Subdural hematoma caused by rupture of a posterior cerebral artery aneurysm

Discussion

Intracranial aneurysm rupture is classically characterized by subarachnoid hemorrhage (SAH), and it is often complicated by intracerebral hematoma (ICH) and intraventricular hematoma (IVH). But the clinical incidence of SDH complication is very low, which was reported to be 0.5-7.9%.1,2 And the most frequently reported site of aneurysm location is the internal carotid artery (ICA)-posterior communicating artery, which is followed by aneurysms of middle cerebral artery and distal anterior cerebral artery.2,5 We described a case of ruptured PCA aneurysm presenting as subdural hematoma, which is relatively rare.

Several mechanisms have been proposed to explain the occurrence of SDH after aneurysm rupture:1,2,5,6 1)Successive minor bleedings case the developing of adhesions, resulting in final rupture into the subdural space; 2) high-pressure hemorrhage may lead to rapid accumulation of blood from the leaking aneurysm, rupturing the arachnoid membrane; 3) intracerebral hemorrhage may rupture through the cortex and cause a tear of the arachnoid membrane; 4) a carotid artery aneurysm arising from the part of carotid artery within the subdural space may rupture and cause subdural hematoma directly; and 5) the acute enlargement of the intracavernous aneurysm may erode the cavernous sinus wall. As in this case, the patient had suffered headache since 4 days before he was admitted to hospital, this warning sign may reflect the presence of successive small bleedings.

Whatever the cause, most cases of aneurysmal SDH show SAH on the CT scans, and this will address the diagnosis upon a vascular cause of hemorrhage. In a small percentage of cases, however, aneurysmal rupture can cause a subdural blood collection without SAH, a rare condition called pure SDH, which may lead to inappropriate diagnosis and management.1,7 Since cranial CT cannot reveal the cause of these pathologies, it is potential for such patients to undergo CTA or digital subtraction angiography as soon as possible to reveal the source of bleeding. Then appropriate therapy should be conducted depending on the location of the aneurysm and the clinical situation promptly.

Aneurysms of the PCA are rare. Because of the presence of complex perforating branches and adjacent to the cranial nerves, the surgical approach and exposure of the PCA is technically challenging.8 So endovascular treatment is relatively a safe and effective approach with low mortality and morbidity for these aneurysms.8,9 In this case we performed stent-assisted coil embolization to treat the aneurysm in the P2 segment of the PCA. Compared with the parent artery occlusion, the advantage of stent-assisted techniques is not only that the tight aneurysm packing with coils is attainable with less risk of coil migration or coil bulging into the parent artery, but that can preserve the parent artery, avoiding ischemic neurological events.10

Even though the patient did not undergo direct surgery, the subarachnoid hemorrhage in the left perimesencephalic space and the extravasation of the blood along the interhemispheric subdural space all suggest a causal association between the subdural bleeding and the aneurysm.

In conclusion, spontaneous arterial SDH due to a P2 segment of PCA has been rare reported earlier. We should be reminded that cerebral aneurysm rupture should be considered in spontaneous subdural hematoma, especially those with no evidence of subarachnoid hemorrhage, and the appropriate treatment should be planned with expediency