American Board of Internal Medicine (ABIM) Certification Practice Exam

What CT finding is considered an absolute contraindication for tPA administration?

1. Hypodensity greater than 1/3 of the MCA territory

2. Hematoma smaller than 1/3 of the MCA territory

3. Subdural hematoma

4. Any midline shift

The correct answer is: Hypodensity greater than 1/3 of the MCA territory

In the context of administering tissue plasminogen activator (tPA) for the treatment of acute ischemic stroke, the absolute contraindication involves specific CT findings that can indicate a significant risk for hemorrhagic complications. The finding of hypodensity greater than one-third of the middle cerebral artery (MCA) territory suggests a significant area of brain tissue that is already infarcted. This finding is critical because administering tPA in the presence of substantial infarction may increase the risk of hemorrhagic transformation, especially in an area where the vascular supply is compromised. If the brain tissue has already undergone major ischemic changes, restoring blood flow rapidly might exacerbate existing damage and lead to bleeding within the area. In contrast, other findings noted, such as a smaller hematoma or subdural hematoma, may still allow for the administration of tPA under certain circumstances and evaluations, as the risks associated with them are generally lower than with a large area of hypodensity or established ischemic tissue damage. Similarly, a midline shift, which can indicate increased intracranial pressure, might also not be as definitive for prohibiting tPA, especially without considering the overall clinical picture. In summary, the presence of hypodensity greater