Treatment of Brain AVMs (TOBAS) Study


About this study

The purpose of this study is to offer the best management possible for patients with brain arteriovenous malformations (AVMs) (ruptured or unruptured) in terms of long-term outcomes, despite the presence of uncertainty.

Participation eligibility

Participant eligibility includes age, gender, type and stage of disease, and previous treatments or health concerns. Guidelines differ from study to study, and identify who can or cannot participate. There is no guarantee that every individual who qualifies and wants to participate in a trial will be enrolled. Contact the study team to discuss study eligibility and potential participation.

Inclusion Criteria:

  • Any patient with a brain AVM.

Exclusion Criteria:

  • Hemorrhagic presentation with mass effect requiring surgical management.
    • In these cases, if a residual AVM is found after the initial surgery, the patient could then be a candidate for TOBAS.

Participating Mayo Clinic locations

Study statuses change often. Please contact the study team for the most up-to-date information regarding possible participation.

Mayo Clinic Location Status Contact

Jacksonville, Fla.

Mayo Clinic principal investigator

Rabih Tawk, M.D.

Open for enrollment

Contact information:

Nigina Amin

More information


  • Management of unruptured brain arteriovenous malformations (AVMs) is controversial, and conducting clinical trials in this area has been a challenge. We sought to determine which, if any, patient/AVM characteristics were most likely to influence clinicians' decisions regarding management and clinical trial enrollment. Read More on PubMed
  • Ethylene-vinyl alcohol copolymer embolization is increasingly used preoperatively in the resection of brain arteriovenous malformations (AVMs). However, the case for embolization improving the outcome of resection has not been evaluated. In this paper the authors set out to compare outcomes after surgery for brain AVMs in 2 consecutive periods of practice. In the first period, selective embolization was used without the use of ethylene-vinyl alcohol copolymer. In the second period, selective embolization with ethylene-vinyl alcohol copolymer was performed. Read More on PubMed
  • The purpose of this report was to provide overall arteriovenous malformation (AVM) hemorrhage rates and, with enhanced statistical power, to elucidate significant risk factors for hemorrhage. Read More on PubMed
  • The development of multimodality approaches for the treatment of cerebral arteriovenous malformations (AVMs), including microsurgery, endovascular therapy, and radiosurgery, has shifted modern treatment paradigms in the last 10 years. This study examines these changes in detail from a nationwide perspective. Read More on PubMed
  • Outcomes following treatment of brain arteriovenous malformations (AVMs) with microsurgery, embolization, stereotactic radiosurgery (SRS), or combinations vary greatly between studies. Read More on PubMed
  • The purpose of this study was to present the authors' clinical experience and long-term angiographic and clinical follow-up results in 350 patients with brain arteriovenous malformations (AVMs) treated using prolonged intranidal Onyx injection with a very slow "staged" reflux technique described by the authors. Read More on PubMed
  • The current clinical and research environment is one that renders any true enquiry into the value of commonly performed surgical acts practically impossible. Drawing from the recent failure of Trial on Endovascular Aneurysm Management (TEAM), a trial on the endovascular management of unruptured intracranial aneurysms, I attempt to identify some principles that sustain the current ways of doing clinical research that have paradoxically become major obstacles to trials that aim to assess the potential benefit or harm due to interventions as currently practiced. Clinical research and practice must coalesce into "clinical care trials" if we are to provide patients with optimal, prudent care in the context of uncertainty. This may require a major change in the mentalities of clinicians, scientists, and patients alike, and the adoption of novel strategies for public agencies to support the integration of clinical research and care. Read More on PubMed
  • Patients harboring brain arteriovenous malformations (bAVMs) are at a lifelong risk for hemorrhagic strokes, but the natural history is poorly understood. We examined the impact of demographic and angiographic features on the likelihood of future hemorrhage. Read More on PubMed
  • Long-term follow-up studies in patients with brain arteriovenous malformations (AVM) have yielded contradictory results regarding both risk factors for rupture and annual rupture rate. We performed a long-term follow-up study in an unselected, consecutive patient population with AVMs admitted to the Department of Neurosurgery at Helsinki University Central Hospital between 1942 and 2005. Read More on PubMed
  • The decision about whether to treat an unruptured brain arteriovenous malformation (AVM) depends on a comparison of the estimated lifetime risk of intracranial haemorrhage with the risks of interventional treatment. We aimed to test whether outcome differs between adults who had interventional AVM treatment and those who did not. Read More on PubMed
  • Therapy of brain arteriovenous malformations (AVMs) often requires the combination of different treatment modalities. Independently assessed data on neurologic outcome after multidisciplinary AVM therapy are scarce. Read More on PubMed
  • Arteriovenous malformations of the brain are congenital vascular lesions that affect 0.01-0.50% of the population, and are generally present in patients aged 20-40 years. The usual clinical presentations are haemorrhage, seizures, progressive neurological deficit, or headache. Results of natural history studies have shown a yearly haemorrhage rate of 1-4%. Frequency of rebleeding has increased over the years, and several factors that increase risk of haemorrhage have been identified. Although substantial, the morbidity associated with haemorrhages could be less than previously thought. Over the past decade, great advances have been made in application of endovascular embolisation techniques, stereotactic radiosurgery, and microsurgery, allowing effective multidisciplinary treatment of arteriovenous malformations, including those previously deemed to be untreatable. Increasing attention has been paid to management of flow-related aneurysms associated with these malformations. Finally, many reports of recurrent arteriovenous malformations have coincided with new theories regarding the embryogenesis of these disorders and laboratory work suggesting their proliferative potential. Read More on PubMed
