•A 50-year-old patient presented acutely with abdominal pain.

•Gynaecological assessment suspected an endometriotic cyst and multidisciplinary review advised a laparoscopic bilateral salpingo-oophorectomy.

•Arising from the left adnexa was a large, benign-appearing mass, measuring approximately 10cm in size.

•The cyst size and adhesions (peritoneal and omental) distorted the pelvic anatomy, obscuring complete assessment of the pelvis; prompting the decision to convert to open. 

•A Pfannenstiel incision offered adequate access to the pelvis.

•Blunt exploration and adhesiolysis revealed the cyst’s retroperitoneal origin, separate to the left ovary and adherent to the pouch of Douglas and left internal iliac artery.

•The left pelvic sidewall was opened, identifying the iliac vessels and ureter. The cyst ruptured spontaneously, releasing clear fluid and then the cyst wall subsequently peeled from the retroperitoneum.

•As both ovaries were normal, there was no indication for removal.

•Post-operative recovery was uneventful.

•Histological examination revealed a benign mullerian cyst. No further follow-up was arranged.

 

Discussion: 

Retroperitoneal mullerian cysts are remanent of the mullerian duct, diagnosed pre-operatively in 25% of cases. They are generally serous, benign and can grow to large sizes or recur in incomplete excision. The pathogenesis is unknown, however oestrogen stimulation is hypothesised as a cause.

The multidisciplinary opinion, suspecting an ovarian cyst, suggested laparoscopic surgical removal. Success of this laparoscopic approach may be dependent on surgical skillset, however removing large cystic structures intact, through laparoscopic ports often poses challenge. If the pathology had been malignant, cyst content spillage would have affected staging.

Decision making about the surgical approach should ensure the incision achieves adequate access and intact specimen retrieval.  Operative technique should consider: surgical skill, operating time and specimen retrieval. Consent should include the risk of open surgery. 

Retroperitoneal masses can mimic other pelvic structures, proving that imaging cannot always offer diagnostic certainty. Operating within the retroperitoneum can be challenging, requiring anatomical knowledge and surgical precision and exploration of this anatomical area may not be commonly practised by benign gynaecologists.

 

Conclusion: 

This report describes the removal of an unknown structure, classified at histological examination. It questions operative approach and highlights surgical vigilance. When unexpected intra-operative findings occur, anatomical principles and systematic approaches must be applied to achieve successful outcomes without complications.