Anatomy clinical correlates: Anterior and posterior abdominal wall

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Introduction0:00–0:22

When we think about the clinical conditions affecting the abdomen, we immediately think about injury to organs such as the liver, intestines or stomach.
However, there are also many conditions that affect the anterior and posterior abdominal wall, as well as the structures adjacent to them.
So let's get started!When examining the gastrointestinal system, first, it’s important to do a general inspection of the abdomen which includes looking for scars and incisions which can indicate what surgeries the patient has had in the past.

Abdominal incisions0:22–4:13

Typically, the location of the abdominal incision indicates what type of surgery the patient has had.First, there’s the Kocher incision, also called the subcostal incision, which is made parallel and at least 2.5 centimeters below the costal margin in order to avoid the 7th and 8th thoracic spinal nerves.
Injury to these nerves results in decreased sensation of the anterior abdominal wall supplied by those respective branches.
This type of incision is usually found on the right side and provides access to the gallbladder and biliary ducts, and can be extended towards the left side of the abdomen to access the spleen.Next up, there are longitudinal incisions, which include midline incisions and paramedian incisions.
They can be used in almost all abdominal surgeries, especially exploratory surgeries which are sometimes needed to diagnose uncertain abdominal pathologies.
Now, longitudinal incisions provide great exposure of the abdominal viscera and can also be extended as needed.The midline or median incision is made along any part or length of the linea alba, so from the xiphoid process all the way towards the pubic symphysis.
This type of incision is preferred because the linea alba only has small vessels and nerves, so there’s a lower risk of bleeding and nerve damage.A paramedian incision, which is lateral to the median plane, is made in a sagittal plane and can extend anywhere from the costal margin to the pubic hairline.
The paramedian incision would therefore go through the anterior rectus sheath, the rectus abdominis muscle, and the posterior rectus sheath.Other surgical procedures may require oblique incisions, depending on muscle fiber orientation and surrounding nerves.
Oblique incisions include the McBurney, or Gridiron incision, and the Rutherford Morison incision.So first, the McBurney incision is typically needed for appendectomies and it’s done inferomedially in an oblique orientation to follow the muscle fiber orientation of the anterior abdominal wall, specifically the external oblique.
This is typically done over McBurney point, which is one third of the way from the anterior superior iliac spine to the umbilicus.This incision can be extended, or mirrored on the left side of the abdomen as a Rutherford Morison incision, which is an oblique incision used for right and left sided colonic resection.
Instead of an oblique incision, surgeons can also use transverse incisions, which are often made through the anterior layer of the rectus sheath and rectus abdominis muscle.
They provide good access and are less likely to damage the nerve supply of the rectus abdominis as the incision is parallel to the nerves, and are used in pediatric or vascular repair cases.Another type of transverse incision is a Lanz incision, which may also be used for appendectomies, and is located in the right iliac fossa and has a more transverse orientation.
These types of incisions leave the anterior branch of the iliohypogastric nerve at risk of injury, which would cause decreased sensation over the suprapubic region.Next up are suprapubic or Pfannenstiel incisions, also called bikini incisions.
These are made at the pubic hairline. These types of incisions are horizontal with a slight convexity and are used for most gynecological and obstetrical operations, like a cesarean section.
Once this incision is made, the linea alba and anterior rectus sheath is resected, and the rectus muscles are retracted laterally.

