Neurosurgical training with simulators: a novel neuroendoscopy model.

PURPOSE: The aim of this study is to present a novel neuroendoscopy simulation model in live animals, with the objective of enhancing patient safety with realistic surgical training. METHODS: A simulation model using live Wistar rats was designed after the approval of the Institutional Committee for the Care and Use of Laboratory Animals. Under anesthesia, a hydroperitoneum was created in order to simulate a cavity with mesenteric membranes and vessels, viscera, and a solid and bleeding tumor (the liver) floating in a liquid environment. For validation purposes, we evaluated trainees' basal and final skills for each neuroendoscopic procedure, and we also acknowledged trainees' and instructors' opinion on the model's realism. RESULTS: This model is simple and low cost effective for complete and real-life training in neuroendoscopy, with the possibility of performing all the basic and advanced endoscopic procedures, such as endoscopic exploration, membrane fenestration, vessel coagulation, hematoma evacuation, and endoscopic tumor biopsy and resection using a ventricular neuroendoscopy set. Although the model does not represent human ventricular anatomy, a reliable simulation is possible in real living tissue in a liquid environment. Trainees' skills improvements were notorious. CONCLUSION: Minimally invasive endoscopic techniques require specific training. Simulation training can improve and accelerate the learning curve. The presented training model allows simulating the different neuroendoscopic procedures. We believe that due to its practical possibilities, its simplicity, low cost, reproducibility, and reality, being live animal tissue, it can be considered a fundamental model within a complete training program on neuroendoscopy.

Ocular and systemic toxicity of intravitreal topotecan in rabbits for potential treatment of retinoblastoma.

Treatment of intraocular retinoblastoma with vitreous seeding is a challenge. Different routes of chemotherapy administration have been explored in order to attaining pharmacological concentrations into the posterior chamber. Intravitreal drug injection is a promissing route for maximum bioavailability to the vitreous but it requires a well defined dose for achieving tumor control while limited toxicity to the retina. Topotecan proved to be a promising agent for retinoblastoma treatment due to its pharmacological activity and limited toxicity. High and prolonged concentrations were achieved in the rabbit vitreous after 5 µg of intravitreal topotecan. However, whether a lower dose could achieve potentially therapeutic levels remained to be determined. Thus, we here study the pharmacokinetics of topotecan after 0.5 µg and the toxicity profile of intravitreal topotecan in the rabbit eye as a potential treatment of retinoblastoma. A cohort of rabbits was used to study topotecan disposition in the vitreous after a single dose of 0.5 µg of intravitreal topotecan. In addition, an independent cohort of non-tumor bearing rabbits was employed to evaluate the clinical and retinal toxicity after four weekly injections of two different doses of intravitreal topotecan (Group A, 5 µg/dose; Group B, 0.5 µg/dose) to the right eye of each animal. The same volume (0.1 ml) of normal saline was administered to the left eye as control. A third group of rabbits (Group C) served as double control (both eyes injected with normal saline). Animals were weekly evaluated for clinical and hematologic values and ocular evaluations were performed with an inverse ophthalmoscope to establish potential topotecan toxicity. Weekly controls included topotecan quantitation in plasma of all rabbits. Electroretinograms (ERGs) were recorded before and after topotecan doses. One week after the last injection, topotecan concentrations were measured in vitreous of all eyes and samples for retinal histology were obtained. Our results indicate that topotecan shows non linear pharmacokinetics after a single intravitreal dose in the range of 0.5-5 µg in the rabbit. Vitreous concentration of lactone topotecan was close to the concentration assumed to be therapeutically active after 5 h of 0.5 µg intravitreal administration. Eyes injected with four weekly doses of topotecan (0.5 or 5 µg/dose) showed no significant differences in their ERG wave amplitudes and implicit times in comparison with control (p > 0.05). Animals showed no weight, hair loss or significant changes in hematologic values during the study period. There were no significant histologic damage of the retinas exposed to topotecan treatments. After intravitreal administration no topotecan could be detected in plasma during the follow-up period nor in the vitreous of treated and control animals after 1 week of the last injection. The present data shows that four weekly intravitreal injection of 5 µg of topotecan is safe for the rabbit eye. Despite multiple injections of 0.5 µg of topotecan are also safe to the rabbit eye, lactone topotecan vitreous concentrations were potentially active only after 5 h of the administration. We postulate promising translation to clinics for retinoblastoma treatment.

