Pathological enhancement of the meninges on MRI following administration of an intravenous paramagnetic contrast agent most commonly reflects inflammatory, infectious or neoplastic processes. However apparent enhancement may also be seen due to oblique sectioning through dural vessels. Therefore in humans pachymeningeal enhancement of less than 3cm in linear segments is considered normal, also the meninges covering the falx cerebri and tentorium cerebelli normally enhance in approximately 50% of humans.
The aim of the study was to use a modified from Quint et al 1996 grading system for the patterns of gadolinium enhancement in the meninges in the normal canine brain, inflammatory central nervous system disease, structural malformation and neoplasia.
The grading system for pachymeningeal enhancement ranged from Grade 1 to 6 and for leptomeningeal enhancement ranged from Grade 0-5 The MRI was performed with a 1.5 tesla Philips Gyroscan NT Intera was used with a slice thickness of 3.5-4.5mm with a 10% interslice gap. The meningeal covering of the cerebral convexities, the falx cerebri, the tentorium cerebelli, the cerebellum and the medulla oblongata were graded. Cytology and protein concentration were recorded on cerebrospinal fluid taken from the cisterna magna and a grade was assigned for cytology from 0-4 and for protein from 0-3.
Two hundred dogs were reviewed retrospectively. The signalment of the dogs, history, neurological localization, MRI and cerebrospinal fluid analysis were recorded. There were 105 males and 85 females. The age range was 3-180 months mean 60 months. Eighty two dogs were considered to be normal, 37 were diagnosed with inflammatory CNS disease and 20 with intracranial neoplasia. Sixty one cases had structural malformations, infarctions, metabolic disease and spinal lesions. Statistical analysis using Kruskal Wallis with follow up pair wise Mann Whitney U tests with the significance set at P<0.005 was performed. The total pachymeningeal enhancement grade was significantly higher in the inflammatory group compared to the control group (P=0.00). Leptomeningeal enhancement was significantly higher in the inflammatory compared to the neoplastic and control groups (P=0.00). Increases in CSF white blood cell count (WBC) and protein correspond to increased meningeal enhancement grades when over the threshold of 20WBC/mm3 (cytology grade 3) and 50mg/dl (protein grade 2) or when activated macrophages, plasma cells or leucocytes are present (cytology grade 2). Pachymeningeal enhancement occurred over the cerebral convexities and falx cerebri in over half the dogs with normal brains. Different patterns of meningeal enhancement are seen with pathological conditions. Further studies are required to confirm the differences, to confirm why some normal areas enhance and to describe the pathology that enables the meninges to enhance.