Visceral Aneurysm

How does it occur?

Most are described as degenerative, in that they have formed due to weakening of the artery wall which can be caused by plaque build up, smoking, genetics or a combination of all of these factors. Some are associated with other disorders such as inflammation with blood vessels (called vasculitis). Another condition called fibromuscular dysplasia (FMD) is often found in younger female patients with aneurysms to one of the kidneys. As with aneurysms of the aorta, the concern is that these aneurysms can enlarge and rupture causing significant blood loss and death.

The most common visceral artery aneurysm occurs within the artery travelling to the spleen (splenic artery) and they are four times more common in females. Pregnancy is a significant risk factor and over 50% of these aneurysms rupture during pregnancy. The second most common visceral aneurysm occurs within the hepatic artery (artery to the liver) with a male-to-female ratio of 3 to 2.

Other visceral aneurysms can occur in the arteries leading to the small intestines (superior mesenteric artery aneurysm). These are more common in males and often occur due to previous or underlying infection. The rupture rate of these aneurysms are up to 50% and they are associated with a high mortality rate (up to 90%). This is thought to be due to the combination of significant blood loss and reduced blood to the bowel causing it to die (intestinal ischaemia). Renal artery aneurysms are quite rare, with an estimated incidence of 0.09% in the general population.

How can they be treated?

Generally open surgery, stenting or coiling is considered – with a preference for more minimally invasive techniques. Open surgery often involves a large incision in the abdomen with the aim of identifying the aneurysm, tying it off and performing a bypass operation to allow for continued blood flow to the target organ. This is a major operation with significant risks so a thorough pre-operative assessment will be required to ensure patient fitness and safety for surgery.

The minimally invasive option involves performing an angiogram to identify the aneurysm and then proceeding to stenting and/or coiling. This is done via cannulation of the femoral artery in the groin to place a sheath. The sheath allows for injection of contrast and to concurrently take x-ray imaging of the target aneurysm. It also allows for passage of wires, stents and coils to treat the aneurysm. The idea is to place coils within the bulge of the artery (aneurysm sac) to encourage laminar flow of blood. A stent may be required to reinforce the coils and prevent any leak.  

When should they be treated?

The current treatment guidelines proposed by the US Society for Vascular Surgery (SVS) provides the best guidelines for when these aneurysms should be treated link.

Splenic artery aneurysms:

• If ruptured
• Pseudoaneurysm or symptoms such left sided abdominal pain without rupture
• Pregnant women or women of child-bearing age.
• Size greater than 3cm diameter or interval growth of more than 0.5cm per year.

Hepatic artery aneurysm:

• Ruptured aneurysm
• Pseudoaneurysm or symptoms such as right sided abdominal pain without rupture
• Size greater than 2cm or interval growth of more than 0.5cm per year.

Superior mesenteric artery aneurysm:

• Ruptured aneurysm
• Aneurysm of any size – However if less than 2.5cm in diameter it may be safe to watch especially if the patient has significant medical issues placing them at high risk of surgical intervention.

Renal artery aneurysms:

• Ruptured aneurysm
• Rapidly expanding aneurysm
• Aneurysm size greater than 3cm
• Pregnant females or those considering pregnancy

Reference:

Sidawy, AN. Perler, BA. Rutherford’s Vascular Surgery and Endovascular Therapy: 10th ed. Elsevier, 2023