Aneurysm Clips and MR procedures

    The surgical management of intracranial aneurysms and arteriovenous malformations by the application of aneurysm clips is a well established procedure. The presence of an aneurysm clip in a patient referred for a magnetic resonance (MR) procedure represents a situation that requires the utmost consideration because of the associated risks. 

   This extract will outline some considerations in selecting a patient for MR examination who has aneurysm clip in situ:-

• Certain types of intracranial aneurysm clips (e.g. those made from martensitic stainless steels such as 17-7PH or 405 stainless steel) are an absolute contraindication to the use of MR procedures because excessive, magnetically induced forces can displace these clips and cause serious injury or death.

　

• By comparison, aneurysm clips classified as "non-ferromagnetic" or "weakly ferromagnetic" (e.g. those made from Phynox, Elgiloy, austenitic stainless steels, titanium alloy, or commercially pure titanium) are safe for patients undergoing MR procedures.

　

• Of note is that only a single fatality has been reported due to the presence of a ferromagnetic aneurysm clip in a patient preparing to undergo an MR procedure. This unfortunate incident was the result of erroneous information pertaining to the type of aneurysm clip used in the patient. That is, the clip was thought to be a non-ferromagnetic Yasargil aneurysm clip (Aesculap Inc., South San Francisco, CA) and turned out to be a ferromagnetic Vari Angle clip (Codman & Shurtleff, Randolf, MA)

　

• There has never been a report of an injury to a patient or individual in the MR environment related to the presence of an aneurysm clip made from a non-ferromagnetic or weakly ferromagnetic material.

　

• In fact, there have been cases in which patients with ferromagnetic aneurysm clips have undergone MR procedures at 1.5T without any injuries. Although these cases do not prove or suggest safety, they do demonstrate the difficulty of predicting the outcome for patients with ferromagnetic aneurysm clips that undergo MR procedures.

Recommendations

   In view of the current state-of-the-art information pertaining to aneurysm clips, the following guidelines are recommended for careful consideration prior to performing an MR procedure in a patient with an aneurysm clip:

1. Specific information (i.e. manufacturer, type or model, material, lot and serial numbers) about the aneurysm clip must be known, especially with respect to the material used to make the aneurysm clip so that only patients with non-ferromagnetic or weakly ferromagnetic clips are allowed into the MR environment. Information pertaining to the material used to make the aneurysm clip is provided in the labeling of the clip by the manufacturer. The implanting surgeon is responsible for properly communicating the information in the patient's records.

　

2. An aneurysm clip that is in its original package and made from Phynox, Elgiloy, MP35N, titanium alloy, commercially pure titanium, or other material known to be non-ferromagnetic or weakly ferromagnetic does not need to be evaluated for ferromagnetism.

　

3. Aneurysm clips made from non-ferromagnetic or weakly ferromagnetic materials in original packages do not require testing of ferromagnetism because the manufacturers ensure the pertinent MR safety aspects of the clips.

　

4. If the aneurysm clip is not in its original package and/or properly labeled, it should undergo testing for magnetic field interactions.

　

5. The radiologist and implanting surgeon should be responsible for evaluating the available information pertaining to the aneurysm clip, verifying its accuracy, obtaining written documentation and deciding to perform the MR procedure after considering the risk vs. benefit aspects for a given patient.

Original article by:

Frank G. Shellock, Ph.D, Adjunct Clinical Professor of Radiology, University of Southern California School of Medicine, Los Angeles, California

emanuel kanal, M.D, Director of Clinical and Educational MR, Associate Professor of Radiology, UPMC Health System, Pittsburgh, Pennsylvania

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