A significant finding in a CT scan for diagnosing stroke would likely be:

The presence of an infarct on a CT scan is crucial for diagnosing a stroke, particularly an ischemic stroke, which is the most common type. An infarct indicates that blood supply to a specific area of the brain has been compromised, leading to tissue death. In the early stages after a stroke, changes on a CT scan may not be immediately visible, but within a few hours, an infarct may become apparent as areas of hypodensity (darker spots) on the scan.

In contrast, while the presence of an aneurysm can denote a risk for hemorrhagic stroke, it does not directly indicate a stroke has occurred. Edema may develop in response to an infarct or other brain injury, but it is not a direct finding that confirms the diagnosis of a stroke. Similarly, herniation is a severe complication that arises due to increasing intracranial pressure, often secondary to edema or increased mass effect but does not directly contribute to identifying a stroke. Therefore, identifying an infarct is the most significant finding that directly supports the diagnosis of stroke on a CT scan.