The N artery is connected to the superficial femoral artery and divided into the anterior tibial artery and posterior tibial artery, etc. It is located behind the knee joint, which is often referred to as the leg curvature area. The so-called N aneurysm is a dilated N artery located in the bend of the leg with a diameter greater than 1.5 times the normal diameter. Here, it is important to clarify the concept that the so-called aneurysm is not a tumor in the traditional sense, there are benign and malignant, it is just a local dilated artery to a certain extent, called aneurysm. To use an analogy: it is like a car inner tube with a very uniform tube diameter that bulges a bag in a certain area. There are two main risks of aneurysm: one is that the local tissue is weak, so it can easily rupture and cause hemorrhage, which can be life-threatening in serious cases; the other is that the aneurysm can easily form a wall clot due to the change of blood flow status, and the clot can easily fall off and block the distal artery, which can lead to limb ischemia and amputation in serious cases. The incidence of N aneurysm is the second highest among peripheral aneurysms in China, second only to femoral aneurysm. In the West, the two are reversed. Clinical presentation In patients with no other discomfort, a pulsating mass in the bend of the leg (within the N fossa) may be the first symptom detected. Other common symptoms are ischemia of the limb distal to the aneurysm, mainly due to thrombus dislodgement, which is the main risk of N aneurysm (the ticking time bomb to which I refer, is said for this point). Manifestations include intermittent claudication (discomfort such as muscle pain and suffocation in the posterior calf after walking a certain distance), blue toe syndrome due to embolism or more severe ischemia and limb ischemia due to acute thrombosis, leading to resting pain or limb gangrene in severe cases. Some studies have confirmed that 38-90% of patients have manifestations of limb ischemia. Another common symptom is local compression due to the tumor. These include pain due to compression of nerves and swelling of the limb due to compression of deep veins. Rupture is a rare complication of N artery aneurysms, with an incidence of 0-7%. Ancillary examinations include N artery ultrasound, CTA, MRA and arteriography, which can clarify not only the diameter of the aneurysm, flow rate, whether there is embolism and whether the outflow tract is open. Arteriography is the best means to obtain information about the arterial outflow tract. CT and MRI can not only confirm these, but also provide three-dimensional information about the artery and the N fossa. It has been reported in the literature that 62% of patients with N aneurysms have bilateral damage, while 36% of patients with N aneurysms also have aortic aneurysms. Therefore, further investigations should be performed after the N aneurysm is clearly identified to avoid missing other sites of aneurysm. Treatment The main treatment for N aneurysms is surgical resection to prevent future amputation due to distal artery embolism. Interventional stenting has not been used in a large number of cases, and given that the overlapping stent crosses the knee joint, it is prone to dislocation and fracture. However, it may be considered for patients with high risk of conventional surgery.