Small (< 10-mm) incidentally found intracranial aneurysms, Part 2: treatment recommendations, natural history, complications, and short-term outcome in 212 consecutive patients

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  • 1 Department of Surgery, University of Arizona, College of Medicine, Tucson, Arizona; and
  • 2 Departments of Neurologic Surgery,
  • 3 Neurology, and
  • 4 Radiology, Mayo Clinic, Rochester, Minnesota
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Object

The management of incidental small unruptured intracranial aneurysms (UIAs) is controversial and many factors need to be considered in the decision-making process. The authors describe a large consecutive series of patients harboring small incidental intracranial aneurysms. Treatment strategy, natural history, complications, and short-term outcomes are presented.

Methods

Between January 2008 and May 2011, the authors prospectively evaluated 212 patients with 272 small (< 10-mm) incidental aneurysms. Treatment recommendations (observation, endovascular treatment, or surgery), complications of treatment, and short-term outcomes were assessed.

Results

Recommended treatment consisted of observation in 125 patients, endovascular embolization in 64, and surgery in 18. Six patients were excluded from further analysis because they underwent treatment elsewhere. In the observation group, at a mean follow-up of 16.7 months, only 1 patient was moved to the embolization group. Seven (6%) of the 125 patients in the observation group died of causes unrelated to aneurysm. Sixty-five patients underwent 69 embolization procedures. The periprocedural permanent morbidity and mortality rates in patients undergoing endovascular treatment were 1.5% and 1.5%, respectively (overall morbidity and mortality rate 3.0%). In the surgery group no periprocedural complications were observed, although 1 patient did not return to her previous occupation. No aneurysmal rupture was documented in any of the 3 treatment groups during the follow-up period.

Conclusions

A cautious and individualized approach to incidental UIAs is of utmost importance for formulation of a safe and effective treatment algorithm. Invasive treatment (either endovascular or surgery) can be considered in selected younger patients, certain “higher-risk” locations, expanding aneurysms, patients with a family history of aneurysmal hemorrhage, and in those who cannot live their lives knowing that they harbor the UIA. Although the complication rate of invasive treatment is very low, it is not negligible. The study confirms that small incidental UIAs deemed to be not in need of treatment have a very benign short-term natural history, which makes observation a reasonable approach in selected patients.

Abbreviations used in this paper: ACA = anterior cerebral artery; ACoA = anterior communicating artery; BA = basilar artery; ISUIA = International Study of Unruptured Intracranial Aneurysms; MCA = middle cerebral artery; NIS = Nationwide Inpatient Sample; PCoA = posterior communicating artery; SAH = subarachnoid hemorrhage.

Object

The management of incidental small unruptured intracranial aneurysms (UIAs) is controversial and many factors need to be considered in the decision-making process. The authors describe a large consecutive series of patients harboring small incidental intracranial aneurysms. Treatment strategy, natural history, complications, and short-term outcomes are presented.

Methods

Between January 2008 and May 2011, the authors prospectively evaluated 212 patients with 272 small (< 10-mm) incidental aneurysms. Treatment recommendations (observation, endovascular treatment, or surgery), complications of treatment, and short-term outcomes were assessed.

Results

Recommended treatment consisted of observation in 125 patients, endovascular embolization in 64, and surgery in 18. Six patients were excluded from further analysis because they underwent treatment elsewhere. In the observation group, at a mean follow-up of 16.7 months, only 1 patient was moved to the embolization group. Seven (6%) of the 125 patients in the observation group died of causes unrelated to aneurysm. Sixty-five patients underwent 69 embolization procedures. The periprocedural permanent morbidity and mortality rates in patients undergoing endovascular treatment were 1.5% and 1.5%, respectively (overall morbidity and mortality rate 3.0%). In the surgery group no periprocedural complications were observed, although 1 patient did not return to her previous occupation. No aneurysmal rupture was documented in any of the 3 treatment groups during the follow-up period.

