A 44 year old woman presented with severe left-sided lower abdominal pain three days after a microwave endometrial ablation for menorrhagia. The pain was described as sharp, worsened with movement and associated with vomiting. She had not opened bowels since the operation. It was severe enough to require opiate analgesia. She had undergone a microwave endometrial ablation procedure three years previously for treatment of menorrhagia. However, over the last eight months, the symptoms had returned and she requested a second microwave endometrial ablation. She had a twin pregnancy following IVF treatment 11 years ago. The twins had been delivered by caesarean section. She was also known to have pelvic endometriosis.The microwave endometrial ablation procedure was preceded by saline hysteroscopy that revealed a normal size, anteverted uterus with a regular endometrial cavity. The saline was then aspirated from the endometrial cavity. An uneventful microwave endometrial ablation was then performed. The treatment lasted 2 1 = 2 minutes and the entire cavity was ablated.On admission, the patient was febrile and tachycardic. Abdominal examination revealed tenderness over the left iliac fossa but was not associated with guarding or rebound. Bowel sounds were present and normal.A full blood count revealed an elevated white cell count of 15.1 Â 10 9 /L with a predominance of neutrophils, C-reactive protein was raised at 374 mg/L (normal <5 mg/L). Abdominal and chest X-ray did not show any evidence of bowel perforation. A working diagnosis of endometritis was made, and a broad-spectrum antibiotic commenced. Her symptoms initially settled with this treatment. Transabdominal ultrasound scan showed a 6-cm mass of mixed heterogeneity in the left iliac fossa. CA125 was found to be mildly elevated at 44 IU/L (normal <25 IU/L).In view of these findings, laparotomy was performed via a midline incision. On the left side, a pelvic abscess of approximate size 7 Â 10 cm was identified. The abscess extended up the left pelvic side wall beneath the sigmoid mesentery and inferiorly to the uterus. Although the sigmoid colon itself was inflamed, the serosa was intact with no evidence of thermal injury. The uterine serosa showed signs of inflammation without any evidence of thermal injury or perforation. The left tube and ovary could not be visualised. The right ovary had an endometrioma of approximately 4 cm, and was adherent to the pelvic wall on that side. The Pouch of Douglas was obliterated by adhesions.Following surgical drainage, treatment with intravenous metronidazole, 500 mg 8 hourly, and ciprofloxacin, 500 mg 8 hourly, was followed by oral antibiotics for two weeks. Microbiological culture from the abscess revealed growth of lactose fermenting coliforms and mixed anaerobes and confirmed sensitivity to the prescribed antibiotics. The patient made a good recovery and was discharged home on the seventh post-operative day.The woman was readmitted 10 days later with a recurrence of symptoms. Full blood count continued to show raised wh...