A diagnostic challenge of primary serous borderline tumor involving the peritoneum: A case report

Primary peritoneal serous borderline tumor (PPSBT) is a rare epithelial tumor that is identical to non-invasive peritoneal implants in patients with ovarian serous borderline tumors.

A 51-year-old woman presented with abdominal swelling. Radiological findings revealed a large, well-defined cystic lesion within the right abdominopelvic cavity, measuring 19 × 14 × 10 cm, without any connection to both ovaries. Given the imaging characteristics, the differential diagnosis primarily included benign cystic neoplasms, mesenteric or peritoneal cysts, and other cystic lesions of gastrointestinal or embryological origin. Laparoscopic excision of the cyst was done. The gross examination showed the smooth outer surface with an intact capsule. The inner surface showed firm yellow-white papillary outgrowths. Microscopic examination revealed numerous irregular papillae with fibro-myxoid cores and a hierarchical branching pattern. The component cells have large hyperchromatic nuclei and a moderate degree of cellular atypia. By immunohistochemical staining, the tumor cells showed a positive reaction for PAX8 and WT1, while calretinin was negative. The diagnosis was reported as a primary peritoneal serous borderline tumor.

The clinical presentation of PPSBT is often misleading. Thorough radiological and laparoscopic examinations are very important to exclude any secondary involvement from ovarian tumors. Microscopic examination and immunohistochemical staining are crucial for establishing the diagnosis of PPSBT and exclusion of other differential diagnoses. Complete surgical excision of the cyst is the standard treatment with follow-up of the patient.

PPSBT is a rare and challenging diagnosis. It requires accurate clinical, radiological, histopathological, and immunohistochemical examination.