A 15-year-old boy with extralobar sequestration torsion is presented, who presented as an acute abdomen. Chest X-ray and computed tomography on admission revealed an apparent posterior mediastinal mass on the right side at the lower thoracic vertebral level. MR imaging, however, clearly showed scanty fluid around the mass and the subpleural fat layer between the vertebral body and the mass, suggesting its extrapulmonary and intrapleural cavity location. Its hemorrhagic nature was also suggested by the reduced signal on the in-phase as compared to out-of-phase chemical shift images, which helped make correct preoperative diagnosis.