General Uses And Limitations

As CT technology has advanced, the role of CT in the emergency department (ED) has also increased enormously. A CT scanner is in, or adjacent to, many EDs today in the United States, in recognition of its fundamental utility and to minimize necessity for patient transport. The only real disadvantages of CT are its relatively high cost and the use of ionizing radiation. Standard charges for conventional and spiral CT are the same. Head CT continues to be the primary imaging study for screening ED patients acutely, particularly for detection of acute hemorrhage, trauma, and cerebrovascular accident. Magnetic resonance imaging (MRI), however, may have an additional role when posterior fossa pathology or subtle parenchymal abnormalities are suspected. In general, CT is the imaging study of choice for the examination of the retroperitoneum and for many disorders of the abdomen and pelvis. At many institutions, spiral CT has become the primary imaging modality for detection of acute appendicitis4 and ureteral calculi. It is also the modality of choice for many disorders of the mediastinum and lungs. Fractures and other bone pathology are often best visualized with CT, and it is excellent for detecting cervical spine, pelvic, and facial bone fractures.

Only a few areas of the body are poorly imaged with CT. The pituitary fossa and the posterior intracranial fossa are difficult to visualize because the adjacent bony structures cause significant streak artifact. MRI is the preferred study in these anatomic areas. CT is not sensitive in differentiating spinal cord or nerve roots from cerebrospinal fluid (CSF) unless contrast has been injected into the CSF space. MRI is the imaging study of choice to evaluate the spinal cord.

Although spiral scanning data can be reformatted into high-quality sagittal and coronal plane images, conventional CT is usually limited to the axial (transverse) plane. There are anatomic areas (such as the head and ankles) that can be positioned in the gantry of conventional CT scanners to obtain direct coronal images.

The role of CT in the evaluation of all potential ED presentations is beyond the scope of this chapter. The reader is referred to specific chapters of chief complaints or diagnoses for a discussion of the potential value of CT for each topic.

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