Retroperitoneal, or psoas, abscess is an unusual problem, which has insidious and occult characteristic. There are often delays in the diagnosis of retroperitoneal abscess due to its insidious nature, and it frequently extends beyond the peritoneum before being identified. Even in those cases with contamination from the gastro-intestinal tract, the course appears relatively benign. Retroperitoneal abscess rarely results from perforation of the colon as most perforations occur into the peritoneal cavity. Those that perforate into the retroperitoneum rarely result in formation of a psoas abscess.
Conversely, necrotising fasciitis is a soft tissue infection associated with high morbidity and mortality. Necrotising soft tissue infections have been recognised and reported for centuries the earliest dating back to Hippocrates in the 5th century BC. A rapidly progressive soft tissue infection (synergistic undermining gangrene) caused by the synergistic action of a β-haemolytic group streptococcus +/- staphylococcus, was described in 1924 by Meleney. Wilson subsequently re-termed this observed phenomenon as necrotising fasciitis, in 1952.
Necrotising fasciitis is rare within the UK with an estimated at 500 new cases each year, however this is difficult to confirm, as different eponyms are given to describe the same condition, as outlined above. The aetiology of necrotising fasciitis is not fully understood, with patients often having a history of trauma, including insect bites, scratches, or abrasions. However in some cases no primary cause can be found. Patients that have pre existing conditions which increase susceptibility to infection seem to be at an increased risk of developing necrotising fasciitis these conditions include diabetes mellitus, peripheral vascular disease, chronic renal failure, drug misuse, and advanced age.
The cornerstone of management of necrotising fasciitis is recognised as being aggressive surgical debridement and intensive support, whilst other severe soft tissue infections do not necessarily require the same amount of aggressive debridement. Therefore it is important that clinicians are able to differentiate between the two.
Necrotising fasciitis should be considered in those patients who have rapidly progressing cellulitis, and palpable subcutaneous crepitus, in association with tachycardia, hypotension, neutropenia or neutrophilia, and hyponatraemia.
Adjuvant diagnostic tools for necrotising fasciitis include CT scanning and plain radiography. In this case the clinical finding of crepitus, and soft tissue air on plain radiograph were both present, however these signs are only seen in 37% and 57% of patients respectively.
The finding of necrotising fasciitis of the anterior abdominal wall associated with a carcinomatous perforation of the colon is rare, having only previously been described with perforation of a sigmoid colon carcinoma directly adherent to the anterior abdominal wall. In addition, this case is unusual in that retroperitoneal abscesses have been described to track along psoas, or through the obturator foramen to give swellings in the thigh or gluteal region, but not to give rise to infection of the anterior abdominal wall[1, 9].
This case illustrates that the principles of management should be two-fold; 1) To rapidly and unequivocally control infection and sepsis through extensive radical debridement of necrotic tissue and; 2) Identify and treat any underlying condition giving rise to the infection, in this case removing the caecal tumour.
Intravenous antibiotics should be started promptly and modified when sensitivities return. However, it is essential to ensure that adequate necrotic material is removed at the first opportunity to reduce the risk of further progression, regardless of the defect that will remain. Defects may be closed using a variety of techniques, including split skin grafts, Vacuum Assisted Closure (VAC) therapy, and flap procedures, including myocutaneous flaps [10–12]. Hyperbaric oxygen therapy in the treatment of necrotising fasciitis remains controversial, conflicting studies have reported contradicting results as to potential benefits.