- There are three regions of the Internal Mammary Artery, each with distinct characteristics, particularly of the branches to the intercostals (not perforators, as they are often called) - There are branches that travel in the opposite direction to the branches to the intercostals. There are typically three of these Pericardial Branches, traveling along the pleura to the thymus, or the pleura to the pericardium. The topmost branch, the Pericardiophrenic Artery goes almost completely medially and is in close proximity to the phrenic nerve. ![[Pericardial and Pericardiophrenic Branches.png]] - Top Region - The subclavian origin to the Angle of Louis - In this region, the mammary is often loosely adherent to the chest wall and the accompanying medial and lateral veins, partially encased in adipose, which can potentially make it easier to harvest - branches to the intercostals tend travel away from you - The intercostal branch to the Angle of Louis is particularly large and daunting, as it is often difficult to determine where the branch begins and the mammary ends - Once this branch is taken, the remainder of the mobilization is much easier - Dissection should not extend to the pericardiophrenic to avoid injury to the Phrenic Nerve - The Phrenic Nerve may travel below OR above the Mammary Artery relative to the chest wall, so care must be exercised as you approach the vicinity of the first rib. - The Phrenic travels anterior to the mammary bilaterally in about half of patients, posterior to the mammary bilaterally in about 14 percent, Anterior to the Left and Posterior to the right in 12, Posterior to the left and anterior to the right in 20% - It is rare to injure the nerve here ![[Phrenic Nerve Anatomy.png]] ![[L Phrenic and Mammary.png]] ![[R Phrenic and Mammary.png]] - Middle Region - The Angle of Louis to the Last Third - In this region, the mammary and its accompanying medial and lateral veins are often a little more adherent to each other and to the ribs - Branches to the intercostals are more notably paired, one towards you and one away. They never occur AT the rib, but can sometimes splay out to hug their tops and bottoms. Relevant to pedicled harvest, they tend to accompany vein branches, but a little imperfectly, leading to the dictum "If you take down the vein, the mammary will follow" - Bottom Region - The Last Third lies underneath fascia and transverse internal muscle fibers. These fibers are not particularly bloody and can easily be cut to expose the artery for harvest if desired. - Branches to intercostals here tend to travel away from you and caudally - The useful extent of the artery ends a little past a larger branch under the sixth rib, and then a bifurcation around the seventh - Occasionally, the artery is still large past this bifurcation, and if needed can be harvested further