JC WCS 28: AORTIC ANEURYSM

Dr Stephen WK Cheng

Surgery

Tue 26-11-02

The Problems

Aneurysm

Definition and Classification
    1. Fusiform (uniform enlargement)
    2. Saccular (bulge on one side),
    3. Dissecting (HT, tear inside intima of BV, blood creates channel within wall of aorta and dissects in longitudinal direction)
  1. True: all 3 layers involved (intima, media, adventitia)
  2. False: eg. Penetrating inj to artery (pseudoaneurysm) ® Laminated thrombus + Compressed fibrous tissue

Aetiology

  1. Degenerative: (a) AS (b) Medial degeneration (usage, HT) - most COMMON
  2. Inflammatory: (a) Infection (mycotic: original infection thought to be from fungus, misnomer) (b) Arteritis (inflam of arterial wall)
  3. Mechanical: (a) Traumatic (eg. Puncture artery for blood) (b) Anastomotic (eg. Bypass operation with graft not sutured correctly)
  4. Congenital: (a) Marfan's (defect in CT; tall male, spider fingers, high arched palate)

Complications

  1. Rupture: most FEARED + COMMON, as ­ size ® walls thinner (if mjr a ® can cause rapid death)
  2. Thrombosis: sac enlargement, BF ¯ laminar \ ­ thrombus
  3. Embolism: blood clot loose ® acute ischaemia (eg. Prox aneurysm ® LL DVT)
  4. Pressure effects: compress surr struc (eg. Oeso = dysphagia; SC = back pain)
  5. Infection: good nutrition from blood

Abdominal Aortic Aneurysm (AAA)

Pathology

Pathogenesis

  1. Atherosclerosis: association
  2. Genetic (defect in CT - collagen/ elastin cross-linking)
  3. Proteolytic (­ collagenase/ elastase: proteolytic enz/ MMPs ® digest elastic fibres)
  4. Haemodynamic (HT)
  5. Others (Mycotic, inflam, trauma - further weakens condition; eg. Chlamydia, bacteria)

AAA a combination of above effects

Natural History and Risk of Rupture
  1. Small: <5cm 20%
  2. Large: >5cm 50% (10% per year)

Rupture rate increases exponentially with size of aneurysm (but small can rupture too)

Clinical Presentation

Physical Examination

  1. Confirm aneurysm
    1. Mass in middle of ab above umbilicus
    2. Expansile puls'n (2 hands pushed apart) (must differentiate from transmitted aortic pulsation in N thin pers)
  1. Extent of aneurysm
    1. Size (max transverse Æ )
    2. Upper border (Infrarenal? Suprarenal - cannot get above aneurysm, behind ribs? Involve iliac a's - into iliac fossa?
    3. Lower border (iliac)
  1. Cardiovascular: Peripheral pulses; Heart + BP (many Pt's HT)

Associated Diseases

Investigations
    1. Plain AXR (AP/ Lateral) - calcifications on degen ab aorta wall (simple, imp)
    2. Ultrasound: simple, non-invasive, lumen dilated, blood clots inside, measure size
    3. CT Scan: can do for every Pt (but if older examiner - reco AXR 1st!), black thrombus deposited on side of aneurysmal sac b/c small BF, measure size/ extent; 3D reconstruction
    4. Arteriogram: (selected cases: renal/visceral associated peripheral vascular disease) (aortogram: when suspect major branch involvement - eg. Look at renal a's B4 operation; not necessary for simple infrarenal aneurysm)

Operative Considerations

Operative Mortality

Pre-operative Preparation (EXAM)

  1. General: blood tests, ECG, CXR
  2. Cardiac: cardiac assessment ± intervention
  3. Preparations: monitoring lines, X-match blood

Open Surgery (Traditional)

Operative Complications: Early
    1. Cardiac* (Clamp/ declamp stress, CHD) - commonest
    2. Respiratory: ab pain after op ® X cough (­ elderly smoker) ® pneumonia
    1. Haemorrhage
    2. Bowel ischaemia: infarction as complication of IMA ligation
    3. Impotence (Parasympathetic): cut parasympathetic nerves esp. over aortic bifurcation, retrograde ejaculation into UB > ED (UB neck control lost), must tell Pt (esp. if younger)
    4. Renal failure
    5. Distal embolism (Trash foot): clots in aneurysm ("trash/ rubbish" flushed down leg, not very amenable to surgery)
    6. Paraplegia (Spinal artery - high): spinal cord ischaemia due to ligation of vertebral arteries, more common if thoracic aorta aneurysm

Operative Complications: Late

[Distinctly uncommon cf. early complications]

  1. Graft infection: rare, high mortality
  2. Anastomotic aneurysm: breakdown of suture lines
  3. Graft - duodenal fistula: breakdown of suture lines near duodenum

Suprarenal AAA
    1. High aortic clamp; proximal HT
    2. Critical ischaemia time: visceral/ renal ischaemia
    3. Vital branches: spinal ischaemia
    4. Bypass (CP)
    5. Reimplant visceral arteries

Ruptured AAA

  1. Retroperitoneal: most common, to back of aorta, buys time b/c bld compressed by peritoneal structures
  2. Intraperitoneal (free): most die immediately
  3. Into duodenum (fistula): massive GI bleeding
  4. Into IVC: most uncommon, causing arterial-IVC fistula, rapid heart failure

Clinical Features
  1. Pain: abdomen/ back
  2. Mass: pulsatile (may be masked) - dep on distension of ab
  3. Shock: Transient or profound (hypovolaemic)

Ruptured AAA

Management (exam)
    1. Open ab - blood everywhere
    2. Same operation as repair, but have to find aorta in all the blood
    3. Once clamp aorta, can do operation at leisure

Specific Complications

  1. Cardiac
  2. Respiratory
  3. Renal failure (shock, low BP, no urine output)
  4. Bleeding tendency (massive transfusion; bank blood without clotting factors and platelets)
  5. Paralytic ileus (retroperitoneal haematoma, Pt cannot eat for long time)
  6. Jaundice (bleeding + transfusion, Hb reabsorbed into body, disturbed liver function)

This is why 50% Pt's die

Endovascular Repair

Issues:
  1. Endoleaks (presence of BF in graft after operation
    1. At top, between attachment of graft and side of aorta, not good
    2. Leakage from junction of graft; most commonly type two leak from branch - eg. Side branch of aorta; most thrombose and if not, have persistent BF inside sac, cause of LT failure
  1. Migration

OTHER ANEURYSMS

Visceral Aneurysms

Peripheral Artery Aneurysms

Pseudoaneurysms

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