Overview of Imaging Procedures Available for Spinal Diagnosis

Plain Radiography

The last few decades have seen several newer imaging techniques become mainstream, yet plain radiographs continue to be used for basic anatomic assessment of the spinal column. The widespread availability of imaging infrastructure, the significant cost benefits, and the lower radiation dose associated with obtaining plain films support their continued and extensive use. Plain films can be obtained from multiple viewpoints with the selection of particular views tailored according to the information sought by the clinician. These include the commonly used lateral and anteroposterior or frontal projections, which are used for initial evaluation and may be supplemented with additional views, such as oblique, swimmers, flexion-extension, and weightbearing.

Conventional radiography provides adequate visualization of bony details and is used to detect defects in bone anatomy such as fractures or misalignment ( Fig. 64.1 ). A lateral viewpoint with the patient alternating between flexion and extension allows for assessment of instability of the spinal column in cases of suspected injury to the spinal column, whereas a ventral viewpoint can be used with the patient bending from side to side. Besides assessment of bone integrity, plain films are good for inspecting proper placement of grafts and instrumentation, both intraoperatively and postoperatively.

With time, the practice of obtaining hard-copy plain films has largely been replaced by digital radiography where, in place of film, a digital detector is exposed to the ionizing radiation transmitted through the patient. This results in the conversion of radiation energy to light energy, which is subsequently converted to a digital image that can be directly transferred to the picture archiving and communication system. The resulting cost savings from transitioning to a digital platform, the flexibility of image access, manipulation, and storage, and the shortened duration for obtaining radiographs have sped up the switch to digital films. The lack of processing time in being able to view films following exposure to ionizing radiation makes digital radiographs suitable for use in an intraoperative setting.

Although radiographs offer excellent visualization of bone characteristics, they are of limited use in the evaluation of spinal cord, bone marrow, and soft tissues like the intervertebral discs (IVDs), ligaments, nerves, and paraspinal tissues. This translates to their limited role in evaluation of myelopathy, IVD pathology, and spinal stenosis. The ability to assess bony anatomy depends upon the application of acceptable radiographic technique and proper interpretation of radiographs. Even if adequately visualized, bony details on radiographs are of inferior resolution compared with computed tomography (CT) scans.

Myelography

Myelography is an invasive technique where an exogenous nonionic contrast agent is injected into the subarachnoid space via a lumbar (midline or oblique approach) or lateral cervical puncture, followed by imaging of the relevant area of the spine. Subsequently, the contrast agent is absorbed into the bloodstream to be ultimately extracted by the kidneys. Myelography is indicated when obtaining magnetic resonance imaging (MRI) is not possible owing to MRI-incompatible implants, when image quality is compromised because of the presence of spinal hardware, or when spinal abnormalities exist that make MRI challenging. The nonionic contrast material allows for delineation of both intradural and extradural spaces, with myelography often used in conjugation with CT (CT myelography) for outlining structures, including spinal cord and nerve roots, and their relationship to the soft tissue and bony anatomy. ^, The ability of newer generations of CT scanners to image the entire spinal column in a matter of seconds allows the acquisition of multiplanar reformatted images for three-dimensional (3D) evaluation of anatomic abnormalities in myelograms.

Myelography, both plain and CT, is a relatively safe and well-tolerated procedure and is associated with a lower rate of complications compared with previously used contrast agents. Currently, postprocedural headache is the most common side effect. Similar to conventional radiography, the use of ionizing radiation and limited utility in defining soft tissue are major limitations of myelography.