I have seen the surgeon post this DX a few times now. Acute perforatated appendicitis with phlegmon. I am wanting to code this to icd 10 K35.20; Acute appendicitis with generalized peritonitis, without abscess. Since the phlegmon definition is: The difference between phlegmon and abscess is as follows: A phlegmon is unbounded and can keep spreading out along connective tissue and muscle fiber. An abscess is walled in and confined to the area of infection (healthline.com). From that definition generalized peritonitis sounds correct because it is not localized to one area. However since we are not clinical and the provider does not specifically state the infection was not localized or generalized I am unsure if we can code for this. Can anyone tell me how you would code or this?