Anatomy of the anterolateral abdominal wall

Chapters:

Watch video only

Review0:00–0:37

The abdominal wall is subdivided into the anterior wall, the right and left lateral walls and the posterior wall. These walls are musculoaponeurotic, meaning they are composed of muscles and fascial layers except for the posterior wall, which is also made up by the lumbar vertebral column.
This musculoaponeurotic wall functions to enclose and protect the abdominal viscera stabilize and contribute to movements of the trunk and also increase the intraabdominal pressure, which is needed during urination, defecation, vomiting and assisting in childbirth.

Boundaries0:37–1:10

Now, the anterior and lateral abdominal walls are collectively known as the anterolateral abdominal wall, mainly because the boundary between the two is not distinct.
So the anterolateral abdominal wall extends from the thoracic cage down to the pelvis. More specifically, it's bounded superiorly by the cartilages of the seventh through 10th ribs, as well as the xiphoid process and inferiorly by the inguinal ligament and superior margins of the anterolateral aspects of the pelvic girdle.

Layers1:10–2:23

The anterolateral wall is composed of many different layers. There are 12 of them in total.
The most superficial layer is the skin which covers a superficial fatty layer of subcutaneous tissue or fat known as camper fascia, which is a major site of fat storage deep to the camper fascia.
There is a membranous layer of subcutaneous tissue known as scarpa fascia, which continues inferiorly with the superficial perineal fascia or kiss fascia and deep to the superficial fascia layers.
There are three muscle layers each covered in a layer of a deep fascia. So six layers in total.
So right after scarpa fascia, there's the superficial investing fascia followed by the most superficial muscular layer. The external oblique muscle then comes the intermediate investing fascia and the internal oblique muscle.
And finally, there are the deep investing fascia and the transversus abdominis muscle deep to the transversus abdominis is the transversalis fascia.
And finally, for our two deepest layers, there is a thin layer of extraperitoneal fat which is just above the parietal peritoneum, which is the deepest layer of the abdominal wall and lines the abdominal cavity.

Quiz2:23–2:36

So just to recap, let's take a quick break and see if you can recall the layers of the anterolateral abdominal wall. Now let's talk muscles.

Flat abdominal muscles2:36–3:20

The external oblique muscle, the internal oblique muscle and the transversus abdominis muscle are considered the flat abdominal muscles and the fibers of each have varying orientations.
All three of these abdominal muscles continue anteriorly and medially as aponeuroses, aponeuroses are simply flat sheets of fibrous tissue that anchor muscles to bone deep fascia or other muscles.
The aponeuroses from the left and right, flat abdominal muscles fuse in the midline to form the linea alba, which is Latin for white line and runs from the xiphoid process to the pubic symphysis.

Flat abdominal muscles3:20–5:16

The external oblique is the largest and most superficial of the anterolateral abdominal muscles. It originates at the external surfaces of the fifth through 12th ribs and inserts on the linea alba pubic tubercle and the anterior half of the iliac crest.
The posterior fibers of the external oblique are nearly vertical as they travel distally toward the ileac crest. The more anterior fibers, however fan out medially, making most of the muscular fibers run infra medially to remember this.
The orientation of the external oblique muscle fibers are in the same direction as your fingers are. When your hands are in your pocket, these muscle fibers eventually become aponeurotic around the midclavicular line forming a sheet of tendinous fibers that cross at the linea alba.
The inferior margin of the aponeurotic portion also forms the inguinal ligament connecting the anterior superior iliac spine to the pubic tubercle.
The muscular portion of the external oblique contributes primarily to the lateral abdominal wall. And the anterior aponeurotic portion contributes to the anterior abdominal wall.
The external oblique is innervated by the thoracoabdominal nerves which are derived from the anterior rami of the T seven to T 11 spinal nerves as well as by the subcostal nerve, which is the anterior ramus of T 12.
The external oblique flexes and rotates the trunk like when you're doing those Russian twists at the gym. It also compresses and supports the organs within the abdominal cavity, particularly during expiration.
Deep to the external oblique muscles are the internal oblique muscles. Most of their fibers run perpendicularly to the external oblique muscle fibers.

