Why you should not have standardly a CBCT-scan of your skull taken before FFS

Posted on October 20, 2017 by Dr Bart van de Ven

A cone beam computerized tomography (CBCT) scan combines a series of X-ray images taken from different angles and uses computer processing to create cross-sectional images, or slices, of the bones, blood vessels and soft tissues inside your body. CBCT scan images provide more detailed information than plain X-rays do.

So the advantage is that a CBCT-scan gives us more details than a plain X-ray does. Question is, do we need that extra information?

Disadvantages of CBCT-scan

The disadvantages are:

  • Costs: The costs of these scans can vary greatly depending on your location. It ranges roughly from $160 (Spain) to $960 (USA)

  • Time: You will often be told by surgeons that time spent on having a CBCT-scan made will sometimes be no more than 5 minutes when the scan is available immediately and can be taken just before the consultation with the surgeon.  This is often not the case. You might have to actually go to another location for the CBCT-scan or even pay an extra money to visit a hospital just for the CBCT-scan.

  • Exposure to radiation: We are exposed to radiation from natural sources everyday. According to recent estimates, the average person in the U.S. receives an effective dose of about 3 mSv per year from naturally occurring radioactive materials and cosmic radiation from outer space. To explain it in simple terms, we can compare the radiation exposure from one chest x-ray as equivalent to the amount of radiation exposure one experiences from our natural surroundings in 10 days. An adult’s  approximate effective radiation dose during a CBCT-scan of the head is about 2 mSv which is the same as the natural background radiation we  endure during 8 months.What the exact consequence of that is we don’t know, but what we do know is that we should try to keep the amount of radiation we encounter  as low as possible.

Information that the scan can give us

Back to the need of CBCT-scan data of the head. Some  important information the scan can give us is the course of the lower alveolar nerve through the lower jaw. This nerve can be at risk of being damaged during recontouring of the jaw and chin which is important to understand as an FFS patient. Especially during a jaw recontouring one can imagine this nerve being damaged when resecting the jaw bone at its lower border, because the nerve can come pretty close to contact.

In an the orthopantomogram (OPG) you can measure exactly the distance between the lower border and the canal in which the nerve runs. By measuring the distance in the midline from the lower border to the edge of the incisors, both on the OPG and on the patient a magnification factor, can easily be calculated. So we will know exactly how much bone we can remove without damaging the inferior alveolar nerve. So why make a CBCT-scan of the lower jaw?

 

This is a panoramic X-ray that is popular with many dentists and used to examine a patient’s teeth. You can ask your dentist to e-mail your  most recent x-ray’s. It doesn’t have to be very recent as the only  area of interest is the position of the lower alveolar nerve, which doesn’t change once you’re over 16 years of age. In case your dentist doesn’t have an OPG of your lower jaw area you will need to have one made in a dental office where they have specific equipment for this type of x-ray. The effective dose you will receive is 0.014 mSv which is equivalent to the exposure of the natural background radiation during 3 days. So the exposure will be 143 times lower than in a CBCT.

So, why make a CT-scan of your forehead?

What else could be of interest seeing on a CT-scan prior to FFS?

The positions and the shape of the frontal sinus maybe? During a type 3 forehead recontouring the frontal sinuses will be opened. But do we need to see them before surgery? Is there any measurement we can do on the CT-scan that is going to help us during the forehead recontouring? No. Does it have any consequence at all for the forehead surgery? No. So why make a CT-scan of the forehead?

I even have heard of doctors who take a CT-scan of the skull AFTER the surgery. Is that to put it as a poster over your bed or what? Expensive poster, not to speak of the radiation you have been exposed to and the time and energy you had to spend on it.

It is my impression some doctors wish to pretend being very careful and therefore ‘better’ doctors because they have a CT-scan made before (and sometimes even after) surgery. But now you know that it doesn’t add in any way to the safety of your surgery, nor does it improve the outcome of it. It will just cost you more  money and time and you will be exposed to more radiation than you need.

My advise: don’t have a CT-scan made before facial feminization surgery unless custom made facial implants will be placed during the surgery. In that case you need a CT-scan and a 3D reconstruction of it. The need for custom made facial implants and pre-tracheal shave (see: https://www.2passclinic.com/will-a-tracheal-shave-compromise-my-voice-feminization-surgery/ ) are the only situations in which we in 2pass Clinic make a CT-scan of the head. Our patient’s safety is our first concern.

Recent Comments
  • EM

    Posted: October 22, 2017


    Isn't it true that in some cases, type 3 reconstruction isn't necessary because the front sinus wall is thick enough that it can be ground down, and this is revealed through a forehead CT
    Reply


    • Bart van de Ven

      Posted: October 23, 2017


      That is correct. But during surgery this will become clear anyway. When the bone becomes transparent it means you can't shave more. If by then the shape of the forehead is not feminine enough the surgeon will have to make it a type 3. An experienced surgeon can see before surgery without a CT-scan 9 out of 10 times which type it will be.
      Reply


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