Aneurysm is defined as enlargement of a blood vessel greater than 50% of its normal diameter at the same level. Aneurysms can happen in any blood vessel in the body, with the abdominal aorta the most commonly affected. Aneurysms can arise rarely in the veins also.
Aortic aneurysms are mainly degenerative in nature, with features of atherosclerosis seen in them like plaques and calcifications. Smoking is the most common cause along with hypertension. People who have undergone heart bypass surgery > 10 yrs ago have an increased risk of developing abdominal aortic aneurysms compared to the general population {9% vs 4% (Epics 1 study)}.
The greatest risk from any aneurysm anywhere in the body is that of rupture. Any aneurysm beyond a particular size is at a risk of rupture which increases exponentially as the size increases. This is similar to blowing up a balloon. The greater the air is pumped into the balloon beyond a particular point, it will burst.
The cutoff size dimensions for treatment of aneurysms generally accepted as 5-5.5cm for men and 4-4.5 cm for women. This is because, women are known to have smaller blood vessel diameters and are known to rupture at smaller diameters compared to men.
Aneurysms are also prone to develop thrombosis within them. This happens due to the turbulent blood flow occuring in the outer parts of the aneurysm. This thrombus carries with it the risk of distal embolisation which can lead to acute blockages in the arteries in the legs. The risk of distal embolisation is maximum with Popliteal artery aneurysms, which can be limb threatening.
The most common site for developing an aortic aneurysm is the Abdominal Aorta. It is also seen frequently in the thoracic and the arch of the aorta and rarely in the ascending aorta.
Majority of the abdominal aortic aneurysms are asymptomatic. Sudden onset of severe abdominal pain in a hypertensive, smoker should raise the suspicion of the presence of Abdominal Aortic Aneurysm. There can be a vague complaint of abdominal pain and back pain. Symptoms arise in an abdominal aortic aneurysm due to either rupture (bursting) or acute expansion of the aneurysm. Acute expansion is considered a precursor of rupture and these patients should be kept in the hospital and prepared for early intervention. Rarely can the thrombus in these aneurysms embolise distally and cause features of acute limb ischemia. Vertebral body erosions are known to occur and can be mistaken for tuberculosis, thus delaying the diagnosis by many months. Aneurysms greater than 4-4.5cm in females, 5-5.5 cm in males and symptomatic aneurysms require urgent intervention. Occasionally an aneurysm is diagnosed while being investigated for other arterial problems like mesenteric or renal artery disease, arterial claudication pain due to iliac artery disease etc.
Once the size of the aneurysm is confirmed on a CT angiography, an abdominal ultrasound should be performed every 6 months to note any increase in the size of the aneurysm. Increase in size > 0.6mm/6 months or 1cm/yr is an indication for treatment. Patients who have received a kidney, liver or heart transplant show a rapid expansion of their aneurysms with a much higher incidence of rupture at smaller diameters compared to the normal population with AAA.
Screening is a highly effective tool to diagnose and helps to treat these aneurysms before they have had a chance to cause any problems, which can be debilitating, catastrophic and life threatening.
The best method for screening is a focused abdominal aortic ultra-sonography documenting the size of the aorta serially. The size can be measured at the level of the mesenteric vessels, mid infra-renal aorta and the aortic bifurcation. The total size of the aneurysm (i.e. length, and transverse diameters in the antero-posterior and medio-lateral planes) should be documented along with the presence of any intraluminal thrombus. In the event of an increase in the size of >0.6mm/6 months or 1cm/ yr is documented, then a CT angiography is indicated to further characterize the aneurysm and to aid in treatment planning.
Small aneurysms are to be observed and maintained under religious follow up, unless symptomatic.
The choice between operative repair and observation is based on the following criterion:
1. Rupture risk of the aneurysm under observation
2. Operative risk of repair
3. Patients life expectancy
4. Personal preferences of the patient.
Open repair of the abdominal aortic aneurysm is performed either via an abdominal or thoraco-abdominal approach. It involves replacing the aneurismal part of the aorta with a synthetic graft (which is completely bio-compatible). The patient remains in the ICU for 24-48hrs (on average). Oral diet is gradually resumed by the 3rd day and the majority of the patients are discharged by the 5-7days post-procedure.
Occasionally associated procedures like revascularization of the arteries of the kidneys and the liver-intestine is also carried out in the same sitting.
The results are durable and long-lasting.
EVAR is the process where the aneurysm is treated from inside the aorta. It involves the placement of a covered stent graft in the aorta, thereby streamlining the flow in the aorta, preventing rupture and other associated complications. The procedure is performed through the groins. The patient is observed in the ward/ ICU (depending on the comorbidities) for a few days, and is often ready for discharge within 2-3days, at times even earlier.
Regular follow-up with the performing physician is imperative post EVAR.
It is used for complex aneurysms where open repair and EVAR/ TEVAR are used simultaneously. This is mainly done for aneurysms that involve the part of the aorta where the blood vessels to the liver- stomach-intestines and the kidneys arise. Hybrid repair can be done as a single stage or a 2 stage procedure, wherein the first stage is the bypass performed to the arteries of the liver-stomach-intestines and kidneys, and the 2nd stage involves placing a covered stent graft in the aorta to exclude the aneurysm and prevent possibility of rupture and distal embolisation of the intraluminal thrombus.
Please ask for treating cardiac Surgeon Dr. Dileep Singh for more information regarding the disease and its treatment modalities.
Dr. Dileep Singh is Senior Consultant, Cardio-thoracic and Vascular surgeon presently associated with Bansal Hospital, Bhopal, Madhya Pradesh. He has special interest in total arterial beating heart bypass surgery (which has better long term results compared to conventional bypass surgery) and complex cardiac and aortic surgeries.