Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-05-19
2002-10-08
Smith, Ruth S. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S420000, C600S424000, C600S427000, C600S435000, C606S194000, C606S195000
Reexamination Certificate
active
06463317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device and method for endovascular treatment of aneurysms, particularly cerebral aneurysms. The method and device fills the volume of the aneurysm, provides material to the locality of the treatment which contains pharmacologically active agents, and may use intrumentalities and materials which are visible with magnetic resonance so that the procedure may be viewed in real time with magnetic resonance imaging systems.
2. Background of the Art
Autopsy studies have estimated that between 1.5% and 8% of the population have intracranial aneurysms. Between 60,000 and 80,000 cerebral aneurysms are diagnosed annually in the U.S., 20,000 to 30,000 following subarachnoid hemorrhage. The annual risk of an aneurysmal rupture is about 2%, producing a mortality rate of 50-60%. If untreated, 25-35% die of recurrent hemorrhage and, if there is patient survival, there is a significant deficit in neurological functions in 20-40% of the patients.
The traditional method for detecting an aneurysm and evaluating its vascular relationships is cerebral angiography, which has a morbidity rate of 1-2%. Non-invasive angiographic techniques with minimal morbidity have been developed recently. Magnetic resonance (MR) angiography (MRA), a form of magnetic resonance imaging (MRI), and computed tomography (CT) angiography (CTA), have demonstrated very high levels of detection (60-100%, depending upon the size of the aneurysm and the technique used). In particular, MRI/MRA have been very effective in detecting the asymptomatic, unruptured aneurysms. Both MRA and CTA also might be excellent techniques for following patients after surgical treatment. Unfortunately, the materials used for treatment frequently degrade the image, making evaluation of residual or recurrent aneurysm difficult or impossible.
The traditional method of treating patients with ruptured and unruptured cerebral aneurysms is surgical clipping, and approximately 15,000 of these surgical procedures are performed in the U.S. each year. Surgical mortality from clipping a previously ruptured cerebral aneurysm varies from 5% to 20% to, depending upon the site of the aneurysm and the neurological condition of the patient at the time of surgery. Surgical mortality for an unruptured aneurysm is from 2% to 10%.
Because of this high surgical mortality rate, a number of endovascular techniques have been developed to treat cerebral aneurysms. In 1974, Serbinenko first reported the successful treatment of intracranial aneurysms with detachable balloons. Using an endovascular approach similar to an angiogram, the balloon would be directed under fluoroscopic guidance to the aneurysm. If possible, the balloon would be placed inside of the aneurysm, leaving the parent artery intact. If the neck of the aneurysm were too large to entrap the balloon completely inside of the aneurysm, occlusion of the parent vein or artery would have to be performed. Large aneurysms typically required multiple balloons. Since 1974, a variety of detachable and nondetachable balloons made of a variety of materials, especially silicone and biocompatible polymeric latices, have been introduced. However, most aneurysms do not have the round or elliptical configuration of a balloon. Consequently, large aneurysms had to be filled with multiple balloons, leaving dead space for continued aneurysmal filling and subsequent rupture. The unfilled volumes could also allow for the development of clot in the aneurysmal remnant, enabling embolization to produce a stroke. Migration of a balloon from the aneurysm into the parent artery, or to a more distal branch of the parent system to produce a stroke, has also been reported in the literature. The use of balloons for direct aneurysm occlusion is therefor no longer performed. Parent artery occlusion using a detachable balloon is still a viable procedure, although the blood flow to the hemisphere may be compromised with such a procedure, producing a stroke.
Aneurysmal occlusion with microcoils is another endovascular technique. Very soft platinum microcoils have been developed recently, with and without fibers that induce thrombus formation. These soft microcoils are placed directly into an aneurysm, and the degree of occlusion is related to the ability to pack the coil mass tightly. A new variety of microcoil is the Guglielmi Detachable Coil (GDC) (U.S. Pat. No. 5,122,136). This utilizes an electrical current to induce thrombosis within the aneurysm. The current also breaks the solder-point connection between the guiding wire and the coil for a non-forceful detachment of the coil. While the morbidity (8%) and mortality (0.3 to 1.1%) are very low with this procedure, especially compared to conventional surgery, the electrically induced intra-aneurysmal thrombus is lysed and the coils compact over time, so that the permanence and therapeutic efficacy of the aneurysm occlusion is still unknown. More importantly, complete occlusion of an aneurysm at the time of initial placement of the coils ranges from 69% for small aneurysms with narrow necks, to 35% or less for larger aneurysms with wide necks. Aneurysms having wide necks relative to their diameters may not be even treatable with this technique. A wide neck allows the coils to herniate into the parent artery, which may produce unwanted parent artery occlusion and stroke. Therefore, aneurysms with wide necks usually must be treated surgically, with a higher morbidity/mortality rate than if an endovascular method had been available. The GDC also produces undesirable artifacts on MR scans, making it impossible to define an aneurysmal remnant or tissue injury in the region of the aneurysm. Lastly, electrolytic detachment of the GDC can result in migration of the solder remnants into the intracranial circulation.
In order to completely fill the lumen of an aneurysm, a device with the properties of a liquid would be preferable to more rigid devices such as the GDC coil. Liquid agents have been used for aneurysm ablation by directly injecting the agent into the aneurysm to produce a cast and subsequent thrombosis. An example of a liquid thrombotic material is cellulose acetate and bismuth trioxide dissolved in dimethylsulfoxide. On contact with blood in the aneurysm, the dimethylsulfoxide diffuses and the concentrating cellulose acetate polymer solidifies in the shape of the aneurysm within minutes. The liquid thrombotic material has a low viscosity and is easily injected through a small gauge catheter placed into the aneurysm via an endovascular approach. However, there are significant problems with this method of aneurysm ablation, including the distal migration of the polymer into normal vessels, producing stroke, and the slow leaking of the chemicals into the blood with dispersion to normal brain tissue, producing neurological dysfunction.
Other liquids, especially the cyanoacrylates (e.g., the iso-butyl and n-butyl forms), have been used for aneurysm occlusion. The cyanoacrylates polymerize in seconds after making contact with an ionic fluid like blood. The polymerization rate is difficult to control, however, and its rapidity makes precise and safe placement difficult. Like any liquid, the cyanoacrylate can flow out of the aneurysm into unwanted locations unless it can be contained.
The guidance of an endovascular catheter system, and the placement of an embolic agent or device into an aneurysm, currently is performed using x-ray fluoroscopy. Catheters and embolic agents are made from radio-opaque materials to allow visualization, and fluoroscopy allows the real-time visualization of the movement of the catheter system and the placement of the intra-aneurysmal occluding agents. However, there would be certain advantages to performing such a procedure under MR guidance. First, x-ray systems give significant levels of radiation to the lens of the eye during aneurysm ablation procedures. Radiobiological effects such as cataract formation may prove to be significant once enough time has elapsed for the effect of these r
Kucharczyk John
Latchaw Richard
Mark A. Litman & Assoc. P.A.
Regents of the University of Minnesota
Smith Ruth S.
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