Chapter 40: Abdominal X-Ray Interpretation

Welcome to Last Minute Lecture!

This free chapter overview is designed to help students review and understand key concepts.

These summaries supplement not replaced the original textbook and may not be redistributed or resold.

For complete coverage, always consult the official text.

Hello and welcome back to the Deep Dive.

We are so glad you're here with us today.

It's great to be back.

We are doing something a little different, a little more visual today, which is, well, it's ironic for an audio format, but stick with us.

It is, but I think it's going to be incredibly useful.

I agree.

We are rolling up our sleeves and tackling a subject that I think intimidates a lot of students, and honestly, plenty of working clinicians, too, when they first see it.

Oh, absolutely.

We are diving deep into chapter 40 of Advanced Health Assessment and Clinical Diagnosis in Primary Care, the sixth edition, specifically, and our topic,

the abdominal x -ray.

It is an absolute classic, and you are so right.

It can be incredibly intimidating.

You know, you look at a chest x -ray and you see the heart, you see the lungs, the ribs.

It's all there on black and white.

Exactly.

It's high contrast.

It feels crisp.

Then you put up an abdominal x -ray, and what do you see?

Gray.

It just looks like varying shades of gray soup.

It's tough.

It really is.

It's like looking at a Rorschach test sometimes.

You're squinting, you're tilting your head, trying to figure out if that shadow is a kidney or just, you know, lunch.

It's an artifact, yeah.

But our mission today is to decode that gray scale.

We are going to strictly follow the roadmap laid out in this chapter to understand not just what we're looking at, but the clinical reasoning behind it.

That's the whole point.

We're talking symptom -based assessment, how to spot the red flags, and really just how to keep from getting completely overwhelmed by all that gray.

And that is the absolute key having a system.

The text makes it very clear that while the abdominal x -ray is a common tool, it has a very specific scope.

It's not a magic wand.

You just wave at every bellyache.

So it's not a fishing expedition.

Definitely not.

Yeah.

It's primarily used for acute conditions.

We aren't just looking for anything.

We're usually looking for the cause of specific symptoms like severe pain, vomiting, or abnormal bowel sounds.

Right.

It's a treasure hunt.

The text actually lists out precisely what we are hunting for.

It does.

We're looking for kidney stones.

We're looking for gallbladder stones, swallowed foreign objects, which is always a fun one.

The stories you hear.

Oh, I'm sure.

And of course, checking air distribution, which we'll see is a huge part of this.

A critical part.

But before we even snap the picture, before we even think about walking into the radiology suite, there's one crucial,

absolute safety step the text highlights.

And it says it's non -negotiable.

Completely.

I know exactly what you're referring to.

Every single patient with a uterus must be asked about pregnancy.

Every.

Single.

One.

No exceptions.

Because as we will see later when we look at the evidence, the radiation dose isn't negligible.

It's not like a quick dental x -ray.

We have to be absolutely sure.

That makes perfect sense.

And it's also worth noting right up top that frequently when you order an abdominal image, a chest image is done at the same time.

Yes.

The text points that out.

Yeah.

And it's because the abdomen and the chest are, well, they're neighbors.

And problems often spill over the fence, so to speak.

Yeah.

Abdominal pain can be referred from the chest and vice versa.

That's a great way to put it.

OK, so we established the why.

Let's get into the how.

The text breaks this down beautifully into diagnostic reasoning and the initial setup.

I love that it starts with a mental checklist.

The key questions to self.

Sounds so basic, but in the heat of a busy clinic or an emergency department, these are the steps that prevent major, major errors.

They seem like common sense, but common sense can fly out the window when you're under pressure.

Let's unpack them one by one.

Question one.

Does this image belong to the correct patient?

Seems obvious, right?

You would think so.

Yeah.

But all that pertinent information is usually in the upper corner of the image.

The name, the date of birth, the medical record number.

You have to physical look and verify it.

You don't want to be diagnosing Mrs.

Smith's kidney stones based on Mr.

Jones's x -ray.

That is a career ending mistake right there.

And it happens.

So step one, always.