Pharmacokinetics of Orbital Topotecan After Ophthalmic Artery Chemosurgery and Intravenous Infusion in the Swine Model.

Purpose: Surgery, multiagent systemic chemotherapy, and radiation are used for patients with orbital retinoblastoma but are associated with unacceptable short- and long-term toxicity (including death). We studied orbital and systemic exposure of topotecan in the swine model after ophthalmic artery chemosurgery (OAC) and intravenous (IV) delivery. Methods: Landrace pigs (n = 3) underwent 30-minute OAC of topotecan (4 mg), and samples were serially obtained from the femoral artery and from a microdialysis probe inserted into the lateral rectus muscle sheath of the infused eye as a surrogate of the orbital irrigation. Animals were recovered, and, after a wash-out period, plasma and microdialysate samples from the contralateral eye were collected after a 30-minute IV infusion of topotecan (4 mg). Samples were quantified by high-performance liquid chromatography, and population pharmacokinetic analysis was conducted using MonolixSuite. Results: After OAC, median topotecan exposure in the orbit was 5624 ng × h/mL (range 3922-12531) compared to 23 ng × h/mL (range 18-75) after IV infusion. Thus, topotecan exposure in the orbit was 218-fold (range 75-540) higher after OAC than after IV infusion despite comparable systemic exposure (AUCpl) between routes (AUCpl, OAC: 141 ng × h/mL [127-191] versus AUCpl, IV: 139 ng × h/mL [126-186]). OAC was more selective to target the orbit because the median (range) orbital-to-plasma exposure ratio was 44 (28-65) after OAC compared to 0.18 (0.13-0.40) after IV infusion. Conclusions: OAC of topotecan resulted in higher orbital exposure than after IV infusion and was a more selective route for local drug delivery. Patients with orbital retinoblastoma may benefit from a multimodal treatment strategy including OAC therapy.

Pharmacokinetic analysis of topotecan after superselective ophthalmic artery infusion and periocular administration in a porcine model.

PURPOSE: To characterize the vitreous and plasma pharmacokinetics of topotecan after ophthalmic artery infusion (OAI) subsequent to superselective artery catheterization and to compare it with periocular injection (POI). METHODS: The ophthalmic artery of 4 pigs was catheterized and 1 mg of topotecan infused over a period of 30 minutes. The contralateral eye was subsequently used for administering topotecan by POI. Serial vitreous specimens were obtained by microdialysis and plasma samples collected and assayed for total and lactone topotecan. RESULTS: Maximum total topotecan concentration in the vitreous (median, range) was significantly higher after OAI compared with POI (131.8 ng/mL [112.9-138.7] vs. 13.6 ng/mL [5.5-15.3], respectively; P < 0.005). Median vitreous exposure calculated as area under the curve for total topotecan attained after OAI was significantly higher than after POI (299.8 ng·hour/mL [247.6-347.2] and 48.9 ng·hour/mL [11.8-63.4], respectively; P < 0.05). The vitreous to plasma exposure ratio was 29 after OAI and 3.4 after POI. Systemic exposure for total topotecan was low after both modalities of administration, with a trend to be lower after OAI compared with POI (10.6 ng·hour/mL [6.8-13.4] vs. 18.7 ng·hour/mL [6.3-21.7]; P = 0.54). CONCLUSION: Superselective OAI resulted in significantly higher vitreous concentrations and exposure and a trend toward lower systemic exposure than POI.

Pharmacokinetics of Melphalan After Intravitreal Injection in a Rabbit Model.

