Radiosurgery Recommended for Unruptured Intracranial Arteriovenous Malformations

They base this recommendation on an assessment of clinical and radiographic outcomes in 444 patients treated with radiosurgery for unruptured AVMs at their institution.

This single-institution patient cohort were published online March 26, 2013, ahead of print, in the Journal of Neurosurgery, by investigators from the University of Virginia (UVA) Health System (Charlottesville, USA). Arteriovenous malformations are vascular anomalies in which arteries feed directly into veins, bypassing the capillary system.

Generally congenital, AVMs occur in approximately 1 in 100,000 persons and present equally in both sexes. Most people with AVMs in the brain live full lives with no knowledge of ever having the anomaly; sometimes the lesions are identified during workup for another disorder. Other patients experience symptoms such as headaches, seizures, and neurologic deficits. Patients who do experience symptoms often do so by the time they are in their 30s. Sometimes, AVMs rupture due to increased blood pressure and damage to the walls of the vessels involved. Past medical studies show the yearly risk of AVM hemorrhage to be 2%–4%.

In the present study, the UVA researchers reviewed a database of 1,204 cases of AVMs that were treated by radiosurgery with a Gamma Knife between 1989 and 2009. The researchers centered on 444 patients whose AVMs were unruptured at the time of radiosurgery and who participated in follow-up for at least two years (less if there was early proof that radiosurgery had obliterated the AVM). The patients’ mean age was 36.9 years; 11% of patients were younger than 18 years at the time of radiosurgery. The patient cohort was evenly split between the sexes. The investigators reported that the mean size of the AVM nidus was 4.2 cubic centimeters (approximately 2 cm in diameter). Nearly 14% of the AVMs were located deep within the brain. Twelve percent of patients presented with neurologic deficits, 28% with headaches, and 47% with seizures.

The median dose of radiation targeted to the edge of the AVM during radiosurgery was 20 Gray and the median maximum dose was 40 Gray. Sixty-four patients underwent radiosurgery as a repeat procedure. Univariate and multivariate Cox regression analyses were performed to identify the effects of various factors on AVM obliteration and determine risk factors associated with radiosurgery.

The researchers state that 62% of unruptured AVMs in this patient cohort were obliterated by radiosurgery. Their analyses revealed that a higher prescribed radiation dose, a single draining vein, radiation-induced alterations seen on the scans, a lower Spetzler-Martin AVM grade, and no earlier embolization procedure performed to treat the AVM were statistically significant positive predictors of AVM obliteration. After radiosurgery, the yearly hemorrhage rate was 1.6%, which is same as or may be slightly better than the 2%–4% estimated for unruptured AVMs left untreated. Once an AVM has been obliterated, however, there is no longer a risk of hemorrhage.

In comparison with the patients’ pre-radiosurgery neurologic symptoms, 7% of patients showed improvement, 7% were worse, and 86% were unchanged. The authors stated, “The risks associated with stereotactic radiosurgery were temporary; those risks that were permanent were typically not debilitating for the patient.”

Statistical analysis showed that worsening of clinical conditions was substantially more commonplace in patients who experienced bleeding after radiosurgery.

Patients typically present with unruptured AVMs when they are young. Without treatment, they must face many years at risk for hemorrhage, which can cause neurologic impairment and even death. The researchers believe that treatment of an AVM is indicated for these younger patients as well as for patients with large AVMs and those with worse radiosurgery-based AVM scores. Treatment of an AVM with the Gamma Knife appears necessary in most patients, even if the AVM has not previously ruptured. These researchers recommended radiosurgery as the means of treatment because of its “reasonable chance of obliteration of unruptured AVMs with relatively low rates of clinical and radiological complications.”

When asked for the take-home message of the study, the senior author, Dr. Jason Sheehan, said, “The essence of this study is that unruptured AVMs can rupture, and rupture has significant morbidity or even mortality. Gamma Knife radiosurgery yielded obliteration in the majority of unruptured AVMs. Obliterated AVMs do not rupture. The overall surgical risks of Gamma Knife radiosurgery in unruptured AVMs seem lower than those in the natural history of an AVM if left untreated, even if the AVM has not previously ruptured.”

The Gamma Knife technology was developed by Elekta (Stockholm, Sweden).

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