Cystic adventitial degeneration (CAD) is a rare, benign lesion involving the vascular adventitia, often resulting in stenosis or occlusion of arteries or veins.The first case of CAD occurring in the external iliac arteries was reported by Atkins and Key in 1974.The first case of CAD occurring in the external iliac arteries was reported by Ejrup and Hiertonn in 1954.The first case of N arterial adventitial cystic degeneration was reported by Ejrup and Hiertonn in 1971. Hiertonn reported the first patient with epiphyseal cystic degeneration of the N artery. CAD has also been reported in the literature to occur in the external iliac arteries, the common femoral artery, and even in the venous epicardium.Velasquez G reported the incidence of arterial epicardial cystic degeneration in patients with intermittent claudication of the lower limbs to be 1 in 1200, the incidence of involvement of the N artery to be approximately 1 in 1000, and the incidence of involvement of other arteries to be unknown. Most patients with CAD tend to present with vascular compression and occlusion and undergo surgical diversion without surgical resection or pathologic diagnosis, making its exact incidence difficult to determine. The pathogenesis of the disease is unclear. Possible pathogenetic mechanisms are microtrauma to the vascular epicardium, embryologic developmental abnormalities, and involvement of tendon sheath cysts. In our patient, the blood sedimentation and C-reactive protein tests were normal and showed no vascular inflammatory lesions. Vascular ultrasound and CTA of the lower extremity arteries suggested that the patient had no significant atherosclerosis in both lower extremity arteries, relatively normal distal vessels, and arterial occlusion due to compression of the N arteries by the vascular epithelial cystic tissue. Ultrasound and arterial CTA can help diagnose the disease, and Flanigan DP reported that intravascular ultrasound is important when diagnosis is difficult with ultrasound and arterial CTA.Radical CAD is a resection of the affected segment of the blood vessel and revascularization with either a vein or a prosthetic vessel, which can prevent local recurrence. The majority of reports have shown that in many cases simple excision of cystic degeneration without revascularization leads to local recurrence. Endoluminal arterial angioplasty is rarely performed because of the propensity for recurrence without excision of the lesion. Ultrasound-guided percutaneous puncture is a therapeutic approach for CAD, but patients who have undergone this treatment have undergone re-surgery a few months later due to local recurrence. In this case, the cystic contents were removed by incision of the peritoneum, the cyst wall was excised, the N artery was decompressed, and blood flow was restored, with normal pulsations in the dorsalis pedis and posterior tibial arteries. The simple excision of cystic degeneration is an effective treatment for CAD because it avoids thrombosis and stenosis after revascularization.Radical surgery for CAD consists of excision of the affected vessel segments and revascularization.