Welcome to First Incision, the podcast about preparing for the General Surgery Fellowship exam. I'm your host, Amanda Nikolic. Welcome to the first episode of First Incision. My name is Amanda and I am an accredited surgical trainee in Australia. I decided to do this podcast because I've started studying towards my fellowship exam.
And when I was looking around, there wasn't really anything out there that was specifically targeted for this exam or for the level of knowledge that's really required. I listen to a lot of podcasts and I especially enjoy listening to them when I'm exercising and when I'm on a long commute, especially when I'm working at a rural hospital.
I know that the further I get into my study, the more I'm going to want this sort of resource in order to make the most of the limited time that I have for study. This is going to be a bit of a journey. I've never recorded a podcast before, and I'm definitely not a specialist in any of the topics that I'm going to be discussing on this podcast.
What I hope this podcast will be is a way for me to talk out loud about different surgical topics as I learn them and I'm studying in a way that hopefully you as a listener will be able to learn and study along with me. In addition, I hope to get specialists on the podcast so we can ask them the real nitty-gritty questions about things that we're not clear on, as well as for guidance on exam technique and how to best present answers during the exam.
I'll also be talking to previous trainees who've sat the exam to learn a little bit more about what to expect. It's highly likely as I go along that I'll say something that you disagree with or that you think that there's another way of doing. There are many, many ways to approach a number of medical and surgical problems.
There's no right or wrong way most of the time. But if you disagree and you want to let me know, feel free to contact me. Send me a message at firstincisionpodcast at gmail.com or follow me on Instagram at firstincision. So with that all said, let's get started with our team timeout. Our patient today is the breast module from the surgical curriculum and the operation or aspect we're going to be covering today is the anatomy and embryology of the breast and axilla.
So the breast is a modified sweat gland, which basically comprises of fatty fibrous tissue with the ducts and lobules of the breast glands mixed throughout. Anatomically, the base of the breast is pretty constant. It lies between the second and sixth ribs and runs from just lateral to the midline to the mid-axillary line.
Some important structures to be aware of within the breast include the fact that there is This is basically a fibrous layer that's a continuation of Scarpa's fascia from the abdomen, and this lies behind the breast. There are also ligaments of Cooper, and basically these are fibrous bands that run from this posterior capsule into the overlying dermis of the skin of the breast.
These help hold the breast up against gravity as well as are clinically relevant because they can be involved in a tumor. And therefore, as a tumor condenses or pulls on these ligaments, that can cause puckering of the skin as well as that. that poda orange appearance that you may have heard of. The duct system of the breast commences with ductules, which form little lobular units.
These lobules drain into small ducts, which then slowly join together into larger and larger duct system to become 15 to 20 lectiferous sinuses, and these sinuses drain into the nipple. Moving on now to the blood supply of the breast. This is extremely important when we're considering oncoplastic breast surgery or reconstructive breast surgery. And basically the breast is supplied in three directions.
Superior laterally, the main blood supply of the breast comes from the lateral thoracic artery. This artery is a branch from the second part of the axillary artery. So let's remind ourselves of the axillary artery. Basically, this is an artery that runs through the axilla. It commences at the lateral border of the first rib and is said to terminate at the inferior border of teres major where it enters the arm and becomes the brachial artery.
It is divided into three parts based on the pec minor muscle. And this is also the key when we're talking about lymph node stations. So be aware of that. The first part of the... axillary artery runs from the lateral border of the first rib to the medial border of the pec minor muscle and this gives off the superior thoracic artery.
The second part of the axillary artery is behind the pectoralis minor muscle, and there's two branches from this part of the axillary artery. The first is the thoracoacromial trunk. This pierces... Anteriorly, the clavipectoral fascia gives off a number of branches, including the clavicular, humeral, acromial, and pectoral branches. And the pectoral branch does actually give a small amount of supply to the breast.
The second branch is the lateral thoracic artery, which, as I've just mentioned, is the major blood supply to the breast. The two other places that the breast receives blood supply from from the internal mammary artery. The internal mammary artery runs behind the sternum laterally and gives off. Branches that pierce between the ribs in the second, third and fourth interspaces to supply the breast from a medial direction.
