Aneurysm

An aneurysm is a permanent, localised dilatation of an artery to at least 150% of its expected normal diameter. Dilatation under that threshold is ectasia, and generalised dilatation is arteriomegaly or aneurysmosis.

Morphological and structural types

• True aneurysm: involves all three layers of the arterial wall (intima, media, adventitia).
• False aneurysm (pseudoaneurysm): contained rupture with a cavity bounded by thrombus and surrounding tissue, usually after trauma, catheterisation, anastomotic disruption, infection or erosion.
• Fusiform: circumferential and symmetric. Saccular: an eccentric outpouching with a neck, with higher rupture risk at smaller size.
• Dissecting aneurysm: dilatation after dissection.

Pathogenesis

• Degenerative disease from matrix metalloproteinase activity and loss of elastin and smooth muscle, with chronic inflammation, is the common pathway in the abdominal aorta.
• Laplace's law explains growth: wall tension increases with radius and pressure, so enlargement accelerates and hypertension speeds rupture.
• Mechanisms include atherosclerosis, medial degeneration (cystic medial necrosis), genetic connective tissue disorders (Marfan syndrome, Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome, familial thoracic aortic aneurysm), vasculitis (Takayasu arteritis, giant cell arteritis, polyarteritis nodosa, Kawasaki disease, Behçet disease), infection (mycotic), trauma, and congenital weakness (berry aneurysm).

Common sites and features

• Abdominal aorta (infrarenal): the commonest, with risk factors of male sex, age over 65, smoking, hypertension and family history.
• Thoracic aorta: root, ascending, arch and descending.
• Iliac arteries: usually with aortic disease, and isolated common iliac aneurysms exceeding 3 cm are repaired at 3.5 cm.
• Popliteal: the commonest peripheral aneurysm, bilateral in about half, with 40% having an abdominal aortic aneurysm. Complications are thrombosis and distal embolisation (more than rupture).
• Femoral: often a false aneurysm after catheterisation or graft anastomosis.
• Visceral: splenic (the commonest, 60%, associated with pregnancy, portal hypertension and pancreatitis), hepatic, superior mesenteric, coeliac, gastroduodenal and renal artery aneurysms.
• Intracranial saccular (berry): at circle of Willis bifurcations. Subarachnoid haemorrhage is the principal complication.
• Mycotic aneurysm: infection of the vessel wall by Staphylococcus aureus, Salmonella, Streptococcus or other organisms, from bacteraemia, endocarditis or contiguous infection.

Complications are rupture, thrombosis, distal embolisation, compression of adjacent structures, aortoenteric or aortocaval fistula, and infection.

Most aneurysms are asymptomatic and are found incidentally or by screening.

Symptoms and signs by site

• Abdominal aortic: pulsatile, expansile abdominal mass, with abdominal, back or flank pain in symptomatic or expanding aneurysms. Rupture presents with the triad of severe abdominal or back pain, hypotension and a pulsatile mass.
• Thoracic: chest or back pain, hoarseness (recurrent laryngeal nerve), dysphagia, stridor or cough from compression, aortic regurgitation murmur, superior vena cava syndrome.
• Popliteal: a pulsatile popliteal mass, calf swelling from vein compression, or acute limb ischaemia and blue toe syndrome.
• Femoral false aneurysm: pulsatile groin mass with a bruit after puncture.
• Splenic: often silent, with left upper quadrant pain. Rupture in pregnancy has a high maternal and fetal mortality.
• Visceral: epigastric pain, or gastrointestinal bleeding and haemobilia (hepatic).
• Intracranial: thunderclap headache, oculomotor palsy (posterior communicating artery aneurysm).
• Mycotic: fever, pain and a rapidly enlarging pulsatile mass with bacteraemia.

Red flags

• Sudden severe pain, new tenderness over a known aneurysm, syncope and hypotension, which indicate rupture or expansion.
• Acute limb ischaemia, which suggests distal embolisation or thrombosis.
• Fever with a pulsatile mass.
• Gastrointestinal haemorrhage after aortic graft surgery, which suggests aortoenteric fistula.

Differential diagnosis includes tortuous aorta, pancreatic mass, lymphadenopathy, abdominal mass overlying the aorta, mediastinal mass, soft tissue tumour and Baker cyst (popliteal fossa).

Imaging confirms the diagnosis and defines size, shape and relation to branches. Measure the maximum diameter perpendicular to the vessel axis, and use the same modality in follow-up for comparison.

Modalities

• Duplex ultrasound: screening and surveillance for the abdominal aorta and peripheral arteries, with accuracy within 3 mm.
• CT angiography: the gold standard for planning, showing wall calcification, thrombus, neck and branch anatomy, rupture and leak.
• MR angiography: for patients unable to receive iodinated contrast, with the caveat that gadolinium in severe renal failure needs group II agents.
• Catheter angiography: reserved for therapeutic access and complex peripheral or visceral disease.
• Echocardiography: for root and ascending aorta, plus screening of the valve and left ventricle.
• Intracranial aneurysm: CT angiography or MR angiography, with catheter angiography for subarachnoid haemorrhage with negative studies.

