The Pallidothalamic Tract in Functional Neurosurgery: A Systematic Review

The pallidothalamic tract (PTT), formed by convergence of the ansa lenticularis and fasciculus lenticularis at Forel's field H1, is a major basal ganglia efferent pathway and an emerging functional neurosurgical target. No systematic review has previously synthesised outcomes across PTT-targeted interventions.

This PRISMA 2020-compliant systematic review was registered on PROSPERO (CRD420251248260). PubMed, OVID, and Web of Science were searched for studies reporting functional neurosurgical outcomes targeting the PTT or Forel's fields. Prospective and retrospective studies, case series, and case reports were eligible. Methodological quality was assessed using design-appropriate risk-of-bias tools.

Forty studies encompassing 483 patients (1966-2025) were included across five modalities: MR-guided focused ultrasound (n=143), radiofrequency ablation (n=167), deep brain stimulation (n=40), cryogenic lesioning (n=82), and oil-wax injection (n=52). Mean follow-up was 21 months. In Parkinson disease (11 studies; n=135), mean UPDRS-III improvement was 39%, with reductions in dyskinesia (UDysRS 90%) and tremor (75%). In dystonia (12 studies; n=87), BFMDRS and TWSTRS improved by 57% and 47%, respectively. Dual-target strategies, particularly PTT-VIM combinations, showed additive effects, including greater tremor reduction (77%) and improved rigidity. In drug-resistant epilepsy (6 studies; n=157), seizure reduction occurred in 71% and seizure freedom in 33%.

PTT-targeted interventions yield meaningful motor improvements in Parkinson disease and dystonia, with preliminary evidence supporting additive dual-target benefits. Seizure-reducing effects in refractory epilepsy have been reported. Evidence remains limited by small uncontrolled studies, heterogeneous outcomes, and inconsistent adverse-event reporting. Prospective trials will elucidate the efficacy, safety, and clinical role of the PTT in neurosurgery.