Internal oblique muscle5:16–6:38

So they head inferolaterally, try giving yourself a hug and placing your hands on your hips. The internal oblique fibers would run in the same direction as your fingers.
The posterior portion of the internal oblique muscles originate from the broad connective tissue attached to the spine known as the thoracolumbar fascia.
And also originates from the anterior two thirds of the iliac crest and tissue deep to the lateral third of the inguinal ligament.
The internal oblique then inserts at the inferior border of the 10th through 12th ribs posteriorly and the linea alba anteriorly, it is innervated by the thoracoabdominal nerves which again are derived from the anterior rami of the T seven to T 11.
And also by the subcostal nerve and branches of L1 anterior ramus, similar to the external oblique, the internal oblique muscle compresses and supports abdominal viscera and also helps to flex and rotate the trunk.
More specifically, since many of their fibers are actually continuous at the linea elbow, the right external oblique and the contralateral left, internal oblique would work together to bring the right shoulder towards the left hip.

Transversus abdominis6:38–7:44

The deepest and final layer of the flat abdominal muscles is the transversus abdominis living up to its name, its fibers run transversely except for the inferior fibers which run parallel to the internal oblique.
This muscle originates from a number of structures including the internal surface of the seventh to 12th costal cartilages, the thoracolumbar, fascia, ileac crest and connective tissue deep to the lateral third of the inguinal ligament along with the external and internal obliques.
It inserts at the linea alba as well as the pubic crest. It also has the same innervation as the internal oblique and the thoracoabdominal nerves, subcostal nerve and the nerves from the L1 anterior ramus and similar to both oblique muscles.
The transversus abdominis helps to compress the abdominal contents in order to increase intraabdominal pressure, which is helpful during forced expiration, defecation and labor.
Unlike the obliques, though it doesn't play a role in trunk movement. Besides the flat abdominal muscles, there are also vertical abdominal muscles, namely the rectus abdominis and pyramidalis muscle.

Vertical abdominal muscles - Rectus abdominis7:44–9:00

The rectus abdominis is a set of vertically oriented paired muscles that lies right at the midline of the anterior abdominal wall and originates at the pubic symphysis and pubic crests and inserts at the xiphoid process and fifth through seventh costal cartilages.
It is innervated by the anterior rami of T seven to T 12 via the thoracoabdominal and subcostal nerves. The rectus abdominis is a powerful flexor of the trunk.
So you can thank this muscle. When you do your crunches, it also helps stabilize the tilt of the pelvis and just like the other abdominal muscles.
It compresses, the abdominal viscera, the pair of rectus abdominis muscles is separated in the midline by the linea alba which is a fibrous band composed of interweaving aponeuroses from the flat abdominal muscles.
The rectus abdominis is mostly enclosed by the rectus sheath where the anterior layer of the rectus sheath anchors the rectus muscle transversely by tendinous intersections which create the bulges seen in people with well defined abs or a six pack.

Pyramidalis muscle9:00–9:27

The second vertical abdominal muscle is the pyramidalis muscle, which is a smaller triangular or pyramidal shaped muscle.
It lies anterior to the lower portion of the rectus abdominis and originates on the anterior surface of the pubis and inserts at the linea alba interestingly, up to 20% of people don't have a pyramidalis muscle.
But luckily, it is not a critical organ considering its only function is to tense the linea alba. Now, the fibrous rectus sheath is a strong, incomplete aponeurotic covering of the pyramidalis muscle and the rectus abdominis muscle.

Rectus Sheath9:27–11:46

It also contains the superior epigastric and inferior epigastric arteries which are an important blood supply for the abdominal wall as well as other veins.
Lymphatic vessels and nerves. The overall function of the rectus sheath is to protect the structures contained within it.
The rectus sheath itself is formed from interweaving of the flatt abdominal muscles, aponeuroses with one another. Now, the rectus sheath is divided into an anterior and posterior layer.
However, the rectus sheath is not uniform throughout. So its composition is different in three main areas above the costal margin below the costal margin to the arcuate line and then below the arcuate line to the pubic crest.
So the anterior layer of the rectus sheath above the costal margin consists only of the external oblique aponeurosis. It doesn't contain a posterior layer and therefore, the rectus abdominis lies directly on the thoracic wall between the costal margin to just below the umbilicus.
The rectus sheath contains an anterior and posterior layer. The internal oblique aponeurosis splits into two layers or a laminae at the lateral border of the rectus abdominis.
The anterior lamina of the internal oblique aponeurosis passes anterior to the muscle and merges with the aponeurosis of the external oblique to form the anterior layer of the rectus sheath.
The posterior lamina of the internal oblique aponeurosis passes posterior to the rectus abdominis and merges with the aponeurosis of the transversus abdominis to form the posterior layer of the rectus sheath.
Finally, the lower portion of the rectus sheath begins approximately one third of the distance from the umbilicus or belly button to the pubic crest.
Here. The anterior layer of the rectus sheath is composed of the aponeuroses from all three flat muscles as the aponeuroses making up the posterior rectus sheath pass anterior to the rectus abdominis, leaving only the transversalis fascia posteriorly, the transition between the thin transversalis fascia covering the inferior quarter of the rectus abdominis and the posterior layer of the rectus sheath covering the superior three quarters is demarcated by an anatomical landmark known as the arcuate line.

