A thin 17 year old male presents with right iliac fossa pain. He has had a recent viral illness and you wonder whether this is mesenteric adenitis.
Describe and interpret these scans
Image 1: Tracing the appendix from its tip to base in the right iliac fossa. The transducer is in the sagittal plane and swept from medial to lateral, from pelvis then over the external iliac vessels and then over the body of psoas.
There is almost no subcutaneous fat. The linear longitudinal fibers of the rectus abdominus muscle are seen superficially. Deep to this at the start and end of the loop some normal small bowel, probably ileum is seen. The circumferential layers of the bowel wall are beautifully demonstrated here. This is sometimes referred to as “bowel wall signature“.
Next we see the distended (to 12mm) blind ending tip of the inflamed appendix. Its wall is thinned but appears intact. Following the appendix proximally some debris is seen within its lumen and then the diameter reduces as an obstructing appendicolith is seen. On the caecal side of the appendicolith the appendix is of normal diameter (≤ 6mm) and retains the normal bowel wall signature. The actual origin from the caecum is not visualised.
The periappendiceal fat is echogenic (bright) as is characteristic when inflamed. There is a trace of free fluid seen adjacent to the ileum at the start of the loop.
Deep to the appendix we initially see bowel, then external iliac vessels with the artery above the vein, then the body of psoas is seen.
Acute appendicitis with appendicolith
The normal appendix.
The appendix has typical bowel wall signature (the histological layers are conveniently well seen on ultrasound).
It is blind-ending and originates from the caecum.
It is normally ≤ 6mm in diameter and in its usual non-distended / inflamed state is compressible with transducer pressure.
The cause of appendicitis is often luminal obstruction. The appendix distal to the obstruction becomes inflamed and distended. Ultrasound may show the obstructing lesion which can be a non-calcified faecal pellet, or in this case a calcified pellet termed an appendicolith or faecolith. Sonographically calcified lesions have an echogenic surface and cast a dense posterior acoustic shadow.