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02 Inlet of thorax and diaphragm | THORAX | DR. ASHWINI — Transcript

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0:05[music]
0:16[music]
0:18>> So let's now start with the thoracic
0:20wall first.
0:21Uh in the thoracic wall, guys, first
0:23we'll be looking at how exactly the
0:24thoracic wall uh
0:26provides you certain landmark in based
0:29on which you can divide
0:30>> the mediastinum also inside.
0:32>> So to start with, let me take a sagittal
0:34section. And in the sagittal section,
0:36obviously, you will see the sternum bone
0:37anteriorly and the vertebral column
0:38posteriorly.
0:40So just just a very schematic view of
0:42the sternum. Let us say this is a
0:44manubrium of the sternum.
0:46Here is the body of the sternum.
0:51And this here is a xiphoid process.
0:55So you're looking at the manubrium. This
0:57here is the manubrium. I'm writing M for
0:59the manubrium.
1:00There goes the body of the sternum, and
1:02this X is for the xiphoid process.
1:06Let us presume this line here represents
1:09the vertebral column. If guys, this here
1:11is the vertebral column,
1:13then
1:14this represents the inlet of the thorax.
1:17This oblique line I'm showing with a
1:18green color here, it represents the
1:20inlet of the thorax.
1:22And here is the diaphragm, which is the
1:24outlet of the thorax. This These are the
1:26two major topics of concern for us here.
1:29And this there is inlet of the thorax
1:31and the outlet of the thorax.
1:37Let me mark that. This is inlet.
1:46Inlet of thorax, which is also called as
1:48the Sibson's fascia.
1:51There's a fascia over there, which is
1:52called as a Sibson's fascia. We can also
1:54call it the supra plural membrane. So
1:56this is Sibson's fascia or supra pleural
1:58membrane. We will come to that. And this
2:00one here is the outlet of the thorax and
2:02that is we all know is by the diaphragm.
2:08Before we move on to the inlet and the
2:09outlet and we'll discuss in more detail,
2:12uh I hope you know that manubrium and
2:14the body of the sternum. This this
2:16angle between the two is called as a
2:18sternal angle or the angle of Louis.
2:21Now, this is a very very important
2:22landmark here, guys. This
2:24here is called as the sternal angle.
2:31I'll tell you more about the sternal
2:32angle or angle of Louis.
2:34The point is if you draw a horizontal
2:36line from the sternal angle, if I just
2:38draw a horizontal line, imaginary line,
2:41from the sternal angle and
2:43stretch it posteriorly, you will see it
2:45passing along the lower border of the
2:48fourth thoracic vertebra.
2:50So, that's the lower border of T4 and
2:53that is the exact level of the sternal
2:54angle if you see it.
2:57Now, by this imaginary plane, we're
2:59basically dividing the thoracic cavity
3:01inside or I should say the mediastinum
3:02inside into two part. We got a superior
3:04mediastinum and the inferior
3:06mediastinum.
3:07We all know mediastinum is the space
3:09between the lungs.
3:10So, the space between the lungs can be
3:12divided into broadly two part. First one
3:14is superior and one is inferior.
3:17But one major structure present in the
3:18inferior mediastinum being heart,
3:21so let us say if this here is the heart
3:23and the pericardium. Let's say this is
3:24heart and fibrous pericardium you're
3:25looking at.
3:27So, that further divides the inferior
3:29mediastinum into three parts. So, we
3:31have anterior part, middle part and
3:32posterior part.
3:34So, overall I can say this here is the
3:36superior mediastinum.
3:41And inferior mediastinum divides into
3:42this one anterior mediastinum one,
3:45this is middle mediastinum two, and here
3:47is the posterior mediastinum. So, we
3:49have three part here. AM, MM, PM, that
3:51is anterior, middle and posterior
3:52mediastinum. Middle mediastinum, as we
3:54said, it is all about heart and its
3:56great vessels and pericardium.
3:59Radiologically,
4:01they usually do not talk about superior
4:03or inferior mediastinum. They simply say
4:04anterior, middle, and like posterior.
4:06So, they basically uh consider this
4:08extension of anterior mediastinum above,
4:10middle like this, and posterior like
4:12this. So, you will find certain
4:13terminology which are a bit different
4:15like when you read it in the anatomy and
4:17then into the the concerned clinical
4:19subject. So, you might not uh hear the
4:21term called as superior mediastinum in
4:22radiology. So, that is okay. I mean,
4:24anatomically, we divide into superior
4:26and inferior, and inferior divides into
4:27three.
4:30Before again before going into the again
4:33inlet and outlet, that is the main topic
4:35in here, let's first talk about the
4:37sternal angle. What is so important
4:38about the sternal angle, guys?
4:40The sternal angle
4:47The sternal angle, which is
4:50approximately 5° only.
4:53This sternal angle, it is also called as
4:55the angle of Louis.
4:59This is also called as the angle of
5:01Louis.
5:03And why this is so important? Because
5:04this is a major landmark for many
5:06structures in the in thorax. Like if I
5:09start with a bony thing, this the
5:11sternal angle or manubriosternal joint
5:14or this junction here,
5:15it is the point where the second
5:18costal cartilage is attached.
5:20When you count the ribs, then the most
5:24uh
5:24what do you say? The the reliable point
5:26for the counting of the ribs would be
5:28the second rib or the second uh costal
5:30cartilage, which is attached exactly at
5:32the sternal angle.
