S5310 Retroperitoneal Free Air Post Peroral Endoscopic Myotomy: It Can Happen!

Introduction: Peroral endoscopic myotomy (POEM) is routinely performed for the treatment of achalasia. Imaging findings after POEM such as pneumomediastinum and pneumoperitoneum are commonly seen and are typically benign. A less common finding is retroperitoneal air, and the clinical significance is not as well described. We present a case of a 60-year-old man with achalasia who underwent POEM with severe post-procedural pain prompting further evaluation. Case Description: A 60-year-old man with type III achalasia previously treated with botulinum toxin injection underwent POEM. A selective circular myotomy for the spastic segment and full thickness myotomy at the lower esophageal sphincter was performed. Final myotomy measured 10 cm in length and extended 1 cm into the gastric cardia. The procedure was challenging due to severe submucosal fibrosis, potentially related to prior botulinum toxin treatment, however no intra-procedural adverse events occurred. He was started on intravenous antibiotics consistent with standard practices at our intuition. Post-procedure course was complicated by severe chest and abdominal pain and tachypnea. Chest x-ray revealed a lucency in the inferior mediastinum consistent with pneumomediastinum, as expected post-POEM. Due to symptom severity, a computed tomography scan of the chest and abdomen was obtained which revealed small volume pneumomediastinum and free air within the retroperitoneum. He remained afebrile and hemodynamically stable. His pain quickly improved with intravenous analgesics and completely resolved by post-operative day one. No esophageal leak was seen on esophagogram obtained post-procedure day one, and the patient was discharged. Discussion: An understanding of expected radiographic findings post-POEM is important when evaluating a potential adverse event. While pneumomediastinum and pneumoperitoneum are expected findings post-POEM, the presence of retroperitoneal free air post-POEM is less commonly seen. Our case highlights that retroperitoneal free air can be seen post-POEM, and these findings may not warrant further intervention in the absence of an esophageal leak identified on imaging.