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.     

INTRACRANIAL INTRA-ARACHNOID CYST WITH INTRACYSTIC HEMORRHAGE IN TWO DOGS

Clinical signs, magnetic resonance imaging (MRI) features, treatment, and outcome of two adult dogs with neurologic dysfunction resulting from hemorrhage into a quadrigeminal intracranial intra-arachnoid cyst are described. In dog 1, the cyst was hyperintense to cerebrospinal fluid (CSF) on T1-weighted MRI and hypointense to CSF on T2-weighted images. In dog 2, the cyst was isointense to CSF on T1- and T2-weighted images. Both dogs were treated with craniotomy and cyst fenestration. A large blood clot was removed from the lumen of the cyst in each dog. Dog 1 is clinically normal 3.5 years post-surgery and has a persistent cyst. Dog 2 had a good initial response to therapy but was euthanized 2.5 years post-operatively due to generalized seizures. The late onset of clinical signs in these dogs most likely resulted from hemorrhage into the cyst. Surgical fenestration and hematoma removal appear to provide a satisfactory treatment for adult dogs with an intracranial intra-arachnoid cyst and intracystic hemorrhage. Persistence of the cyst may occur in some dogs.     

Clinical and magnetic resonance imaging features of canine compressive cervical myelopathy with suspected hydrated nucleus pulposus extrusion

Objective : To describe clinical and magnetic resonance imaging features in dogs with compressive cervical myelopathy due to acute suspected hydrated nucleus pulposus extrusion. Design : Retrospective case series. Animals : Ten dogs with compressive cervical myelopathy caused by acute suspected hydrated nucleus pulposus extrusion. Materials and Methods : Medical records and magnetic resonance images of dogs evaluated from 2005 through 2010 were reviewed. The inclusion criteria were clinical signs compatible with cervical myelopathy, magnetic resonance imaging of the spine performed within 48 hours after onset, magnetic resonance imaging findings consistent with compressive suspected hydrated nucleus pulposus extrusion, complete medical records and follow‐up information. Results : Six dogs were presented with acute onset tetraplegia and four dogs with acute onset of nonambulatory tetraparesis. Compromised respiratory function was present in three dogs. Compressive suspected hydrated nucleus pulposus extrusion was found on magnetic resonance imaging at the C4‐C5 (n=6), C3‐C4 (n=3) and C5‐C6 (n=1) intervertebral disc spaces. Seven dogs underwent surgical treatment and three dogs were treated conservatively. All dogs except one regained ambulatory status within two weeks after the onset, and had a favourable outcome. Clinical Significance : Compressive myelopathy caused by acute suspected hydrated nucleus pulposus extrusion has not been reported previously and, even though neurological deficits can be severe on presentation, outcome is favourable.     

Cervical vertebral malformation-malarticulation syndrome in the Bernese mountain dog: clinical and magnetic resonance imaging features

O bjectives : To describe the clinical and magnetic resonance imaging features of cervical vertebral malformation-malarticulation in Bernese mountain dogs.
M ethods : Seven Bernese mountain dogs (four males and three females) were diagnosed with cervical vertebral malformation-malarticulation by magnetic resonance imaging. The following data were evaluated retrospectively: (1) abnormalities of the cervical vertebral column and spinal cord, (2) spinal cord compression, (3) intervertebral disc degeneration and herniation, (4) severity of clinical signs pretreatment and after treatment, (5) type of treatment and (6) outcome.
R esults : Spin echo T1-weighted and T2-weighted images disclosed multi-level, extradural compressive spinal cord lesions (ventral, dorsolateral or both) spanning from intervertebral disc spaces C3-4 to C6-7. In all seven dogs, T2-weighted images disclosed one or more intramedullary hyperintensities associated with extradural spinal cord compression. Surgery was performed in five dogs. Two dogs were managed medically. The prognosis for surgical or conservative management in Bernese mountain dogs was similar to cervical vertebral malformation-malarticulation in other breeds.
C linical S ignificance : Cervical vertebral malformation-malarticulation is an important differential diagnosis for young to middle-aged Bernese mountain dogs with a C1-5 or C6-T2 neuroanatomic localisation. Dorsolateral spinal cord compression associated with articular process hypertrophy was the most common feature of cervical vertebral malformation-malarticulation in the seven Bernese mountain dogs evaluated.     

