 Good day everybody. Dr. Sanger Sanyal, Professor Department Chair. In this dissection we noticed some abnormality of the brachial plexus. So I thought I'll make a quick video to demonstrate what exactly is the abnormality of the brachial plexus. So this is the right side of the cadaver and this is the right side lateral cervical region. So this is the scaleness medius muscle that we see here and this is the scaleness anterior muscle. So therefore this is the scalene triangle and as we know both of these are inserted onto the first rib and the remnant of the first rib is seen here. Now we know from emerging through the scalene triangle we have the roots of the trunks of the brachial plexus and the subclavian artery. So here we see one structure, second structure, a third structure. So these are the parts of the brachial plexus and this we see at one more part of the brachial plexus. So if there were roots of the brachial plexus then we should see five roots and if there were trunks of the brachial plexus we should see three trunks but here's we are seeing neither three nor five instead we are seeing four. One, two, three, four and this is the subclavian artery. So in order to determine what exactly is the abnormality we decided to go further distally into the axilla and this is the axilla here. So now we have come to the axilla and let me trace out all the structures that we can see in the axilla here. This is a very important landmark which is referred to as the M landmark. This is the M. So this is the musculocutaneous nerve, this is the lateral cord of the brachial plexus, this is the medial cord of the brachial plexus, this is the lateral root of the lateral cord, median nerve. This is the medial root of the medial cord forming the median nerve and this is the ulnar nerve. So having mentioned this important landmark we know that this is the lateral cord because it is situated lateral to the axillary artery. We know this is the medial cord because it is situated medial to the axillary artery and then this is the posterior cord because it is situated posterior to the axillary artery. Now we know that the lateral cord is formed by the union of the anterior division of the upper trunk and the anterior division of the middle trunk. So there should be two parts uniting to form the lateral cord. So we see one part here and one part here. If this is the case then there should be upper trunk but here we do not see a distinct upper trunk. We see only this is the anterior division of the so-called upper trunk and this is the anterior division of the middle trunk but there is no distinct middle trunk. Now let's take a look at the medial cord. The medial cord is supposed to be the continuation of the anterior division of the lower trunk of the brachial plexus. So if this is the lower trunk and this is continuing as the medial cord and now let's take a look at the posterior cord. The posterior cord is formed by the union of the posterior divisions of the upper middle and the lower trunks. So we see one posterior division. We see another posterior division here and but we don't see a third posterior division but on searching further down and pushing the axillary artery we see a small posterior division coming from here and this is seen also from this view. So we see three posterior divisions one very large posterior division one medium posterior division and then very small posterior division forming the posterior cord of the brachial plexus. So now let's go back again to the brachial plexus. Our diagnosis is that this person does not have a distinct upper trunk middle trunk lower trunk. This person has got C5, C6, C7, C8. The roots themselves are dividing. The C5 root has divided into an anterior and a posterior. C6 root has divided into an anterior and a posterior. C7 root is this one which is again divided into an anterior and a posterior and this is the C8 root. So C5, C6 anterior roots and C7 anterior root all of them have united to form the lateral cord. C8 anterior division has continued as the medial cord and all of them posterior divisions have united to form the posterior cord and we can see that the posterior division of the C5 and C6 is very big. C7 is medium and the posterior division of C8 is very small forming the posterior cord. So we noticed two things. We did not find five roots instead we found only four roots. So we would assume that this is C5, C6, C7, C8. We could not find the T1 and we noticed that there is no distinct union of the roots to form the trunks. This is the left side of the cadaver and we wanted to demonstrate an abnormality of the brachial plexus. So we are in the lateral cervical region and this is the region of the scalyne triangle. So this is the scalyness anterior and this is the scalyness medius and therefore this is the scalyne triangle and we can see emerging through the scalyne triangle we have 1, 2, 3 and then we have 4. These are the parts of the brachial plexus and this is the subclavian artery. Now we know that the scalyne triangle should have either five roots of the brachial plexus or three trunks of the brachial plexus but instead we are seeing neither three nor five but four. So in order to determine what was the abnormality we decided to go further distally to the axilla and now we are in the axilla here. This is the left side of the cadaver. Let's take a look at this important M landmark here. This is the lateral cord of the brachial plexus. This is the musculocutaneous nerve. This is the lateral root of the median nerve. This is the medial root of the median nerve forming the median nerve and this is the ulnar nerve. So therefore this is M. Having mentioned that we know that this is the lateral cord and therefore this is the medial cord. The lateral cord we know is formed by the union of the anterior division of the upper trunk and the anterior division of the middle trunk. So there should be two anterior divisions. If this is the lateral cord, yes we do see two. We see one and we see two but we do not see any distinct trunk. We see this anterior division coming from C5, C6 and we can see this anterior division coming from C7 but there is no distinct trunk and we know that the medial cord is formed by the continuation of the anterior division of the lower trunk and that is what we are seeing here. Now let us go behind the axillary artery. This is the axillary artery which is the continuation of the subclavian artery and this is the posterior cord and we know that the posterior cord is formed by the union of the posterior divisions of the upper, middle and lower trunk. So therefore we should see three structures uniting to form the posterior cord. So when we retract like this, we notice that this is one structure coming from C5, C6. This is another structure and this is the small other structure coming from C8 forming the posterior cord. So therefore essentially what we see here is very much similar to the what we saw on the right side and therefore to summarize this patient did not have a fifth root of the brachial plexus C5, C6, C7, C8 and this is the subclavian artery. We could not find a T1 and secondly this patient does not have a distinct union of the roots to form an upper trunk. Thank you very much for watching ladies and gentlemen. Dr. Sanjay Sanyal signing out. If you have any questions or comments please put them in the comment section below. Have a nice day.