Correlation between fluorodeoxyglucose positron emission tomography and magnetic resonance imaging findings of non-suppurative meningoencephalitis in 5 dogs.

This study characterized the [(18)F]2-deoxy-2-fluoro-D-glucose positron emission tomography (FDG-PET) findings of encephalitis in dogs and assessed the role of FDG-PET in the diagnosis of meningoencephalitis. The medical records, magnetic resonance (MR), and FDG-PET images of 3 dogs with necrotizing meningoencephalitis (NME), 1 dog with granulomatous meningoencephalitis (GME), and 1 dog with meningoencephalitis of unknown etiology (MUE) were reviewed. On the FDG-PET, glucose hypometabolism was identified in the dog with NME, whereas hypermetabolism was noted in the dog with GME. The T2-weighted images (WI) and fluid attenuated inversion recovery (FLAIR) images were characterized by hyperintensity, whereas the signal intensity of the lesions on the T1-WI images was variable. The metabolic changes on the brain FDG-PET corresponded well to the hyper- and hypointense lesions seen on the MR imaging. This type of tomography (FDG-PET) aided in the differentiation of different types of inflammatory meningoencephalitis when the metabolic data was combined with clinical and MR findings.

Three-dimensional time-of-flight magnetic resonance angiography of intracranial vessels in a canine model of ischemic stroke with permanent occlusion of the middle cerebral artery.

The purpose of this study was to evaluate the potential efficacy of 3-dimensional time-of-flight magnetic resonance angiography (TOF-MRA) to validate a canine ischemic stroke model. Ischemic stroke was induced through permanent middle cerebral artery occlusion (MCAO) in 5 healthy Beagle dogs. T2-turbo spin echo images and TOF-MRA were obtained with a 1.5-T magnetic resonance system before and 3 and 10 d after MCAO. In 3 dogs, angiograms of the brain obtained at 3 d after MCAO showed complete occlusion of the MCA; in addition, T2 hyperintensities were present unilaterally in the striatocapsular and cerebral cortex lesions. Partial occlusion of the proximal part of the MCA was identified in the 2 remaining dogs, with T2 hyperintensities present only in the striatocapsular lesions. The occluded sites were confirmed at necropsy. The results of this study demonstrate the potential of TOF-MRA to provide a detailed description of intracranial arteries and aid in the evaluation of flow impairment in a canine MCAO model.

18F-fluorodeoxyglucose positron emission tomography and magnetic resonance imaging findings of primary intracranial histiocytic sarcoma in a dog.

A 10-year-old, neutered male, Maltese dog presented with a three week history of intention tremor, right hind limb rigidity, poor coordination, and occasional circling to the left. On magnetic resonance imaging (MRI) of the brain, a mass was identified in the right occipital lobe and cerebellum. Three weeks after the initial MRI scan, we performed an (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) of the brain. The FDG-PET demonstrated areas of hypermetabolism in the right occipital lobe, cerebellum, pons, and medulla oblongata. When the standardized uptake value was calculated, the hypermetabolic lesion was higher than the gray matter values. The anatomical location of the hypermetabolic lesion was more precisely identified by the PET-MRI fusion images. The dog was definitively diagnosed as a primary histiocytic sarcoma of the brain. This is the first report of PET findings of an intracranial histiocytic sarcoma in a dog.

A comparison of combination therapy (cyclosporine plus prednisolone) with sole prednisolone therapy in 7 dogs with necrotizing meningoencephalitis.

Administration of immunosuppressive doses of glucocorticosteroids is the traditional primary treatment in necrotizing meningoencephalitis (NME) in dogs. However, response is variable and clinical signs often recur quickly with tapering dosage. Prognosis is poor and long-term therapy causes many complications. In the present study, we compared the long-term effects of combination (cyclosporine plus prednisolone) therapy with sole prednisolone therapy in management in dogs with NME. All NME cases in this study were examined with magnetic resonance imaging and cerebrospinal fluid analysis, and confirmed by histopathologic examination. The mean survival time of combination therapy group was 305.7 +/- 94.7 days. The mean survival time of sole prednisolone therapy group was 58.3 +/- 30.5 days. This case report demonstrates that combination treatment of cyclosporine with prednisolone is more effective in survival time than administration of only prednisolone in NME cases.

Canine model of ischemic stroke with permanent middle cerebral artery occlusion: clinical and histopathological findings.

