Focused-Ultrasound (FUS) Thalamotomy

Introduction

Focused-ultrasound thalamotomy, often shortened to FUS thalamotomy, is a brain procedure used to reduce tremor. It is different from traditional brain surgery because it does not involve cutting the scalp, drilling the skull, or placing any device inside the head. Instead, beams of ultrasound (sound waves) are aimed through the skull and focused on a small target deep in the brain — an area called the thalamus — to create a very small, controlled lesion that interrupts the brain circuit causing the tremor.

If you are reading this, you most likely have essential tremor or tremor-dominant Parkinson’s disease, and your neurologist has mentioned FUS thalamotomy as a possible option. This article explains what the procedure is, who it is suited for, how it compares with alternatives such as deep brain stimulation, what happens on the day of treatment, and what recovery and life after the procedure typically look like. It is written to help you prepare for the conversation with your neurologist and neurosurgeon, not to replace it.

What Is FUS Thalamotomy?

FUS thalamotomy uses high-intensity, focused ultrasound waves to heat and destroy a precisely chosen spot inside the brain. The full medical name is magnetic resonance-guided focused ultrasound thalamotomy, sometimes written as MRgFUS thalamotomy. The procedure is “magnetic resonance-guided” because it is performed inside an MRI scanner, which allows the surgical team to see the brain in detail, plan the target, and monitor temperature and tissue response in real time.

The target is the ventral intermediate nucleus (VIM) of the thalamus. The thalamus is a deep structure that acts as a relay station for movement signals. In tremor, a particular circuit through the VIM fires abnormally, producing the rhythmic shaking. By creating a tiny lesion at this point, the abnormal signal is interrupted. This is called a thalamotomy, which simply means “making a lesion in the thalamus.”

The word “incisionless” is often used to describe FUS. There is no skin incision, no skull opening (no burr hole or craniotomy), and no implant. All the work happens through hundreds of individual ultrasound beams that pass harmlessly through skin, bone, and other brain tissue and only converge with enough energy to cause heating at the precise focal point.

Why Is FUS Thalamotomy Performed?

FUS thalamotomy is performed to reduce medication-resistant tremor — that is, tremor that has not been controlled well enough by tablets, or where the medications have caused side effects the patient cannot tolerate.

The two main conditions treated are:

Essential tremor

Essential tremor (ET) is one of the most common movement disorders. It causes rhythmic shaking, most often of the hands, that worsens with action — for example, when holding a cup, writing, or eating. It is different from the tremor of Parkinson’s disease, which is typically worst at rest. Essential tremor usually affects both hands but is often worse on one side. First-line treatments include medications such as propranolol and primidone. When these are not effective or not tolerated, FUS thalamotomy is one of the procedural options doctors may consider, alongside deep brain stimulation.

Tremor-dominant Parkinson’s disease

In Parkinson’s disease, tremor is one of several motor symptoms, but in some patients tremor is the dominant problem and is poorly controlled by levodopa and other Parkinson’s medications. For these patients, FUS thalamotomy can be used to reduce tremor on one side of the body. It is important to understand that FUS thalamotomy targets tremor specifically — it does not treat the other features of Parkinson’s such as stiffness, slowness of movement, or gait problems in a sustained way, and it does not slow the progression of the disease.

Some centres also use focused ultrasound for other targets in Parkinson’s disease (such as pallidotomy or subthalamotomy) and for tremor in conditions like multiple sclerosis. These uses are evolving, and your neurologist will explain whether they apply to your situation.

Who Is a Candidate?

Not everyone with tremor is a candidate for FUS thalamotomy. The procedure is generally considered for adults who:

• Have a confirmed diagnosis of essential tremor or tremor-dominant Parkinson’s disease made by a neurologist with experience in movement disorders
• Have tremor that significantly interferes with daily life — eating, drinking, writing, dressing, or work
• Have tried adequate doses of appropriate medications without enough benefit, or cannot tolerate the medications
• Are in reasonably good general health for the planning sessions and the procedure itself
• Can lie still inside an MRI scanner for several hours and can communicate with the team during treatment

There are also factors that may make a person not a candidate, or that need careful evaluation:

• Skull density ratio (SDR). Before the procedure, a CT scan is used to measure how much of the ultrasound energy the skull will absorb. People whose skulls absorb too much energy may not be able to reach the temperature needed at the target. Centres typically have a minimum SDR threshold.
• MRI safety issues. Certain implanted devices (some pacemakers, cochlear implants, aneurysm clips) and severe claustrophobia can prevent MRI use.
• Bleeding tendency. Significant bleeding disorders or the need to remain on strong blood thinners may require careful planning or rule out the procedure.
• Severe cognitive impairment or unstable medical illness, which can make it unsafe to lie still and communicate during the procedure.
• Significant balance, walking, or speech problems at baseline, which may be worsened by a thalamic lesion and require careful weighing of risks and benefits.