Conclusions

A cautious and individualized approach to incidental UIAs is of utmost importance for formulation of a safe and effective treatment algorithm. Invasive treatment (either endovascular or surgery) can be considered in selected younger patients, certain “higher-risk” locations, expanding aneurysms, patients with a family history of aneurysmal hemorrhage, and in those who cannot live their lives knowing that they harbor the UIA. Although the complication rate of invasive treatment is very low, it is not negligible. The study confirms that small incidental UIAs deemed to be not in need of treatment have a very benign short-term natural history, which makes observation a reasonable approach in selected patients.

Abbreviations used in this paper: ACA = anterior cerebral artery; ACoA = anterior communicating artery; BA = basilar artery; ISUIA = International Study of Unruptured Intracranial Aneurysms; MCA = middle cerebral artery; NIS = Nationwide Inpatient Sample; PCoA = posterior communicating artery; SAH = subarachnoid hemorrhage.

Management of small incidentally discovered UIAs is controversial. The prospective yearly risk of rupture is very low, particularly in selected locations, but outcome once rupture occurs is dismal.3–5 Despite advancements in neuroendovascular and microsurgical techniques, however, there is still some risk of invasive treatment.10,13 Several studies have focused on the results of specific treatments (for instance, medical, endovascular, or surgical treatment) in patients with unruptured aneurysms. The ISUIA13 was a large multicenter study with retrospective and prospective cohorts of patients with unruptured aneurysms undergoing observation, surgery, or endovascular treatment. However, patients enrolled in the ISUIA were treated in the 1990s, and therefore treatment outcomes do not necessarily reflect current practice, particularly for those patients who underwent endovascular treatment. Therefore, the optimal management of these small incidental UIAs remains uncertain. In the present study, we analyze treatment recommendations, natural history, and short-term outcomes in a large consecutive contemporary series of 212 patients with 272 small incidental aneurysms.

Methods

The study was approved by the local institutional review board. We reviewed a prospectively maintained database of consecutive patients with UIAs evaluated by the senior author (G.L.) from January 2008 until May 2011. Information collected included demographic data, factors that led to the discovery of the target aneurysm, potential risk factors for intracranial aneurysm formation and rupture (smoking, hypertension, and family history of intracranial aneurysms and aneurysmal SAH), known medical disorders associated with an increased occurrence of UIAs, and aneurysm location, size, and multiplicity. Aneurysm size was measured using digital subtraction angiography when available; otherwise, measurement was obtained from the available CT/MR angiograms. Patient inclusion and exclusion criteria, associated medical conditions, risk factors, demographics, and factors leading to diagnosis have been described in detail in the accompanying manuscript.9

The natural history of incidental aneurysms and the risks of treatment (observation and correction of risk factors, embolization, or surgery) were routinely discussed with the patients and their family members, and a final recommendation was made based on various factors that included aneurysm characteristics (location, size, shape, geometry, and presence of calcifications), the individual patient's characteristics (age, comorbidities, risk factors, family history, and personality), and the patient's preference. Reasons for recommending observation or invasive treatment were also prospectively annotated. In some patients the final decision before recommending treatment was based on additional high-resolution 3D angiography studies to better assess characteristics of the aneurysm as well as potential risks of treatment.

Except for extenuating circumstances (such as very advanced age or important medical comorbidities limiting life expectancy), patients with newly diagnosed aneurysms undergoing observation usually received a recommendation to have a follow-up noninvasive imaging study after 6–12 months to document stability of the aneurysm, with repeat imaging performed intermittently over time. In patients undergoing treatment, the type of treatment (surgical or endovascular) and details of treatment were collected. Any clinical complication resulting in a transient or permanent deficit was recorded. Length of hospital stay in treated patients was annotated. Follow-up information was obtained regularly through office visits where patients were asked to rate themselves on the modified Rankin Scale or they were contacted over the phone by a nurse practitioner or a nurse who was not directly involved with patients' treatment. Short-term and long-term cognitive outcomes were not available in this cohort.

