Treatment Of Cerebral Arteriovenous Malformations Research Articles

Application of intraoperative real-time ultrasound in the surgical treatment of cerebral arteriovenous malformation

To investigate the value of intraoperative real-time ultrasound during surgery of cerebral arteriovenous malformations (AVMs). Thirteen patients with cerebral AVMs, 12 supratentorial and 1 infratentorial, underwent microsurgical treatment. Intraoperative ultrasound (IOUS) with multimodality was performed before the starting of resection in order to: (1) localize and delineate the AVM, (2) differentiate the embolized and perfused parts of AVM, and (3) identify the feeding arteries and draining veins. After removal of the lesion, sonographic examination was repeated to detect the residual AVM tissue and the findings were compared with the intra- and/or post-operative angiographic finding. Total resection was achieved in all 13 patients with AVM under real-time ultrasonographic navigation. The niduses of AVM were localized and defined precisely by IOUS due to their dichromatic flow pattern. The embolized parts of AVM exhibited hyperechogenicity without blood signals. The feeding and draining vessels were distinguished from normal ones morphologically and hemodynamically. Complete removal of the AVM determined sonographically was then confirmed by angiography. Intraoperative real-time ultrasound allows accurate localization and navigation of the cerebral AVMs, provides valuable information during surgery, and helps determine the degree of removal of the cerebral AVM.

Risk of hemorrhage from an arteriovenous malformation confirmed to have been obliterated on angiography after stereotactic radiosurgery

Radiosurgery has been widely adopted for the treatment of cerebral arteriovenous malformations (AVMs) in which the practical endpoint is angiographic evidence of obliteration, presumed to be consistent with elimination of the risk of hemorrhage. To test this unverified assumption, the authors followed 236 radiosurgery-treated AVMs between 1 and 133 months (median 77 months) after angiographic evidence of obliteration. Four patients experienced hemorrhage between 16 and 51 months after angiographic confirmation of AVM obliteration, and two underwent resection. The histological findings in these patients showed occlusion of the AVM by thickening of the intimal layer with dense hyalinization as well as a small amount of residual AVM vessels and a tiny vasculature. The risks of hemorrhage from these presumaby obliterated AVMs were 0.3% for the annual bleeding risk and 2.2% for the cumulative risk over 10 years. Continuous enhancement of the nidus on computerized tomography (CT) or magnetic resonance (MR) imaging was the only significant factor positively associated with hemorrhage in the statistical analysis (p = 0.0212). Because the study was based on limited follow-up data, its significance for defining predictive features of hemorrhage after angiographic evidence of obliteration is still indeterminable. Nevertheless, disappearance of the AVM on angiography after radiosurgery does not always indicate total elimination of the disease, especially when CT or MR imaging continues to demonstrate an enhancing lesion. The authors therefore recommend continual follow up even after evidence of AVM obliteration on angiography.

A simple method for predicting imaging-based complications following gamma knife surgery for cerebral arteriovenous malformations

Object. The authors studied the relationship between dose planning parameters and complications in the treatment of cerebral arteriovenous malformations (AVMs). Methods. There were 41 continuous unselected patients. The mean follow-up period was 19 months; the mean age was 28 years; the male/female ratio was 2.2:1.0; the median prescription dose was 25 Gy (range 14–25 Gy); the median prescription isodose was 50%. The median lesion volume was 4.4 cm3. The median lesion coverage was 93%; and the mean conformity index was 1.22. The authors found no relationship between lesion volume or integral dose and the development of the clinical effects based on the adverse radiation effects (AREs); however, there was a significant relationship between both target volume and integral dose with the development of AREs as well as the severity of the AREs. Conclusions. The integral dose could be used as a guideline for the prescription dose. Arguments are made for maximizing the prescription dose for the long-term safety of the patient.

