Pipe Dreams and Guide Wires
Endovascular embolization revolutionizes treatment of aneurysm
By Lucio Victor Jr.
The past decade ushered in tremendous changes in the application of transcatheter treatment. Achieved through real-time fluoroscopic imaging, transcatheter treatment, initially conceived as a work in progress by many physicians, is continually evolving, gaining more acceptance worldwide.
One of the most recent and promising developments in transcatheter treatment is endovascular embolization. In the recently concluded International Subarachnoid Aneurysm Trial (ISAT), 2,143 patients with a ruptured intracranial aneurysm treatable with either neurosurgical clipping or endovascular coiling were chosen in random to receive either treatment.
Although the study showed that "the long term risks of further bleeding from the treated [intracranial] aneurysm are low with either therapy, the outcome in terms of survival free of disability in one year is significantly better with endovascular coiling."
Dr. Benjamin Adapon, head of Makati Medical Center's CT-MRI department, says that endovascular coiling has come a long way. While appropriate for several diseases, its most important application remains for endovascular cranial embolization.
Diagnostics to Therapeutics
Dr. Adapon says that embolization somehow owes its roots to angiography, the minimally invasive diagnostic procedure that uses a flexible catheter inserted through the femoral artery up the aorta. Depending on which arterial supply needs to be viewed on film, radioopaque dye is injected into the carotids or the coronaries to view the circulation in the cerebral cortex or myocardium.
The procedure commonly done by neurosurgeons and interventional radiologists and cardiologists soon evolved. Thoracic and cardiovascular surgeons and interventional cardiologists were using the catheters to insert and inflate special "balloons" into coronary arteries occluded with atherosclerotic plaque, flattening the plaque against the vessel wall and eventually opening it up to accommodate blood flow. With this, percutaneous transluminal coronary angioplasty (PTCA) became commonplace. Patients likely to benefit equally from either PTCA or CABG now had a less invasive option.
Still not satisfied with a PTCA, thoracic and cardiovascular surgeons developed stenting, which required a stent to be inserted across a clogged vessel, now serving as the conduit for circulation. Stents from various materials were soon developed, taking into account the need to halt recurrence of atherosclerotic plaques. Soon after, stents were used to open up peripheral arteries and veins in disorders like type 2 diabetes mellitus or Buerger's disease. The use of stenting in vessels of the extremities is limited and most cases of DM and Buerger's usually end up with amputation. Still, the technology may be used where appropriate.
Aside from PTCA and stenting, occlusion of a patent ductus arteriosus (PDA) with the use of a catheter to release a substance that blocks the shunting of blood from the aorta to the pulmonary vein, has also become a treatment option.
Before the advent of catheterization, the only other means of PDA closure was the use of the NSAID indomethacin, which induced contraction of the smooth muscle layer of the PDA eventually closing it. However, indomethacin only worked well in small PDAs and in premature infants whose PDAs still had a muscular layer (MEDICAL OBSERVER, February 2001).
Later on, transcatheter treatment was initiated and implants that "plugged" the PDA were introduced. These included the Ivalon Plug, Rashkind and Modified Rashkind and the umbrella devices. Umbrella devices turned out to be more expensive than open-heart surgery MEDICAL OBSERVER, February 2000).
By the 1990s, using Amplatzer Duct Occluders (ADO) or Gianturco Coils for coil embolization became vogue. A study concluded in 1999 reported that coil embolization using Gianturco coils worked best in PDAs less than 2mm in size while ADOs were best for PDAs larger than 2mm. However, the study also disclosed that while devices were increasingly being used for PDA occlusion, not all PDAs can be effectively occluded and open heart surgery still remains to be the surest method of ensuring PDA closure. The study aslo stated that device selection for PDA occlusion should be well reviewed.
Gianturco coils are considered among the more affordable devices. Effective only for small to medium PDAs, these coils are lined with Dacron which are highly thrombogenic-inducing quick epithelialization of the PDA thus sealing it off. Patients are usually up and about in hours after the procedure. But close follow-up has to be done to ensure total occlusion of the PDA. This procedure can be done by any especially trained interventioanl cardiologist or thoracic and cardiovascular surgeon.
Filling Up
Embolization, whether using platinum coils or Sodium-butyl-cyano acrylate glue, has been used for many diseases. Dr. Adapon says that aside from PDAs, the procedure is used by ENT surgeons to stop epistaxis especially in cancer patients who are on radiotherapy for tumors of the head and neck. Embolization can also be used for aortic aneurysms, hepatoportal arteriovenous fistulas, and upper gastrointestinal bleeding.
Surgical and medical oncologists have recently started using embolization in neo-adjuvant chemotherapy. Reduction in tumor size is acheived when coils laced with chemotherapeutic agents are implanted into the blood supply of tumors. "This not only delivers chemotherapeutic agents directly to the tumor but also deny the tumor nutrients by block off the arteries that feed these."
Despite all these, Dr. Adapon says the "most challenging use of endovascular embolization is in the treatment of aneurysms and arteriovenous malformations (AVM) in acute and chronic stroke." He says that surgical clipping of intracranial aneurysms and AVMs to avoid hemorrhagic stroke is the most common treatment currently in use. However, there are cases in which aneurysm size, location, or character can encumber surgical clipping, making endovascular embolization an effective alternative.
Explains the interventional radiologist: "Endovascular embolization is an important armamentarium for treatment in the brain. In the chest or abdomen it is fairly easier to incise and say 'I will look and see.' You cannot 'look and see in the brain.' In the brain you cannot explore. You cannot expect to open up the skull and have a very good recovery. Before, doing a craniectomy meant a high chance of mortality. This is why now, the diagnosis by doctors is exact and their planning is precise so that when they open up the skull they know exactly where to go." True enough, despite the great leaps in neurosurgical skills, there are still instances where access to the nidus of the lesion presents difficulty.
Dr. Adapon notes that with embolization, platinum coils are brought to the aneurysm or AVM via catheter, and deployed into the aneurysm sac or AVM. The size and number of coils to be used are estimated from the size of the lesion to be filled.
Although aneurysms can be found anywhere in the body, they pose the greatest risk in the brain where a rupture can lead to a hemorrhagic stroke, which could be fatal. In some cases, open surgical treatment is complicated or prevented by the size, location, and morphology of the aneurysm.
Ophthalmic artery aneurysms for instance are frequently referred for endovascular coil embolization in developed countries because its location makes it difficult to clip. Preliminary studies indicate that 85 percent of on ophthalmic artery aneurysms show more than 90 percent occlusion with more than 83 percent of patients having good recovery.
Dr. Adapon notes that about 30,000 aneurysms worldwide have been successfully treated using endovascular coil embolization.
On the other hand, stereotactic radiosurgery (SRS) can also be used to treat AVMs. This procedure entails the concentration of a radioactive beam on the lesion within a period of six months to as long as two years. Eventually the aberrant vessels close off and are replaced with scar tissue. SRS is effective only for small AVMs and can be used alongside endovascular embolization.
Dr. Adapon points out that endovascular coil embolization can be more expensive than neurosurgical clipping. "A coil costs about US$500 while a clip costs PhP10,000 to 20,000. There are times you need two, three, or four coils, depending on the size and kind of lesion." However, he stresses that hospital stay is about two to three days and the only incision is the one done on the femoral artery where the catheter was inserted.
Endovascular coil embolization was developed by neurosurgeon Guido Guglielmi who took a decade to perfect the procedure. The Guglielmi Detachable coil, is named after him, and the procedure can be performed by neurosurgeons or interventional radiologists with adequate training.
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