5:33So, this is the point where the
5:35second costal cartilage
5:41second costal cartilage is attached.
5:45It's very, very important, clinically
5:47very important to know that
5:49point level of the second rib or the
5:51second coastal cartilage attachment.
5:53What other important things you will
5:54notice at the sternal angle? I mean,
5:56because when you talk about sternal
5:57angle, we are talking about that lower
5:59border of T4. So, either you say sternal
6:01angle or you can say we are looking
6:03at the level of lower border of T4. What
6:07other changes
6:08What other changes you will expect to
6:10see at the lower border of the T4?
6:13And they will be
6:14that one change will We already saw that
6:16when we draw an imaginary line, it
6:18divides the superior and the inferior
6:19mediastinum.
6:21So, this level here is a division of the
6:26superior and inferior mediastinum.
6:31Okay, what else?
6:35It's a very important landmark for the
6:37bifurcation of the trachea. Now, I'll
6:39I'll add something to this, but you can
6:41write it first.
6:42Bifurcation of trachea.
6:47Bifurcation of trachea takes place at
6:49the lower border T4. That's
6:51uh how we
6:52it's
6:54always been said. But, if you look at
6:56certain updates in the latest Gray's and
6:57in some other
6:59uh books also, they mention that when
7:01you say bifurcation of trachea, this is
7:03basically a cadaveric level we talk
7:04about. In cadavers, when you look at
7:07this, okay, lower border of T4, that is
7:08the right answer. But, in living,
7:11the bifurcation of trachea is not at the
7:13lower border of T4. It is actually at
7:15the lower border or you can say at the
7:17level of the T6. So, it's way lower than
7:20what we see here.
7:21So, lower border of T5 or the body of T5
7:24or in fact, it can even extend to the T6
7:26vertebrae. That is the bifurcation of
7:28trachea. So, it it does vary uh from
7:31person to person. I mean, that is how it
7:32is mentioned. There's a complete
7:34uh statistics given regarding it in the
7:36Gray's also that that a certain
7:37percentage shows the division is at the
7:39T5, certain that shows even below the
7:41T5. So, that and even deep inspiration
7:43it can go even further down. It can
7:45reach almost to the level of T7 also.
7:48So when you say bifurcation of trachea
7:49at the lower border of T4, the one thing
7:51that you have to keep in mind is that
7:52here we are talking about the cadaveric
7:54level.
8:03This
8:05sternal angle, what other thing we have
8:07here? This is the level for the arch of
8:10azygos. Arch of azygos vein will come
8:12and drain into superior vena cava. So
8:14this is done exactly at this level only.
8:16So the arch of azygos
8:22arch of azygos
8:25drains into superior vena cava. We will
8:28discuss that how exactly the arch of
8:30azygos is coming and draining into it.
8:31You can write it down for now that arch
8:33of azygos vein will come and the drain
8:35into superior vena cava at the level of
8:36T4.
8:39This is the level for the beginning
8:44beginning and end of arch of aorta.
8:50Be careful about this. I'm not saying it
8:52is the level for arch of aorta. No, no.
8:53Arch of arch is present at the T3 level.
8:56That is higher level.
8:58T4 is the point where the arch of aorta
9:00begins and it ends. So if you take a
9:02transverse section at the level of T4,
9:04you will not see the arch as such. You
9:06will see the two vessels, one in front,
9:08one behind in the transverse section. We
9:09will discuss that at the end.
9:11And that is beginning basically the
9:13initiation or the beginning of arch of
9:14aorta and the other one would be the So
9:16that's the section through the end of
9:18the arch of aorta.
9:21This also is the level for the apex
9:25of fibrous pericardium.
9:31This is the level for the apex of the
9:32fibrous pericardium. Please remember one
9:34thing when we talk about pericardium,
9:37the serous pericardium is the one which
9:39behaves more like a heart. I mean, if
9:41you look at the base of the heart is
9:43posteriorly placed and the apex of the
9:45heart is toward the left side. And
9:46that's how the the serous pericardium is
9:48covering it.
9:49But the fibrous pericardium is like a
9:51pouch in which the heart is placed. That
9:53That's how you should believe uh take
9:55it. So, for the fibrous pericardium, the
9:57base of the heart and the apex of the
9:59heart doesn't matter.
10:01Fibrous pericardium is is like a pouch
10:03in which the heart is placed. So, base
10:04of the fibrous pericardium is below
10:07and the apex is above. Unlike heart
10:09which is having the base behind and the
10:11apex more toward the left side.
10:13So, apex of fibrous pericardium I mean,
10:15it's it's fibrous
10:17pericardium which is also reaching the
10:18level of the T4.
10:22This also is the level
10:24for the location of the cardiac plexus.
10:27We'll discuss these cardiac plexuses,
10:29superficial and deep cardiac plexuses.
10:30They are lying more or less at the level
10:32of the the sternal angle only.
10:36This is the level for the attachment of
10:39superior
10:43sternopericardial
10:44ligament.
10:46Attachment of superior sternopericardial
10:49ligament.
10:50There are two sternopericardial
10:51ligament. One is superior, one is
10:52inferior. That basically is attaching
10:54the sternum bone to the fibrous
10:56pericardium. So, we have a superior
10:58sternopericardial and we have inferior
10:59sternopericardial. So, superior is the
11:01one which is present at the level of the
11:03sternal angle. Another landmark to
11:05remember.
