Arteriovenous Malformations Score Research Articles

Complications Following Linear Accelerator Based Stereotactic Radiation for Cerebral Arteriovenous Malformations

Primarily, gamma knife centers are predominant in publishing results on arteriovenous malformations (AVM) treatments including reports on risk profile. However, many patients are treated using a linear accelerator-most of these at smaller centers. Because this setting is different from a large gamma knife center, the risk profile at Linac departments could be different from the reported experience. Prescribed radiation doses are dependent on AVM volume. This study details results from a medium sized Linac department center focusing on risk profiles. A database was searched for all patients with AVMs. We included 50 consecutive patients with a minimum of 24 months follow-up (24-51 months). AVM occlusion was verified in 78% of patients (39/50). AVM occlusion without new deficits (excellent outcome) was obtained in 44%. Good or fair outcome (AVM occlusion with mild or moderate new deficits) was seen in 30%. Severe complications after AVM occlusion occurred in 4% with a median interval of 15 months after treatment (range, 1-26 months). We applied an AVM grading score developed at the Mayo Clinic to predict probable outcome after radiosurgery in a large patient population treated with Gamma knife. A cutoff above and below a score of 1.5 could not discriminate between the likelihood of having an excellent outcome (approximately 45%). The chance of having an excellent or good outcome was slightly higher in patients with an AVM score below 1.5 (64% vs. 57%).

Micromultileaf collimator-based stereotactic radiosurgery for selected arteriovenous malformations: Technique and preliminary experience

To report our experience of stereotactic radiosurgery (SRS) in consecutively treated patients with arteriovenous malformations (AVMs). Of the 87 patients, 23 patients qualified and were treated with SRS as per predefined protocol according to AVM size, location, neurological status, prior bleeding, and the AVM score. All had Spletzer-Martin grade II/III and AVM scores <2.5. Patients underwent SRS using micromultileaf collimators delivering multiple noncoplanar fixed fields. Doses were prescribed using the Flickinger model. Patients were followed up with magnetic resonance angiography (MRA) and digitally subtracted angiography (DSA). The mean nidus volume was 3.65 cc. The mean prescribed maximum dose was 22 Gy and the marginal dose was 19.24 Gy; 12 Gy normal brain volume was 8.39 cc and 12 Gy marginal volume was 5.03 cc. Mean dose to brain stem, pituitary hypothalamic axis, and optic chiasm was 2.5, 0.72, and 0.49 Gy, respectively. At a median follow-up of 22 months (range 1.5-71.2 months), 7 of 10 patients presenting with a neurological deficit showed significant improvement. All 15 patients who underwent MRA 1.5-2 years after SRS had no residual nidus yielding an MRA complete obliteration rate of 100%. Twelve patients also underwent a check DSA, which confirmed obliteration in 11 of them resulting in an accuracy of MRA of 92%. One patient after SRS had transient deterioration of motor power, which resolved completely after a short course of steroids and another had mild worsening of the hemiparesis. All patients are able to lead an active functional life. Careful selection of cases suitable for SRS provides optimum obliteration rates with low toxicity.

MODIFICATION OF THE RADIOSURGERY-BASED ARTERIOVENOUS MALFORMATION GRADING SYSTEM

The radiosurgery-based arteriovenous malformation (AVM) grading scale was developed to predict patient outcomes after radiosurgery. The purpose of this study was to determine whether simplifying this grading system using location as a two-tiered variable detracted from the accuracy of the scale. Regression analysis modeling on 220 patients who underwent AVM radiosurgery between 1987 and 1992 at the University of Pittsburgh Medical Center using location as a two-tiered variable resulted in the following equation: AVM score = (0.1) (volume, mL) + (0.02) (age, yr) + (0.3) (location, hemispheric/corpus callosum/cerebellar = 0; basal ganglia/thalamus/brainstem = 1). Testing of the modified grading system was performed on 247 patients who underwent AVM radiosurgery between 1990 and 2001 at the Mayo Clinic. The mean modified AVM score was 1.62. The mean duration of patient follow-up was 70 months. There was no difference between the original and modified radiosurgery-based AVM scale with regard to AVM obliteration without new neurological deficits (F = 0.92, P = 0.53) or decline in Modified Rankin Scale (F = 0.83, P = 0.56) after radiosurgery. The modified radiosurgery-based AVM scale correlated with the percentage of patients with AVM obliteration without new deficits (<or=1.00, 89%; 1.01-1.50, 70%; 1.51-2.00, 64%; >or=2.00, 46%) (r = -0.98, P < 0.01) and a decline in Modified Rankin Scale (<or=1.00, 0%; 1.01-1.50, 13%; 1.51-2.00, 20%; >2.00, 36%) (r = 0.99, P < 0.01). Simplifying the radiosurgery-based AVM grading system using location as a two-tiered variable did not detract from the accuracy of the scale. This system has been validated by numerous centers performing both gamma knife- and linear accelerator-based procedures and should be used in future studies on AVM radiosurgery to stratify patients for more accurate comparative analyses.