That would be a bad start to the day.

OK, question two on the checklist.

Do I have all the views?

And this is where the terminology can get a little tricky for beginners.

The text starts with the flat plate.

Or the AP view.

Right.

Walk us through what that means.

What is the patient doing?

So AP stands for anteroposterior.

The position.

The x -ray plate, the cassette, is behind them underneath their back on the table.

And the machine is up top?

The machine is above them.

So the x -ray beam passes from the front,

the anterior through their body, to the back of the posterior where it hits the plate.

And there's a specific breathing instruction here, isn't there?

The patient has to exhale.

Correct.

You ask them to take a breath in, then blow it all the way out and hold it.

You do that to get the diaphragm up and out of the way as much as possible.

What happens if they inhale?

If they take a deep breath in, the lungs fill up and that pushes the diaphragm way down.

And it can obscure some of the upper abdominal organs, like the top of the liver or the spleen.

Exhaling gives you a better view of the whole abdominal cavity.

That makes sense.

Now here's a detail the text mentions that's really practical.

Something you might not think about until it happens.

What if you have a really tall patient?

The tall patient problem.

Exactly.

Yes, this is a great point.

You need to be able to see everything from the diaphragm all the way down to the groin, specifically the symphysis pubis.

That's the bone at the very bottom of the pelvis.

So one picture might not cut it.

Sometimes if the patient is very long -waisted or just tall, one cassette isn't big enough to cover all that real estate.

So you might need a second image, sort of a lower shot, just to make sure you've included the entire pelvic region.

Okay, so that's the flat plate, the AP view.

But then there's this tongue twister that always trips people up when they're first learning.

The left lateral decubitus view.

It is a mouthful.

It really is.

But the logic behind it is pure, beautiful physics.

Break it down for us.

Okay, so decubitus just implies lying down.

Yeah.

In this view, the patient lies specifically on their left side.

And crucially, they need to stay in that position for about 10 to 15 minutes before the image is taken.

Right.

So why the, wait, and why the left side?

Why not the right?

That seems so specific.

It's all about air.

The weight is to let gravity do its work.

We are usually ordering this specific view because we're looking for free air, air that has escaped the bowel due to something like a perforation or a severe obstruction.

And air rises.

Air rises.

Yeah.

So if the patient is lying on their left side, any free air inside the abdominal cavity will float up towards the right side of the body.

And what's on the right side?

The liver.

Oh, okay.

The liver is a big, solid, dense organ.

If you have air riding and collecting just above the liver, it creates this beautiful, stark contrast.

You'll see a dark sliver of air against the whitish gray density of the liver.

It's much easier to spot there.

So what if we laid them on the right side?

If we laid them on the right side, the air would rise up to the left side of the abdomen.

And what's over there?

The stomach.

The stomach already has a big air bubble in it normally.

So free air would get lost and be much harder to differentiate.

We use the liver as a clean backdrop.

That is such a cool bit of clinical engineering.

So left side down, wait a few minutes, let the air go up over the liver.

Got it.

You've got it.

Then we have the erect view, which is just what it sounds like.

Patient is standing up or erect.

This is also a way to check for free air because again, air will rise and collect right under the diaphragm.

But the text notes a limitation here.

It does.

It says the erect view will usually only show free air if there's an excessive amount of it.

So if it's a very small, subtle perforation, the erect view might actually miss it.

The decubitus view is more sensitive for smaller amounts of air.

Get to know.

And before we move off terminology completely, we see the acronym KUB thrown around a lot.

KUB.

Yes.

What's that about?

KUB just stands for kidneys, ureter, and bladder.

In practice, it's often used as a synonym for that first view we talked about, the flat plate or AP view.

So it's the same picture.

It's basically the same picture.

The term KUB just implies that the primary reason for the x -ray is to look at the urinary system.

You're hunting for kidney stones or other abnormalities in that tract.

But the physical act of taking the image is the same as a flat plate abdominal x -ray.

Okay, we've got our patient.

We've verified who they are.

We've chosen our views.

Now we have to actually look at the thing.

And the text brings up image quality control.