11:06Then, one very very important thing that
11:08is thoracic duct. Guys, thoracic duct,
11:10it runs in the center. We will again
11:11discuss that in the later part. Thoracic
11:14duct, the largest lymphatic duct of the
11:15body, runs in the center.
11:18And then this thoracic duct actually
11:19deviates toward the left side to drain
11:22into the junction of internal jugular
11:24and subclavian.
11:25So, what is the level of deviation? It
11:27starts deviating at the T5 only.
11:30When you look at the fifth thoracic
11:32vertebrae, it starts deviating at the T5
11:34only and at the lower border of T4 or
11:36you can say at the sternal angle, you
11:38consider that the duct has come toward
11:40the left side now. It is now completely
11:42come toward the left side.
11:43So, the thoracic duct
11:49the thoracic duct
11:55deviates to left side.
11:59Thoracic duct deviates to the left side.
12:00That is also happening at the level of
12:02the sternal angle. And there are many
12:04other things. I mean, you can you can
12:06keep on adding to this list. This goes
12:08on and on, but we just have to look into
12:10the important one first. I would say out
12:12of all these
12:13uh
12:14the one which are the most important
12:16here, one is a second costal cartilage
12:17attachment is very important.
12:19The bifurcation of the cadaveric
12:21trachea, that is another important. Arch
12:23of azygos is important.
12:26I would say uh this thoracic duct one is
12:28important.
12:30So, very precisely for the exam point of
12:32view, out of all these I should I would
12:34say that these are the one that you
12:35should remember all the time.
12:39After the sternal angle, now let's move
12:41on to the the inlet and the outlet of
12:43the thorax. So, guys, let me just take
12:44you back here. So, we said inlet and the
12:46outlet. Now, I one what First, look at a
12:49picture here in which you can see how
12:51exactly things will look like and then
12:53we'll go into more details of the
12:55the
12:56inlet and the outlet part.
12:57Here is the one. This is the kind of
12:58picture we drew. We can see the sternum
13:00there. We can see that is the sternum of
13:02uh this manubriosternal angle or
13:04angle of Louis.
13:05You can see the vertebral column there.
13:07That's 1 2 3 4 fourth thoracic
13:09vertebrae. And can you see that line
13:10over there? You can see a a difference
13:11in the color which is showing you this
13:13imaginary line which is dividing the
13:15superior mediastinum and this whole
13:17thing here is a inferior mediastinum.
13:19And you can see the inferior mediastinum
13:21is further divided into anterior, that
13:22is blue one here.
13:24This orange one here shows the heart and
13:26obviously related blood vessels, so it
13:27is middle mediastinum and everything at
13:29the back here is a posterior mediastinum
13:31in which as I already said will be the
13:32descending aorta, there will be
13:34esophagus, thoracic duct, sympathetic
13:36chain, azygos, hemiazygos vein and many
13:39other things very very important
13:40mediastinum to be discussed that is the
13:42one posterior.
13:44So
13:45now we going to talk about one is the
13:47inlet of the thorax from where the
13:48structures of the neck will go into the
13:50thorax or thoracic structures goes into
13:52neck from here
13:53and then we will talk in detail about
13:55this very important topic that is the
13:57diaphragm.
13:58How it is attached, what are the
14:01openings in the diaphragm, what
14:03structures are passing through it.
14:06So there we go the inlet of the thorax
14:09which we said
14:10can also be called as the Sibson's
14:12fascia
14:13it is also known as suprapleural
14:16membrane.
14:20It is present above the pleura so you
14:22can obviously call it supra it is also
14:24known as the suprapleural membrane.
14:27Now it is believed that the Sibson's
14:28fascia or suprapleural membrane it is
14:31the remnant of
14:35it is a remnant of the muscle and that
14:37muscle is the scalenius
14:41minimus.
14:42Well we do have scalenus anterior,
14:44scalenus medius and posterior so there
14:46is no question about the remnant.
14:48So it's a remnant of scalenus minimus
14:49muscle which is called as a suprapleural
14:52membrane or Sibson's fascia.
14:54The question here is in the Sibson's
14:56fascia is
14:57that they do ask question about the
14:59attachment of this fascia here.
15:01Because you know when you think about
15:02the inlet of thorax the thing that
15:04should come to your mind is okay the
15:05inlet has to be somewhere at the
15:07superior border of the
15:08what do you say the sternum and it
15:10should be till the T1 vertebrae. Now
15:11obviously T1 is the vertebrae from where
15:13the thorax starts.
15:15But no that is the important thing to
15:16note here that the attachment of
15:18Sibson's fascia posteriorly
15:20is not to the T1 vertebrae it is
15:22actually to the C7 vertebrae.
15:25Let me diagrammatically represent this
15:26to you. So, what I'm saying is if this
15:28here
15:30is the body of
15:32C7
15:34and let's say this is a body of T1
15:35vertebrae.
15:37That is C7 and that is T1.
15:40Here we have the transverse processes.
15:46Obviously, the first rib will be
15:48attached to the T1 only if this is the
15:50first rib here.
15:52No question about that. The first rib is
15:54attached to the T1 vertebrae only
15:56posteriorly.
16:01And this here is the manubrium. Now,
16:03that's the transverse section that we're
16:04looking at.
16:05This is the first rib.
16:11Here you got the manubrium and
16:13posteriorly you can see the C7 and the
16:15T1 vertebrae.
16:17About the attachment of the Sibson's
16:19fascia, as I said, it is attached not to
16:21the transverse process of T1.
16:24It is attached to the transverse process
16:25of C7.