Commentary

To corroborate which pretreatment angioarchitectural characteristics and posttreatment magnetic resonance imaging (MRI) features were associated with better seizure and antiepileptic drug outcomes in patients with brain arteriovenous malformations (AVMs) treated by Gamma Knife radiosurgery.During the period 2007–2010, 220 patients with intracranial AVMs undergoing radiosurgery at our hospital were evaluated. Imaging features on digital subtraction angiography and follow-up MRI, medical records, and direct patient interview were retrospectively assessed. Seizure outcome was assessed using the Engel classification and the status of antiepileptic drug use.At the last follow-up, 21 of 31 patients (68%) who met the recruitment criteria had AVM obliteration on digital subtraction angiography or MRI. Seizure-free status (Engel class 1) was achieved in 20 patients (65%), and 13 of 20 (65%) seizure-free patients were medication-free. The presence of total obliteration at last imaging follow-up (P = 0.013), absent retrograde cortical veins on digital subtraction angiography before GKRS (P = 0.013), nidus <3.7 cm (P = 0.006), and lower modified radiosurgery-based AVM score (P = 0.026) were significant predictors of seizure-free outcome. The strongest independent predictor of seizure-free status was absence of retrograde veins (odds ratio = 9.9). No angioarchitectural feature, postradiosurgery imaging finding on MRI, or radiosurgical treatment parameter was a significant predictor of seizure control or cessation of medication in seizure-free patients.This study suggests that radiosurgery provides favorable outcomes in patients with AVM-related epilepsy. Patients with intracranial AVMs can benefit from seizure control after GKRS before undergoing AVM obliteration. Absence of retrograde veins is associated with better seizure-free outcomes, regardless of the parenchymal changes after radiosurgery.

Intracranial arteriovenous malformations treated with LINAC-based conformal radiosurgery: validation of the radiosurgery-based arteriovenous malformation score as a predictor of outcome

Objective: To validate the radiosurgery-based arteriovenous malformation score (RBAS) as a predictor of outcome in patients with arteriovenous malformations (AVMs) treated with LINAC-based conformal radiosurgery.Methods: We analysed 40 patients with a mean follow-up of 22 months. One patient (2.5%) pertained to Spetzler–Martin Grade I, 11 (27.5%) to Grade II, 19 (47.5%) to Grade III, eight (20%) to Grade IV and one (2.5%) to grade V. The mean RBAS was 2.0 (range: 0.76–5.56). The mean obliteration prediction index (OPI) and the Karlsson index (KI) were 0.74 (range: 0.2–2.86) and 109.48 (range: 3.0–350.7) respectively. Outcomes were analysed according to the OPI, KI and RBAS.Results: We analysed different cutoff points in the RBAS and found a significant difference to predict the outcome in four scores: 1.2, 1.6, 1.7 and 1.8. In the group with RBAS ≤ 1.8, 13 (68%) had an excellent outcome and six (33%) did not, while with RBAS>1.8, seven (32%) had an excellent outcome and 14 (67%) did not (p = 0.02). We did not find any correlation between Spetzler–Martin grading scale or OPI and outcome (p = 0.7 and p = 0.3 respectively). The KI predicted the excellent outcome in 8/9 patients (89%) with KI ≤ 27 and in 12/31 patients (39%) with KI>27 (p = 0.08).Conclusion: The RBAS seems to be a good predictor of outcome in patients with AVMs treated with LINAC-based conformal radiosurgery as in patients treated with Gamma Knife. It remains only to find the best cutoff point based on a larger series and longer follow-up.

