Partial thrombosis of canine carotid bifurcation aneurysms with cellulose acetate polymer

Synthesis and characterization of radiopaque iodine-containing degradable PVA hydrogels

Poly (vinyl alcohol) (PVA) hydrogels are highly attractive for biomedical applications, especially for controlled release of drugs and proteins. Recently, degradable PVA hydrogels have been described, having the advantage that the material disappears over time from the implantation site. Herein, we report the synthesis of radiopaque degradable PVA, which gives a further advantage that the position of the hydrogel can precisely be determined by X-ray fluoroscopy. Radiopacity has been introduced by replacing 0.5% of the pendent alcohol groups on the PVA with 4-iodobenzoylchloride. This level of substitution rendered the polymer adequately radiopaque. The subsequent modification of 0.8% of the pendent hydroxyl groups with an ester acrylate functional group allowed for cross-linking of the macromers. The radiopaque hydrogels degraded over a time span of 140 days. Rheology data suggested that the macromer solutions were appropriate for injection.

Iodine-containing cellulose mixed esters as radiopaque polymers for direct embolization of cerebral aneurysms and arteriovenous malformations

The present study deals with the synthesis and characterization of radiopaque polymers which could, when solubilized in an appropriate water-miscible solvent, be useful embolic materials for the treatment of cerebral aneurysms and arteriovenous malformations. For this purpose cellulose (both microcrystalline and powdered) and partially substituted cellulose acetate (two different viscosity grades) were selected as starting materials to prepare iodine-containing polymers through various synthetic routes. The materials obtained were characterized by IR and NMR spectroscopy, molecular weight, iodine content, radiopacity and solubility in selected injectable organic solvents. The embolic liquids were evaluated for their precipitation behavior in a phosphate buffer solution (pH 7.4) mimicking physiological conditions using an in vitro aneurysm model. A sheep model was also used to assess in vivo the radiopacity and precipitation properties of a highly concentrated solution of a cellulose acetate 2,3,4-triiodobenzoate mixed ester. All materials with 4-iodo- and 2,3,5-triiodobenzoyl groups gave sufficient radiopacity to be regarded as possible embolization materials, whereas iododeoxycellulose and iododeoxycellulose acetate were not radiopaque because of their low iodine content. Esters synthesized using cellulose as starting material were not soluble in the selected organic solvents due to the presence of many residual hydroxyl groups, but could be used for other biomedical applications where insoluble radiopaque materials are used. In contrast, solubility of the materials as well as satisfactory precipitation properties were ensured using cellulose acetate as the starting material. In conclusion, cellulose acetate iodobenzoate mixed esters dissolved in diglyme or dimethyl isosorbide (dimethyl sulfoxide is probably less appropriate because of its toxicity and hemolytic properties) could be useful embolic liquids for the treatment of cerebral aneurysms or arteriovenous malformations.

Embolization of cerebral arteriovenous malformations with cellulose acetate polymer. Histological study of the resected specimens

SUMMARY

To test the usefulness of a cellulose acetate polymer(CAP) solution for brain arteriovenous malformations (AVMs), we analyzed the clinical and histological results of patients with AVMs embolized using CAP solution. We reviewed the cases of six patients with cerebral AVMs treated by embolization prior to surgical resection. We used two types of CAP solutions, CAP-M and CAP-L, which are mixtures of 250 mg of solid CAP and 1800 or 2250 mg of bismuth trioxide dissolved in 5.5 or 7.0 ml of dimethyl sulfoxide, respectively. All patients underwent surgical resection 1 to 37 days after the embolization procedure. Resected specimens were fixed in formalin and stained for light microscopic examination. Eighteen feeding vessels were embolized. The reduction rate of the nidus volume was between 20% and nearly 100%. Mild ischemic deficits occurred in one patients but there were no hemorrhagic complications related to the embolization procedures. All AVMs were completely resected by surgery. Direct inspection at surgery revealed that there was no apparent swelling or hematomas in the normal brain areas adjacent to the nidus, and the AVMs were soft enough to be easily retracted. The histological examinations disclosed no or mild inflammatory reactions within two weeks after embolization. The internal elastic lamina was preserved in every case. Recanalization of embolized vessels was not observed until 37 days after embolization. CAP solution is a safe and useful embolic agent for brain AVMs. Further study is needed to resolve the issue of recanalization.

Re-evaluation of cellulose acetate polymer: angiographic findings and histological studies

BACKGROUND

Cellulose acetate polymer (CAP) is a new liquid embolic material that has been used experimentally in intravascular treatment of intracranial aneurysms. But this compound is still controversial in some aspects such as safety, efficiency, and histological changes. In this study, we re-evaluated the material with regard to intravascular treatment of aneurysms.

METHODS

The carotid arteries of rats and experimental aneurysms in canines were embolized with CAP. The effects of CAP were evaluated according to angiographic and histological results.

