TABLE 2291 Considerations for Nonenhanced Head CT for Headache

FIG. 229-3. Axial CT demonstrates areas of increased density compatible with subarachnoid hemorrhage (SAH) (straight arrows). There is also early hydrocephalus with the temporal horns dilated (curved arrow).

Headache associated with unexplained fever is also an indication for neuroimaging, particularly when there is associated meningismus and photophobia. Although diagnosis is made by lumbar puncture, imaging is typically recommended to exclude hydrocephalus. Despite the absence of scientific validation, it has become the standard of care to precede lumbar puncture with nonenhanced head CT (NECT). Secondary hydrocephalus tends not to obviate performing lumbar puncture, but it will lead the physician to performing a low-volume lumbar puncture. Further, it can alert the physician to the possible need for shunt placement.

Acute or recurrent hydrocephalus can present with headache as well as nausea, incontinence, and ataxia. There is generally an increase in the intraventricular volume. Hydrocephalus can be caused by a number of processes including prior subarachnoid hemorrhage, prior trauma, meningitis, masses obstructing the ventricular system, or masses external to the ventricles but causing obstructing compression due to size or edema. In the evaluation of patients with suspected hydrocephalus, NECT is an adequate evaluation. It will enable detection of patients requiring emergency placement of intraventricular shunt catheters. If hydrocephalus is identified and the etiology remains undefined, a contrast-enhanced MRI examination with its superior ability to image in multiple planes should be performed. Lastly, in examining patients with an intraventricular shunt catheter and suspected recurrent hydrocephalus, the NECT should be accompanied with a plain film shunt series. The latter will detect possible kinks or disruptions of the catheter (see Chap, 228 for detailed discussion).

Generally an intraparenchymal mass, large enough to cause headache will be associated with neurologic signs prior to, or concurrent with, the development of headache. Thus, in instances where tumors are associated with headache, they are large and readily detectable on NECT; indirect effects, such as obstruction to CSF outflow, will also be evident on NECT.

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