Lesioning in the Modern Era

Evidence status. Focused-ultrasound indications and labeling have expanded, including staged bilateral treatments for specific populations. Approval does not make bilateral lesioning low risk; target, laterality, staging interval, and adverse-event counseling must follow the exact current label and evidence.

1.The First Decision

A destructive lesion and a stimulating electrode placed at the same target produce, broadly, the same acute clinical effect: a Vim lesion and Vim stimulation both abolish tremor; a posteroventral pallidotomy and GPi stimulation both reduce rigidity and dyskinesia. The targets are shared. What differs is everything around the therapy.

Stimulation is adjustable and can be turned off. Parameters can be titrated over years as the disease evolves, side effects can be dialed back, and the hardware can be removed, although removal does not undo the surgical risks already taken at implantation. That flexibility is the reason DBS became the default. It comes at the cost of an implanted system that must be maintained: a pulse generator that needs replacement, leads and extensions that can fracture, erode, or become infected, and a programming relationship that requires the patient to return, sometimes repeatedly, to a center with the right expertise.

A lesion avoids implanted hardware, charging, battery replacement, and chronic programming. It still requires postoperative surveillance, and symptom recurrence or progression can lead to further treatment. Anticoagulation and medical fragility must be considered separately for RF, radiosurgery, and MRgFUS using the relevant contraindications and perioperative plan. The lesion cannot be adjusted or reversed. Historical bilateral lesions caused substantial speech, swallowing, gait, and cognitive morbidity; modern staged indications require separate selection and counseling, and comparative evidence against bilateral DBS is limited.

Schuurman and colleagues randomized patients with severe tremor to thalamotomy or thalamic stimulation. Tremor suppression was similar, while stimulation produced greater functional improvement and fewer adverse effects. This supports an important benefit–risk distinction, but the trial does not establish the safety ranking of every contemporary lesion modality or of staged bilateral MRgFUS versus bilateral DBS.

2.Who Is a Lesioning Candidate

The cleanest lesioning candidate is a patient with a disabling, predominantly unilateral, medication-refractory movement disorder who would benefit from a single procedure without implanted hardware. Tremor-dominant essential tremor and tremor-dominant or asymmetric Parkinson disease are the prototypes. Beyond the symptom itself, several features push toward a lesion rather than a lead:

• Strong patient preference to avoid implanted hardware, or a lifestyle or occupation in which device maintenance is impractical.
• Geographic distance from a center capable of long-term DBS programming.
• Anticoagulation or comorbidity that makes the open implantation and hardware burden of DBS less attractive, particularly relevant for the incisionless modalities.
• Advanced age or frailty, where a single, less invasive procedure may be preferable to a lifelong device relationship.
• Predominantly unilateral symptoms, so that one lesion addresses the dominant disability.

The features that push the other way, toward DBS, are equally worth naming: a clear need for bilateral treatment, a need to adjust therapy over time, younger patients in whom decades of disease evolution favor an adjustable system, and any situation where the ability to reverse or fine-tune the effect is clinically important.

Once a lesion is the plan, three technologies create it in the movement-disorder targets: radiofrequency thermocoagulation, stereotactic radiosurgery, and MR-guided focused ultrasound. MR-guided laser interstitial thermal therapy is a fourth ablative tool, but its established functional applications lie in epilepsy (including hypothalamic hamartoma and callosotomy), with smaller experiences in cingulotomy and capsulotomy for pain and psychiatric indications; small thalamotomy reports do not give it an evidence base equivalent to the three modalities discussed here. The three reach the same targets but differ in incisiveness, in whether the surgeon can confirm the target physiologically before committing, in how quickly the effect appears, and in their characteristic risks.

3.Radiofrequency Thermocoagulation

Radiofrequency (RF) ablation uses a stereotactically positioned electrode to heat a focal target. Clinical examination and macrostimulation, with microelectrode recording where used, help assess benefit and capsular or sensory thresholds before lesioning. Some protocols include low-temperature test heating, but temperature alone does not establish reversibility: injury depends on temperature, duration, electrode geometry, repeated exposures, and tissue conditions, so heating below 60 °C should not be taught as reliably recoverable. Definitive lesion parameters and any additional lesions follow target-specific, validated protocols, and the absence of an immediate deficit does not exclude later edema or delayed injury. The educational principle is progressive verification before an irreversible lesion, not a transferable temperature-and-time recipe.