Arcuate line11:46–12:09

Quiz12:09–12:26

Now, can you identify the three flat abdominal muscles and the two vertical muscles on this image? Next, let's take a look at the internal surface of the anterolateral abdominal wall.

Internal surface12:26–13:46

The internal surface of the anterolateral abdominal wall is covered with parietal peritoneum. The part of the peritoneum directly below the umbilicus folds into five distinct umbilical peritoneal folds.
One in the median plane and two on each side. The fold in the median plane is the median umbilical fold which extends from the apex of the bladder to the umbilicus and covers a structure known as the median umbilical ligament, which is a remnant of the fetal urachus that originally served to connect the fetal bladder to the umbilicus moving laterally on each side of the median umbilical fold.
There are the left and right medial umbilical folds covering the medial umbilical ligaments which are remnants of the fetal umbilical arteries.
To remember the median from the medial umbilical folds think that median means in the middle. So it's the one on the midline.
Also the word medial has an L in it which should prompt you to remember that it is lateral to the median fold, moving even further laterally on each side.
We come to the last pair of umbilical folds known as the lateral umbilical folds. These lateral folds are the only ones that don't cover an embryologic remnant and instead cover the inferior epigastric arteries.
So, now let's have a look at the sensory innervation of the abdominal wall. The skin and muscles of the anterolateral abdominal wall are mainly innervated by the thoracoabdominal nerves.

Sensory innervation13:46–14:09

The subcostal nerve and the iliohypogastric and ilioinguinal. So first, as we've mentioned, the thoracoabdominal nerves are derived from the anterior rami of the T seven to t 11 spinal nerves.

Thoracoabdominal nerves14:09–15:08

Specifically, these nerves are actually the continuation of the lower intercostal nerves distal to the costal margin where they run in the neurovascular plane between the internal oblique and transversus abdominis.
Some of the thoracoabdominal nerves then branch into the lateral and anterior cutaneous branches which emerge anywhere between T seven and T 11.
More specifically, the lateral cutaneous branches enter the subcutaneous tissue along the anterior axillary line. In comparison to the anterior cutaneous branches which enter the subcutaneous tissue.
Closer to the median plane or midline of the body. The anterior cutaneous branches of T seven to T nine innervate the skin above the umbilicus.
T 10 supplies the skin at the level of the umbilicus and T 11 innervates a portion of the skin below the umbilicus. Next, the subcostal nerve is the anterior ramus of the T 12 spinal nerve.

Subcostal nerve15:08–15:36

And as the name suggests, it runs along the lower border of the 12th rib before entering the neurovascular plane of the abdominal wall.
Similar to the thoracoabdominal nerves, the subcostal nerves also divide into anterior and lateral cutaneous branches which provide sensory innervation to the skin between the umbilicus and iliac crest.
The anterior ramus of the L1 spinal nerve divides into the iliohypogastric and ilioinguinal nerves. The ileo hypogastric nerve innervates the internal oblique and transversus abdominis muscles and supplies sensory innervation to the skin overlying the ileac crest, upper inguinal and hypogastric regions.

Iliohypogastric and ilioinguinal nerves15:36–16:11

In contrast, the ilioinguinal nerve supplies the inferior portion of the internal oblique and transversus abdominis and provides sensory innervation of the skin overlying the lower inguinal region.
Mons pubis, anterior scrotum or labia majora and medial thigh. The dermatome map matches the distribution of these nerves where each dermatome begins posteriorly where the spinal nerve exits the vertebral column and generally follows in the direction of the ribs as it wraps around the lateral portion of the trunk to the anterior abdomen.

Dermatomes16:11–16:38

Remember the nerves as well as the blood vessels can generally be found running in the neurovascular plane of the anterolateral abdominal wall, which is the space between the internal oblique and transversus abdominis muscle.

