An 18-year-old patient with an intact hymen presented with severe, cyclical dysmenorrhea, representing a common diagnostic challenge. Initial evaluation at an outside institution, including transabdominal ultrasound (TAUS) and magnetic resonance imaging (MRI), yielded an inaccurate initial radiological report, creating a diagnostic impasse. As transvaginal ultrasound (TVUS) is not feasible in this patient group, point-of-care transrectal ultrasound (TRUS) was performed, leveraging its superior near-field resolution, providing the definitive diagnosis of a non-communicating rudimentary uterine horn. The diagnosis established by TRUS was corroborated by intraoperative findings at laparoscopy. Surgical resection of the rudimentary horn resulted in complete and sustained symptom resolution, validating the clinical decision to pursue further investigation. This case, involving a routine application of a well-established technique, illustrates the diagnostic gap created by conflicting international guidance. This disconnect between recommendations and necessary clinical practice is particularly challenging in low-resource settings where advanced imaging is inaccessible. To address this uncertainty, we propose a pragmatic diagnostic algorithm positioning TRUS as a second-line, problem-solving modality. The pathway applies when initial non-invasive evaluation with TAUS and transperineal ultrasound (TPUS) is inconclusive due to limited fundal visualization. This highlights a key paradox: while guidance frameworks champion patient-centered principles, their rigid interpretation can create practical barriers in outlier cases. TRUS is then offered as a potential diagnostic step for consenting older adolescents when access to expert-interpreted MRI is either delayed or unavailable. This framework provides a clear pathway for formal studies to generate the evidence currently lacking in this specific population.