It is not often that good blogs come from family stories, but here is one that was irresistible to Hearing International this week.

In the 1970s, most Audiology students were required to conduct a number of routine hearing evaluations in the development of clinical skills. In 1973, as part of that practical learning process, like many of my peers, I found a few people to evaluate, scheduled my clinic time and practiced the craft that would later become a livelihood. Most of these evaluations, of course, were on normal hearing individuals but there was one very important hearing test among that group.  One of the subjects, kind enough to submit to being evaluated by the “want to be” audiologist, was my sister who felt that she had not been hearing very well. 

The results were definitely very different from the others and definitely NOT normal, even to an Audiology student early in his training.   After a thorough evaluation, I found she had a mild conductive hearing loss on the right ear and a moderate conductive hearing loss on the left ear (not quite as severe as the one presented in the audiogram to the left).  After a recheck of this impairment by the clinical supervisor, it was recommended that she see an otolaryngologist (ENT) to determine the etiology of her hearing deficit.  Otosclerosis was suspected as she was 23 years old at the time, with obvious Carhart Notches, and she felt  her hearing been decreasing for the past year or so.  The ENT scheduled and conducted stapedectomy surgery to restore hearing for the left ear.

We all know that the success of surgery for conductive hearing loss is 85-90%, but this one was unsuccessful. Over the years, she has consulted with various otolaryngologists and found that further surgical intervention would probably not be successful. Revisions of stapedectomy surgery, according to Gros et al (2005) only have a success rate of about 54%, so for all of these years she has greatly benefited from amplification.  In her case, the surgeon has now passed away, and the audiologist does not remember the type of prosthetics used at the time, so now……

Fast forward to July 2017 

She is now in need of Magnetic Resonance Imaging (MRI) for another condition. 

It is well known that the MRI is conducted in a powerful magnetic field that will attract iron containing or ferromagnetic objects, causing them to move with great force and cause great risk to patients.  Great care is taken that these ferromagnetic objects are not brought into the MRI area. Of course any metallic item such as hearing aids, watches, jewelry, cell phones, even items of clothing that have metal fasteners are not brought close to the these systems. Makeup, nail polish, or other cosmetics should be removed when undergoing the MRI examination as they may also have some metallic characteristics.  Since the powerful magnetic field of these MRI systems will pull on any iron-containing object in the body, such as some aneurysm clips or medication pumps, every MRI facility has a comprehensive screening procedure and protocol that, when carefully followed, ensures that the MRI technologist and the radiologist knows about the presence of any metallic implants and materials so that special precautions can be taken.

In some unusual cases, due to the presence of an unacceptable or unknown implant or device, the exam may have to be canceled. For example, the MRI exam will not be performed if a ferromagnetic aneurysm clip is present because there is risk of the clip moving and causing serious harm to the patient. In some cases, certain medical implants can heat substantially during the MRI examination as a result of the radiofrequency energy that is used for the procedure, which may also result in patient injuries. Therefore, it is very important to inform the MRI technologist about any implants, bullets or other metallic objects.  

 

“What type of wire prosthesis was used for the Stapedectomy in 1973?”   

The reason for this question is that there are horror stories of problems about the results of MRI on patients that have had the stapedectomy procedure.  The various types of stapes prosthetics used over the years have different ferromagnetic properties .  Ferromagnetic properties of prosthetic materials are their susceptibility to magnetization, the strength of which depends on that of the applied magnetizing field. The unit of measurement for the strength of a magnetic field is the Tesla. Most of the MRI units are 1.5 Tesla devices, but the new generation is twice that or 3.0 Tesla. A 1991 study by Shelleck and Curtis evaluated many of the prosthetic devices used in various parts of the body including the ear and found many of these prosthetics had little or no movement due to magnetism up to 1.5 Tesla, but many are unsafe for MRIs at 3.0 Tesla. Later, Fritsch (2007) found that many of these otologic prosthetic devices were safe for MRI.  He states that ” Physicians and patients alike rightly question the possibility of a prosthesis interacting with a Magnetic Resonance field and the effects on the implanted patient.  Of major consideration is the possibility of stapes prosthesis movement or heating within the patient causing disruption of hearing or harm to the ear.  That there is the potential for some SS prosthesis [stainless steel prosthesis] to move is abundantly clear from multiple types of referenced experiments.  In contrast, prostheses made of nonmagnetic metals and alloys, including titanium, platinum, and tantalum showed no potential for movement.” 

Then the questions from my sister still remain. What kind of a prosthesis do I have?  Will it move during the MRI? Am I safe? Am I safe tor 1.5 Tesla or 3.0 Tesla?

Since MRI is a routine procedure these days, here are some things to consider if you have a prosthetic device in the ear, no matter if it is beneficial or not….

  1. Contact your otologic surgeon to determine the type of prosthesis that was implanted and determine its magnetic make up.
  2. Ask advice of your otologic surgeon whethr you should have an MRI.
  3. If the prosthesis is not beneficial, consider explanting the device.
  4. It is likely that early prostheses such as those from the 1960s and 1970s are stainless steel wires which would contraindicate the MRI.
  5. Later prostheses may be OK, but you need to know for sure!  Otherwise do not conduct the MRI.

My advice to my sister, with as much brotherly love as possible, was that since the surgeon is no longer available and the preponderance of stapedectomy prosthetics at the time of her surgery were stainless steel, a number of studies suggest that she should not have the MRI.  Her second option, of course, would be to explant the non beneficial prosthesis and then conduct the MRI.

 

 

References:

Fritsch, M. (2007).  MRI scanners and stapes prosthesis. Oto. Neuro. Vol 28, pp. 733-738.

Gros, A., Vatovec, J., Zargi, M. & Jenko, K. (2005).  Success rate in revision stapes surgery for otosclerosis.  Otol Neurotol. Nov;26(6), pp.1143-8.

Shellock, F. & Curtis, J. (1991). MR Imaging and Biomedical Implants, Materials, and Devices: An Updated Review.  Radiology, Volume 180, pp. 541-550.  

 

One Response to Stapedectomy Wires and MRI

  1. Anonymous says:

    STAPENDECTOMY???????

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