The college loves this condition, and it crops up rather regularly.
Without digressing into deep dark microbiology, one may summarise the issues in the following manner:
The definitive resource for this is probably Wong et al (2005). However, much of the summary below actually comes from the 1995 article by McHenry et al, and represents the historical and clinical features found in a retrospective case series of necrotising fasciitis patients.
Features of history
Features of physical examination
The key factors in its management:
For some reason this keeps coming up in the exam (Question 25.1 from the first paper of 2009 and Question 3.2 from the first paper of 2014). Specifically, the college keeps asking about the Gram-positive rods in the blood culture (it turns out to be a Clostridium species).
According to an authoritative source, "postoperative necrotizing fasciitis of the abdominal wall is usually caused by peritonitis in patients who have undergone multiple procedures for complications of emergency laparotomy".
However, the typical case will present as a polymicrobial zoo, and whereas Clostridium species will likely flourish in the smelly pockeds of avascular fat necrosis, it is unlikely that they will be found in the blood culture, particularly as the blood is so well oxygenated (much of the time). It is more likely that Clostridium perfringens would the sole organism in the cultures of a patient with gas gangrene of the abdominal wall. If the college mentioned subcutaneous emphysema of the abdominal wall, there would be no guesswork involved in this question. This is supported by an article from 1966 (back in the day when surgeons actually palpated people's abdomens instead of scanning them). It reports on ten patients; nine had proper crackly gas gangrene due to C.perfringens or C.multifermentans. One patient with a C.tertium infection only had abdominal wall cellulitis, just like in the college question.
Cancer-related perforations followed by necrotising fasciitis of the abdominal wall do exist in case report literature. One case from the UK reported early debridement so aggressive that it left some small bowel and kidney on show (that time, β-haemolytic strep was responsible).