Risk of Hemorrhage and Obliteration Rates of LINAC-Based Radiosurgery for Cerebral Arteriovenous Malformations Treated After Prior Partial Embolization

We investigate patient outcome, risk of hemorrhage, and factors affecting obliteration after LINAC-based radiosurgery (RS) for cerebral arteriovenous malformations (AVM) treated after partial embolization. This analysis is based on 50 patients treated after prior embolization. According to the Spetzler-Martin criteria the AVM classification was as follows: 9 patients, Grade I (18%); 19, Grade II (38%); 18, Grade III (36%); and 4, Grade IV (8%). Median RS-based AVM score was 1.41. Median single dose was 18 Gy/ 80% isodose (range, 15-22 Gy) and median AVM volume was 4.0 cc (range, 0.2-22.6 cc). In all, 34 patients (68%) experienced hemorrhage before RS. Median follow-up was 3.1 year (range, 8.5 months to 15 years). Actuarial complete obliteration rate was 67% after 3 years and 78% after 4 years. The complete obliteration rate was significantly higher in AVM <3 cm (92% vs. 60%, p < 0.01) and in AVM Spetzler-Martin Grade I/II (90% vs. 59%, p < 0,01). Intracranial hemorrhage after RS was seen in 6 patients (12%) after 8.5 months median. Annual bleeding risk was 7.9% after 1 year and 2.2% after 2 years. It was found that AVM diameter > or =3 cm (p < 0.006), AVM volume > or =4 cc (p < 0.01), AVM score > or =1.5 (p < 0.03), and single dose <18 Gy (p < 0.03) were associated with a significant higher bleeding risk. The rate of obliteration after RS in AVM treated after prior partial embolization depends on size as well as Spetzler-Martin grade. The risk of intracranial hemorrhage is not increased after RS and depends on AVM score, size, and volume, as well as on applied single dose.

EMBOLIZATION BEFORE RADIOSURGERY REDUCES THE OBLITERATION RATE OF ARTERIOVENOUS MALFORMATIONS

To evaluate the arteriovenous malformation (AVM) obliteration rate and the clinical outcome after radiosurgery in patients with and without previous embolization. Of 244 patients who underwent linear accelerator radiosurgery for AVMs at the Sunnybrook Health Sciences Centre between 1989 and 2000, 61 patients had embolization before radiosurgery and complete follow-up for at least 3 years. For 47 of these 61 patients (Group A, embolization plus radiosurgery), we were able to find 47 matching patients without previous embolization (Group B, radiosurgery alone). This group of matching patients had the same AVM volume (after embolization in Group A), location, and marginal dose. The radiosurgery-based AVM score and the obliteration prediction index were calculated. The median follow-up period was 44 months. Nidus obliteration was achieved in 22 patients in Group A (47%) and 33 patients in Group B (70%, P = 0.036). Permanent deficit related to hemorrhage or radiation occurred in three patients (6%) in Group A and three patients (6%) in Group B. During the first 3 years after radiosurgery, two patients (4%) in Group A experienced hemorrhage; in Group B, five patients (11%) experienced hemorrhage (P = 0.2). In Group B, two patients (4%) died and two patients (4%) had their AVM surgically removed. Both deaths were related to hemorrhage during the latency period. The excellent outcome (obliteration plus no deficit) in Group A was 47% compared with 64% in Group B (P = 0.146). There was no difference in the obliteration prediction index and the radiosurgery-based AVM score between Groups A and B. The predicted rates of obliteration and excellent outcome were 55 and 62.5%, respectively, according to the obliteration prediction index and the radiosurgery-based AVM score. Embolization before radiosurgery significantly decreases the obliteration rate, even in AVMs with the same volume, location, and marginal dose. Although an excellent outcome rate was higher in the group without embolization, this was not statistically significant.

Use of the Modified Rankin Scale to assess outcome after arteriovenous malformation radiosurgery

To present the results of arteriovenous malformation (AVM) radiosurgery using the Modified Rankin Scale (MRS) as the primary outcome measure and to analyze whether previous AVM rupture or other factors have an effect on outcomes after AVM radiosurgery. We reviewed outcomes after AVM radiosurgery for 243 patients from 1990 and 2001. The mean follow-up after radiosurgery was 65 months. Forty-one patients (17%) sustained a decline in MRS (median -2) after AVM radiosurgery. We noted a decline in MRS in 4% of patients 1 year after radiosurgery, 8% of patients at 3 years after radiosurgery, and 15% of patients at 7 years after radiosurgery. The radiosurgery-based AVM score correlated with a decline in MRS after AVM radiosurgery in multivariate testing (odds ratio 2.1; 95% CI 1.2 to 3.6; p < 0.01). Previous AVM rupture did not influence neurologic deterioration after AVM radiosurgery. The radiosurgery-based AVM score predicted the chance of a worse MRS after radiosurgery.

