Primary retroperitoneal mucinous cystadenoma is a rare benign cystic tumor.

Preoperative radiological diagnosis of benignity is fundamental.

Histologically composed of tall columnar cells and low cuboidal cells, on a collagenous stroma.

Surgical resection is the recommended treatment.

Primary Retroperitoneal mucinous cystadenoma (PRMC) is an extremely rare benign tumor, predominantly occurring in women, with unclear pathogenesis.

A 31-year-old woman, with no medical or surgical history, presented with left flank pain.

An abdominal computed tomography (CT) scan revealed an 11cm retroperitoneal cyst. Due to its large size, percutaneous CT-guided drainage followed by a laparotomy surgical resection, were performed. Post-operative course was uneventful. Histological and immunohistochemical findings were consistent with PRMC. The patient was disease-free after a 6-month follow-up.

Mucinous cystadenoma is a very odd finding in the retroperitoneum. Multiple differential diagnoses are to be considered beforehand, as most of cystic lesions in this anatomical region are malignant and require a different surgical approach. Radical resection, by laparotomy or laparoscopy, is the treatment of choice.

Retroperitoneal cyst

Benign retroperitoneal tumor

Mucinous cystadenoma

Primary retroperitoneal mucinous cystadenoma

Surgical pathology

Case report

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