Basically, is the picture even good enough to read?

This is huge.

A bad picture can be worse than no picture at all because it can mislead you.

The text talks about exposure.

Right.

The Goldilocks Principle.

Exactly.

You're dealing with exposure, which is the amount of x -ray beams delivered to the patient.

If you have too few beams, the image is underexposed.

It looks too light, too white.

And the text says that for the abdomen, that's usually okay?

Surprisingly, yes.

An underexposed lighter image isn't usually deal breaker for most abdominal structures.

We aren't looking for the really fine details you need in, say, a lung field.

The bigger problem is the opposite.

Overexposure.

Overexposure.

Too many beams.

The image comes out way too dark or burned out.

And if it's too dark, you can't see the subtle gray differences between organs.

Everything just kind of blends into a black mess.

Precisely.

You lose all that crucial soft tissue detail.

But the text offers a fix for this, which sounds like something from an old detective movie.

I know.

The high density spotlight.

Hot light.

Yeah.

It's an old school trick from the days of physical film.

If the film is too dark, you can take it to a special viewing box with a very strong focused light to kind of blast through the dark areas.

You're using it specifically to look for the blackness of free air.

So even if the image is bad, you can sometimes salvage that one critical finding.

You can try.

But generally, the rule of thumb the text gives for overall quality is this.

Look for the spine.

If you can see the vertebrae of the spine clearly through the image, you should be able to see most other structures pretty well.

The spine is a good landmark for adequate penetration.

Okay, so we've got a good quality image.

Now we enter the matrix.

The text calls this next section the physics of seeing.

And it starts by asking, why is the abdomen so much harder to read than the chest?

It all comes down to one word.

Contrast.

In the chest, you have these huge air -filled lungs, which are black on an x -ray, right next to a dense blood -filled heart, which is white.

You have bone.

It's high contrast.

It's easy to see the borders.

But the abdomen.

The abdomen is a big cavity filled with a bunch of soft tissue organs that are all roughly the same density.

It's like trying to see a polar bear in a snowstorm versus a brown bear in a green forest.

That's a good analogy.

Or maybe even more accurately.

It's like trying to see a gray bear in a gray room.

The text breaks it down into three basic densities you need to know.

First,

you have radiodense objects.

These absorb the most x -rays, so they show up as white.

That's primarily bone and calcium like in kidney stones.

White is dense.

Got it.

Then you have radiolucent objects.

They let x -rays pass right through, so they show up as dark or black.

That's air and to a lesser extent, fat.

Dark is lucent.

And then there's everything else.

The solid organs, the liver, spleen, kidneys, muscles.

They're all intermediate density.

They're all just different shades of gray.

And the problem, as the text explains it, is that gray densities next to each other are invisible.

That's the crux of it.

If the liver is sitting right up against the spleen and there's nothing between them, you can't tell where one ends and the other begins because they are basically the same shade of gray on the film.

So how do we see anything?

We rely on varying densities.

We need something of a different density next to an organ to see its edge.

We need a border.

And usually that something different is fat or air.

Exactly.

Fat is slightly darker or more radiolucent than muscle or organ tissue.

So the reason we can often see the lower border of the liver is because there is a layer of abdominal fat right next to it.

That fat creates a subtle, darker line that gives us the outline of the liver.

So in this one specific context, fat is our friend in radiology.

In this context, absolutely.

It provides the outline.

It gives us the map.

The text also suggests a physical technique for the initial viewing.

It calls it the two to four feet rule.

Yes.

This is all about not getting lost in the weeds or the pixels right away.

You shouldn't have your nose pressed against the screen or the view box initially.

Step back.

Step back.

Literally.

Stand two to four feet away.

Look at the whole picture.

Getting a sculpt.

Ask yourself those initial questions.

What is my overall impression?

Why did I order this film in the first place?

What pathology do I expect to see based on the patient's symptoms?

It's like looking at a painting in a museum.

You step back to see the whole composition before you lean in to look at the individual brushstrokes.

Precisely.

From a distance, you can evaluate the overall gas pattern, look for any big obvious masses or large calcifications.

