Thoracic Aortic Aneurysm

Thoracic aortic aneurysm is dilatation of the aorta to more than 150% of the expected diameter at a given segment. Incidence is around 6 to 10 per 100,000 per year. Normal diameters are about 3.5 cm at the ascending aorta, 3.0 cm at the arch and 2.5 cm at the descending aorta, varying with age, sex and body size.

Segments

• Root and ascending (60%): from degenerative disease, bicuspid aortic valve, and heritable disease.
• Arch (10%).
• Descending (30%).
• Thoracoabdominal: classified by Crawford types I to V.

Causes

• Degenerative (medial degeneration) and atherosclerotic: most descending aneurysms, with hypertension and smoking.
• Bicuspid aortic valve: present in 1 to 2% of the population, with aortopathy in about 30 to 50%.
• Heritable thoracic aortic disease:
• Marfan syndrome (FBN1): root dilatation, ectopia lentis, skeletal features.
• Loeys-Dietz syndrome (TGFBR1, TGFBR2, SMAD3, TGFB2, TGFB3): dissection at small diameters, arterial tortuosity, hypertelorism, bifid uvula.
• Vascular Ehlers-Danlos syndrome (COL3A1): arterial rupture without dilatation.
• Familial thoracic aortic aneurysm and dissection (ACTA2, MYH11, others).
• Turner syndrome, and ADPKD.
• Inflammatory and infectious: Takayasu arteritis, giant cell arteritis, syphilitic aortitis, IgG4-related disease, Behçet disease, and bacterial aortitis.
• Traumatic: pseudoaneurysm at the isthmus after deceleration.
• Post-dissection aneurysm.

Natural history: growth averages 0.1 cm per year in the ascending aorta and 0.3 cm per year in the descending aorta. Dissection and rupture risk is low until diameters reach 5.5 cm and rises steeply after 6 cm, with annual risk of rupture or dissection of about 3.6% at 5.0 to 5.9 cm in the ascending aorta and about 6.9% at 6.0 cm or above. The aortic size index (diameter divided by body surface area) and aortic height index are used in short individuals.

Most patients are asymptomatic and are found incidentally on imaging or echocardiography.

Symptoms from expansion or compression

• Chest or back pain (constant, boring), though sudden severe tearing pain indicates dissection.
• Dyspnoea and stridor (tracheal or bronchial compression), cough, haemoptysis.
• Dysphagia (dysphagia aortica), hoarseness (left recurrent laryngeal nerve), Horner syndrome, hiccups from phrenic nerve irritation.
• Superior vena cava syndrome.
• Heart failure from aortic regurgitation in root dilatation.

Signs

• Diastolic murmur of aortic regurgitation, bounding pulses, a widened pulse pressure.
• Bruits, pulse deficits, upper limb blood pressure differences, and signs of connective tissue disease (arachnodactyly, pectus deformity, joint hypermobility, skin hyperextensibility, high arched palate, striae).
• Findings of bicuspid valve: ejection click, systolic murmur.

Rupture and dissection present with sudden severe pain, syncope, shock, haemothorax, haemoptysis or haematemesis (aorto-oesophageal fistula), or tamponade.

Differential diagnosis includes mediastinal tumour, lymphadenopathy, hiatal hernia, oesophageal disease, acute coronary syndrome, pulmonary embolism, pericarditis and musculoskeletal pain.

Red flags: new pain in a known aneurysm, rapid growth (over 0.5 cm per year), family history of dissection, young age, and syndromic features.

Imaging

• Transthoracic echocardiography: root and proximal ascending aorta, valve morphology, regurgitation and ventricular function. Use as screening in first-degree relatives and in bicuspid valve disease.
• CT angiography (ECG-gated): the standard for sizing the entire aorta, wall thrombus, calcification and branch involvement. Measure inner wall to inner wall or outer to outer consistently.
• MR angiography: serial surveillance without radiation, particularly in younger patients and genetic syndromes.
• Transoesophageal echocardiography: for intraoperative assessment and dissection.
• Chest radiograph is insensitive but may show a widened mediastinum, tracheal deviation or calcified aortic knuckle.

Laboratory and genetic testing

• Lipids, HbA1c, creatinine, ESR and CRP, syphilis serology, and ANCA or IgG4 in inflammatory aortitis.
• Genetic panel for FBN1, TGFBR1, TGFBR2, SMAD3, TGFB2, TGFB3, ACTA2, MYH11, COL3A1 and others, with cascade testing. Ophthalmology slit-lamp examination for ectopia lentis and revised Ghent criteria for Marfan syndrome.
• Screening: first-degree relatives of those with thoracic aneurysm or dissection, imaging of the whole aorta, and screening of the intracranial arteries in Loeys-Dietz syndrome and ADPKD.
• Evaluate aortic valve (bicuspid) and associated coarctation.
• Preoperative coronary evaluation (CT angiography or catheter angiography), carotid duplex, and pulmonary function tests.

