Title: Catheter Misplacement During Chemoport Insertion Reveals Persistent Left Superior Vena CavaAuthors: Chin-Hu Tsai, MDAffiliation: Division of General Surgery, E-Da Hospital, Kaohsiung, TaiwanCorresponding Author: Jian-Han Chen, MDDivision of General Surgery, E-Da Hospital, Kaohsiung, Taiwan.Director of Bariatric and Metabolism International Surgery Center, E-Da Hospital, Kaohsiung, TaiwanEmail: tigertsai0705@gmail.comKey Clinical Message: Persistent left superior vena cava may lead to unexpected catheter malposition and hemodynamic instability during central venous access. Awareness of this vascular anomaly is crucial to avoid misinterpretation.Ethical Statement: Written informed consent was obtained from the patient for publication of this case report and the accompanying images.Funding: The authors received no specific funding for this work.Acknowledgement: NoneAuthor Contributions: Dr. Chin-Hu Tsai contributed to literature review, image interpretation and writing article. Dr. Chung-Yen Chen contributed to conception of case and clinical management. Dr. Jian-Han Chen contributed to literature review and revising the article. All three authors approved the final version of the manuscript.A 57-year-old man with newly diagnosed esophageal squamous cell carcinoma was scheduled to undergo chemoport implantation via the left subclavian vein. During the procedure, the patient developed acute tachycardia (>130 bpm) and hypotension, with a systolic blood pressure decreasing to 80 mmHg. Portable chest radiography demonstrated that the chemoport catheter failed to cross the midline and was positioned within the left mediastinum (Figure 1 ), raising suspicion of inadvertent arterial cannulation during the puncture. However, arterial blood gas analysis revealed venous characteristics, and the patient’s hemodynamic instability resolved following intravenous fluid resuscitation and administration of antiarrhythmic agents.A retrospective review of preoperative contrast-enhanced computed tomography identified a persistent left superior vena cava (PLSVC), a congenital venous anomaly with an estimated prevalence of 0.3% to 0.5% in the general population [1,2], as demonstrated in Figure 2 . The PLSVC was found to drain into the coronary sinus, accounting for the abnormal catheter trajectory. Although often asymptomatic, PLSVC can pose challenges during procedures requiring central venous access, such as pacemaker lead placement or chemoport implantation [2,3]. Recognition of this anatomical variation prior to device placement is essential to optimizing procedural success and minimizing the risk of complications [1].