The procedures were performed under approval by the local governmental animal care committee (registration number TVA 11-2023) and were in accordance with the UKCCCR Guidelines for the Welfare of Animals in Experimental Neoplasia (Br J Cancer 1998; 77:1–10) and the Interdisciplinary Principles and Guidelines for the Use of Animals in Research (New York Academy of Sciences Ad Hoc Committee on Animal Research, NY). Sprague–Dawley rats with a minimum weight of 250 g were obtained from Charles Rivers Laboratories, Sulzfeld, Germany. The animals were housed in cages at a room temperature of 22–24 °C and a relative humidity of 60–65% with a 12-h light/dark cycle. The rats were allowed free access to drinking water and standard laboratory chow (Altromin®, Lage, Germany). The animals were anesthetized by initial inhalation of isoflurane. Anesthesia was induced by intraperitoneal injection of 90 mg/kg bodyweight ketamine (Ketavet®, Parke Davis; Freiburg, Germany) and 8 mg/kg bodyweight xylazine (Rompun®, Bayer; Leverkusen, Germany). All animals received 5 mg/kg body weight carprofen (Vetranal™, Sigma‒Aldrich; St. Louis, USA) subcutaneously in addition to pain relief.

The animals were fixed in the supine position, and the limbs were fixed with tape. The anesthesia was constantly evaluated, and additional ketamine was applied if necessary. A median skin incision was made to access the peritoneal space (Fig. 2). An endoscope was inserted, and the skin was closed with a circular suture. There are two options: the model can be applied under water and constant irrigation with Ringer’s solution or under air conditions. The authors suggest the use of antifogging fluids to avoid forging of the lenses if the second method is used. The surgical steps were demonstrated to the trainees by the tutor on videos or pictures before the surgery. The following surgical steps were performed by the trainee.

Overview of the murine model. The rat was placed in the supine position (A), and the abdominal wall was opened (B). The liver was identified (C). The biopsy was performed with biopsy forceps (D). The falciform ligament is identified (E) and cut with scissors (F). The diaphragm was identified and perforated with perforating forceps (G, H). The balloon catheter was inflated, and the stoma was enlarged (I). The stoma can be inspected, and the procedure ends with a lethal dose of pentobarbital (J)

First, the endoscope is introduced, and an inspection of the abdominal space is performed. Second, the liver lobes are identified, and coagulation at the rim of the liver lobe is performed. Then, the coagulated tissue was removed with biopsy forceps. Possible bleeding from the parenchyma can be stopped with a bipolar probe.

After this step, the endoscope can be rotated 180 degrees to expose the bladder. This procedure simulates tumor removal. The attaching ligaments can be cut with scissors, and the bladder can be removed with grasping forceps.

Then, the endoscope is turned again and moves up to the upper part of the liver and the diaphragm. As a next step, the ligamentum falciforme is exposed and can be cut.

The last step is fenestration of the diaphragm. Here, coagulation is performed, the diaphragm is perforated with blunt perforating forceps, and the stoma is enlarged with balloon catheters. This simulates an ETV. The animal was then euthanized with a lethal dose of pentobarbital as it otherwise died due to collapse of the lung.

The endoscopic procedures can also be trained on cadaver models. The Institute of Anatomy and Cell Biology of the Saarland University provides the human cadavers. The education of physicians was performed under approval by the local governmental ethic committee (registration number 245/22). In general, these fresh frozen or prefixed cadavers allow surgical procedures, including borehole trepanation, endoscopic puncture of the ventricle and inspection and perforating steps (Fig. 3). The trainees were instructed to perform a ventricle puncture 2.5 cm parasagittal and before the coroner suture by themselves under instructions. Then, the ventricles were inspected with different angled optics. They then perform ETV. As a next step, a more lateral base hole was cut 4–5 cm parasagittally, and a septostomy was performed.

Overview of the cadaver model. After the trocar is introduced, the third ventricle is identified, and perforation is performed between the mammillary bodies and the infundibular recess (A). Enlargement of the stoma with the balloon catheter (B). The stoma was viewed to identify the basilar artery and perforating vessels on both sides (C, D). Inspection of the dorsal part of the third ventricle with the entrance of the aqueduct (E). Visualization of the triangular-shaped aqueduct (F)

Surgical hands-on workshops require adequate equipment. The endoscope sets were provided from major companies and are comparable in size with working trocars from 4 to 6 mm diameter. The instruments were basically comparable as standard instruments like scissors, dilation forceps, grasping forceps and coagulation probes were used. However, depending on the availability of the endoscope sets variating from workshop to workshop we did not compare the differences between the different types due to the reason, that those well-established sets enable the basic steps of neuroendocopy on a similar level in our experience.

A questionnaire, as added to the supplemental section, was distributed to the participants at the end of the workshop. The questionnaire included general questions regarding age, educational level, and experience in neuroendoscopy. The model was subsequently rated concerning the handling, realism and overall learning effect. The trainees were also asked for their desired qualities of an ideal training model for neuroendoscopy. The questions were ruled out in open answers, a Likert like scale or numeric rating scale, as reported before [14].

The questionnaires were transferred to SPSS (IBM, Armonk, USA). The results were analyzed by the chi-square test and likelihood test. A level of statistical significance was assumed at p ≤ 0.05. The data are presented as the mean and standard error of the mean.