IMAGING DIAGNOSIS—DEGENERATIVE INTRASPINAL CYST ASSOCIATED WITH AN INTERVERTEBRAL DISC

A 6-year-old neutered male Rottweiler had chronic episodic signs of thoracolumbar pain and inability to stand that did not improve after rest and nonsteroidal antiinflammatory medication. In magnetic resonance images, an extradural mass was identified between the spinal cord and the T13/L1 intervertebral disc; the mass was compressing the cord in a dorsoventral direction. The lesion had a low signal intensity rim that enhanced slightly after gadolinium administration, and contents with similar signal intensity to cerebrospinal fluid. The lesion was removed surgically by severing its attachments to the annulus fibrosus. The histologic diagnosis was degenerative intraspinal cyst. The origin of such cysts, and their relationship to synovial and ganglion cysts is discussed.     

MAGNETIC RESONANCE IMAGING OF CANINE DEGENERATIVE LUMBAR SPINE DISEASES

Degenerative lumbar spine diseases, i.e., sacrolumbar stenosis, intervertebral disk degeneration and protrusion and spondylosis deformans of the canine lumbar spine were studied in eleven canine patients and three healthy controls using radiography and 0.02 T and 0.04 T low field magnetic resonance imaging. The T1 and T2 weighted images were obtained in sagittal and transverse planes. The loss of hydration of nucleus pulposus, taken as a sign of degeneration in the intervertebral disks, could be evaluated in both T1 and T2 weighted images. As a noninvasive method magnetic resonance imaging gave more exact information about the condition of intervertebral disks than did radiography. Sacrolumbar stenosis and compression of the spinal cord or cauda equina and surrounding tissue could be evaluated without contrast medium.     

CORRELATIVE IMAGING FINDINGS IN SEVEN DOGS AND ONE CAT WITH SPINAL ARACHNOID CYSTS

Information regarding 7 dogs and 1 cat with a spinal arachnoid cyst is presented. All patients were evaluated with survey radiographs and myelography. Computed tomography (CT) following myelography, magnetic resonance (MR) imaging, and sonography, were used in some of the patients. These imaging techniques were evaluated to determine their efficacy in diagnosing arachnoid cysts, ascertaining the extent and internal cyst architecture and detecting associated spinal cord abnormalities. Survey radiographs were nondiagnostic in all patients. Myelographically, the arachnoid cyst was visible in all patients, with partial blockage to flow of contrast medium. CT provided additional information on localization and lateralization of the cyst, and allowed measurement of the degree of spinal cord compression. MR imaging enabled identification of an associated syringomyelia. Sonography was useful for defining the cyst wall and characterizing the internal architecture of the cyst cavity and adjacent spinal cord. Measurements of the degree of spinal cord compression could be made and were similar to measurements made from CT. Additionally, sonography was considered a useful technique for orientating the surgeon to the location and extent of the cyst. In the absence of the availability of CT or MR imaging for evaluating patients with an arachnoid cyst, sonography is considered a valuable technique for directly assessing the spinal cord for associated disease. Decompressive surgery was performed on 4 dogs and 1 cat, all with successful outcomes.     

IMAGING DIAGNOSIS—MAGNETIC RESONANCE IMAGING FINDINGS OF AN INTRACRANIAL EPIDURAL TUBERCULOMA IN A DOG

Magnetic resonance (MR) imaging is highly sensitive for detecting tuberculomas in human patients but the specificity of the MR imaging features is low. Misdiagnosis with intracranial neoplasia is common, especially with dural‐based lesions or lesions located in the epidural space. We describe the MR imaging characteristics of an intracranial epidural tuberculoma caused by Mycobacterium tuberculosis infection in a dog. The intracranial mass and skull flat bone lysis and erosion are similar to those described in human caseating tuberculomas and can mimic intracranial neoplastic disease.     