The cost of RF is that it is the only one of the three that requires passing an electrode through the brain, with the attendant small risk of hemorrhage along the trajectory. It is, however, the most physiologically informed: the surgeon tests the target through the lesioning electrode before heating, examines the patient during and after each lesion, and can enlarge the lesion stepwise with additional or slightly repositioned heating. What RF does not offer is real-time imaging of the lesion itself.

4.Stereotactic Radiosurgery

Radiosurgical lesioning (most commonly Gamma Knife thalamotomy for tremor) delivers a high single dose, typically on the order of 130–140 Gy at the maximum, to a small focal target with no incision and no electrode. It is one incisionless option for carefully selected patients who cannot tolerate or decline an invasive procedure, including some patients whose anticoagulation cannot safely be interrupted, the medically fragile, and those for whom open surgery is contraindicated.

Its two limitations are intrinsic to the physics. First, there is no physiological confirmation: the dose is planned entirely on imaging, with no recording or test stimulation, so the surgeon cannot verify the functional target before committing. Second, the effect is delayed: the lesion matures over weeks to months, so tremor relief is not immediate and the final result cannot be assessed on the day of treatment. A minority of patients develop delayed, sometimes unpredictable, radiation effects (perilesional edema or an enlarging lesion) that can appear months later and occasionally cause new deficits. The risk that matters most, however, is not transient edema but permanent deficit. In a large single-center series (Young and colleagues, one hundred sixty-one patients treated by radiosurgical thalamotomy), fourteen patients had neurological complications, some of them permanent, involving sensory, motor, or speech function. Published permanent-complication rates are generally low, but the series are retrospective, heterogeneous, and unblinded, so quote them as such. Enlarging or misplaced lesions can reach the posterior limb of the internal capsule laterally or the sensory thalamus posteriorly, and the deficits follow the anatomy. Note also that the anticoagulated patient, so often described as the ideal radiosurgical candidate, does not escape hemorrhagic risk entirely: delayed hemorrhage and expanding hematoma within a radiosurgical thalamotomy lesion have been reported. Avoiding an intracranial electrode trajectory removes the procedural bleeding risk but not the risk of bleeding into a maturing lesion, and that belongs in the consent. Radiosurgical pallidotomy has a less favorable record, with delayed complications in small series, including contralateral homonymous hemianopsia from optic-tract dose, and is rarely the right operation when pallidal stimulation or focused ultrasound is available.

5.MR-Guided Focused Ultrasound

MR-guided focused ultrasound (MRgFUS) is the technology responsible for the current revival. About a thousand individually phased transducer elements in a hemispheric helmet focus ultrasound transcranially onto a millimetric target. Where the beams converge, tissue reaches ablative temperature; because the energy is spread across many entry paths, heating elsewhere is limited, although scalp and skull heating remain real safety constraints, managed with chilled water circulation and limits on sonication energy. Element-by-element phase correction, computed from the screening CT, is what compensates for the skull's heterogeneous thickness and density. The entire procedure occurs inside the MR scanner, which provides both anatomical targeting and real-time MR thermometry, a continuous temperature map of the developing lesion.

Two features make MRgFUS distinctive. It is incisionless: no burr hole, no electrode, no implanted hardware, and therefore essentially no hemorrhage-along-trajectory or hardware-infection risk. And it permits stepwise low-energy sonications with thermometry and serial examination before the final ablative exposure. These sonications help verify heating, location, and emerging clinical effects, but cumulative thermal injury may begin before the nominal final sonication; “test” should not be promised as fully reversible.

The constraints are specific to the technology. Transcranial sonication depends on skull composition and geometry; a screening CT measures the skull density ratio (SDR). A low SDR predicts difficulty reaching ablative temperature, but no single cutoff defines feasibility, and centers have treated progressively lower ratios as technique has evolved. The patient must tolerate prolonged immobilization in the MR scanner and serial examinations. Current FDA labeling includes unilateral and specific staged-contralateral applications; eligibility and interval are indication- and supplement-specific.

One further point, and it is not a technical one. Because MRgFUS is delivered inside a scanner and leaves no incision, it has attracted the argument that it is an imaging procedure rather than an operation. The ASSFN addressed that question directly in a 2026 position statement on focused ultrasound lesioning of the brain by non-neurosurgeons, and a 2026 Journal of Neurosurgery editorial argued for upholding the principles of stereotactic and functional neurosurgery in MR-guided focused ultrasound. Read both before your institution settles its staffing model, and understand why the profession drew the line where it did: the hardest part of this operation was never the sonication.

6.Targets by Symptom

The target follows the symptom, exactly as it does in DBS, and atlas-based coordinates are only starting points for image-guided, anatomy-driven planning rather than fixed destinations.