Once you have the general lay of the land, then you move in closer and begin your systematic examination.

And the text is very, very strict about this.

The phrase it uses is systematic examination is mandatory.

It has to be.

You concentrate on one part at a time.

You can't just let your eyes wander, hoping to stumble on something.

You need a system.

If you don't have a system, you will miss things.

Guaranteed.

Okay, so let's follow their system.

It says to start with the solid structures and the bones.

Right.

The bones are the easiest because they're the whitest, the most radiodense.

They form the frame of the picture.

So you scan the whole frame.

What's included in that scan?

You start at the top and look at the lower rig cage.

Then you trace the lumbar spine all the way down.

Then you look at the sacrum, the whole pelvis and the hip joints on both sides.

And what are we looking for specifically?

Obvious things like fractures, especially in a trauma patient.

But you also look at cortical density.

That's the outer layer of the bone.

Does it look strong and white or does it look thinned out like an osteoporosis?

You also check the disc spacing in the spine to see if any of the discs have collapsed.

So you're getting a lot of bonus information beyond just the abdomen itself.

A ton of it.

You can pick up all sorts of orthopedic or metabolic issues.

Okay, bones are done.

Moving on to the urinary tract.

Let's start with the bladder.

The bladder is located down deep in the pelvis.

The text gives a specific landmark.

The inferior or bottom aspect of it is about five to ten millimeters above the simpsons pubis.

That's the pubic bone you can feel at the front.

Exactly.

Can we always see it?

Not always.

If the bladder is empty, it just collapses and disappears into the other gray soft tissues of the pelvis.

But if it is full of urine, it distends and appears as a smooth, round, soft tissue density, a gray shape in the pelvis.

And sitting right on top of the bladder in a female patient is the uterus.

Yes.

But, and this is important, you typically don't see the uterus on a plain x -ray.

It just blends in with all the other gray structures.

But there's an exception.

The exception the text mentions is if there are uterine fibroids that have become calcified over time, calcification turns them white so they'll pop out.

You might see these kind of popcorn -like white densities in the pelvis and realize you're looking at calcified fibroids.

Okay, let's move up from the pelvis to the kidneys.

I feel like the kidneys are the celebrities of the KUB x -ray.

They are definitely the central characters.

And we can see them, again thanks to our friend,

fat.

There's a layer of fat called perirenal fat that surrounds each kidney.

And that creates the contrast we need to see their outline.

Exactly.

Without that fat, they'd be invisible against the psoas muscles behind them.

Where exactly are they parked in the body?

They are retroperitoneal, which means they're technically behind the main abdominal cavity.

They sit on either side of the lumbar spine, roughly between the T11 and L3 vertebrae.

And they aren't level with each other, right?

I remember that from Anatomy.

Correct.

The liver is a bit of a bully on the right side.

It's so big that it pushes everything down a little bit.

So the right kidney is usually a centimeter or two lower than the left kidney.

And what are we looking for in terms of their visual appearance?

You're looking for a smooth, bean -shaped shadow on each side.

The text points out that the superior pole, the top part of the kidney, should be closer to the midline, closer to the spine than the bottom part.

They kind of tilt inward at the top.

Got it.

Now for the big boss of the abdomen,

the liver.

The liver lives in the right upper quadrant.

It's a very large homogeneous grade density.

It should look smooth.

We primarily look for its lower border, which should be near the costal margin, the edge of the ribs.

And again, we can see that edge because of the adjacent fat.

Precisely.

That little line of fat helps us see if the liver's enlarged and pushing down past the ribs.

Okay.

And on the other side of the upper abdomen, we have the spleen.

In the left upper quadrant.

But here's the reality check from the text that's really important for students.

The spleen is roughly the size of an adult fist.

On a normal abdominal x -ray, it is usually not seen.

Really?

So it's another one of those invisible organs.

For the most part, yes.

Yeah.

It's tucked up under the diaphragm and its density is very similar to the structures around it.

So if I can see the spleen, that's a bad sign?

Usually, yes.

If you can clearly see the spleen shadow, it often means it is significantly enlarged.

