Cystic Adventitial Disease of the Popliteal Artery

Cystic adventitial disease is a rare condition in which mucin filled cysts form in the adventitia of an artery and compress the lumen. It causes intermittent claudication, and sometimes acute occlusion, in people with few atherosclerotic risk factors.

It accounts for about 1 in 1000 cases of claudication. The popliteal artery is involved in about 85% of cases, and the external iliac, common femoral, radial and ulnar arteries are sometimes affected. It occurs mostly in men aged 30 to 50 (male to female ratio of about 5 to 15 to 1) and is almost always unilateral.

Several theories exist. Most evidence supports a ganglion like origin from the adjacent joint capsule, with a connecting channel to the knee joint, or ectopic mesenchymal cells in the adventitia. Repeated trauma and a systemic mucin forming process are less favoured.

Natural history is progression to occlusion in many patients, and spontaneous resolution is rare. A sudden increase in cyst size can cause abrupt worsening of claudication.

Pathophysiology.

Mucoid material accumulates between the media and adventitia, which narrows the lumen in a smooth, eccentric or concentric way. Flow reduces first with exertion, then at rest, and thrombosis can follow.

The cyst may communicate with the knee joint, which explains recurrence after simple aspiration. Intact intima and media separate it from atherosclerosis and entrapment, and endovascular dilatation fails because the cyst fluid and wall recoil.

Sudden or progressive calf claudication in a healthy man of middle age, sometimes with a short history, and rapid worsening. Foot pulses are present at rest in many patients and disappear with knee flexion (the Ishikawa sign), which is a distinguishing feature. A popliteal bruit or a palpable fullness may be found. Occlusion causes rest pain, coldness and critical ischaemia. Some have knee joint symptoms.

• Resting ankle brachial index may be normal or reduced, with a fall on knee flexion. The index does not fall with active plantar flexion, unlike in entrapment.
• Duplex ultrasound: anechoic or hypoechoic cystic wall lesion in the popliteal artery with luminal narrowing (the cyst is seen in the adventitia), and flow velocity change.
• MRI is the best test: a well defined, T2 hyperintense cystic lesion in the arterial wall with a normal lumen proximal and distal, and a possible communication with the joint.
• CT angiography: smooth, eccentric stenosis (the scimitar sign) or a smooth hourglass narrowing with a low density mural cyst, or occlusion. Catheter angiography is used only when planning intervention.
• Routine bloods for atherosclerotic risk: lipids, glucose, full blood count.

Differential diagnosis.

• Popliteal artery entrapment syndrome and popliteal aneurysm.
• Atherosclerotic stenosis and fibromuscular dysplasia.
• Baker cyst, ganglion and soft tissue tumour.
• Buerger disease, embolism and arterial dissection.

Surgical treatment is the definitive treatment. The choice depends on artery patency.

• Patent artery with stenosis: cyst excision with enucleation (evacuation of the cyst through an arteriotomy or from the outside, with resection of the cyst wall and ligation of any joint communication), with or without a vein patch. Symptoms usually resolve and recurrence is low when the connecting channel is divided.
• Occluded or severely damaged artery: resection of the diseased segment with an interposition graft or bypass using reversed great saphenous vein. Five year patency is high, and results are better than with prosthetic grafts.
• Percutaneous aspiration under ultrasound or CT control relieves symptoms for a short time, with recurrence in about one third of patients or more. It is used for patients unfit for surgery or as a bridge.
• Endovascular angioplasty and stenting give poor and short lived results, and stents fracture or fail, so they are avoided except as rescue in unfit patients.
• Cefazolin 2 g intravenously within 60 minutes before incision (3 g when weight is over 120 kg); heparin 70 to 100 units/kg intravenously before clamping, reversed with protamine 1 mg for each 100 units given in the previous 2 to 3 hours (maximum 50 mg, given slowly).

Acute occlusion.

• Unfractionated heparin 80 units/kg intravenous bolus (usual 5000 units), then 18 units/kg/h, aPTT 1.5 to 2.5 times control.
• Catheter directed thrombolysis for a viable or marginally threatened limb: alteplase 0.5 to 1 mg/h (usual total up to about 40 mg) with low dose heparin 500 units/h, then definitive surgery. Contraindications are previous intracranial haemorrhage, ischaemic stroke in the last 6 months, intracranial neoplasm, active bleeding, and major surgery or trauma in the last 3 weeks.
• Surgical thrombectomy and reconstruction for an immediately threatened limb, with fasciotomy when indicated.

Medical therapy.

• Aspirin 75 to 100 mg orally once daily, lifelong after reconstruction.
• Anticoagulation for 3 months after thrombosis (apixaban 5 mg twice daily, 2.5 mg twice daily if two of age 80 or over, weight 60 kg or under, creatinine 133 micromol/L or over).
• Atorvastatin 40 to 80 mg daily only if atherosclerosis is present.
• Analgesia as needed, and supervised exercise for residual claudication.

Monitoring. Duplex and ankle brachial index at 1 month, 3 months, 6 months and 12 months, then yearly (recurrence is possible for 5 years or more). MRI when symptoms return.

Referral and escalation. Refer every confirmed case to a vascular surgeon. Same day referral for acute ischaemia and rest pain.

Special groups.

• Pregnancy: rare; use enoxaparin 1 mg/kg subcutaneously every 12 hours when anticoagulation is needed, and avoid warfarin and direct oral anticoagulants.
• Women and extra-popliteal sites: the same principles apply to iliofemoral and upper limb disease, with surgery again the usual treatment.
• Kidney impairment: limit contrast volume and give enoxaparin 1 mg/kg once daily when creatinine clearance is under 30 mL/min.
• Region specific: ultrasound and MRI are enough for diagnosis where catheter angiography is unavailable.