Risks and complications4:13–6:09

Care must be taken to not damage the iliohypogastric or ilioinguinal nerves, as damage to these could result in sensory deficits of the suprapubic and genital region.
Sometimes, during a cesarean section, there isn’t enough space to properly finish the procedure and take the baby out safely.
In this case, a horizontal transection of the rectus abdominis muscle might be done in addition to the vertical incision along the linea alba.In order to perform a horizontal incision, first you need to locate the arcuate line, which lies below the umbilicus posterior to the rectus abdominus and marks the inferior limit of the posterior rectus sheath.
This is done in order to identify the inferior epigastric arteries, which supply the inferior portion of the rectus abdominis as they ascend on its posterior surface to enter the lateral aspect of the muscle at the arcuate line.Since there’s no supporting posterior rectus sheath below the arcuate line, this is where the inferior epigastric arteries are most susceptible to injury, so they need to be located and ligated when performing a horizontal incision in order to prevent significant hemorrhage.Now, bear in mind that any abdominal surgery comes with a risk of nerve injury.
The inferior thoracic spinal nerves, those from T7 to T12, and the iliohypogastric and ilioinguinal nerves provide innervation of the abdominal muscles.
They are distributed across the anterolateral abdominal wall where they run oblique, but mostly horizontal. They can be injured during any surgical incision or from trauma at any level, leading to muscle weakness of that area of innervation.
Muscle wall weakness can lead to herniation of underlying abdominal viscera through the abdominal wall.In addition to a general inspection of the abdominal wall, another key step in clinical examination is abdominal palpation, which is when you palpate the abdominal wall and the abdominal viscera while the individual lies in a supine position with exposure from their nipples to their pubic symphysis.

Guarding6:09–7:30

One clinically relevant sign to look out for when palpating the abdomen is guarding, which is when the muscles of the abdomen get tense and produce spasms.Guarding can be either voluntary or involuntary.
Voluntary guarding is a voluntary contraction of the abdomen performed by the patient in order to avoid pain during examination and usually represents a diffuse abdominal pain, meaning the entire abdomen tenses up.Involuntary guarding, on the other hand, also referred to as rigidity, happens when there’s involuntary contraction of the abdominal muscles in order to protect the underlying abdominal viscera from pressure as they are irritated.
Involuntary guarding is a reflexive muscular rigidity caused by an inflamed organ, such as the appendix, which results in peritonitis, or an inflammation of the abdominal peritoneum.
This is often an indication of an acute abdomen, which is the sudden onset of severe abdominal pain, and why abdominal palpation is so important during a clinical exam.Next up we’re going to look at the psoas major muscle, which originates along the anterior surface of the transverse processes and lateral surface of T12-L5 vertebral bodies, and eventually combines with the iliacus muscle to form the iliopsoas muscle.

Psoas abscess7:30–9:42

The main clinical condition affecting the psoas major muscle is a psoas abscess, which is a walled off collection, typically pus filled, found along the psoas fascia.This can be caused by things such as spread of infection from the thoracic or lumbar vertebral bodies, such as vertebral tuberculosis, other nearby abdominal infections such as appendicitis, colitis, or hip joint infections, as well as hematogenous seeding from a distant site like a skin infection.
Risk factors include diabetes, IV drug use, HIV infections, and other forms of immunosuppression.A psoas abscess can result in severe pain in the back or flank region, which can also be referred to the hip, thigh, or knee joint.
Other symptoms of a psoas abscess include fever and difficulty walking. A psoas abscess may be visualized and palpated in the inguinal region, and may be mistaken as an inguinal hernia, an enlarged lymph node, or a saphenous vein varix.Furthermore, it is important to note the femoral nerve emerges laterally between the psoas major muscle and iliacus muscle, so an abscess can result in femoral neuropathy and quadriceps weakness, decreased patellar reflex, as well as sensory loss over the anterior and medial thigh and leg.To test for a psoas abscess, you can perform the iliopsoas test, which is when the individual is asked to lie on the unaffected side and contralateral hip is put into extension by the examiner.
A positive sign is when pain appears during movement and can indicate a psoas abscess. Other things that can cause a positive psoas sign are an inflamed or infected appendix, sigmoid colon, and iliac lymph nodes.Another important structure located along the posterior abdominal wall is the Inferior Vena Cava, or IVC for short.