A simple method for predicting imaging-based complications following gamma knife surgery for cerebral arteriovenous malformations

The authors studied the relationship between dose planning parameters and complications in the treatment of cerebral arteriovenous malformations (AVMs). There were 41 continuous unselected patients. The mean follow-up period was 19 months; the mean age was 28 years; the male/female ratio was 2.2:1.0; the median prescription dose was 25 Gy (range 14-25 Gy); the median prescription isodose was 50%. The median lesion volume was 4.4 cm3. The median lesion coverage was 93%; and the mean conformity index was 1.22. The authors found no relationship between lesion volume or integral dose and the development of the clinical effects based on the adverse radiation effects (AREs); however, there was a significant relationship between both target volume and integral dose with the development of AREs as well as the severity of the AREs. The integral dose could be used as a guideline for the prescription dose. Arguments are made for maximizing the prescription dose for the long-term safety of the patient.

Complications of Embolization for Cerebral Arteriovenous Malformations

Embolization is recognized as an important adjunct in the treatment of cerebral arteriovenous malformations (AVMs). We reviewed our results of embolizations for AVMs and discussed procedure-related complications. Eleven complications were recorded in 68 consecutive patients (16%). Of these, four were technical problems including a glued catheter, inability to withdraw the catheter, vessel perforation by the microcatheter, and coil migration. Other complications included three cases of ischemic symptoms due to retrograde thrombosis, two cases of asymptomatic cerebral infarction, one case of asymptomatic small haemorrhage due to venous occlusion, and one case of post-embolization haemorrhage of unknown etiology. Our morbidity rate was 7%, mortality rate was 0%, and asymptomatic complication rate was 9%, retorospectively. Further improvements to endovascular techniques and devices are required.

Microsurgical treatment of cerebral arteriovenous malformations of Spetzler-Martin grade III or higher following endovascular treatment

目的 探讨复杂难治性脑动静脉畸形(AVM)的血管内栓塞辅助显微手术治疗的临床效果.方法分析1999年11月～2003年12月治疗Spetzler分级Ⅲ级以上脑AVM的33例临床资料.Spetzler分级Ⅲ级22例,Ⅳ级9例,Ⅴ级2例.脑AVM体积最大为7.0 cm×8.6 cm×6.1 cm,最小为2.5 cm×3.0 cm×2.8 cm.所有病例均接受了血管内栓塞辅助显微手术治疗.结果33例中31例术后恢复良好,其余2例中度致残.术后行MRI、MRA及DSA检查,未见血管流空影像及畸形血管影像.术后6个月内行DSA血管造影检查证实33例脑AVM完全切除,未见畸形血管影像.结论Spetzler分级Ⅲ级以上脑AVM是难治性疾病.血管内栓塞辅助显微手术切除可以取得良好的临床疗效。

Endovascular treatment of cerebral arteriovenous malformations with emphasis on the curative role of embolisation

Cerebral arteriovenous malformations are complex and only partially understood vascular lesions of the central nervous system with a natural history characterised by significant morbidity and mortality mainly due to an increased haemorrhagic risk. Microneurosurgical removal, radiosurgical obliteration and neuroendovascular embolisation are the principal therapeutic modalities applied individually or in various combinations according to varying selection criteria for the treatment of cerebral arteriovenous malformations. In this context embolisation plays a central role either as a complementary or as the sole treatment technique. This report summarises the evolutive 18 years of continuous experience of the senior author with the neuroradiological evaluation and endovascular treatment of 644 patients with a cerebral arteriovenous malformation. Special emphasis is given to the underlying concepts and specific endovascular techniques developed for the complete, i.e. curative embolisation of cerebral arteriovenous malformations. Precise angiographic analysis of the vascular composition and intrinsic angioarchitecture of the nidus of the arteriovenous malformation by superselective microcatheterisation is required to identify the types of feeding arteries and patterns of their supply, the number and vascular connections of nidal compartments, the types of arteriovenous shunts, the morphology of the vascular spaces composing the nidus and the number and exit patterns of draining veins. Complete angiographic investigation for recognition of secondarily induced phenomena of the cerebral vasculature, such as arterial and venous high-flow angiopathy and so-called perinidal angiogenesis is essential for a comprehensive evaluation and assessment of the associated haemorrhagic risk. Based on a precise topographic classification, detailed angioarchitectural analysis, application of superselective multimicrocatheterisation techniques along with a controlled intranidal injection of non-absorbable liquid embolic materials, nearly 40% of cerebral arteriovenous malformations can be completely and stably obliterated and therefore curatively treated by single session or multistaged embolisation with a morbidity of 1.3 % and a mortality of 1.3%, which are lower than the known natural history of this disease.