These vessels are often encountered when doing a mastectomy or medial surgery on the breast and are often large enough that they are required to be clipped, so good to be aware of. In addition, there is a small amount of blood supply that's just... derived laterally from lateral branches of the intercostal arteries. These branches pierce again between the ribs laterally to supply blood to the breast.
The venous drainage of the breast follows the arterial supply. So there is venous drainage back to the auxiliary vein. There's also venous drainage into the internal mammary vein. And there is also venous drainage laterally through the intercostal veins. And this is clinically relevant as these veins communicate with the vertebral plexus and can be a spread of tumor cells to the bone.
There isn't much to know about the nerve supply of the breast. Basically, there is a cutaneous nerve supply to the skin of the breast that comes from the fourth to sixth intercostal nerves.
via lateral and anterior branches, and the nipple is supplied by the thoracic level 4 nerves. Getting to lymphatic drainage, however, which I'm sure is what you've all been hanging out for, This is definitely examinable and is clinically very relevant when we talk about breast cancer and regional spread to lymph nodes.
lymph drainage of the breast, the majority of the breast, about 75% drains into lymph glands in the axilla. These lymph nodes are... considered to be in three levels level one two and three basically level one nodes are the nodes that are found lateral to the pec minor muscle The level 2 nodes are found posterior to the pec minor muscle and the level 3 nodes are found medial to the border of the pec minor muscle. These can also be considered infraclavicular nodes.
Clinically, again, very relevant. Most of the auxiliary surgery that we do is in level one and level two. For an auxiliary clearance for breast cancer, it's mostly agreed on that that would involve a level one and two clearance, which is different from, say, for a melanoma auxiliary clearance where you would want to also clear the level three nodes.
The remaining 25% of the breast can have lymphatic drainage by way of other routes. These include the internal mammary nodes, so specifically the medial aspect of the breast may drain to internal mammary nodes. In addition...
there can be drainage across the midline to the contralateral breast or the contralateral axilla to extraperitoneal or mediastinal lymph nodes and also to supraclavicular lymph nodes. Another place that... you should know about is the interpectoral groove so this is the space between the pec minor and pec major muscle there can be lymph nodes in this area and especially when you're doing a clearance it's good to feel along that area to make sure
If you can feel any other nodes that you ensure that you remove them as well. That's enough about the breast. Let's move on to the axilla. So the axilla is a... space that I really struggled especially as a medical student to get my head around there's a really great picture or demonstration in Grey's Anatomy, if you have a copy of that or can get access to a copy of that, that really gave me a better understanding of what the space actually looks like and the borders of the space.
Essentially, it is described as a pyramidal space. So this is sort of a four-sided pyramid with the small apex area being the inlet and the... the larger base area being the outlet. And this is essentially the space that allows access of neurovascular structures between the posterior triangle of the neck and the arm. In terms of borders, it's... I find it easiest to first think about the medial border being the chest wall, specifically the serratus anterior muscle.
posterior wall is mostly muscular and is a lot bigger than the anterior wall and this includes the subscapularis muscle teres major and the latissimus dorsi tendon. The lateral border of the axilla is really the arm, the humerus or specifically the intertubercular sulcus on the humerus. And the anterior wall of the axilla is the clavipectoral fascia. And this is important clinically because we usually are piercing the anterior.
border of the axilla when we're entering the axilla and you need to make sure that you see that you've incised the clavipectoral fascia and often you'll notice that the fat then changes into obviously different fat that you encounter deep in the axilla proper. So the contents of the axilla pretty much are the axillary artery, axillary vein. The cords and some of the nerves of the brachial plexus are in the axilla, and most importantly are all of the lymph nodes, which we have already discussed.
When we talk about auxiliary surgery, there are a couple of key landmarks that you need to identify, especially when we're considering an auxiliary clearance. So the first is usually the auxiliary vein and this sits sort of anterior inferior to the arteries. So it's usually the first thing that you'll...
come across up in the apex of the axilla. And it's really important to identify this as your sort of superior border of dissection. The other important structures are the long thoracic nerve and this comes from the roots of c5 c6 and c7 and supplies serratus anterior this actually runs on the surface of serratus anterior just
around or posterior to the mid-axillary line, so on that medial border of the axilla. The other nerve to be aware of is the thoracodorsal nerve, and this is the nerve that supplies latismus dorsi. This nerve is a little bit more difficult in that it runs down the... posterior surface of the axilla. So it can be a bit hard to get your head around where it is exactly. It usually runs with the thoracodorsal artery and supplies latissimus dorsi.