Magnetic resonance imaging findings of hepatic encephalopathy in a dog with a portosystemic shunt

A 6-year-old ShihTzu presented with tonic-clonic cluster seizure. T2-weighted magnetic resonance (MR) images showed bilateral diffuse hyperintense lesions at the cerebral cortex with enlarged sulci. Computed tomography revealed a portosystemic shunt (PSS) and azygos continuation. Based on the clinical signs, blood examinations and diagnostic images, the dog was diagnosed with hepatic encephalopathy secondary to PSS. The neurologic signs were gradually improved after medical therapy for hyperammonemia. This is the first report of hyperintensity of the cerebral cortex on T2-weighted MR images associated with acute hepatic encephalopathy in a dog.     

BRAIN MAGNETIC RESONANCE IMAGING CHARACTERISTICS IN DOGS AND CATS WITH CONGENITAL PORTOSYSTEMIC SHUNTS

Animals with a portosystemic shunt (PSS) often have neurologic abnormalities. Diagnostic imaging, including brain magnetic resonance (MR) imaging, is not performed routinely in these animals. In this study, brain MR images were obtained in 13 dogs and three cats with a PSS, and in 15 dogs and five cats that were neurologically normal and used as controls. All animals with a PSS had widened sulci. In addition, 10 out of 13 dogs with a PSS and one out of three cats with a PSS had hyperintense focal areas in the lentiform nuclei on T1-weighted (T1W) images, which did not enhance after intravenous gadolinium. Following surgical correction of the PSS, MR imaging examinations were repeated in one dog and one cat. The hyperintensity of the lentiform nuclei had decreased. This study indicates that MR imaging findings of widened sulci and hyperintensity of the lentiform nuclei on T1W images may be found in dogs and cats with a PSS.     

Association of clinical and magnetic resonance imaging findings with outcome in dogs suspected to have ischemic myelopathy: 50 cases (2000-2006)

OBJECTIVE: To determine whether clinical signs or magnetic resonance imaging findings were associated with outcome in dogs with presumptive ischemic myelopathy. DESIGN: Retrospective case series. ANIMALS: 50 dogs. PROCEDURES: Medical records and magnetic resonance images were reviewed. A neurologic score from 1 (normal) to 5 (most severe degree of dysfunction) was assigned on the basis of neurologic signs at the time of initial examination. Follow-up information was obtained from the medical records and by means of a telephone questionnaire completed by owners and referring veterinarians. RESULTS: Median neurologic score at the time of initial examination was 3 (range, 2 to 5). Median follow-up time was 584 days (range, 4 to 2,090 days). Neurologic score at the time of initial examination and extent of the lesion seen on magnetic resonance images (quantified as the lesion length-to-vertebral length ratio and as the percentage cross-sectional area of the lesion) were significantly associated with outcome. Sensitivity of using a lesion length-to-vertebral length ratio > 2.0 or a percentage cross-sectional area of the lesion > or = 67% to predict an unsuccessful outcome was 100%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that severity of neurologic signs at the time of initial examination and extent of the lesions seen on magnetic resonance images were associated with outcome in dogs with ischemic myelopathy.     

MRI features of CNS lymphoma in dogs and cats

The magnetic resonance (MR) imaging features of central nervous system lymphoma in eight dogs and four cats are described. Intracranial lesions affected the rostrotentorial structures in six dogs and caudotentorial structures in two cats. Lesions affected the spinal cord in two dogs and in two cats. One dog and one cat with intracranial lymphoma had signs of local extracranial extension and lymphadenopathy. Lesions were considered extraparenchymal in four dogs and three cats, intraparenchymal in two dogs and one cat, and appeared to have both intra- and extraparenchymal components in two dogs. All lesions were hyperintense in T2-weighted images when compared to white matter, most were hypointense in T1-weighted images (7/12), and most were hyperintense in fluid-attenuated inversion recovery (FLAIR) images (5/9). When compared to grey matter, these lesions appear either isointense (5/12) or hyperintense (7/12) on T2-weighted images, half of them were hypointense in T1-weighted images (6/12), and most were isointense in FLAIR images (7/9). Lesion margins were usually indistinct in T2-weighted images (10/12) and had perilesional hyperintensity in FLAIR images (7/9). The majority of lesions (10/12) had abnormal meninges around the lesion and half (6/12) had generalized contrast enhancement. Mass effect was evident in all lesions. Although not specific, when combined with the history and neurologic signs, MR features aid presumptive diagnosis that should be confirmed by cytology or histopathology.     

