Postoperative pneumothorax in posterior fusion using pedicle screws is uncommon, but the complication needs to be kept in mind. There are reports of a pseudopneumothorax resulting from artifacts. We report a unique case of a pseudopneumothorax in a patient with scoliosis, diagnosed using O-arm intraoperative computed tomography. The pseudopneumothorax, initially appearing on a chest radiograph, turned out to be an area of partial atelectasis at the lateral border of the right lower lobe. Spine surgeons and anesthesiologists must recheck images and maintain a high degree of suspicion for a pseudopneumothorax when the radiographic image during scoliosis surgery does not match the patient’s condition.