Advances in neuroimaging and its widespread use for screening have increased the diagnosis of unruptured intracranial aneurysms (UIAs), including small-sized UIAs. The clinical management of these small-sized UIAs requires a patient-specific judgment of the risk of aneurysm rupture, if not treated, versus the risk of complications from surgical or endovascular treatment. Experienced cerebrovascular teams recommend treating small UIAs in young patients or in patients with more than one aneurysm rupture risk factor who also have a reasonable life expectancy. However, individual overall assessment of risk is critical for patients with UIAs to decide the next steps of care.
Key points
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The decision-making process for treatment of small intracranial aneurysms (UIAs) is based on aneurysm rupture risk factors and needs to be weighed against the complication risk during aneurysm treatment.
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Scores to calculate the individual rupture risk in patients with unruptured intracranial aneurysms are helpful during the decision-making process.
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Microsurgical or endovascular aneurysm treatment is recommended for small UIAs in a high-volume neurosurgical center with a low complication risk.
Introduction
Advances in neuroimaging and its widespread use for screening have increased diagnosis rate of unruptured intracranial aneurysms (UIAs), including small-sized UIAs ( Figs. 1–3 ). This growing rate of patients presenting with small, incidental UIAs raise the question whether treatment is needed. Although the estimated 3% prevalence of intracranial aneurysms is low, aneurysm rupture causing subarachnoid hemorrhage (SAH) can be devastating, with morbidity and mortality rates around 25% and 40%, respectively. Patients presenting with ruptured aneurysms need to be treated because they are at high risk for rerupture within the first days and weeks. Both microsurgical clipping as well as endovascular coiling are the current treatment options of choice for ruptured or unruptured aneurysms. Clinical management of patients with UIAs requires a fine judgment of the risk of aneurysm rupture and a decision to observe, versus the risk of complications from surgical or endovascular treatment and a decision to intervene, which is patient specific. Rupture risk ranges between 0.1% and 4% per year and depends on different risk factors, such as aneurysm size and location. Aneurysm size is one of the most important factors in assessing rupture risk in UIAs. Patients with larger aneurysms have a higher risk of aneurysm rupture. The International Study of Unruptured Intracranial Aneurysms (ISUIA) trial and the Unruptured Cerebral Aneurysm Study (UCAS) stratified the risk of rupture for UIAs according to aneurysm size, which showed a small annual rupture risk for UIAs less than 7 mm. This review discusses the current evidence for the management of small UIAs.
Introduction
Advances in neuroimaging and its widespread use for screening have increased diagnosis rate of unruptured intracranial aneurysms (UIAs), including small-sized UIAs ( Figs. 1–3 ). This growing rate of patients presenting with small, incidental UIAs raise the question whether treatment is needed. Although the estimated 3% prevalence of intracranial aneurysms is low, aneurysm rupture causing subarachnoid hemorrhage (SAH) can be devastating, with morbidity and mortality rates around 25% and 40%, respectively. Patients presenting with ruptured aneurysms need to be treated because they are at high risk for rerupture within the first days and weeks. Both microsurgical clipping as well as endovascular coiling are the current treatment options of choice for ruptured or unruptured aneurysms. Clinical management of patients with UIAs requires a fine judgment of the risk of aneurysm rupture and a decision to observe, versus the risk of complications from surgical or endovascular treatment and a decision to intervene, which is patient specific. Rupture risk ranges between 0.1% and 4% per year and depends on different risk factors, such as aneurysm size and location. Aneurysm size is one of the most important factors in assessing rupture risk in UIAs. Patients with larger aneurysms have a higher risk of aneurysm rupture. The International Study of Unruptured Intracranial Aneurysms (ISUIA) trial and the Unruptured Cerebral Aneurysm Study (UCAS) stratified the risk of rupture for UIAs according to aneurysm size, which showed a small annual rupture risk for UIAs less than 7 mm. This review discusses the current evidence for the management of small UIAs.
Patient evaluation overview
There are several modifiable and nonmodifiable patient risk factors for small UIA rupture, which must be taken into account during decision-making ( Table 1 ). These factors influence the treating physician to recommend aneurysm treatment or clinical follow-up with or without medical treatment. In general, patients with small but symptomatic UIAs should be treated to prevent neurologic deficit progression or persistence. An example of such a case would be a posterior communicating artery (PCoA) aneurysm causing oculomotor nerve palsy due to compression or irritation of the nerve, without aneurysm rupture. Younger patients will benefit from aneurysm surgery, because the cumulative risk of rupture leads to a higher rupture risk than the aneurysm treatment complication risk. Also, other instances whereby the treatment risk is lower than the rupture risk include a history of SAH from another ruptured aneurysm, aneurysmal family history in first-degree relatives, and an underlying genetic disease, including polycystic kidney disease or Marfan syndrome. Aneurysm characteristics, such as anatomic location, a borderline size of 5 to 7 mm, and aneurysm shape (such as blebs or multi-lobulated aneurysms), are factors that favor treatment. Useful tools to calculate the individual aneurysm rupture risk are the PHASES score ( Table 2 ) and the UIA treatment score ( Table 3 ), which can be used to compare with the possible complication rate during aneurysm treatment ( Fig. 1 ). Another risk factor score for UIA proposed by Chalouhi and colleagues includes type A factors that favor intervention over observation and type B factors that warrant a strong consideration for treatment independent of size. Type A factors include active smoking, arterial hypertension, posterior circulation aneurysm, prior SAH, familial SAH, and/or aspect ratio greater than 3. Type B factors include young patient age, change in size or configuration of aneurysm, presence of multiple aneurysms, multilobed configuration, or symptomatic aneurysm (emboli or mass effect). In patients with unruptured aneurysm measuring 5 to 7 mm, treatment is recommended if any risk factor (A or B) is present, whereas patients with unruptured aneurysms less than 5 mm should only be treated in the presence of 2 or more type A or any type B risk factors.
| Nonmodifiable Factors | In Favor of Aneurysm Treatment | In Favor of Clinical Follow-up |
|---|---|---|
| Patient age (y) | <50 | >70 |
| Ethnic background | — | Japanese, Finnish |
| Genetic diseases | Polycystic kidney disease, Marfan syndrome | — |
| Family history | Two first-degree relatives | Second- or third-degree relatives |
| Previous SAH | Generally recommended | — |
| Aneurysm characteristics | ||
| Size | 5–7 mm | — |
| Location | Posterior circulation, MCA, ACoA | <5 mm |
| Blebs/multi-lobulated | Generally recommended | ICA (cavernous sinus) |
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