What is the standard size of a large aneurysm? What are the risks of surgery? What is the cost? Huang Qinghai, Department of Neurosurgery, Changhai Hospital, Shanghai, China A: There are many classifications of aneurysms. In addition to etiological classification, aneurysms can also be classified according to their size, the latter being the more commonly used classification method: <3mm for micro aneurysms, 3-10mm for small aneurysms, 10-25mm for large aneurysms, and 25mm or more for giant aneurysms. Surgical treatment of aneurysms, regardless of size, faces some common risks, including intraoperative rupture and bleeding, thromboembolic events, etc. Overall the surgical complication rate is still relatively low, around 2-3% in the high volume center treatment team. However, the results of long-term follow-up show that the recurrence rate is significantly higher with existing endovascular treatments than with small aneurysms, which is an important challenge for current neurointerventional treatment. The high cost of interventional treatment is the starting point for the need to investigate new therapeutic devices (e.g., flow-directed devices or dense mesh stents), which can effectively improve procedural complications and reduce recurrence rates while reducing the cost of the procedure.