Inferior vena caval filter9:42–11:03

The IVC ascends in the abdomen along the right side of the vertebral bodies to the right of the abdominal aorta. On a coronal section of a CT scan however, the IVC can be seen along the vertebral bodies, but on the left side of the image, which corresponds to the right side of the body.
This is because when looking at a transverse slice of a CT or MRI scan, we are viewing the section from below, which is why the structures on the right hand side of the body are shown on the left hand side of a transverse radiology scan and vice versa!
Sometimes, an IVC filter, which is a tiny device able to stop blood clots and prevents them from traveling towards the heart and lungs, needs to be placed within the IVC.To do this, a long catheter is placed by surgeons through the internal jugular vein or the femoral vein until it reaches the inferior vena cava.
The main indication for placing an IVC filter in someone is to prevent embolization of deep venous clots from the legs to the lungs, which would cause a pulmonary embolism.
An IVC filter is often used in patients who have contraindications to anticoagulation, typically those who are at an increased risk of bleeding.Now, before we wrap up, let’s look at abdominal aortic aneurysms, which is defined as a pathological dilation of the aorta usually greater than 50 percent of the normal aortic diameter.

Abdominal aortic aneurysms11:03–13:08

Typically, the normal infrarenal aortic diameter is 2.0cm and an aneurysm is considered anything larger than 3.0cm, where a large aneurysm is defined as over 5.5cm in diameter.Risk factors include being a biological male, old age, cigarette smoking, hypertension, a family history of abdominal aortic aneurysms and last, but not least, atherosclerosis.
Even though atherosclerotic build up contributes to the formation of abdominal aortic aneurysms, the pathophysiology of an abdominal aortic aneurysm is complex and involves systemic inflammation, as well as smooth muscle cell apoptosis and extracellular matrix degradation resulting in thinning and weakening of the aortic wall and enlargement in aortic diameter.The most common location of an abdominal aortic aneurysm is just below the renal arteries and is referred to as an infrarenal aneurysm.
Now, the majority of abdominal aortic aneurysms are asymptomatic, but people can also present with abdominal pulsations, compression of surrounding structures, abdominal, back or flank pain, and if the aneurysm ruptures, it leads to severe abdominal pain, along with a pulsatile mass in the abdomen and arterial hypotension.Okay, let’s take a look at this coronal section of a computed tomography scan.
Can you see the balloon shaped structure in front of the vertebral body? That’s the dilated abdominal aorta.
In a CT or MRI cross sectional scan, the aorta is found on the right hand side of the vertebral bodies in the image, which actually corresponds to the aorta being on the left hand side of the vertebral bodies in the individual being scanned.Alright, as a quick recap… Different surgical incisions are used to access the abdomen for different surgical procedures.

Review13:08–14:47

These include kocher or subcostal incision, median or paramedian incision, the Mcburney or gridiron incision, as well as the lanz, pfannenstiel, and rutherford morison incisions.During abdominal surgery, the inferior thoracic spinal nerves, as well as the iliohypogastric and ilioinguinal nerves can be injured.
During a horizontal transection of the rectus abdominis muscles, the inferior epigastric arteries need to be ligated to avoid hemorrhage.Voluntary guarding is a voluntary contraction by the patient of the abdomen in order to avoid pain during examination and is usually diffused over the entire abdomen.
Involuntary guarding or rigidity happens when there’s involuntary contraction of the abdominal muscles, usually caused by peritoneal inflammation and indicates an acute abdomen.The iliopsoas test can be used to indicate certain abdominal pathologies such as psoas abscess, appendicitis, or irritation to nearby structures.
A psoas abscess happens when there is a walled off collection, typically pus filled, found along the psoas fascia. IVC filters are placed to prevent emboli from reaching the heart and the lungs.
Aortic abdominal aneurysms are dilations of the abdominal aorta that are usually infrarenal. Symptoms of a ruptured aneurysm can include severe abdominal pain, along with a pulsatile mass in the abdomen and arterial