RESULTS

A strong chemo-corrosive effect was observed. This led to severe damage to vessels and rupture of two thrombosed canine aneurysm models. There were significant technical difficulties including out-flow of CAP and a high rate of occlusion of the parent arteries.

CONCLUSIONS

We conclude that currently CAP is not an ideal embolic material for intracranial aneurysms. Further tests and improvements are needed before it can be widely used clinically.

Endovascular treatment of cerebral aneurysms: An in vitro study with detachable platinum coils and tricellulose acetate polymer

OBJECTIVE

The purpose of our experimental study was to determine the effectiveness of filling the cavity of in vitro aneurysms with detachable platinum coils and the combination of detachable platinum coils and liquid embolic agent.

MATERIALS AND METHODS

Silicone aneurysm models were connected to a circulatory system to simulate arterial flow. A microcatheter was used to introduce detachable coils into the aneurysm cavities. First, platinum coils were introduced until the point of minimal dense packing, indicated by aneurysmal circulatory exclusion. Packing was continued up to maximal dense packing, indicated by protrusion of the coil into the parent artery. Volumetric ratios (coil volume-aneurysm volume) were calculated for minimal and maximal dense packing. Then, after purposeful undercoiling of aneurysm models, a micropump system was used to fill the aneurysm by stepwise injection of tricellulose acetate polymer through the coil mesh until angiographic aneurysm exclusion was completed. The volumetric ratios of maximal packing with coils and tricellulose acetate polymer in relation to the aneurysm volume were calculated.

RESULTS

Maximal dense packing ratios with coils (mean, 32.5%; standard deviation [SD], 3%) were slightly higher than those with the minimal dense packing (mean, 28. 2%; SD, 3%) but were always less than 37%. The ratios of packing with the combined use of coils and tricellulose acetate polymer were greater than 100% (mean, 124.4%; SD, 15%).

CONCLUSION

Knowledge of the volumetric ratio of maximal dense packing was useful for effective filling with coils and tricellulose acetate polymer. The combined use of coils and liquid polymer appeared more effective than the use of coils alone for the complete occlusion of the aneurysm lumen.

Curative treatment of cerebral arteriovenous malformations by embolisation using cellulose acetate polymer followed by surgical resection

AIM

To investigate the usefulness of embolising cerebral arteriovenous malformations (AVMs) with a cellulose acetate polymer solution before surgical resection.

METHODS

The cases of 12 patients with AVMs treated by embolisation before surgical resection were renewed. Two types of cellulose acetate polymer solutions were used to occlude 40 feeding vessels. All patients underwent surgical resection 1-51 days after embolisation.

RESULTS

Reduction of the nidus volume after embolisation ranged from 20% to nearly 100%. Transient neurological deficits occurred in three patients, persistent deficits occurred in one and there were no haemorrhagic complications. All but one arteriovenous malformation were completely resected. Embolisation helped to identify feeding vessels and ease dissection. Histopathological examination of resected specimens disclosed mild inflammatory reactions in the acute stage and no unfavourable granulomatous changes in the chronic stage.

CONCLUSION

Embolisation with cellulose acetate polymer solutions followed by surgical resection is safe and efficacious for treating cerebral AVMs.

Embolization of cerebral arteriovenous malformations with cellulose acetate polymer: a clinical, radiological, and histological study

OBJECTIVE

A cellulose acetate polymer (CAP) solution was hypothesized to be useful for the embolization of arteriovenous malformations (AVMs). To investigate this possibility, we analyzed the clinical, radiological, and histological results of patients with AVMs embolized by using a CAP solution.

METHODS

We reviewed the cases of 11 patients with AVMs treated by embolization before surgical resection. We used two types of CAP solutions, CAP-M and CAP-L, which are mixtures of 250 mg of solid CAP and 1800 or 2250 mg of bismuth trioxide dissolved in 5.5 or 7.0 ml of dimethyl sulfoxide, respectively. After the embolization procedure, percent reduction of the nidus volume was measured, and thereafter, the clinical course and computed tomographic scans and/or magnetic resonance imaging scans were evaluated. All patients underwent surgical resection 1 to 51 days after embolization. Resected specimens were stained for light microscopic examination.

RESULTS

Thirty-nine feeding vessels were embolized. The reduction rate of the nidus volume ranged from 20% to nearly 100%. Transient and persistent ischemic deficits occurred in three patients and one patient, respectively, and there were no hemorrhagic complications. All AVMs but one were completely resected by surgery. The embolized AVMs were soft enough to be easily cut and retracted. The histological examinations disclosed no or mild inflammatory reactions within 2 weeks after embolization. The internal elastic lamina was preserved in every case. Recanalization through the cast of the CAP mass was not observed until 51 days after embolization.

CONCLUSION

CAP solution is a safe and useful embolic agent for AVMs.