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.     

MAGNETIC RESONANCE IMAGING OF INTRACRANIAL INFLAMMATORY CONDITIONS IN DOGS: SENSITIVITY OF SUBTRACTION IMAGES VERSUS PRE‐ AND POST‐GADOLINIUM T1‐WEIGHTED IMAGE PAIRS

Ante mortem diagnosis of canine meningoencephalitis is usually based on the results of neurologic examination, cerebrospinal fluid analysis and magnetic resonance (MR) imaging. It has been hypothesized that subtraction MR imaging may increase the sensitivity of MR for intracranial inflammatory lesions compared to conventional post‐gadolinium T1‐weighted imaging. Sensitivity of pre‐ and post‐gadolinium (C‐/C+) image pairs and dynamic subtraction (DS) images was compared in a retrospective diagnostic accuracy study of 52 dogs with inflammatory cerebrospinal fluid and 67 dogs with idiopathic epilepsy. Series of transverse C‐/C+ and DS images were reviewed independently for signs of abnormal enhancement affecting the pachymeninges, leptomeninges or intra‐axial structures. Sensitivity of C‐/C+ image pairs and DS images was 48% (95% CI: 35–61%) and 65% (95% CI: 52–77%), respectively (P = 0.01). Intra‐axial lesions were observed more frequently than meningeal lesions in both C‐/C+ (43% vs. 31%) and DS images (61% vs. 22%). The difference in sensitivities of C‐/C+ and DS series was entirely due to increased sensitivity of DS images for intra‐axial lesions. Eight (12%) dogs with epilepsy had evidence of intra‐axial gadolinium accumulation affecting the cerebral cortex in DS images. This finding may represent a false‐positive result or a true sign of pathology, possibly associated with a leaky blood–brain barrier in areas of the brain affected by neovascularization secondary to repeated seizures. Results suggest that DS imaging has higher sensitivity than comparison of pre‐ and post‐gadolinium image pairs for inflammatory intra‐axial lesions.     

MAGNETIC RESONANCE IMAGING CHARACTERISTICS IN FOUR DOGS WITH CENTRAL NERVOUS SYSTEM NEOSPOROSIS

Neosporosis is a polysystemic disease that can affect dogs of any age and can cause inflammation of the central nervous system. Antemortem diagnosis can be challenging, as clinical and conventional laboratory test findings are often nonspecific. A previous report described cerebellar lesions in brain MRI studies of seven dogs and proposed that these may be characteristic for central nervous system Neosporosis. The purpose of this retrospective study was to describe MRI characteristics in another group of dogs with confirmed central nervous system neosporosis and compare them with the previous report. The hospital's database was searched for dogs with confirmed central nervous system neosporosis and four observers recorded findings from each dog's MRI studies. A total of four dogs met inclusion criteria. Neurologic examination was indicative of a forebrain and cerebellar lesion in dog 2 and multifocal central nervous system disease in dogs 1, 3, and 4. Magnetic resonance imaging showed mild bilateral and symmetrical cerebellar atrophy in three of four dogs (dogs 2, 3, 4), intramedullary spinal cord changes in two dogs (dogs 3, 4) and a mesencephalic and metencephalic lesion in one dog (dog 2). Multifocal brain lesions were recognized in two dogs (dogs 1, 4) and were present in the thalamus, lentiform nucleus, centrum semiovale, internal capsule, brainstem and cortical gray matter of the frontal, parietal or temporal lobe. Findings indicated that central nervous system neosporosis may be characterized by multifocal MRI lesions as well as cerebellar involvement in dogs.     

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.     

COMPARISON BETWEEN PROTON MAGNETIC RESONANCE SPECTROSCOPY FINDINGS IN DOGS WITH TICK‐BORNE ENCEPHALITIS AND CLINICALLY NORMAL DOGS