Radiosurgery for arteriovenous malformations in children

The authors present the results of stereotactic radiosurgery performed in a consecutive series of children with arteriovenous malformations (AVMs) and analyze factors associated with successful radiosurgery for this condition. Between 1990 and 2001, 38 patients 18 years of age or younger underwent radiosurgery for AVMs. The median patient age was 15 years; 20 patients (53%) had experienced a prior hemorrhage. Twenty-seven AVMs (71%) were Spetzler-Martin Grade III or higher; 16 patients (42%) had AVMs located in the basal ganglia, thalamus, or brainstem. The median AVM volume was 3.4 cm3. The median radiosurgery-based AVM score was 1.08 according to the following formula: AVM score = 0.1 volume (cm3) + 0.02 x age (years) + 0.3 x location (frontal/temporal = 0; parietal/occipital/corpus callosum/cerebellar = 1; basal ganglia/thalamus/brainstem = 2). The median follow-up period was 42 months. One patient (3%) had an intraventricular hemorrhage 26 months after radiosurgery but experienced no new deficit. No patient had a permanent radiation-related complication after radiosurgery. Twenty-six patients (68%) had excellent outcomes (as defined by complete obliteration of the AVM with no new deficit) after radiosurgical treatment (21 cases determined using angiography and five using magnetic resonance imaging). Twelve patients (32%) remained unchanged (incomplete obliteration but no new deficit). Univariate analysis found that patient age, AVM volume, location, or Spetzler-Martin grade did not correlate with excellent outcomes. Patients whose radiosurgery-based AVM scores were 1 or lower experienced an excellent outcome more frequently than patients with an AVM score higher than 1 (88% compared with 52%, p = 0.03). Radiosurgery was successful in the treatment of the majority of pediatric patients suffering from AVMs, and morbidity levels were minimal. The radiosurgery-based AVM grading scale accurately predicted these outcomes. Children whose AVMs are obliterated after radiosurgery should undergo repeated angiography after they reach adulthood to rule out the possibility of a recurrent nidus that would expose them to an ongoing risk of hemorrhage.

Stereotactic linac-based radiosurgery in the treatment of cerebral arteriovenous malformations located deep, involving corpus callosum, motor cortex, or brainstem

To evaluate patient outcome and obliteration rates after radiosurgery (RS) for cerebral arteriovenous malformations (AVM) located deep, in the motor cortex or brainstem and those involving corpus callosum. This analysis is based on 65 patients. AVM classification according to Spetzler-Martin was 13 patients Grade 2, 39 Grade 3, 12 Grade 4, and 1 Grade 5. Median RS-based AVM score was 1.69. Median single dose was 18 Gy. Mean treatment volume was 5.2 cc (range, 0.2-26.5 cc). Forty patients (62%) experienced intracranial hemorrhage before RS. Median follow-up was 3.0 years. Actuarial complete obliteration rate (CO) was 50% and 65% after 3 and 5 years, respectively. CO was significantly higher in AVM <3 cm (p < 0.02) and after doses >18 Gy (p < 0.009). Annual bleeding risk after RS was 4.7%, 3.4%, and 2.7% after 1, 2, and 3 years, respectively. AVM >3 cm (p < 0.01), AVM volume >4 cc (p < 0.009), and AVM score >1.5 (p < 0.02) showed a significant higher bleeding risk. Neurologic dysfunction improved, completely dissolved, or remained stable in 94% of patients. Surgically inaccessible AVM can be successfully treated using RS with acceptable obliteration rates and low risk for late morbidity. The risk of intracranial hemorrhage is reduced after RS and depends on RS-based AVM score.

