Phenomenon of straitening at proximal end of the coil during parent artery occlusion for the internal carotid artery aneurysm: Case report

Objective: Straightening of the coil at its proximal end is rare but possible. We report a case of internal carotid aneurysm in which this phenomenon was encountered during parent artery occlusion. Case presentation: A 69-year-old woman underwent endovascular trapping of an unruptured left cavernous internal carotid artery (ICA) aneurysm, 15 mm in diameter. Three coils were deployed with incomplete occlusion, and a segment of the ICA distal to the aneurysm remained to be occluded. Therefore, an additional coil (ED coil, extrasoft type, 5 mm in diameter, 10 cm in length; Osaka, Japan) with a diameter larger than the diameter of the ICA was introduced. After smooth insertion of the first part, the remaining 3 cm part of the coil became considerably less flexible. The straightened coil was detached without further modification. Thereafter, endovascular trapping was completed in the standard manner without any technical problems and complications. Conclusion: The straightening of the coil may occur due to the shortening of stretch resistant (SR) filaments. This shortening is due to excessive widening of the pitch of the primary coil following insertion into a cavity that is smaller in diameter than the diameter of the secondary loop of the coil. This phenomenon seemed to arise in our patient because the inserted coil, which was larger than the diameter of the ICA, became folded too compactly.