Neuroradiology Case of the Week

Case 10

Matthew Cham, MD, Manoj Ketkar, MD, and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 45-year-old patient presented with sudden onset severe headache. CT scan showed a subarachnoid hemorrhage and MRI was requested to evaluate for an aneurysm.

Radiographic Findings: MRI demonstrates two aneurysms: one in the basilar artery tip (Fig. 1) and another at the left middle cerebral artery (MCA) bifurcation (Fig. 2). Each aneurysm measures approximately 12 mm in diameter. The flair images demonstrates diffuse subarachnoid hemorrhage along the left Sylvian fissure (Fig. 3). There is essentially no blood around the basilar tip and therefore, this is less likely to be the aneurysm that bled at this time.
   Digital subtraction angiography again demonstrates the two aneurysms, one at the basilar tip (Figs. 4-5) and the other in the left MCA bifurcation (Figs. 6-7).
   Three-dimensional angiographic images based on a rotational angiographic sequence demonstrates a more detailed anatomy of the basilar tip aneurysm (Figs. 8-11) and the left MCA bifurcation aneurysm (Figs. 12-14).

Figure 1	Figure 2
Figure 3
Figure 4	Figure 5
Figure 6	Figure 7
Figure 8	Figure 9
Figure 10	Figure 11
Figure 12
Figure 13	Figure 14

Diagnosis: Cerebral aneurysms

Discussion: This patient had two aneurysms, one of which bled and resulted in acute onset headache. It is clinically often difficult to distinguish which of two aneurysms has bled. In this case, the distribution of blood along the Sylvian fissure and the irregular appearance of the left MCA aneurysm indicate that this was the source of bleeding.
   Despite improvements and contribution of MR imaging, CT is still the imaging procedural choice for the diagnosis of acute subarachnoid hemorrhage.
   Approximately 85% of all intracranial aneurysms arise from the carotid circulation, which include the anterior communicating artery (30-35%), the internal carotid artery (ICA) at the posterior communicating artery origin (30-35%), and the MCA bifurcation (20%).
   About 15% of all intracranial aneurysms arise from the vertebrobasilar circulation. Five percent arise from the basilar artery bifurcation, and the remaining 1-5% arise from other posterior fossa vessels.
   Intracranial aneurysms are multiple in 15-20% of all cases. About 75% of patients with multiple intracranial aneurysms have two aneurysms, 15% have three, and 10% have over three. A strong female predilection is observed with multiple aneurysms. While the overall female-to-male ratio for intracranial aneurysms is 5:1, the ratio rises to 11:1 in patients with more than three aneurysms.
   Other lesions that might mimic the appearance of an aneurysm include vascular malfomation, hemorrhagic neoplasm cyst, and coagulopathy. Angiography and computer-assisted 3D reconstruction can help distinguish between these by generating detailed vascular anatomy.
Several large-scale studies measuring the outcomes of aneurysms, based on size, have shown that the critical size for rupture is between 7-10 mm, with larger aneurysms more likely to rupture.
    Vasospasm is the leading cause of disability and death from aneurysm rupture. Among patients with subarachnoid hemorrhage, 10-15% die, often within a month. Of those who survive, 50% have neurological deficits. Ruptured aneurysms have their highest rebleeding rate within the first day. If untreated, at least 50% rebleed during the 6 months after the initial hemorrhage.
   Treatment options for intracranial aneurysms include surgically craniotomy and clipping or endovascular surgery.
   The goal of surgical treatment is to place a clip across the neck of the aneurysm and exclude the aneurysm from the circulation without occluding normal vessels. After performing a craniotomy, microsurgical techniques with an operative microscope is used to dissect the aneurysm free from its feeding vessels without rupturing the aneurysm. Final treatment involves the placement of a surgical aneurysm clip around the neck of the aneurysm, thereby obliterating the flow into the aneurysm. The clips are manufactured in various types, shapes, sizes, and lengths and are usually MRI compatible. The operative mortality rate is less than 5%.
   The goal of endovascular treatment is to introduce platinum coils into the aneurysm and induce trombosis at the site of deployment. For each embolization procedure, a 6F guide catheter is placed in the cervical internal carotid or vertebral artery via femoral approach. A 0.014-inch microguidewire is navigated into the aneurysm cavity using magnified road-mapping technique. A microcatheter with two radiopaque markers is then advanced into the aneurysm cavity. Coils of decreasing sizes are delivered into the aneurysm cavity and electrolytically detached. Angiograms are obtained before detaching each coil to ensure preservation of the parent vessel. This process is continued until maximal angiographic obliteration of the aneurysm cavity is achieved.
   Treatment selection ultimately depends several factors, including location and size of the aneurysm and the age of the patient. Younger patients tend to undergo surgical clipping because coiling has a higher recurrence rate. Basilar artery tip aneurysms tend to be treated using the coil procedure. Wide-necked aneurysms are usually treated with clipping. In patients with small unruptured intracranial aneurysms, it is necessary to weigh the risk of intracranial hemorrhage against the risks associated with interventional procedures.
   In one study involving 68 patients treated surgically and 62 patients treated with endovascular coil embolization, surgical patients were more likely to report persistent new symptoms or disability at 4-year follow-up (34% of surgical patients vs 8% of endovascular patients) and a longer period for recovery to normal (50% returning to normal in one year for surgery and in 27 days for coil embolization).

References:

1. Biousse V, Newman NJ: Aneurysms and subarachnoid hemorrhage. Neurosurg Clin N Am 1999 Oct; 10(4):631-51.
2. Johnston SC, Wilson CB, Halbach VV, et al: Endovascular and surgical treatment of unruptured cerebral aneurysms: comparison of risks. Ann Neurol 2000 Jul; 48(1):11-9.
3. Ogawa T, Inugami A, Shimosegawa E et al. Subarachnoid hemorrhage: evaluation with MR imaging. Radiology 1993;186:345-351.
4. Olafsson E, Hauser WA, Gudmundsson G: A population-based study of prognosis of ruptured cerebral aneurysm: mortality and recurrence of subarachnoid hemorrhage. Neurology 1997 May; 48(5):1191-5.