CT assessment in canine meningoencephalomyelitis

Meningoencephalomyelitis (MEM) is an inflammatory process of the CNS that may have viral, bacterial, rickettsial, fungal or parasitic causes. When no pathogen is identified these are defined as non infectious MEMs (Bagley 2000; Cauzinille 1999; Suzuki et al. 2003). The diagnosis of MEM is based on clinical examination, blood tests and on the Cerebral Spinal Fluid (CSF) test (Fisher 2002). In fact CSF modifications can often be observed during inflammatory, infectious, neoplastic and traumatic diseases as well as in some degenerative diseases of the brain and the spinal marrow (Munana 1996; O'Neill 2005). The assessment of antibody titers, in the CSF and serum, allows us to diagnose etiologically suspect cases. For some MEM forms, it is necessary to make a biopsy of the CNS to make an intra-vitam diagnosis (Platt 2004). Amongst all the imaging techniques, Magnetic Resonance (MRI) has proven to be the most effective in defining the CNS morpho-structural lesions due to MEMs (Lamb et al. 2005). On MRI lesions appear as hyper-intense areas in T2-weighted sequences or FLAIR or hypo-intense in T1-weighted images (Lamb et al. 2005). In 1992 Plummer and collaborators used Computerised Tomography (CT) in MEM cases and observed post-contrast impregnation areas, frequent lesions of the encephalic lacunary system and mass effect lesions. Nevertheless, based on the results obtained, the authors of this study concluded that CT was not sufficiently specific and not very sensitive in MEM diagnosis (Plummer et al. 1992). Still,nowadays, MRI veterinary services are not so widespread, particularly in Italy, while CT equipped centres are becoming more and more numerous.In 5 subjects (5/13) the cytological examination showed a mild, moderate or severe pleiocytosis which was then differentiated into neutrophilic, mononuclear and mixed pleiocytosis and was therefore considered as positive to MEM. In the other 8 subjects, the CSF test was negative. With the CT scan a MEM diagnosis was made in 7 subjects (5 true positive and 2 false positive cases) All the subjects considered as CT-positive presented relatively hyperdense single or multiple focal lesions before contrast and impregnating single or multiple focal lesions after contrast. Encephalic lesions were mainly located in the posteroventral districts whereas spinal cord lesions had a variable location. In none of the CT-positive subjects did these lesions show a mass effect and only one subject showed a moderate hydrocephalus. In the remaining 6 CT-negative dogs, two did not show any alteration, 1 showed a small defect of the left temporal cortical region, compatible with the outcome of an ischemic lesion, 1 showed a small non-impregnating mass on the foramen magnum floor, 1 showed a spondylitis at T2 and, finally, 1 showed a disc hernia between T2 and T3. The CT scan showed 100% sensitivity, 71% specificity and 83% accuracy. Our results, despite the small number of cases and the fact that the CSF test is not conclusive as to whether the inflammation is of a primary origin, lead us to conclude that the CT scan can be considered a valid diagnostic aid in dogs' MEM, when it is impossible to access MRI.