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

Abstract

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.

Figure 1

Imaging characteristics and necropsy findings in a Yorkshire terrier with NME (dog 1). Multiple lesions are present in the left parietal and left and right temporal lobes. The lesions are hyperintense on T2-WI (A), hypointense on T1-WI (B), and iso- to hypointense on FLAIR images (C). In the internal capsules bilaterally (*) and the dorsal portion of the parietal lobe (arrows), the lesions are hyperintense on FLAIR images (C). (D) FDG-PET image depicts marked hypometabolism, which is shown with the bluish to greenish color. The distribution of hypometabolism corresponds to the abnormal regions noted on the MRI. On the MR and FDG-PET images, both lateral ventricles and third ventricle are enlarged. (E) In the cerebral cortex, diffuse severe atrophy was noted at necropsy. (F) Histopathologically, in the cerebral cortex, inflammatory lesions with cavitation and macrophage infiltration (arrows) are observed. Hematoxylin and eosin (H & E) × 200.

Figure 2

Image characteristics and necropsy findings of a Maltese with NME (dog 2). In the dorsal aspect of the left cerebral cortex and subcortical white matter (thick arrows), piriform lobe (*), and thalamus (thin arrows), multifocal lesions are hyperintense on T2-WI (A) and FLAIR (B) images. (C) These lesions are isointense on T1-WI. (D) On the equivalent regions compared to the MR images, the FDG-PET image depicts marked hypometabolism, which is shown with yellowish to greenish color (*). In all images, both lateral ventricles and the mesencephalic aqueduct are severely dilated. (E) At necropsy, the atrophy of the left cerebral cortex and subcortical white matter (thin arrows), and the dilation of lateral ventricles were identified. (F) Histopathologically, in the cerebral cortex and meninges, malacic foci and mononuclear inflammatory changes are observed (H & E, ×100).

Figure 3

Image characteristics of a monglish dog with MUE (dog 4). In the left cerebral cortex and subcortical white matter (thick arrows), lesions are hyperintense on T2-WI (A) and FLAIR (B) images. (C) These lesions are hypointense on T1-WI (*). (D) FDG-PET image depicts diffuse cerebral hypermetabolism, shown with a strong reddish color (*). This high metabolism is also shown in the ventral portion of the occipital lobe (thin arrow).

Figure 4

Image characteristics and necropsy findings of a miniature pinscher with GME (dog 5). In the left myelencephalon (arrows), a focal lesion is characterized by hyperintense on T2-WI (A) and FLAIR (B) images. On the right side, a smaller but similar lesion is observed (*). (C) These lesions are hypointense on T1-WI (*). In all MR images, the fourth ventricle is moderately dilated. (D) On the equivalent regions compared to the MR images, the FDG-PET images depict hypermetabolism, shown with a strong reddish color (*). (E) At necropsy, on the dorsolateral portion of the left myelencephalon (arrows), granulomatous lesions were found. (F) Histopathologically, in the myelencephalon, perivascular (arrows) and parenchymal infiltration of macrophages, lymphocytes and plasma cells is present (H & E, ×200).