[Fleischner Society] A juxtaphrenic peak is a small triangular opacity based at the apex of the dome of a hemidiaphragm, associated with upper lobe volume loss of any cause (eg, postirradiation fibrosis or upper lobectomy) (74). It is most readily appreciated on a frontal chest radiograph (Fig 32). The peak is caused by upward retraction of the inferior accessory fissure (75) or an intrapulmonary septum associated with the pulmonary ligament (76).