Tubular Retractor Assisted Minimal Invasive Parafascicular (trMIPS) Approach to Deep Seated Lesions: Neurological Outcomes per Anatomo-Functional Zones

Introduction: Surgical access to deep-seated lesions is challenging due to potential compromise of non-involved neuronal tissue. Tubular Retractor Assisted Minimal Invasive Parafascicular Surgery (trMIPS) is a safe surgical approach which allows minimal disruptive access to deep seated lesions. Different anatomo-functional zones are identified according to tumour location its relationship with the involving cortical and subcortical structures.

Methods: Single centre prospective study including patients that underwent trMIPS for deep-seated tumours. Patients were divided into 4 anatomo-functional zones that followed a clockwise distribution from medial frontal (zone 1) to medial parietal (zone 4) respecting two main white matter boundaries: anterior-posterior (formed by association tracts such as arcuate fasciculus and inferior fronto-occipital fasciculus) and medial-to-lateral (formed by projection fibres of corticospinal tract and thalamic radiations).

Results: 74 patients were included: 50% Zone 1, 9% Zone 2, 12% Zone 3 and 29% Zone 4. Preoperatively, no significant differences were observed in motor, language and visual deficits between zones (p>0.05). Postoperatively, patients with lesions in Zone 1 were more likely to develop a new motor deficit (Zone 1: 24.3%; Zone 2: 14.3%; Zone 3: 11.1%; Zone 4: 4.8%, p=0.048). For language, patients in Zone 1 were more likely to develop a new deficit – 13.5% - but this has not reached statistical significance when comparing with other zones (p=0.11). When comparing the 2 most representative zones – Zones 1 and 4 – Zone 4 has a better motor outcome profile: 33.3% improvement versus 16.2% and 4.8% deterioration versus 24.3%, p=0.039) and a trend towards better language outcome profile: 19.0% improvement versus 8.1% and no deterioration versus 13.5%, p=0.050). For vision, there is no impact of the anatomo-functional zones in the postoperative outcome.

Conclusion : Zone 1 (anterior to projection fibers and medial to association fibers) lesions are related with worse motor and language outcome after trMIPS.