Is the Cessation of Blood Flow Faster than the Polymerization of an n-Butyl Cyanoacrylate-Lipiodol Mixture? An In Vitro Phantom Study

Optimal combination of microcoils, flow control, and n-butyl cyanoacrylate-Lipiodol-iopamidol (2:3:1) for feasible embolization of medium-sized arteries in an in vitro vascular model

PURPOSE

To evaluate the behavior of n-butyl cyanoacrylate-Lipiodol-iopamidol at a ratio of 2:3:1 (NLI231) with and without microcoils and/or flow control in embolization of medium-sized arteries in an in vitro vascular model.

MATERIALS AND METHODS

A vessel model representing a common hepatic artery was prepared. Six scenarios were set for embolization, each ran three times: 1) NLI231 injected alone with flow control to 0 ml/min during and up to 5 min after embolization; 2) NLI231 injected into a mesh of microcoil of 5% density with the flow control; 3) NLI231 injected into a microcoil of 10% density with the flow control; 4) NLI231 injected alone without the flow control; 5) NLI231 injected into microcoil of 5% density without the flow control; 6) NLI231 injected into a microcoil of 10% density without the flow control. The microcoils were delivered to the embolization site, and NLI231 was injected. After 1 h of observation, distal filters were collected, and grades of migration (I = none, II = partial, III = almost all-all) were assessed for each scenario.

RESULTS

Embolization was achieved in scenarios with NLI231 and microcoils regardless of flow control (p < 0.01). NLI231 did not migrate in scenarios with microcoils and flow control (p < 0.05). NLI231 with microcoils without flow control can embolize the vessel, but partial migration occurred, and the distal distance of the NLI231 complex from the embolization site was longer (p < 0.01).

CONCLUSION

Combining sparse coiling with NLI231 may be feasible but is limited to use when flow control is available, or where distal embolization is permissible to some extent.

Iodinated Cyanoacrylate-Based Novel Liquid Embolic Compositions with Inherent Radiopacity for Endovascular Embolization

Endovascular embolization is a promising therapeutic approach broadening its application area due to its minimal invasiveness and short operation time, wherein lesional blood vessels are occluded with liquid embolic agents under X-ray imaging guidance. Histoacryl and its composition with Lipiodol are one of the most widely used liquid embolic agents, however, Histoacryl has critical limitations, such as lack of innate X-ray visibility and strong adhesion to microcatheter. In this study, three different iodinated cyanoacrylates are newly synthesized as alternatives to Histoacryl and employed to develop liquid embolic compositions. Among them, 4-iodobutyl 2-cyanoacrylate (IBCA) is most preferable with high iodine content (730 mgI mL-1) and fast polymerization. The IBCA-based embolic compositions containing ethyl oleate and acetic acid showed moderate viscosity and reduced catheter adhesiveness (≈0.80 N), and their polymerization time is freely controllable from 2 to 15 s. In the embolization test with rabbit models, the renal artery is successfully occluded by IBCA-based embolic compositions without vascular recanalization or nontarget embolization for 4 w. Their embolic effect is further evaluated using swine models, demonstrating the practical applicability in the clinic. In conclusion, IBCA and its compositions are determined to have great potential as novel liquid embolic agents.

X-ray Microtomography to Assess Determinants of In Vivo N-Butyl Cyanoacrylate Glubran®2 Polymerization: A Rabbit-Model Study