A condition called splenomegaly.

The text explicitly says that if you're concerned about the spleen, ultrasound is a much, much better imaging modality.

Okay.

That's a key clinical pearl.

Before we leave the solid structures, there is one last muscle group the text highlights.

The psoas muscles.

Yes.

The psoas shadows.

These are actually really useful landmarks.

They're visible as these long diverging lines on both sides of the spine.

Where do they run?

They start up around the L1 vertebra and they angle down and outwards towards the pelvis.

If you can see those sharp straight diagonal lines clearly, it's a good sign of image quality and normal anatomy.

And if you can't see them?

If one of the psoas margins is blurred or totally obliterated, it might mean there's some pathology like fluid or blood or a mass in the retroperitoneum that's hiding it.

Fascinating.

Okay.

We have done the frame, which is the bones, and we've done the solid organs.

Now we have to dive into the plumbing, the gastrointestinal tract.

This seems to be where the most common diagnoses live.

Absolutely.

This is where you find your obstructions, your perforations.

And this is where understanding air and fluid dynamics becomes absolutely critical.

The text says to start at the top with the stomach.

Makes sense.

Identification first.

How do we know what we're looking at is the stomach?

It's typically located above the transverse colon in the upper abdomen.

In a supine or flat view, the text says you might see these band -like shadows.

Those are the rugae, the folds inside the stomach lining.

And the air in the stomach moves depending on the patient's position.

Physics again.

It's just a container with air and liquid.

When you're lying on your back, supine, air is lighter.

So it rises to the most anterior or front part of the stomach.

Fluid, which is heavier, pools in the back, the posterior part.

But if you stand the patient up for an erect view...

Now, gravity really shows its stuff.

The air and fluid separate perfectly.

You look for a gas fluid level, which appears as a perfectly straight horizontal line beneath the left hemidiaphragm.

You'll see black air sitting right on top of gray fluid, seeing that level as normal in the stomach.

Okay.

Moving down the GI tract to the colon, or the large bell, the text gives it a very specific, almost onomatopoic description.

Bubbly.

Bubbly is the key word.

That appearance comes from the fact that the colon normally contains a mixture of gas and feces.

The text also describes the look of fecal matter as modeled, which is just a mixture of gray densities.

It's a gas -liquid -solid soup in there.

And just like with the solid organs, location matters.

Where does the colon live?

The colon forms the picture frame of the abdomen.

It lives on the periphery.

It starts in the lower quadrant, goes up the right side, across the top.

That's the transverse colon, and then down the left side to the rectum.

It frames the small bowel.

Now let's talk pathology.

What if something is blocked?

We are looking for an obstruction.

A mechanical obstruction of the large bowel causes the bowel proximal to the blockage to dilate with trapped air and fluid.

The magic number the text gives to remember here is six centimeters.

If the colon is dilated more than six centimeters in diameter, that is a red flag for obstruction.

And what's the telltale sign that tells us it is a mechanical obstruction and not something else?

It's all about what's happening below the blockage.

The dilated, air -filled colon will be visible above the point of obstruction.

But the key sign is that there should be no air, or very little air, visible in the bowel distal to that point.

If the road is closed, no cars get through.

Okay, that's clear.

Now let's compare that to another condition that sounds similar.

Paralytic Elias.

This is a classic differential.

It can look similar initially because the bowel is dilated, but clinically an Elias is a functional problem, not a mechanical one.

The bowel just stops moving.

Maybe after surgery or due to an electrolyte imbalance, it's paralyzed.

So how does that look different on the x -ray?

In an Elias, because the whole system is just slowed down, gas is present throughout both the small and the large intestines.

The text says there is no clear delineation.

It's just air everywhere, in both the central small bowel and the peripheral large bowel.

So to simplify, obstruction equals a clear cutoff point with no air below.

Elias equals air everywhere.

That is a crucial distinction to make.

It's one of the main reasons these films get ordered.

What about the small bowel, then?

The small bowel lives in the central part of the abdomen, nestled inside that frame made by the colon.

Normally you see very little of it on an x -ray, maybe a few small pockets of air.

