Brain arteriovenous malformations cause sudden out-of-hospital deaths only very seldom

AVMs are rare vascular deformities in the brain. Their incidence worldwide is approximately one case per 100,000 people per year.

“Usually, brain arteriovenous malformation are diagnosed at the age of about 30. In about half of the cases, the AVM is revealed as a result of intracranial hemorrhage. The second most common cause for the discovery of an AVM is an epileptic seizure,” says researcher Anni Pohjola, a physician specializing in neurosurgery from HUS.

The disease often affects working-age people, and it is one of the most significant causes of brain hemorrhage among children and young adults.

When a unruptured AVM is detected as an incidental finding or as the cause of an epileptic seizure, careful consideration is required as to whether preventive treatment is justified and safe. Preventive treatment is aimed at reducing the mortality and morbidity related to AVM hemorrhages. Assessing the effectiveness of treatment has been complicated by the fact that the number of sudden out-of-hospital deaths caused by AVM hemorrhages was previously not known.

The study conducted in the collaborative area of the Helsinki University Hospital combined forensic data from the National Cause of Death Register and the Helsinki AVM Register of the HUS Department of Neurosurgery for the period 1998–2015. The population-based study published in the Neurology journal determined for the first time how often an AVM causes an unexpected, out-of-hospital death.

“The mortality of AVM patients has previously been studied only with regard to patients who reached hospital in time. We wanted to determine how many die unexpectedly before reaching hospital and before the AVM has even been diagnosed,” Pohjola says.

Sudden deaths are rare and usually caused by epilepsy

The study revealed that over a period of 18 years there had been only six cases of sudden out-of-hospital deaths resulting from an AVM. The number corresponds to two per cent of all initial diagnoses of symptomatic cases of AVM. Four of these sudden deaths were caused by epileptic seizures and two by intracranial hemorrhages. Four of the deceased had not been diagnosed with an AVM during their life.

Compared to another serious type of intracranial hemorrhage, aneurysmal subarachnoid hemorrhage (SAH), the proportion of sudden out-of-hospital deaths resulting from AVM hemorrhage is surprisingly low. Approximately 20–25 per cent of patients with SAH die suddenly from the first hemorrhage outside of hospital, and approximately 50 percent of all deaths from SAH occur suddenly out-side of hospital.

“The study covers a population of over 1.6 million inhabitants over a period of almost two decades. Such rare figures reveal that a sudden out-of-hospital death caused by AVM is an exceptional event,” Pohjola emphasizes.

Surprisingly, in contrary to previous assumptions, epilepsy proved to be a more common cause of sudden deaths than intracranial hemorrhage. According to researchers, a sudden epileptic death related to an AVM is a risk that may previously have been underestimated.

“Epilepsy in AVM patients requires special attention because it may lead to a life-threatening seizure even before the AVM ruptures and causes hemorrhage,” Pohjola says.

The results cause a debate about the current care guidelines

Because out-of-hospital deaths from an AVM are extremely rare, previous hospital-based mortality studies have not significantly underestimated total mortality from AVMs. Patients with a diagnosed unruptured AVM therefore do not need to fear a sudden death from AVM hemorrhage to the same extent as previously thought.

“This is important information when we consider the risks and benefits of preventive treatment, particularly when some of the treatment modalities may themselves cause complications,” Pohjola says.

The study is based on data collected at the population level of HUS’s collaborative area and on forensic autopsies, which are performed exceptionally extensively in Finland. Owing to this, it was possible to determine the exact number of out-of-hospital deaths from a previously undiagnosed AVM for the first time in the world.

Link to research article: Sudden Prehospital Deaths From Brain Arteriovenous Malformations. A Population-Based Study. Neurology. Published online 23 June, 2025.

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