Abdomen, Emergency, Pelvis, MR, Education, Inflammation
A. Somasundaram, C. Jeavons; Gold Coast, QLD/AU
Imaging findings OR Procedure details
Step 1. Localise the appendix.
As with CT, localising the appendix can be a difficult task given its wide variation in position. The caecal tilt angle can be assessed on sagittal T2 – an angle of at least 90 ° localizes the appendix to the right upper quadrant with high specificity irrespective of gestational age.
Subsequent localisation of the appendix may require concurrent use of multiple planes. The T2 non-fat saturated HASTE sequence often provides sufficient spatial resolution to identify the appendix, while T2 fat saturated HASTE can help localise the region of interest through its high sensitivity for fluid and oedema. In difficult cases, the GRE sequence may assist by emphasising appendiceal intraluminal gas or calcifications through blooming artefact.
Step 2. Identify primary and secondary signs of acute appendiceal inflammation.
An obstructing appendicolith, appendiceal diameter >6 mm (outer wall to outer wall) and T2 wall hyperintensity are all suggestive of acute appendicitis. Without other primary or secondary findings, an appendix diameter >6 mm alone has demonstrated less sensitivity than the other aforementioned primary findings of acute appendicitis.
Secondary features include T2 hyperintense oedema of the mesoappendix or surrounding mesentery, intraperitoneal free fluid and para-appendiceal or para-caecal phlegmonous mass. The presence of secondary appendiceal signs without primary signs should raise suspicion for a diagnosis of early appendicitis in the absence of any alternate abdominal pathology.
Step 3. Review for other common causes of acute abdominal pain.
Haemorrhagic fibroid degeneration is commonly associated with pregnancy and can be identified as a T1 hyperintense rim around a fibroid.  The ovaries should be specifically reviewed to evaluate for ovarian cyst rupture and ovarian torsion. A large field of view T2 sequence can be used to localise acute inflammation of the kidney or gallbladder, and similarly, obstructing renal calculi, hydronephrosis, or small bowel obstruction can be identified.