Interventional radiology polymer update: acrylic

Embolized cerebral arteriovenous malformations: a multivariate analysis of 101 excised specimens

OBJECTIVE

Endovascular approaches have evolved from a technique practiced at very few centers to a widely available option in the management of arteriovenous malformations (AVMs) of the central nervous system. Embolization can be employed as definitive therapy or as an adjunct to surgical excision. A wide variety of embolic agents have been successfully developed and used in the clinical setting. In addition to facilitating vascular occlusion, embolic agents induce a number of reactive and destructive changes in vessel walls and the surrounding tissue. However, studies examining the pathological changes induced by different embolic agents and varying times of exposure are scarce. The goal of the present study was to compare embolic agents and time of exposure on the pathology in excised specimens.

METHODS

The records of the Department of Pathology at the London Health Sciences Centre were searched for embolized AVMs for the 35-year period 1980–2015. All cases were reevaluated for clinical and technical variables and standardized histopathological findings. Cases were grouped by embolic agent, volume of agent used, and time to excision.

RESULTS

A total of 101 specimens were identified. Embolic agents were invariably associated with a range of pathological findings, some of which may affect the integrity of vessel walls or the reestablishment of flow, thrombosis, acute and chronic inflammatory changes, angionecrosis, extravasation, and recanalization. The type of embolic agent did not predict differences in the incidence or severity of histopathological changes. Larger volumes of embolic agent were associated with a greater proportion of vessels containing embolic material. AVMs excised early (< 1 week postembolization) contained more acute vasculitis, while those excised later (≥ 1 week postembolization) were more likely to exhibit recanalization and foreign body giant cell infiltrates.

CONCLUSIONS

Embolic agents induce a predictable range and temporal progression of pathological changes in cerebral AVMs. The embolic agents studied are indistinguishable in terms of the range and frequency of pathological reactions induced. Greater volumes of embolic agent are associated with more abundant agent within the lesion, but the proportion of vessels and vascular cross-sectional areas containing agent is small. Several changes are significantly associated with time postembolization. Acute vasculitis is a more common finding in the 1st week, while recanalization and foreign body–type granulomatous inflammation are more common at 1 week and beyond.

A nonadhesive liquid embolic agent of ethylene vinyl alcohol copolymer and ethanol mixture for cerebral arteriovenous malformations. Clinical experience

SUMMARY

We report our experience using our new nonadhesive liquid embolic agent, an ethylene vinyl alcohol copolymer (EVAL)/Ethanol mixture, to treat human arteriovenous malformations (AVM). Between June 1995 and April 2001, 57 patients with confirmed AVM underwent embolization with the EVAL/Ethanol mixture. Using 87 procedures consisting of one to three stages, we embolized 185 feeding arteries to occlude as much of the AVM as possible. Repeated injections under fluoroscopic control could be performed smoothly without encountering cementing of the catheter in the vessel wall. Among 87 procedures undertaken in 57 patients, seven (8.0%) procedures in six patients produced new postembolization symptoms. Resolution of these symptoms occurred within hours or days following four of the seven procedures; permanent neurological deficits remained after three embolization procedures (3.4%). Of the 57 patients, three underwent postembolization radiosurgery, 54 were radically treated with microsurgical extirpation. Histopathological examinations of the 54 specimens disclosed mild inflammation within the embolized lumen without inflammatory reactions in the media or adventitia. Follow-up angiograms obtained three years after they underwent radiosurgery showed that in all three patients the nidus had completely disappeared. The EVAL/Ethanol mixture is handled easily and appears to be an effective and safe embolic agent for the preoperative embolization of AVM.

Tissue response to N-butyl-2-cyanoacrylate after percutaneous injection into cutaneous vascular lesions

Despite the fact that cyanoacrylates, a group of rapidly polymerizing adhesives, are used widely in general surgery, neuroradiology, otolaryngology, and plastic surgery, scientific data on histopathological changes resulting from the deposition of -butyl-2-cyanoacrylate (NBCA), a new-generation cyanoacrylate derivative, in human tissues is based largely on experimental observations in animals and sporadic postmortem studies in humans. The authors report the consecutive pathological findings of a patient who underwent surgery for facial hemangioma after percutaneous injection of NBCA for devascularization of a lesion, and underwent additional surgery 1 and 6 months after the initial operation for the removal of the residual NBCA cast from the injection site. Acute inflammatory findings after injection of NBCA and the development of a chronic granulomatous foreign body reaction support the histological findings of experimental animal studies and postmortem examinations on humans. Additionally, their findings support the proposed hypothetical sequence of events for the recanalization of cyanoacrylate-embolized vascular structures.

