Blood Thinners

Due to concerns about the risk of hemorrhage, one of the most common questions asked by individuals with cavernous malformation is, “Can I take antithrombotics if I have a cavernous malformation?”

Antithrombotics are drugs that are used for the prevention and treatment of blood clots. They include both antiplatelet and anticoagulant drugs. An example of an antiplatelet drug is aspirin. Anticoagulant drugs include warfarin (Coumadin) and heparin.

Until now, the medical community was unclear about the safety of using these types of drugs in patients with cavernous malformation. A 2019 study from an international collaborative team representing the Scottish Audit of Intracranial Vascular Malformations Steering Committee (SAIVMSC) aimed to determine the effects these drugs have on cavernous malformation patients. An additional retrospective analysis of medical records from 364 patients at Mayo Clinic in Rochester, MN provided further data.

Their findings indicate that the use of antithrombotic therapy in cavernous malformation patients is associated with a lower risk of hemorrhage or focal neurological deficit. They report no safety concerns.

What might be the science behind this finding?

The study team hypothesizes that hemorrhage or focal neurological deficits may be caused by the development of a clot inside a CCM lesion or neighboring DVA. A clot in a DVA could result in blood backing up into the cavernous malformation, potentially causing hemorrhage. If this is the mechanism, antithrombotics may be useful only to those with DVAs, so predominantly people with the sporadic illness. Imaging studies, although perhaps only at a few centers with 7T MRI machines, could help answer this question. The association between antithrombotic therapy and a lower risk of these outcomes in patients supports that idea.

It is important to note that this study is NOT a clinical treatment trial for cavernous malformation and taking any antithrombotics (including low dose aspirin) outside of a trial is not advisable. The purpose of this study was not to test whether antithrombotics prevent CCM hemorrhage in people who were already on them for other indications. The goal was to determine if those drugs posed a safety risk to the cavernous malformation community.

It remains unclear how this class of drugs may affect those who have experienced past hemorrhage and are at the greatest risk of re-hemorrhage.

What are the current recommendations?

According to senior author, Dr. Rustam Al-Shahi Salman, “the findings of our study allow me to continue to reassure other physicians about the use of these drugs in people with a cerebral cavernous malformation who have another medical condition – like an irregular heartbeat – where we already know that these drugs are beneficial for reducing the risk of clotting problems.”

Furthermore, recommendations from Dr. Kelly Flemming include:

Do not start aspirin daily or anti-coagulants unless your doctor has recommended it.

If you have a condition that may require an anti-coagulant and your CCM disease has been stable for a year or more, particularly if you have the sporadic form of the illness, you should feel reassured that you can do so safely.

Consultation with a doctor well-versed in CCM who can verify that your illness is stable.

Keeping the course of blood thinners short, if possible.

More studies are likely to investigate the protective effect of aspirin and other anti-coagulants and whether these findings apply to sporadic, familial, [those with or without prior hemorrhage], or all patients with cavernous malformation.

The Mayo study concluded, “Use of select medications with antithrombotic properties do not increase the risk of CM hemorrhage. Vitamin D supplementation, any antithrombotic, fish oil, and SSRI were associated with a lower prospective hemorrhage risk.”

Listen to the CCM experts weigh in on the SAIVMSC research, including the recommendations, on our YouTube channel.


Flemming KD, Kumar S, Brown RD Jr, Lanzino G. Predictors of Initial Presentation with Hemorrhage in Patients with Cavernous Malformations. World Neurosurg. 2020 Jan;133:e767-e773

Previch L et al. The Influence of Select Medications on Prospective Hemorrhage Risk in Patients with Spinal or Cerebral Cavernous Malformations. World Neurosurg. 2022 Mar 29;S1878-8750(22)00395-3. doi: 10.1016/j.wneu.2022.03.101

Zuurbier, Susanna M et al. Long-term antithrombotic therapy and risk of intracranial haemorrhage from cerebral cavernous malformations: a population-based cohort study, systematic review, and meta-analysis. The Lancet Neurology. 2019;18(10):935-941.

Updated: 2022.4.3