The GDC coil system was developed by Italian neurosurgeon Guido Guglielmi and Target Therapeutics, Fremont, California. The device gives the surgeon the ability to insert a coil into an aneurysm or blood vessel, assess its position, and withdraw it if the result is less than satisfactory.121-127 Other coil systems are not detachable but rather pushed or injected into position. Once these coils leave the catheter they are difficult, if not impossible, to retrieve.

In order to treat an aneurysm with GDC coils, the surgeon must first place a microcatheter into the aneurysm fundus. Once properly positioned, a coil is inserted through the catheter and into the aneurysm. If the operator does not like the coil's configuration he or she can remove it and reposition it or choose another size coil. The GDC system consists of a soft platinum coil soldered to a stainless steel delivery wire. When the coil is properly positioned within the fundus a 1 mA current is applied to the delivery wire. The current dissolves the stainless steel delivery wire proximal to the platinum coil by means of electrolysis. At the same time, the positively

Figure 8.4 Oblique vertebral arteriogram demonstrating vertebrobasilar junction aneurysm

charged platinum theoretically attracts the negatively charged blood elements such as white and red blood cells, platelets, and fibrinogen, thus inducing intraaneurysmal thrombosis. Once electrolysis occurs the delivery wire can be removed, leaving the coil in place. Another coil can now be introduced into the fundus. The process is continued until the aneurysm is densely packed with platinum and no longer opacifies during diagnostic contrast injections (Figures 8.4, 8.5).

The mechanism by which GDC coils occlude aneurysms is still debated. We have made observations at surgery on recently coiled aneurysms that lead us to question the theory that the positive charge within the aneurysm during electrolysis induces significant thrombus formation. Coils probably provide immediate protection against rehaemorrhage by reducing blood flow within the aneurysm sac, buffering arterial pulsations within the fundus, and sealing the weak

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