Radiosurgery of cerebral arteriovenous malformations in children: A series of 57 cases

Purpose To evaluate the efficacy and outcome of Linac radiosurgery (RS) as treatment of cerebral arteriovenous malformations (cAVM) in a series of 57 children. Methods and materials Between 1984 and 2000, we used Linac radiosurgery to treat 792 patients with cAVM. This series included 57 children (7.2%) under the age of 15 years at the time of RS (range = 7–15 years, median = 12 years). We were able to evaluate 49 of the children (86%) by angiography, 21 boys and 28 girls (sex ratio = 0.75). First symptoms were: hemorrhage, 34 patients (69.4%); seizures, 6 patients (12.5%); headache, 6 patients (12.5%); and progressive neurologic deficit, 1 patient (2.1%). Nidus size ranged from 5 to 50 mm (median = 20 mm). Nidus volume ranged from 0.6 to 16 cc (median = 3.5 cc). Patient distribution according to Spetzler-Martin grade was as follows: Grade 1, n = 5 (11%); Grade 2, n = 18 (35%); Grade 3, n = 21 (40%,); Grade 4, n = 5 (14%); and Grade 5, n = 0%. Twenty-seven patients (55.1%) had other treatment before RS: embolization, n = 14 (31.1%); neurosurgery, n = 9 (20.5%); embolization and neurosurgery, n = 3 (6.1%). RS was performed with the system used for adults. Patients were seated in a Betti armchair. Circular 15 MV X-ray minibeams (6 to 20 mm) were delivered in coronal arcs by a GECGR Saturne 43 Linac. Planification and dosimetry were carried out using the Associated Target Methodology and Dosigray TPS dosimetric systems. The dose at the peripheral isodose (50–70%) ranged from 18 to 28 Gy. Median and mean doses were 25 Gy and 23.8 Gy. Mono-isocentric planification was used in 25 patients (53.2%) and multi-isocentric in 24 patients (2 to 5 isocenters). The overall follow-up ranged from 7 to 172 months (mean 40 months, median 34 months). Results The overall rate of obliteration (OR) was 30/49 (61.2%). Mean time to obliteration was 34 months (range = 7 to 172 months). OR varied according to nidus size and volume: OR was 80% for nidus <15 mm, 67% for nidus between 15 and 25 mm, and 42% for nidus >25 mm ( p = 0.058). OR was 100% for nidus <1 cc, 73% for nidus between 1 and 4 cc, and 40% for nidus of 4 to 10 cc ( p = 0.019). OR according to patient gender was 84.2% for boys and 40% for girls. OR according to minimum dose (Dmin) was 44% for Dmin < 15 Gy ( p = 0.01), 89% for D min from 15 to 20 Gy, and 100% for Dmin > 20 Gy ( p = 0.01). OR was 62% in nonembolized AVM and 58% in previously embolized AVM (NS). OR according to the number of isocenters was 68.2%, 55.6%, 80%, 50%, and 0% for 1, 2, 3, 4, and 5 isocenters, respectively. After multivariate analysis, only Dmin closely correlated with OR (β = 0.462; SE = 0.244, p = 0.057). Of the 6 patients with seizures before RS, 5 (80%) were seizure-free without medication after RS. One patient died of pneumonia. Morbidity Four patients (8.2%) had bleeding after RS at 39, 45, 51, and 59 months. No new neurologic deficit was found during the follow-up period. Twenty-nine patients underwent magnetic resonance imaging. Thirteen patients (44.8%) showed no parenchymal changes. Thirteen patients (44.8%) had Grade 2 changes, that is, T2 hypersignals. Two patients (6.9%) had Grade 3 changes, and 1 patient (3.4%) had Grade 4 “necrosis-like” changes. Conclusion In our experience, Linac RS has proven to be a safe and effective method to treat cerebral AVM in children <15 years, whether used alone or in association with embolization and/or neurosurgery.