In vivo diagnosis of tick‐borne encephalitis is difficult due to high seroprevalence and rapid viral clearance, limiting detection of antibodies in blood and cerebrospinal fluid. Magnetic resonance imaging (MRI) characteristics of tick‐borne encephalitis have been reported, however MRI studies can also be negative despite the presence of neurologic signs. Magnetic resonance spectroscopy (¹H MRS) is an imaging method that provides additional information about the metabolic characteristics of brain tissues. The purpose of this retrospective cross‐sectional study was to describe brain metabolites using short echo time single‐voxel ¹H MRS in dogs with confirmed tick‐borne encephalitis and compare them with healthy dogs. Inclusion criteria for the affected dogs were neurological symptoms suggestive of tick‐borne encephalitis, previous endemic stay and tick‐bite, diagnostic quality brain MRI and ¹H MRS studies, and positive antibody titers or confirmation of tick‐borne encephalitis with necropsy. Control dogs were 10, clinically normal beagles that had been used in a previous study. A total of six affected dogs met inclusion criteria. All dogs affected with tick‐borne encephalitis had ¹H MRS metabolite concentration alterations versus control dogs. These changes included mild to moderate decreases in N‐acetyl aspartate and creatine peaks, and mild increases in glutamate/glutamine peaks. No lactate or lipid signal was detected in any dog. Myoinositol and choline signals did not differ between affected and control dogs. In conclusion, findings supported the use of ¹H MRS as an adjunctive imaging method for dogs with suspected tick‐borne encephalitis and inconclusive conventional MRI findings.     

MAGNETIC RESONANCE IMAGING FEATURES OF ORBITAL INFLAMMATION WITH INTRACRANIAL EXTENSION IN FOUR DOGS

This retrospective study describes the clinical and magnetic resonance (MR) imaging features of chronic orbital inflammation with intracranial extension in four dogs (two Dachshunds, one Labrador, one Swiss Mountain). Intracranial extension was observed through the optic canal (n=1), the orbital fissure (n=4), and the alar canal (n=1). On T1-weighted images structures within the affected skull foramina could not be clearly differentiated, but were all collectively isointense to hypointense compared with the contralateral, unaffected side, or compared with gray matter. On T2-, short tau inversion recovery (STIR)-, or fluid-attenuated inversion recovery (FLAIR)-weighted images structures within the affected skull foramina appeared hyperintense compared with gray matter, and extended with increased signal into the rostral cranial fossa (n=1) and middle cranial fossa (n=4). Contrast enhancement at the level of the affected skul foramina as well as at the skull base in continuity with the orbital fissure was observed in all patients. Brain edema or definite meningeal enhancement could not be observed, but a close anatomic relationship of the abnormal tissue to the cavernous sinus was seen in two patients. Diagnosis was confirmed in three dogs (one cytology, two biopsy, one necropsy) and was presumptive in one based on clinical improvement after treatment. This study is limited by its small sample size, but provides evidence for a potential risk of intracranial extension of chronic orbital inflammation. This condition can be identified best by abnormal signal increase at the orbital fissure on transverse T2-weighted images, on dorsal STIR images, or on postcontrast transverse or dorsal images.     

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.     

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.     

MAGNETIC RESONANCE IMAGING FEATURES OF PRIMARY BRAIN TUMORS IN DOGS

Magnetic resonance images of twenty-five dogs with histopathologically confirmed primary brain tumors were evaluated. A lesion was visible in each dog. Meningiomas were extra-axial lesions that enhanced markedly withj gadolinium-DTPA. Glimas were Characteized by intra-axial location, significant mass effect and surrounding edema, and variable enhancement patterns. Choroid plexus tumors and pituitary tumors were differentiated by their location and marked enbancement. Prediction of general typeof tumor was correct in 24 of 25 dogs.     

MAGNETIC RESONANCE IMAGING AND PATHOLOGIC FINDINGS ASSOCIATED WITH NECROTIZING ENCEPHALITIS IN TWO YORKSHIRE TERRIERS

Two young adult Yorkshire terriers had neurologic signs consistent with forebrain and brainstem involvement or forebrain involvement alone. On magnetic resonance imaging studies there were asymmetric bilateral lesions mainly in the cerebral cortex, and in the diencephalon. These areas were hyperintense on T2-weighted and FLAIR images, but hypointense or isointense on T1-weighted images. Lesions had a varying degree of contrast enhancement. Areas which were isointense on T1-weighted images had no contrast enhancement or only foci of contrast enhancement. Lesions with hypointensity in T1-weighted images had no enhancement or more frequently ring-like enhancement around the lesion. Necrotizing encephalitis was confirmed pathohistologically in both dogs. The degree of contrast enhancement appeared to be related to the degree of lymphohistiocytic inflammation on histologic examination.     