Screening

• Single ultrasound of the abdominal aorta in men aged 65 to 75 who have ever smoked, and selectively in women who have smoked or have a family history. First-degree relatives of those with aneurysm are screened.
• Screen for associated aneurysms: popliteal and femoral duplex when abdominal aortic aneurysm is present, and vice versa.

Additional evaluation

• Fasting lipids, HbA1c, creatinine and eGFR, CBC, ESR and CRP.
• Blood cultures and syphilis serology, and PET CT or labelled white cell scan for suspected infected aneurysm.
• Genetic testing (FBN1, TGFBR1/2, SMAD3, TGFB2/3, ACTA2, MYH11, COL3A1) for young patients, family history or syndromic features.
• Preoperative cardiac, pulmonary and renal risk assessment.

Medical therapy for all patients

• Smoking cessation (the most effective measure for slowing growth), with varenicline (0.5 mg daily for 3 days, 0.5 mg twice daily for 4 days, then 1 mg twice daily for 12 weeks).
• Blood pressure below 130/80 mmHg. Beta blockers (propranolol 40 to 160 mg twice daily or bisoprolol) and ACE inhibitors or ARBs are useful.
• High-intensity statin (atorvastatin 40 to 80 mg daily) and aspirin 75 to 100 mg daily for cardiovascular protection.
• Avoid fluoroquinolones (ciprofloxacin, levofloxacin), which increase aortic aneurysm and dissection risk. Avoid heavy isometric straining.
• Doxycycline and other matrix metalloproteinase inhibitors have not reduced growth in trials.

Surveillance intervals (abdominal aorta)

• 3.0 to 3.4 cm: every 3 years.
• 3.5 to 4.4 cm: every year.
• 4.5 to 5.4 cm: every 3 to 6 months.

Repair thresholds by site

• Abdominal aortic: 5.5 cm in men, 5.0 cm in women, growth over 1 cm per year (or over 0.5 cm in 6 months), symptoms, or saccular morphology.
• Thoracic: ascending 5.5 cm (lower thresholds in Marfan syndrome, bicuspid valve and Loeys-Dietz syndrome), descending 5.5 cm for endovascular repair.
• Popliteal: 2 cm or greater, any size when thrombosed with acute ischaemia, or with distal embolisation.
• Femoral: 2.5 to 3 cm, or when false aneurysm is enlarging.
• Iliac: 3.5 cm.
• Visceral: splenic 2 cm or greater in women of childbearing age, those pregnant, and those with portal hypertension or planned transplant, or when symptomatic. Renal 2 to 3 cm, and hepatic, superior mesenteric and coeliac aneurysms at any size when symptomatic or 2 cm and above.
• Mycotic aneurysms need repair irrespective of size.

Open and endovascular repair

• Endovascular aneurysm repair has lower 30-day mortality (about 1 to 2% versus 3 to 5% for open repair) but requires lifelong imaging, and carries re-intervention rates of 10 to 20% from endoleak. It needs suitable proximal neck anatomy.
• Open repair offers durability in younger, fit patients and in unsuitable anatomy.
• Perioperative care includes continuation of aspirin and statin, cefazolin 2 g IV, heparin during clamping, and coronary assessment.

Specific situations

• Ruptured aneurysm: immediate transfer, permissive hypotension (systolic 70 to 90 mmHg), limited crystalloid, early blood product resuscitation, and emergency endovascular or open repair.
• Popliteal aneurysm with acute ischaemia: thrombolysis or thrombectomy, then bypass with exclusion of the aneurysm using vein.
• Femoral false aneurysm: ultrasound-guided thrombin injection (500 to 1,000 units) for small, narrow-necked lesions, otherwise surgical repair.
• Mycotic aneurysm: prolonged IV antibiotics (vancomycin 15 to 20 mg/kg every 8 to 12 hours plus piperacillin-tazobactam 4.5 g every 6 hours, adjusted to cultures) for 6 weeks or longer, with debridement and in situ or extra-anatomic reconstruction.
• Intracranial aneurysm: coiling or clipping, and nimodipine 60 mg every 4 hours after rupture.
• Genetic aneurysm syndromes: beta blocker or losartan (50 to 100 mg daily), earlier surgical thresholds, and screening of first-degree relatives.
• Inflammatory aneurysm: immunosuppression before repair if there is active vasculitis (prednisolone 40 to 60 mg daily, then tocilizumab or methotrexate as appropriate).

Follow-up

• Surveillance imaging after repair: CT angiography at 1 month and 12 months after endovascular repair, then duplex annually if stable. Endoleak management depends on type (type I and III need urgent treatment, type II is observed unless the sac grows).
• Lifelong cardiovascular risk management.