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INTRODUCTION

The basic modalities available for imaging the central nervous system are plain films, computed tomography (CT), magnetic resonance imaging (MRI), myelography and post-myelography CT, catheter angiography, ultrasonography, and nuclear medicine techniques. The strengths and weakness of each modality, and guidelines regarding the “right” test to order, are included in the following discussion.

PLAIN FILMS

General Considerations

Although largely replaced by CT and MRI, plain films of the skull and spine are still used for screening purposes in various clinical situations (Figure 3–1). The term plain films is becoming increasingly anachronistic in the digital age. Plain radiographs is more accurate.

Figure 3–1.

Lateral plain film of the cervical spine reveals traumatic occipitovertebral dissociation manifested by separation of the occipital condyles from the atlas (C1) and marked prevertebral soft tissue swelling.

Advantages

Plain films are inexpensive and easy to obtain. Portable x-ray machines can be moved to the patient’s bedside and into operating rooms. The entire spine can be rapidly surveyed. Plain films provide good detail of bone in an easily understood format.

Disadvantages

Overlapping structures obscure pathology and complicate film interpretation. As plain films are replaced by CT and MRI, expertise in their interpretation is disappearing. Plain films provide virtually no soft tissue information.

When to Order

1. Foreign bodies

Plain films can identify and locate metallic foreign bodies in the skull or spine. They often are used to screen patients suspected of having metallic foreign bodies near vital structures before MRI examination.

2. Spinal alignment and stability

Plain films are used to evaluate spinal alignment in patients with spinal trauma, rheumatoid arthritis, and scoliosis. Comparison of films taken in flexion and extension is a good method of ascertaining spinal stability.

3. Spinal fractures, infections, and metastases

Plain films are sometimes used in the initial evaluation of patients with suspected fractures, infections, and metastases of the spine.

4. Spinal anomalies

Plain films are also used to identify congenital spinal anomalies, such as segmentation anomalies, hemivertebrae, and spina bifida.

5. Degenerative disk disease

Many physicians use plain films as an inexpensive survey of degenerative changes in patients with chronic back or neck pain.

6. Bone lesions

Plain films remain the mainstay in the diagnosis of focal primary bone lesions of the skull and spine.

7. Ventriculoperitoneal shunt

A shunt series, consisting of plain films of the skull and neck, chest, and abdomen, is often used in the initial evaluation ...

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