ABC of arterial and venous disease Arterial aneurysms

M M Thompson, PRF Bell

True arterial aneurysms are defined as a 50% increase in the normal diameter of the vessel. Clinical symptoms usually arise from the common complications that affect arterial aneurysms—namely, rupture, thrombosis, or distal embolisation. Although the aneurysmal process may affect any large or medium sized artery, the most commonly affected vessels are the aorta and iliac arteries, followed by the popliteal, femoral, and carotid vessels.

Abdominal aortic aneurysms

Aneurysms of the infrarenal abdominal aorta and iliac arteries coexist to such a degree that they may be considered a single clinical entity. Abdominal aneurysms usually affect elderly men (> 65 years), with a prevalence of 5%. In England, abdominal aneurysm is responsible for over 11 000 hospital admissions and 10 000 deaths a year. Interestingly, unlike other atherosclerotic vascular disorders, the prevalence of abdominal aortic aneurysms is increasing rapidly, and aneurysmal rupture is now the 13th commonest cause of death in the Western world.

Clinical presentation

Although abdominal aneurysms may cause symptoms because of pressure on surrounding structures, about three quarters remain asymptomatic at initial diagnosis. With the exception of vague abdominal pain, clinical symptoms usually result from embolisation or rupture of the aneurysm.

The appearance of microembolic lower limb infarcts in a patient with easily palpable pedal pulses may suggest the presence of either popliteal or abdominal aneurysms. Additionally, patients with embolisation of mural thrombus from an abdominal aneurysm may present with acute limb ischaemia due to femoral or popliteal occlusion.

The diagnostic triad of hypovolaemic shock, pulsatile abdominal mass, and abdominal or back pain is encountered in only a minority of patients with ruptured abdominal aneurysms. In general, ruptured abdominal aortic aneurysm should be considered in any patient with hypotension and atypical abdominal symptoms. Similarly, the presence of abdominal pain in a patient with a known aneurysm or pulsatile mass must be considered to represent a rapidly expanding or ruptured aneurysm and be treated accordingly. In the community setting, the death rate from ruptured abdominal aortic aneurysms is almost 90%, as 80% of patients will die before reaching hospital and about 50% die during surgery to repair the rupture.

Methods of diagnosis

The sensitivity of abdominal palpation to detect aortic aneurysms increases with the diameter of the aneurysm, but palpation is not sufficiently reliable for routine diagnosis. Similarly, plain abdominal radiography shows a calcified aneurysmal aortic wall in only half of cases.

The simplest diagnostic test is B mode ultrasonography, which gives an accurate assessment of both the diameter and the site of the aneurysm. If more accurate morphological data are required to determine the exact relation of the aneurysm to the visceral or renal arteries, detailed cross sectional imaging

Large infrarenal abdominal aortic aneurysm before surgical repair
Clinical picture of "trash foot." The appearance is caused by multiple microscopic atheromatous emboli from a large infrarenal aortic aneurysm. The presence of digital infarcts in a patient with easily palpable pulses may point to an aneurysmal source of emboli
Ruptured abdominal aneurysm. Rupture usually occurs posteriorly into the retroperitoneum, which produces a contained leak and allows the possibility of surgical repair. Free anterior intraperitoneal rupture usually results in exsanguination

may be obtained by computed tomography or magnetic resonance angiography.

The diagnosis of ruptured abdominal aortic aneurysms relies on clinical symptoms. Ultrasonography is used to confirm an aneurysm if it is difficult to palpate. Computed tomography has a low specificity (about 75%) for determining the presence of a rupture and adds little information to routine clinical assessment.

Indications for surgery

Elective surgery

The decision to operate on a patient with an asymptomatic abdominal aneurysm is based on an analysis of the risk of aneurysmal rupture compared with the mortality of elective surgical repair. The risk of rupture is related to many factors, but the diameter of the aortic aneurysm has historically been used as the principal determinant.

Unfortunately, little information is available on the rupture rates of large abdominal aneurysms, but pooled analysis of existing data suggests that the risk of rupture increases exponentially in aneurysms above 55-60 mm. This has led to a broad surgical consensus that aneurysms exceeding 55 mm in diameter should be surgically repaired if there are no confounding factors that would substantially increase the risk of elective surgery.

The treatment for smaller aneurysms has recently been clarified by the UK small aneurysm trial, which studied 1090 patients with aneurysms of 40-55 mm. The study found a 30 day operative mortality of 5.8%, mean risk of rupture for small aneurysms of 1% a year, and no difference in survival between treatment groups at two, four, or six years. The cost for early surgery was higher than for surveillance, but early surgery was associated with improvement in some measures of quality of life.

Emergency treatment

Patients with suspected ruptured aneurysms should be considered for emergency surgical repair. Several studies have looked at preoperative risk factors and survival after emergency repair of an aneurysm. Although there is no precise scoring system that will allow accurate prediction of survival, the presence of several predictive factors (age > 80 years, unconsciousness, low haemoglobin concentration, cardiac arrest, severe cardiorespiratory disease) can be used to determine patients in whom the risk of dying during surgery approaches 100%.

Patients with symptomatic aneurysms should be treated as urgent cases and have the aneurysm repaired. The aetiology of pain from abdominal aneurysms is not well understood, although it has been attributed to stretching of the aneurysm sac or severe inflammation within the aneurysm wall (inflammatory aneurysms, see below).

Conventional surgical repair

Traditional surgical repair for asymptomatic abdominal aortic aneurysms involves exposure of the abdominal aorta, aortic and iliac clamping, and replacement of the aneurysmal segment with a prosthetic graft. Graft replacement is an effective, durable procedure, and most centres report 30 day mortality of about 5%, although this varies with the volume of work and type of hospital.

The mortality associated with surgical repair of aneurysms is closely related to the "fitness" of the patient for surgery; patients with severe cardiorespiratory disease have a perioperative mortality approaching 40%, with most deaths caused by cardiac events.

Endovascular repair

One of the major developments in vascular surgery over the past five years has been the introduction of endovascular repair

Computed tomogram showing large infrarenal abdominal aortic aneurysm
0 0

Post a comment