Although introduced decades ago, few cyanoacrylate glues have been approved for endovascular use, despite evidence of their usefulness, notably for complex procedures suchas hemostatic embolization. Indications include massive bleeding requiring emergent hemostasis and prevention of severe bleeding during scheduled surgery to remove a hypervascular tumor. Adding radiopaque Lipiodol Ultra Fluid® (LUF) modulates glue polymerization and allows fluoroscopic guidance, but few comparative in vivo studies have assessed the impact of the resulting change in glue concentration or of other factors such as target-vessel blood flow. In a rabbit model, we used ex vivo X-ray microtomography to assess the results of in vivo renal-artery embolization by various mixtures of N-butyl cyanoacrylate (NBCA), metacryloxysulfolane, and LUF. Overall, penetration to the superficial interlobular arteries was achieved in about two-thirds of cases and into the capillaries in nearly half the cases, while cast fragmentation was seen in slightly more than half the cases. Greater NBCA dilution and the blocked-blood-flow technique were independently associated with greater distality of penetration. Blocked-blood-flow injection was independently associated with absence of fragmentation, capillary penetration, a shorter cast-to-capsule distance, and higher cast attenuation. A larger mixture volume was independently associated with higher indexed cast ratio and deeper penetration. Finally, microtomography is an adapted tool to assess ex vivo distribution of glue cast.

Raman Spectroscopic Characterization of Polymerization Kinetics of Cyanoacrylate Embolic Glues for Vascular Embolization

Endovascular glue embolization is a minimally invasive technique used to selectively reduce or block the blood supply to specific targeted vessels. Cyanoacrylate glues, mixed with radiopaque iodized oil, have been widely used for vascular embolization owing to their rapid polymerization rate, good penetration ability and low tissue toxicity. Nevertheless, in clinical practice, the selection of the glue–oil proportion and the manual injection process of mixtures are mostly based on empirical knowledge of operators, as the crucial physicochemical effect of polymerization kinetics has rarely been quantitatively investigated. In this study, the Raman spectroscopy is used for studying the polymerization kinetics of n-butyl-cyanoacrylate-based glues mixed with an iodized oil. To simulate the polymerization process during embolization, glue–oil mixtures upon contact with a protein ionic solution mimicking blood plasma are manually constructed and their polymerization kinetics are systematically characterized by Raman spectroscopy. The results demonstrate the feasibility of Raman spectroscopy in the characterization of polymerization kinetics of cyanoacrylate-based embolic glues. The polymerization process of cyanoacrylate-based mixtures consists of a fast polymerization phase followed by a slow phase. The propagation velocity and polymerization time primarily depend on the glue concentrations. The commonly used 50% mixture polymerizes 1 mm over ∼21.8 s, while it takes ∼51 min to extend to 5 mm. The results provide essential information for interventional radiologists to help them understand the polymerization kinetics of embolic glues and thus regulate the polymerization rate for effective embolization.

Sustained volume decreases in simple renal cysts after sclerotherapy using NBCA with or without hydrodissection

The present study aimed to determine the effectiveness of sclerotherapy using NBCA (Histoacryl Blue®; B. Braun, Melgungen, Germany), with or without hydrodissection, for the treatment of simple renal cysts. Materials and Methods: Patients who presented to an interventional radiology clinic for the diagnosis of symptomatic renal cysts which had previously been identified at an outpatient clinic were selected for inclusion in this study. A total of 28 patients were randomly divided into 2 groups, based on whether or not they underwent hydrodissection along with ultrasound-guided NBCA-based sclerotherapy. Sonographs were performed at 0, 7, and 180 days post-procedure to record the residual volume of the renal cysts and to determine the efficacy of the procedure. Results: A total of 32 cysts in 28 patients were treated with sclerotherapy, 18 (64%) females and 10 (36%) males. The average age of the patients was 61.8 years (range: 33-89 years). All patients reported an improvement in symptoms associated with the existing renal cysts at 7 and 180 days post-procedure, and at 7 days post-procedure a statistically significant reduction in cyst volume was observed (all patients: 96.8%; group A: 96%; group B: 97.6%). The reduced cyst volume was still observed 180 days post-procedure (all patients: 98.6%; group A: 98.2%; group B: 98.9%). There was no significant difference between the two treatment groups. Conclusion: There is a significant and persistent reduction in the volume of renal cysts, in addition to an improvement of the associated symptoms, after treatment with NBCA-based sclerotherapy, with or without hydrodissection.