Cerebral saccular aneurysm rupture after head injury.

When seen after head trauma, subarachnoid hemorrhage (SAH) often leads to an angiogram to look for vascular injury. Usually the study is negative; sometimes a traumatic aneurysm or dissection is seen. Occasionally, a conventional saccular aneurysm is found. The clinical history, physical examination, and computed tomography (CT) scan in such a patient may suggest that an aneurysmal SAH was the primary event, with the trauma resulting from SAH-associated incapacity. But this scenario is not usually apparent and, if a saccular cerebral aneurysm is found on angiogram after a patient has been injured, it is often difficult to know if the aneurysm is incidental, caused the SAH and trauma, or bled as a result. Most traumatic aneurysms in the carotid distribution are located at the base of the skull and are associated with skull fractures. Those located inside the cranium proper that result from nonpenetrating injury are less often linked to skull fractures. They are likely caused by contusion of the vessel, in which there is stretching or torsion of the wall. By analogy, similar forces acting on the wall of pre-existing cerebral aneurysms should cause some to bleed. Given a conservative estimate that 2% of the population harbors unruptured saccular aneurysms, a certain percentage of traumatic SAH must be caused by trauma-induced aneurysmal rupture. A couple of published case reports have verified this mechanism, though the intensity of the trauma in these cases was quite severe. The case presented here suggests that, if SAH is seen after trauma in a pattern suggestive of aneurysmal rupture, there should be a low threshold for looking for and treating “nontraumatic” saccular aneurysms. Mild to moderate trauma should not exclude such consideration.