Spatiotemporal Heterogeneity in Isolated Neurosarcoidosis: Diagnostic Insights from Multimodal Imaging

Isolated neurosarcoidosis (INS) is a rare inflammatory disorder of the central nervous system that lacks systemic manifestations and mimics neoplastic or infectious conditions, making diagnosis challenging. We report a case of a previously healthy 30-year-old man who presented with recurrent transient loss of consciousness and progressive right leg weakness. Brain magnetic resonance imaging (MRI) demonstrated multiple uniformly contrast-enhancing nodular lesions involving the pachymeninges and cranial nerves, while spinal MRI revealed conus medullaris enhancement with associated lumbosacral nerve root thickening. Stereotactic biopsy of an MRI-enhancing pachymeningeal lesion demonstrated chronic granulomatous inflammation, with infectious and neoplastic etiologies excluded, leading to a diagnosis of INS. Subsequent 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) revealed marked metabolic heterogeneity, with mixed hyper- and hypometabolic cerebral nodules and metabolically inactive pachymeningeal and spinal lesions. This case illustrates spatiotemporal inflammatory heterogeneity in INS and highlights multimodal imaging findings demonstrating structural-metabolic discordance. Early incorporation of PET/CT alongside MRI may provide complementary metabolic information that assists lesion characterization in diagnostically complex central nervous system inflammatory diseases.