Pregnancy Deciduosis Mimicking Abdominal Tuberculosis and Peritoneal Carcinomatosis: A Case Report.

Background and clinical significance: Gestational deciduosis is a benign, progesterone-related ectopic decidual reaction that commonly involves pelvic and peritoneal surfaces and usually regresses after delivery. Although generally asymptomatic, diffuse peritoneal deciduosis may present as multiple nodular implants and closely mimic peritoneal carcinomatosis, mesothelioma, or miliary tuberculosis, creating a challenging intraoperative differential diagnosis. Prompt histopathological assessment is essential to prevent unnecessary staging procedures or oncological treatment. Case presentation: A 30-year-old primigravida at 40 weeks' gestation underwent unplanned intrapartum cesarean section after a premature rupture of membranes, the induction of labor, and failed progression. Multiple friable, gray-yellow subcentimetric nodules were incidentally observed on the uterine serosa, adnexa, omentum, visceral intestinal peritoneum, and appendix. The macroscopic appearance raised concern for peritoneal carcinomatosis and abdominal miliary tuberculosis. No ascites or intra-abdominal masses were identified. CA-125 was elevated (207.7 U/mL), Quantiferon testing was indeterminate, and postoperative chest computed tomography showed no pulmonary disease. Histological examination showed ectopic decidual cells with abundant eosinophilic cytoplasm in a perivascular and septal distribution. The cells showed diffuse vimentin, CD10, and progesterone-receptor expression and lacked epithelial and mesothelial marker expression, supporting diffuse peritoneal deciduosis. The postoperative course was uncomplicated, and pelvic ultrasonography at 40 days postpartum showed no residual lesions. Conclusions: Diffuse peritoneal deciduosis should be considered when disseminated peritoneal nodules are encountered during pregnancy or cesarean delivery. In this setting, elevated CA-125 is nonspecific and may heighten concern for tuberculosis or malignancy without distinguishing among these entities. Correlation of the clinical context, operative findings, morphology, and targeted immunohistochemistry is essential to avoid unnecessary oncological treatment or extensive staging procedures.