PURPOSE: Although widely used for vitreous seed control in retinoblastoma patients, currently there are no data on melphalan pharmacokinetics after intravitreal injections. Therefore, in this study, we characterized the ocular and systemic disposition of melphalan after intravitreal injection in the rabbit eye. METHODS: New Zealand rabbits received a single intravitreal injection of 15 µg of melphalan. Vitreous, aqueous, retina, and blood samples were collected at different times up to 12 h after the injection. Melphalan was quantitated in the biological samples using a validated high-performance liquid-chromatography technique and pharmacokinetic parameters were calculated by means of compartmental models. RESULTS: Model-predicted melphalan maximum vitreous, aqueous, and retina concentrations were 7.8 µg/mL, 0.024 µg/mL, and 9.8 µg/g tissue, respectively, attained immediately and at 0.8 and 0.25 h after intravitreal injection. Melphalan vitreous concentrations were higher than 0.3 µg/mL for 5 h after dosing. The elimination half-life from the vitreous, aqueous humor, and retina was 1.0, 0.2, and 1.2 h, respectively. Aqueous exposure [area under the curve (AUC)] was only 0.7% of that of the vitreous AUC. Melphalan concentrations in the retina were still detectable 12 h after dosing, while plasma exposure was under the limit of quantitation. CONCLUSION: Intravitreal administration of 15 µg melphalan leads to pharmacological vitreous levels with low aqueous exposure. Melphalan concentrations in the retina were measurable up to 12 h after dosing, but we report nondetectable systemic exposure in the rabbit. The results correlate with the clinical features of retinoblastoma patients that show control of vitreous seeds without systemic toxicity using intravitreal melphalan.

Topotecan Delivery to the Optic Nerve after Ophthalmic Artery Chemosurgery.

Extraocular retinoblastoma is a major challenge worldwide, especially in developing countries. Current treatment involves the administration of systemic chemotherapy combined with radiation, but there is a clear need for improvement of chemotherapy bioavailability in the optic nerve. Our aim was to study the ophthalmic artery chemosurgery (OAC) local route for drug delivery assessing ocular and optic nerve exposure to chemotherapy and to compare it to exposure after intravenous infusion (IV) of the same dose in an animal model. Topotecan was used as a prototype drug that is active in retinoblastoma and based on the extensive knowledge of its pharmacokinetics in preclinical and clinical settings. Five Landrace pigs received 4mg of topotecan via OAC as performed in retinoblastoma patients. At the end of the infusion, the eyes were enucleated, the optic nerve and retina were dissected, and the vitreous and plasma were separated. After recovery and a wash-out period, the animals received a 30-min IV infusion of topotecan (4 mg). The remaining eye was enucleated and tissues and fluids were separated. All samples were stored until quantitation using HPLC. A significantly higher concentration of topotecan in the optic nerve, vitreous, and retina was obtained in eyes after OAC compared to IV infusion (p<0.05). The median (range) ratio between topotecan concentration attained after OAC to IV infusion in the optic nerve, retina and vitreous was 84(54-668), 143(49-200) and 246(56-687), respectively. However, topotecan systemic exposure after OAC and IV infusion remained comparable (p>0.05). The median optic nerve-to-plasma ratio after OAC and IV was 44 and 0.35, respectively. Topotecan OAC delivery attained an 80-fold higher concentration in the optic nerve compared to the systemic infusion of the same dose with similar plasma concentrations in a swine model. Patients with retinoblastoma extension into the optic nerve may benefit from OAC for tumor burden by increased chemotherapy bioavailability in the optic nerve without increasing systemic exposure or toxicity.

Ophthalmic artery microcatheterization for research purposes in pigs. A technical note.

PURPOSE: To describe a technique for micro catheterization of the external ophthalmic artery (EO) in pigs for investigational and training purposes. METHODS: Carotid angiography was performed in seven male domestic pigs. The external ophthalmic artery was reached with a microcatheter in order to administer a neoplastic drug in the eye. RESULTS: The external ophthalmic artery could be found arising from the infraorbital (IO) artery in the bend of the internal maxillary (IM) artery. It could be reached in every animal. CONCLUSION: Following anatomic landmarks of the external carotid (EC) artery the ophthalmic artery can be easily reached and catheterized for training and investigational purposes.

