EG-UC5T EUS-guided real-time electrode marking for completely endophytic renal tumors during laparoscopic partial nephrectomy: A preliminary case series

Background and Objectives: Completely endophytic renal tumors, which are invisible on the renal surface, present substantial challenges during laparoscopic partial nephrectomy (LPN). These tumors frequently result in prolonged warm ischemia time, higher rates of positive surgical margins, and excessive loss of renal parenchyma. This preliminary retrospective case series evaluated the feasibility, safety, and efficacy of real-time electrode marking guided by the EG-UC5T EUS system for precise intraoperative projection of tumor contours onto the renal surface. Methods: Five patients with completely endophytic renal tumors (RENAL E score = 3 in all cases; mean RENAL score 9.4 ± 0.9; mean diameter 2.6 ± 0.7 cm) underwent retroperitoneal LPN with EG-UC5T EUS-assisted marking. The flexible echoendoscope was introduced through a laparoscopic port for systematic real-time ultrasound scanning to delineate tumor boundaries, depth, and relationships to adjacent structures. Immediate surface marking was then performed using a metal electrode loop advanced through the integrated 4.0-mm working channel under continuous EUS guidance. Perioperative outcomes, renal functional preservation, and early oncologic results were analyzed descriptively. Results: In this series of 5 patients, tumor localization and surface marking were successfully achieved in all 5 cases (100% success rate), with a mean localization time of 8.6 ± 2.1 min. Mean operative time was 141.6 ± 18.9 min, estimated blood loss 71 ± 47.8 mL, and warm ischemia time 27 ± 8.5 min. No intraoperative complications or conversions to open surgery occurred. Mean renal parenchymal preservation reached 92% ± 4%. Estimated glomerular filtration rate declined by 3.7 ± 1.8 mL/min/1.73 m 2 on postoperative day 1 and recovered to a decline of only 1.2 ± 0.8 mL/min/1.73 m 2 at 3 months. Negative surgical margins were obtained in all cases (mean margin distance 3.2 ± 1.1 mm). One Clavien–Dindo grade I perinephric hematoma occurred and resolved conservatively. At a median follow-up of 8 months (range 6–12 months), no local recurrence or distant metastasis was detected. Conclusions: EG-UC5T EUS-guided real-time electrode marking is a feasible, safe, and effective technique for localizing completely endophytic renal tumors during LPN. It enables precise surface projection, reduces blind resection, and achieves favorable perioperative and early oncologic outcomes. Larger prospective studies are warranted.