pain and shorter length of stay) but no difference in long-term outcomes compared to open surgery. Conflict of interest statement AB no conflicts of interest – KS no conflicts of interest – SDS no conflicts of interest – JA no conflicts of interest – FTD no conflicts of interest – Contribution by authors: AB and KS planned the review. Each author drafted a topic section outline. AB collated the sections and drafted the first version. AB, KS, SDS, JA, FTD performed rounds of revisions, edited the draft and approved the final manuscript. Table 1: Stratified disease approach to acute appendicitis. Disease Underlying Macroscopic Microscopic Clinical relevance state pathology appearances appearances Normal Normal No visible changes Absence of any Consider (figure 1A) abnormality causes Acute No visible changes Luminal neutrophils May be cause of only with no symptoms; inflammation mucosal consider other abnormality causes. Acute mucosal/ No visible changes Mucosal/ May be cause of submucosal submucosal symptoms; inflammation neutrophils and/or consider other ulceration causes Simple, Suppurative/ Congestion, colour Transmural Likely cause of phlegmonous changes, increased inflammation/ symptoms (figure 1B) diameter, exudate, ulceration/ pus. thrombosis, +/- extramural pus Complex Gangrenous Friable appendix Transmural Impending (figure 1C) with purple, green inflammation with perforation or black colour necrosis changes Perforated Visible perforation Perforation; Higher risk of not always visible in post-operative microscope complications Abscess (pelvic/ Mass found during Transmural Higher risk of abdominal) examination or inflammation with post-operative abscess seen on pre- pus +/- perforation complications imaging; abscess or found at surgery
pain and shorter length of stay) but no difference in long-term outcomes compared to open surgery. Conflict of interest statement AB – no conflicts of interest KS – no conflicts of interest SDS – no conflicts of interest JA – no conflicts of interest FTD – no conflicts of interest Contribution by authors: AB and KS planned the review. Each author drafted a topic section outline. AB collated the sections and drafted the first version. AB, KS, SDS, JA, FTD performed rounds of revisions, edited the draft and approved the final manuscript. Table 1: Stratified disease approach to acute appendicitis. Disease state Underlying pathology Macroscopic appearances Microscopic appearances Clinical relevance Normal (figure 1A) Normal No visible changes Absence of any abnormality Consider causes Acute inflammation No visible changes Luminal neutrophils only with no mucosal abnormality May be cause of symptoms; consider other causes. Acute mucosal/ submucosal inflammation No visible changes Mucosal/ submucosal neutrophils and/or ulceration May be cause of symptoms; consider other causes Simple, (figure 1B) Suppurative/ phlegmonous Congestion, colour changes, increased diameter, exudate, pus. Transmural inflammation/ ulceration/ thrombosis, +/- extramural pus Likely cause of symptoms Complex (figure 1C) Gangrenous Friable appendix with purple, green or black colour changes Transmural inflammation with necrosis Impending perforation Perforated Visible perforation Perforation; not always visible in microscope Higher risk of post-operative complications Abscess (pelvic/ abdominal) Mass found during examination or abscess seen on imaging; abscess or found at surgery Transmural inflammation with pus +/- perforation Higher risk of post-operative complications pre-
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