Dose-volume prediction of radiation-related complications after proton beam radiosurgery for cerebral arteriovenous malformations.

The use of radiosurgery for the treatment of cerebral arteriovenous malformations (AVMs) and other lesions demands an accurate understanding of the risk of radiation-related complications. Some commonly used formulas for predicting risk are based on extrapolation from small numbers of animal experiments, pilot human treatment series, and theoretical radiobiological considerations. The authors studied the incidence of complications after AVM radiosurgery in relation to dose, volume, and other factors in a large patient series. A retrospective review was conducted in 1329 patients with AVM treated by Dr. Raymond Kjellberg at the Harvard Cyclotron Laboratory (HCL) between 1965 and 1993. Dose and volume were obtained from HCL records, and information about patient follow up was derived from concurrent clinical records, questionnaires, and contact with referring physicians. Multivariate logistic regression with bootstrapped confidence intervals was used. Follow up was available in 1250 patients (94%); the median follow-up duration was 6.5 years. The median radiation dose was 10.5 Gy and the median treatment volume was 33.7 cm(3). Twenty-three percent of treated lesions were smaller than 10 cm(3). Fifty-one permanent radiation-related deficits occurred (4.1%). Of 1043 patients treated with a dose predicted by the Kjellberg isoeffective centile curve to have a less than 1% complication risk, 1.8% suffered radiation-related complications. Actual complication rates were 4.7% for 128 patients treated at Kjellberg risk centile doses of 1 to 1.8%, and 34% for 61 patients treated at risk centile doses of 2 to 2.5%. The fitted logistic model showed that complication risk was related to treatment dose and volume, thalamic or brainstem location, and patient age. The Kjellberg isoeffective risk centile curve significantly underpredicted actual risks of permanent complications after proton beam radiosurgery for AVMs. Actual risks were best predicted using a model that accounted for treatment dose and volume, lesion location, and patient age.

Role of frameless stereotaxy in the surgical treatment of cerebral arteriovenous malformations: technique and outcomes in a controlled study of 44 consecutive patients.

To describe a frameless stereotactic technique used to resect cerebral arteriovenous malformations (AVMs) and to determine whether frameless stereotaxy during AVM resection could decrease operative times, minimize intraoperative blood losses, reduce postoperative complications, and improve surgical outcomes. Data for 44 consecutive patients with surgically resected cerebral AVMs were retrospectively reviewed. The first 22 patients underwent resection without stereotaxy (Group 1), whereas the next 22 patients underwent resection with the assistance of a frameless stereotaxy system (Group 2). The patient characteristics, AVM morphological features, and percentages of preoperatively embolized cases were statistically similar for the two treatment groups. The mean operative time for Group 1 was 497 minutes, compared with 290 minutes for Group 2 (P = 0.0005). The estimated blood loss for Group 1 was 657 ml, compared with 311 ml for Group 2 (P = 0.0008). Complication rates, residual AVM incidences, and clinical outcomes were similar for the two groups. Frameless stereotaxy allows surgeons to 1) plan the optimal trajectory to an AVM, 2) minimize the skin incision and craniotomy sizes, and 3) confirm the AVM margins and identify deep vascular components during resection. These benefits of stereotaxy were most apparent for small, deep AVMs that were not visible on the surface of the brain. Frameless stereotaxy reduces the operative time and blood loss during AVM resection.