An important practical point: FUS thalamotomy is currently performed on one side of the brain in most patients. Because the brain controls the opposite side of the body, treating the left thalamus reduces tremor in the right hand, and vice versa. Most patients choose to treat the dominant hand. The use of FUS on both sides (staged bilateral treatment) is being studied and is offered in some specialised centres, but it carries a higher risk of side effects affecting speech, swallowing, and balance, and is not standard practice for all patients.

Alternatives to FUS Thalamotomy

FUS thalamotomy is one option among several for medication-resistant tremor. A thorough discussion of alternatives is part of any good consultation.

Optimising medication

Before any procedure, neurologists usually confirm that medical therapy has been tried fully. For essential tremor, propranolol and primidone are the most commonly used first-line drugs, with other options including topiramate, gabapentin, and benzodiazepines. For tremor-dominant Parkinson’s disease, levodopa and dopamine agonists are adjusted, and sometimes anticholinergic medications are tried for tremor specifically.

Deep brain stimulation (DBS)

Deep brain stimulation is the most established procedural alternative. In DBS, thin electrodes are surgically placed into the same VIM target (or other targets for Parkinson’s disease) and connected to a pacemaker-like device implanted under the skin of the chest. The device delivers continuous electrical pulses that suppress the abnormal circuit. Key differences from FUS thalamotomy:

• DBS involves a craniotomy (small openings in the skull) and an implanted device that requires battery changes or recharging.
• DBS is reversible and adjustable — settings can be tuned over time and the system can be turned off.
• DBS can be performed on both sides of the brain in a single setting, which is important for patients with significant tremor in both hands.
• DBS is performed in many high-volume centres and has decades of follow-up evidence.

FUS thalamotomy, by contrast, is incisionless, does not involve an implant, and produces an immediate result — but the lesion is permanent and not adjustable, and standard practice is currently one-sided treatment.

Radiofrequency thalamotomy

Before FUS became available, thalamotomy was sometimes performed by inserting a thin probe through a small hole in the skull and heating the target with radiofrequency energy. This is still done in some centres. It is more invasive than FUS but does not require an MRI scanner during treatment.

Gamma Knife thalamotomy

Stereotactic radiosurgery (Gamma Knife) can also be used to create a thalamic lesion using focused radiation. Unlike FUS, the effect develops gradually over weeks to months because the lesion forms after tissue response to radiation, and the result cannot be assessed during the procedure itself.

Which option is most suitable depends on the type of tremor, how badly both sides are affected, general health, MRI compatibility, skull characteristics, and the patient’s own preferences about implanted devices, reversibility, and recovery. Major movement disorder societies recommend that patients considering procedural treatment for tremor be evaluated by a team that can offer or discuss more than one option, so the choice fits the individual.

Preparing for FUS Thalamotomy

Preparation usually unfolds over several visits, sometimes weeks apart.

Evaluation by a movement disorder neurologist

A neurologist confirms the diagnosis, documents the severity of tremor using standardised rating scales, reviews medication history, and decides whether procedural treatment is appropriate.

Neurosurgical consultation

The neurosurgeon discusses the procedure in detail, explains the risks and benefits, and answers questions. This is a good time to bring a written list of concerns and a family member who can help remember the conversation.

Imaging

An MRI of the brain is done to plan the target and to rule out conditions that might change the plan. A CT scan of the head is also done to measure the skull’s density and shape, which determines how the ultrasound energy will pass through. The skull density ratio (SDR) calculated from this scan is one of the key numbers in deciding whether the procedure is technically feasible.

Medical clearance and medication review

Routine blood tests and a basic medical check confirm fitness for the procedure. Blood-thinning medications (such as aspirin, clopidogrel, warfarin, or newer anticoagulants) often need to be stopped before treatment, under instruction from the prescribing doctor. Tremor medications may also be adjusted around the procedure date.

Head shaving

On the day of, or just before, the procedure, the entire scalp is shaved. This is needed because hair traps air bubbles that interfere with ultrasound transmission. Many patients find this the most emotionally difficult part of preparation. The hair grows back.

Stereotactic frame fitting

A lightweight metal frame is fitted to the head using four pins that are gently screwed into the outer surface of the skull after numbing the skin with local anaesthetic. The frame keeps the head perfectly still during the procedure and provides the reference points the system uses to aim the ultrasound. Frame placement is usually well tolerated but can feel uncomfortable. Most patients describe a sensation of pressure rather than pain.

The procedure is performed while you are awake. Being awake is important — the team needs you to move your hand and answer questions throughout the treatment so they can confirm that the target is correct and that side effects are not occurring.

