A mathematical model of the natural history of intracranial aneurysms: quantification of the benefit of prophylactic treatment

Abstract

Object The International Study of Unruptured Intracranial Aneurysms (ISUIA) data raised new controversy regarding the threshold size that requires treatment. In particular, this study has been criticized for disagreeing with previous epidemiological data. Methods The author first used a Markov model to simulate the natural history of intracranial aneurysms, making three key assumptions based on prospective ISUIA data and other recent reports: that the rate of de novo aneurysm formation is constant after the age of 20 years; that unruptured aneurysms gain volume at a constant rate; and that unruptured aneurysms rupture at a volume-dependent rate. Next, he expressed outcomes for patients with unruptured aneurysms in terms of expected number of quality-adjusted life years (QALY) and compared two hypothetical cohorts, one receiving treatment and the other not being treated. These assumptions enabled the construction of a mathematical model with epidemiologically compatible findings. The benefits of treatment for unruptured aneurysms were highly influenced by aneurysm size and were calculated as −0.28, 0.25, and 1.07 QALY for patients having unruptured aneurysms with diameters of 7, 10, and 13 mm, respectively. Conclusions Under the author’s assumptions, the prospective ISUIA data may be consistent with epidemiological findings. Prophylactic treatment for unruptured aneurysms may produce some benefits in large aneurysms if acceptable treatment risks can be assured, but it is not likely to offer improvement over the natural history for patients with small aneurysms.