CANINE MENINGEAL DISEASE: ASSOCIATIONS BETWEEN MAGNETIC RESONANCE IMAGING SIGNS AND HISTOLOGIC FINDINGS

In order to compare the accuracy of MR sequences for diagnosis of meningeal disease, MR images of the brain, and histopathologic specimens including the meninges of 60 dogs were reviewed retrospectively by independent observers in a cross‐sectional study. MR images included T1‐weighted pre‐ and postgadolinium images, subtraction images, T2‐weighted images, and T2‐weighted fluid‐attenuated inversion‐recovery (FLAIR) images. Pathologic changes affected the pachymeninges in 16 dogs, leptomeninges in 35 dogs, and brain in 38 dogs. The meninges were normal in 12 dogs. Meninges were classified histopathologically as normal (grade 0), slightly or inconsistently affected (grade 1), or markedly affected (grade 2). When applying relaxed pathologic criteria (grades 0 and 1 considered normal), the results of ROC analysis (area under curve, AUC) were: T1‐weighted postcontrast images 0.74; subtraction images 0.7; T2‐weighted images 0.68; FLAIR images 0.56. The difference in AUC between T1‐weighted postgadolinium images and FLAIR images was significant (P = 0.04). AUC for FLAIR images was not significantly different from 0.5. When applying strict pathologic criteria (only grade 0 considered normal), none of the MR sequences had AUC significantly different from 0.5. On the basis of T1‐weighted postgadolinium images and subtraction images, correct anatomic classification of lesions occurred more often for pachymeningeal than leptomeningeal lesions (P < 0.001). Overall, MR imaging had low sensitivity for diagnosis of meningeal pathology in dogs, particularly for changes affecting the leptomeninges. Subtraction images had similar accuracy to T1‐weighted postgadolinium images for meningeal lesions in dogs. T2‐weighted FLAIR images appear to have limited diagnostic utility for meningeal lesions.     

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 BRAIN INFARCTION IN SEVEN DOGS

Magnetic resonance imaging was performed in seven dogs with histopathologically-confirmed brain infarcts. The infarcts were non-hemorrhagic in four dogs and hemorrhagic in three dogs. Six dogs had single infarcts involving the cerebrum and one dog had multiple infarcts involving the cerebrum and brain stem. Non-hemorrhagic infarcts were typically wedge-shaped, hypointense on T1-weighted images, hyperintense on T2-weighted images, and did not enhance with gadolinium-DTPA. Hemorrhagic infarcts had mixed intensity on T1- and T2-weighted images, with variable patterns of enhancement.     

MAGNETIC RESONANCE IMAGING FINDINGS OF PRESUMED CEREBELLAR CEREBROVASCULAR ACCIDENT IN TWELVE DOGS

The magnetic resonance imaging (MRI) findings of presumed cerebrovascular accident in 12 dogs are described. Fourteen lesions were seen, commonly (11 of 14) within the gray matter of the cerebellar hemispheres or vermis. Thirteen lesions were hyperintense on T2-weighted images (in 11 dogs) and one was hypointense. Eleven of 14 lesions were within the region supplied by the rostral cerebellar artery or one of its main branches and there was no, or minimal, mass effect. Contrast enhancement was only seen in six lesions and was mild in all. Gradient-echo images provided additional information in two dogs. The appearance of infarction in dogs with diffusion-weighted images (DWI) is similar to that in humans, and provided supportive evidence for the diagnosis of infarction in five dogs. The use of gradient-echo and DWI is recommended for the evaluation of suspected cerebrovascular accidents in dogs. Six of the 12 affected animals were spaniels or spaniel crosses, suggesting a possible breed predisposition.     

MENINGEAL ENHANCEMENT ON MAGNETIC RESONANCE IMAGING IN 15 DOGS AND 3 CATS

A retrospective study of 15 dogs and three cats was done to characterize the appearance of meningeal enhancement on magnetic resonance (MR) images of the brain, and to correlate this appearance with its underlying cause. Two patterns of meningeal enhancement (pial and dural) were identified. Enhancement of the pia mater was evident in four dogs and one cat, while enhancement of the dura mater was seen in 11 dogs and 2 cats. A variety of causes of meningeal enhancement were identified, including bacterial and cryptococcal meningitis, plasmacytic meningitis with associated subdural fluid accumulation, granulomatous meningoencephalomyelitis, inflammation secondary to otitis interna, feline infectious peritonitis, and neoplasia. The present study confirms that pial or dural meningeal enhancement may be present on MR images of the brain of dogs or cats in association with a variety of central nervous system diseases. A larger prospective study is required to further establish the incidence of specific patterns of meningeal enhancement seen in association with specific diseases.     

