Aneurysms and other peripheral arterial disorders
Aneurysms (see Table 42.1)
Table 42.1
Clinical presentation and pathophysiology of aortic, iliac, femoral and popliteal aneurysms
| Clinical presentation | Pathophysiology |
| Asymptomatic—discovered incidentally as pulsatile mass in abdomen, groin or popliteal fossa, on abdominal X-ray, CT or ultrasound scan | Progressive aneurysmal dilatation. May be self-limiting if hypertension and smoking controlled |
| Symptomatic—abdominal or back pain with tender aneurysm. Needs urgent surgery | Rapidly expanding aneurysms cause pressure on adjacent structures |
| Sudden death—acute, usually fatal, cardiovascular collapse. Often misdiagnosed as myocardial infarction | Sudden rupture of aneurysm only detected at autopsy or in the dissection room |
| Leaking/ruptured aneurysm—ill-defined back or abdominal pain often simulating ureteric colic or other abdominal emergency. Diagnostic if accompanied by transient collapse. Sometimes a history of recent similar episodes. Pulsatile abdominal mass palpable in 50% | Dilatation and thinning of the wall of an aneurysm leading to leakage of blood into retroperitoneal tissues—usually leads to catastrophic rupture within hours |
| Symptoms and signs of acute severe leg ischaemia; often pulsatile popliteal aneurysm on contralateral side | Sudden thrombotic occlusion of aneurysmal popliteal artery |
| Complete arterial occlusion—sudden distal ischaemia affecting lower limb due to embolism of thrombus from within aneurysm | Thrombotic occlusion of popliteal artery |
| Screening—discovered on population screening or opportunistic screening for aneurysm |
Degenerative aneurysms are usually fusiform, slowly expanding in diameter. As it enlarges, the vessel wall thins, expansion accelerates and the risk of rupture increases. Most abdominal aortic aneurysms involve only the infrarenal aorta; some extend distally to involve common iliac arteries; sometimes there are separate aneurysms of internal iliac arteries (see Fig. 42.1). A few extend proximally to become thoraco-abdominal aneurysms.
Fig. 42.1 Patterns of aneurysm formation
About 25% have more than one aneurysm either in continuity (common iliac, internal iliac, thoraco-abdominal) or not (femoral 10%; popliteal 20%; thoracic 5%). Abdominal aortic aneurysms rarely extend above the renal arteries. External iliacs are never aneurysmal
Clinical presentation of aneurysms (see Table 42.1)
Aorto-iliac aneurysms are often found incidentally. The patient may notice a pulsatile abdominal mass or a pulsatile mass may be discovered on abdominal examination. An aneurysm may also be noticed incidentally on radiological investigation—as calcification on a plain abdominal X-ray, as an obvious aneurysm on CT or, most commonly, on ultrasound scanning for obstructive urinary symptoms (see Fig. 42.2). More recently in the UK, a national AAA screening programme has been approved, with the aim of offering all men an ultrasound scan of the abdominal aorta on reaching 65. Similar schemes are appearing in Denmark, Australia and other countries.
Case History
Fig. 42.2 Abdominal aortic aneurysm
(a, b) This very obese 64-year-old man complained of continuous aching back pain for 2 weeks. (a) Plain abdominal X-ray showing huge abdominal aneurysm (outlined by arrows). Note calcification C along its left-hand aspect. (b) CT scan of a different patient with a 6 cm AAA. The thrombus lining the wall can clearly be seen (arrowed). Calcification is visible in the anterior wall where the third part of the duodenum is closely applied to it. Rarely, a primary aorto-duodenal fistula develops at this point
Femoral and popliteal aneurysms are relatively uncommon and usually present as pulsatile masses. The larger they become, the more likely complications are to ensue. Femoral aneurysms occasionally rupture causing pain and massive swelling in the groin. Popliteal aneurysms are liable to undergo thrombosis or embolise, causing an acutely ischaemic leg (see Table 40.2). A thrombosed popliteal aneurysm carries a 50% risk of limb loss. In any patient presenting with an acutely ischaemic leg, it is vital to exclude this diagnosis as successful treatment often requires thrombolysis as well as surgery. Popliteal aneurysms can also rupture and cause a variety of other presentations listed in Table 40.2.
