased ventricular size ( P =0.0054): syringomyelia also was associated with increased ventricular size ( P =0.0009). In conclusion, a CSF signal-void sign was seen in dogs with various conditions. In small-breed dogs, a CSF signal-void sign in the aqueduct was associated with ventricular enlargement and syringomyelia.     

A PROSPECTIVE CLINICAL TRIAL COMPARING METRIZAMIDE AND IOHEXOL FOR EQUINE MYELOGRAPHY

A prospective clinical trial comparing adverse postmyelographic effects and myelographic quality of metrizamide and iohexol was conducted. Using a predetermined, randomized assignment, 24 horses exhibiting neurologic signs were administered either metrizamide (180 mgl/ml) or iohexol (180 mgl/ml) via cerebellomedullary puncture. Each horse was evaluated postmyelographically for adverse effects. Myelographic quality was assessed by a numerical scoring method. Adverse effects were observed more frequently with metrizamide (21) compared with iohexol (6) myelography (p < 0.05). Seizures, intensification of preexisting neurologic signs and prolonged anesthetic recovery were the most common complications after myelography. There was no difference in myelographic quality (p > 0.05). We conclude that iohexol is safer than metrizamide for equine myelography and that quality myelograms can be obtained with either contrast medium.     

METRIZAMIDE MYELOGRAPHY IN FIVE DOGS AND TWO CATS WITH SUSPECTED SPINAL CORD NEOPLASMS

Metrizamide myelography was used in five dogs and two cats with signs of spinal cord disease. The history, clinical signs, cerebrospinal fluid examination, and myelography supported a presumptive diagnosis of spinal cord neoplasia in all seven animals. Myelography demonstrated a deviation of the subarachnoid space in each of them. Five of the animals had an expansile intramedullary spinal cord lesion causing thinning and peripheral deviation of the subarachnoid space. Two had extramedullary lesions causing a central deviation of the subarachnoid space. Spinal cord tumors in six of the seven animals were confirmed by necropsy or surgical excision and histopathologic examination. In the seventh animal, a spinal cord fungal grapuloma was diagnosed by necropsy.     

ASSOCIATIONS BETWEEN CARDIOPULMONARY VARIABLES AND THE CEREBROSPINAL FLUID SIGNAL-VOID SIGN IN SMALL-BREED DOGS

The cerebrospinal fluid (CSF) signal-void sign is a CSF signal loss, especially on T2-weighted magnetic resonance (MR) images. The CSF signal-void sign is often seen in small dogs with hydrocephalus and syringomyelia. In people, this sign is attributed to high velocity or turbulent CSF flow resulting from normal arterial pulsations, but is more pronounced in hydrocephalic patients with reduced intracranial compliance. If dogs are similar, then detection of this sign might be influenced by cardiovascular variables affected by anesthesia or related to intracranial compliance (e.g., blood pressure) or that affect CSF flow (e.g., heart rate). Therefore, the purpose of this study was to investigate whether the CSF signal-void sign is associated with these cardiovascular variables. The sample population consisted of 53 small-breed (<15 kg) anesthetized dogs undergoing spin echo, T2-weighted MR imaging of the neurocranium. Heart rate, blood pressure (systolic, mean, diastolic, pulse), and end-tidal CO₂ were recorded and dogs were grouped as having a CSF signal-void sign in the mesencephalic aqueduct (19/53) or not (34/53). Normality was confirmed and t -tests used. No statistical difference was detected between groups for any of the cardiovascular variables. However, the sample size was too small to accept the null hypothesis that no difference existed between groups for any of the variables assessed. Therefore, although it is uncertain whether the investigated variables alter the frequency of detecting a CSF signal-void sign, any possible relationship does not appear strong.     

USE OF COMPUTED TOMOGRAPHY AND COMPUTED TOMOGRAPHIC MYELOGRAPHY FOR ASSESSMENT OF SPINAL TUMORAL CALCINOSIS IN A DOG

Spinal tumoral calcinosis is reported in a Berner sennenhund puppy. The condition was manifested clinically as a non-ambulatory tetraparesis associated with neck pain. On survey radiographs there was a focal calcified mass at the atlantoaxial articulation. Computed tomography and computed tomographic myelography gave additional information on the extent of the mass and on the degree of spinal cord compression. The mass was removed surgically and the dog made a complete recovery.     

