[Imaging of lumbar stenosis]

The spinal canal is a type of articulated pipe, with rigid rings articulated by joints. It can be divided into a central part, which contains the dural sac, and lateral parts, which contain the nerve roots. The role of imaging is to detect the presence and characterize the nature, level, and severity of stenotic lesions and their impact on neural elements. Stenoses can be constitutional or acquired and involve the central and/or lateral canal. Constitutional stenoses affect both rigid and soft segments whereas acquired stenoses affect mainly the mobile segments. Signs of constitutional stenoses at conventional radiography, CT and MRI will be described. Acquired stenoses are multi-factorial in etiology and more difficult to evaluate. Intra-spinal soft tissues and dynamic factors, poorly assessed at CT and MRI (static imaging), play a major role in this type of stenoses. Currently, only myelography with dynamic evaluation is able to demonstrate the importance of these factors or degree of dynamic stenosis. The lateral canal is divided in three parts: two mobile segments (disco-articular interval, and intervertebral foramen) on each side of a fixed bony segment (lateral recess). The different types of stenoses involving these segments and best imaging technique to demonstrate their presence are described.