Retroperitoneal necrotizing soft tissue infection post perforated diverticulitis: a rare case reiterating the need for caution in patients with delayed presentation

Abstract

We report a rare case of a 62-year-old gentleman with a severe necrotizing soft tissue infection (NSTI) of the retroperitoneum requiring extensive life-saving debridement. Patient consent was obtained in written form. He presented to a peripheral hospital with a 2-week history of abdominal pain. Examination revealed abdominal distension and generalized peritonitis. He was febrile but haemodynamically stable. Blood tests were significant only for a white cell count of 21 × 10 cells/L. A contrast-enhanced computed tomography (CT) scan of the abdomen showed extraperitoneal gas extending up to the left anterior abdominal wall and down the left pelvic side wall (Fig. 1). A likely bowel perforation was identified at the level of rectosigmoid junction, in keeping with perforated diverticulitis. An emergency laparotomy followed, during which a rectosigmoid abscess was encountered. This was formalized as a Hartmann’s procedure. Laparostomy was necessary due to colonic distension. The patient was transferred to the intensive care unit. Four days later, with persistently high fevers and a high ionotropic requirement, a perineal abscess was noted. The patient returned to theatre for exploration. Extensive retroperitoneal NSTI was identified involving the left abdominal wall, pelvis and into the perineum (Figs 2,3). After debridement, the patient was urgently transferred to a tertiary centre. He required serial returns to theatre with ultimate debridement of the peritoneum from the left hemidiaphragm, paracolic gutter, presacral peritoneum, cystic peritoneum and pelvic sidewall. Circumferential mesorectal soft tissue necrosis necessitated abdominoperineal resection (Fig. 2). Palliation was considered when diaphragmatic involvement was noted, but fortunately the patient’s overall condition improved and no further resection was necessary. Post-operative issues included a pulmonary embolism despite appropriate prophylaxis. Temporary laparostomy closure was performed using a bridging vicryl mesh and skin graft. Negative pressure wound therapy was applied to the abdomen and perineum, with effective perineal contracture. Local skin flaps were performed by the plastic surgical team to cover the perineal defect. The patient was subsequently discharged to the rehabilitation unit, and will be followed up with a view to delayed abdominal wall reconstruction. Blood cultures from presentation and tissue cultured from the perineal tissue and abdominal wall tissue revealed Escherichia coli, Streptococcus constellatus, Streptococcus milleri and mixed anaerobic flora. Histopathology revealed diverticular abscess with evidence of a perforation into the sigmoid mesentery. Retroperitoneal NSTIs are a diagnostic and therapeutic challenge to the surgeon due to their variable clinical manifestations, delay in diagnosis, high virulence of organisms and a mortality rate which can be as high as 20–40%. There are only a few case reports and a small case series in the literature on retroperitoneal NSTIs, with the case series review showing a mortality rate of 37% when adequate debridement was delayed. The aetiology of retroperitoneal NSTIs varied, including perforated diverticulitis or appendicitis, perineal infection post haemorrhoid surgery, pyelonephritis and gynaecological complications to occasionally necrotizing fasciitis of the extremities. A major predisposing factor for NSTIs is immunocompromised patients. Diagnosis of retroperitoneal NSTIs is more challenging than that of NSTIs, as traditionally NSTIs present with subtle skin changes. Retroperitoneal NSTIs usually do not present with abdominal wall manifestations such as pain, subcutaneous emphysema or erythema until late in the disease course. Due to the lack of specific clinical signs in retroperitoneal NSTIs, there is often a delay in diagnosis until late in the course when patients are in septic shock, as was the