MAGNETIC RESONANCE IMAGING FEATURES OF THE TEMPOROMANDIBULAR JOINT IN NORMAL DOGS

Evaluation of the canine temporomandibular joint (TMJ) is important in the clinical diagnosis of animals presenting with dysphagia, malocclusion and jaw pain. In humans, magnetic resonance imaging (MRI) is the modality of choice for evaluation of the TMJ. The objectives of this study were to establish a technical protocol for performing MRI of the canine TMJ and describe the MRI anatomy and appearance of the normal canine TMJ. Ten dogs (one fresh cadaver and nine healthy live dogs) were imaged. MRIs were compared with cadaveric tissue sections. T1‐weighted (T1‐W) transverse closed‐mouth, T1‐W sagittal closed‐mouth, T1‐W sagittal open‐mouth, and T2‐W sagittal open‐mouth sequences were obtained. The condylar process of the mandible and the mandibular fossa of the temporal bone were hyperintense to muscle and isointense to hypointense to fat on T1‐W images, mildly hyperintense to muscle on T2‐W images, and were frequently heterogeneous. The articular disc was visible in 14/20 (70%) TMJs on T1‐W images and 13/20 (65%) TMJs on T2‐W images. The articular disc was isointense to hyperintense to muscle on T1‐W images and varied from hypointense to hyperintense to muscle on T2‐W images. The lateral collateral ligament was not identified in any joint. MRI allows evaluation of the osseous and certain soft tissue structures of the TMJ in dogs.     

CARDIAC MAGNETIC RESONANCE IMAGING IN NORMAL DOGS AND TWO DOGS WITH HEART BASE TUMOR

We describe the technique for in vivo cardiac‐gated magnetic resonance imaging (MRI) in normal dogs and its application in two dogs with a large right atrial tumor. The dogs with a cardiac tumor were also imaged using contrast‐enhanced magnetic resonance angiography (CE‐MRA). Cardiac‐gated MRI and CE‐MRA are both feasible in animals with short acquisition times compatible with breath‐hold imaging under anesthesia, and provide detailed two‐ and three‐dimensional (3D) depiction of the cardiac anatomy and great vessels with or without contrast medium. Although cardiac MRI will not replace echocardiography, it is a powerful alternative technique to use when knowledge of the 3D anatomy of the vasculature is required, when precise volume measurements are needed or when myocardial characterization is indicated. As opposed to contrast‐enhanced computed tomography angiography, cardiac MRI does not use ionizing radiation or iodinated contrast medium.     

MAGNETIC RESONANCE IMAGING FINDINGS IN HORSES WITH SEPTIC ARTHRITIS

Fourteen horses with septic arthritis underwent high‐field (1.5 T) magnetic resonance imaging (MRI). Septic arthritis was diagnosed based on results from historical and clinical findings, synovial fluid analyses and culture, and radiographic, ultrasonographic, arthroscopic, and histopathologic findings. MR findings included diffuse hyperintensity within bone and extracapsular tissue on fat‐suppressed images in 14/14 horses (100%), joint effusion, synovial proliferation, and capsular thickening in 13/14 horses (93%), bone sclerosis in 11/14 horses (79%), and evidence of cartilage and subchondral bone damage in 8/14 horses (57%). Intravenous gadolinium was administered to five of the 14 horses and fibrin deposition was noted in all horses. Other findings after gadolinium administration included synovial enhancement in 4/5 (80%) horses, and bone enhancement in 1/5 (20%) horses. The MR findings of septic arthritis in horses were consistent with those reported in people. MRI may allow earlier and more accurate diagnosis of septic arthritis in horses as compared with other imaging modalities, especially when the clinical diagnosis is challenging. It also provides additional information not afforded by other methods that may influence and enhance treatment.     

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.