A mixture of ethylene vinyl alcohol copolymer and ethanol yielding a nonadhesive liquid embolic agent to treat cerebral arteriovenous malformations: initial clinical experience

OBJECT

The authors report their clinical experience with their new nonadhesive liquid embolic agent, an ethylene vinyl alcohol copolymer (EVAL)/ethanol mixture, to treat arteriovenous malformations (AVMs).

METHODS

Between June 1995 and April 2001, 57 patients with confirmed AVMs underwent embolization of their lesions with the EVAL/ethanol mixture. In 87 procedures consisting of one to three stages, the authors embolized 185 feeding arteries to occlude as much of the AVM as possible. Repeated injections under fluoroscopic control could be performed smoothly without encountering cementing of the catheter to the vessel wall. Among the 87 embolizations undertaken in 57 patients, seven procedures (8%) in six patients produced new postembolization symptoms. Resolution of these symptoms occurred within hours or days after four of the seven procedures; permanent neurological deficits remained after the other three procedures (3.4%). Of the 57 patients, three underwent postembolization radiosurgery, and 54 underwent radical treatment with microsurgical extirpation. Histopathological examination of the 54 specimens disclosed mild inflammation within the embolized lumen without inflammatory reactions in the media or adventitia. Follow-up angiograms obtained 3 years after radiosurgery was administered showed that in all three patients treated in this fashion the nidus had completely disappeared.

CONCLUSIONS

The EVAL/ethanol mixture is handled easily and appears to be an effective and safe agent for preoperative embolization of AVMs.

Embolic materials for endovascular treatment of cerebral lesions

Recently developed soft microcatheters can be maneuvered endovascularly into the brain, permitting treatment of lesions without conventional neurosurgery. Progress in biomaterial science has contributed significantly to the development of this new therapeutic modality termed intravascular neurosurgery or interventional neuroradiology. Although embolic materials play an important role, ideal materials have yet to be devised. Various embolic materials in clinical use are reviewed, such as cyanoacrylates, ethylene-vinyl alcohol copolymer mixtures, Ethibloc, ethanol, estrogen, poly(vinyl acetate), cellulose acetate polymer, poly(vinyl alcohol), gelatin sponges, microfibrillar collagen, surgical silk sutures, detachable balloons, and coils. The materials are reviewed in the context of treatment application for various brain lesions, such as arteriovenous malformations, cerebral aneurysms, and head and neck tumors. Further developments in biomaterial polymer science can bring about progress against brain diseases.

Gamma knife radiosurgery for cerebral arteriovenous malformations: an autopsy report focusing on irradiation-induced changes observed in nidus-unrelated arteries

BACKGROUND

In radiosurgical treatment for an arteriovenous malformation (AVM), the effects of irradiation on the intranidal and perinidal angioarchitectures have seldom been analyzed histologically. An autopsy case is reported, studying an AVM treated by gamma knife radiosurgery. Postmortem studies following AVM-unrelated death were performed after a 2-year angiography had demonstrated complete nidus obliteration. Irradiation-induced changes were also observed in surrounding nidus-unrelated arteries and the choroid plexus, both of which were within the irradiation target.

METHODS

Microscopic studies were performed using a coronal section of the brain including the center of the AVM, on which the percent isodose volume gradient, corrected with a magnification rate, was superimposed.

RESULTS

This study disclosed that intimal hypertrophy can occur in a normal, AVM-unrelated pial artery due to irradiation of 10 Gy or more and that more remarkable intimal hypertrophy with fragmentation of the elastic laminae, or even complete occlusion, can occur in these arteries with 25 Gy. Similarly, irradiation-induced degeneration was present in the choroid plexus, which had been exposed to doses varying from 10 Gy to 25 Gy.

CONCLUSIONS

A normal surrounding blood vessel may also be affected by high-dose, single-fraction irradiation though the abnormal vessels have been reported to be more susceptible.

Traumatic arteriovenous fistula treated by superselective embolisation with microcoils: case report

A 27-year-old man with a traumatic direct dural arteriovenous fistula (DAVF) was treated using embolisation microcoils. He had suffered blunt trauma to the head while drunk and was aware of no neurological deficit. A few days after the accident, however, he noticed a bruit in the right temple. Angiography demonstrated a direct DAVF fed by the right middle meningeal artery and draining into a right temporal dural vein and the ipsilateral cavernous sinus. A Tracker-18 catheter was passed without difficulty through the fistula and the draining vein was then embolised from distal to proximal with microcoils, and finally the fistula was occluded with microcoils, resulting in total obliteration of the fistula. Immediately after the embolisation, the patient could no longer hear the bruit. Thus, when a microcatheter can be introduced into the draining vein, microcoils can be used as emboli in the treatment of direct DAVF.