  • We sought to define determinants of neurological deficit after surgery for brain arteriovenous malformation (AVM). Read More on PubMed
  • Decisions on invasive arteriovenous malformation (AVM) treatment are currently based on natural-course risk estimates of AVM bleeding and assumptions on morbidity from cerebral hemorrhage in general. However, morbidity of AVM hemorrhage has rarely been reported. We sought to assess the morbidity of intracranial hemorrhage in patients with cerebral AVMs. Read More on PubMed
  • The purpose of this study was to determine the symptoms at presentation and the incidence of intracranial hemorrhage (ICrH) caused by intracranial vascular malformations (IVMs) in a defined population. The authors used the Mayo Clinic medical records linkage system to detect all cases of IVM among residents of Olmsted County, Minnesota, during the period 1965 through 1992. Forty-eight IVMs were detected over the 27-year period. Twenty-nine of the 48 patients were symptomatic at presentation. The most common presenting symptom was ICrH, which was present in 20 patients, 69% of all symptomatic cases. Sixty-five percent of arteriovenous malformations (AVMs) presented with ICrH. The most common subtype of ICrH was intracerebral hemorrhage, which was found in nine of 20 patients; the second most common subtype was subarachnoid hemorrhage. The peak occurrence of hemorrhage was during the fifth decade of life. The age- and gender-adjusted occurrence of a first ICrH from an IVM among residents of Olmsted County, Minnesota was 0.82 per 100,000 person years (95% confidence interval 0.46-1.19). There was no increase in the detection of IVM-related ICrH throughout the study period. The 30-day mortality rate following ICrH was 17.6% for patients with an AVM and 25% for all patients with IVMs. This study provides unique data on symptoms at presentation and the incidence of ICrH and hemorrhage subtypes from IVMs on a population basis. Read More on PubMed
  • The authors conducted a long-term follow-up study of 168 patients to define the natural history of clinically unruptured intracranial arteriovenous malformations (AVM's). Charts of patients seen at the Mayo Clinic between 1974 and 1985 were reviewed. Follow-up information was obtained on 166 patients until death, surgery, or other intervention, or for at least 4 years after diagnosis (mean follow-up time 8.2 years). All available cerebral arteriograms and computerized tomography scans of the head were reviewed. Intracranial hemorrhage occurred in 31 patients (18%), due to AVM rupture in 29 and secondary to AVM or aneurysm rupture in two. The mean risk of hemorrhage was 2.2% per year, and the observed annual rates of hemorrhage increased over time. The risk of death from rupture was 29%, and 23% of survivors had significant long-term morbidity. The size of the AVM and the presence of treated or untreated hypertension were of no value in predicting rupture. Read More on PubMed
  • An important factor in making a recommendation for treatment of a patient with arteriovenous malformation (AVM) is to estimate the risk of surgery for that patient. A simple, broadly applicable grading system that is designed to predict the risk of morbidity and mortality attending the operative treatment of specific AVM's is proposed. The lesion is graded on the basis of size, pattern of venous drainage, and neurological eloquence of adjacent brain. All AVM's fall into one of six grades. Grade I malformations are small, superficial, and located in non-eloquent cortex; Grade V lesions are large, deep, and situated in neurologically critical areas; and Grade VI lesions are essentially inoperable AVM's. Retrospective application of this grading scheme to a series of surgically excised AVM's has demonstrated its correlation with the incidence of postoperative neurological complications. The application of a standardized grading scheme will enable a comparison of results between various clinical series and between different treatment techniques, and will assist in the process of management decision-making. Read More on PubMed
  • It is difficult to assess the natural history of intracranial vascular malformations because they are varied in nature, they are frequently silent clinically, they are often treated when they are discovered, and untreated lesions are not often followed in an organized way. Capillary telangiectasias are usually occult lesions of no clinical significance. Cavernous hemangiomas may cause seizures and may bleed, but the approximate yearly risks of bleeding and of death have not been determined. Venous angiomas seldom cause symptoms, with the exception that those in the cerebellum seem to have a propensity to bleed. Intracranial dural arteriovenous malformations (AVMs) may bleed and may cause brain injury if there is insufficient outflow into a dural venous sinus. The dural AVMs that drain into the cavernous sinus have a more benign course than those that drain into the transverse or sigmoid sinus. The aneurysm of the vein of Galen presents a different clinical picture and threat to health according to whether the patient is a neonate, an infant, or an older child. The AVM of the brain encountered in the adult usually presents with hemorrhage or seizures. An unruptured AVM has approximately a 2 to 3% risk of bleeding per year, with about a 1% risk of death per year. The mortality rate of the first hemorrhage is about 10%. Among the survivors, there is about a 6% chance of rebleeding during the 1st year and then approximately a 2 to 3% risk of bleeding per year subsequently. The mortality rate associated with a second hemorrhage is about 13%, and for subsequent hemorrhages the mortality is roughly 20%. Read More on PubMed