16:28Let me highlight that so that you don't
16:29forget this thing. The attachment is to
16:32the transverse process of
16:34the C7 and then this will the fascia
16:37will come down, the Sibson's fascia will
16:38come down and it is attached to the
16:40inner border of the first rib. Look at
16:43that.
16:44Attached to the inner border of the
16:46first rib. That is how our Sibson's
16:48fascia or suprapleural membrane is
16:51present.
16:52So, I I This question is asked like more
16:54than twice and uh
16:58most of the time the question is about
16:59the attachment here. The which of the
17:00following statement is not true, which
17:02of the following statement is true about
17:03the attachment. And every time they try
17:05to trick on that where it is not
17:07attached to. So, it is not attached to
17:08the T1 vertebrae.
17:10It is attached to the transverse process
17:11of C7 to the inner border of the first
17:15rib. Inner border of the first rib.
17:18So, this is the fascia or this is the
17:19membrane, the supra pleural membrane
17:20because the pleura will be below that,
17:22which is separating the root of the next
17:24structures and the superior mediastinal
17:26structures. So, this here is the
17:28Sibson's fascia or supra pleural
17:31membrane.
17:33Right?
17:34>> [snorts]
17:35>> Okay.
17:36Now, let's talk about the outlet of
17:38thorax. Coming to the main thing that is
17:39the outlet of thorax and that is
17:41diaphragm.
17:43To understand the outlet of thorax or
17:44diaphragm, let us look at a picture of
17:46the from the atlas first. Let's
17:47understand that and then we'll try to
17:49replicate the same image.
17:53So, here we go. This is a picture, guys.
17:54This is a picture of the diaphragm
17:55you're looking at from the under
17:56surface. You're not looking at obviously
17:58the from the inferior aspect, from the
18:00abdominal side you're looking at the
18:01diaphragm here.
18:03Now, things to be noted here. If you
18:04look at the diaphragm, obviously clearly
18:05you can see it is attached anteriorly to
18:07the xiphoid process. It is attached to
18:09the costal margin. It is attached
18:11posteriorly to the 12th rib. Like this.
18:13That is the attachment of the diaphragm
18:15on the on its peripheral surface.
18:17Diaphragm is having this whitish central
18:20tendon that you're looking at. So, we
18:21have muscle fiber coming from all the
18:22side and we have a tendon in the center,
18:24the so-called central tendon.
18:27Now, if you first pay attention to this
18:29posterior part of the diaphragm here,
18:31the posterior attachment, you can see
18:33first of all the two crura here. This
18:34here is the right crus of the diaphragm.
18:37And this one here is the left crus of
18:39the diaphragm. Look at this long right
18:40crus of the diaphragm here. And that is
18:42the left crus of the diaphragm. Can see
18:44in there, which is shorter than the
18:45right.
18:47Apart from the crura, you can see these
18:49arc-like structures called as arcuate
18:50ligament, this one and this one. We call
18:52this as medial arcuate ligament and this
18:55one is a lateral arcuate ligament.
18:58Medial and lateral arcuate ligament,
19:00which you can see more clearly on this
19:01side because the muscles are removed.
19:03So, you have medial and lateral arcuate
19:04ligament. What these ligaments are and
19:06how they are formed? Basically, if you
19:08look at these medial and lateral arcuate
19:09ligament, they are formed by the
19:11thickness of or thickening of a fascia
19:15of the muscle present deep to them. Now,
19:17look at this here. Can you see a muscle
19:18here and here? Now, guys, this muscle,
19:20which is present more medially, this is
19:21a psoas major muscle.
19:23And the one which is present laterally,
19:24that is a quadratus lumborum muscle.
19:27So, I can say that medial arcuate
19:29ligament is a thickening of the psoas
19:31major fascia only, whereas quadratus
19:34lumborum
19:35fascia thickening forms the lateral
19:36arcuate ligament.
19:38Either you call quadratus lumborum
19:40fascia or you can even call it
19:41thoracolumbar fascia. Same thing.
19:44Thoracolumbar fascia covers this muscle.
19:46So, you can say quadratus lumborum
19:47fascia or thoracolumbar fascia, which
19:49wraps around this quadratus lumborum
19:51muscle,
19:52is forming this thickening called as
19:54lateral arcuate ligament.
19:56Why do we need to uh know about all
19:58these? Because when you when you talk
19:59about diaphragm, we talk about certain
20:01openings in the diaphragm, the major
20:03openings and the minor openings.
20:04There are three major openings present
20:06in the diaphragm. The one that you see
20:07here, which is more toward the
20:09right side in the central tendon. It's
20:11more toward the right side in the
20:12central tendon. That is the opening for
20:14the inferior vena cava.
20:16Then, second opening that you see more
20:18or less in the center only, that is the
20:19opening for the esophagus. You can say
20:22it is in the center or you can say it is
20:23slightly toward the left side. A very
20:25slightly you can see, not exactly in the
20:27midline, a bit toward the left side.
20:30And then we have a opening which is dead
20:31in the center, and that is the aortic
20:33opening.
20:34So, we have a venacaval opening, we have
20:36a esophageal opening, and then we have a
20:37aortic opening. We will discuss all of
20:39them in detail. These are major
20:40openings.
20:42And then we got some minor openings in
20:44the diaphragm allowing the structures to
20:45pass through. Like we have a minor
20:46opening present just beside the xiphoid
20:49process, you can see over there. We call
20:50it actually foramen of Morgagni.