Testing the radiosurgery-based arteriovenous malformation score and the modified Spetzler—Martin grading system to predict radiosurgical outcome

The aim of this study was to validate the radiosurgery-based arteriovenous malformation (AVM) score and the modified Spetzler-Martin grading system to predict radiosurgical outcome. One hundred thirty-six patients with brain AVMs were randomly selected. These patients had undergone a linear accelerator radiosurgical procedure at a single center between 1989 and 2000. Patients were divided into four groups according to an AVM score, which was calculated from the lesion volume, lesion location, and patient age (Group 1, AVM score <1; Group 2, AVM score 1-1.49; Group 3, AVM score 1.5-2; and Group 4, AVM score >2). Patients with a Spetzler-Martin Grade III AVM were divided into Grades IIIA (lesion >3 cm) and IIIB (lesion <3 cm). Sixty-two female (45.6%) and 74 male (54.4%) patients with a median age of 37.5 years (mean 37.5 years, range 5-77 years) were followed up for a median of 40 months. The median tumor margin dose was 15 Gy (mean 17.23 Gy, range 15-25 Gy). The proportions of excellent outcomes according to the AVM score were as follows: 91.7% for Group 1, 74.1% for Group 2, 60% for Group 3, and 33.3% for Group 4 (chi-square test, degrees of freedom (df) = 3, p < 0.001). Based on the modified Spetzler-Martin system, Grade I lesions had 88.9% excellent results; Grade II, 69.6%; Grade IIIB, 61.5%; and Grades IIIA and IV, 44.8% (chi-square test, df = 3, p = 0.047). The radiosurgery-based AVM score can be used accurately to predict excellent results following a single radiosurgical treatment for AVM. The modified Spetzler-Martin system can also predict radiosurgical results for AVMs, thus making it possible to use this system while deciding between surgery and radiosurgery.

Radiosurgery for Basal Ganglia, Internal Capsule, and Thalamus Arteriovenous Malformation: Clinical Outcome

Radiosurgery is accepted as the first option for treating deep arteriovenous malformations (AVMs), although the clinical outcome in this subgroup of brain AVMs is not well studied. The objective of this study is to review our experience with radiosurgical treatment for these AVMs. Between October 1989 and December 2000, 45 patients with deep AVMs (including basal ganglia, internal capsule, and thalamus) underwent stereotactic radiosurgery. Three patients were lost to follow-up and therefore were excluded from this study. Patient characteristics and outcomes were collected and analyzed. The obliteration prediction index and the radiosurgery-based AVM score were calculated and tested. Forty-two patients were followed up for a median of 39 months (range, 25-90 mo; mean, 45.8 mo). The median maximum AVM diameter during the radiosurgery was 1.8 cm (range, 0.9-4.0 cm; mean, 2.07 cm), and the median AVM volume was 2.8 cm(3) (range, 0.2-18.3 cm(3); mean, 4.74 cm(3)). The mean marginal dose was 16.2 Gy (median, 15 Gy), and the median maximum dose was 22.4 Gy (range, 16.6-30 Gy). The AVM cure rate after the first radiosurgical treatment, using angiography- and magnetic resonance imaging-confirmed obliteration, was 61.9%. The predicted obliteration using the obliteration prediction index was 60%. Eight patients developed radiation-induced complications (19%). The deficit was transient in three patients (7.1%) and permanent in five patients (11.9%). The risk of postradiosurgical hemorrhage in this cohort was 9.5% for the first year, 4.7% for the second year, and 0% thereafter. Excellent outcome (obliteration plus no new deficit) was achieved in 70% of the patients in the group with radiosurgery-based AVM score less than 1.5 compared with 40.9% in the group with radiosurgery-based AVM score greater than 1.5% (P = 0.059). Radiosurgery for deep AVMs has a satisfactory obliteration rate and acceptable morbidity, considering the risk of hemorrhage without treatment and the risk of morbidity associated with other treatment modalities.

Congested residual nidus after preoperative intranidal embolization in midsize cerebral arteriovenous malformations of 3-6 cm in diameter.

