After obtaining approval from the Institutional Review Board (n 0029354), a retrospective analysis was conducted on all patients who underwent RARP with ePLND between January 2018 and September 2019 in our academic center. According to NCCN guidelines on Prostate cancer, the indication for ePLND was the probability of nodal metastases ≥ 2% based on preoperative characteristics [8]. All procedures were performed by a single experienced surgeon (G.A.). The retrograde technique, which represented the standard approach for the surgeon, was used from January 2018 to December 2018, whereas from January 2019 onwards, the antegrade or retrograde approach were applied based on the surgeon's preference and patient’s anatomy. During the surgical procedure the chosen technique (antegrade vs retrograde dissection) was applied to both the left and right sides of the dissection for each patient, ensuring a consistent approach within the same individual. Previous abdominal surgical interventions may have led to the presence of intestinal adhesions, making exposure of the iliac area more challenging. However, this condition did not act as an exclusion factor: in all cases where lymphadenectomy was indicated, the procedure was still performed Peri-operative variables included: demographic data, preoperative PSA (iPSA), clinical and pathological stage of the disease (according to 2017 TNM classification) [9], ISUP grade, number of resected lymph nodes and percentage of positive ones, rate of overall perioperative complications, overall operating time (OT), estimated blood loss (EBL), complications at 30 days according to the Clavien-Dindo classification [10], pathological staging, length of hospital stay and total days of catheterization. In order to measure the surgeon’s overall satisfaction in terms of ability to follow the surgical steps and to perform an en-bloc dissection, each procedure was classified as either "efficient" or "inefficient," disregarding the dissection direction. The categorization depended on criteria, including the absence of bleeding, clear identification of anatomical landmarks, and the prevention of iatrogenic injuries to surrounding anatomical structures.

Complications such as fever and lymphocele formation were reported in medical reports, outpatient evaluations during follow-up and accesses to the emergency department. Lymphoceles were defined as clinically significant in case of fever, monolateral leg oedema, compression of the iliac vessels (demonstrated by eco-color doppler ultrasound) or visible mass on physical examination.

Follow up included cystography 6 days after RARP, blood exam 15 days after the discharge and PSA dosage at 45 days. No systematic pelvic ultrasound was performed during follow up in absence of symptoms.

The study was conducted in accordance with the Declaration of Helsinki (1964) and its later amendments. All patients signed an informed consent at the time of hospitalization to share their clinical information anonymously for research purposes. Data were prospectively collected in an encrypted multivariable database and were analysed retrospectively.

All RARPs were performed with Da Vinci Si (Intuitive Surgical, Sunnyvale, CA, USA) with a transperitoneal approach. Patients were operated in the lithotomy position, as described by Menon [11]. The Trendelenburg was set at 25° and the robot was positioned between the legs of the patient for docking. All RARPs were performed according to Patel’s technique [12]. The ePLND was performed before the prostatectomy. The following instruments were employed for ePLND: monopolar scissors on arm 1, bipolar maryland on arm 2, and prograsp on arm 3.

Cefazoline 2 g was administrated for antibiotic prophylaxis.

After the surgery, a 18 ch percutaneous abdominal drain was positioned, and usually removed on postoperative day 1. Patients were usually discharged on postoperative day 2.

In the antegrade en-bloc technique, the peritoneum is incised where the ureter crosses the common iliac artery (Fig. 2A). Both the artery and the ureter are then exposed. The lymph node dissection starts on the common iliac artery at the level of the ureter’s crossing and it proceeds in an antegrade direction, until the femoral canal and the vas deferent are exposed. The dissection continues further deeply exposing the common iliac vein right under the ureter and proceeds again in an antegrade fashion down to the femoral canal. The hypogastric artery, which is the medial border of the surgical field, is isolated, and the umbilical obliterated artery is exposed at its origin (Fig. 2B). Access to the Marceille’s triangle is developed in antegrade fashion starting from the medial border of the psoas major. The obturator nerve is then identified (Fig. 2C). The isolated lymphatic tissue is pulled anteriorly and released in the obturator fossa at the level of the iliac vessels. The vas deferens is then identified and divided. The lymphatic tissue over the obturator nerve is resected with a combined blunt and sharp dissection. The umbilical artery is followed, and the lymphatic tissue is divided in antegrade direction (Fig. 2D). The en-bloc antegrade lymph node dissection is then completed.

A. The peritoneum is incised where the ureter crosses the common iliac artery exposing both the artery and the ureter. B. Exposition of iliac vein, umbilical artery at its origin, and of Marceille’s triangle in antegrade fashion. C. Exposition of obturator nerve in obturator fossa. D. enbloc antegrade lymph node dissection is completed. The lymphatic tissue is isolated from umbilical artery

In the retrograde technique the peritoneum is incised at the level of the external iliac artery, at the level of inferior epigastric vessels, medial to the spermatic cord (Fig. 3A). The incision advances in a retrograde direction, until the ureter is identified (Fig. 3B). The lymph node dissection starts on the external iliac artery close to the vas deferent. The vas deferent is then divided and the dissection continues distally, in the femoral canal, until the external iliac vein is exposed. The external and the common iliac arteries are exposed up to the ureter, as for the iliac vein, with a combined blunt and sharp dissection (Fig. 3C). After the iliac vessels are completed exposed, the dissection proceeds in the obturator fossa. The obturator nerve is identified distally at the level of obturator foramen (Fig. 3D). The access to the Marceille’s triangle is achieved in a retrograde fashion, in the same fashion as in the antegrade dissection, towards the medial border of psoas major, exposing the obturator nerve both medially and laterally. The en-bloc retrograde lymph node dissection is completed by detaching the lymphatic tissue from the umbilical artery (Fig. 3E).

A. The peritoneum is incised at the level of the external iliac artery, at the level of inferior epigastric vessels, medial to the spermatic cord. B. The incision advances in a retrograde direction, until the ureter is identified. C. The lymph node dissection starts on the external iliac vessels and proceeds in a retrograde fashion until the ureter. D. The obturator nerve is identified distally at the level of obturator foramen. E. The enbloc retrograde lymph node dissection is completed by detaching the lymphatic tissue from the umbilical artery

Distribution of data was tested with the Shapiro–Wilk test. Data are presented as medians (interquartile range; IQR) or frequencies (proportions). Demographics characteristics, intraoperative and postoperative data were compared between antegrade (Group A) and retrograde (Group R) ePLND procedures with the Mann–Whitney test and the Fisher exact test. Multivariable (MVA) linear regression analysis were used to identify variables (e.g., previous abdominal surgery, technique of en-bloc ePLND, lymphadenomegaly, BMI) associated with ePLND time. Likewise, MVA logistic regression analysis tested the association between the same variables and the surgeon’s satisfaction of the ePLND.

Statistical analyses were performed using SPSS v.26 (IBM Corp., Armonk, NY, USA). All tests were two sided, and statistical significance level was determined at p < 0.05.