This is Barry Bellosis, one of the musculoskeletal radiology fellows at Stanford University. 19 year old male with three year history of bilateral exertional leg pain concerned for popliteal artery entrapment. The patient in this case initially presented with his ultrasound of the popliteal fossa. Here on our at-rest imaging, we can see a widely patent popliteal artery. At our active plantar flexion and dynamic study, we can see that there is complete collapse of the popliteal artery. Here we can see the same imaging. We can see a widely patent popliteal artery and here in our plantar flexion, we can see that it's completely compressed. The patient also underwent a diagnostic angiogram. Diagnostic angiogram has been the modality used for a long time for diagnosis of popliteal artery entrapment. However, it cannot show the soft tissue structures leading to the occlusion of the artery and cannot identify the underlying cause. Such as for instance in this patient, we have this right lower extremity showing widely patent popliteal artery at rest and active plantar flexion, we can see that there is severe narrowing of the popliteal artery. On the contralateral side, we can again see a patent popliteal artery at rest and severe stenosis on active plantar flexion. This patient's diagnosis is compatible with popliteal artery entrapment. However, the cause could not be elucidated from this diagnostic angiogram. This is on a different patient. I see the angiogram with contrast. Here the patient at rest, we can see that the popliteal artery is widely patent from the popliteal fossa all the way to the tibia and fibula. On active plantar flexion, here we can see that there is narrowing of the popliteal artery by larly at the level of the popliteal fossa and at the level of the tibial plateau, we can see that it is severely narrowed and again opacified normally at the level of the mid tibial diaphysis. CT angiogram is also favored for evaluating this as it is more accessible and can give us a sense of a possible cause for the popliteal artery entrapment. However, there is associated ionizing radiation. This is on the same patient just demonstrating this region. Here we can see at the active plantar flexion a widely narrowed popliteal artery also seen on the contralateral side on the left leg. MRI and MRA without contrast has been a promising modality in evaluating popliteal artery entrapment. The advantages intrinsic to this modality include the non-ionizing radiation, the multi-planar capabilities, high soft tissue contrast and and even avoidance of iodinated contrast material and non-invasive nature. You can also show the abnormal anatomy responsible for the entrapment if there is any. Here, this is an MRA without contrast. We can see that at rest we have a widely patent popliteal artery and active plantar flexion. We can see that there is mildly narrowed popliteal artery compared to the contralateral side, which is normal both at rest and in active plantar flexion. Just one of the common anatomic variants predisposing to popliteal artery entrapment. So this is our MRI without contrast demonstrating accessory slip of the medial head of the gastrocnemius. This slip of the gastrocnemius may arise from the intercondylar notch and passing between the popliteal artery as we can see here and the popliteal vein and can cause mass effect on the adjacent popliteal artery. Additional accessory slip that may predispose patients to popliteal artery entrapment includes the lateral head of the gastrocnemius. It is an accessory slip that may arise more medially from the posterior femur but maintaining its position that is lateral to the popliteal artery right here and its attachment more medial to the femoral condyle as we can see here.

2nd Edition, CASE 56

2nd Edition

Vascular

popliteal artery entrapment

MRI

diagnostic angiogram

gastrocnemius muscle

soft tissue assessment