Modern delicate microcatheters allow intranidal embolization of cerebral arteriovenous malformations (AVM). The aim of the current analysis was to assess effects of preoperative intranidal deployment of embolic material on surgical time and blood loss in cerebral arteriovenous malformations of 3-6 cm in diameter. The case records of 38 cerebral AVM between 3 and 6 cm in maximum diameter were reviewed, that had been embolized intranidally with N-butyl 2-cyanoacrylate (Histacryl) and subsequently operated on. Surgical time and blood loss as well as particular intraoperative findings such as a congested nidus and thrombosis of draining veins were registered and correlated with the extent of embolization and the time interval between embolization and surgery. Preoperative embolization occluded an estimated range of 10 to 90% of the nidus. Minor embolization related bleeding without clinical relevance occurred in 5 patients. Significant embolization related bleeding resulting in earlier than planned surgery occurred in another 5 patients. All embolization related haemorrhages occurred within 24 hours. Average total operating time was 343+/-106 min and average blood loss was 684+/-858 ml. Unequivocal bleeding difficulty from the nidus and a total blood loss of more than 1000 ml were encountered in 7 instances and dissection was tedious due to a bleeding AVM core in 5 other cases. A congested AVM core was the source of bleeding in 11 patients and paraventricular neovascularization in one. 6 of the 11 cases with a congested AVM core had suffered minor or substantial haemorrhage after a preoperative endovascular procedure. Intraoperative nidus congestion was noted in this series after an interval as long as 2 weeks after the last embolization. Combined management resulted in permanent morbidity in 6 of the 38 cases. In 4 of them the neurological deficit was associated with an intraoperative bleeding problem, in all due to congested nidus. Morbidity had to be correlated with major haemorrhage resulting from preoperative embolization in 2 instances. Intranidal embolization prior to surgical removal of AVM can lead to a congested residual nidus and intraoperative bleeding. Minor leakage after preoperative embolization is an inconsistent warning sign of nidus congestion. Nidus outflow after intranidal embolization appears to require a few weeks for normalization. Delay of surgery after embolization should be considered in cases of suspected congested residual nidus. The danger of major haemorrhage or arterial revascularization during this waiting period appears small.

Radiosurgery for arteriovenous malformations of the basal ganglia, thalamus, and brainstem.

Although stereotactic radiosurgery is frequently performed for arteriovenous malformations (AVMs) in deep locations, outcomes after radiosurgery for these patients have not been well studied. The goal of this paper was to study these outcomes. Between 1990 and 2000, 56 patients underwent radiosurgery for AVMs located in the basal ganglia (10 patients), thalamus (30 patients), or brainstem (16 patients). The median age of these patients was 34.2 years. Thirty-five patients (62%) had experienced previous bleeding. The AVMs were classified Grade IIIB in 62% of patients and Grade IV in 38% according to the modified Spetzler-Martin Scale; the median radiosurgery-based AVM score was 1.83. The median volume of the lesion was 3.8 cm3 and the median radiation dose delivered to its margin was 18 Gy. The median duration of follow-up review after radiosurgery was 45 months (range 3-121 months). In seven patients (12%) hemorrhage occurred at a median of 12 months after radiosurgery; five patients (9%) died and two recovered without any deficit. Permanent radiation-related complications occurred in six (12%) of 51 patients (excluding the five patients who died of hemorrhage) after one procedure and in three (18%) of 17 patients after repeated radiosurgery. Obliteration of the AVM was noted in 24 patients (43%; obliteration was confirmed by angiography in 18 patients and by magnetic resonance [MR] imaging in six patients) after a single procedure and in 32 patients (57%; confirmed by angiography in 25 patients and by MR imaging in seven patients) after one or more procedures. Excellent outcomes (obliteration of the lesion without any new deficit) were obtained in 39% of patients after one radiosurgical procedure and in 48% after one or more procedures. Twelve (67%) of 18 patients with AVM scores lower than 1.5 had excellent outcomes compared with 15 (39%) of 38 patients with AVM scores greater than 1.5 (p = 0.053). Less than half of the patients with deeply located AVMs were cured of the future risk of hemorrhage without new neurological deficits. This experience emphasizes the difficulty in treating patients with deeply located AVMs; the majority of whom are also poor candidates for resection or embolization.

