Chapter 111. Neurologic Imaging

1. What are the indications for a noncontrast head CT?

2. What are the indications for a contrast head CT?

3. What are the limitations of CT neuro imaging?

4. What are the indications for MRI neuro imaging?

5. What are the limitations for MRI imaging in the hospital setting?

This chapter will present the thought processes behind general guiding principles for neurologic imaging. This chapter does not provide an exhaustive array of images because the goal is not to train hospitalists to interpret medical images but rather to provide a framework so that they can more effectively communicate with radiologists and order the most appropriate imaging modality to optimize timely evaluation and treatment. It will always be the responsibility of practitioners to provide radiologists with relevant clinical information so that recommendations regarding specific imaging and the actual interpretation are made in the context of the patient. A number of cases will be presented that highlight the limitations of imaging when this process does not occur.

Any patient with new neurologic symptoms and signs requires prompt imaging and appropriate specialty consultation to avoid catastrophic effects upon patient outcome. This is particularly true for processes that profoundly affect the homeostasis of anatomy and physiology with or without preexisting abnormality. Therefore, this chapter will review the characteristic findings to be expected for key “do-not-miss” diagnoses that would require the practitioner to contact the appropriate specialty services for emergent consultation and/or initiate steps for transfer to a tertiary care facility.

Correlation of the neurological examination with any imaging study obtained is of paramount importance. Anatomic references may help clinicians localize abnormalities. When subtle, as at the onset of a stroke syndrome, the conviction that a potential finding is in the precise location indicated by the focal neurological deficit can make the difference between the radiologist overlooking the possibility and confidently confirming the abnormality. In turn, this approach leads to decreased imaging during the acute illness. The workup of incidental findings can also then be deferred for outpatient workup when the imaging study will often be of higher quality due to the greater ability of the recuperated patient to understand and cooperate for the imaging study.

Several drawings accompany this text to refresh memory of neuroanatomy. It can be invaluable to consult an interactive Internet atlas, especially when immediate radiologic consultation is not available, and particularly in situations in which the patient condition evolves during the hospitalization. The clarity of anatomy is greater on MRI than CT so it may prove most helpful to use an MRI reference atlas, even for looking at the more commonly obtained in the acute care setting CT scan (Figure 111-1).