STANDING MYELOGRAPHY IN SIX ADULT HORSES

Standing myelography was conducted in six neurologically normal adult horses. Myelograms were performed without general anesthesia or tranquilization. Four horses were premedicated orally with 2.2 milligrams/kilogram (mg/kg) of phenobarbital 16 hours and 4 hours prior to myelography to raise their seizure threshold. One-hundred milliters (ml) of cerebral spinal fluid (CSF) was withdrawn from the lumbosacral space prior to injection. Approximately 100 ml of technical grade metrizamide * was injected into the subarachnoid space via a lumbosacral tap. After injection the horse's head was lowered for approximately 10 minutes to facilitate cranial movement of the metrizamide. Lateral cervical radiographs were taken in a standing position. Filling of the subarachnoid space in the cranial cervical region was good to excellent in five horses. In one horse there was poor definition of the cranial cervical region. There was good to excellent filling of the subaranoid space in the caudal cervical region in all six horses. Reactions to metrizamide injection varied. The most severe reaction was generalized seizure.     

MAGNETIC RESONANCE IMAGING FINDINGS IN 25 DOGS WITH INFLAMMATORY CEREBROSPINAL FLUID

To describe the signs that may be associated with intracranial inflammatory conditions, magnetic resonance (MR) images of 25 dogs that had inflammatory cerebrospinal fluid (CSF) were mixed with those of a control group of 40 dogs that had CSF negative for inflammatory disease and reviewed without knowledge of the clinical signs or diagnosis. CSF was considered inflammatory if the protein level was > 0.25 g/l and the white cell count was > 5 mm(-3). Abnormalities were found by MR imaging in 19 (76%) dogs with inflammatory CSF. Two dogs had focal lesions, 10 had multifocal lesions, and seven had diffuse lesions. Lesions affected all divisions of the brain. Mass effect was identified in seven (28%) dogs, including one that had a choroid plexus carcinoma. Lesions were hyperintense in T2-weighted images in 18 dogs and hypointense in T1-weighted images in six dogs. Multifocal or diffuse intraaxial lesions that were hyperintense in T2-weighted images were observed in 17 (68%) dogs with inflammatory CSF. Administration of gadolinium resulted in enhancement of intraaxial lesions in nine (36%) dogs and enhancement of meninges in seven (28%) dogs. Six (24%) dogs with inflammatory CSF had images interpreted as normal.     

COMPARISON BETWEEN MAGNETIC RESONANCE IMAGING ESTIMATES OF EXTRACRANIAL CEREBROSPINAL FLUID VOLUME AND PHYSICAL MEASUREMENTS IN HEALTHY DOGS

Dosages for myelography procedures in dogs are based on a hypothetical proportional relationship between bodyweight and cerebrospinal fluid (CSF) volume. Anecdotal radiographic evidence and recent studies have challenged the existence of such a defined relationship in dogs. The objectives of this prospective cross‐sectional study were to describe CSF volumes using magnetic resonance imaging (MRI) in a group of clinically healthy dogs, measure the accuracy of MRI CSF volumes, and compare MRI CSF volumes with dog physical measurements. A sampling perfection with application optimized contrast using different flip‐angle evolution MRI examination of the central nervous system was carried out on 12 healthy, male mongrel dogs, aged between 3 and 5 years with a bodyweight range of 7.5–35.0 kg. The images were processed with image analysis freeware (3D Slicer) in order to calculate the volume of extracranial CSF. Cylindrical phantoms of known volume were included in scans and used to calculate accuracy of MRI volume estimates. The accuracy of MRI volume estimates was 99.8%. Extracranial compartment CSF volumes ranged from 20.21 to 44.06 ml. Overall volume of the extracranial CSF increased linearly with bodyweight, but the proportional volume (ml/bodyweight kilograms) of the extracranial CSF was inversely proportional to bodyweight. Relative ratios of volumes in the cervical, thoracic, and lumbosacral regions were constant. Findings indicated that the current standard method of using body weight to calculate dosages of myelographic contrast agents in dogs may need to be revised.     