Statistical Analysis

To determine whether a difference observed between the groups was statistically significant, we used a 2-sided t-test for continuous data and a chi-square test for categorical variables. The Fisher exact test was used when more than 20% of the tables had a value less than 5. All statistical analysis was performed using JMP software version 9.0.1 (SAS Institute Inc.). A predefined p value of 0.05 was considered the cutoff point of statistical significance.

Results

Patient Population

Two hundred seventeen patients (64.8% of the entire cohort of patients with unruptured aneurysms evaluated by the senior author during the study period) were assessed for 278 newly discovered incidental small aneurysms. Five of these patients had 6 small incidental aneurysms located within the cavernous sinus and were also excluded from further analysis. Thus, 212 patients (63.3%) with 272 small incidental aneurysms are the focus of this study.

Aneurysm Characteristics and Treatment Recommendations

Aneurysm location and size are summarized in Table 1. The mean size of the aneurysms was 5.5 mm (in patients with multiple aneurysms, only the largest aneurysm was considered for this calculation). The recommended treatment was observation with risk factor control in 126 cases (57.8%), endovascular in 72 cases (33%), and surgical in 20 cases (9.2%). Six patients were considered in the analysis of recommended treatment but excluded from further follow-up analysis because they elected to undergo treatment elsewhere. Recommended treatment in these 6 patients was endovascular embolization in 4, surgery in 1, and observation in 1. Table 2 summarizes demographic data and aneurysm size and location in the 3 management cohorts (in patients with multiple aneurysms, only the largest aneurysm is considered). Figure 1 illustrates management approach stratified by age.

TABLE 1:

Characteristics of incidental small UIAs*

CharacteristicValue (%)
no. of patients212
overall no. of aneurysms272
no. of aneurysms treated†89 (32.7)
no. of patients w/ multiple aneurysms41 (19.34)
location of aneurysm
 cavernous8 (2.9)
 ICA107 (39.3)
  paraclinoid60
  ICA-PCoA28
  ICA-AChA5
  ICA-bifurcation14
 ACoA/ACA55 (20.2)
 MCA74 (27.2)
 vertebrobasilar28 (10.3)
  BA22
  BA-PICA4
  BA-SCA2
maximum diameter (mm)§
 mean5.5 ± 2.09
 median5.00
 range2–10

* AChA = anterior choroidal artery; ICA = internal carotid artery; PICA = posterior inferior cerebellar artery; SCA = superior cerebral artery. † Surgery or embolization.

‡ In patients with coexisting small incidental aneurysms in other locations.

§ Calculation is based on the maximum diameter of the largest aneurysm in patients with multiple aneurysms.

¶ Mean value presented ± SD.

TABLE 2:

Summary and comparison of the 3 management cohorts*

CharacteristicManagement Approachp Value
ObservationEndovascularSurgery
no. of patients (M/F)126 (34:92)68 (15:53)19 (5:14)
no. of patients treated (M/F)125 (33:92)64 (13:51)18 (5:13)
no. of proceduresNA6819
mean age in yrs (range)64.4 ± 11.8 (27–88)55.34 ± 11.1 (30–79)53.36 ± 8.36 (25–66)a) <0.001; b) <0.001; c) 0.5008
no. of patients
 >65 yrs72 (57.1%)13 (19.1%)1 (5.3%)<0.001
 w/ multiple aneurysms22 (17.4%)13 (19.1%)7 (36.8%)
aneurysm characteristic
 total no.1608925
 size (mm)§
  mean4.91 ± 2.026.37 ± 1.935.84 ± 1.98a) <0.001; b) 0.058; c) 0.305
  range2–103–9.823–9
  median4.56.765.8
location of treated aneurysms
 ICANA345<0.001
  paraclinoidNA210
  ICA-PCoANA92
  ICA-AChANA11
  ICA-bifurcationNA32
 ACoA/ACANA153
 MCANA512
 vertebrobasilarNA140
mean length of hospital stay (days)NA1.4 ± 2.022.7 ± 1.150.0078

* NA = not applicable.

† Paired t-test between a) observation and embolization, b) observation and surgery, and c) embolization and surgery.

