Diagnostic challenge: functional non-communicating rudimentary horn with ovarian endometriosis and ipsilateral renal agenesis.

A teenage girl presented with sudden lower abdominal pain following exercise, prompting initial consideration of ovarian cyst rupture by the attending emergency physician. However, the presence of unilateral renal absence on Computed Tomography (CT) imaging strongly suggested a reproductive tract malformation, later confirmed by Magnetic Resonance Imaging (MRI). Surgical exploration during laparotomy revealed a functional non-communicating rudimentary horn with associated ovarian endometriosis, in the setting of chronic dysmenorrhea. This rare case underscores the essentiality of comprehensive preoperative assessment to identify anatomical variations, guide surgical decision-making, and prevent diagnostic errors. Subsequent literature review focused on the co-occurrence of endometriosis in rudimentary horns and congenital urinary system abnormalities.