this is an implantable vaso - occlusive coil which is implanted using minimally invasive surgical techniques . it is a complex , helically wound coil made up of a primary helically wound coil which is then wound into a specific secondary shape . the secondary shape is itself a series of helical turns . at least a portion of the turns in the secondary shape form a cylindrical region and adjacent that region on at least one end is a conical region which tapers from a diameter approximating that of the central cylindrical region to a smaller diameter . the device is desirably self - forming upon exit from the distal end of a delivery catheter . also , the conical tipped vaso - occlusive device may also utilize thrombus - enhancing filamentary material .