‡ One patient with 2 aneurysms had 2 different recommended and final treatments: 1 aneurysm was treated with surgery and the other with embolization.

§ For the endovascular and surgical groups, size refers to the treated aneurysm's dimensions.

¶ Mean values presented ± SD.

Fig. 1.
Fig. 1.

Bar graph showing age group distribution by management approach.

Observation Group

Included in this group are 125 patients with 160 aneurysms representing 58.9% of the 212 patients with small incidental UIAs. The most common reasons for selecting observation were (either alone or in combination) age, presence of comorbidities, lack of risk factors, “benign” appearance of the lesion, imaging-documented location of the aneurysm, and patient preference for observation.

There were 2 complications in the observation group among patients who underwent digital subtraction angiography for aneurysm definition. One patient suffered a dissection of his femoral artery without significant clinical sequelae. The second patient, a 65-year-old woman, was evaluated for an unexplained left cranial nerve VI palsy in the setting of a complicated medical history. She was found to have an incidental left MCA aneurysm and endovascular treatment was recommended, but embolization was not carried out because 2 large vessel branches arose from the aneurysm neck, and treatment was considered to be extremely risky. One day following digital subtraction angiography, the patient was admitted with left facial weakness and left upper-extremity weakness. Magnetic resonance imaging of the brain demonstrated subacute infarcts in the right basal ganglia region. The patient was discharged 4 days later and her symptoms gradually improved.

Most of the patients in the observation group were advised to undergo follow-up imaging within 6–12 months to document the stability of the aneurysm. Clinical follow-up was available for 122 patients (97.6%) after a mean of 16.7 months (median 15.1 months). Seven patients (5.73%) died after an average of 14.31 months after initial evaluation and the causes were not related to the aneurysm (pneumonia in 1, cancer in 3, cardiac arrest in 1, respiratory failure after hypertensive intracerebral hemorrhage in 1, and unknown cause but unrelated to the intracranial aneurysm in 1). No documented SAH occurred in this cohort.

At least one type of follow-up angiographic study (digital subtraction, MR, or CT) was available for 69 (56.5%) of the available patients after a mean interval of 14.04 months (median 12.06 months). In 3 patients (4.3%), follow-up imaging studies suggested a possible increase in aneurysm size. Based on these changes, invasive treatment was recommended for 1 patient with a basilar trunk aneurysm, whereas in the remaining 2 the changes were not considered significant and further observation was recommended. The patient who underwent treatment was a 73-year-old woman who originally was evaluated for a possible ischemic stroke and was found to have an incidental basilar trunk aneurysm. Follow-up imaging 22.1 months later suggested aneurysm enlargement, and she underwent stent-assisted coil embolization (see Endovascular Treatment).

Endovascular Treatment

Our approach has been to favor endovascular treatment over other options when it is judged a feasible and safe choice. Because of the very benign natural history of incidental small UIAs, we have had a very low threshold for aborting treatment (this occurred in 8 cases) very early in the procedure because of perception that the procedure posed a higher risk than the benign natural history of the disease. Management of these 8 patients included observation in 5 cases, surgery in 2, and subsequent stenting in 1 patient in a separate sitting. Overall, 65 patients (30.6% of 212 patients evaluated for small incidental aneurysms) underwent 69 endovascular procedures for 69 aneurysms (including the case initially assigned to the observation group). The type of endovascular treatment is summarized in Table 3.

TABLE 3:

Type of endovascular treatment in 65 patients with 69 aneurysms

ProcedureNo. of Treated Lesions (%)
coiling51 (73.91)
stent-assisted coiling6 (8.70)
balloon-assisted coiling10 (14.49)
flow diversion1 (1.45)
stent only1 (1.45)

The mean length of hospital stay in this cohort was 1.4 days (median 1 day). Immediate digital subtraction angiography demonstrated complete obliteration in 14 cases (20.29%), near complete (≥ 90%) in 46 cases (66.67%), and incomplete (< 90%) in 9 cases (13.04%).

