Aortic Arch Aneurysm

An aortic arch aneurysm is dilatation of the transverse arch, with or without its three branch vessels. It is uncommon, about 10% of thoracic aortic aneurysms, and it often extends from the ascending or descending aorta.

Causes are atherosclerosis and degeneration, chronic dissection, aortitis (Takayasu, giant cell), infection (syphilis, tuberculosis, bacterial), traumatic pseudoaneurysm at the isthmus, coarctation, genetic aortopathy, and congenital arch anomalies.

Most are found incidentally. Symptoms come from compression of neighbouring structures, embolisation or rupture.

The operation is among the most demanding in cardiac surgery because the brain and spinal cord must be protected.

Pathophysiology. Medial degeneration weakens the arch wall. Compression of the left recurrent laryngeal nerve, trachea, left main bronchus, oesophagus and superior vena cava produces symptoms. Atheroma and thrombus within the sac can embolise to the brain.

Risk of rupture rises with diameter, and 55 to 60 mm or more is a common surgical threshold.

• Often asymptomatic.
• Hoarseness (left recurrent laryngeal nerve palsy, Ortner syndrome), cough, stridor, dyspnoea, dysphagia, and facial swelling from superior vena cava obstruction.
• Chest, neck or interscapular pain. Horner syndrome.
• Stroke, transient ischaemic attack or arm embolism.
• Haemoptysis or haematemesis from erosion into the airway or oesophagus (sentinel bleed).
• Arm pressure difference or absent pulses with branch involvement or aortitis.

Red flags.

• Sudden severe pain, syncope or hypotension (rupture or dissection)
• Haemoptysis or haematemesis
• Stroke or transient ischaemic attack
• Rapid growth (5 mm or more in 1 year) or diameter of 55 mm or more
• Fever and raised inflammatory markers

• Chest X-ray. Widened or distorted aortic knuckle, tracheal deviation.
• CT angiography. Maximum diameter, extent, branch vessel involvement, wall thrombus, calcification, and relation to the trachea and oesophagus. Needed for planning, together with imaging of the whole aorta.
• MR angiography for follow up without radiation. Transoesophageal echocardiography for plaque and valve disease.
• Laryngoscopy for vocal cord palsy. Bronchoscopy or endoscopy only with suspected erosion and a stable patient.
• Cause. ESR, CRP, syphilis serology, tuberculosis tests, blood cultures, ANCA and IgG4. FDG PET-CT for inflammatory or infected disease.
• Preoperative. Carotid and vertebral imaging, coronary assessment, spirometry and creatinine.

Differential diagnosis.

• Aortic dissection and intramural haematoma
• Penetrating atherosclerotic ulcer
• Aortic pseudoaneurysm and mycotic aneurysm
• Kommerell diverticulum and other arch anomalies
• Mediastinal mass, thyroid goitre and lymphadenopathy
• Aortitis

Medical.

• Blood pressure under 130/80 mm Hg and resting heart rate 60 to 70/min where tolerated.
• Bisoprolol 2.5 mg orally once daily, increased to 5 to 10 mg once daily, maximum 20 mg daily (do not exceed 10 mg daily at creatinine clearance under 20 mL/min or in severe liver impairment). Contraindicated in severe asthma, sinus node disease and high grade atrioventricular block without a pacemaker.
• Atorvastatin 40 to 80 mg orally once daily for atherosclerotic disease, with liver enzymes at baseline and 3 months, and aspirin 75 to 100 mg once daily (usual maximum 325 mg daily) for atherosclerotic disease or embolic events.
• Stop smoking, avoid fluoroquinolones and stimulants.

Indications for intervention. Diameter of 55 mm or more, or 50 mm or more in connective tissue disease. Also symptoms, rapid growth, saccular morphology, rupture or contained rupture, and embolisation. Smaller sizes in genetic disease.

Options.

• Open total arch replacement with a frozen elephant trunk, under moderate hypothermic circulatory arrest (24 to 28 degrees Celsius) with selective antegrade cerebral perfusion. Operative mortality is about 5 to 10% in experienced centres, with stroke in about 5 to 8% and spinal cord injury in about 2 to 8% when a stented segment extends into the descending aorta.
• Hybrid repair: surgical debranching of the neck vessels with thoracic endovascular repair, for patients at high risk for open surgery.
• Branched or fenestrated endovascular repair in specialist centres with suitable anatomy.
• Spinal cord protection with cerebrospinal fluid drainage (keep pressure under 10 mm Hg) and a mean arterial pressure of 80 to 90 mm Hg when the stented segment is long.
• Prophylaxis for endovascular repair: cefazolin 2 g intravenously as a single dose 30 to 60 minutes before incision (3 g if over 120 kg), with vancomycin 15 mg/kg intravenously for severe penicillin allergy or MRSA.
• After an endovascular graft, aspirin 75 to 100 mg once daily long term. Anticoagulation only when another indication exists.

Contained rupture or acute syndrome (emergency). Esmolol 500 microgram/kg intravenously over 1 minute, then infusion 50 microgram/kg/min, repeating the bolus and increasing the infusion by 50 microgram/kg/min every 4 to 5 minutes, maximum 200 microgram/kg/min, to a heart rate near 60/min and systolic pressure of 100 to 120 mm Hg. Morphine 2.5 to 5 mg intravenously, titrated. Immediate CT angiography, crossmatched blood, and urgent open or endovascular repair.

Inflammatory and infected aneurysm. Treat with the specialist team: prednisolone 0.5 to 1 mg/kg orally once daily (maximum 60 mg) for Takayasu or giant cell arteritis with a slow taper, and operate when inflammation is controlled. Infected aneurysm needs prolonged intravenous antibiotics by organism with surgical resection.

Special groups.

• Pregnancy: surgery during pregnancy is reserved for life threatening disease. Continue metoprolol tartrate 25 to 100 mg orally twice daily, maximum 200 mg daily in this setting, and stop statins.
• Older adults: favour hybrid or endovascular options when frailty is significant.

Monitoring. CT or MR angiography at 6 months after diagnosis, then yearly if stable and every 6 months at 45 mm or more or with growth. After endovascular repair, CT at 1 month, 6 months and 12 months, then yearly for endoleak and migration. After open repair, imaging at 1 year then every 2 to 3 years.

Referral and escalation. Refer to a centre with an aortic team and cerebral and spinal protection. Emergency for rupture, dissection or haemoptysis.