Background <p>Pleural effusion can occur in type B acute aortic dissection. Similar to pleural effusion, extrapleural hematoma is also a type of fluid located in the thoracic cavity. The manifestation of extrapleural hematoma on the chest X-ray is similar to pleural effusion; therefore, extrapleural hematoma can be misdiagnosed as pleural effusion by cardiovascular surgeons who are not familiar with it. We encountered a case of a large extrapleural hematoma in a patient with Stanford type B acute aortic dissection. After searching literature, we find that extrapleural hematoma is poorly described in literature and is an uncommon complication of acute aortic dissection, with few reports. To the authors’ knowledge, our case is the second description of extrapleural hematoma in acute aortic dissection. Regarding the treatment of extrapleural hematoma in acute aortic dissection, there is not much information available and no common rules in the literature. The first reported case of extrapleural hematoma in acute aortic dissection adopted the surgical approach. We attempted nonsurgical conservative treatment, and the results proved it to be feasible.</p> Case presentation <p>A 45-year-old Asian male patient from Chinese Han population presented to our emergency department complaining of abdominal pain for a second time. The second time he underwent contrast-enhanced computed tomography, which revealed an acute type B aortic dissection complicated by massive left hemothorax. Considering the rapid progression of the dissection, an emergency thoracic endovascular aortic repair was successfully performed. A chest tube was placed in the left pleural space; however, we failed to drain the fluid. Accordingly, surgical exploration via video-assisted thoracoscopic surgery was performed. Upon entering the pleural space, we observed a large extrapleural hematoma next to the aorta. Considering an inner leak in the aorta, the hematoma was managed conservatively. The patient showed rapid recovery without significant respiratory or circulatory compromise and was discharged nearly 1&#xa0;month later without any symptoms of dyspnea and with stable hemoglobin levels. The extrapleural hematoma disappeared 5&#xa0;months later. At 21&#xa0;months after surgery, the patient was followed up telephonically and was found to be in good condition.</p> Conclusion <p>Firstly, it is crucial to learn radiographic or ultrasonographic diagnostic features to reduce misdiagnoses of extrapleural hematoma. Secondly, extrapleural hematoma cannot be drained by chest tube drainage of the intrapleural space similar to pleural effusion. If classical chest tube drainage is unsuccessful, extrapleural hematoma should be suspected. Furthermore, we need to know how to deal with this rare entity of extrapleural hematoma in acute aortic dissection. Our case demonstrates that conservative treatment of extrapleural hematoma in acute aortic dissection is also an option, in addition to surgical treatment. We aim to share this conservative measure that has never been reported before. Our experience can serve as a reference for other doctors and fill the gap in literature.</p>