Medical therapy and lifestyle

• Blood pressure below 130/80 mmHg and heart rate below 70 beats/minute. First line is a beta blocker (propranolol 40 to 160 mg twice daily, atenolol 50 to 100 mg daily, or metoprolol succinate 50 to 200 mg daily), or an ARB (losartan 50 to 100 mg daily) in Marfan and related syndromes. ACE inhibitors are alternatives.
• Statin (atorvastatin 40 to 80 mg daily) for atherosclerotic disease. Avoid fluoroquinolones.
• Avoid heavy isometric exercise (weightlifting, straining), contact sports and stimulants. Moderate aerobic exercise is encouraged.
• Stop smoking, and counsel on pregnancy risk (pregnancy with root over 4.0 to 4.5 cm carries high dissection risk).
• Beta blockers and losartan slow growth in Marfan syndrome, with modest benefit.

Surveillance

• Imaging at 6 to 12 months initially to establish the growth rate, then annually if stable. Moderate-sized aneurysms of 4.0 to 4.9 cm are imaged every 12 months. Syndromic disease or rapid growth needs 6 monthly imaging.

Indications for surgery

• Root and ascending aorta:
• 5.5 cm or more in degenerative disease.
• 5.0 cm or more in bicuspid valve with risk factors (family history of dissection, coarctation, growth over 0.3 cm per year, uncontrolled hypertension), in Marfan syndrome with risk factors, and in selected short patients.
• 4.5 to 5.0 cm in Marfan syndrome (5.0 cm standard, 4.5 cm with family history of dissection, rapid growth, severe regurgitation or planned pregnancy), and 4.0 to 4.5 cm in Loeys-Dietz syndrome (smaller thresholds with TGFBR2 mutations or severe extra-aortic features).
• 4.5 cm or more when undergoing aortic valve or coronary surgery.
• Growth of 0.5 cm in 1 year (0.3 cm per year in repeated measurements in high-risk groups), symptoms, or severe regurgitation.
• Aortic arch: 5.5 cm or more, or concomitant with ascending repair.
• Descending and thoracoabdominal: 5.5 cm or more for endovascular repair (6.0 cm or more for open repair), or earlier in connective tissue disease. Saccular aneurysms are repaired earlier.
• Symptomatic aneurysm or rupture is an emergency at any size.

Surgical and endovascular techniques

• Root and ascending replacement:
• Composite valve graft (Bentall procedure) with coronary button reimplantation, needing lifelong anticoagulation with a mechanical valve (warfarin target INR 2.5 to 3.5 for root grafts with bileaflet mechanical valve plus risk factors, or 2.0 to 3.0 with none).
• Valve-sparing root replacement (David or Yacoub procedures) in selected patients with normal leaflets, notably in Marfan syndrome.
• Supracoronary ascending graft when root is normal.
• Arch: hemiarch or total arch replacement with deep hypothermic circulatory arrest and selective cerebral perfusion, frozen elephant trunk for extensive disease.
• Descending: thoracic endovascular aortic repair (TEVAR) when landing zones are suitable (at least 2 cm of normal aorta distal to the left subclavian artery, often with carotid-subclavian bypass or chimney for zone 2). Open repair in connective tissue disease, infection or unsuitable anatomy.
• Thoracoabdominal: open repair with cerebrospinal fluid drainage (maintain CSF pressure at 10 mmHg or lower), distal perfusion, and meticulous blood pressure maintenance (mean arterial pressure at or above 80 to 90 mmHg), or branched and fenestrated endovascular devices.
• Perioperative risks: operative mortality 1 to 3% for elective root and ascending surgery in experienced centres, and 5 to 10% for arch or open thoracoabdominal repair. Stroke 2 to 5% (arch), spinal cord ischaemia in 3 to 15% for extensive descending and thoracoabdominal repair, renal failure, and bleeding.
• Perioperative antibiotic prophylaxis with cefazolin 2 g IV, plus vancomycin when MRSA risk.

Emergency care of rupture

• Immediate resuscitation with permissive hypotension (systolic 80 to 100 mmHg), blood products, control of heart rate with esmolol, and emergency TEVAR or open repair.

Postoperative and long-term follow-up

• Lifelong imaging: CT or MRI at 1, 6 and 12 months after intervention, then yearly. Residual aorta continues to be monitored, since new aneurysms and dissections occur.
• Endocarditis prophylaxis for mechanical valve or prosthetic material (amoxicillin 2 g orally one hour before dental procedures).
• Family screening and genetic counselling.
• Pregnancy: beta blockers throughout, vaginal delivery with epidural for root under 4 cm, and caesarean delivery for larger roots or dissection risk.