Complications

Periprocedural Complications (Within the First 30 Days)

There were 6 (9.23%/patient, 8.69%/procedure) periprocedural (within 30 days) complications, which resulted in permanent morbidity in 1 patient (1.53%/patient, 1.45%/procedure) and death in another patient (periprocedural mortality 1.53%/patient, 1.45%/procedure). Major periprocedural complications consisted of thrombus formation in 2 patients, ischemia in 2, periprocedural rupture in 1, and death in 1. It is noteworthy that short- and long-term cognitive outcomes were not available in this cohort.

In 1 patient, treated for a basilar tip aneurysm, there was transient development of in-stent thrombosis that resolved after initiation of pharmacological therapy with no sequelae. The patient was discharged on the 1st postoperative day without any complaints. The second patient with a thrombotic complication was a 39-year-old woman who underwent treatment for a superior hypophyseal and a BA aneurysm in 2 different sittings. The second procedure (treatment of the BA aneurysm) was complicated by in-stent thrombosis, which rapidly resolved with systemic abciximab administration. The patient was discharged on the 3rd postoperative day without any complaints except minimal headache. One patient experienced transient dysarthria following uncomplicated embolization of an ACoA aneurysm. His symptoms quickly improved, and he was discharged on the 2nd postoperative day without any deficits. One additional patient underwent uneventful embolization of a left PCoA aneurysm. She was discharged the following day without any symptoms. She was readmitted 2 days later with multiple small cerebellar, thalamic, and parietal ischemic strokes that resulted in a permanent mild disability after hemorrhagic transformation of the parietal lesion. A 60-year-old woman was evaluated for episodes of transient global amnesia. During embolization of a left PCoA aneurysm, perforation of the aneurysm sac occurred, causing SAH. The patient required placement of a temporary external ventricular drain but recovered without sequelae.

The only death in this series occurred after an expanding basilar trunk aneurysm was treated by stent-assisted coiling in a 74-year-old woman. The procedure was complicated by in-stent thrombosis, and the patient suffered a thalamic and pontine infarct despite prompt pharmacologically induced recanalization of the offending thrombus. Eventually she died after hemorrhagic conversion of the thalamic infarct.

Minor early-onset complications were observed in 4 patients and consisted of systemic infection treated with antibiotic therapy (1 patient), groin infection requiring antibiotic treatment (1 patient), rectal bleeding in 1 patient receiving dual-antiplatelet therapy, and iatrogenic non–flow limiting vertebral artery dissection in 1 patient.

Late-Onset Complications

There was one significant late (> 30-day) complication occurring at approximately 7.4 months following treatment. This 50-year-old man underwent an uncomplicated stent-assisted embolization of an ACoA aneurysm. Catheter angiography performed 1.6 and 7.4 months later suggested partial aneurysm obliteration, progressive coil compaction, and significant aneurysm recurrence. The geometry of the aneurysm precluded further embolization. It was decided to proceed with surgery and the patient was taken off clopidogrel first and aspirin afterward. This resulted in thrombus formation around the stent with distal emboli and a disabling stroke in the ACA territory. The stroke caused permanent cognitive dysfunction and rendered the patient unable to return to work. No surgery was performed in this case.

Clinical and Radiological Follow-Up

Imaging follow-up was available in 41 of the patients (43 procedures); the studies were obtained at an average of 10.6 months. In the last available imaging evaluation, obliteration was complete in 21 aneurysms (48.8%), near complete (≥ 90% obliterated) in 16 (37.2%), and incomplete (< 90% obliterated) in 6 (14%). Angiographic results in patients with at least 1 follow-up imaging study are summarized in Table 4. Clinical follow-up (mean 12.6 months, range 0.5–35.6 months) was available in all 64 survivors (after 68 procedures). There was no rupture documented in this group of patients and there were no new symptoms that could be ascribed to the aneurysm. No patient underwent repeat embolization for residual/recurrent aneurysm.