A nonadhesive liquid embolic agent composed of ethylene vinyl alcohol copolymer and ethanol mixture for the treatment of cerebral arteriovenous malformations: experimental study.

The authors have developed a mixture of ethylene vinyl alcohol copolymer (EVAL) and iopamidol, which is dissolved in ethanol, as an alternative solvent to provide a safe means of embolizing arteriovenous malformations (AVMs). A two-stage delivery technique is required to prevent premature precipitation in the catheter when using this material: the catheter is first infused with 30% ethanol and this is followed by the delivery of the EVAL-ethanol mixture. Acute angiographic changes were analyzed after superselective delivery of dimethyl sulfoxide (DMSO) and 30% ethanol into the renal artery of rabbits. Histological changes following the embolization of the renal artery achieved using the EVAL-ethanol mixture were recorded at 1 hour and at 2 and 16 weeks after the procedure. Although DMSO always produced severe, rapidly progressive vasospasm in the renal artery during a 1- to 60-minute postinfusion, 30% ethanol did not. Microscopically, the lumens of embolized vessels examined 1 hour after embolization with EVAL-ethanol appeared to be filled with EVAL sponges, leaving almost no open spaces. The space between the EVAL sponges and the inner surface of the vessels was filled with fresh thrombus. In the vessel walls of specimens examined 2 weeks after embolization there was no or a slight inflammatory reaction. Scattered in the EVAL sponges were almost equal numbers of neutrophilic granulocytes and mononuclear cells, indicative of a mild inflammatory response. In specimens examined 16 weeks postembolization, the changes noted at 2 weeks were intensified. There was no definite histopathological evidence of mural hemorrhage, perivascular extravasation of the mixture, or perivascular hemorrhage in any specimen that was examined. Although the degree of permanence of this embolization material is yet unknown, the mixture was easy to handle, and appeared safe and effective for AVM embolization. Its nonadhesive characteristic and its ability to be infused by repeated injections make it an attractive alternative to currently available materials. The good results obtained in this study led us to undertake a clinical trial, the results of which are contained in a companion article in this issue of the Journal of Neurosurgery.

Hemodynamic Changes in Drainage Systems following Treatment of Cerebral Arteriovenous Malformations

The authors studied 61 patients undergoing effective embolization for cerebral arteriovenous malformations (AVMs) and analyzed the hemodynamic changes in their drainage systems following embolization. The changes were classified into following 5 types: type A, disappearance of all the draining veins; type B, disappearance of a part of the cortical veins; type C, disappearance of a part of the deep-seated veins; type D, combined type Band C patterns; type E, disappearance of reflux into normal cortical veins. Each case was evaluated on the basis of these criteria from comparing pre- and post-embolization angiograms. The delay and reduction of shunt were observed in all cases. Forty-nine of them showed obvious hemodynamic changes in the draining systems including type A change in 9, type B in 19, C in 5, Din 3 and E in 13 cases, respectively. Two cases showed a spontaneous shift in the dominance of the main drainers. Thirteen of 15 cases showing successful results in subsequent radiosurgery exhibited various changes in draining pattern. Changes in drainage systems may be affected by the compartmentalization of the nidus, reduction in shunt flow, and spontaneous or progressive thromboses. These can be promoted by embolization and may be regarded as one of the indicators of successful pretreatment for radiosurgery.

The Göteborg cohort of embolized cerebral arteriovenous malformations: a 6-year follow-up.

To present a follow-up of the results after endovascular treatment of cerebral arteriovenous malformations (AVMs) with acrylic glue. An initial follow-up was published in 1996. A cohort of 150 patients with cerebral AVMs underwent embolization between 1987 and 1993. Fifty-seven patients had supplemental stereotactic irradiation, and 13 had subsequent surgery. The follow-up was carried out clinically and radiologically. The mean follow-up time was 6.2 years. Only four patients were lost to follow-up. If at least 90% of the AVM had been obliterated, the clinical course was stable and there were no new manifestations from the AVM. No recanalization occurred in any AVM that had been totally obliterated with glue. For patients in whom it was not possible to totally obliterate the AVM either with glue alone or glue supplemented with stereotactic irradiation or surgery, the long-term outcome was discouraging. Obliteration of an AVM with acrylic glue seems to offer stability. If the AVM is totally obliterated, the patient had a stable clinical course. Patients with large AVMs with minor occlusion after embolization may have a worse clinical outcome than expected.