The rule for diameter here is that it should not exceed three centimeters.

The 369 rule is starting to form here.

You're getting it.

Small bowel under three, large bowel under six.

So if the small bowel is obstructed, what do we see?

You'll see multiple dilated loops of small bowel stacked up in the central abdomen.

They often look like a stepladder.

And again, the key sign to differentiate it from an Elias is that there will be no air in the large bowel.

The obstruction has stopped anything from getting through to the colon.

Okay, that makes sense.

Let's move to section five of our roadmap, anomalies, artifacts, and air.

We have touched on some of this, but let's go a bit deeper.

Calcifications first.

The mechanism is simple.

Calcium is dense, so it absorbs x -rays and shows up as white.

The text lists several places where seeing calcifications is abnormal and points to specific pathologies.

In the pancreas, it could be chronic pancreatitis.

In the kidney, that's nephrocalcinosis or kidney stones.

In the gallbladder, you're looking at gallstones.

And in the aorta.

Wait, you can see calcification in the aorta?

Oh, yes.

In older patients with significant atherosclerosis, the walls of the abdominal aorta can calcify.

You can actually see the tram tracks of the aortic walls running down the front of the spine.

It's a sign of vascular disease.

And the text also mentions a very specific, and I think very cool one, the appendicolith.

Sounds like a dinosaur, doesn't it?

It does.

An appendicolith is a small calcified stone that forms in the appendix.

If you have a patient with classic right lower quadrant pain and you see a tiny little white stone sitting in that exact area on the x -ray, your suspicion for appendicitis goes way, way up.

It's a very specific sign.

We also mentioned the calcified uterine fibroids showing up here, too.

Yes, if they're calcified, they appear as these sort of amorphous popcorn -like white masses down in the pelvis.

Okay, we've covered the white anomalies.

Now let's talk about the dark anomalies, gas patterns and extra -luminal air.

So we've established what normal gas looks like.

You expect some in the stomach, maybe a little bit in the small bowel, usually in the left mid or lower central abdomen, and of course bubbly gas and stool in the colon.

But the dangerous term, the one that should set off alarm bells,

is pneumoperitonium.

That is the critical term for free air or extra -luminal air that is outside the GI tract, floating free in the abdominal cavity.

And that is always abnormal.

Always.

It almost always indicates a perforated viscous hole in the stomach or the intestine.

And visually, it appears as that classic crescent of radiolucent gas between the diaphragm and the liver on an upright film.

It's a surgical emergency.

Finally, in this section, we have artifacts.

The strategy the book gives is pretty simple.

Don't mistake jewelry for pathology.

It sounds funny, but it's important.

You have to be aware of the obvious things, navel rings, genital piercings, surgical clips from a prior surgery.

You don't want to be chasing a piercing, thinking it's a foreign body the patient swallowed.

That brings us to section six, advanced imaging strategy.

And this is about when to escalate the exam, when to order those other views like the upright and lateral films.

Right.

So you've got your additional supine film and you're suspicious of something.

The text gives clear guidance on what to do next.

Let's say you suspect an obstruction versus an ileus.

The initial film is confusing.

What's the next step?

You order an upright abdominal x -ray.

Why?

Because standing the patient up will show you the air fluid levels.

In a mechanical obstruction, you'll see multiple distinct air fluid levels in the dilated bowel.

In an ileus, you might see some long, lazy levels, but it's not the same classic stepladder pattern.

Okay.

What if you suspect free air, but the supine film is normal?

You order a standing chest x -ray or an upright abdominal film.

A chest x -ray for free air in the abdomen.

Yes, because free air rises to the highest point in the abdomen, which is right under the diaphragm.

A standing chest x -ray gives you the sharpest, clearest view of the space just under the diaphragm, making it the most sensitive plane film for detecting even small amounts of pneumoperitoneum.

What if your patient is too sick to stand up?

They can't do an upright film.

That's where our friend the left lateral decubitus view comes in.

You lay them on their left side.

Remember the wait time.

10 to 15 minutes.

Gravity needs time to work.

Exactly.

