Accuracy of frameless stereotactic brain biopsy: a retrospective cohort study with MRI-only and MRI-CT fusion...

Stereotactic-guided biopsy remains the gold standard for diagnosing intracranial lesions not amenable to surgical resection. Frameless techniques, such as the VarioGuide® system (Brainlab AG, Munich, Germany), offer a minimally invasive alternative, typically using MRI-based navigation. However, MRI-based navigation may be affected by geometric distortions that impair targeting precision. CT imaging provides superior geometric fidelity. This retrospective analysis evaluates the accuracy of frameless stereotactic biopsies in clinical routine. Patients were grouped based on the imaging modality used for neuronavigation-either MRI-only or MRI-CT fusion-allowing secondary comparison between both approaches.

In this retrospective cohort study, 99 patients who underwent frameless stereotactic biopsy between February 2022 and September 2024 were analysed. Patients were grouped by neuronavigation modality: CT-MRI fusion-based (n = 18) and MRI-only (n = 81). Accuracy was assessed by measuring entry and target deviations using postoperative CT. Lesion volume, depth, procedure duration, and complication rates were also evaluated.

Entry and targeting accuracy was comparable between groups (entry deviation: 5.2 ± 3.9 mm vs. 5.4 ± 3.0 mm, p = 0.84; target deviation: 4.2 ± 3.0 mm vs. 4.4 ± 2.7 mm, p = 0.85). Lesion volume and target depth showed no significant differences. No statistically significant differences in complication rates were observed between groups (27.8% vs. 11.1%, p = 0.14).

MRI-only and CT-MRI fusion-based frameless stereotactic biopsies showed no statistically significant difference in targeting accuracy. While CT-based registration may theoretically reduce distortion-related errors, this was not reflected in our data. The choice of imaging modality should therefore be guided by clinical context and imaging availability. Further prospective studies are needed to clarify the value of CT integration in specific clinical scenarios.