TABLE 4:

Comparison of immediate and final angiographic occlusion rates in a subgroup of patients who underwent immediate and final follow-up imaging

Extent of OcclusionNo. of Procedures (%)
Immediate Occlusion RateFinal Occlusion Rate
complete (100%)11 (25.6)21 (48.8)
near complete (≥90%)28 (65.1)16 (37.2)
incomplete (<90%)4 (9.3)6 (14)

Surgery

In the period between January 2008 and May 2011, 18 patients underwent craniotomy for the treatment of small incidentally discovered UIAs, representing 8.5% of the total number of patients. Surgical treatment was considered when the aneurysm was deemed not to be amenable to endovascular treatment based on aneurysm characteristics and patient-related factors. Eighteen patients underwent 19 procedures for 20 aneurysms: 16 patients with 16 aneurysms and 2 patients with 2 aneurysms each. All of the treated aneurysms were treated by clipping. Table 2 provides a summary of patient demographics as well as characteristics of the treated aneurysms. The mean length of hospital stay in patients undergoing surgery was 2.7 days (range 1–5 days, median 3 days). There were no periprocedural transient or permanent neurological deficits in this small subgroup. However, 1 patient, a 51-year-old woman with a small MCA aneurysm, did not return to her previous occupation after surgery. She was discharged on the 2nd postoperative day after uncomplicated aneurysm clipping. A month later she started complaining of fatigue, memory issues, and problems with focus and concentration. At the last follow-up, 16.3 months following surgery, she had developed obsessive-compulsive disorder and was unable to go back to work (modified Rankin Scale score of 2). A CT scan of the head obtained by her local physician was reported to show postoperative changes but no evidence of complications.

Intraoperative indocyanine green angiography in every patient and postoperative catheter angiography in selected cases demonstrated complete aneurysm obliteration in 18 cases (90%) and near-complete obliteration (small neck remnant) in 2 cases (10%). Clinical follow-up information was available for all 18 patients after an average of 14.6 months (median 16.3 months, range 0.1–29.2 months).

Discussion

With the widespread use of noninvasive brain imaging techniques, small incidental intracranial aneurysms are commonly detected. When a small UIA is found, the treating physician is often left with a significant management dilemma. The majority of small aneurysms likely do not rupture. However, the risk of rupture of small incidental UIAs, particularly when located in certain regions, is not zero, and, more importantly, when aneurysms do rupture, the prognosis is poor.13 Although the follow-up duration in the present study is short, only a few patients were lost to follow-up (clinical follow-up available in > 95% of patients in the observation cohort). Furthermore, findings in our observation cohort confirm that the short-term risk of rupture for those patients deemed not in need of invasive treatment is very low, as suggested by the fact that no episodes of aneurysm rupture occurred in the “observation” group. This observation is consistent with the results of ISUIA13 and is in disagreement with some studies from Japan, although in these latter studies all patients with unruptured aneurysms, irrespective of size and symptomatic status, were considered together.11,12 The lack of UIA rupture in the follow-up period in our observation cohort is also in disagreement with another widely quoted study on the natural history of UIAs by Juvela and coworkers.7,8 However, the 2 studies are not comparable to other studies, including the ISUIA (patients without a prior SAH), because careful analysis of the Juvela et al. study reveals that 102 of the 105 patients considered had an unruptured aneurysm discovered in the setting of a prior SAH from another aneurysm. It has been reported that in patients with a history of SAH the aneurysm has a worse natural history and higher risk of rupture,13 and these patients were not included in our study because we focused exclusively on patients with truly incidental unruptured aneurysms.