Arterial supply16:38–18:27

Next up, there's the arterial supply of the abdominal wall. First off, there's the superior epigastric artery which is a continuation of the internal thoracic artery.
It descends inferiorly and goes through the rectus sheath deep to the rectus abdominis into the posterior layer and provides blood supply to the superior portion of the rectus abdominis at the level of the umbilicus, the superior epigastric artery anastomoses with the inferior epigastric artery which originates from the external iliac artery, superior to the inguinal ligament and descends upwards in the transversalis fascia to enter the rectus sheath below the arcuate line, like the superior epigastric artery.
The musculophrenic artery is a terminal branch of the internal thoracic artery. It descends along the costal margin or the rib cage and provides blood supply to the hypochondriac region and anterolateral parts of the diaphragm.
The rest of the abdominal wall is supplied by smaller branches. The deep circumflex iliac artery originates from the external iliac artery and provides blood supply to the deep abdominal wall of the inguinal region.
The superficial circumflex iliac artery arises from the femoral artery and provides blood to the superficial inguinal region.
Another artery that originates from the femoral artery is the superficial epigastric artery which provides blood to the superficial abdominal wall of the pubic and inferior umbilical regions.
Finally, there are the 10th and 11th posterior intercostal arteries as well as the subcostal arteries which originate from the aorta and provide blood supply to the lateral region of the anterolateral abdominal wall and where there are arteries, you know it, there must be veins.

Venous drainage18:27–19:35

So the skin over the anterolateral abdominal wall is drained by a superficial subcutaneous venous plexus into the internal thoracic vein supremely.
The lateral thoracic vein superolaterally and inferiorly. It drains to the superficial and inferior epigastric veins which eventually carry the blood to the femoral vein and external iliac vein, cutaneous veins around the umbilicus, anastomose with the paraumbilical veins which are tributaries of the hepatic portal vein.
A superficial anastomotic channel may exist laterally called the thoraco epigastric vein running between the superficial epigastric vein and the lateral thoracic vein.
The deep veins of the anterolateral abdominal wall accompany the arteries bearing the same names a deeper more medial anastomosis can also exist between the inferior epigastric vein which drains into the external iliac vein and the superior epigastric vein which drains into the internal thoracic vein.

Lymphatic drainage19:35–20:09

Finally, regarding lymphatic drainage, the superficial lymph vessels accompanying subcutaneous veins and those found above the umbilicus, mainly drain into the axillary lymph nodes and parasternal lymph nodes, those found inferior to the umbilicus will drain into the superficial inguinal lymph nodes.
The deep lymphatic vessels accompany deep veins of the abdominal wall and drain into the external and common iliac lymph nodes or the right and left lumbar lymph nodes, all right as a quick recap.

Review20:09–22:41

The anterolateral abdominal wall is the area between the thoracic wall and pelvis and is composed of multiple layers of muscles and fascia.
The flatt abdominal muscles include the external oblique, internal oblique and transversus abdominis. These muscles eventually become aponeurotic and these aponeuroses go on to create the rectus sheath.
The anterior layer of the rectus sheath is mainly formed by the external oblique and anterior lamina of the internal oblique.
Whereas the posterior layer is formed by the transversus abdominis and posterior lamina of the internal oblique, a third of the way from the umbilicus to the pubic crest.
This posterior layer passes anterior to the rectus abdominis ending the posterior rectus sheath and leaving only the thin transversalis fascia.
Posteriorly. This transition is demarcated by the arcuate line.
This rectus sheath incompletely envelops the vertical abdominal muscles which are the rectus abdominis and pyramidalis on the internal surface of the abdominal wall.
There are five umbilical folds, a median umbilical fold and on either side of it, there are two medial and two lateral umbilical folds between the internal oblique and the transversus abdominis.
There's the neurovascular plane that innervates the anterolateral abdominal wall. The skin and muscles of the anterolateral abdominal wall are innervated by the thoracoabdominal nerves from thoracic nerves, T seven to T 11.
The subcostal nerves at T 12 and the iliohypogastric and ilioinguinal nerves from lumbar nerve, L1. Some of the major arteries that supply the anterior abdominal wall include the superior and inferior epigastric artery, as well as the musculophrenic artery.
Superficial lymph vessels above the umbilicus, primarily drain towards the axillary lymph nodes. Whereas below the umbilicus, they drain towards the superficial inguinal lymph nodes.
Deep lymph vessels drain into the external iliac lymph nodes and common ileac lymph nodes, as well as the lumbar lymph nodes.