20:53Then we have uh these are the minor
20:55openings also. Like uh there are certain
20:58structures which will be passing deep to
20:59the lateral arcuate ligament. There will
21:01be certain structure passing deep to the
21:02medial arcuate ligament. Okay? And you
21:04will also see there are certain
21:05structures which will be piercing the
21:09right crus of the diaphragm. Can you see
21:10those nerves piercing the right crus of
21:12the diaphragm and piercing the left crus
21:13of the diaphragm. So they are also
21:15considered as a minor openings of the
21:16diaphragm.
21:18So let's put it in a more schematic way
21:20and talk about the attachments of the
21:22diaphragm, about the arcuate ligaments,
21:24the crus, the major and the minor
21:26openings, so everything in there.
21:41Okay.
21:43So I'm going to draw go with the same
21:45diagram only. So this is how it was.
21:49That's a dome that we're we're looking
21:50at.
21:53Then we have lateral arcuate,
21:56the medial arcuate ligament. This is a
21:57long right crus.
22:01This is a
22:02left crus.
22:07There we go. Right? That that's how we
22:09saw that. So again, you have to presume
22:11that you're looking at the picture from
22:12the inferior aspect.
22:14This is the right crus.
22:20And there's the left.
22:30Lateral arcuate ligament.
22:40The medial arcuate ligament.
22:43I told you which fascia they are
22:45concerned or related to. So when I say
22:46lateral arcuate ligament, it was the
22:48quadratus lumborum fascia or
22:50thoracolumbar fascia.
22:57Thoracolumbar fascia or quadratus
22:59lumborum fascia and medial arcuate
23:01ligament
23:03is made up of the psoas major fascia.
23:07It was a thickening of the psoas major
23:09fascia.
23:11So, that's first thing.
23:12Right crus of the diaphragm is longer,
23:14right left crus is smaller, and then
23:16look at look at the arcuate ligament,
23:17lateral arcuate ligament, and medial
23:19arcuate ligament formed by the
23:20thickening of the fasciae of the muscle
23:21which are passing deep to them only,
23:22present deep to them.
23:25Then, we said in the center we have the
23:27central tendon. Let's say this this huge
23:30thing here is the central tendon of the
23:31diaphragm.
23:43This is the central tendon.
23:48And then we said we got the three major
23:50openings. Now, where was the first major
23:51opening? It was on the central tendon,
23:53but more toward the right side. So, if
23:56even even when you draw it, make sure
23:57you draw it toward the right side. I'm
23:58writing number one here. That's the
24:00opening number one, the major opening,
24:02but more toward the right side. The
24:04second major opening is more or less in
24:06the center only. You can say it is like
24:08by few millimeters toward the left.
24:11And then the opening which is right in
24:13the center is between the right and the
24:15left crus of the diaphragm, the third
24:16major opening.
24:18So, guys, let's first talk about these
24:20major openings and then only we'll go
24:21any further here.
24:31Major openings of the diaphragm. Now,
24:34when I say major openings in the
24:35diaphragm,
24:36I've numbered them as one,
24:39two,
24:41and three,
24:43which you can remember it like
24:45V
24:46O A.
24:48Voice of America. There used to be a
24:50program called as the Voice of America,
24:52VOA.
24:53So, opening of one, two, three is VOA.
24:55Voice of America, V here obviously
24:57represents what? That is V is for vena
24:58caval opening.
25:00O is for the esophageal opening and A is
25:02for the aortic opening. I'm going to
25:03write that again. You don't have to
25:04write it here. So, vena caval,
25:06esophageal, aortic opening.
25:08And their level at which they open in
25:10the diaphragm or present in the
25:11diaphragm is or can be remembered like
25:15vena caval opening is at the level of
25:16T8.
25:18Esophageal opening is at the level of
25:19T10. And aortic opening is present at
25:22the level of T 12. 8 10 12. 8 10 12.
25:26So, this is how we can remember the
25:28three major openings
25:29briefly
25:31that we have first, second, third major
25:32opening we're talking about. That's vena
25:34caval, esophageal, aortic opening. And
25:36their level of opening, level of these
25:37openings
25:39on the diaphragm is T8, T10, and T12.
25:42Let's take all of these in more detail
25:45one by one. Number one opening is V and
25:47V we said is what? That is vena caval
25:49opening.
25:53V is for the vena caval opening.
25:56And this vena caval opening is present
25:58in what? It is present in the central
26:00tendon.
26:01I'll tell you the way to remember it
26:02that where they are present because
26:04again there is a logic behind. You don't
26:05have to mug it up again why it is in the
26:06central tendon. So, there's there's a
26:09reason for that.
26:10Now guys, vena caval opening first of
26:12all what it is giving passes to? Now,
26:14undoubtedly it will give passes to
26:15inferior vena cava.
26:17And it also gives passes to the right
26:20phrenic nerve.
26:23It gives passes to the right phrenic
26:24nerve.
26:25If you find it difficult to remember
26:26that how right phrenic nerve is going
26:28through it and why not left is there,
26:29well again, you just all you have to do
26:31is remember the simple diagram
26:33of the heart. Now, if this is the right
26:35border of the heart, this is inferior
26:37border and that is the left border. We
26:39all know that right border of the heart
26:41is a vertical border. It's a straight
26:42border.
26:44And this is the superior vena cava and
26:47along this border only we have inferior
26:48vena cava. And that's how it is.
26:51So, what you will see that right phrenic
26:52nerve will be descending along the right
26:54border vertically downward in this
26:56manner.
