PMC9477003_01
Magnetic resonance imaging (MRI) of a Yorkshire Terrier with meningoencephalitis of unknown origin (case 1). Transverse plane at the level of the mesencephalon (A,B) and interthalamic adhesion (C) (see blue lines in the schematic overview upper right), A: T2 weighted (w), B, C: T1w post contrast injection. Intraaxial lesion of the subcortical white matter of the cerebral hemisphere, identified on histopathology as predominantly necrotic (A,B: white arrow). Intraaxial lesion of the striated body identified as granulomatous lesion (C: blue arrow).
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F1
On MRI of the brain (Figure 1), multifocal bilateral asymmetric forebrain lesions were seen, mainly affecting the subcortical white matter but also the gray matter of the left parietal lobe, the right occipital lobe, the left hippocampus, and thalamus with no to mild mass effect.
Combined necrotizing leukoencephalitis and granulomatous meningoencephalitis in the brain of a Yorkshire Terrier (case 1). (A) right striatal body; marked granulomatous inflammation with severe lymphocytic perivascular cuffing. (B) cerebrum, left parietal lobe; marked necrotizing leukoencephalitis in subcortical white matter with gitter cells (malacia) and severe lymphohistiocytic perivascular cuffing; bars = 500 mum.
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F2
On pathological examination of the brain, multifocal marked necrotizing leukoencephalitis was evident with many gitter cells (malacia) and severe lymphohistiocytic perivascular cuffing in the subcortical white matter of the left parietal lobe (Figure 2). Additionally, there was marked granulomatous inflammation with severe lymphocytic perivascular cuffing in the right striatal body and caudate nucleus (Figure 2).
PMC9477003_02
Combined necrotizing and granulomatous meningoencephalitis in the brain of a Maltese (case 2). (A) Focal-extensive malacia in the midbrain (arrows). (B) Subgross picture of a H&E stained section of the midbrain shown in A. Focal-extensive pallor indicates necrosis and edema, which is associated with a prominent inflammatory process (dark blue color due to nuclei of infiltrating inflammatory cells). (C) Area of granulomatous inflammation with lymphocytes (arrows) and activated macrophages (arrowheads) around a vessel. The activated macrophages markedly extend into the neuroparenchyma (asterisk).
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F3
On histopathology, extensive necrosis and edema were associated with marked nodular and perivascular infiltration with epithelioid macrophages and lymphocytes in the midbrain, cerebellum, and brain stem (Figure 3).
PMC9477003_03
Combined necrotizing and granulomatous meningoencephalitis in the brain of a Yorkshire Terrier (case 3). (A) Severe, focal-extensive and delineated malacia in the right rhinal cortex and extending to the surface. This lesion mimicks NME. Additionally, there are multifocal areas of beige discoloration in the corona radiata (arrows). (B) Severe and multifocal-coalescing perivascular cuffs with lymphocytes and large activated macrophages. Macrophages tend to compartmentalize within these cuffs. (C) The same dog is affected by a marked cerebellar meningitis that extends into the molecular layer.
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F4
Lesions were most evident in the gray and white matter of the frontal lobes and basal nuclei, but they also affected the brain stem, midbrain, thalamus, and hippocampus, and extended into the subarachnoid space (Figure 4).
PMC9477003_04