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.

脳動静脈奇形の外科的治療 : Surgical riskを軽減するための方策とその根拠

脳動静脈奇形の外科的治療 : Surgical riskを軽減するための方策とその根拠

脳動静脈奇形手術における術中赤外線画像の応用

Infrared imaging has been developed for intraoperative assessment of regional hemodynamic changes during the surgical treatment of cerebral arteriovenous malformations (AVM's). The infrared images, obtained by a digital infrared camera installed on the operating microscope, demonstrated the hemodynamic status and changes of preoperatively embolized AVM nidus during the open surgery. The anatomical structures of AVM nidus and its surrounding tissues were easily observed as the difference of surface temperature on the operative field. The hemodynamic changes according to operative manipulations were immediately demonstrated as thermal change of the surface of the nidus and its components. Intraoperative infrared imaging is an easy and effective manner for intraoperative monitoring and real-time and noninvasive evaluation of the hemodynamic change during the AVM surgery.

The value of intraoperative angiography for surgical treatment of cerebral arteriovenous malformations in eloquent brain areas.

Intraoperative digital subtraction angiography (DSA) allows intraoperative assessment of outcome of cerebral arteriovenous malformations (AVM). This study reports on 21 patients with AVMs in eloquent areas of the brain extirpated between July 1995 to March 1998. Extirpation was always followed by intraoperative DSA. Intraoperative angiography disclosed an occult residual nidus in 4 cases (19%). Complete extirpation of the AVM was achieved in all cases. Following surgery the neurological condition improved in 15 cases (71%), remained unchanged in 5 (24%), and worsened in 1. There were no secondary postoperative haemorrhages, nor complications related to the angiography. These results indicate that intraoperative DSA should be considered in the course of surgical treatment of cerebral AVMs in eloquent areas of the brain.

Nonadhesive liquid embolic agent for cerebral arteriovenous malformations: preliminary histopathological studies in swine rete mirabile.

To assess acute and chronic histopathological changes observed in a swine arteriovenous malformation model after endovascular delivery of Embolyx E (Micro Therapeutics Inc., San Clemente, CA) and its organic solvent dimethyl sulfoxide (DMSO). To develop standard endovascular delivery techniques of Embolyx through microcatheters into swine rete mirabile (RMB). Forty RMBs in 22 swine were used to analyze acute and chronic angiographic and histological changes after superselective delivery of Embolyx E and/or its organic solvent (DMSO). Four RMBs (two for DMSO and two for Embolyx E study) were used as control specimens. Angiographic and histological evaluations were obtained 18 days, 1 month, 3 months, and 6 months after the procedure. Particular attention was paid to the presence of focal or diffuse angionecrosis, arterial revascularization, and perivascular inflammatory response. Staged and/or continuous delivery of Embolyx E were performed through the DMSO-compatible microcatheters without untoward catheter "gluing." All subacute/chronic specimens embolized with Embolyx E showed no evidence of angiographic recanalization. Twelve RMBs were used in acute studies, and all specimens showed no evidence of angionecrosis or aggressive inflammatory reaction. Subacute and chronic (total, n = 14) histological examinations of the RMBs showed mild inflammatory response manifested by monocellular infiltration and scattered foreign body giant cell reaction. In the 9 of 14 subacute and chronic specimens, focal disruption of elastica was observed along with embolic materials. Fourteen RMBs in eight swine were used to determine the safety range for DMSO injection. Two RMBs were used as control specimens. Rapid intra-arterial delivery (0.5 ml/5-15 s, n = 6) of DMSO caused angiographic vasospasm and histological endothelial necrosis. Slow injection (0.5 ml/30-120 s, n = 8) of DMSO showed minimum or no angiographic vasospasm, minimal adventitial inflammatory response, and no clinical complications. Embolyx E, an occlusive and nonadhesive embolic agent, is capable of producing permanent occlusion of swine RMB with the development of mild intra- and perivascular inflammatory changes and no clinical complications. The slow endovascular delivery of DMSO produces no untoward angiographic, pathological, or clinical changes. A fast injection of DMSO causes endothelial necrosis and severe inflammatory response in the arterial wall. This embolic material seems to have appropriate biochemical, anatomic, and histopathological characteristics to be used in the treatment of cerebral arteriovenous malformations or vascular cranial base tumors.