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.     

Long-term functional outcome of dogs with severe injuries of the thoracolumbar spinal cord: 87 cases (1996-2001)

OBJECTIVE: To determine long-term (> 6 months) outcome of dogs with paraplegia and loss of hind limb deep pain perception (DPP) resulting from intervertebral disk herniation or trauma. DESIGN: Retrospective study. ANIMALS: 87 dogs. PROCEDURE: Outcome was determined as successful or unsuccessful. The association of neuroanatomic localization, breed, age, weight, sex, and (for dogs with intervertebral disk herniation) speed of onset of signs and duration of paraplegia prior to surgery with outcome was evaluated. Owners were contacted by telephone to identify long-term health problems. RESULTS: Nine of 17 dogs with traumatic injuries were treated, and 2 regained the ability to walk; none of the 17 dogs regained DPP. Sixty-four of 70 dogs with intervertebral disk herniation underwent surgery; 9 (14%) were euthanatized within 3 weeks after surgery (7 because of ascending myelomalacia), 37 (58%) regained DPP and the ability to walk, 7 (11%) regained the ability to walk without regaining DPP, and 11 (17%) remained paraplegic without DPP. Outcome was not associated with any of the factors evaluated, but speed of recovery of ambulation was significantly associated with body weight and age. Fifteen (41%) and 12 (32%) dogs that regained DPP had intermittent fecal and urinary incontinence, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that the prognosis for paraplegic dogs without DPP because of trauma was guarded, while dogs with disk herniation had a better chance of recovering motor function. A third of the dogs that recovered motor function had intermittent incontinence. Persistent loss of DPP did not preclude recovery of motor function, but such dogs remained incontinent.     

Influence of intervertebral disc fenestration at the herniation site in association with hemilaminectomy on recurrence in chondrodystrophic dogs with thoracolumbar disc disease: a prospective MRI study

Objective— To describe the influence of fenestration at the disc herniation site on recurrence in thoracolumbar disc disease of chondrodystrophoid dogs.
Study Design— Prospective clinical study.
Animals— Chondrodystrophic dogs (n=19).
Methods— Dogs were divided into 2 groups: group 1 (9 dogs) had thoracolumbar disc extrusion (Hansen type I) treated by hemilaminectomy and concomitant fenestration of the affected intervertebral disc and group 2 (10 dogs) had hemilaminectomy without fenestration. All dogs had 3 magnetic resonance imaging (MRI) examinations: preoperatively, immediately postoperatively to assess removal of herniated disc material, and again 6 weeks after surgery.
Results— There were 13 male and 6 female dogs; mean age, 7.1 years. Thoracolumbar disc herniation was confirmed with MRI. Immediate post surgical MRI revealed that the herniated disc removal was complete in all but 1 dog and that fenestration did not lead to complete removal of nucleus pulposus within the intervertebral disc space. On the 3rd MRI examination, none of the group 1 dogs had further disc material herniation at the fenestrated site. Six of the 10 group 2 dogs had a recurrence of herniation leading to clinical signs in 3 dogs (pain in 2 dogs, paresis in 1 dog).
Conclusion— In thoracolumbar disc herniation, fenestration of the affected intervertebral disc space prevents further extrusion of disc material.
Clinical Relevance— Fenestration reduces the risk of early recurrence of disc herniation and associated postoperative complications.     

MRI features can help to confirm a diagnosis of progressive myelomalacia,but may not be accurate in dogs lacking characteristic clinical signs at the time of imaging

Progressive myelomalacia (PMM) is a fatal sequela of acute thoracolumbar intervertebral disc extrusion in dogs, with unpredictable onset in the days after the inciting injury. No single reliable diagnostic test is currently available. Magnetic resonance imaging (MRI) features such as T2-weighted spinal cord hyperintensity and loss of subarachnoid signal in a half-Fourier single-shot turbo spin echo (HASTE) sequence have been associated with PMM, but are sometimes present in other dogs with severe deficits. Magnetic resonance imaging findings in 22 dogs with a clinical or histopathologic diagnosis of PMM and 38 deep pain-negative paraplegic dogs were compared in a retrospective case-control study. Length of T2-weighted hyperintense spinal cord change and HASTE signal loss were significantly associated with clinically evident PMM (P = .0019 and P = .0085), however, there were no significant differences between groups when analysis was restricted to dogs not yet showing clinical signs of PMM. The PMM group also had significantly shorter compressive lesions than the control group (P = 0.026), suggesting a possible role of more severe focal pressure at the extrusion site. A segment of total loss of contrast enhancement in the venous sinuses and meninges, a feature not previously described, was more common in the PMM group and the difference approached significance (P = 0.054). Findings show that MRI features can support the diagnosis in dogs with clinical evidence of PMM, and absence of these features supports absence of PMM at time of imaging. However, their absence does not reliably differentiate dogs with imminent progressive myelomalacia from other dogs with severe deficits following intervertebral disc extrusion.     

