What's around the spinal cord? Imaging features of extramedullary diseases

Diagnosis of extramedullary spinal diseases is often complex, firstly requiring a good anatomic knowledge for a precise localization of pathologies. The spinal canal, a tubular space delimited by vertebral bodies and neural arches, contains the spinal cord, nerve roots and cauda equina. Neural structures are surrounded and supported, from outer to inner, by meninges: dura, arachnoid and pia mater; meningeal layers divide extramedullary spaces in epidural, subdural and subarachnoid. Extramedullary diseases may be broadly classified in degenerative, neoplastic, traumatic, infective or miscellaneous. Imaging (MRI, CT) plays a fundamental role in the identification of pathologies, providing elements of differential diagnosis and accurate informations (location, extension, tissue characteristics) to guide further management. MRI is the best imaging modality technique to investigate extramedullary spaces and their diseases; however, CT may be useful in cases of bone involvement. The purposes of this article are to depict extramedullary anatomy, describe the most important extramedullary diseases following physiopathological and space-to-space criteria, illustrate imaging features of extramedullary pathologies, and underline imaging clues for differential diagnosis.