The combined management of cerebral arteriovenous malformations. Experience with 100 cases and review of the literature

A series of 100 patients treated for a cerebral arteriovenous malformation (AVM) is presented. Patients were admitted between 1985 and April 1992. Two groups are considered: the first group including 52 patients treated before the availability of radiosurgery (1985-1988), and the second group including 48 patients treated after the availability of radiosurgery (1989-1992). AVM's were classified in five grades according to the Spetzler's Grading System. Three techniques of treatment were used: surgical resection, intravascular embolization (with cyanoacrylate), and radiosurgery (linear accelerator). These three techniques were used either alone or in association, giving four types of management: surgical resection alone, embolization and resection, embolization alone, and radiosurgery (alone, or after embolization, or after surgical resection). From 1989 on, the availability of radiosurgery was responsible for the decrease of the "embolization and resection" group, which until then was predominantly used as well for low-grade (I, II, III) as for high-grade AVM's (IV, V). Overall, for the low-grade AVM's, the treatment of choice was surgical resection (79% of cases), with pre-operative embolization in one-half of these cases; the other low-grade AVM's were irradiated, with various combinations. For the high-grade AVM's, the treatment of choice was intravascular embolization (95% of cases), either alone, or followed by resection (45%) or radiosurgery (9%). Results were evaluated in terms of deterioration following treatment, in five groups: no deterioration (59%), minor deterioration (20%), long-lasting deficit (10%), major deterioration (5%), and death (6%). Overall, results improved after 1989: favourable outcome (no deterioration and minor deterioration) increased from 67% to 90%. Results were not related to the patients' age. More favourable results were obtained for low-grade AVM's (93%) than for high-grade AVM's (60%). For the low-grade AVM's the evolution from 1989 on (favourable outcomes increasing from 89% to 96%) occurred with the lowering of the mortality rate. For the high-grade AVM's, the evolution from 1989 onwards (favourable outcome increasing from 46% to 78%) occurred with the decrease of the cases with deficits. The angiographic results were strongly related to the management: 95% of complete eradication after surgical resection and 5% only after embolization alone. Concerning the results in irradiated cases, the follow-up is not long enough. The review of the neurosurgical literature since 1972 demonstrates progressive modifications in the therapeutic attitude as regards AVM's. The surgical management which was predominantly used at the beginning gave way progressively to a combined management, with a combination of embolization, surgery, and lately radiosurgery.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicity test of biodegradable polymers by implantation in rabbit cornea

To evaluate whether or not the corneal micropocket implantation is effective for determining the toxicity of polymeric materials, currently used biodegradable polymers such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), LA-GA copolymers, and three kinds of poly(2-cyano-acrylate)s (PCA) were implanted in a rabbit corneal pouch and the tissue responses were observed macroscopically and microscopically. It was found that PLA induced no vascularization, whereas a residual solvent and ethylene oxide gas remaining in the PLA matrix invoked vascularization. Vascularization clearly took place when PGA was implanted in the cornea, which became opaque, probably because of cellular infiltration. In the case of PCA implantation, severe inflammation as well as vascular invasion occurred in the initial stage. It is likely that these tissue reactions were caused by the leachables from the implanted materials, the extent being dependent on the leaching rate and the toxicity. It was concluded that the corneal micropocket assay is a good means to detect trace amounts of leachables from implanted materials without sacrificing the animals with the implanted materials.

Long-term pathological follow-up of cerebral arteriovenous malformations treated by embolization with bucrylate

We examined 17 intracranial arteriovenous malformations that were resected after treatment by embolization using bucrylate (isobutyl-2-cyanoacrylate). In nine specimens removed 5 days to 16 months after embolization therapy, a series of pathologic changes was seen, including patchy mural angionecrosis (adjacent to bucrylate fragments) up to six weeks after embolization, the presence of bucrylate in vessel walls and fibromuscular intimal cushions, and the occurrence (after several months) of entirely extravascular bucrylate. Occasional parts of recanalized vascular malformations were identified. Bucrylate was present within arteriovenous malformations as late as 16 months after embolization, although the amount appeared to be diminished. These findings suggest a specific sequence of events in the interaction between bucrylate and mural components within the malformations and may explain some important complications of embolization therapy (e.g., delayed hemorrhage after embolization).