PATOLOGIA DEGENERATIVA DISCO-VERTEBRALE ED ERNIA DISCALE

Aging and disk degeneration cause a progressive dehydration of the nucleus pulposus and the anulus fibrosus leading to fibrotic degeneration. These are the most important preliminary changes in the pathogenesis of herniated disk. As degeneration progresses the structures containing the soft nucleus start to disintegrate and herniation occurs. Disk degeneration is often associated with changes to the adjacent vertebral bodies characterized by structural changes to the bone marrow of the vertebral spongiosa, osteosclerosis of the endplates, osteophytosis and Schmorl's nodules. Conventional X-ray of the spine is still the first investigation in the patient presenting with spinal cord and root symptoms, despite its poor sensitivity for degenerative disk disease, especially herniated disk. Straight X-ray offers rapid overall assessment of the spine, to determine the alignment of the vertebral metameres and display congenital, degenerative, inflammatory or neoplastic changes. Although saccoradiculography and myelography offer little information on the degenerative process, they are diagnostic for herniated disk, demonstrating typical signs of extradural compression (CSF block, dural displacement and root pocket changes). These are invasive techniques, but compared with more recent imaging methods (CT and MR) they have the advantage of displaying the effects of load and posture on spinal cord and root compression. Discography will demonstrate early and late degenerative changes to the vertebral disks and any herniated material. It is an invasive method and is currently performed mainly in the work up to percutaneous treatment for herniated lumbar disc (nucleoaspiration and nucleolysis). Many new insights into degenerative disease of the spine have been gained from new imaging techniques, particularly computed tomography and magnetic resonance. These non-invasive methods have supplied more detailed information on ageing and intervertebral disk degeneration, herniated disk and concomitant osteovertebral changes. In the diagnosis of disk disease, particularly herniated disk, both these methods offer a wealth of information. CT clearly demonstrates more advanced changes to disk (discal bulging, vacuum phenomenon and calcifications) and bone (sclerosis and osteophytic outgrowths from the endplates, intervertebral joint degeneration), but will not detect early degenerative events (nuclear dehydration and spinal bone marrow changes). It displays the exact site (median, paramedian, foraminal, extraforaminal), size (small, medium, large), direction of development (cranial or caudal with respect to the disk of origin) and structural features (soft, hard) and will gauge how much of the vertebral canal is occupied (1/3, 1/2, 2/3). In the diagnosis of herniated disk CT scanning is much more reliable in the lumbosacral spine than in the cervical and dorsal because of the more favourable anatomical conditions (large intervertebral disk, wide spinal canal and abundant epidural fat which creates a natural contrast). Because MR is a non-invasive imaging technique offering high contrast resolution and direct multiplanar investigation (sagittal views!), it has revolutionized diagnostic imaging for disk diseases. Although conventional (and more recently turbo) Spin Echo sequences are mostly used in scanning to disclose spine degeneration, gradient echo sequences are also useful, especially to focus on bone changes (sclerosis of the endplates, osteophytic and interapophyseal outgrowths) and in the search for calcifications and discal gas. Spin Echo sequences are preferred for the lumbosacral spine as average thickness (3-5 cm) layers are enough to assess the intervertebral disks in this region where the abundance of epidural fat tissue enhances the contrast between vertebrae, ligaments and disks. At cervical and dorsal level where disk thickness is inferior, Gradient Echo sequences are preferred as they require thinner layers (1-3 mm) and hence volumetric acquisitions; these sequences also distinguish osteophytes from herniated material which is a common problem in the cervical spine.