Pharmacokinetic analysis of melphalan after superselective ophthalmic artery infusion in preclinical models and retinoblastoma patients.

PURPOSE: To characterize melphalan pharmacokinetics after superselective ophthalmic artery infusion (SSOAI) in animals and children with retinoblastoma. METHODS: Vitreous and plasma samples of five Landrace pigs were obtained over a 4-hour period after SSOAI of melphalan (7 mg). Melphalan cytotoxicity was evaluated in retinoblastoma cell lines with and without topotecan. Plasma samples were obtained from 17 retinoblastoma patients after SSOAI of 3 to 6 mg of melphalan to one (n=14) or two eyes (n=3). Correlation between plasma pharmacokinetics and age, dosage, and systemic toxicity was studied in patients. RESULTS: In animals, melphalan peak vitreous levels were greater than its IC50 and resulted in 3-fold vitreous-to-plasma exposure. In patients, a large variability in pharmacokinetic parameters was observed and it was explained mainly by body weight (P<0.05). A significantly higher systemic area under the curve was obtained in children receiving more than 0.48 mg/kg for bilateral tandem infusions (P<0.05). These children had 50% probability of grades 3-4 neutropenia. Plasma concentrations after 2 and 4 hours of SSOAI were significantly higher in these children (P<0.05). A synergistic cytotoxic effect of melphalan and topotecan was evident in cell lines. CONCLUSIONS: Potentially active levels of melphalan after SSOAI were achieved in the vitreous of animals. Low systemic exposure was found in animals and children. Doses greater than 0.48 mg/kg, given for bilateral tandem infusions, were associated with significantly higher plasma levels and increased risk of neutropenia. Synergistic in vitro cytotoxicity between melphalan and topotecan favors combination treatment.

Aneurismas experimentales en conejos por angioplastia con balón / Experimental aneurysms in rabbits by ballon angioplasty

Objetive. To perform a new model of experimental aneurysms in rabbits and to achieve a training in basic endovascular techniques. Material and method. We introduce a new aneurysm model in rabbits. First we performed a balloon angioplasty in the right carotid artery in the neck, then three weeks later we carry out an angiography with a diagnostic catheter from the right femoral artery to check aneurysm patency. Results. We were able to perform 10 aneurysms in ten rabbits; they were patent three weeks after their creation. The aneurysmscreation and the angiography performed to evaluate the aneurysm patency required a similar skill necessary to perform basic endovascular interventions. Conclusion. Aneurysms created from balloon angioplasty in the carotid artery in rabbits are a suitable model at least in the short term. The process of aneurysm formation and its study is an useful training in basic endovascular techniques.

Aneurismas experimentales en ratas / Experimental aneurysms in rats

Objective. 1. The creation of an aneurysm model in an arterial bifurcation for microsurgical training in rats. 2. To verify angiographically the aneurysms patency performing endovascular maneuvers. Material and method. 10 Wistar rats weighted 400-600g were used. Ten aneurysms were performed, 9 in the final aortic bifurcation and one in the origin of the renal artery. The aneurismal sac derived from the external iliac vein. Angiography in each animal was done to examine aneurysm patency. At the same time we tried to manipulate microcateter and microguidewire in the aortic lumen. After that the aneurysm was microscopically inspected in order to verify the angiographic findings. Results. The aneurysms and the angiographic study could be performed in every animal. Four aortic and the renal artery aneurysms were not visualized in the angiography (totally thrombosed). The other five were partially thrombosed. Under microscopic aneurismal inspection could be found thrombus into the sac. The endovascular navigation was difficult due to the animal size. Conclusion. The bifurcation aneurysm model is a good microsurgical training. In our hands the aneurysms created had a high rate of spontaneous thrombosis. Because of animal size it is not a good model for endovascular training.