Case 7: Introduction to appendicitis.
This patient has appendicitis. The appendix is enlarged. It does not fill with oral contrast. It is surrounded by mesentery with increased attenuation (mesenteric stranding). The appendiceal mucosa enhances more than the surrounding bowel. The cecum is thickened at the appendiceal orifice.
Appendicitis is one of the most common emergency
room diagnosis. The criteria for an abnormal appendix are as follows:
distended
greater than 6 mm from outer wall
to outer wall;
non filling with air or oral contrast;
hyper-enhancing mucosa; and
stranding in the surrounding (i.e. have increased attenuation when compared to the rest of the
intra-abdominal fat). Often, the cecum is thickened in the region where the appendix originates. All
of these findings are seen in this case.
The first step in evaluating for appendicitis is to find the appendix.
The appendix is a blind ending tubular
structure that arises from the cecum opposite the ileocecal
valve from the ascending colon. Normally, the ascending colon is superior to
the ileocelcal valve and the cecum is inferior. The appendix then originates from the
medial surface of the cecum, inferior to the ileo-cecal valve. A common strategy
for identifying appendix is to find the ileocecal valve, scroll down 3-5 images,
and there you will magically find the appendix.
However this does not always work: many people have a mobile right lower
quadrant and the structures can move. A technique that works consistently is to "run" the large bowel from the rectum to the cecum.
(Surgeons "run" the bowel with their hands. The CT scanner is cleaner and
less malodorous.) Start at the anus, scroll through the rectum, up through the
sigmoid colon and descending colon. Follow
the lumen of the bowel up and down as you need to. Don't skip segments. Identify
the splenic flexure, traverse rightwards along the transverse colon, then follow
the ascending colon to the ileocecal valve. The valve is easy to find because a
loop of terminal ileum will merge with the colon. Follow the lumen of the colon past the ileocecal valve
into the cecum. The origin
of the appendix is located on the same side of the cecum as the ileocecal valve. If the cecum has
flipped this area may be superior to the valve, not inferior.
However, its origin will be opposite the ileocecal valve from the ascending
colon. Once the appendix leaves the cecum it can travel in any direction.
Coronal images often help with visualization, but I am rarely unable to find the
appendix on the axial images. Using this method I can almost always find the appendix quickly. I
also know that I have evaluated the entire bowel for other things like colitis
or diverticulitis.
Go back to the cine and trace
the bowel from anus to cecum. You can easily find the
ileocecal valve. The
ascending colon is above this level. The cecum is below. The
appendix originates in the
expected location.
Incidentially, this patient has a
horseshoe kidney, an
abdominal aortic aneurysm with
intraluminal thrombus, and a left common iliac artery aneurysm with
intraluminal thrombus.
Take home points
A nice recent review article is found in the American Journal of Roentgenology:
Pinto Leite et al. CT Evaluation of Appendicitis and Its Complications: Imaging Techniques and Key Diagnostic Findings. AJR 2005; 185:406-417.