Unruptured Cerebral Aneurysm



Not all aneurysms will inevitably rupture. As medical imaging technology has improved and becomre more easily accessible unruptured aneurysms are increasingly discovered when magnetic resonance (MR) and computerised tomography (CT) scans are carried out for unrelated reasons.

Discovering an unruptured aneurysm raises difficult questions. Will it rupture in the future? What are the risks of treatment? Are those risks worth taking up- front to prevent the risks form aneurysmal subarachnoid haemorrhage in the future?

What is the risk of Bleeding in the Future?

Brain aneurysmA great deal of effort has gone into efforts to understand the natural history of a cerebral aneurysm- that is; what occurs if the aneurysm is left without treatment. The truth is that we cannot predict the future reliably and your specialist will only be able to offer an estimate of the risk of rupture over time. The best quality research we can presently refer to comes from The International Study of Unruptured intracranial Aneurysms (ISUIA2). and a large Japaneese clinical trial called the Unruptured Cerebral Aneurysm Study (UCAS). From these and similar studies we have learned that two factors in particular seem to influence the risk the aneurysmal will sometimes bleed.:

  • The size of the aneurysm
  • The exact location of the aneurysm within the brain

The smallest aneurysms appeared to have relatively small risks of bleeding in the short term. The results of ISUIA2 are frequently, but erronously, cited as indicating small anterior circulation aneurysms below 7mm in diameter have no risk of bleeding in the short term. It is more correct to say their risk of bleeding may be less than the risks of treatment in the short term. We also see that the risk of treatment increase as the aneurysms grow larger. A careful balance must therefore be struck between the risk of intervening and what could be gained from treating the aneurysm. As we get older the number of life-years one might gain by treating an unruptured aneurysm reduces. Inevitably the risks assosciated wiith treatment tend to rise later in life and the risk to benefit. Furhtermore the above is likely to be rather an oversimplification of what promotes aneurysmal bleeding. The shape and size of the affected blood vessels may have a hydrodynamic affect which increases the stresses on the wall of the aneurysm

For some the discovery of an unruptured aneurysm, even if believed to be of relatively low risk, may become a psychological burden. The management of each aneurysm must therefore be considered on a case-by-case basis. There is usually not pressure to reach a final decision quickly and it is important to take time to arrive at the right decision for the individual.

Can I do anything to reduce the risk from my aneurysm?

There are factors which we understand increase the chances that an aneurysm will bleed in the future. Some have a greater effect than others but it stands to reason that where we can modify our behaviour or lifestyle to remove or control such factors we should be able to reduce the risk of an aneurysm rupturing. These risk factors include:

  • Cigarette Smoking
  • Uncontrolled High Blood Pressure
  • Excessive Alcohol Intake
  • Cocaine Use

Some of these factors probably act in concert to damage blood vessels and the benefits of controlling them likely to take time to be realised.

Not every risk factor is within our control. It is increasingly understood that because of their individual genetic make-up certain people will have a suscpetibility to aneurysm formation and rupture. That is not to say they inherit this trait from theor parent or indeed that they will pass it on to their own children. It is simply part of their individual blueprint. In years to come it is likely we will be able to provide more indivudualised estimates of risks based on screening of the persons genetic profile combined with more sophisticated studies of the stresses on the blood vessel wall.


Other Conditions Assosciated with Cerebral Aneurysms.

Certain diseases are assosciated witht he development of cerebral aneurysms either indirectly because elevated blood pressure forms part of the condition, or because of a suscpetibility conferred by changes in the induviduals genetic make-up. What follows is a sample of the conditions assosciated witht he development of brain aneurysms:

  • Autosomal dominant polycystic kidney disease
  • Ehler-Danlos syndrome types II and IV
  • Marfans's syndrome
  • Coarctation of the aorta
  • Alpha1 anti-trypsin deficiency
  • Neurofibromatosis type 1

Screening for cerebral anuerysms in patients with these other diseases carries many of the diffiiculties of looking for unruptured aneurysms generally. Treatment of aneurysm may be indicated if it can be shown to benefit the patient in the longer term. It is worthwhile to discuss the condition with an experienced specialist before carrying out imaging. The research data we have on risk from unruptured aneurysm may not apply to aneurysms assosciated with other conditions and they may have a somewhat higher lifetime risk of bleeding.