A proposed radiosurgery-based grading system for arteriovenous malformations

Radiosurgery is an effective treatment strategy for properly selected patients harboring arteriovenous malformations (AVMs). Grading scales that are currently used to predict patient outcomes after AVM resection are unreliable tools for the prediction of the results of AVM radiosurgery. A grading system was developed to predict outcomes following AVM radiosurgery, based on the multivariate analysis of data obtained in 220 patients treated between 1987 and 1991 (Group 1). The dependent variable in all analyses was excellent patient outcome (complete AVM obliteration without any new neurological deficit). The grading scale was tested on a separate set of 136 patients with AVMs treated between 1990 and 1996 at a different center (Group 2). One hundred twenty-one (55%) of 220 Group 1 patients had excellent outcomes. Multivariate analysis identified five variables related to excellent patient outcomes: AVM volume (p = 0.001), patient age (p < 0.001), AVM location (p < 0.001), previous embolization (p = 0.02), and number of draining veins (p < 0.001). Regression analysis modeling permitted removal of two significant variables (previous embolization and number of draining veins) and resulted in the following equation to predict patient outcomes after AVM radiosurgery: AVM score = (0.1)(AVM volume in cm3) + (0.02)(patient age in years) + (0.3)(location of lesion: frontal or temporal) = 0; parietal, occipital, intraventricular, corpus callosum, cerebellar = 1; or basal ganglia, thalamic, or brainstem = 2). Seventy-nine (58%) of 136 Group 2 patients had excellent outcomes. All variables in the model remained significant for the Group 2 patients: AVM volume (p = 0.01), patient age (p = 0.01), and AVM location (p < 0.001). Testing of the entire model on the Group 2 patients demonstrated that the AVM score could be used to predict patient outcomes after radiosurgery (p < 0.0001). All patients with an AVM score of 1 or lower had an excellent outcome compared with only 39% of patients with an AVM score higher than 2. The Spetzler-Martin grade (p = 0.13), the K index (p = 0.26), and the obliteration prediction index (p = 0.21) did not correlate with excellent patient outcomes. Despite significant differences in preoperative patient characteristics and dose prescription guidelines at the two centers, the proposed AVM grading system strongly correlated with patient outcomes after single-session radiosurgery for both patient groups. Although further testing of this model by independent centers using prospective methodology is still required, this system allows a more accurate prediction of outcomes from radiosurgery to guide choices between surgical and radiosurgical management for individual patients with AVMs.

Endoscopic procedures for resection of arteriovenous malformations

BACKGROUND Resection of arteriovenous malformations (AVMs), particularly those located in functional areas, requires precision. To enhance that precision, endoscope-assisted microsurgery has been employed at Loma Linda University. METHODS Twenty-five consecutive cases of AVM were treated microsurgically with endoscopic assistance. Patients were divided into two groups: (1) those having AVMs in functional areas, and (2) those whose AVMs extended into the ventricle, either in the trigonal area or the capsulocaudatothalamic area. The endoscope was inserted into the subarachnoid space to interrupt communicating venules around the major draining vein and into the cleavage developed between the AVM venous loops and surrounding brain tissue as shunting arterioles and communicating venules were interrupted. For surgery of intraventricular AVMs, the curved endoscope was inserted into the ventricle, providing visualization of the AVM core, which was dissected from the ventricular side. RESULTS AVMs were totally resected in all cases except for two patients with capsulocaudatothalamic AVMs, which were decreased in size sufficiently to receive radiosurgery. CONCLUSION Endoscope-assisted microsurgery enhances magnification, illumination, and technical precision while the surgeon is dissecting the AVM core vessels and while operating on AVMs extending into the ventricle.

Heavy-Charged-Particle Radiosurgery for Intracranial Arteriovenous Malformations

We have treated over 400 patients with symptomatic inoperable intracranial arteriovenous malformations (AVMs) with stereotactic heavy-charged-particle Bragg peak radiosurgery at the University of California at Berkeley in a collaborative program with Stanford University Medical Center and the University of California Medical Center, San Francisco. A long-term dose-searching clinical trial protocol has been developed and we have followed more than 250 patients for more than 2 years. Initially, radiation doses ranged from 45 to 35 GyE, and now doses of 25, 20, 15 and, under special circumstances, 10 GyE, depending on a number of factors, are being evaluated. The characteristics of charged-particle beams provide a relatively homogeneous dose distribution with the 90% isodose contour to the periphery of the lesion. When the entire arterial phase of the AVM core is included in the treatment field, the rates for complete obliteration 3 years after treatment are: 90-95% for volumes less than or equal to 4 cm3; 90-95% for volumes greater than 4 and less than or equal to 14 cm3; and 60-70% for volumes greater than 14 cm3. The total obliteration rate for all volumes up to 70 cm3 is approximately 80-85%. For complete radiation-induced obliteration there is a relationship of dose and volume primarily, and location secondarily. Results on relationships between dose, AVM obliteration, and complications and sequelae of the radiosurgical procedure are presented and discussed.