Given that the natural history of very small incidental UIAs appears to be benign in Caucasian populations, any interventional treatment must be carefully considered. The availability of endovascular techniques has fostered a perception of treatment being available and safe, and there has been a significant increase in the number of patients with UIAs evaluated and treated in the past decade.6 Analysis of data from the NIS shows that the fraction of treated UIAs managed with endovascular coiling increased from 20% in 2001 to 63% in 2008.2 However, even though endovascular treatment is relatively well tolerated and less invasive than open surgery, complications do occur. In our study, there was 1 permanent periprocedural stroke resulting in minor disability and 1 periprocedural death, resulting in a combined short-term periprocedural morbidity and mortality rate of 3%. Given that previous data suggest that adverse cognitive outcomes are a key contributor to interventional morbidity and mortality,13 it is important to note that such data were not available in the current cohort. These outcome data are in line with those previously reported. In a large prospective study on coiling of UIAs conducted mostly in experienced French centers,10 the periprocedural morbidity and mortality rates were 3.1% for the standard approach with coils and 3.7% for the remodeling technique, respectively. In overall clinical practices, however, treatment complications are probably higher than noted in the literature. Following analysis of the NIS, a large administrative database containing data on a random sample of 1000 US hospitals, discharge to a site other than home (used as a surrogate for perioperative complications) was 4.1% in patients undergoing endovascular treatment and 13.8% in patients undergoing surgery.6 Although these NIS data included unruptured aneurysms of all sizes and there was no differentiation made between truly incidental and symptomatic aneurysms, these data underscore once again that, despite recent progress in techniques, treatment of UIAs continues to be associated with serious and clinically relevant complications.

Ongoing uncertainty regarding risks and benefits of treating small incidental UIAs can only be clarified through a well-designed, randomized clinical trial. The need for such a trial is exacerbated by the large amount of health care expenditures focused on imaging follow-up of both treated and observed small aneurysms, as well as on interventional management for these cases. Although such a proposed trial will require many years of follow-up (given the low occurrence of end points in the observation group) and significant resources, it is the responsibility of the medical community to make it happen.

We believe that only a minority of patients with small incidental intracranial aneurysms should be considered for treatment, and this belief is in line with current guidelines.1 Less than one-half of small incidental aneurysms in our cohort were recommended for treatment. Furthermore, we have maintained a low threshold to abort endovascular procedures if any difficulty is encountered. Notably, many of the patients were sent to us for a second opinion after invasive treatment had been recommended elsewhere. In our opinion, interventional treatment is likely not indicated in most older patients, for those with incidental UIAs in specific benign locations such as the paraclinoid carotid artery and selected other anterior circulation locations, and for those with significant comorbid conditions affecting their life expectancy. Factors that increase the potential recommendation for interventional treatment include a younger age patient, particularly with a family history of aneurysmal hemorrhage, a UIA in a posterior circulation or PCoA location, selected UIA morphological features, patient perspective regarding the need for treatment after hearing an unbiased presentation of the comparison of natural history and risks of intervention, and occurrence of aneurysm growth during the follow-up period. When these factors were present, especially in younger patients, invasive treatment was recommended even in those with very small aneurysms, which explains why some aneurysms as small as 3 and 4 mm were treated in this cohort.

It is notable that all deaths unrelated to the aneurysm in our cohort were in the observation group, indicating that patients with UIAs considered by us not to be in need of intervention have a substantially greater likelihood of dying from non–aneurysm related disorders compared with potential SAH as noted in other large UIA cohort studies.13 It is also important to consider the management of risk factors for aneurysm formation and rupture in all patients, including those who undergo observation and those who undergo intervention. In patients who are cigarette smokers, appropriate counseling and medical managements strategies should be implemented to increase the likelihood of smoking cessation. Elevation in blood pressure consistent with hypertension should be treated to attain normal blood pressure levels and should be monitoring closely over time.

Our study has limitations related to being a single-institution series reflecting treatment recommendations and primarily the bias of the senior author who has dual training in surgical and endovascular procedures. In addition, cognitive outcomes were not available. Nevertheless, there are many strengths, including concentration on a very specific and homogeneous group of patients such as those with truly incidental small aneurysms, the complete follow-up, having no patient who underwent invasive treatment lost to follow-up, follow-up data available in more than 95% of the patients who underwent observation, the strict criteria adopted in reporting complications (based on patients' self-assessment of the modified Rankin Scale score), and inclusion of patients in whom complications developed in the course of evaluation or beyond the “traditional” 30-day time window used to assess treatment-related complications. Moreover, our study population represents a contemporary series during which there have been few changes in terms of technology or patient assessment.