Injury to either of these nerves will result in a functional deficit for the patient. So injury to the long thoracic nerve and therefore serratus anterior will result in winging of the scapula. This is essentially... an inability of the scapula to be pulled down onto the chest wall so the scapula rotates out laterally and also wings off posteriorly from the chest wall.
And injury to the thoracodorsal nerve and therefore latismus dorsi will cause weakness with overhead movements and arm abduction. The other nerve to be aware of that runs through the axilla is actually the intercostobrachial nerve. This nerve is essentially the lateral branch or sensory branch of the second intercostal nerve, and this travels transversely usually between the... second and third ribs across the axilla and supplies sensation to the medial aspect of the arm.
There's a lot of discussion about whether injury to this nerve during axillary dissection contributes to a chronic pain syndrome post-axillary clearance and therefore, if possible, to preserve whilst also maintaining good oncologic surgery. then this nerve should be preserved. You should always warn your patients preoperatively about the risk of chronic pain and also of numbness on the medial aspect of the arm as it's not always possible to preserve this nerve and still remove all.
involve lymph nodes. I think that is enough about breast and auxiliary anatomy. The next topic I want to briefly touch on is that of breast embryology. I always really struggled with embryology because the same thing will slightly change throughout the development of the fetus and will go through about 100 different names. And I always got really lost as to what exactly was happening. But lucky.
Breast embryology is not too complex. So the basic summary is in the fourth to sixth fetal week, there is the development of ridges down the... ventral surface or what becomes the anterior surface of the fetus. These ridges are called milk ridges or milk lines and they develop from the primitive axilla to the inguinal region.
As the weeks go on, by about week eight or nine, these regions start to atrophy in the proximal and distal aspects. And the remaining areas of ridging over the pectoral region therefore become... the pair of primary buds or breast buds. The breast is derived from ectodermal and mesodermal origin. So let's remind ourselves that ectoderm is the outside layer of the primitive fetus and the mesenchyme is the middle layer.
of the primitive fetus and the ectoderm essentially will form the ducts and the alveoli of the breast with the mesodermal aspect developing into the connective tissue and blood vessels. of the breast the ectodermal ridge then starts developing into buds. So these buds sort of grow into the underlying mesodermal layer and those buds then develop into those lactiferous ducts, sinuses, ductules, lobules.
Therefore, these ducts having grown into that mesodermal layer, the mesodermal then becomes the supporting aspect of the breast, being the connective tissues and vessels of the breast. So why is all of this important? basically so that we can be aware of developmental abnormalities associated with the breast. Some developmental abnormalities that you may encounter include polythelia, and this is where there's more than two nipples. These nipples will develop or be found anywhere along.
where this original milk line or milk ridge was. So that's a line that runs pretty much from the axilla over the breast, lateral to the midline and down all the way to the inguinal. region. You can also get polymastia which is presence of more than two breasts. Again these would be found along that mammary ridge and can be associated with other developmental abnormalities. In addition to having extra
breasts and nipples, you can have absence of breasts or nipples. So amastia, which can either be bilateral or unilateral, is the congenital absence of a breast or two breasts. Most of the time... If this is encountered, it is associated with other congenital malformations. And the absence of a nipple, which is called athelia, is very rare and is always associated with other abnormalities. That is all I have time for for this first episode of First Incision.
It's a little bit content heavy and there will be some episodes that are just content and learning whilst others will be focused more around bigger picture summaries and having guests on the show. For our next episode, we will take a deep dive into benign breast diseases and the way that I've managed to come up with a little bit of a structured summary for this very complex topic.
It's time to close up. Thanks for listening to First Incision. If you have any comments or feedback, send us a message at firstincisionpodcast at gmail.com or follow us on Instagram at firstincision. Happy studying!