MAGNETIC RESONANCE IMAGING OF A MEDULLARY DERMOID CYST WITH SECONDARY HYDROCEPHALUS IN A DOG

Magnetic resonance images were acquired of the brain of a 7-year-old male Golden Retriever with hydrocephalus secondary to a medullary lesion. Images were acquired prior to and 4 weeks following surgical treatment for the hydrocephalus, and the dog was euthanased following the second imaging session. The MR images demonstrated a medullary lesion with patchy but predominantly hyperintense signal with both T1- and T2-weighting, within which small areas of low signal were scattered. There was little edema associated with this lesion and no enhancement with gadolinium. Postmortem examination revealed the medullary mass to be a dermoid cyst. Several small nodular lesions were identified within the central nervous system on the magnetic resonance images whose origin was uncertain on postmortem examination.     

IMAGING DIAGNOSIS: CRANIAL CERVICAL INTRASPINAL SCHWANNOMA IN A DOG

A 3‐year‐old, intact female Golden Retriever was presented with acute tetraplegia. Neurologic examination was consistent with a C1–C5 myelopathy. On magnetic resonance (MR) imaging a well‐defined, extradural mass was detected within the spinal canal at the level of C1–C2. The mass was isointense to normal spinal cord gray matter on T1‐weighted (T1W) images, hyperintense on T2‐weighted (T2W), and gradient‐echo (GE) images, and enhanced homogeneously after intravenous contrast administration. MR imaging features were mainly consistent with a meningioma. Surgical treatment was refused by the owners, and the dog was euthanized. Postmortem examination demonstrated that the intraspinal mass was a schwannoma.     

MAGNETIC RESONANCE IMAGING OF THE CAUDAL LUMBAR AND LUMBOSACRAL SPINE IN 13 DOGS (1990–1993)

The caudal lumbar and lumbosacral spine of 13 dogs with pain or neurologic deficits were evaluated using magnetic resonance imaging (MRI). Spin echo T1, proton density, and T2 weighted and gradient echo T2* imaging sequences were utilized. MRI permitted direct, multiplanar, tomographic visualization of the spine facilitating evaluation of all components of degenerative caudal lumbar and lumbosacral stenosis. Abnormalities detected included intervertebral disc degeneration, intervertebral disc protrusion involving both the vertebral canal and intervertebral foramina, articular process osteophytosis, articular process fracture, nerve root impingement by spondylosis deformans, and the presence of low signal material within the vertebral canal of 2 dogs with recurrent pain following previous spinal surgery. In all 7 dogs treated surgically, MRI findings were consistent with surgical findings.     

MAGNETIC RESONANCE IMAGING OF THE CERVICAL SPINE IN 27 DOGS

The cervical spine of 27 dogs with cervical pain or cervical myelopathy was evaluated using magnetic resonance imaging (MRI). Spin echo T1, T2, and post-contrast T1 weighted imaging sequences were obtained with a 0.5 Tesla magnet in 5 dogs and a 1.5 Tesla magnet in the remaining 22 dogs. MRI provided for visualization of the entire cervical spine including the vertebral bodies, intervertebral discs, vertebral canal, and spinal cord. Disorders noted included intervertebral disc degeneration and/or protrusion (12 dogs), intradural extramedullary mass lesions (3 dogs), intradural and extradural nerve root tumors (3 dogs), hydromyelia/syringomyelia (1 dog), intramedullary ring enhancing lesions (1 dog), extradural synovial cysts (1 dog), and extradural compressive lesions (3 dogs). The MRI findings were consistent with surgical findings in 18 dogs that underwent surgery. Magnetic resonance imaging provided a safe, useful non-invasive method of evaluating the cervical spinal cord.     

MAGNETIC RESONANCE IMAGING AND COMPUTED TOMOGRAPHY CHARACTERISTICS OF INTRACRANIAL INTRA-ARACHNOID CYSTS IN 6 DOGS

Magnetic resonance imaging (MRI) and computed tomographic imaging (CT) characteristics of intracranial intra-arachnoid cysts in six dogs are described.Of the six dogs, three were less than one year of age and 4 were males. Five of the six dogs weighed less than 11 kg. Five cysts were located in the quadrigeminal cistern.On CT images, the intracranial intra-arachnoid cysts had sharply defined margins, contained fluid isodense to CSf and did not enhance following IV administration of contrast. On MRI images, the intracranial intra-arachnoid cysts were extra-axial, contained fluid isointense with CSF and did not enhance following IV contrast. While spinal arachnoid cysts of dogs have been reported in the literature, other than the six dogs contained in this report, intracranial intra-arachnoid cysts have not to our knowledge been described in animals. These six dogs have a similar age, sex, arachnoid cysts.     

