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Q1: What is the differential diagnosis?
The differential diagnosis of this swelling with late onset after surgery include organised haematoma, stitch abscess granulomatosis, incisional hernia, endometrioma, and neoplasm which is either intra-abdominal or neoplasm of the abdominal wall itself as sarcoma, desmoid tumour, or metastatic cancer.1-3
Q2: What investigations should you consider?
An ultrasound scan will help to determine if the mass is cystic or solid and exclude underlying intra-abdominal pathology. This was done (fig 1) and showed a 2 cm hyperechoic area in the abdominal wall musculature with no posterior defect, which excluded the possibility of incisional hernia. There was no associated intra-abdominal pathology.
Other investigations which could be considered include computed tomography and fine needle aspiration cytology.
Q3: How would you treat this patient?
Surgical exploration of the scar and excision of the swelling should be considered. This was performed and there was 2 × 2 cm firm mass in the subcutaneous tissue which was extremely adherent to the anterior rectus sheath. The sheath was partially excised to ensure complete removal of the mass. Histopathology examination of the resected tissue confirmed the presence of endometriosis.
The cause of surgical scar endometriosis is believed to be iatrogenic transplantation of endometrium into the surgical wound particularly during late pregnancy and delivery where endometrial tissue has the maximum potential for ectopic implantation.4
The reported incidence after term or near term caesarean sections ranges from 0.1%–0.4%.5
The endometrial tissue inoculum is subsequently stimulated by oestrogens to proliferate until it becomes large enough to cause symptoms. The time interval between surgery and the onset of symptoms is variable and ranging from a few months to several years with average interval of 4.5 years.6 Incisional endometriosis usually occurs in the right side of the scar as it is the usual side of the operator and it is densely attached to fascia.
The typical presentation is a tender mass adjacent to surgical scar of gynaecological procedure. The tenderness is usually intermittent and is associated with the menstrual cycle, but this pattern is not always present. The rare incidence and late onset with slow and intermittent progression of symptoms after surgery is usually misleading and is the main cause of misdiagnosis.6 7 It is also interesting to note that incisional endometriosis is rarely found in association with symptoms or findings of pelvic endometriosis.6
Medical treatment of surgical scar endometriosis is similar to treatment of other forms of endometriosis but it only produces temporary alleviation of symptoms followed by recurrence after cessation of the treatment.8 Therefore, surgical excision is the treatment of choice and should include the mass and a clean surgical margin which may include part of the rectus sheath in order to prevent recurrence. Synthetic mesh may be necessary to close large defects of rectus sheath.9 A preoperative period of suppression of ovulation may be considered to reduce vascularity of the lesion, which may facilitate surgery and reduce postoperative complications.