Introduction: Ectopic pregnancy occurs when a fertilized ovum implants outside the uterine cavity, most commonly within the fallopian tube. Rare implantation sites include the ovary, cervix, abdominal cavity, and retroperitoneal space. Retroperitoneal ectopic pregnancy (REP) is exceedingly rare and potentially lifethreatening. Its deep location near major vessels and retroperitoneal structures often results in delayed diagnosis due to nonspecific clinical manifestations. Because of its rarity and diagnostic difficulty, documentation of such cases is important to improve clinical recognition and management. Case Description: A 30-year-old gravida presented with a two-week history of severe lumbar pain and difficulty in ambulation, without vaginal bleeding or systemic symptoms. Transabdominal ultrasonography revealed a viable extrauterine gestation located beneath the pancreas, corresponding to a gestational age of 9 weeks and 5 days. Exploratory laparotomy identified a 5 × 4 cm ectopic mass adjacent to the right lateral aspect of the abdominal aorta, which was successfully excised. Histopathologic examination demonstrated immature chorionic villi and extravillous trophoblasts without associated decidual tissue, confirming the diagnosis of retroperitoneal ectopic pregnancy. This represents a rare documented case from Davao del Norte, Philippines. Discussion: The vast majority of ectopic pregnancies occur within the fallopian tube, while retroperitoneal implantation is exceptionally uncommon. Accounting for less than 1% of all ectopic gestations, REP is associated with significant morbidity due to delayed recognition and the technical complexity of surgical management. This case, which followed natural conception and presented solely with lumbar pain, underscores the importance of considering rare implantation sites in women with unexplained abdominal or back pain. Early imaging and prompt surgical intervention are critical to achieving favorable outcomes. Conclusion This report highlights a rare presentation of retroperitoneal ectopic pregnancy and emphasizes the vital role of comprehensive clinical, radiologic, and pathologic correlation in establishing the diagnosis. Increased awareness may facilitate earlier detection and improved management of future cases.
Female ; Pregnancy ; Pregnancy, Abdominal ; Pain