Inferior Mesenteric Artery (IMA)

(At any time you can rotate the image or add or subtract structures. Clicking the link will always bring you back to a starting point. Remember to use rollovers to see the labels for the various structures. Also, by moving the axial plane to any point in the image on the right, you can see the cross-section on the lower left. Any coloration in the right image will be shown in the cross-sections.)



Begin by looking at the Abdominal aorta, vertebral column and pelvic girdle. Rotate the image 90 degrees to appreciate how the course of the aorta follows the curve of the vertebral column.

Add on the Inferior mesenteric artery (IMA). Identify the left colic and superior rectal branches. To appreciate how most of the IMA and its branches are retroperitoneal and course along the posterior body wall, rotate the image to 280 degrees and remove the ilium. Rollover the arteries to identify which ones are not associated with the body wall. Candidates include the sigmoid branches of the superior rectal artery. To make a case that these are peritoneal, rotate the image to 335 degrees. Only the sigmoid branches are highlighted. Use the <Ctrl> or <apple> key and directional arrows to rotate the image incrementally between 0 and 275 degrees (go slow, the computer is crunching a lot of data). You may remain unconvinced, because the posterior body wall is thick. Let's add some retroperitoneal structures, the descending colon and kidney . Rotate the image as before. Now add on a peritoneal structure, the sigmoid colon. Rotate the image. Note how the sigmoid colon departs from the curvature of the vertebral column, because it is peritoneal. Be sure to rollover highlighted and unhighlighted structures to recall their names.

Let's look for anastomoses with the superior mesenteric artery (SMA). Add on the SMA and rotate to 290 degrees to contrast the peritoneal course of the SMA from the retroperitoneal course of the IMA. Now add the middle colic branch. Rotate to 90 degrees to demonstrate that the middle colic artery arcs posteriorly to anastomose with the left colic branch of the IMA. This arc is often called the marginal artery of Drummond. Note how it follows the course of the transverse colon, which it supplies.

The anastomosis of the superior and inferior rectal arteries is not demonstrated by this program, but you should be aware of it as it is also clinically relevant. Further, the accompanying venous anastomosis is one of the three important porto-caval anastomoses.