Magnetic Resonance Imaging Of The Spine

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Since the mid 1980s, MRI of the spine has attained acceptance as the premier modality in the evaluation of spine diseases. MRI is eloquent in the evaluation of both benign or malignant spinal processes and is unique in its inherent noninvasive ability to image the spinal cord and surrounding structures such as CSF, dura, and adjacent ligaments. The utility of spine MRI can therefore be discussed in terms of the three classic categories of spine disease: extradural, intradural-extramedullary, and intramedullary processes.

A frequent cause of epidural disease is intervertebral disc pathology. MRI can uniquely image the intervertebral disc directly, without the use of contrast material. Disc integrity can be assessed in terms of degeneration, abnormal disc bulges, or herniations. High-resolution T2-weighted images of the disc can diagnose annular and circumferential tears that previously required injection of contrast material (i.e., CT discography). Any affect on spinal contents, either the spinal cord or existing nerves in the cervical and thoracic regions, or nerve impingement on

Figure 23-12 Brain stem glioma. Midline sagittal T1-weighted image shows a focal enlargement of the pons with decreased signal.

Figure 23-13 Central neurocytoma. Axial post-contrast T1-weighted image show a heterogeneously enhancing, rounded intraventricular mass within the anterior portion of the lateral ventricle.

either the cauda equina or existing nerve roots in the lumbar region can be assessed. Additionally, inherent signal aberrations within the intervertebral discs can also be analyzed for primary intrinsic disc abnormalities such as infectious discitis and associated vertebral osteomyelitis.

Although MRI is inherently poor for showing dense, cortical bone, it is extremely useful in the evaluation of infiltrative bone marrow diseases. Both degenerative and malignant bone marrow changes can be detected and categorized based on MR signal patterns. Benign processes such as post-traumatic bone edema, fatty bone marrow infiltration, or benign neoplasms such as primary vertebral hemangiomas can be readily distinguished from carcinomatous changes (i.e., vertebral plasmacytoma or frank metastatic disease with or without vertebral destruction or paravertebral soft tissue involvement). MRI is also useful in the analysis of degenerative spondylosis and complications of spondyloarthropathies as well as in the evaluation of benign or malignant spinal canal or foraminal stenosis. MRI is pivotal in the emergency evaluation of post-traumatic spinal cord compression.

Infrequently, intradural extramedullary masses present for evaluation. In the cervical and thoracic regions, meningiomas, neuromas, and arachnoid cysts predominate, whereas, in the lumbar spine, schwannomas, ependymomas, or, rarely, intradural disc herniations are more common. Occasionally, intradural extramedullary metastases are encountered that may stud the spinal cord and meninges with metastatic deposits.

MRI is uniquely sensitive in detecting the presence of intramedullary spinal cord diseases. Common primary intramedullary neoplasms that can be elucidated include astrocytoma, ependymoma, and spinal cord hemangioblastoma. Contrast medium-enhanced MRI can help differentiate tumoral cord edema, as seen in these entities from the primary tumoral masses. Other causes of abnormal signal within the spinal cord include inflammatory or demyelinating diseases such as acute disseminating encephalomyelitis, transverse myelitis, or multiple sclerosis. The evaluation of spinal cord edema, secondary to trauma, either from chronic discogenic disease or in situations of acute complex fracture injuries is becoming increasingly essential, particularly in national trauma centers.

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