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Magnetic resonance imaging (MRI) has become the examination of choice for imaging the spine and its contents. Although diseases of the spine are very common, clinical syndromes may mimic each other, necessitating imaging such as MRI for diagnosis and patient management. When considering performing and interpreting imaging of the spine, it is important to first understand the clinical context. The most common symptom is back pain. While back pain is epidemic and associated with great disability, back pain without neurologic compromise is usually not an emergency. Fever or history of malignancy should raise suspicion and urgency. Patients with spine disorders may also present with radiculopathy and myelopathy. Radiculopathy results from mechanical compression or irritation of a spinal nerve, often within a lateral recess or neural foramina. This results in specific sensory deficits and muscle group weakness. However, myelopathy is caused by mechanical spinal cord compression or by intrinsic lesions of the spinal cord. Classic symptoms of myelopathy include bladder and bowel incontinence, spasticity, weakness, and ataxia. As the spinal cord has limited healing ability, an acute myelopathy is an emergency and should prompt urgent imaging, preferably with MRI given its superior evaluation of the spinal cord and canal.
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ANATOMY AND TECHNIQUE
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Given its complex anatomy and length, the spine remains one of the most difficult parts of the skeletal system to evaluate. The spine is composed of multiple vertebrae, which protect the spinal cord and proximal spinal nerves. The spine is composed of seven cervical, twelve thoracic, and five lumbar vertebrae as well as the fused sacrum and coccyx vertebral elements. Except for the first and the second cervical vertebrae, the vertebrae share a similar structure including a vertebral body containing trabecular bone. The posterior elements include the articulating processes, lamina, and spinous process. Intervertebral discs separate the vertebrae and serve as shock absorbers.
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The standard spine MRI protocol includes imaging in the sagittal and axial planes using T1- and T2-weighted sequences (Figures 14-1 and 14-2). Additional coronal images may be helpful especially in the setting of scoliosis. Short tau inversion recovery (STIR) or fat-saturated T2-weighted sequences are also invaluable for increased sensitivity of marrow edema. In the adult, the normal vertebral marrow generally has intermediate to high signal intensity on the T1-weighted images and low signal intensity on T2-weighted images. The intervertebral disc is normally high signal intensity on T2-weighted images because of its high water content but frequently loses signal over time with loss of water content. Contrast-enhanced T1-weighted sequences are helpful for evaluation of suspected neoplasm, infection, and inflammatory diseases. Proton density (PD) sequences may be useful in detecting cord signal abnormalities associated with demyelinating diseases such as multiple sclerosis (MS). Gradient-recalled echo (GRE) sequences are helpful for detecting blood products associated with cord hemorrhage in the setting of trauma.
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