Structural limitations of currently available microcatheters and coils for endovascular coiling of very small aneurysms

Introduction: Coil embolization for very small aneurysms (<3 mm in maximum diameter) has been considered a technically challenging method due to increased risk of potential aneurysm perforation during the procedure. We present our observations about the structural limitations of eight types of microcatheters and three types of detachable coils, and technical pitfalls in the coiling of very small aneurysms. Methods: The structures of each type of microcatheter and coil were carefully evaluated under a stereoscopic microscope. The evaluation the microcatheters was focused on the distance between the distal end of the distal marker and the tip of microcatheter. The evaluation of the coils was focused on the length of the detachment zone. Results: With markers of the coil delivery systems and microcatheters aligned under fluoroscopic visualization according to the manufacturers' recommendations, the stiff detachment zones protruded approximately 0.2-1 mm from the microcatheter tip. The lengths of the detachment zone, which is known to be a stiff segment, of the currently available coils were approximately 0.5-0.8 mm. The distance between the distal end of the distal markers of the microcatheters and the detachment zone of the coil ranged from approximately 1.2 to 2.8 mm. Conclusion: To prevent rupture of very small aneurysms during coiling, the distal marker of the selected microcatheter should be carefully located near the aneurysm neck, considering all the structural characteristic of the currently available coils and microcatheters. Refinement of currently available devices may be essential to achieve safer coiling of very small aneurysms.