Failure in radiosurgery treatment of cerebral arteriovenous malformations.

The aim of this study was to retrospectively analyze the reasons for the failure of radiosurgical treatment of cerebral arteriovenous malformations (AVMs). Seventeen cases of noncured AVMs were reviewed 3 years after radiosurgical treatment. Follow-up ranged from 33 to 54 months (mean, 44.3 mo). Lesion dimensions varied from 9 to 55 mm (mean, 29.2 mm). The lesions were located in critical or near-critical brain regions. Angiography was performed under Talairach's stereotactic conditions. Two large AVMs bled 36 and 39 months after receiving irradiation, respectively. These two AVMs had been incompletely irradiated. Retrospectively, in four cases (23.5%) we observed errors in determining AVM target shape and size because of inaccurate definition of the nidus and/or because of stereoangiographic incompleteness (absence of external carotid artery injections). In five large and/or irregularly shaped AVMs (29.4%), a strategy of partial volume irradiation had been used. In one patient (5.8%), we observed the recanalization of previously embolized AVMs. In another case (5.8%), the target had been partially missed. The AVMs in one case (5.8%) had been treated with an ineffective peripheral dose. In one (5.8%), the failure occurred because of the lesion angio-architecture. In four cases (23.5%), no evident reasons for failure were determined. The results of this study suggest the necessity of complete irradiation of the nidus. The strategy of partial volume irradiation might be avoided, even if it necessitates lowering the doses to treat large AVMs. Accuracy in the target determination is required, and complete stereoangiography is necessary.

Recurrent cerebral arteriovenous malformations after negative postoperative angiograms.

Angiography has been considered to be the gold standard to judge the success of treatment for cerebral arteriovenous malformations (AVMs). Patients without residual nidus or early draining veins on postoperative angiograms are considered cured, with the risk of hemorrhage eliminated. A series of five patients with recurrent AVMs after negative postoperative angiography is described. All patients had hemispheric AVMs, presented initially with hemorrhage, and were between 5 and 13 years of age. Recurrence was noted 1 to 9 years later (at 12-16 years of age); after a hemorrhage in three patients, seizures in one, and on follow-up magnetic resonance imaging in one. Four patients underwent angiography that showed recurrence of the AVM at or adjacent to the original site. Three years postsurgery, the fifth patient died from a large intracerebral and intraventricular hemorrhage originating in the previous location of the AVM; however, the patient did not undergo angiography at the time of recurrence. The initial negative angiograms obtained postoperatively in these patients may be explained by postoperative spasm or thrombosis of a small residual malformation. However, in the authors' cumulative experience with 808 patients who have undergone complete surgical removal of AVMs (of whom 667 were older than 18 years of age), no case of recurrent AVM has been observed in an adult. Therefore, actual regrowth of an AVM may occur in children and could be a consequence of their relatively immature cerebral vasculature and may involve active angiogenesis mediated by humoral factors. The present findings argue against the assumption that AVMs are strictly congenital lesions resulting from failure of capillary formation during early embryogenesis. It is concluded that delayed imaging studies should be considered in children at least 1 year after their initial negative postoperative arteriogram to exclude a recurrent AVM.