Single burr hole rigid endoscopic third ventriculostomy and endoscopic tumor biopsy: What is the safe displacement range for the foramen of Monro?

Summary Objective To investigate the safe displacement range of the foramen of Monro (FM) during single burr hole rigid endoscopic third ventriculostomy (ETV) and endoscopic tumor biopsy (ETB). Methods Eleven patients who received ETV/ETB for third ventricular and pineal region tumor were reviewed. The burr-hole location, the size, and the virtual displacement of FM were measured using neuronavigation software. Results Hydrocephalus was resolved, and no subsequent cerebrospinal fluid (CSF) shunting was required in all cases. Histological diagnosis was established in 11 patients. Ten cases received instrumental cognitive and memory assessment postoperatively. The results were within the normal range for eight cases. The mean burr-hole location was 1.7 cm anterior to coronal suture and 3 cm from the midline. The mean diameters of FM measured on the axial, coronal, sagittal, and views were 5.7, 7.8, and 5.6 mm, respectively. The mean virtual displacements of the FM were 1.9 ± 2.0 mm (range = 0–4.8) for ETV and 2.4 ± 2.1 mm (range = 0–5.5) for ETB. The maximum displacements were 4.8 mm anteriorly for ETV and 5.5 mm posteriorly for ETB. Conclusion Single burr hole rigid ETV/ETB is likely to be safe within maximum FM displacements of 4.8 mm anterior for ETV and 5.5 mm posterior for ETB. Preoperative trajectory planning using neuronavigation software is recommended.