Magnetic Resonance Imaging Findings in Histologically Confirmed Pug Dog Encephalitis

Abstract

The purpose of the study was to describe magnetic resonance (MR) imaging features of histologically confirmed necrotizing encephalitis in four Pugs and to compare those findings with MR imaging characteristics of necrotizing encephalitis in other breeds. All dogs had the following common findings: lesions restricted to the forebrain, both cerebral hemispheres diffusely but asymmetrically affected, lesions affected gray and white matter resulting in loss of distinction between both, most severe lesions in occipital and parietal lobes, lesions were irregularly T2-hyperintense and T1-isointense to slightly T1-hypointense, and no cavitation. There were various degrees of contrast enhancement of brain and leptomeninges. Asymmetry of lateral ventricles and midline shift was seen in one dog each. Two dogs had brain herniation, which may have contributed to the progression of neurologic signs. Hyperintensity on T2-weighted and fluid attenuated inversion recovery images in the hippocampus and piriform lobe was consistent with excitotoxic edema, whereas similar imaging features in other forebrain areas corresponded to areas of inflammation or liquefaction on histopathology. In comparison with necrotizing encephalitis in other canine breeds, Pug dog encephalitis has some unique MR imaging features. Therefore, these characteristics cannot be applied to other breeds, nor should imaging features of necrotizing encephalitis of other canine breeds be used for interpretation of MR images in Pug dogs.

Perspectives on Meningoencephalomyelitis of Unknown Origin

“…108 Moreover, lack of meningeal (ie, leptomeningeal) enhancement does not rule out meningeal disease that still can be evident on histopathology. 106,107 None the less, within the subtypes of MUO leptomeningeal enhancement is characteristic in Pug dogs 79,82 and other breeds 3 with NME, but is not a typical imaging feature of GME 107 or NLE. The histologic characteristics that form the basis of the diagnosis of CNS disease cannot be determined using MR imaging, but a clinical diagnosis may be based on the pattern and number of lesions detected on MR images, 109 which can aid differentiation of intracranial neoplasia and meningoencephalitis.…”

“…1,3,79,82,113 However, although meningeal enhancement, mass effect, and ventricular dilation are frequent in Pugs with NME, NME and GME cannot be differentiated according to these features alone. 79,82 MR imaging characteristics of mass effect and contrast enhancement in NME also share similarities to those of neoplastic lesions; therefore, MR imaging findings common to NME lack specificity. 82,114,115 Increased lesion burden as evidenced on imaging in Pugs with NME has been correlated with increased disease time but not with prognosis.…”

“…112 NME is typically associated with asymmetric, multifocal cortical gray and white matter lesions with loss of gray/white matter demarcation and variable contrast enhancement; forebrain predilection, perilesional edema, mass effect, and irregular lesion margins are common. 1,79,82 Lesions appear isointense to hypointense on T1W images and hyperintense on T2W and FLAIR images, 3,79,113 and the mass effect may be sufficient to cause herniation. 1,3,79,82,113 However, although meningeal enhancement, mass effect, and ventricular dilation are frequent in Pugs with NME, NME and GME cannot be differentiated according to these features alone.…”

“…1,79,82 Lesions appear isointense to hypointense on T1W images and hyperintense on T2W and FLAIR images, 3,79,113 and the mass effect may be sufficient to cause herniation. 1,3,79,82,113 However, although meningeal enhancement, mass effect, and ventricular dilation are frequent in Pugs with NME, NME and GME cannot be differentiated according to these features alone. 79,82 MR imaging characteristics of mass effect and contrast enhancement in NME also share similarities to those of neoplastic lesions; therefore, MR imaging findings common to NME lack specificity.…”

Human Induced Rotation and Reorganization of the Brain of Domestic Dogs

“…Canine brain research has thus far focused on clinical reports of breed specific disorders, such as pug encephalitis [11], or syringohydromyelia in Cavalier King Charles spaniels [12], or of comparisons between two or three breeds on a given morphological metric, and often these studies have used only one breed to represent a skull type. While the comparison of skull extremes is informative, it would also be of value to investigate whether morphological differences in skull shape across a wide variety of breeds are accompanied by differences in brain organization.…”