26:57Whereas left phrenic nerve has to go
26:59obliquely along with the left border of
27:01the heart and then it comes down.
27:04So, when it when they when they go
27:05through the diaphragm now let's say this
27:06is the diaphragm here.
27:08When they go through the diaphragm
27:09obviously with the inferior vena cava
27:11which phrenic nerve you will see? That's
27:13the right phrenic nerve and the reason
27:14is a vertical border the right border of
27:17the heart is vertical.
27:19So, you can see both right phrenic nerve
27:20this is the right phrenic nerve here and
27:22this one is inferior vena cava they're
27:24running together they're present in the
27:25common opening only.
27:27And this also tells me that why left
27:29phrenic nerve is longer. We all know
27:31that left phrenic nerve is longer than
27:32the right. The reason is right in front
27:34of you because it has to first go
27:35obliquely along the left border of the
27:37heart and then descend downward and that
27:40makes the left phrenic nerve longer
27:41also.
27:43So, this first major opening the vena
27:45caval opening.
27:46The second major opening guys it was
27:49esophageal opening.
27:56That is the esophageal opening. Where is
27:58the esophageal opening? Well, either you
28:00can say that esophageal opening is
28:01present in the muscular part that is
28:03fine over this this was present in the
28:04muscular part only or you can say it is
28:07surrounded
28:10It is surrounded by right crus of the
28:14diaphragm.
28:16Now, you'll be like surrounded by right
28:18crus of the diaphragm how it is
28:19surrounded by right crus of diaphragm?
28:20Well, maybe you you did not see the
28:22picture carefully
28:24which you will do now.
28:27And look at this if if you can see
28:29Look guys look carefully look at this
28:31second major opening here. Here is the
28:33right crus of the diaphragm.
28:34If I trace this right crus of the
28:35diaphragm upward this right crus of the
28:37diaphragm is going somewhat in this
28:40manner.
28:42And that's why I'm saying it is
28:43surrounded by the right crus. So, right
28:44crus basically winds around the
28:45esophagus and then it descends downward.
28:48And imagine still right crus is longer
28:49than the left crus.
28:51You can very well imagine how long right
28:53crus is despite of winding around the
28:56esophagus, it is still longer than the
28:58left here.
28:59So, either you say that esophageal
29:01opening is present in the muscular part
29:03or you will say it is present in the
29:05surrounded by the right crus, it is both
29:07are true.
29:10And to help you remember one thing, see,
29:11we said vena caval opening is in this
29:14one, that is in the central tendon.
29:16Esophageal opening is here and aortic
29:17opening is here. How will you remember
29:18that if there is no confusion between
29:20the two?
29:21Guys, when you think of inferior vena
29:23cava or superior vena cava for that
29:25matter, now these are the capacitance
29:27vessels. These are the big veins we're
29:28talking about.
29:30We cannot
29:32allow the vein to go through a muscle
29:34because every time the muscle will
29:36contract, the vein will also collapse.
29:38So, imagine if the vein was passing from
29:40this opening or anywhere in the
29:42diaphragm apart from this central
29:43tendon,
29:44then every time the diaphragm will
29:45contract, the inferior vena cava will
29:47also close. You cannot afford to do
29:49that. You cannot close the inferior vena
29:50cava.
29:51That is why thankfully God has gifted it
29:53with this opening present where in the
29:55central tendon
29:56which is allowing the passage for the
29:58inferior vena cava no matter how much
30:00diaphragm will contract, there is no
30:01effect, there is no contraction. Central
30:03tendon is non-yielding, so it will not
30:05obviously neither it will stretch too
30:07much, neither it will contract, so it
30:08will not allow, what do you say, the the
30:10collapse of the inferior vena cava.
30:13Secondly, when the diaphragm will
30:14contract, when the diaphragm contracts,
30:16the diaphragm goes down and when the
30:18diaphragm goes down, obviously the
30:19intra-abdominal pressure will increase.
30:21More intra-abdominal pressure increase
30:23means there are chances of that gastric
30:25content to come back into the esophagus.
30:28And for that, we are gifted with another
30:30opening, that is esophageal opening in
30:32the muscular part
30:34because more the muscle will contract,
30:36more the diaphragm will contract,
30:38this right crus of the diaphragm will
30:40also contract and what will happen? It
30:41will close the esophagus. The
30:43contraction of this right crus or the
30:45contraction of the diaphragm will close
30:47the opening for the esophagus and will
30:49prevent the regurgitation of the stuff
30:51from the gastric from the stomach into
30:53the esophagus.
30:54So, it's a win-win situation in both
30:56ways.
30:57So, diaphragm going down,
30:58intra-abdominal pressure is increasing,
31:00your inferior vena cava is still patent
31:02and allows the blood to come inside the
31:04heart, no problem.
31:05But, esophagus is also going through the
31:07diaphragm and because of the contraction
31:09of the diaphragm the esophagus will
31:10close, which is called as a pinchcock
31:13action. This is called as a pinchcock
31:14action.
31:15So, because of the pinchcock action the
31:17esophagus is closed and thankfully the
31:19content from the stomach will not go
31:21back into the the esophagus. Basically,
31:23the purpose of telling you all these
31:24details is so that you don't confuse
31:26that which opening is where. Don't mug
31:27it up. There's there's a reason behind
31:29there's a simple basic reason behind it
31:31why we have a certain structure going
31:32through a certain opening.