Characteristics of magnetic resonance images of granulomatous meningoencephalomyelitis in 11 dogs

The characteristics of magnetic resonance imaging (mri) of the brains and spinal cords of 11 dogs with histologically confirmed granulomatous meningoencephalomyelitis (gme) were determined. The lesions were in the brain of eight of the dogs, in the brain and spinal cord of two, and in the spinal cord alone in one dog. A single lesion was present in four of the dogs and multiple lesions were found in six. In one dog with intracranial signs, no visible lesions could be detected on mri. No meningeal enhancement was detected in T1-weighted images post-contrast, or in fluid attenuation inversion recovery (flair) images, but there were histological lesions in the meninges in nine of the dogs. The T2-weighted images and flair sequences were characterised in all cases by hyperintensity, whereas the signal intensity of the lesions on T1-weighted images was variable. After the administration of paramagnetic contrast, some of the lesions showed no enhancement, but others showed marked patterns of enhancement. The lesions in 10 of the dogs were easily identifiable by mri and the images had several unifying characteristics, but they could not be considered disease-specific.     

SUBFASCIAL SEROMA CAUSING COMPRESSIVE MYELOPATHY AFTER CERVICAL DORSAL LAMINECTOMY

Dorsal surgical approach to the cervical vertebral canal is indicated for a variety of spinal cord diseases. Compressive myelopathy due to subfascial seroma following dorsal laminectomy has not previously been documented in dogs. We describe neurologic findings, magnetic resonance (MR) imaging characteristics and clinical outcome in a young Rottweiler experiencing this complication after a successful dorsal decompression for treatment of cervical stenotic myelopathy. MR imaging allowed detection of pockets of high signal intensity material on T2-weighted images and low signal intensity in T1-weighted images. Prompt surgical revision and drainage allowed complete recovery.     

Traumatic Intervertebral Disc Herniation with Paraplegia in a Black-Tailed Prairie Dog (Cynomys ludovicianus)

A 2-year-old castrated male black-tailed prairie dog (Cynomys ludovicianus) was presented 48 hours after peracute onset of rear limb paraplegia secondary to a traumatic incident. The prairie dog was nonambulatory in the rear legs with absent deep pain; hematuria and pollakiuria were also observed. Diagnostic imaging revealed intervertebral disc herniation with compression of the spinal cord at the L1-L2 disc spaces. Hemilaminectomy at the L1-L2 disc space was performed. After 48 hours, the prairie dog regained anal tone, and a deep pain response was noted. Azotemia developed during the course of hospitalization likely secondary to neuromuscular damage causing an obstruction in the lower urinary tract but resolved with supportive care. The prairie dog recovered complete use of its hind legs and had normal excretory function at a 3-month recheck. Practitioners should consider intervertebral disc herniation secondary to trauma as a differential diagnosis for neurologic deficits affecting the rear limbs of prairie dogs. Surgical management of intervertebral disc herniation is a viable treatment option in appropriate cases.     

Iatrogenic brainstem injury during cerebellomedullary cistern puncture

Cerebrospinal fluid collection is fundamental to the investigation of central nervous system disorders although it carries potential risks. Herein we report the clinical signs and magnetic resonance (MR) imaging findings associated with needle injury to the brainstem during cerebellomedullary cistern puncture in four dogs. Three dogs were nonambulatory tetraparetic with cranial nerve deficits and one dog had unexplained left thoracic limb paresis. In MR images, there were conspicuous T2 hyperintensities in the myelencephalon in all dogs. In T2* gradient echo images, the lesions were hypointense in two dogs with multiple cranial nerve deficits, and hyperintense in another dog. One dog was euthanized due to sudden neurologic deterioration 12 days later, one died shortly after MR imaging, and a third was euthanized due to concurrent cervical spondylomyelopathy. The fourth dog recovered gradually. Diagnosis was confirmed histopathologically in one dog and was presumptive based on clinical signs and MR findings in three dogs. None of the dogs with cranial nerve deficits recovered, only the one dog with left thoracic limb paresis and concurrent syringomyelia.     