IMAGING FINDINGS IN DOGS WITH CAUDAL INTERVERTEBRAL DISC HERNIATION

The radiographic and magnetic resonance imaging (MRI) findings for four dogs with herniation of the Cd1–Cd2 intervertebral disc are described. All dogs were 7 years of age at the time of presentation, with one neutered male and three neutered females. Breeds included one Beagle, one Bassett hound, and two large, mixed breed dogs. All dogs had tail pain on manipulation, two had pain during defecation, and two maintained an abnormal tail position. Three dogs had radiographs in which mineralization within the disc space was apparent. Two of these dogs also had mineralization within the vertebral canal. Three dogs underwent MRI, which was characterized by varying degrees of disc herniation and nerve root compression at Cd1–Cd2. Mobility may be a factor predisposing to disc herniation in the cranial aspect of the caudal spine. We documented that caudal disc herniation does occur occasionally in dogs and that radiography and MRI may be used to identify this disease. Caudal intervertebral disc herniation should be considered as a differential for dogs with caudal vertebral pain, pain with tail manipulation, pain during defecation, or abnormal tail carriage.     

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.     

IMAGING DIAGNOSIS—MAGNETIC RESONANCE IMAGING FEATURES OF A CEREBRAL HEMANGIOBLASTOMA IN A DOG

The magnetic resonance (MR) imaging features of a cerebral hemangioblastoma in a 9‐year‐old dog are described. Imaging revealed a well‐defined contrast‐enhancing lesion of the rostral forebrain that appeared extraparenchymal. Histopathology of the excised mass showed clusters of small blood vessels interspersed with interstitial cells staining positive for neuronal specific enolase, features consistent with a cerebral hemangioblastoma; the mass also appeared intraparenchymal after further immunohistochemistry study. This neoplasm should be considered a rare differential diagnosis for intracranial masses in dogs.     

MAGNETIC RESONANCE IMAGING FEATURES OF EXTRADURAL HEMATOMAS ASSOCIATED WITH INTER VERTEBRAL DISC HERNIATION IN A DOG

Myelography and magnetic resonance imaging (MRI) were performed on a 4-year-old neutered female Rottweiler with bilateral pelvic limb paresis. On the myelogram, there was extradural spinal cord compression at the level of the T11-12 intervertebral disc. Inadvertent placement of epidural contrast medium also allowed identification of a 1-cm circular filling defect in the epidural space dorsal to the compressed spinal cord. MRI showed partial loss of the nucleus pulposus signal of the T11-12 disc, a focal signal void within the vertebral canal at T11 compatible with a free disc fragment, and extradural masses compressing the spinal cord at T10-11 and T11-12. Hemorrhage within the masses was confirmed on T2*-weighted images. A mixture of hematoma and mineralized disc material was found at surgery, and there was no histopathologic evidence of neoplasia. In this article, the appearance on MRI of hemorrhage associated with intervertebral disc herniation is discussed.     

MAGNETIC RESONANCE IMAGING CHARACTERISTICS OF ASCENDING HEMORRHAGIC MYELOMALACIA IN A DOG

A 4-year-old neutered female terrier-cross was evaluated for an acute onset of paraplegia. Utilizing magnetic resonance (MR) imaging, the cause of the neurologic deficits was determined to be a lumbar intervertebral disc extrusion. The MR study additionally demonstrated parenchymal hyperintensity on T2-weighted images and similarly located diffuse hypointensity on gradient echo images, cranial and caudal to the compressive extradural lesion. Hemorrhagic myelomalacia was suspected based on these MR characteristics, which was subsequently confirmed surgically and histopathologically.     

MAGNETIC RESONANCE IMAGING OF OTITIS MEDIA IN A DOG

Otitis media/interna was diagnosed in a 20-month-old German shepherd with the assistance of magnetic resonance (MR) imaging. The MR images were acquired primarily to exclude a brain lesion responsible for vestibular signs. No brain lesion was detected, but obvious signs of chronic changes in the left bulla and external ear canal were confirmed. Thickening of the epithelium and soft tissue surrounding the external ear canal and a laminated appearance of high and low T2 intensities in the tympanic bulla's mucosa were present. The hypointense lines were suspected to be fibrous tissue, indicating chronic changes. This report suggests that MR imaging may serve as a useful imaging tool for otitis media and that it supplies information not obtained with radiography or computed tomography.     

