Zinboonyahgoon N, et al. - In this anatomical study, researchers assessed the anatomical spread of large-volume proximal intercostal block (PICB) injections as well as focused on its significance to breast surgery analgesia. They found that the anatomical spread of PICB at the 2nd and 4th intercostal space was along the corresponding intercostal space, laterally; to the adjacent paravertebral/epidural space, medially; and cranio-caudal spread along the endothoracic fascial plane. The clinical consequences of combined PICBs at the same levels included consistent segmental chest wall analgesia and attenuation in perioperative opioid use following breast surgery. In the multi-level coverage afforded by this block technique, a possibly significant clinical role of additional non-paravertebral routes of injectate distribution, such as the endothoracic fascial plane, was suggested by the incomplete overlap between paravertebral spread in the anatomical study and area of hypoesthesia in experts' clinical findings.