Primary Retroperitoneal Mucinous Tumours Diagnosed in Pregna
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Primary retroperitoneal mucinous tumours (PRMTs) are rare neoplasms occurring predominantly in women, many of whom are in their reproductive age. Histologically, PMRTs can be categorised into three main types: mucinous cystadenomas (MC), mucinous borderline tumours or tumours of low malignant potential (MLMP), and mucinous carcinomas (MCa)

Here, presents the case of a 36-year-old female,was found to have a right ovarian cyst during an anomaly scan performed at 20 weeks’ gestation. The right ovarian cyst measured 11.5 × 9.8 × 8.8cm with a ground-glass appearance with two papillary projections with grade 1 flow on Doppler, the largest of which measured 4.1 × 3.3 × 3.1cm . The mass was non-tender, and there was no free fluid in the pelvis.

Notably, all tumour markers were within normal range: CA125 31U/mL (0–35), CA19-9 11U/mL (0–35), CEA 2ng/mL (0–4.7). Differential diagnoses included mucinous borderline tumour, ovarian malignancy, and decidualised endometrioma.

The patient underwent an MRI at 20 weeks’ gestation and a repeat scan three weeks later did not show a significant increase in the cyst size. Following a multidisciplinary team meeting, the patient was offered ultrasonographic monitoring of cyst every 4 weeks, with a preliminary plan to deliver by elective Caesarean section at 34 weeks and perform an oophorectomy at the same time. The cyst size and characteristics remained generally unchanged.

At 34 weeks, the patient underwent an elective Caesarean section. However, both tubes and ovaries appear normal. The mass previously observed on imaging appeared to be retroperitoneal, extending to the lower border of the liver. For this reason, no further surgical procedure was carried out at the time.

An MRI done postnatally confirmed that the mass was retroperitoneal in origin (Figure 3) and after further surgical planning, the patient underwent a laparotomy, 6 weeks after her Caesarean section. An encapsulated retroperitoneal mass measuring 19 × 19 × 18cm was removed with no spillage of tumour contents. No other intraabdominal pathology was noted.

Histopathological analysis of the mass revealed a moderately differentiated, intestinal-type adenocarcinoma suggestive of primary retroperitoneal MCa. She was followed-up by the oncology team. A whole-body fluorodeoxyglucose-positive emission tomography (FDG-PET) was repeated at 1 year, and did not show any evidence of recurrence.

In conclusion, PRMT is rare and difficult to diagnose preoperatively. No clear consensus has been met regarding the origins of these tumours. Tumour resection is the mainstay of treatment. The role of adjuvant chemotherapy continues to be unclear. Close follow-up and appropriate management based on histological appearance are crucial in these patients so that recurrence can be identified and treated at an early stage.