Cystic Adventitial Disease of the Popliteal Artery on Ultrasound: Duplex Diagnosis
Definition and Pathogenesis
Cystic adventitial degeneration (CAD) is the accumulation of mucinous (gel-like) fluid in a cyst between the adventitia and media of the arterial wall, compressing the lumen from within the wall. The classic location is the popliteal artery (approximately 85% of cases), less commonly the femoral or iliac arteries.
Ultrasound Appearance
The key feature is an anechoic cyst within the wall of the popliteal artery, narrowing the lumen, without calcium and without atheroma. On color Doppler/spectral examination, there is lumen narrowing by the cyst. In B-mode, a cyst is identified in the wall. The typical patient is middle-aged with intermittent claudication and normal resting ABI.
Dynamic Tests
Dynamic tests may exacerbate the narrowing. A clinical clue is the Ishikawa sign: disappearance of the foot pulse when the knee is flexed.
Differential Diagnosis of Non-Atherosclerotic Arteriopathies
| Parameter | Muscle Compression (RAES) | Cystic Adventitial Degeneration (CAD) | Endofibrosis (EIAE) |
|---|---|---|---|
| Mechanism | Muscle compression | Cyst in adventitia | Mechanical wall trauma, intimal fibrosis |
| Segment | Popliteal artery | Popliteal (~85%) | External iliac |
| ABI rest / stress | Normal / ↓ | Normal / ↓ | Normal / ↓ |
| B-mode | Normal or compression | Cyst in wall | Wall thickening/tortuosity |
| Color Doppler / test | Flow disappearance on flexion | Lumen narrowing by cyst | Normal → ↓ with stress |
Clarifying Imaging
Duplex is usually sufficient for diagnosis; CTA/MRA clarify the extent and nature of the cyst.
Frequently asked questions
What is the characteristic ultrasound appearance of CAD?
An anechoic cyst within the wall of the popliteal artery, narrowing the lumen, without calcium and without atheroma in a middle-aged patient with claudication and normal resting ABI.
Where is CAD most commonly located?
The classic location is the popliteal artery (approximately 85% of cases), less commonly the femoral or iliac arteries.
Is duplex sufficient for diagnosis or is additional imaging needed?
Duplex is usually sufficient for diagnosis; CTA/MRA clarify the extent and nature of the cyst.
What is the Ishikawa sign?
A clinical clue is the disappearance of the foot pulse when the knee is flexed.
How to differentiate CAD from muscle compression of the popliteal artery in a test?
In CAD, color Doppler shows lumen narrowing by the cyst, whereas in muscle compression (RAES), there is flow disappearance on flexion; also, in RAES, provocation results in flow disappearance/inversion or a drop in PSV >50%.