Purpose or Case Report: In the diagnosis of acute appendicitis, unenhanced MRI provides an efficient and comprehensive evaluation of the appendix. However, on the daily clinical basis, there are cases that generate a diagnostic dilemma with subtle/indeterminate inflammatory changes. For these questionable cases, the morphology of the appendix could play a role as an aid for the radiologist to increase the confidence diagnosing or ruling out acute appendicitis. The aim of this study is to evaluate the morphology of the appendix as an additional tool for the diagnosis of appendicitis.
Methods & Materials: We conducted a retrospective search in the last 2 years. All children with MRI with appendix protocol were included. Exclusion criteria were: frank appendiceal perforation, periappendiceal abscess, partial or no visualization of the appendix and diameter of the appendix larger than 12 mm. Morphology of the appendix was evaluated on the axial, sagittal and coronal T2 HASTE non-fat-sat sequences. Diffusion images and T2 fat-sat sequences were not evaluated to avoid selection bias. Maximal diameter of the appendix was recorded. Morphology was classified in 2 groups: Straight/Open curve and Pigtail/Narrow curve. Interobserver reliability test of the morphology was performed with 40 randomly selected cases.
Results: We included 95 children, 51 girls, mean age 11yrs (3-17 yrs) and 33 (35%) with surgically proven acute uncomplicated appendicitis. As expected, children without appendicitis had smaller appendiceal diameters (median of 6mm (4-7mm)) in comparison to children with acute appendicitis (median of 8 mm (6-12 mm)) (p<0.01). Children with and without appendicitis demonstrated a significant difference in appendiceal morphology (p=0.19), as 65% (40/62) of the cases without appendicitis exhibited a Pigtail/Narrow curve morphology; whereas 60% (20/33) of the cases with acute appendicitis had a Straight/open curve morphology. Interobserver reliability in the morphology evaluation was 0.66.
Conclusions: Normal appendices usually demonstrate narrow curves or Pig-tail morphology. In cases where the MRI diagnosis of appendicitis is not straightforward, the morphology of the appendix could play a role as an additional diagnostic tool. Although normal appendices can be straight in morphology; the lower incidence of narrow curves or Pig-tail morphology in cases of acute appendicitis could be related to increase in intra-appendiceal pressure, resulting in straightening of the appendix.