A 39-YEAR-OLD man with a 4-month history of dysphagia and a biopsy-proven adenocarcinoma was admitted for esophagectomy. A cerebral arteriovenous malformation had been diagnosed more than 20 years ago, and the patient had a history of epilepsy. The patient was still treated with anticonvulsants at the time of surgery but had had no seizures for at least 3 years. On the day of surgery, the patient received morphine and hyoscine as premedication. A low thoracic epidural was placed on arrival in the induction room, and bupivacaine 0.5% was injected into the epidural space. General anesthesia was induced with a combination of fentanyl and midazolam. Vecuronium was used as a muscle relaxant. A double-lumen left-sided endobronchial tube was inserted without difficulty, and correct positioning was confirmed clinically and with a fiberoptic bronchoscope. The surgeon performed a 2-stage Ivor-Lewis esophagectomy without encountering any difficulties. A gastric tube was fashioned to replace the excised lower esophagus, and no pyloroplasty was performed at the gastric outlet. The patient was extubated the next day. He subsequently had 3 focal seizures despite the fact that anticonvulsant therapy had been maintained throughout his care. The patient later became confused, and in the course of agitation, he pulled out his nasogastric tube. He remained obtunded but was able to maintain his airway. A computed tomography scan of the brain was unremarkable and in particular showed no changes in the arteriovenous malformation. The anticonvulsant therapy was modified. Over the next days, the patient experienced several focal seizures, but he remained responsive. A chest radiograph was taken on postoperative day 6 and showed an abnormality (Fig 1). What is the abnormality?