My Clinical Notes

• An aneurism is a localised abnormal dilation of a vessel or the wall of the heart
• True aneurysm
  • When an aneurism is bounded by the vessel or heart wall
  • Includes;
    • Atherosclerotic
    • Syphilitic
    • Congenital
    • Left ventricular aneurisms (can follow an MI)
• False aneurism (pseudoaneurism)
  • A breach in the vascular wall leading to an extravascular haematoma that freely communicates with the intravascular space

 

Causes of aortic aneurisms;

• Most common;
  • Atherosclerosis
  • Cystic degenerative change of the arterial media
• Other causes;
  • Trauma
  • Congenital defects e.g. those potentiating berry aneurisms
  • Infections – myoctic aneurisms
  • Syphilis
  • Vasculitis

 

• Aneurisms can be classified by macroscopic size and shape;
  • Saccular are round and vary in size from 5cm to 20cm in diameter
  • Fusiform involve a long segment and may be up to 20cm in diameter

 

Abdominal aortic aneurisms

 

• Atherosclerotic aneurisms occur most frequently in the abdominal aorta

 

Morphology

• Usually positioned around the renal arteries above the aortic bifurcation
• May be saccular or fusifom , up to 15cm in diameter and up to 25cm long
• Wall is weakened by thinning of the media due to atherosclerosis
• There may be granular mural thombi  which may lodge in the vessels of the kidneys and lower limbs
• May affect the origins of the renal and superior and inferior mesenteric arteries either via direct pressure of the vessels or by occluding their ostia
• Two particular types of AAA;
  • Inflammatory – of unknown origin, surrounded by fibrosis with an infiltrate of lymphocytes, plasma cells and macrophages
  • Mycotic  - atherosclerotic AAA that have become infected by circulating organisms that have become lodged in the wall – particularly associated with the bacteraemia of salmonella gastroenteritis. In these cases suppuration destroys the vessel media

 

Pathogenesis

• Most common cause is atherosclerosis
• Occurs over the age of 50, more commonly in men
• There is a genetic susceptibility beyond which the predisposes to atherosclerosis and hypertension, which may be related to connective tissue disorders
• There may be an association with increased levels of MMP which degrade components of the extracellular matrix or decreased levels of tissue inhibitor of metalloproteinases (TIMP)

 

Clinical course

• Clinical consequences include;
  • Rupture into the peritoneal cavity or retroperitoneal tissues
  • Obstruction of a vessel, particularly, iliac, renal, mesenteric or vertebral
  • Embolism
  • Impingement on an adjacent structure e.g. ureter or erosion of vertebrae
  • Presentation of an abdominal mass that simulates a tumour

 

Risk of rupture is related to the size of the vessel

• 1% per year risk of rupture for vessels 4-5cm
• 11% risk of rupture for vessels 5-6cm
• 25% risk of rupture for vessels greater than 6cm
• Most expand at a rate of 0.2 – 0.3 cm per year but 20% expand more rapidly
• The most important factor affecting aneurism growth is blood pressure

 

Syphilitic aneurisms

 

• Syphilitic involvement of the vasa vasorum of the thoracic aorta can lead to aneurismal dilation
• Morphology
• Obliterative endarteritis of the vasa vasorum rimmed by an infiltrate of lymphocytes and plasma cells
• The narrowing of the lumen of the vasa causes ischaemic injury of the aortic media
• Destruction of the media result in loss of elastic recoil and dilation
• Syphilitic involvement of the aorta favours the development of superimposed atheromatosis of the aortic rot which can envelope and occlude the ostia
• May also cause aortic valve dilatation and insufficiency resulting in left ventricular hypertrophy

 

Signs and symptoms of thoracic aneurisms are due to;

• Encroachment on mediastinal structures
• Respiratory difficulties due to encroachment on the lungs and airways
• Swallowing difficulties due to oesophageal compression
• Persistent cough due to irritation of recurrent laryngeal nerves
• Pain caused by bone erosion
• Cardiac disease as the aortic aneurism can lead to aortic valve dilation with valvular insufficiency or narrowing of the coronary ostia
• Rupture

 

 

 

Aortic dissection

 

• Dissection of blood between and along the laminar planes of the media, with the formation of a blood filled channel within the aortic wall which may rupture
• Principally occurs in 2 patient groups
  • More than 90% occur in mean aged 40 – 60 with preceding hypertension
  • The second group are younger individuals with CT abnormalities e.g. Marfan syndrome
• Other causes;
  • Iatrogenic – complication of arterial cannulation
  • Pregnancy – rarely for unknown reasons

 

Morphology

• In spontaneous dissection there is an intimal tear which extends into but not through the media
• Generally occurs within 10cm of the aortic valve
• The dissection can extend proximally along the aorta towards the heart as well as distally
• It usually ruptures outwards but can rerupture inwards into the lumen of the aorta producing a false channel
• False channels may endothelialise over time resulting in chronic dissection

 

Pathogenesis

• Risk factors;
  • Hypertension
  • Medial damage e.g. cystic degeneration
  • CT disorders e.g. Marfan syndrome (autosomal dominant disease of CT fibrillin)
• Regardless of the underlying aetiology the underlying trigger for the dissection is generally unknown
• However, once the tear has occurred, high blood pressure exacerbates progression

 

Clinical course

• Aortic dissections can be classified into 2 types;
  • Proximal lesions involving either the ascending portion of the aorta or both the ascending and descending aorta. This type is more common and are commonly called Type A
  • Distal lesions, not involving the ascending part and generally beginning distal to the subclavian artery. These are called Type B

 

• Sudden onset excruciating pain usually beginning in the anterior chest and radiating towards the back. This may be confused with that of MI
• The most common cause of death is rupture of the dissection outwards into any of the three body cavities – pericardial, pleural or peritoneal
• Retrograde dissection into the aortic root can cause disruption of the aortic valvular apparatus
• Thus the most common clinical manifestations are;
  • Cardiac tamponade
  • Aortic insufficiency
  • MI
  • Extension of the dissection into the arteries of the neck, coronary, renal, mesenteric or iliac vessels causing vascular obstruction. Compression of spinal arteries may cause transverse myelitis

This entry was posted on Wednesday, February 6th, 2008 at 3:49 pm and is filed under Cardiovascular. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.