Abdominal aortic aneurysm is a local bulging or diffuse expansion of the aortic wall in its abdominal region. An abdominal aortic aneurysm may be asymptomatic or manifest itself by pulsation, abdominal pain of varying intensity, with rupture of an aneurysm – by the clinic of intra-abdominal bleeding. Diagnosis of an aneurysm includes an overview radiography of the abdominal cavity, ultrasound of the abdominal aorta, radiopaque angiography, CT. Treatment is exclusively surgical: open resection of the aneurysmal sac with replacement of the excised part with a synthetic prosthesis or endoprosthetics.
Abdominal aortic aneurysm is a pathological expansion of the abdominal part of the aorta in the form of protrusion of its wall in the area from the XII thoracic to IV—V lumbar vertebra. In cardiology and angiosurgery, abdominal aortic aneurysms account for up to 95% of all vascular aneurysmal changes. Among men over 60 years of age, abdominal aortic aneurysm is diagnosed in 2-5% of cases. Despite the possible asymptomatic course, an abdominal aortic aneurysm is prone to progression; on average, its diameter increases by 10% per year, which often leads to thinning and rupture of the aneurysm with a fatal outcome. Abdominal aortic aneurysm ranks 15th in the list of the most common causes of death.
Causes of abdominal aortic aneurysm
The formation of aortic aneurysms can be caused by various reasons. A prerequisite for the subsequent formation of an abdominal aortic aneurysm may be fibromuscular dysplasia – congenital inferiority of the aortic wall. Among the acquired factors , the most important are:
- Atherosclerosis of blood vessels. According to studies, the main etiological factor of aortic aneurysms (aortic arch aneurysms, thoracic aortic aneurysms, abdominal aortic aneurysms) is atherosclerosis. In the structure of the causes of acquired aortic aneurysms, it accounts for 80-90% of cases of the disease.
- Inflammatory changes of the vascular wall. The rarer acquired origin is associated with inflammatory processes: nonspecific aortoarteritis, specific vascular lesions in syphilis, tuberculosis, salmonellosis, mycoplasmosis, rheumatism.
- Aortic injuries. The rapid development of vascular surgery in recent decades has led to an increase in the number of iatrogenic abdominal aortic aneurysms associated with technical errors during angiography, reconstructive operations (dilation/ stenting of the aorta, thromboembolectomy, prosthetics). Closed injuries to the abdominal cavity or spine can contribute to the occurrence of traumatic abdominal aortic aneurysms.
About 75% of patients with abdominal aortic aneurysm are smokers; at the same time, the risk of developing an aneurysm increases in proportion to the length of smoking and the number of cigarettes smoked daily. Age over 60 years, male gender and the presence of similar problems in family members increase the risk by 5-6 times.
The probability of rupture of an abdominal aortic aneurysm is higher in patients suffering from arterial hypertension and chronic lung diseases. In addition, the shape and size of the aneurysmal sac matters. It is proved that asymmetric aneurysms are more prone to rupture than symmetrical ones, and with an aneurysm diameter of more than 9 cm, mortality from rupture of the aneurysmal sac and intra-abdominal bleeding reaches 75%.
Pathogenesis of abdominal aortic aneurysm
Inflammatory and degenerative atherosclerotic processes in the aortic wall play a role in the development of abdominal aortic aneurysm. An inflammatory reaction in the aortic wall occurs as an immune response to the introduction of an unknown antigen. At the same time, infiltration of the aortic wall by macrophages, B- and T-lymphocytes develops, cytokine production increases, and proteolytic activity increases. The cascade of these reactions, in turn, leads to the degradation of the extracellular matrix in the middle layer of the aortic membrane, which manifests itself in an increase in collagen content and a decrease in elastin. In place of smooth muscle cells and elastic membranes, cyst-like cavities are formed, as a result of which the strength of the aortic wall decreases.
Inflammatory and degenerative changes are accompanied by thickening of the walls of the aneurysmal sac, the occurrence of intense perianeurysmal and postaneurysmal fibrosis, fusion and involvement of the organs surrounding the aneurysm in the inflammatory process.