• Tremor (essential tremor, tremor-dominant PD): the ventral intermediate nucleus of the thalamus (Vim). Vim thalamotomy is the best-established lesioning indication and the first to be tested against sham with focused ultrasound.
• Parkinson disease, beyond tremor: the globus pallidus internus (pallidotomy) for rigidity, bradykinesia, and especially levodopa-induced dyskinesia; the pallidothalamic tract (pallidothalamic tractotomy, the target of the staged bilateral focused-ultrasound label discussed above) for motor fluctuations and dyskinesia; or the subthalamic nucleus (subthalamotomy) for the cardinal motor features in asymmetric disease. Subthalamotomy deserves a separate line in the consent. Lesioning the STN carries a particularly important risk of hemiballismus and hemichorea, historically the feared complication of the operation and a principal reason surgeons long avoided the STN as a lesion target, although how often it occurs with modern stereotactic technique is debated. Even in the randomized focused-ultrasound trial, where the technique was at its most controlled, speech disturbance occurred in fifteen of twenty-seven actively treated patients and gait disturbance in thirteen; off-medication and on-medication dyskinesia each occurred in six, weakness of the treated side in five, and facial weakness in three. At twelve months, speech disturbance persisted in three, off-medication dyskinesia in three, and gait disturbance and weakness in two each. Most of this resolves. Not all of it does. Treat STN as the target with the widest gap between the trial headline and the consent conversation.
• Dystonia: pallidal targeting, though dystonia is more commonly treated with stimulation given its frequently bilateral and evolving nature. Ventral oral (Vo) thalamotomy for focal, task-specific hand dystonia has been reported in selected series, mostly by radiofrequency.

7.What the Trials Show

The modern evidence base for lesioning is strongest for focused ultrasound, because it entered practice in the trial era and was tested against sham. The pivotal randomized, sham-controlled trial of MRgFUS Vim thalamotomy for medication-refractory essential tremor established a clinically meaningful reduction in hand tremor and disability against sham (hand-tremor score improved about forty-seven percent at three months, versus essentially no change after sham). Its five-year follow-up is the more useful number for consent: among the forty of seventy-five treated patients still assessed at five years, the combined hand-tremor score had improved about forty percent from baseline and disability about forty-five percent, with no new serious procedure-related late adverse events reported. That is durable, but attenuated from the early result, and with an attrition rate that should temper how firmly you quote it. The side-effect profile is dominated by paresthesia and by gait or balance disturbance. Most of this settles within months; some of it does not. At five years, paresthesia persisted in eight patients and imbalance in six, all mild to moderate. Tell the patient that a minority keep a sensory or balance change for good, and that this is the price of a lesion that cannot be turned down. Subsequent randomized work extended focused ultrasound to Parkinson disease: subthalamotomy improved motor features in asymmetric PD, and pallidotomy reduced motor impairment and dyskinesia in selected patients. Radiofrequency and radiosurgical thalamotomy have the longer track record for tremor, but it is not the same kind of evidence. Radiofrequency offers immediate lesions with prelesion physiological testing; much of its evidence is observational, although randomized comparisons with stimulation exist. Radiosurgery has never been tested against sham, and its prospective blinded data are mixed: one fifty-patient prospective single-blind series reported a fifty-four percent improvement in upper-limb tremor score at twelve months, while a smaller blinded video-rated evaluation found only modest change that did not reach statistical significance. Radiosurgery remains an option for selected patients unsuitable for electrode-based surgery or MRgFUS. It is not the only incisionless option, and its evidence should be described separately from sham-controlled focused-ultrasound trials.

8.Counseling the Patient

Honest counseling for a lesioning procedure rests on three points. The effect is permanent and cannot be reversed or fine-tuned; this is a feature for the patient who wants a one-time solution and a limitation for the patient whose disease will evolve. The first-side benefit is unilateral; staged contralateral treatment is available only for defined indications and remains a separate decision with a higher cumulative risk calculus. And the common side effects (sensory disturbance, gait or balance change, and speech effects) are usually mild or transient but are real, target-dependent, and worth naming explicitly before the procedure rather than after.

Framed this way, lesioning and stimulation are complementary rather than competing. The skill is matching the tool to the patient: the unilateral, hardware-averse, or geographically isolated patient is often best served by a lesion, while a patient requiring bilateral symptom control may benefit from an adjustable system. Rapid progression, prominent levodopa-resistant axial impairment, and diagnostic uncertainty require reassessment of whether either operation is appropriate.