A brain aneurysm is a weakened area in the wall of a cerebral artery, often occurring where a vessel branches. Constant blood flow pressure causes this weak spot to balloon outward, resembling a small sac. If the aneurysm ruptures, it causes a severe, life-threatening brain hemorrhage known as a subarachnoid hemorrhage. Endovascular treatment is a minimally invasive option that repairs the aneurysm by accessing the blood vessels from within, avoiding traditional open brain surgery. Stents are specialized mesh devices used in this method to secure the weakened vessel wall and prevent rupture.
The Purpose and Function of Intracranial Stents
Intracranial stents are placed within the parent blood vessel, directly across the neck of the aneurysm, to provide internal structural support. Their primary function is to act as a scaffold for platinum coils in a technique called stent-assisted coiling. For wide-necked aneurysms, the stent holds the coils tightly packed inside the sac, preventing them from protruding back into the main artery. This support promotes clot formation within the aneurysm, sealing it off from circulation.
Another major function is to change the hemodynamics, or blood flow patterns, within the affected vessel. Placing a fine-mesh stent across the aneurysm opening redirects the majority of the blood flow along the main artery wall, away from the sac. Reducing the force of blood entering the sac encourages stagnation and clotting. This natural clotting process eventually leads to the aneurysm shrinking and being absorbed, allowing new tissue to reconstruct the vessel wall.
Distinguishing Between Stent Types
The two main categories of stents are distinguished by their mesh density and mechanism of action.
Conventional Stents
Conventional stents have a relatively low mesh density, meaning they have more open space between the wires. These devices are primarily used to assist coiling, providing a mechanical barrier and support structure for the coils, especially in wide-necked aneurysms. The low density of the mesh helps maintain the patency of any small branching vessels covered by the stent.
Flow Diversion Devices
Flow diversion devices represent a newer generation of implants with a significantly higher mesh density, often featuring 30–35% metal coverage. These devices are designed to be monotherapies, often working without the need for additional coils. The dense mesh acts as an immediate barrier to blood flow, forcing it to travel down the path of least resistance within the parent artery. By reconstructing the vessel wall at the aneurysm site, flow diverters promote long-term biological healing and complete exclusion of the aneurysm sac. They are effective for large or complex aneurysms challenging to treat with coiling alone.
The Procedure for Stent Placement
The placement of a brain aneurysm stent is a neuroendovascular procedure, performed under general anesthesia or deep sedation. The process begins by accessing the arterial system, usually through a small incision over the femoral artery in the groin or the radial artery in the wrist. A guide catheter is threaded through this access point into the bloodstream.
Using continuous X-ray imaging (fluoroscopy), the surgeon guides the catheter through the body’s network of arteries, up to one of the main arteries leading to the brain. Contrast dye is injected to make the blood vessels and the aneurysm visible, creating a roadmap. Once the guide catheter is positioned near the target site, a smaller, flexible microcatheter containing the collapsed stent is advanced through it.
The microcatheter is maneuvered across the aneurysm neck within the parent artery. The surgeon slowly deploys the stent, which self-expands to conform snugly against the artery wall, bridging the aneurysm opening. After the stent is fully expanded and confirmed via angiography, the catheters are withdrawn. The stent remains permanently in place, providing immediate support and modifying blood flow.
Recovery and Potential Complications
Following stent placement, patients are monitored closely in the hospital for one to two days before discharge. Minor discomfort at the catheter insertion site is common, and strenuous activity is restricted for about a week. The most important aspect of post-procedure care is the use of antiplatelet medication to prevent blood clots from forming on the newly implanted stent.
This regimen involves dual antiplatelet therapy (DAPT), a combination of aspirin and a P2Y12 inhibitor. DAPT is started before the procedure because the stent’s metal mesh can trigger the body’s clotting response. This therapy is necessary until the inner lining of the blood vessel grows over and incorporates the stent. Dual therapy continues for three to six months, sometimes up to a year, followed by indefinite monotherapy with aspirin.
Potential complications must be carefully managed. The primary risks include thromboembolic events, where a blood clot forms on the stent and travels to block a smaller vessel, leading to a stroke. There is also a risk of hemorrhage, either from the aneurysm or due to the antiplatelet drugs. Long-term follow-up is mandatory and involves periodic imaging, such as angiograms or MRIs, to monitor the stent’s function and ensure the aneurysm remains sealed or continues to shrink.