Arteriographic Evaluation of Cerebrovascular Disease

Diagnostic Indications

Catheter-based angiography provides a very high spatial resolution (200–300 μm) with excellent temporal resolution, making it invaluable in assessing primary neurovascular disease. Diagnostic indications include evaluation of intracranial hemorrhagic and ischemic disease, characterization of intracranial aneurysms, arteriovenous malformations (AVMs), dural arteriovenous fistulas, acute ischemic stroke, cerebral vasculopathy of various causes, and cerebral vasospasm. Diagnostic angiography in certain circumstances is followed by endovascular therapy.

Intraoperative Indications

Angiography may be performed in the operating suite using mobile or embedded C-arm technology. Intraoperative angiography is most often used during surgery for intracranial aneurysms or AVMs. Angiography allows immediate assessment of the surgical results, facilitating operative modifications that may be necessary before closing the skull. During aneurysm surgery, up to 11% of cases undergo clip adjustment as a result of intraoperative angiography findings. Radiolucent surgical equipment (head holder, operating table) is helpful but not essential.

Surveillance

Angiography is used to follow patients who have undergone previous endovascular treatments or patients who have lesions for which intermittent monitoring is safer than direct intervention. It is particularly important for assessing posttreatment recurrence of aneurysms or AVMs.

Access to the Arterial System

The first step in catheter-based angiography of the cerebral vessels is safe arterial access. This is most typically accomplished through a transfemoral route. The common femoral artery is punctured at the femoral head ( Figure 1 ).

The location of the puncture site is important because it allows effective compression of the arteriotomy site after the procedure. A puncture location too low (in the superficial femoral artery) risks inadequate postprocedural compression because of the absence of a firm structure to compress against, and a puncture too high (above the inguinal ligament) risks retroperitoneal hematoma formation. Transfemoral angiography is usually performed with a sheath but can be accomplished without one. By convention, the right groin is the site of access unless extenuating circumstances (e.g., previous right iliofemoral surgery, right iliofemoral atherosclerotic occlusion) are present, in which case the left groin is used.

The artery may be located by manual palpation for the femoral pulse and the underlying femoral head or, if location by palpation is difficult, with ultrasound guidance. Arterial puncture can be single or double walled and is typically accomplished using a micropuncture kit, and then the Seldinger technique is used to dilate the arteriotomy enough to allow the sheath to be inserted.

If femoral access is not an option because of the patient's anatomy or comorbid disease, alternative routes of access may be used. The most common of these is a radial artery approach. This should be preceded by an Allen test to ensure adequate collateral circulation to the hand from the ulnar artery. Data suggest poor collateral circulation in the hand is present in approximately 23% of patients, and if it is noted with the Allen test, it is a reason to avoid the radial approach. The technique of access resembles the transfemoral approach, with placement of a 4 or 5 French (Fr) sheath. A spasmolytic medication (e.g., calcium-channel blocker) infused through the radial sheath is often required to prevent reactive spasm and possible thrombosis of the radial artery. A second alternative is a brachial artery approach, but because this artery is the sole vascular supply to the distal upper extremity, the consequence of access complications is more pronounced.

The advantages of the radial and brachial approaches include avoiding the risk of retroperitoneal hemorrhage and the need for bed rest associated with femoral artery puncture. In addition, an upper extremity approach may be useful for access to subclavian artery branches when vessel tortuosity prohibits a femoral approach. When an upper extremity approach is necessary, we favor the high brachial approach over the axillary approach because it provides a better opportunity for compression after the procedure.

Other, much less common options for arterial access include direct carotid artery puncture with sheath placement or a retroperitoneal lumbar stick, but these are rarely performed in current practice.

Sheath and Catheter Principles

The presence of a sheath allows rapid catheter exchange and decreases the risk of intraprocedural bleeding at the puncture site by minimizing trauma to the arteriotomy. Typically, a short sheath (10–13 cm) is used, though in the presence of significant iliofemoral tortuosity or atherosclerosis, sheath lengths up to 25 cm may be useful. Sheath diameters are measured where 1 Fr = 0.33 mm. The range of sheath sizes is from 4 Fr to 9 F for cerebral angiography, and the typical sheath size for diagnostic angiography is 5 Fr. It is important to note that the size refers to the inner diameter of the sheath and therefore determines what size catheter or device can be placed through the sheath. The outer diameter is approximately 1.5 to 2 Fr larger than the listed size and reflects the diameter of the actual arteriotomy.

Diagnostic catheters are inserted through the sheath. A wide range of catheters are available, with a variety of distal tip shapes to accommodate variations in vascular anatomy. Less distal catheter curvature is typically required in younger patients because of their more linear vasculature. In patients with markedly tortuous vessels, a reverse-curve catheter is required to access vessels off the aortic arch.

Diagnostic catheters are typically advanced over a hydrophilic guidewire. The guidewire allows atraumatic navigation of the catheter by keeping the catheter tip away from the wall of the vessel and therefore preventing dissection. A sufficient length of wire should protrude from the distal tip of the catheter to provide support for catheter advancement and to maximize the flexibility of the wire. If the distal wire protrudes only a short distance from the catheter tip, the exposed wire segment becomes exceedingly stiff and risks injury to the vessel. While catheters are measured in F, wire measurements are in thousandths of an inch (for example, a 0.038 wire is 0.038 inches in diameter).