Unruptured intracranial aneurysms: indications for treatment
Vivek Deshmukh, M.D., F.A.C.S.
Medical director, Providence Neurointerventional Services
Neurosurgeon, Providence Cranial and Spine Services
Unruptured intracranial aneurysms are common incidental findings on brain imaging. The challenge is to determine which aneurysms pose a significant risk for future subarachnoid hemorrhage. This review outlines the natural history of intracranial aneurysms and identifies those aneurysms that pose a particularly high risk to the patient.
Several studies have identified the incidence of intracranial aneurysms to be approximately 1 to 5 percent of the general population. Annually, nearly 30,000 patients suffer a spontaneous subarachnoid hemorrhage, and most are dead or disabled as a result. With few exceptions, patients with a ruptured intracranial aneurysm warrant treatment.
One cannot be as dogmatic when enumerating the indications for treatment of unruptured intracranial aneurysms. Recent studies have identified risk factors for bleeding and have clarified indications for treatment.
The majority of unruptured intracranial aneurysms are discovered incidentally on imaging obtained for work-up of a neurological symptom – most commonly, a headache. Incidentally discovered aneurysms are infrequently symptomatic; only when they become large or giant do they typically cause symptoms. These symptoms are usually the result of local mass effect.
Aneurysms in the vicinity of the cavernous sinus can cause facial numbness or diplopia as a result of direct compression on the cranial nerves traveling within the cavernous sinus. Aneurysms adjacent to the optic nerve can result in gradually progressive visual field deficit. Rarely, partially thrombosed aneurysms can cause ischemic stroke symptoms.
There are several patient characteristics and angiographic characteristics that define the natural history of unruptured intracranial aneurysms. These include age, prior history of ruptured aneurysm, family history, history of tobacco use or hypertension, and the presence of other medical comorbidities.
An aneurysm discovered in a younger patient typically carries a higher risk for future subarachnoid hemorrhage. The calculation for subarachnoid hemorrhage risk is heavily based on the patient’s age and is cumulative: younger patients carry a greater lifetime risk for hemorrhage than do older patients with the same-size aneurysm.
A family history of subarachnoid hemorrhage increases the likelihood of rupture, particularly if the relationship is first-degree. Both tobacco use and hypertension are modifiable lifestyle risk factors. Underlying collagen vascular disorders such as polycystic kidney disease and Ehlers-Danlos syndrome also increase the risk of future bleeding.
Angiographic characteristics include the size of the aneurysm, its location and morphology, the presence of daughter aneurysms and the number of aneurysms present. The largest natural history study (ISUIA) suggests that an aneurysm greater than 7 mm carries a significant risk for future subarachnoid hemorrhage, with increasing size portending a higher risk. Giant aneurysms in particular are especially ominous.
Aneurysms at the anterior communicating artery, posterior communicating artery and posterior circulation are more likely to hemorrhage regardless of their size. Aneurysms in the cavernous or petrous ICA are very unlikely to cause subarachnoid hemorrhage because they are located outside the subarachnoid space. Aneurysms with an irregular morphology on angiography are more likely to bleed.
Accessory daughter aneurysms are frequently present on the primary dome of the aneurysms; this can be a site for future bleeding. Because multiple aneurysms each carry an independent risk for bleeding, the cumulative risk can be significant.
Indications for treatment
Any evaluation of indications for treatment must balance the risk of treatment with the natural history of the disease. Naturally, if aneurysm treatment carried no risk, then far more aneurysms would be treated. However, both surgical and endovascular therapies carry a small but real risk for stroke and other complications. For this reason, treatment is reserved for patients in whom the natural history risk of bleeding is higher than the risk for treatment.
The following treatment recommendations are based on the above natural history data, existing data on treatment risk, and the senior author’s experience with nearly 1,500 aneurysm patients over the past 12 years.
The primary criteria for treating aneurysms can be outlined as follows:
- Generally, any unruptured aneurysm that is symptomatic with mass effect should be treated.
- Typically, patients over age 80 should not be treated for an unruptured asymptomatic intracranial aneurysm because the risk of treatment for patients in this age group is exceedingly high.
- Aneurysms 5 mm or larger should be given greater consideration for treatment. This size criterion arises from the fact that neurosurgeons commonly see aneurysms smaller than 7 mm present with subarachnoid hemorrhage.
- Greater consideration should be given to treating aneurysms in the posterior circulation, even at smaller sizes. Patients with a strong family history or a history of tobacco use or hypertension should be more strongly considered for treatment.
- If the patient carries a significant amount of anxiety related to the aneurysm, then treatment should be considered. This anxiety can be psychologically crippling in some patients.
- Aneurysms with irregular morphology and those with daughter aneurysms should be more strongly considered for treatment.
- Cavernous or petrous ICA aneurysms should not be treated unless they are symptomatic or reach a giant size.
Due to recent well-conducted natural history studies, the indications for treating unruptured intracranial aneurysms have been further clarified. Ultimately, the decision for treatment varies for each patient, and should take into account the patient’s characteristics, the features of the aneurysm, and treatment risks. A thoughtful appraisal of each patient’s risk profile can optimize patient outcomes and patient satisfaction.
Clinical articles by Vivek Deshmukh, M.D.