MRA reveals higher prevalence of unruptured cerebral aneurysms than previously reported

Image: PD 

1. Prevalence of unruptured cerebral aneurysms (UCAs) detected by magnetic resonance aniography (MRA) in adults was found to be 7.0%. 

Evidence Rating Level: 3 (Average)       

Study Rundown: The prevalence of unruptured cerebral aneurysms (UCAs) have been previously been reported as 1-5% with an annual rupture rate of 0-1%.  Given the significant morbidity and mortality associated with rupture, there is an interest in detecting UCAs among asymptomatic populations.  This particular study used 3 dimensional time of flight magnetic resonance angiography (3D-TOF MRA) to evaluate the prevalence of unruptured cerebral aneurysms (UCAs) in two districts in Shanghai, China.  The study included adulated aged 35-75 years old.  The results demonstrated a prevalence of 7.0%.  The rates of UCA were noted to be lower for men than for women.  UCAs were primarily seen in the internal carotid artery, and tended to be small (mean diameter 3.5 mm).  The range of estimated UCA prevalence in literature is varies widely, but this study reports a higher prevalence than shown in previous studies.  The major limitation of this study is in the poor generalizability due to study populations coming only from two districts in Shanghai.  UCAs found by MRA were also not verified via a gold standard diagnostic modality such as digital subtraction angiography.

Click to read the study, published today in the Annals of Internal Medicine

Relevant Reading: Prevalence of unruptured intracranial aneurysms, with emphasis on sex, age, comorbidity, country, and time period: a systematic review and meta-analysis

In-Depth [cross-sectional study]: This study recruited subjects from the populations of two districts in Shanghai with demographics similar to that of a 2007 Shanghai census.  One district represented a ‘well-developed’ area, while one represented a ‘developing’ area.  Eligible participants were aged 35-75 and were excluded for conditions that would preclude a MRA.  Aside from predefined exclusion criteria, individuals were also excluded from analysis if they chose not to participate or if their imaging was uninterpretable due to artifacts.  Subjects completed surveys documenting demographics, medical and family history, as well as lifestyle risk factors.  All imaging was conducted with the same 3D-TOF MRA protocol, and were analyzed by three blinded observers.  These observers calculated sizes of vessels and used a 5-point ranking scale to assess confidence in presence or absence of an aneurysm.  Statistical analysis was conducted with Mann-Whitney U tests for continuous variables and chi-square, t-tests, and Fisher exact tests for categorical variables.

Of 5448 eligible individuals in the two districts combined, 4813 (88%) participated in this study.  Interobserver agreement on presence of aneurysms was high (κ = 0.98).  The overall prevalence of UCAs was found to be 7.0% (CI 6.3%-7.7%), with lower rates for men (5.5%, CI 4.6%-6.4%) than for women (8.6%, CI 7.4%-9.7%).  Prevalence trended upwards with age, from 4.5% (CI 3.4%-5.7%) from age 35-44 to 8.6% (CI 6.5-10.6) from age 65-75.  81% of the aneurysms were located in the internal carotid artery.  90% were smaller than 5 mm in diameter (mean 3.5).

By Steven Zhao and Aimee Li MD

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