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Intracranial Aneurysms


There is an irregular verb Bandolier uses in its office. It's declension is: "I despair, you can't understand it either, he has another paper on his CV so why worry!" Almost every paper to which this verb applies gets filed in the round receptacle in the corner.

Perhaps that is unfair. A systematic review of critical appraisal skills training [1] provides some evidence that critical appraisal is of benefit. Though it does not have much to work with, knowledge, and attitudes to the medical literature benefit form training. So while Bandolier likes to concentrate on the good, rather than the bad or just plain ugly, occasionally a paper begs to be held up as one to be used for critical appraisal training.


This one [2] used MEDLINE to find papers on prevalence and natural history of intracranial aneurysms, plus reference lists.

Eligible studies had to give numbers of patients studied and the number with aneurysms, and it had additional, apparently reasonable, conditions for autopsy and angiography studies. Indications for angiography were family history of subarachnoid haemorrhage, autosomal dominant polycystic kidney disease, atherosclerosis, suspected pituitary tumour, brain tumour, or other.


The frequency of incidental aneurysms varied considerable between different types of study (Table 1). The reasons are not given. While there was an inverse relationship between size and incidence (Figure), this was an artefact. The main reasons lay in the method for estimating the aneurysm, or the population, or both. For instance, one of the large retrospective autopsy studies examined aneurysms in an autopsy file of a hospital between the years 1914 and 1956. The prospective angiography studies examined small populations with particular disorders, like a family with a history of subarachnoid haemorrhage. What is frustrating is that the only source of information on the populations studied is the titles in the references.

Table 1: Intracranial aneurysm by type of study
Type of study Number of studies Number of patients Percent with aneurysm
Restrospective autopsy 4 43676 0.4
Prospective autopsy 4 5943 3.6
Restrospective angiography 6 2934 3.7
Prospective angiography 9 3751 6.0

Figure: Percent of patients with intracranial aneurysms in each study plotted against the total number of patients included

But useful information is there. For instance, 93% of the aneurysms were 10 mm or less. High rates were found with some conditions and not others (Table 2). Risk of rupture was higher with large aneurysms, in women, people over 60 years, with symptoms, and in the posterior circulation.

Table 2: Intracranial aneurysm by indication for angiography
Indication Number of studies Number of patients Percent with aneurysm
Family history 3 476 9.5
Autosomal dominany polycystic kidney disease 3 202 10.0
Atherosclerosis 5 3676 5.3
Pituitary tumour 2 183 6.0
Brain tumour and other 5 2052 2.3


Perhaps Bandolier is a bit harsh, but we've read this paper many times before understanding it. Like all systematic reviews, at least it provides a start if you think you can do better.


  1. R Taylor et al. A systematic review of the effectiveness of critical appraisal skills training for clinicians. Medical Education 2000 34: 120-125.
  2. GJ Rinkel, M Djibuti, A Algra, J van Gijn. Prevalence and risk of rupture of intracranial aneurysms: a systematic review. Stroke 1998 29: 251-256.
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