Setting up

You lie on your back on the MRI table. The stereotactic frame is locked to the table so the head stays still. A helmet-like device called the transducer is fitted around the head; this contains the more than one thousand individual ultrasound elements that will deliver the energy. A flexible membrane filled with cool, degassed water surrounds the scalp inside the helmet. The water cools the skin and helps the ultrasound travel efficiently.

Imaging and planning

MRI scans are taken to map the brain in detail. The neurosurgeon, together with the radiologist and physicist, identifies the precise target in the thalamus and plans the path of the ultrasound beams.

Test sonications

The procedure begins with low-energy “test” sonications. A sonication is a single delivery of focused ultrasound lasting several seconds. The first sonications are intentionally too weak to cause a permanent lesion. Their purpose is to gently warm the target so the team can:

• Confirm with MRI thermometry that the heat spot is in the right place
• Ask you to perform tasks (such as drawing a spiral or holding out a hand) and watch for tremor reduction
• Check for any side effects — numbness, weakness, speech changes, balance problems — and adjust the target if needed

Therapeutic sonications

Once the team is confident the target is correct, higher-energy sonications are delivered to heat the tissue to a temperature that creates a small permanent lesion (typically between 55 and 60°C). Each sonication lasts roughly 10 to 30 seconds. Between sonications, you rest, and the team checks tremor and side effects again. Most patients describe sensations such as warmth, dizziness, mild headache, or a feeling of movement during sonications. These sensations stop when the sonication stops.

Confirming the result

By the end of the procedure, the team confirms reduction of tremor on the treated side — often dramatically, while you are still on the table. Final MRI scans document the lesion.

The whole experience typically takes between three and four hours from frame fitting to leaving the scanner, though this varies by centre and individual.

Recovery and Healing

Recovery from FUS thalamotomy is generally faster than recovery from open brain surgery, because there is no incision and no implant.

The first 24 hours

After the helmet and frame are removed, you are observed for several hours. Many centres keep patients overnight in hospital for safety. Common immediate experiences include:

• A general feeling of tiredness
• Mild headache
• Soreness or small marks where the frame pins were placed
• Imbalance or unsteadiness when first walking, often improving over hours to days
• Numbness or tingling around the mouth or in the fingers on the treated side, usually mild and often improving

The dramatic reduction in tremor is usually visible immediately. Many patients are able to write, hold a cup, and eat without spilling within hours of the procedure for the first time in years — an experience patients often describe as emotional.

The first weeks

Most patients return to ordinary daily activities within a few days to a week. You will usually be advised to avoid heavy lifting, strenuous exercise, and contact sports for a short period. The pin sites on the scalp are kept clean and typically heal within a couple of weeks.

Some side effects that may appear in the early days — mild gait unsteadiness, taste changes, finger numbness — tend to improve gradually over weeks. Your team will arrange follow-up appointments to check tremor, neurological function, and the appearance of the lesion on MRI.

Longer-term recovery

By six to eight weeks, most of the post-procedure changes have settled. Tremor control is reassessed using the same rating scales used before treatment. If side effects such as numbness or mild balance changes persist, your team will discuss whether physiotherapy or other supportive care is helpful.

Risks and Complications

FUS thalamotomy is generally considered a relatively safe procedure for an appropriately selected patient, but it is brain surgery, and risks exist. Major neurology and neurosurgery societies emphasise that all candidates should be informed about both the common temporary effects and the small risk of permanent ones.

Common, usually temporary effects

• Headache during or after the procedure
• Dizziness or nausea during sonications
• Mild scalp soreness from the frame
• Numbness or tingling in the lip, tongue, fingers, or hand on the treated side
• Mild imbalance or unsteadiness when walking
• Taste changes
• Mild weakness on the treated side

Most of these effects improve substantially within days to weeks.

Less common or persistent effects

• Persistent numbness or tingling
• Persistent gait unsteadiness
• Persistent mild weakness or coordination changes
• Speech changes, particularly slurred speech (dysarthria)
• Swallowing difficulty

The risk of persistent side effects is higher when both sides of the brain are treated, which is one reason most patients have only one side treated.

Rare but serious complications

• Bleeding within the brain (intracranial haemorrhage)
• Skin burns from the ultrasound or scalp
• Blood clots in the legs from prolonged lying still
• Serious neurological injury

Centres performing FUS thalamotomy report low rates of serious complications, but the procedure is not risk-free, and the discussion of risks should be specific to your situation and the centre’s experience.

Loss or partial loss of benefit over time

For some patients, tremor benefit gradually reduces over months or years. Studies have shown that a substantial majority of patients maintain meaningful tremor improvement at several years of follow-up, but some experience partial return of tremor. Repeat treatment may be considered in selected cases. The durability of the result is one of the topics where evidence is still maturing and where your neurosurgeon’s honest discussion of expectations is important.

