Inferior mesenteric artery aneurysm

Inferior mesenteric artery aneurysms are among the rarest of all visceral artery aneurysms.

Epidemiology

Aneurysms of the inferior mesenteric artery (IMA) only account for less than 1% of all visceral artery aneurysms ^1,2. These aneurysms are more common in men than in women ³.

Clinical presentation

Most patients with IMA aneurysms are commonly asymptomatic and these aneurysms are usually discovered incidentally ^3-6. Some patients may present with a palpable pulsatile abdominal mass or bruit around the umbilicus ^3,6. In cases complicated by rupture, patient may present with abdominal pain, low back pain, collapse or hemorrhagic shock ³.

Pathology

Atherosclerotic disease is the most common cause of aneurysmal dilatation of the IMA ^3-6.  These aneurysms usually occur in the presence of chronic stenosis or occlusion of either or both the coeliac artery and superior mesenteric artery (SMA). The IMA becomes part of the collateral formation through the arc of Riolan or marginal artery Drummond resulting to increased intraluminal flow. The increased flow in combination with atherosclerotic disease can lead to arterial wall weakness and subsequent formation of aneurysms.

Other causes include ^3-6:

• Infection
  • mycotic
  • tuberculous
• vasculitis
  • Takayasu disease
  • polyarteritis nodosa
  • Behçet disease
• segmental arterial mediolysis
• fibromuscular dysplasia
• dissection
• trauma

Radiographic features

Ultrasound

Ultrasound with Doppler may show IMA aneurysms as dilated vessels lying parallel to the lower part of the abdominal aorta ⁴.

Angiography: CTA/MRA/DSA

IMA aneurysms are best visualised by arterial imaging like CT angiography (CTA), MR angiography (MRA) and digital subtraction angiography (DSA). These aneurysms can be saccular or fusiform (commonly pear-shaped) in morphology. Associated stenosis or occlusion of the coeliac artery and SMA as well as the collateral vessels (e.g. arc of Riolan and marginal artery of Drummond) can also be demonstrated.

Treatment and prognosis

Surgical treatment by way of revascularization with reimplantation of the resected IMA along with either angioplasty or bypass of the stenosed or occluded coeliac and SMA seem to be the best way to prevent death from rupture ^1-6. It is suggested that if an aneurysm is greater than 2 cm at the proximal IMA or 1 cm at the distal of the IMA, surgical intervention should be performed due to an increased risk of rupture ³. If an IMA aneurysm ruptures, prognosis is poor ^3-6.