According to the shape of the protrusion of the vessel wall, there are baggy, diffuse fusiform and delaminating aneurysms of the abdominal aorta; according to the structure of the wall – true and false aneurysms. The anatomical classification is of the greatest clinical value, according to which there are:
- infrarenal aneurysms located below the divergence of the renal arteries (95%);
- supra-renal with localization above the renal arteries.
Taking into account etiological factors, abdominal aortic aneurysms are divided into congenital and acquired. The latter may have non-inflammatory etiology (atherosclerotic, traumatic) and inflammatory (infectious, syphilitic, infectious-allergic).
According to the variant of the clinical course, an abdominal aortic aneurysm can be uncomplicated and complicated (exfoliating, ruptured, thrombosed). The diameter of the abdominal aortic aneurysm allows us to speak of a small (3-5 cm), medium (5-7 cm), large (over 7 cm) and giant aneurysm (with a diameter 8-10 times higher than the diameter of the infrarenal aorta).
Based on the prevalence, A.A. Pokrovsky et al. distinguish 4 types:
- I – infrarenal aneurysm with sufficient distal and proximal isthmus;
- II – infrarenal aneurysm with a proximal isthmus of sufficient extent; extends to aortic bifurcation;
- III – infrarenal aneurysm involving bifurcation of the aorta and iliac arteries;
- IV – infra- and suprarenal (total) abdominal aortic aneurysm.
Symptoms of abdominal aortic aneurysm
In the uncomplicated course of an abdominal aortic aneurysm, there are no subjective symptoms of the disease. In these cases, an aneurysm can be diagnosed accidentally by palpation of the abdomen, ultrasound, abdominal radiography, diagnostic laparoscopy for other abdominal pathology.
The most typical clinical manifestations are constant or periodic aching, dull pains in the mesogastric or left half of the abdomen, which is associated with the pressure of the growing aneurysm on the nerve roots and plexuses in the retroperitoneal space. Pain often radiates to the lumbar, sacral or inguinal region. Sometimes the pain is so intense that it requires the appointment of analgesics to relieve it. Pain syndrome can be regarded as an attack of renal colic, acute pancreatitis or sciatica.
Some patients, in the absence of pain, note a feeling of heaviness, abdominal distension or increased pulsation. Due to mechanical compression of the abdominal aortic aneurysm of the stomach and duodenum 12, nausea, belching, vomiting, flatulence, constipation may occur.
Urological syndrome can be caused by ureteral compression, kidney displacement and is manifested by hematuria, dysuric disorders. In some cases, compression of testicular veins and arteries is accompanied by the development of a painful symptom complex in the testicles and varicocele.
The ischioradicular symptom complex is associated with compression of the nerve roots of the spinal cord or vertebrae. It is characterized by lower back pain, sensory and motor disorders in the lower extremities. Isolated dissecting aneurysm of the abdominal aorta is extremely rare; more often it is a continuation of the dissection of the thoracic aorta. With an aneurysm of the abdominal aorta, chronic ischemia of the lower extremities may develop, occurring with the phenomena of intermittent lameness, trophic disorders.
Rupture of an abdominal aortic aneurysm is accompanied by a clinic of acute abdominal pain and in a relatively short time can lead to a tragic outcome. The symptom complex is accompanied by a characteristic triad: pain in the abdomen and lumbar region, collapse, increased pulsation in the abdominal cavity. The features of the abdominal aortic aneurysm rupture clinic are determined by the direction of the rupture (into the retroperitoneal space, free abdominal cavity, inferior vena cava, duodenum, bladder).
Retroperitoneal rupture of an abdominal aortic aneurysm is characterized by a permanent pain syndrome. With the spread of retroperitoneal hematoma in the pelvic region, there is an irradiation of pain in the hip, groin, perineum. The high location of the hematoma can simulate cardiac pain. The amount of blood poured into the free abdominal cavity during retroperitoneal rupture of an aneurysm is usually small – about 200 ml.
With intraperitoneal localization of this disease rupture, a clinic of massive hemoperitoneum develops: the phenomena of hemorrhagic shock are rapidly increasing – sharp pallor of the skin, cold sweat, weakness, thready, rapid pulse, hypotension. There is a sharp bloating and tenderness of the abdomen in all departments, a diffuse symptom of Shchetkin-Blumberg. Percussion determines the presence of free fluid in the abdominal cavity. Fatal outcome with this type of rupture of an abdominal aortic aneurysm occurs very quickly.