Life After FUS Thalamotomy

For many people, the most striking change after FUS thalamotomy is the immediate ability to do everyday tasks that had become difficult or impossible: drinking from a glass without spilling, signing a document, eating soup, threading a needle, holding a child. These restorations of ordinary function can be powerful.

What changes

• Tremor in the treated hand is typically substantially reduced, sometimes nearly eliminated
• Confidence in social situations — eating in restaurants, public speaking, signing in front of others — often improves
• Activities such as writing, drawing, using a phone, and doing fine work with tools become easier

What does not change

• Tremor on the untreated side continues, unless and until further treatment is considered
• Other features of Parkinson’s disease (in patients with Parkinson’s) — stiffness, slowness, gait freezing, non-motor symptoms — are not treated by VIM thalamotomy and progress according to the underlying disease
• Essential tremor is a progressive condition; the treated tremor may slowly return to some degree over years

Medication after the procedure

Tremor medications are often reduced or stopped after treatment, but this is decided by your neurologist based on your specific response. For patients with Parkinson’s disease, other Parkinson’s medications are continued because they address symptoms other than tremor.

Driving, work, and daily activities

Most patients return to driving, work, and ordinary activities within a few weeks, depending on the type of work and any residual side effects such as mild imbalance. Your team will give specific guidance.

Follow-up and imaging

Follow-up visits are typically scheduled at intervals over the first year and then annually. MRI scans may be repeated to assess the lesion. Tremor severity is rechecked using the same scales as before.

Frequently Asked Questions

Is FUS thalamotomy considered brain surgery?

Yes, in the sense that a permanent lesion is created in the brain. It is incisionless, but it is still a neurosurgical procedure that creates a real, lasting change in brain tissue. The implications — including risks — should be considered with that in mind.

Will I be awake during the procedure?

Yes. Being awake allows the team to test tremor reduction and check for side effects in real time, before the lesion is made permanent. Most patients tolerate this well. Sedation is generally not given because it would prevent meaningful interaction.

Why is only one side treated?

Treating both sides of the thalamus carries a higher risk of side effects affecting speech, swallowing, and balance, because these functions involve both halves of the brain. Standard practice for FUS thalamotomy has been single-sided treatment of the side that controls the more affected hand (usually the dominant hand). Staged treatment of the second side is being studied and is offered in some centres for carefully selected patients.

How is FUS different from deep brain stimulation?

FUS creates a permanent lesion with no implant, in a single session, on one side. DBS implants electrodes and a stimulator that can be adjusted, turned off, or removed, and can be placed on both sides. FUS has no incision and a faster physical recovery; DBS allows for fine-tuning over time and bilateral treatment. Neither is universally better — the choice depends on the individual and the discussion with your team.

Does the tremor come back?

Tremor reduction is usually maintained for years in most patients. Some patients experience partial return of tremor over time, and the underlying disease (essential tremor or Parkinson’s) continues to evolve. Long-term outcomes are still being studied, and expectations should be discussed with your neurosurgeon.

Will my hair grow back?

Yes. The scalp is shaved to allow the ultrasound to pass cleanly, and the hair grows back normally afterwards.

How soon will I see results?

Tremor reduction is typically visible during the procedure itself and is usually clearly noticeable as soon as you sit up after treatment.

Can FUS thalamotomy be repeated?

Repeat FUS on the same side is being studied in selected cases where tremor has partially returned. Treatment of the other side is also possible in some centres. These decisions depend on a careful individual evaluation.

Does FUS thalamotomy cure essential tremor or Parkinson’s disease?

No. It reduces tremor on one side. It does not cure or slow the underlying condition. For patients with Parkinson’s disease in particular, it is important to understand that other symptoms continue to be managed with medications and other approaches.

Is FUS thalamotomy suitable for tremor caused by other conditions?

The strongest evidence is for essential tremor and tremor-dominant Parkinson’s disease. FUS thalamotomy has been studied for tremor in other conditions, such as multiple sclerosis, but use in these conditions is more selective. Your neurologist can advise whether it is appropriate in your specific case.

Conclusion

Focused-ultrasound thalamotomy is an option that has changed the landscape of tremor treatment for many patients. By creating a precise, small lesion in the thalamus without any incision or implant, it can reduce or nearly eliminate tremor on one side of the body in a single session. It is most established for essential tremor and tremor-dominant Parkinson’s disease that has not responded well enough to medication, and it sits alongside deep brain stimulation and other procedural options as part of the discussion when medication is no longer sufficient.

The decision to pursue FUS thalamotomy is not only about the procedure itself but about understanding what it can and cannot do: it treats tremor, not the whole condition; it is usually performed on one side; and it creates a permanent change in the brain that has both benefits and risks. A careful evaluation by an experienced movement disorder neurologist and neurosurgeon, an honest discussion of alternatives, and clear expectations about the result are the foundations of a good outcome. With those in place, many patients find that the return of steady hands meaningfully changes their daily lives.