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Imaging in Subarachnoid Hemorrhage

Overview

Subarachnoid hemorrhage (SAH) is a condition in which there is bleeding into the subarachnoid space around the brain and spinal cord, as shown in the images below. This space is normally filled with clear, colorless cerebrospinal fluid (CSF). The most common causes of subarachnoid hemorrhage are head trauma and rupture of an intracranial aneurysm. Atraumatic subarachnoid hemorrhage accompanied by the sudden onset of neurologic symptoms has been termed hemorrhagic stroke. Radiologic evaluation is essential for determining the prognosis and treatment of subarachnoid hemorrhage. Radiologic interventional procedures have become increasingly important for the management of this condition.

Subarachnoid hemorrhage (SAH). A nonenhanced compu

Subarachnoid hemorrhage (SAH). A nonenhanced computed tomography scan of the brain that demonstrates an extensive SAH filling the basilar cisterns in a patient with a ruptured intracranial aneurysm.

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An angiogram showing the onset of an aneurysmal ru

An angiogram showing the onset of an aneurysmal rupture, with extravasation of contrast material into the subarachnoid space from the anterosuperior aspect of a bilobed aneurysm in a posteroinferior cerebellar artery.

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A late angiogram demonstrating contrast medium fil

A late angiogram demonstrating contrast medium filling the posterior fossa subarachnoid spaces, including the ambient, prepontine, and perimedullary cisterns.

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Anatomy

Rupture of a saccular intracranial aneurysm causes approximately 80% of nontraumatic subarachnoid hemorrhage. Intracranial aneurysms develop predominantly at vessel bifurcation or branching points. Saccular aneurysms are acquired lesions that rarely present before the third decade of life.

Most intracranial aneurysms occur at typical locations within or near the circle of Willis. The most common specific locations of intracranial aneurysms are at the middle cerebral artery bifurcation and along the anterior communicating artery. These 2 locations account for approximately 60% of all intracranial aneurysms. Other common sites of aneurysm formation in the anterior circulation are at the origins of the posterior communicating and ophthalmic arteries. Approximately 10-20% of aneurysms arise from the vertebral and basilar arteries.

The tip of the basilar artery is the most common location of aneurysm formation in the posterior circulation. The origins of the posterior inferior cerebellar arteries also are common sites of aneurysm formation. Arteriovenous malformations (AVMs) occur throughout the brain without predisposition for a particular anatomic area.

Neuroradiologic intervention

Approximately 10-30% of patients with subarachnoid hemorrhage die before reaching medical attention. For those reaching a hospital alive, mortality rates for nontraumatic subarachnoid hemorrhage have been reported in the 30-60% range.
In-hospital mortality has been shown to be lower at facilities with interventional neuroradiology.

The endovascular treatment of intracranial aneurysms has evolved rapidly. The initial experience in the treatment of intracranial aneurysm with catheter-based techniques relied predominantly on parent-vessel occlusion by various mechanisms, including endovascular detachable balloons and coils. With widespread physician acceptance and approval of the Guglielmi detachable coil (GDC) by the US Food and Drug Administration (FDA), the emphasis of endovascular management has changed to aneurysm occlusion with the preservation of patency of the parent vessel.

Although the primary indication for GDC embolization of an intracranial aneurysm is for patients with surgically high-risk aneurysms, a growing body of evidence indicates that endovascular treatment should be considered as a primary option for aneurysm in certain anatomic locations. Specifically, patients with basilar tip aneurysms appear to have better outcomes with endovascular therapy than with open craniotomy and surgical aneurysm clipping. The technical expertise and experience of the local treating physicians may determine the optimal treatment for aneurysms at other locations.

Improvements in small-vessel angioplasty balloon catheters and promising initial therapeutic results have led to increased use of intracranial angioplasty for the treatment of subarachnoid hemorrhage–induced vasospasm. In general, intracranial angioplasty may be performed in the internal carotid, proximal middle or anterior cerebral, and vertebral and basilar arteries. Selective intra-arterial papaverine infusion has also been used in the treatment of intracranial vasospasm.

Preferred examination

Computed tomography (CT) scanning without intravenous contrast enhancement is the preferred initial diagnostic study, with cerebral angiography the next procedure of choice.

Advances are being made in the noninvasive vascular imaging modalities of CT angiography and magnetic resonance angiography (MRA). At institutions with a high degree of expertise and experience, these noninvasive imaging technologies may be used in addition to or even replace catheter angiography.

At most institutions in the United States, conventional angiography remains the standard for evaluating patients with subarachnoid hemorrhage. If a CT scan of the brain is negative and a strong clinical suggestion of subarachnoid hemorrhage exists, a CSF tap may be of value for confirming this diagnosis. If the CSF reveals no evidence of subarachnoid hemorrhage (ie, either overt hemorrhage or xanthochromia), cerebral angiography may not be indicated.

For SAH caused by rupture of an intracranial aneurysmal vessel or arteriovenous malformation, emergency physicians have classically performed a noncontrast CT (NCCT), followed by a lumbar puncture. However, as CT technology has advanced, many studies have questioned the need for lumbar puncture and have advocated for noninvasive techniques, such as NCCT alone or NCCT with CT angiography.

Limitations of techniques

Nonenhanced CT scanning may fail to depict small subarachnoid hemorrhages, particularly if imaging is performed several days after the onset of bleeding. Furthermore, CT scans are degraded by patient motion. If a patient cannot cooperate because of an alteration in mental status, sedation may be necessary to obtain satisfactory diagnostic images.

Cerebral angiography is an invasive procedure with a small but significant risk of complication. Without the use of a special hemostasis device, at least 6 hours of bed rest is required after the procedure to prevent bleeding at the puncture site. Additionally, because of its small false-negative rate for aneurysm, cerebral angiography must be repeated after 1-2 weeks to further improve its diagnostic sensitivity.

Differential diagnosis and other problems to be considered

The differential diagnosis includes cerebral aneurysm, cerebral arteriovenous malformation, and stroke.

Traumatic subarachnoid hemorrhage must be distinguished from spontaneous subarachnoid hemorrhage. Cerebral angiography may sometimes be avoided if it can be confidently established that the hemorrhage is caused by trauma. This distinction can be difficult to make, because the traumatic event may not have been witnessed and the patient may be unable to provide a reliable history. There is often a question as to whether a spontaneous subarachnoid hemorrhage has caused a traumatic event or the trauma caused the hemorrhage. When in doubt, it is usually best to obtain a cerebral angiogram to exclude an underlying aneurysm or vascular malformation; such angiograms can sometimes be limited to the location of the hemorrhage, if no pathology is detected.

Special concerns

Complete and proper written informed consent must be obtained before diagnostic and interventional procedures are performed.
The informed consent form should specifically include the possibility of stroke with diagnostic cerebral angiography and neurovascular interventional procedures.

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