Magnetic Resonance Imaging Characteristics of Necrotizing Meningoencephalitis in Pug Dogs

Abstract

Background: The magnetic resonance imaging (MRI) characteristics of necrotizing meningoencephalitis (NME) are not well documented.Objectives: To describe common MRI features of NME, to compare the MRI features to histopathologic findings, and to determine whether or not MRI lesions are predictive of survival time.Animals: Eighteen Pugs with NME. Methods: Retrospective MRI case study of Pugs identified by a search of medical records at 6 veterinary institutions. Eighteen dogs met inclusion criteria of histopathologically confirmed NME and antemortem MRI exam. MRI lesions were characterized and compared with histopathology with the kappa statistic. Survival times were compared with MRI findings by use of Mann-Whitney U-tests and Spearman's r.Results: Twelve of 18 lesions were indistinctly marginated with mild parenchymal contrast enhancement. Prosencephalic (17/18) lesion distribution included the parietal (16/18), temporal (16/18), and occipital (16/18) lobes. There were cerebellar (4/18) and brainstem (3/18) lesions. Asymmetric lesions were present in both gray and white matter in all dogs. Falx cerebri shift was common (11/18), and 6 dogs had brain herniation. Leptomeningeal enhancement was present in 9/18 dogs. A moderate positive association was found between parenchymal contrast enhancement and both necrosis (k 5 0.45; P 5 .045) and monocytic inflammation (k 5 0.48; P 5 .025). Higher MRI lesion burden was correlated with longer time from disease onset to MRI (P 5 .045). MRI lesion burden did not correlate to survival time.Conclusions and Clinical Importance: Asymmetric prosencephalic grey and white matter lesions with variable contrast enhancement were consistent MRI changes in Pugs with confirmed NME. While not pathognomonic for NME, these MRI characteristics should increase confidence in a presumptive diagnosis of NME in young Pugs with acute signs of neurologic disease.

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.…”

“…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.…”

“…4 Dogs with NME commonly manifest forebrain signs, especially seizures, because of lesions in the cerebral cortex. 3,58,80,82 Other forebrain signs include lethargy, anorexia, central blindness, circling, and head-pressing. 78,80 Cervical spinal hyperesthesia may be evident depending on the extent of leptomeningitis.…”

An update on meningoencephalomyelitis of unknown aetiology in dogs

“…In necrotising leucoencephalitis, multiple, asymmetric bilateral prosencephalic lesions appear mainly in the subcortical white matter. The lesions are hyper-intense on T2-weighted and fluid-attenuated inversion recovery images and hypo-intense or iso-intense on T1-weighted images, with variable contrast enhancement (von Praun et al, 2006;Young et al, 2009). Computed-tomography scan may also contribute to the diagnosis.…”

Most commonly used sequences and clinical protocols for brain and spine magnetic resonance imaging allowing better identification of pathological changes in dogs

“…There are different reports that have distinguished the MR signs in dogs with hydrocephalus, cerebellar degeneration, necrotizing encephalitis, granulomatous meningoencephalitis, infarcts, age-related degeneration, spinal cord hernias, wobbler syndrome, arachnoid cysts, syringohydromyelia associated with Chiari-like malformation in the Cavalier King Charles spaniel (Fig. 1), discospondylitis, atlantoaxial instability, meningeal calcification, hydromyelia, mechanical damage, and brain and spinal tumors (Vullo et al 1997, Gonzalo-Orden et al 2000, Kimotsuki et al 2005, Besalti et al 2006, Garosi et al 2006, Okada et al 2006, Matiasek et al 2007, Couturier J et al 2008, Sturges et al 2008, Carrera et al 2009, Cerda-Gonzalez S et al 2009, Young et al 2009, Gavin PR 2011.…”