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INTRODUCTION

MRI has become the examination of choice for imaging the spine canal and its contents. While common, diseases involving the spine 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. Although 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 sensory deficits and muscle group weakness in the part of the body served by that nerve. On the other hand, myelopathy is caused by mechanical compression or intrinsic lesions of the spinal cord. Classic symptoms of myelopathy include bladder and bowel incontinence, spasticity, weakness, and sensory deficits. 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 canal and cord.

ANATOMY AND TECHNIQUE

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 second cervical vertebrae, the vertebrae share a similar structure including a vertebral body containing trabecular bone and posterior elements containing the articulating processes, lamina, and spinous processes. Intervertebral discs separate the vertebrae and serve as shock absorbers.

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 allow for increased sensitivity for edema. Following infancy, the normal vertebral marrow has higher signal intensity on the T1-weighted images relative to the intervertebral disc spaces at 1.5 T and muscle at 3 T due to high fat content. The intervertebral disc is normally high signal intensity on T2-weighted images due to high water content but frequently loses signal over time due to 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. Newer sequences that are useful in spinal ...

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