MAGNETIC RESONANCE IMAGING FEATURES OF DISCOSPONDYLITIS IN DOGS

The diagnosis of discospondylitis is based mainly on diagnostic imaging and laboratory results. Herein, we describe the magnetic resonance imaging (MRI) findings in 13 dogs with confirmed discospondylitis. In total there were 17 sites of discospondylitis. Eleven (81.1%) of the dogs had spinal pain for >3 weeks and a variable degree of neurologic signs. Two dogs had spinal pain and ataxia for 4 days. Radiographs were available in nine of the dogs. In MR images there was always involvement of two adjacent vertebral endplates and the associated disk. The involved endplates and adjacent marrow were T1‐hypointense with hyperintensity in short tau inversion recovery (STIR) images in all dogs, and all dogs also had contrast enhancement of endplates and paravertebral tissues. The intervertebral disks were hyperintense in T2W and STIR images and characterized by contrast enhancement in 15 sites (88.2%). Endplate erosion was present in 15 sites (88.2%) and was associated with T2‐hypointense bone marrow adjacent to it. In two sites (11.8%) endplate erosion was not MR images or radiographically. The vertebral bone marrow in these sites was T2‐hyperintense. Epidural extension was conspicuous in postcontrast images at 15 sites (88.2%). Spinal cord compression was present at 15 sites (88.2%), and all affected dogs had neurologic signs. Subluxation was present in two sites (11.8%). MRI shows characteristic features of discospondylitis, and it allows the recognition of the exact location and extension (to the epidural space and paravertebral soft tissues) of the infection. Furthermore, MRI increases lesion conspicuity in early discospondylitis that may not be visualized by radiography.     

Surgical technique, postoperative complications and outcome in 14 dogs treated for hydrocephalus by ventriculoperitoneal shunting

Objective: To report frequency and type of complications, and outcome in dogs with severe neurologic signs secondary to internal, suspected obstructive hydrocephalus treated by ventriculoperitoneal (VP) shunting. Study Design: Case series. Animals: Dogs (n=14). Methods: Medical records (2001–2006) was reviewed for dogs that had VP shunting. Inclusion criteria were complete medical record, progressive forebrain signs unresponsive to medical treatment, normal metabolic profile, negative antibody titers and/or cerebrospinal PCR for Toxoplasma gondii, Neospora caninum, and canine distemper virus, magnetic resonance images of the brain, confirmed diagnosis of VP shunting, and follow‐up information. Results: Hydrocephalus was idiopathic in 5 dogs and acquired (interventricular tumors, intraventricular hemorrhage, inflammatory disease) in 9 dogs. Four dogs developed complications 1 week to 18 months postoperatively, including ventricular catheter migration, infection, shunt under‐drainage, kinking of the peritoneal catheter, valve fracture, and abdominal skin necrosis. Three of these dogs had 1 or more successful revision surgeries and 1 dog was successfully treated with antibiotics. All, but 1 dog, were discharged within 1 week of surgery, and had substantial neurologic improvement. Median survival time for all dogs was 320 days (1–2340 days), for dogs with idiopathic hydrocephalus, 274 (60–420) days and for dogs with secondary hydrocephalus, 365 (1–2340) days. Conclusions: VP shunting was successful in relieving neurologic signs in most dogs and postoperative complications occurred in 29%, but were resolved medically or surgically.     

Discal cysts of the cervical spine in two dogs

Discal cysts, which lie directly over intervertebral discs, are rare. Two old dogs with tetraparesis were referred to our facility. In both animals, magnetic resonance imaging revealed intraspinal extradural cystic mass lesions that were dorsal to degenerative intervertebral discs at the C3-C4 level. These lesions had low signal intensity on T1-weighted images, and high signal intensity on T2-weighted images. A ventral slot approach was used to perform surgical decompression, after which the symptoms improved remarkably. Discal cysts should be included in the differential diagnosis of dogs with cervical pain and tetraparesis. One effective treatment for discal cysts is surgical intervention.