Introduction: The endoscopic techniques are increasingly performed to reduce iatrogenic trauma in microvascular decompression (MVD) operations. The superior petrous vein (SPV) is purposely sacrificed to gain adequate exposure of the trigeminal nerve during the surgery for refractory trigeminal neuralgia (TN). Our focus is to study the operability of the trigeminal root entry zone (REZ) of the ventral brainstem by the endoscopic application with preserving the SPV.
Methods: Both cerebellopotine angles in six cadaveric heads were studied. Standard MVD procedure was simulated with aids of the operative microscope (Moller, Cologne Germany). Two fixed-angled (0 and 30°) rigid endoscopes with outer diameters of 4 mm (Aesculap, Pennsylvania, US) were introduced.To compare the practical advantages of MVD and endoscopic assisted MVD(EMVD), we made the approaches into four subcategories: (1) microscopic approach alone without cutting the SPV; (2) endoscopic assisted approach without cutting the SPV; (3) microscopic approach alone with cutting of the SPV; (4) endoscopic assisted with cutting of the SPV. Each approach and its anatomical details were recorded and documented with videos and photos.
Results: The offending vessel loops were mainly SPV then SCA and seldom AICA in our cadaveric specimens. On purpose to quantify the operability of REZ, we proposed an exposure grading system. The visibility and maneuverability of either microscopic or endoscopic assisted approach were scored accordingly. The medial quadrant to the trigeminal nerve was never reached without the endoscope. SPV was always occupied in superior quadrant to the trigeminal nerve. Maneuverability and visibility gained benefit with cutting SPV in both superior and medial quadrants during MVD and EMVD procedures.
Conclusions: Based on the REZA (root entry zone access) score, this study demonstrates that using the endoscope in an assisted mode facilitates us to be able to better visualize the REZ and to better operate (decompress) on it without cutting the petrosal vein.
Patient Care: With preserving petrous vein, we minimize the venous compromise complications after MVD. Hence this assisted application lessens the hospital stay and improves the clincal outcomes.
Learning Objectives: Our study demonstrates that using the endoscope in an assisted mode, we are able to better visualize the REZ and to better operate on it without cutting the petrosal vein. Also even if the operator does not want to use the endoscope in an operative way he may select in which patients cutting the petrosal vein may lead to further vascular decompression and in which patients it will not by using the visualization information provided by the endoscope.