The aim of the present study was to assess the clinical and histopathological findings in a canine model of ischemic stroke. Cerebral ischemic stroke was induced by middle cerebral artery occlusion in four healthy beagle dogs using silicone plugs. They showed neurological signs of forebrain dysfunction such as reduced responsiveness, head turning, circling, postural reaction deficits, perceptual deficits, and hemianopsia. These signs gradually regressed within 4 weeks without therapy. On magnetic resonance imaging, T2 hyperintensity and T1 hypointensity were found in the cerebral cortex and basal ganglia. These lesions were well-defined and sharply demarcated from adjacent brain parenchyma with a homogenous appearance. No abnormalities of the cerebrospinal fluid were observed. At necropsy, atrophic and necrotic lesions were observed in the cerebral cortex. The cerebral cortex, basal ganglia, and thalamus were partially unstained with triphenyl- tetrazolium chloride. Histopathologically, typical features of infarction were identified in cortical and thalamic lesions. This study demonstrates that our canine model resembles the conditions of real stroke patients.

Detection of cerebral metabolites in a canine model of ischemic stroke using 1H magnetic resonance spectroscopy.

Proton magnetic resonance spectroscopy ((1)H MRS) provides in vivo biochemical information on tissue metabolites. The purpose of this study was to investigate the serial metabolic changes of (1)H MRS in the cerebrum of ischemic dogs. An ischemic stroke was induced in five health laboratory beagle dogs by permanent middle cerebral artery occlusion using a silicone plug. (1)H MRS was serially performed three times with a 1.5-T MR system: before, three days after and 10days after the stroke. Immunohistochemical staining was performed to determine the expression of neuronal nuclei (NeuN) and glial fibrillary acidic protein (GFAP) at both the ipsilateral and contralateral cerebral cortex. Reduced levels of N-acetyl-asparate (p<0.05), choline (Cho), creatine (Cr) and myo-inositol (mI), and a marked increase in the lactate (Lac) level (p<0.01) were found at three days after the stroke. At 10days after the stroke, the levels of Lac significantly increased (p<0.01); however, the other metabolites were partially elevated. The changes of Cr, Cho and mI were not statistically significant (p>0.05) when the before and after stroke values were compared. There was a significant loss of NeuN and GFAP immunoreactivity at the ischemic core. (1)H MRS may be to a useful diagnostic tool for the evaluation of ischemic stroke in dogs.

MRI features in a canine model of ischemic stroke: correlation between lesion volume and neurobehavioral status during the subacute stage.

The purpose of this study was to evaluate the diagnostic value of magnetic resonance imaging (MRI) and assess the correlation between the volume of the ischemic lesion and neurobehavioral status during the subacute stage of ischemic stroke. Ischemic stroke was induced in 6 healthy laboratory beagles through permanent occlusion of the middle cerebral artery (MCAO). T2-weighted and fluid-attenuated inversion recovery (FLAIR) imaging, diffusion-weighted imaging (DWI), measurement of the apparent diffusion coefficient (ADC) ratio, and neurobehavioral evaluation were performed 3 times serially by using a 1.5-T MR system: before and 3 and 10 d after MCAO. Ischemic lesions demonstrated T2 hyperintensity, FLAIR hyperintensity, and DWI hyperintensity. The ADC ratio was decreased initially but then was increased at 10 d after MCAO. Ischemic lesion volumes on T2-weighted and FLAIR imaging were not significantly different from those on DWI. The lesion volume and neurobehavioral score showed strong correlation. Our results suggest that conventional MRI may be a reliable diagnostic tool during the subacute stage of canine ischemic stroke.

Positron emission tomography features of canine necrotizing meningoencephalitis.

A Yorkshire terrier and a Chihuahua were referred for acute onset, generalized tonic-clonic seizures and were suspected to have meningoencephalitis based on magnetic resonance (MR) imaging findings. Brain lesions appeared hyperintense with T2-weighted imaging and hypointense with T1-weighted imaging, and were characteristic of necrotizing meningoencephalitis. Both dogs were diagnosed with necrotizing meningoencephalitis based on pathologic findings. Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) was performed on both animals before euthanasia with the permission of the owner. In FDG-PET images, these lesions seen in MR images were characterized by multifocal or diffuse hypometabolism. Our FDG-PET results provided evidence of glucose hypometabolism in areas of necrosis and cavitation associated with necrotizing meningoencephalitis. FDG-PET has the potential to provide valuable diagnostic information in dogs with suspected necrotizing encephalitis.