Understanding categories or subgroups and a common clinical reasoning error: the example of aneurysm size and neck...

Individualized clinical decisions are often made by considering some patient or lesion characteristics that are thought to have an impact on the efficacy or safety of treatment. For example, aneurysm size and neck width have often been determinants of treatment choices in neurovascular practice.

We review observational and randomized data on the influence of aneurysm or neck size on angiographic results of coiling, stent-assisted coiling, or surgical clipping. New RCT data are used to demonstrate the shortcomings of managing patients using clinical judgment regarding patient or lesion characteristics. We discuss why clinical decisions should not be based on comparisons of different patients treated by the same treatment. Clinical decision making requires a comparison between the same patients treated with different treatments in a randomized trial.

The results of endovascular treatment of large or wide-necked aneurysms are always inferior to those of small or narrow-necked aneurysms, in observational as well as in randomized studies. However, this fact alone is not sufficient to infer that patients with small aneurysms should be coiled, while those with large aneurysms should be managed with stenting or surgical clipping. The purported superiority of clipping for large aneurysms could not be demonstrated in recent RCTs (while surgery was found superior for small aneurysms). Similarly, the superiority of stent-assisted coiling for wide-necked aneurysms was not shown in another recent RCT.

Clinical experience and observational studies alone can mislead practice. Proper clinical decisions for individuals requires randomized evidence.