A 68-year-old woman was referred to the emergency department with poor stoma output, abdominal distension and tender parastomal lump for 5 days. She had a past medical history of abdominal hysterectomy, renal transplantation on the left side, Hartmann’s procedure for acute diverticulitis and atrial fibrillation (AF).The parastomal swelling was growing slowly and had been present for nearly 3 months. It had increased in size and became tender for the last 5 days. She took cyclosporin and warfarin for her renal transplantation and AF, respectively, in addition to her other regular medication. On examination, she was dehydrated and febrile. Her abdomen was distended but non-tender with exaggerated bowel sound. The stoma bag was empty. An erythematous, oval-shaped (8 cm × 6 cm), hard and tender lump was found at the outer aspect of the stoma (figure 1), which gave initial impression of an incarcerated parastomal hernia. On questioning, the patient reported that she had used a hot water bottle over that area for comfort.

Her blood results showed raised levels of white cell count, C reactive protein, urea and creatinine. Her international normalised ratio (INR) was 4. Abdominal x-ray showed faecal loading in the right colon without any features of obstruction. No bowel gas shadow was found in the parastomal mass. A phosphate enema was given through the stoma after digital examination, which worked well and the stoma started working immediately. A CT with intraluminal contrast through the stomal orifice (without intravenous contrast considering high creatinine level) was arranged subsequently to determine the exact nature of the parastomal swelling. It showed oedematous colon with multiple diverticuli and an organised abscess adjacent to the mesocolon of the colostomy (figure 2). A diverticulum adjacent to the mesocolon was suggested as the possible source of it.

She was started on intravenous antibiotics and therapeutic dose of low molecular weight heparin after stopping warfarin. Given her history of previous multiple laparotomies, on-going sepsis, renal impairment, immunosuppression and raised INR, she was not considered as an ideal candidate for surgical intervention. A CT-guided aspiration and drainage was performed after stabilising her general condition, which produced nearly 60 ml of feculent pus immediately and drained a total of 200 ml over the subsequent week through the pigtail drain placed in situ (figure 3).The swelling reduced considerably a week later (figure 4). Pus culture demonstrated mixed flora.

Though parastomal abscess from an impacted chicken bone has been previously reported,⁴ it is the first reported case of organised parastomal abscess from a mesocolic diverticulum. Low-grade infection in an immunosuppressed patient with compromised renal function may give rise to dehydration, poor oral intake and constipation. This, with a parastomal swelling, gave the impression of an obstructed parastomal hernia as the incidence rate of parastomal hernia is as high as 33%.⁵ The organised mesocolic abscess was detected by a subsequent CT scan. Justifiably, CT scan remains the ‘gold standard’ investigation for suspected diverticular abscess.² Ambrosetti et al states that mesocolic abscesses can usually be managed conservatively without drainage and, should surgery be necessary, en bloc resection with immediate anastomosis can usually be performed.⁶ This was not a valid option in the above case for obvious comorbidities and technical difficulties. Since the original communication between the diverticular abscess and the lumen of the bowel is obliterated,³ percutaneous drainage can safely be performed in patients with a diverticular abscess under radiological guidance. It can be used as a bridge before definitive surgery but it is a treatment option in its own right in high-risk surgical patients,⁷ such as this case. Successful percutaneous drainage can be performed in 70–90% of patients with an amenable diverticular abscess.⁷