Principles of management of aneurysms
Indications for operation (see Box 42.1)
A leaking or ruptured abdominal aortic aneurysm (AAA) is a surgical emergency. Less than half the patients reach hospital alive, and only about half of those undergoing surgery survive. The majority of patients die of shock before reaching the operating theatre or else of myocardial infarction or acute renal failure after operation. The true mortality of rupture is thus more than 85%. On the other hand, the mortality after elective operation or endovascular repair (EVAR, see p. 513) for aneurysm can be less than 5%. Thus, the decision to operate electively on a known aneurysm depends on the estimated risk of rupture. Indications for operation are summarised in Box 42.1.
Investigation of aneurysms (see Fig. 42.2)
Non-ruptured AAA: For asymptomatic aneurysms considered too small to warrant operation, ultrasonography is used for periodic monitoring, with referral to a surgeon once the size reaches an index diameter (usually 5 or 5.5 cm) or is seen to expand more than 0.5 cm in a year.
Leaking or ruptured AAA: Any patient with a suspected leaking or ruptured AAA should be treated as a true surgical emergency but not necessarily by immediate transfer to the nearest operating theatre. There is good evidence that the survival rate increases when ruptured AAAs are treated by a specialist team of surgeons and anaesthetists, and this may mean transfer to a different centre. Over-aggressive blood pressure resuscitation of the hypotensive patient may convert a stable contained leak into a free rupture, and many clinicians support the use of permissive hypotension to facilitate transfer (see Ch. 15), i.e. not treating relative hypotension whilst the patient remains conscious and free from cardiac symptoms. This principle has increased the time available for transfer and/or further investigation.
Principles of aneurysm surgery
The dilated aneurysmal segment is surgically corrected by means of a graft. Over recent years, there has been a trend towards treating AAAs using minimally invasive stent-graft placement (endovascular repair, EVAR) via the femoral artery. Many patients still, however, undergo traditional open surgery. The indications and relative merits of each technique are shown in Table 42.2. Tube grafts or bifurcation grafts of synthetic material (usually Dacron) are used for aorto-iliac and femoral aneurysms, whilst autogenous saphenous vein is preferred for popliteal aneurysms.
Table 42.2
Comparison of conventional and endovascular therapy for aortic aneurysm
| Conventional surgery | Endovascular therapy | |
| Mortality related to procedure | Approximately 5% | 1.7% |
| Length of hospital stay | 7–10 days | 2–4 days |
| ITU/HDU care needed | Likely | Unlikely |
| Overall cost | £6500 | £8000 |
| Anatomical constraints | Distance between AAA and renal arteries can be less than 15 mm | Needs 15 mm of relatively normal aorta below renals |
| Past medical history | More difficult with previous surgery or peritonitis | Unaffected by previous abdominal surgery |
| Follow-up | Discharge at 3 months. Rescan after 5–7 years. Reintervention unlikely | Frequent CT and ultrasound for life. Reintervention rates high but improving |
Open abdominal aortic aneurysm surgery (Fig. 42.3):
Case History
Fig. 42.3 Abdominal aortic aneurysm
(a) A 70-year-old asymptomatic man in whom a pulsatile abdominal mass was an incidental finding. This cast of thrombus was removed from within the aortic aneurysm at operation; note the false lumen and concentric lamellae of thrombus progressively laid down as the aneurysm expanded over many months. (b) This shows the aneurysm sac opened at operation on a different patient who had complained of chronic back pain. The posterior wall of the aorta is completely deficient in part and the anterior longitudinal ligament is visible in its base
For abdominal aneurysms, the standard open approach is a long midline or a transverse abdominal incision. The aorta is usually reached via the peritoneal cavity or sometimes via an extraperitoneal approach. The patient is usually anticoagulated perioperatively with intravenous heparin to prevent distal thrombosis, and the iliac arteries and the infrarenal aorta are clamped (see Fig. 42.4). The aneurysm is incised longitudinally and any clot within it removed. Bleeding lumbar arteries opening into the posterior aortic wall are closed with sutures.
