CT angiography of the splanchnic vessels (protocol)

Multi-slice CT angiography of the splanchnic vessels is a powerful minimally invasive technique for evaluation of the splanchic vascular system.

Technique 

Actual procedure will vary depending on institutional protocol/guidelines but below is a typical description ^{2, 4}:

• patient receives 500-800 ml of negative oral contrast water to opacfiy the stomach and small bowels
• patient in supine position with arms up behind his head
• peripheral venous access (18-20G) in an antecubital vein
• a volume of 100–120 mL of iodinated contrast material is administered at a rate of 4-5 mL/sec.
• because both the mesenteric arterial and venous systems must be adequately evaluated, arterial and venous phases are obtained.
  • arterial phase (obtained 25-30 seconds after contrast agent injection), images are obtained from above the level of the coeliac axis to the level of the common iliac arteries.
  • portal phase (obtained 60–70 seconds after contrast agent injection), images in this phase are obtained from above the level of the diaphragm to below the level of the symphysis pubis. 

Data acquisition and analysis

• images are analyzed on a dedicated workstation.
• two-dimensional (2D) multi-planar images, as well as rendering techniques such as maximum intensity projection (MIP),surface shaded displays (SSD) and volume rendering (VR)
• for 3D images of the splanchnic veins, coronal images of the portal vein and the proximal portion of SMV with its confluence to the splenic vein ^1,3

Image interpretation

CT angiograms are assessed for evidence of arterial stenosis or occlusion e.g.

•  vessel occlusion is defined as complete obstruction of the lumen
• hemodynamically significant vessel stenosis is defined as a reduction in lumen diameter  > 50,
• hemodynamically insignificant stenosis is defined as a reduction in lumen diameter < 50% ¹

Axial CT images should be evaluated for secondary signs of ischemia e.g. bowel wall thickening , focal lack of bowel wall enhancement, bowel dilatation, mesenteric stranding, ascites, pneumatosis intestinalis,free superior mesenteric or portal venous gas, intraperitoneal air,solid organ infarction.

Contraindications

general CT contraindications such as pregnancy, claustrophobia, etc

Advantages 

Mesenteric CT angiography has several advantages over conventional angiography as,

• it is a minimally invasive procedure
• low cost examination
• takes less time

Findings 

Arterial pathology:

• ischemia (Occlusion or stenosis)
• vasculitis
• aneurysm
• dissection
• coeliac artery compression syndrome
• superior mesenteric artery syndrome
• segmental arterial mediolysis

Venous pathology:

• venous thrombosis