IMAGING DIAGNOSIS—MAGNETIC RESONANCE IMAGING FEATURES OF METASTATIC CEREBRAL LYMPHOMA IN A DOG

We describe histopathologically confirmed intracranial metastasis of cutaneous lymphoma. In magnetic resonance (MR) images there was a heterogeneous, contrast‐enhancing, extraaxial mass in the right parietal and piriform lobes at the level of the optic chiasm. Our MR imaging findings are consistent with reports in humans in that lymphoma masses have indistinct borders that are iso‐ to hyperintense relative to adjacent gray matter on T2‐weighted images. Our report varies from findings in humans in that the mass was extraaxial, whereas masses reported in humans are intraaxial. Contrast enhancement can be heterogeneous, as in our report, or homogeneous.     

MAGNETIC RESONANCE IMAGING FEATURES OF PARASPINAL INFECTION IN THE DOG AND CAT

The magnetic resonance (MR) imaging findings in 22 dogs and two cats with confirmed paraspinal infection of the thoracolumbar spine were characterized. These findings included extensive T2-hyperintense areas (24/24), abscessation (20/24), mild inherent T1-hyperintensity of muscle and abscesses (18/24), and postcontrast enhancement (24/24). Changes involved the vertebral canal in four patients. The longus coli muscles were affected in one cat. Thoracolumbar changes in the remaining 23 patients involved the iliopsoas and epaxial muscles in 23/23 and 19/23 patients, respectively. Iliopsoas muscle abscessation was unilateral in 12/23, and bilateral in 6/24 patients. Abscessation involved both epaxial and iliopsoas muscles in 2/23 patients and the epaxial muscles alone in one patient. A contrast-enhancing sinus tract within the deep thoracolumbar fascia was present in 10/23 patients. Lumbar vertebrae periosteal reactions were identified in 19/23 patients on MR images compared with 15/17 patients with radiography. A focal area of signal void suspected to represent foreign material was seen in 5/23 patients but foreign material was actually found in only two of these five. There was no recurrence of clinical signs following MR imaging and revision surgery. MR imaging permits the severity and extent of changes associated with paraspinal infection to be characterized and allows the location, number and any communication of sinus tracts to be documented.     

IMAGING DIAGNOSIS—THROMBOSED ORBITAL VARIX IN A DOG

A 9‐week‐old female Rhodesian Ridgeback presented with exophthalmos following minor blunt trauma to the left orbital area. Ocular ultrasound showed an extraconal retrobulbar mass ventromedial to the left globe. Magnetic resonance (MR) imaging demonstrated a thrombosed orbital vascular malformation without intracranial extension. Doppler ultrasound features of nonpulsatile slow flow were consistent with an orbital varix. Contrast‐enhanced dynamic time‐resolved and high‐resolution MR angiography demonstrated the varix arose from the anastomotic branch of the dorsal and ventral external ophthalmic veins. Conservative management led to a positive outcome defined as a visual eye and nearly normal cosmetic appearance at 8‐month follow‐up.     

COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING OF CAVERNOUS SINUS ENLARGEMENT IN A DOG WITH UNILATERAL EXOPHTHALMOS

Computed tomography (CT), magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) were performed on a dog with a two year history of unilateral exophthalmos occurring two years following head trauma. On CT images, an expansile enhancing mass was present along the right intracranial cavernous sinus and extended through the orbital fissure into the retrobulbar space. With MRI, the structure appeared as a signal void due to the presence of rapidly flowing blood. Gadolinium enhancement of the adjacent brain was not present. A vascular origin of the lesion was confirmed with MRA. Based on the CT and MRI findings, the enlarged cavernous sinus and associated ophthalmic plexus were believed to represent an arterialized aneurysm, most likely the result of traumatic arteriovenous fistulization. Treatment consisted of surgical enucleation. At the time of this report, 29 mouths later, the dog remains free of clinical signs.