HIFU treatment is a new technology used for the treatment of brain diseases, such as tremor, which does not require any opening of the skin or skull, or the introduction of surgical instruments into the brain.
How does this system work?
High Intensity Foscused Ultrasound (HIFU) produces a small, high-precision surgical lesion to interrupt the tremor brain circuit.
This disruption is achieved by focusing multiple high-intensity ultrasound beams on the appropriate “target” point in the brain. The ultrasound beams pass through the skin and skull, so no incision or trepanation is necessary to perform the treatment. At the point where the ultrasound beams are focused (and only at that point) a temperature increase of up to about 60º Celsius is generated, which is the one that obtains the disconnection of the tremor circuit.
What kind of diseases can be treated with HIFU?
At present, HIFU has been approved for the treatment of tremors that do not respond to medication, such as Essential Tremor or Parkinsonian Tremor, among others.
It is likely that, in the future, HIFU may also be used for the treatment of other brain diseases.
Contraindications of HIFU
The skull bone of some people does not allow ultrasound to pass through, so these people cannot benefit from HIFU treatment. This happens in a few cases, and can be checked in advance by doing a cranial CT scan, also called a CAT scan. In this way we can study what the skull bone of each patient is like, and inform the patient properly before deciding on the treatment.
On the other hand, patients with metallic material in the skull cannot benefit from HIFU treatment, because the effect of high intensity ultrasound on the metal could be harmful to the patient.
Nor can patients with metallic prostheses that are not compatible with MRI be treated with HIFU. For this reason, it is necessary to check whether or not the prosthesis a patient has (for example, a cardiac pacemaker) is compatible with MRI. Fortunately, many of the metallic prostheses currently implanted are compatible.
Finally, MRI can be a serious inconvenience for some people who suffer from claustrophobia.
The effects of the therapy
The effect of HIFU therapy is immediate, as the temperature increase at the target site occurs during the application of high intensity ultrasound.
Advantages of HIFU treatment
The main advantage of HIFU is that it is a method of “bloodless neurosurgery”, without openings, so the risks of bleeding or infection are minimal. For the same reason, recovery after treatment is usually very rapid and the patient is discharged the next day. As HIFU is a minimally invasive treatment, it can be used on elderly people or those who cannot benefit from open brain surgery.
Another very important advantage of HIFU is that the treatment is not performed in the operating room, but in a Magnetic Resonance Imaging (MRI) and with the patient awake. The images obtained with the MRI allow the condition and temperature of the brain to be monitored. In addition, the possibility of conversing with the patient, making a continuous clinical exploration during the treatment, makes it easier to observe the improvement of the tremor and to control the appearance of undesirable effects.
During HIFU treatment we apply the ultrasound in the form of a few-second bursts, which we call “sonications”. The sonications are started at low power, to be sure that no undesirable effects appear. If undesirable effects appear, the target point is modified until they are controlled. Sonications of increasing intensity are then administered in steps until a temperature of about 60 centigrade is reached at the target point, which causes a lasting disconnection. Throughout the HIFU treatment, the improvement of the tremor is checked after each sonication and also at the end of the treatment.
What are the disadvantages of HIFU treatment?
On the one hand, some degree of edema or swelling may appear around the lesion. If swelling appears, it may cause some temporary discomfort in some patients, such as transient balance disorder.
On the other hand, another disadvantage is that high-intensity ultrasound cannot pass through spongy materials, such as hair, so it is necessary to shave the patient’s head completely. Since this is a normal shaving, and not a toxicity effect (as happens with some oncological treatments), the hair grows back at a rate of approximately one centimeter per month.
For the treatment of tremor it is essential to fix the patient’s head in a restraint system called a “stereotactic frame”. The stereotactic frame is essential for the treatment, as it prevents movements that could alter the precision of the HIFU, especially in patients suffering from head tremor (cephalic tremor). To make the fixation with the frame as atraumatic as possible, we use local anesthesia on the skin, such as that used in dental treatment.