AssessmentsAnatomy clinical correlates: Anterior and posterior abdominal wall
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 74-year-old man presents to the emergency department to evaluate syncope and right flank pain. The patient experienced severe right-sided flank pain radiating to the groin while getting out of bed this morning. He subsequently “blacked out.” His partner found him on the ground moaning in pain and brought him to the emergency department. The patient has a remote history of kidney stones. He has not seen a physician in many years. He has been smoking one pack of cigarettes daily for fifty years. Temperature is 36.4°C (97.5°F), blood pressure is 93/67 mmHg, pulse is 102/min, and O2 saturation is 94% on room air. Physical exam demonstrates a tachypneic male in moderate pain. The remainder of the physical examination is unremarkable. An abdominal radiograph is shown below:
Image reproduced from Radiopedia
Which of the following best identifies the anatomic location of this patient’s clinical condition?
Content Reviewers:Viviana Popa, MD, Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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