The 16 month old female went on to have a laparoscopic appendectomy which revealed a gangrenous, perforated appendix with phlegmon.
Periappendiceal hyperechoic structure (PHS) is an ultrasound finding described as an amorphous hyperechoic structure (usually greater than 10mm) seen surrounding a noncompressible appendix with a diameter greater than 6mm 1. The appendix imaged above had a maximum antero-posterior dimension of 11 mm, with the PHS measuring >10 mm.
PHS is thought to represent an inflammatory process of the adjacent omental or mesenteric fat encapsulating the inflamed appendix. It has been associated with severe appendicitis such as gangrenous and phlegmonous appendicitis 1.
Microscopy of appendix indicated ulceration of the mucosa of the appendix and a florid, transmural acute, suppurative inflammatory cell reaction with areas of necrosis of the wall of the appendix and obvious perforation. The inflammation extends into the mesoappendix where there is purulent exudate on the serosal surface, indicating at least localised peritonitis.
Summary: Gangrenous appendicitis with perforation and at least localised appendicitis.