When you see a trauma patient with a subarachnoid hemorrhage, it's easy to assume that the hemorrage was a direct result of the trauma. But what if the occurence of the trauma was actually secondary to the hemorrhage? In this video, from our Brain CT Essentials course, we'll discuss two unusual cases involving patients who present with subarachnoid hemorrhages after trauma, and why you shouldn't always believe what you see.
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Subarachnoid hemorrhage is frequently evident in patients after head trauma. But, we need to consider its presence carefully since in some cases, subarachnoid hemorrhage contributes to the traumatic event, rather than its consequence. A reasonable approach is to consider the extent of the hemorrhage, and how it corresponds with the magnitude of trauma based on the history and other signs of head trauma, such as scalp swelling or fractures.
Traumatic subarachnoid hemorrhage is frequently limited to a few sulci over the convexities of the brain, as in this example, of a patient who struck his head on a concrete floor after a fall. But the pattern of hemorrhage alone is not sufficient to predict its cause. The nature of the traumatic injury is an important predictive factor as well.
For example, subarachnoid hemorrhage on the scan of a pedestrian who is struck by a car while crossing the street is most likely traumatic. But diffuse subarachnoid hemorrhage in a 50 year old patient, found unconscious after a unwitnessed minor car crash should lead you to consider that the hemorrhage was secondary to an underlying ruptured aneurysm.
This patient was noted to have subarachnoid hemorrhage on CT after a motor vehicle collision. But because of poor history regarding the nature of the accident, this patient had CT angiography with volume reconstructions because there was concern for a vascular cause of the hemorrhage since the patient had no evidence of head trauma. The CTA was negative and no further imaging was recommended.
This 45 year old woman was found unconscious off the road in a car that it hit a tree, but the event was unwitnessed. She had no memory of the accident, which is common. Her CT demonstrated diffuse subarachnoid hemorrhage and an incidental colloid cyst. Based on the extent of hemorrhage on her CT scan, vascular imaging was obtained.
Her digital subtraction angiogram demonstrated in anterior communicating artery aneurysm. So her subarachnoid hemorrhage was from a ruptured aneurysm that was most likely the cause of the accident as well. CT imaging of this patient after a car accident revealed subarachnoid hemorrhage, but there was also a typical traumatic hemorrhage in the splenium of the corpus callosum, left frontal lobe, along with scattered subarachnoid hemorrhage, seen here in the cortical sulci.
In a case like this, unless there's compelling clinical history to the contrary, the imaging is entirely consistent with subarachnoid hemorrhage secondary to trauma. Even when you see uncommon patterns of hemorrhage, as in this case, where the subarachnoid hemorrhage has filled the basilar cisterns, but is accompanied by a parenchymal hemorrhage, you cannot conclude that the hemorrhage is not due to a ruptured aneurysm.
This case also demonstrates another finding associated with aneurysmal subarachnoid hemorrhage. Notice that the temporal horns are dilated. This is a sign of communicating hydrocephalus, that is not commonly encountered with subarachnoid hemorrhage when it's the result of trauma. A few times in a career you'll see cases like this one where there was rupture of a pseudo-aneurysm that resulted from an injury to the arterial wall from trauma.
A pseudo-aneurysm differs from a typical aneurysm since it has fewer layers in its wall. This patient was found unconscious in her car after they'd gone off the road, at night, at high velocity. Her CT had an unusual pattern of subarachnoid hemorrhage that was seen in the pericallosal cistern rather than within the corpus callosum itself. A CT angiogram was ordered while the patient was still in the emergency room.
Sagittal reconstructions of that CTA revealed a small aneurysm of the anterior cerebral artery that was confirmed on digital subtraction angiography. The change in its appearance between the CTA and the DSA that followed, suggest there was enlargement of this pseudo-aneurysm.
This particular injury of the anterior cerebral artery has been reported after trauma and is thought to be the result of an injury to the pericallosal, as a result of its contact with Falx during the trauma. This other patient had a penetrating injury to the skull that resulted in a parenchymal hemorrhage and diffuse subarachnoid hemorrhage that filled the suprasellar cistern and interpeduncular cisterns.
A digital subtraction angiogram in this case revealed that the cause of the subarachnoid hemorrhage was a middle cerebral artery pseudo-aneurysm, that was a result of trauma but in this case, the penetrating injury. The point of these last two unusual cases is to illustrate that subarachnoid hemorrhage in a patient after trauma is not always an either or question of trauma versus ruptured aneurysm.
Rarely, the subarachnoid hemorrhage is from a ruptured pseudo-aneurysm that formed at time of the trauma. So when you see subarachnoid hemorrhage in a patient after head trauma put on your Sherlock Holmes hat, and consider the case in the context of the magnitude of the trauma, the circumstances of the trauma, and the pattern of bleeding.
In the ER CT angiography is a valuable non-invasive test that can help establish the diagnosis in most cases, when uncertainty regarding the cause of the subarachnoid hemorrhage persists.