Conclusions

We describe our experience in the management of incidental UIAs. Cautious patient selection can yield excellent outcomes with minimal morbidity and mortality even with aggressive approaches. Coil embolization has the potential to be a cost-effective treatment approach which, unfortunately, still harbors a finite risk of serious complications. It is unlikely that this morbidity will decrease significantly, especially in view of the fact that an increasing number of elderly patients are diagnosed with intracranial aneurysms and the documentation of a high prevalence of smoking and hypertension in these patients, which increase the likelihood of atherosclerosis and increase the risk or periprocedural complications.

Acknowledgment

The authors wish to acknowledge the kind help of David Xu in formatting the references for the final submission.

Disclosure

Dr. Cloft is the Central angiogram reader for the trial Evaluate the Safety and Performance of the MindFrame IRIIS Device sponsored by Mindframe, Inc. He is site PI for SAPPHIRE (Stenting and Angioplasty with Protection in Patients at HIgh Risk for Endarterectomy) registry sponsored by Cordis Endovascular. Dr. Kallmes has received research support from ev3, Micrus, MicroVention, Penumbra, Sequent, and NFocus. He has participated in the preparation of educational materials for ev3 and has received reimbursement for travel by MicroVention. Dr. Lanzino has received unrestricted educational grants from ev3 and Synthes and has received reimbursement for travel from ev3.

Author contributions to the study and manuscript preparation include the following. Conception and design: Lanzino. Acquisition of data: Loumiotis, Vine. Analysis and interpretation of data: Loumiotis. Drafting the article: Lanzino, Loumiotis. Critically revising the article: Lanzino. Reviewed submitted version of manuscript: Lanzino, Loumiotis, Brown, Cloft, Kallmes. Approved the final version of the manuscript on behalf of all authors: Lanzino. Statistical analysis: Loumiotis. Administrative/technical/material support: Lanzino. Study supervision: Lanzino.

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  • 11

    Tsukahara T, , Murakami N, , Sakurai Y, , Yonekura M, , Takahashi T, & Inoue T: Treatment of unruptured cerebral aneurysms—a multi-center study of Japanese national hospitals. Acta Neurochir Suppl 82:310, 2002

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  • 12

    Tsukahara T, , Murakami N, , Sakurai Y, , Yonekura M, , Takahashi T, & Inoue T, : Treatment of unruptured cerebral aneurysms; a multi-center study at Japanese national hospitals. Acta Neurochir Suppl 94:7785, 2005

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    • Export Citation
  • 13

    Wiebers DO, , Whisnant JP, , Huston J III, , Meissner I, , Brown RD Jr, & Piepgras DG, : Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 362:103110, 2003

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Contributor Notes

Address correspondence to: Giuseppe Lanzino, M.D., Department of Neurologic Surgery, 200 First Street SW, Rochester, Minnesota 55905. email: Lanzino.Giuseppe@mayo.edu.
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    Bar graph showing age group distribution by management approach.

  • 1

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  • 2

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  • 11

    Tsukahara T, , Murakami N, , Sakurai Y, , Yonekura M, , Takahashi T, & Inoue T: Treatment of unruptured cerebral aneurysms—a multi-center study of Japanese national hospitals. Acta Neurochir Suppl 82:310, 2002

    • Search Google Scholar
    • Export Citation
  • 12

    Tsukahara T, , Murakami N, , Sakurai Y, , Yonekura M, , Takahashi T, & Inoue T, : Treatment of unruptured cerebral aneurysms; a multi-center study at Japanese national hospitals. Acta Neurochir Suppl 94:7785, 2005

    • Search Google Scholar
    • Export Citation
  • 13

    Wiebers DO, , Whisnant JP, , Huston J III, , Meissner I, , Brown RD Jr, & Piepgras DG, : Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 362:103110, 2003

    • Search Google Scholar
    • Export Citation

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