Aneurysms & Dissections

 

• Background

  Definitions

  • Aneurysm: dilation of artery which is bound by all 3 walls of the vessel (intima, media, adventitia). At risk of dissection and/or rupture.
  • Pseudoaneurysm: bleed from an artery which pools in an enclosed compartment next to the vessel.
  • Dissection: intima tears and blood enters, separating it from the media and forming a false lumen, which can become aneurysmal and/or lead to reduction of distal blood flow.

  Aneurysm locations

  Can occur anywhere, but common sites are:

  • Aorta: abdominal (commonest) or thoracic. The former is more likely to rupture, and the latter is more likely to dissect (or dissection may come first and lead to aneurysm).
  • Major arteries: popliteal (commonest), femoral, axillary, carotid.
  • Circle of Willis (saccular/berry aneurysms).

• Complications

  • Rupture
  • Dissection
  • Thrombosis or embolism.
  • Pressure on neighbouring structures.
  • Fistula into neighbouring structures.
  • Infection: mycotic aneurysm.

• Abdominal aortic aneurysm (AAA)

  Location

  Usually below the level of the renal arteries ('infrarenal').

  Risk factors

  • Atherosclerosis and its risk factors: smoking, HTN, cholesterol.
  • Demographic: male, ↑age.
  • Family history.
  • Rarely, due to a specific inflammatory (e.g. Behcet's) or connective tissue (e.g. Marfan's) cause.

  Presentation

  Stable aneurysm:

  • Usually asymptomatic. May be detected through screening.
  • On examination, there may be a pulsatile mass visible or palpable in the abdomen. Pain on palpation suggests ↑risk of rupture.

  Rupture:

  • Abdominal, flank, or back pain.
  • Shock
  • Syncope. Consider ruptured AAA in all older men (>55) or women (>70) presenting with collapse.

  Investigations

  Bloods:

  • Basic bloods: FBC, coag, U&E, LFT.
  • Pre-op: cross-match.

  Imaging:

  • Diagnosis is usually with US. One off screening is offered to all men in the UK at age 65, and considered for women with risk factors at age 70.
  • CT contrast or MRI angio provide more information, and are used if US not clear or before planned surgery. CT may show 'high-attenuating crescent', a bleed within the aneurysmal wall suggesting imminent rupture.
  • If ruptured, may proceed to surgery without imaging (or just bedside US) if unstable, otherwise CT if stable.

  Management

  Conservative:

  • Regular US monitoring if small and asymptomatic.
  • Manage risk factors.
  • Contact DVLA if >6 cm.

  Surgery:

  • Indications: aneurysm ≥5.5 cm. At this point, the risk of rupture overtakes the risk of surgery for most, though this may differ in those who are not operatively fit.
  • Open repair involves clamping the artery and sewing a graft inside the aneurysm sac to replace it.
  • Endovascular aneurysm/aortic repair (EVAR) is a less invasive alternative, whereby stents are inserted through the femoral artery. Quicker recovery, lower short-term mortality, and no long-term mortality difference. Risk of endovascular leaks ('endoleaks'), which need to be monitored with regular CT or US. Preferred if patient has co-morbidities (esp. multiple previous abdo surgeries).
  • 1.5% in-hospital mortality risk after elective repair.

  Ruptured AAA:

  • Resuscitation with blood products.
  • Emergency repair: open repair or EVAR.
  • 80% mortality risk, 40% if operated.

• Thoracic aortic aneurysm and aortic dissection

  Background

  Distinct but related pathologies:

  • Aneurysms are at increased risk of dissection.
  • Conversely, the false lumen of a dissection can become aneurysmal.

  Causes

  • CVD risk factors: hypertension, cholesterol, smoking.
  • Aortic regurgitation. This can also be a complication of TAA.
  • Marfan's or Ehlers-Danlos.
  • Familial
  • Mycotic aneurysm: cause by infection, usually bacterial (despite name sounding fungal).
  • Syphilitic aortitis. By convention, not considered a mycotic aneurysm.
  • Inflammatory: RA, Behcet's, Takayasu's, giant cell arteritis.

  Presentation

  Aneurysm:

  • Usually asymptomatic, with pain suggesting a high risk of rupture.
  • Unlike abdominal aneurysm, TAA's tend to dissect first rather than rupture. However, it can then progress to rupture.

  Dissection:

  • Tearing or sharp pain, maximal at onset (unlike MI, which builds), radiating to back. Anterior pain suggests ascending aorta, while posterior (infrascapular) pain suggests descending.
  • BP: hypotension, pulse deficit (unequal BP between arms, seen in 15%).
  • New murmur of aortic regurgitation.
  • May lead to MI through extension to coronary arteries.
  • Neurological deficits.
  • Defined as chronic if symptoms >2 weeks. Lower risk of complications.

  Rupture:

  • Shock, haemoptysis, or tamponade.

  Investigations

  • ECG: may show MI.
  • CXR may show widened mediastinum, but ↓sensitivity.
  • Definitive diagnosis usually on CT, though may also be seen on echo and MRI.

  Management

  Aneurysm:

  • Repair via open surgery or EVAR if: unstable, symptomatic, or >5.5 cm. Risk of paraplegia.

  Dissection:

  • Aggressive BP lowering with labetalol IV or esmolol IV.
  • Type A involves the Ascending aorta and requires surgery.
  • Type B involves the descending aorta, Beyond the left subclavian artery, and only requires surgery if there is rupture or worsening pain.
  • Chronic, stable dissections can often be managed medically with antihypertensives.

• Popliteal aneurysm

  Presentation

  • Sign: easily palpable popliteal pulse.
  • May have co-morbid abdominal aneurysm.
  • More likely to cause thrombosis than rupture, leading to acute limb ischaemia.

  Management

  • Treat acute ischaemia with femoropopliteal bypass.
  • If aneurysm discovered before thrombosis occurs, treat with grafting.