cystic adventitial degeneration ( cad ) is a rare disease but a serious claudication that causes vascular stenosis , usually in middle - aged men.1,2 in ~85% of cases reported , cad affects the popliteal artery.1,2 typically , duplex sonography , angiography , contrast - enhanced computed tomography , and magnetic resonance imaging ( mri ) are used to establish a diagnosis.3,4 earlier studies on cad are almost single case reports or small case series.3,4 as little is known about intra - vascular ultrasound ( ivus ) findings and their importance in patients with cad , we report here our experience of a case in which ivus correctly identified cad of the popliteal artery when angiography was inconclusive . an 87-year - old male was referred to our hospital with a com - plaint of intermittent claudication in the left calf with a walking distance of about 100 m. his coronary risk factors were hypertension , diabetes mellitus , dyslipidemia , and chronic kidney disease ( estimated glomerular filtration rate 51 ml / minute/1.73 m ) . there was no cyanosis of the left lower limb , no ulceration , and no dystrophic signs . he had no history of connective tissue disease , which was also excluded by physical and laboratory examinations . his ankle - brachial index ( abi ) was 0.92 on the right leg and 0.46 on the left leg . , as shown in figure 1 , digital subtraction angiography ( dsa ) of the left lower extremity showed that the left popliteal artery had a severe eccentric stenosis . attempt to pass the stenotic site by a 0.014 inch chevalier floppy wire ( future medical design corporation ) was performed , and the guide wire was easily crossed . ivus ( viewit ; terumo corporation ) revealed a nonatherosclerotic lesion and cystic appearance ; the area of extravascular hypodensity was clearly visualized , which was causing extrinsic compression of the lumen ( fig . 2 ) . because we considered a differential diagnosis , including cyst , tumor , and cad by these ivus findings , we stopped endovascular therapy and performed mri . the axial view of mri revealed cystic lesions encompassing the left popliteal artery circumferentially ( fig . , these cystic lesions also exhibited high signal intensity on t2-weighted images clearly ( fig . because of the characteristic location and clinical signs , we diagnosed cad of the popliteal artery . thus , we considered that ivus may be used as an adjunctive tool to diagnose and evaluate cad when angiography was inconclusive . the segment was resected , and an interposition graft was completed with a segment of reversed saphenous vein . histopathologic analysis of the segment demonstrated myxoid change with formation of cystic spaces , primarily involving the adventitia ( fig . spinner et al.5 recently reported the joint connection of the middle genicular artery in patients with cad , that is , the conduit for cyst propagation from the knee joint to the parent vessel . however , in our case , a joint connection was not identified on mri or at operation . the follow - up abi was normalized , and clinical success with symptom resolution was achieved . here , we report a rare case in which ivus finding was useful for diagnosis and evaluation of cad of the popliteal artery . although stenotic lesions in lower extremities arteries are mostly caused by arteriosclerosis obliterans , nonatherosclerotic causes such as popliteal artery entrapment syndrome , cad , and thrombosed aneurysm must be considered in lesions of the popliteal artery as this case . atkins and key6 first reported cad of the iliac artery in 1947 and hiertonn and lindberg7 first described cad of the popliteal artery in 1957 . ishibashi et al.8 reported age and sex distribution of cad : males ( 83.2% ) and average age 44.6 years . most of the patients with cad are less than 50 years of age in general , and case reports of patients older than 80 years are uncommon , with only two cases . thus , it was difficult to diagnose in our case because the patient was of advanced old age ( 87 years ) . several hypotheses have been put forward : microtraumatic origin , repeated stretch injuries causing degeneration of the arterial adventitia,9 embryologic origin , embryological displacement of mucin - secreting cells into the adventitia of the artery from endothelium of the knee joint,10 and ganglion formation ; cyst is a true ganglion of the vessel wall.11 treatment of cad typically consists of complete surgical resection of the diseased arterial segment with reversed saphenous vein graft interposition.4 because of both the high incidence of recurrence and the risk of dissection or rupture , percutaneous transluminal angioplasty and needle aspiration were ineffective.12 thus , we decided to treat by resection and autovein grafting because of the lowest recurrence rate . typically , duplex sonography , angiography , and mri are used to establish a diagnosis.3,4 body surface sonography is useful for identifying the cyst and diagnostic imaging of cad . unfortunately , the specificity of duplex sonography is dependent on the skill of the technician . although ivus is an invasive imaging device , ivus finding might be one of the adjunctive tools as our case . ivus excluded atherosclerosis , hematoma , aneurysm , and dissection and clearly identified the extravascular cyst that compressed the lumen in real time ( fig . cad is a rare disease ; thus , ivus findings might provide unique diagnostic clues in patients with cad and be one of the useful and feasible methods for evaluating cad . although uncommon , cad should be considered as a potential cause of intermittent claudication by the lesion of the popliteal artery . our report raises the possibility that diagnosis of cad supported by ivus device is suitable .