31:38If I take you back to this picture here,
31:40so we're talking about the esophageal
31:41opening. The esophageal opening is
31:43giving passage to mainly three things.
31:47It is giving passage obviously to the
31:48esophagus.
31:53Esophageal opening gives passage to the
31:55right
31:56as well as left
31:58right as well as left vagus nerves.
32:03Right and left vagus nerve See, vagus
32:05nerve they run along with the esophageal
32:08opening and as soon as they crosses the
32:10diaphragm
32:12they will turn like this.
32:13The left phrenic nerve the left vagus
32:16nerve will come in front and the right
32:18vagus will come behind and they form the
32:20anterior and posterior gastric nerves.
32:23So, when you look at the gastric nerves
32:24the anterior gastric and posterior
32:26gastric nerve, that's the same vagus
32:27nerve continuing down. So, it is coming
32:29along with the esophagus and if anything
32:31continues with esophagus that obviously
32:33is going in relation to the stomach
32:34only.
32:37What else we have here? We also have the
32:40esophageal branch.
32:42The esophageal branch of left gastric
32:45artery. We will discuss that in the in
32:47the abdomen part. Left gastric artery is
32:49a direct branch from the celiac trunk.
32:51And that left gastric artery also
32:53supplies the lower end of esophagus.
32:55And that's why from this esophageal
32:56opening you will see one artery
32:58ascending upward to come up and supply
33:00the lower part of esophagus here.
33:02So, three things: esophagus, the vagus
33:05nerve, right and left vagus nerves,
33:06esophageal branch of the left gastric
33:08artery is to be seen.
33:12Third major opening
33:14of the diaphragm is the aortic opening.
33:20Aortic opening. And where is the aortic
33:22opening? Aortic opening is present
33:23between the crura of the diaphragm.
33:26Again, a very strategical location.
33:29Vena cava was going from the central
33:31tendon because central tendon will not
33:33contract and vena cava should not
33:35collapse.
33:37Esophagus was going for the muscular
33:39part because we want to have a pinchcock
33:40action on the esophagus.
33:42And thankfully, aorta being the largest
33:44artery, the main artery which is for the
33:46systemic circulation, so obviously, the
33:49aorta is has to go through something
33:52which is not affected
33:54by the movement of diaphragm above or
33:55below.
33:56So, because it is passing between the
33:58crura of the diaphragm, there is a arch
33:59which is present between the crura of
34:01diaphragm. So, it doesn't matter
34:02diaphragm goes down, goes up, contracts,
34:04relax, whatever, the esophagus maintain
34:06its
34:07uh the lumen and there is no, you know,
34:09alteration in the blood flow through the
34:12the aorta.
34:13So, it is passing between the crura of
34:15the diaphragm.
34:16Aorta is giving passage to the
34:18aortic opening is giving passage to the
34:20obviously to the aorta, that is for
34:21descending aorta more precisely.
34:24It also gives passage to the
34:28azygous vein.
34:30Azygos vein always
34:32and and sometime
34:36and sometime hemi azygos also.
34:41And sometime hemi azygos, not always
34:43guys. Not always hemi azygos is a
34:44different opening. So it it gives passes
34:46to azygos vein, but sometime it gives
34:48passes to hemi azygos also.
34:51And number three, it is giving passes to
34:53the thoracic duct.
34:56That largest lymphatic duct we're
34:57talking about the thoracic duct is also
34:59going through it here.
35:00We'll be discussing all these aorta,
35:01azygos, thoracic duct, everything in
35:03detail subsequently in the thorax part.
35:06So these are the three major openings
35:08here. The aortic, the esophageal, and
35:10the vena cava.
35:12Now let's come to the some minor
35:14openings. Well,
35:15though they are minor openings, but in
35:16the exam sometime they become major
35:18question only. So minor openings of the
35:20diaphragm goes like
35:23like we have a minor opening present
35:24anteriorly close to the xiphoid process.
35:26I showed you that in the picture also,
35:28somewhere here. And that is what you
35:30called as the foramen
35:32of Morgagni.
35:37We call it foramen of Morgagni or space
35:38of Larrey also.
35:40Foramen of Morgagni or space of Larrey.
35:44Larrey's space.
35:46And please be careful guys, it is
35:47foramen of Morgagni. It is not the sinus
35:50of Morgagni, of course. Sinus of
35:52Morgagni is present in the pharynx, in
35:53the pharyngeal wall.
35:55So this is a foramen of Morgagni or the
35:57Larrey's space. And this foramen of
35:59Morgagni or Larrey's space is giving
36:01passes to
36:02the superior epigastric vessels.
36:06It is giving passes to the superior
36:09epigastric vessels, superior epigastric
36:12vessels.
36:15Superior epigastric vessels or superior
36:16epigastric artery is a branch of
36:18internal thoracic artery. Again,
36:19something which we will discuss in a
36:20while.
36:21And again, please be careful it is
36:22superior epigastric, not superficial
36:25epigastric. Superficial epigastric
36:27artery comes above. That is a branch of
36:29external iliac which will come above.
36:31That is a superficial epigastric.
36:34Superficial epigastric artery
36:36branch of femoral artery, sorry. That
36:39you will discuss in the roof of the
36:40femoral triangle. That is coming above.
36:41This is the one which is going down. It
36:43is superior epigastric.
36:47Okay. Another minor opening
36:50are the crus of the diaphragm here, the
36:51right crus and the left crus. Now, what
36:53is the crus of the diaphragm giving
36:54passage to? Both the crus of diaphragm
36:56are giving passage to the nerves called
36:57as a splanchnic nerves. We call them the
36:59right and left splanchnic nerves. I'll
37:01tell you a little bit bit more about it.
