A 30-year-old woman presented to the gynaecology clinic with a painful lump in the right-hand side of a five-year-old caesarean section scar. She had first noticed this lump 18 months before, when at the gym, and since then she had felt that it had grown slightly in size and become increasingly painful. She described this pain as an ache that was worse at the time of her period. She had regular periods and at the time of the clinic was on day 23 of her cycle. She had had two previous pregnancies: one normal delivery seven years ago and one elective caesarean section five years ago for a breech presentation. She had no other gynaecological history, had had regular smears, all of which were normal. She had no relevant medical or surgical history, no relevant family history. She was a non-smoker and drank alcohol socially.

On examination, her abdomen appeared normal with a Pfannensteil scar noted. There was no obvious mass seen. On palpation her abdomen was soft and non-tender. There was a lumpy mass felt under the right lateral edge of the scar, which was irregular in nature, soft, non-tender and immobile. An MRI scan showed a 3×2.5x2cm mass anterior to the right rectus muscle indicative of scar tissue or inflammatory in nature. A biopsy was suggested to confirm the nature of the mass.

The patient was taken to theatre to perform an excision of the lump. The lump removed was 4x5cm diameter (see Figures 1–2) and, although tethered to the underlying muscle, there was no continuity with the abdominal cavity. The lump appeared to be mainly fatty tissue on initial inspection, although it was noticed that several small bluish/black dots appeared on the lump. The whole lump was excised with some surrounding fatty tissue and sent for histology. There were no postoperative complications and the patient returned home the same day. The histology report showed that the lump was benign in nature and contained endometriosis.

Figures 1–2. Excising the caesarean section scar lump.


Endometriosis is the presence of endometrial tissue outside the uterus and can be seen in intra- and extra-abdominal locations. Extra-pelvic endometriosis is rare, but there are reports of endometriosis in almost all locations, including kidneys, lungs and the central nervous system.1 Previous reports of endometriosis in caesarean section scars have reported the incidence as between 0.03 and 0.4 per cent.2 A study by Akbulut et al in 2010 reported the incidence as 0.1 per cent of women who undergo a caesarean section – a rare complication of this surgery. These lumps are often misdiagnosed when they first present, as a lipoma, abscess, suture granuloma, cyst or haematoma.

The patient in the above case report presented with the typical symptoms seen in cases of scar endometriosis: a palpable mass and cyclical pain. However, it should be noted that in several studies more than half of the presentations have been non-cyclical pain.

The development of this mass of ectopic endometrial tissue in the surgical scar is most likely explained by dissemination of the endometrium or from pre-existing intraperitoneal endometriosis.3 In this patient’s case there was no known history of endometriosis so it is likely that this was caused by seeding of endometrial tissue during the caesarean section. Contamination of the wound with endometrial tissue is likely to occur often and is sometimes inevitable4, but the cases such as the one above are rare. This suggests that there is some predisposition to the development of scar endometriosis. It is worth noting the length of time (three-and-a-half years) before symptoms became apparent. This is likely because the endometrial tissue must grow to a size large enough to cause symptoms. Other case reports have published intervals of between six months to 20 years.5

Although a rare event, malignant transformation of abdominal wall endometriosis is a possibility.6 A case study by Stevens et al suggested that endometriosis in a caesarean scar can transform into metastatic adenocarcinoma.7 Therefore, wide excision with at least 1cm margin is considered the treatment of choice, even for recurrent lesions. The MRI scan and subsequent measurements of the lesion excised show that this was achieved in our patient.


Endometriosis should be considered as a diagnosis in a patient presenting with a painful lump in an abdominal scar, particularly with a history of a caesarean section, even many years after the original surgery. Careful closure and avoidance of contamination (changing gloves, needles before closure) following caesarean section may prevent scar endometriosis.