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A 75-year-old man was found lying on the sidewalk outside a bar. There was a 2-cm laceration on the back of his head. Upon arrival in the ED, he appeared intoxicated. His speech was slurred, but he followed simple commands appropriately. There were no focal neurological deficits. The scalp laceration was cleaned and sutured.

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He was given intravenous hydration and thiamine, and was observed for 4 hours in the ED. During this time, his mental status gradually improved. His blood tests were unremarkable aside from an ethanol level of 295 mg/dL. Because of the patient’s age, history of alcoholism, and evident head trauma, a head CT was obtained (Figure 1).

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The CT is interpreted as being negative.

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After four hours, he was alert and at his “baseline” mental status and wanted to leave.

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  • Do you agree with the CT interpretation?

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A subtle but significant injury was present but difficult to see. Is anything else needed to make the finding more evident?

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  • How is a CT image created?

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To correctly interpret a head CT, it is important to consider whether it has been performed using correct technique and whether all the information needed is being displayed.

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The slice orientation should be parallel to the base of the skull and the head should not be tilted. Head tilt can cause apparent asymmetry.

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In this CT, there is asymmetry of the Sylvian fissures—the fissure appears larger on the left than the right (image 7). This is, in part, due to improper positioning of the patient. The patient’s head was slightly tilted and so within each slice, the right side of the brain is shown at a slightly more superior level than the left side. This is confirmed by noting the asymmetry of the petrous bones of the skull base in image 9.

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Even accounting for the effect of head tilt, the left Sylvian fissure and adjacent cortical sulci are slightly enlarged compared to the right (images 6 and 7). This was due to mild loss of brain tissue of the left cerebral hemisphere (encephalomalacia), which was likely the result of old trauma or cerebrovascular disease in this elderly patient.

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To visualize the significant but subtle acute traumatic abnormality ...

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