37:02Just just
37:03draw
37:04draw these nerves and leave it for now.
37:07And another minor opening is the
37:08structures passing deep to the arcuate
37:10ligament. Now, passing deep to the
37:12medial arcuate ligament is the
37:14sympathetic chain.
37:16You can draw it in the same diagram
37:17only. So, you will see the sympathetic
37:19chain
37:21passing deep to the medial arcuate
37:22ligament. That's how it goes down. And
37:24deep to the lateral arcuate ligament,
37:25you will see subcostal nerves and
37:28vessels. You will see subcostal vein,
37:32subcostal artery,
37:34and subcostal nerve. VAN, V A N.
37:38I hope you know this VAN. This is
37:39subcostal.
37:44Subcostal vein, artery, and nerve.
37:46>> [snorts]
37:47>> Lateral arcuate ligament is present at
37:49the level of the 12th rib. So, obviously
37:51below the 12th rib, you will see the
37:5212th nerve and artery and vein only. So,
37:55we call them subcostal nerves and
37:57vessels. Just for a quick comparison, if
37:58I just again take you back to this
38:00picture, look at that.
38:02Although you cannot see the subcostal
38:03nerves and vessels, they did not draw it
38:05in this picture, but you can see the
38:06sympathetic chain at least. Look at the
38:07sympathetic chain coming deep to the
38:09medial arcuate ligament only.
38:11And you can even see these nerves. Look
38:13at these nerves which are which I'm like
38:14putting a circle here.
38:15These are the splanchnic nerves I was
38:17talking about.
38:18The right and the left splanchnic
38:20nerves, the visceral nerves. These are
38:21sympathetic nerves, which do not relay
38:24in the sympathetic chain. They simply
38:26come out of the sympathetic chain
38:28to relay in the ganglion close to the
38:30organ only, like celiac ganglion and
38:32aorticorenal ganglion, other ganglions
38:34like these.
38:35So, they are sympathetic nerve. You will
38:37see them coming out of sympathetic chain
38:38only, but without relaying in the
38:40sympathetic chain. They just simply come
38:42out of the sympathetic chain without
38:44relaying there.
38:46Let me write this thing also finally for
38:48you. That is the
38:50arcuate ligament I was talking about,
38:51this uh
38:52crus here, that is the right crus.
38:59And this is the left.
39:01So, as I said, both the crus are giving
39:03passes to these splanchnic nerves.
39:06Splanchnic word actually came from the
39:08viscera, visceral nerves.
39:10So, these are all right splanchnic
39:11nerves.
39:18Those splanchnic nerves
39:20We have a greater splanchnic, lesser
39:21splanchnic, least splanchnic. We'll
39:23discuss that not here. We'll discuss
39:24them in the the neuroanatomy part.
39:27And these are the left splanchnic.
39:37And additionally from the left crus of
39:38diaphragm, additionally from the left
39:40crus of diaphragm,
39:41you might also see the opening for
39:44hemiazygos vein.
39:47Hemiazygos vein. I told you hemiazygos
39:49vein can be seen going from this aortic
39:51opening only in the center. But some
39:53most of the time hemiazygos vein it
39:55pierces the crus of the diaphragm to go
39:56above.
39:57So, azygos vein is definitely there in
39:59here in between the two crus.
40:01But hemiazygos vein sometime in through
40:03the crus, sometime through the the same
40:05aortic opening.
40:06So, this is about the the right crus and
40:08the left crus of the diaphragm.
40:11So, guys, this is about basically about
40:12the major openings and the minor
40:14openings in the diaphragm. Well,
40:15needless to say, we all know the
40:17diaphragm is supplied by phrenic nerve,
40:18but one interesting fact that you should
40:20note that is there anything in the
40:22diaphragm which is supplied by both
40:23phrenic nerve, right and the left? Now,
40:25we know obviously right phrenic nerve
40:26will supply the right dome, left will
40:28supply the left dome of the diaphragm,
40:29but do we have anything in the diaphragm
40:31which is supplied by both the phrenic
40:32nerve? And the answer is again very
40:35evident in the picture here.
40:38If you look carefully, let me just rub
40:40everything else so that you have a clear
40:42view.
40:45Now, can you see this right phrenic
40:46nerve here? I'm just marking that.
40:47That's the right phrenic nerve there.
40:49And this one you can see there is a left
40:50phrenic nerve.
40:51And if you look carefully,
40:55this here is what? That is the right
40:56crus of the diaphragm.
40:58And the right crus of the diaphragm, if
41:00you see, it is slightly goes toward the
41:01left side and then it descend downs on
41:03the right side. So, in a way I can say
41:05that right crus of diaphragm, it is
41:07present it starts from the left side and
41:10then comes toward the right side, and
41:11that's why you see the branches of the
41:14right phrenic nerve coming to this. You
41:15can see it here. And you can see the
41:16branches of left phrenic nerve also
41:18coming to it. So, please note that the
41:20right crus of the diaphragm is one
41:21structure
41:23of the diaphragm which is supplied by
41:25both phrenic nerve. Please note, right
41:28crus of diaphragm is supplied by both
41:29phrenic nerves. Supplied by both phrenic
41:32nerves.
41:37So, this concludes the first thing for
41:39us, that is the
41:41the inlet and the outlet of the thorax.

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