The breakthrough of an abdominal aortic aneurysm into the inferior vena cava is accompanied by weakness, shortness of breath, tachycardia; edema of the lower extremities is typical. Local symptoms include abdominal and lower back pain, a pulsating formation in the abdomen, over which systolic-diastolic noise is heard. These symptoms increase gradually, leading to severe heart failure.
When the abdominal aortic aneurysm ruptures into the duodenum, a clinic of profuse gastrointestinal bleeding develops with sudden collapse, bloody vomiting, melena. In diagnostic terms, this variant of rupture is difficult to distinguish from gastrointestinal bleeding of another etiology.
In some cases, a general examination, palpation and auscultation of the abdomen allows you to suspect the presence of an abdominal aortic aneurysm. To identify familial forms of aneurysm, it is necessary to collect a thorough anamnesis. Diagnostic methods:
- Inspection. When examining thin patients in the supine position, an increased pulsation of the aneurysm through the anterior abdominal wall can be determined. Palpation in the upper abdomen on the left reveals a painless pulsating dense elastic formation. During auscultation, systolic noise is heard above the abdominal aortic aneurysm.
- X-ray diagnostics. The most accessible method of diagnosing an abdominal aortic aneurysm is an overview radiography of the abdominal cavity, which allows you to visualize the shadow of the aneurysm and calcification of its walls. CT of the abdominal aorta allows you to get an image of the lumen of an aneurysm, calcification, dissection, intracellular thrombosis; to identify the threat of rupture or an accomplished rupture. In addition to these methods, aortography and intravenous urography are used in the diagnosis of abdominal aortic aneurysm.
- Ultrasound of the aorta. Currently, ultrasound, duplex scanning of the abdominal aorta and its branches is widely used in angiology. The accuracy of ultrasound detection is approaching 100%. Ultrasound is used to determine the condition of the aortic wall, the prevalence and localization of the aneurysm, the location of the rupture.
Treatment of abdominal aortic aneurysm
The detection of an abdominal aortic aneurysm is an absolute indication for surgical treatment. A radical type of surgery is resection of an abdominal aortic aneurysm followed by replacement of the resected area with a homotransplant. The operation is performed through a laparotomy incision. When the iliac arteries are involved in aneurysm, bifurcation aorto-iliac prosthetics is indicated. The average mortality in open surgery is 3.8-8.2%.
Contraindications to elective surgery are recent (less than 1 month) myocardial infarction, CVA (up to 6 weeks), severe cardiopulmonary insufficiency, renal insufficiency, widespread occlusive lesion of the iliac and femoral arteries. In case of rupture or rupture of an abdominal aortic aneurysm, resection is performed according to vital indications.
Modern low-traumatic methods of abdominal aortic aneurysm surgery include aortic endoprosthetics using an implantable stent graft. The surgical procedure is performed in an X-ray operating room through a small incision in the femoral artery; the course of the operation is controlled by X-ray vision. The installation of a stent graft allows you to isolate the aneurysmal sac, thereby preventing the possibility of its rupture, and at the same time creates a new channel for blood flow. The advantages of endovascular intervention are minimal trauma, lower risk of postoperative complications, and rapid recovery. However, according to the literature, distal migration of endovascular stents is observed in 10% of cases.
Prognosis and prevention
Abdominal aortic aneurysm is an insidious and unpredictable vascular pathology. The probability of death from a large aneurysm rupture is more than 75%. At the same time, from 30 to 50% of patients die at the prehospital stage.
In recent years, there has been noticeable progress in the diagnosis and treatment of abdominal aortic aneurysms in cardiac surgery: the number of diagnostic errors has decreased, the contingent of patients subject to surgical treatment has expanded. First of all, this is due to the use of modern imaging studies and the introduction of aortic aneurysm endoprosthetics into practice.
To prevent the potential threat of an abdominal aortic aneurysm, persons suffering from atherosclerosis or having a family history of this disease should undergo regular examinations. An important role is played by the rejection of unhealthy habits (smoking). Patients who have undergone surgery for an abdominal aortic aneurysm need the supervision of a vascular surgeon, regular ultrasound and CT.