Q)  What is a natural history of unruptured brain arteriovenous malformations (bAVMs) ?

A) A 2018 system review of 18 studies with a total of 8,418 bAVMs cases demonstrated the average of annualized hemorrhage of 2.2% for unruptured bAVMs and 4.3% for patients that presented with hemorrhage. The risk of hemorrhage in the first year of unruptured bAVMs mean of 2.9% versus 7.8% for patients presenting with hemorrhage. The longest follow-up natural history of bAVMs also showed that the risk of hemorrhage is the highest during the first 5 years, decreasing after.

Prior hemorrhage and deep locations were the most consistently reported risk factors for future hemorrhage. Infratentorial location was reported to increase the risk in 2 studies (RR of 2.89 or 3.89). Deep venous drainage (6 studies) and associated aneurysms (4 studies) were not significantly associated with an increased risk of future hemorrhage (multivariable analyses). Increasing age; only 2/9 studies demonstrated increasing risk of hemorrhage with increasing age with RR per year increase (RR=1.05) or per decade increase (RR=1.34). Large AVM size; only 2/6 studies showed large AVM size (either ≥ 5 mm (RR=3.13) /≥  6 mm, RR=3.97) increased risk of future hemorrhage. 
Female sex; only 1/9 studies reported to increase future hemorrhage (RR= 2.39). 


1) Goldberg J, Raabe A, Bervini D. Natural history of brain arteriovenous malformations:
systematic review. J Neurosurg Sci. 2018;62(4):437-443. 
2) Hernesniemi JA, Dashti R, Juvela S, Väärt K, Niemelä M, Laakso A. Natural history of
brain arteriovenous malformations: a long-term follow-up study of risk of hemorrhage
in 238 patients. Neurosurgery. 2008;63(5):823-831.

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