Acute Appendicitis on Ultrasound

Acute appendicitis is an inflammation of the appendix.  The appendix is a finger like pouch that comes off the large intestine in the right lower abdomen.   Acute appendicitis causes pain, nausea, vomiting, and fever.  It is most common in young patients below 30, but can occur in anyone.   CT is the best test to diagnose appendicitis, however, ultrasound can be very useful as well.

What Causes Acute Appendicitis?

Acute appendicitis is causes by obstruction of the lumen of the appendix.  Fluid builds up, it becomes inflamed, infected, and can eventually rupture.  The opening of the appendix can be blocked by lymphoid tissue proliferation, appendicolith (hard feces with calcification), and other rarer causes like a foreign body.

Why do Ultrasound of The Appendix Instead of CT?

Ultrasound uses no radiation.  This is important because many patients who get appendicitis are young. Ultrasound does not use IV contrast or oral contrast.  There is no need to wait for the oral contrast to pass through the intestine with ultrasound.  One of the limitations is that the test depends on the skill of the ultrasound technologist more than CT.  It may be difficult to find the appendix because bowel loops may cause it to be obscured.

What Does Appendicitis Look Like on Ultrasound?

The appendix will be greater than 6 mm in outer diameter.  It will not be compressible.  The wall will be thicker than 3 mm.  An appendicolith can be seen.  There may be fluid around the appendix.  There will be tenderness to ultrasound probe pressure.  It is important that the ultrasound technologist confirms that the structure does represent the appendix as a bowel loop can have a similar appearance.

What If The Appendix Is Not Seen?

This is a common problem.  Since the appendix is surrounded by bowel loops, it may not be found.  Sometimes even when found, the appendix may be slightly abnormal but not definitive for appendicitis.   In these cases CT can be done.  CT is more definitive and can help in these cases.   The possibility of diagnosing appendicitis with ultrasound without using radiation is worth the effort.

Acute appendicitis on ultrasound can be done for young patients in an attempt to diagnose appendicitis without using radiation.  If the appendix is abnormal, acute appendicitis can be diagnosed on ultrasound.  In cases that are not clear, or the appendix is not found, than CT can be done.  MRI can be done in pregnant patients since we want to avoid radiation exposure.