Comprehensive insight in the anatomy of the intercostal spaces is mandatory for everyone who practices medicine. One particular concept is that the neurovascular bundle has a strict order: V-A-N, or vein-artery-nerve, from top to bottom (as illustrated). This neurovascular bundle runs high in the intercostal space, and the collateral neurovascular bundle runs just superior to the inferior rib of the space (in the order N-A-V from superior to inferior). Invasive procedures such as thoracentesis are thus performed with oblique entry of the instrument, directly above the upper margin of the relevant rib.
In reference to the muscles of the thoracic wall, the intercostal nerves and vessels run just behind the internal intercostal muscles: therefore, they are generally covered on the inside by the parietal pleura, except when they are covered by the innermost intercostal muscles, innermost intercostal membrane, subcostal muscles or the transversus thoracis muscle.