IOHEXOL AND IOPAMIDOL MYELOGRAPHY IN THE DOG: A CLINICAL TRIAL COMPARING ADVERSE EFFECTS AND MYELOGRAPHIC QUALITY

In a blind clinical trial, adverse effects after iohexol and iopamidol myelography were evaluated in 151 dogs. Eighty-one dogs were given iohexol (240 mgI/ml) and 70 dogs were given iopamidol (200 mgI/ml) by pre-determined assignment. Each dog was evaluated postmyelographically for seizures, hyperthermia, prolonged recovery from anesthesia and intensification of pre-existing neural signs. Myelographic quality was evaluated with a subjective scoring method. In comparing iohexol and iopamidol groups, there was not a statistically significant difference in the incidence of adverse effects or in myelographic quality. Iopamidol and iohexol appeared to be equally efficacious for routine canine myelography.     

A COMPARISON OF TWO-DIMENSIONAL ULTRASONOGRAPHY AND RADIOGRAPHY FOR THE DETECTION OF SMALL AMOUNTS OF FREE PERITONEAL FLUID IN THE DOG

The detection of small amounts of free peritoneal fluid in the canine patient can be a diagnostic dilemma. Ultrasonography and radiography have been advocated to detect intraabdominal fluid not detectable by physical exam. The purpose of this study was to determine the more sensitive method for detecting small amounts of free peritoneal fluid. Ultrasound examinations and radiographs were performed after increments (1 ml/lb body weight) of fluid were injected intraperitoneally. Ultrasonography detected fluid in one animal at 2 ml/lb. AH other animals had fluid detected at 3 ml/lb. With radiographs fluid could be detected with a high degree of accuracy at 4 ml/lb. The lateral view was more accurate than the ventrodorsal view in detecting fluid. The authors concluded that Ultrasonography is more sensitive than radiography and is the method of choice to detect small amounts of free peritoneal fluid.     

COMPARISON OF RADIOGRAPHY, MYELOGRAPHY AND COMPUTED TOMOGRAPHY FOR THE EVALUATION OF CANINE VERTEBRAL AND SPINAL CORD TUMORS IN SIXTEEN DOGS

Radiographic, myelographic and computed tomographic (CT) studies from sixteen dogs with histologically diagnosed vertebral or spinal cord neoplasia (seventeen lesions) were retrospectively evaluated. Radiographs were compared with CT images to evaluate vertebral bony changes (bone production, lysis or both). Myelographic and CT images were evaluated to separate lesions into one of three categories, extradural, intradural/extramedullary, or intramedullary. These findings were compared to histologic tumor type from surgical or necropsy samples. Histologically, seven lesions were vertebral tumors and were classified as extradural lesions; ten lesions were spinal cord tumors of which eight were classified as intradural/extramedullary and two as intramedullary. Using CT, the amount of bony change associated with extradural lesions was greater than or equal to the amount of bony change visualized using radiographs. Myelography more correctly differentiated between intradural/ extramedullary and intramedullary lesions than did CT, although three open diagnoses detracted from the CT results. This study suggests that when evaluating extradural lesions, the amount of bony change was better visualized using CT than survey radiographs. Myelography was better when compared to CT for classifying spinal cord lesions, however, standardization of the CT imaging protocol may help determine the specific clinical indications for using CT in dogs with suspected vertebral or spinal cord tumors.     

SUBDURAL INJECTION OF CONTRAST MEDIUM DURING CERVICAL MYELOGRAPHY

Three patients (1 dog, 2 horses) ae described where myelography was complicated, purportedly by injection of contrast medium into the meninges superficial to the subarachnoid space. Contrast medium injected in this locationin a cadaver tended ot accoumulate dorsally within the vertebarel canal, deep to the dura mate but superficial to the subarachnoid space. The ventral marginof the pooled contrast medium had a wavy or undulating margin and the dorsal margin was smooth. Pooled contrast medium was believed to be sequestered within the structurally weak dural border cell layer between the dura mater and arachnoid membrane, or so-called subdural space.