Aneurysm Aspect Ratio

The aspect ratio of an aneurysm is the ratio of its depth to the width of its neck. Aneurysms with high aspect ratios are thought to be more prone to rupture because they are low-flow and set the sac up for stasis, thrombosis, and the fibrinolytic cascade and resultant intimal breakdown. Initial studies suggested 1.6 as the cut-off for increased risk of rupture. Subsequent studies have come up with different numbers, and it's unclear to me what number should be used as a threshold in clinical practice.

References

Dhar S, Tremmel M, Mocco J, Kim M, Yamamoto J, Siddiqui AH, Hopkins LN, Meng H. Morphology parameters for intracranial aneurysm rupture risk assessment. Neurosurgery. 2008 Aug;63(2):185-96; discussion 196-7.