Neuroendoscopy improves operability and reduces hazardous vermian manipulation during the telovelar approach to the fourth ventricle's floor: an anatomical study.

Approaching the fourth ventricle’s floor (FVF) is challenging. The transvermian approach (TRVE) provides wide access, but splitting the cerebellar vermis carries the risk of cerebellar mutism syndrome. Alternatively, the telovelar approach (TLV) enables entering the FVF without transecting neural tissue. However, the entrance through the cerebellomedullary fissure is narrow and pronounced microscope tilt or excessive and hazardous vermian retraction may still be required, especially when approaching the most rostral FVF portions. We hypothesize that neuroendoscopy during the TLV may improve operability and reduce vermian manipulation compared with classical microsurgical TLV and transvermian techniques. We also report two illustrative surgical cases (epidermoid cyst and pontine cavernoma) resected via an endoscopy-assisted TLV with favourable outcomes. We performed a within-subject comparison of operability scores and vermian retraction requirements between neuroendoscopic TLV (TLV_Endo), TRVE, and classical microsurgical TLV (TLV_Micro) when approaching the FVF in 8 formalin-fixed heads. At equal vermian retraction levels (0, 5, and 10 mm), TLV_Endo enabled significantly higher operability scores than TLV_Micro, especially along the middle and superior ventricular portions (p < 0.01), reaching even comparable scores to those obtained with the TRVE. Significantly lower vermian retraction was needed during TLV_Endo to achieve maximal operability scores along the middle (p < 0.01) and superior (p < 0.001) portions of the FVF versus TLV_Micro. In both illustrative cases, endoscopy-assisted TLV enabled safe lesion resection with good postoperative outcomes. TLV_Endo facilitates surgery along the FVF, particularly in its middle and superior portions, while minimizing vermian manipulation and potentially neurocognitive risks associated with vermian injury.