Then you take the film,

and you're looking for that dark shadow of air that has risen to float between the white abdominal wall on the right and the gray density of the liver.

It's all about using physics to your advantage.

And what about that chest connection we mentioned at the very beginning?

Why check the chest for tummy pain?

The text reminds us that things like pleurisy, a lower lobe pneumonia, or pleural effusion, can irritate the diaphragm and present as upper abdominal pain.

Right.

You don't want to miss a chest problem because you were only looking at the abdomen.

The book then gives a brief but important overview of other alternative modalities.

Yes.

It puts the plane x -ray in context.

It's not the only tool in the shed.

Let's quickly run through them.

Barium studies.

This is where the patient drinks barium, or has it given as an enema.

An upper GI series looks for hiatal hernias or reflux.

A small bowel series follows the barium down to look for tumors or malabsorption.

A lower GI, or barium enema, is for polyps or diverticular disease.

Then we have endoscopy and scopes.

Colonoscopy looks at the whole colon, while the sigmoidoscopy just looks at the last two feet.

These are great because you can take biopsies or remove polyps.

And an upper endoscopy goes down the esophagus into the stomach, good for finding stuck objects or sources of bleeding.

What about CT scans?

Computed tomography.

It gives you detailed cross -sectional slices.

The text says it's much better for things like appendicitis, diverticulitis, or finding causes of pain that are outside the colon itself.

And finally, ultrasonography.

Ultrasound uses sound waves, so no radiation.

It's the best test for gallstones, kidney stones, checking for an aortic aneurysm, measuring spleen size, and evaluating pelvic masses.

Okay.

This brings us to the final, and maybe most important, section.

Section 7, evidence -based practice and differential diagnosis.

There's an evidence box in the chapter.

There is, and it's a sobering one.

It reviews a study on patients who came into the emergency department with undifferentiated abdominal pain.

What were the stats?

A staggering 75 % of the abdominal x -rays they did were completely normal and non -contributory.

And of the 25 % that were abnormal, half of those findings were totally unrelated to the patient's final diagnosis.

So what's the big takeaway from that?

The takeaway is that the radiation from an abdominal x -ray is significant.

The text says it's about 35 times that of a chest x -ray.

Given it's low yield for general pain, you should not use it routinely as a screening tool.

You should only order it when you have a specific high -yield question you need answered.

And the main high -yield question is...

Is there a bowel obstruction?

That is the number one indication where a plain film still really shines.

The chapter ends with a fantastic table.

A normal versus abnormal framework that really summarizes everything.

Let's walk through the key findings to wrap it all up.

It's a great summary.

Let's start with the liver.

Abnormal would be...

Enlarged.

If you see hepatomegaly, you're thinking things like congestive heart failure, hepatitis, or maybe alcohol abuse.

The spleen.

Abnormal is if you can see it at all.

If it's visible, you worry about trauma, infection like mono, or even cancer like lymphoma.

What about the kidneys?

If they're enlarged or you see calcifications, you're thinking about hydronephrosis, which is swelling from a blockage, or renal calculi, which are kidney stones.

And the bowel.

The magic numbers again.

Greater than three centimeters for the small bowel, or greater than six centimeters for the large bowel.

That points towards obstruction.

Finally, the diaphragm.

An elevated hemidiaphram.

Could be a sign of a rupture of a hollow viscous.

The air pushes it up.

A flattened diaphragm.

That's usually a chest finding spilling over.

It suggests air trapping from something like emphysema or a bad asthma attack pushing the diaphragm down.

And the most critical finding under the diaphragm.

Free air visible under it.

That crescent of illicency.

That's your perforated ulcer or other viscous until proven otherwise.

It's an incredible amount of information to pull from what looks like a simple gray picture.

Let's do a final synthesis here.

We've really recapped our mission.

We really have.

We moved from the most basic step checking the patient's ID on the film, all the way to spotting that subtle critical crescent of free air.

The whole journey is about applying a system.

It really emphasizes the clinical mindset.

It's not just about memorizing what things look like.

It's about making these logical connections between anatomy, the physics of density, and the patterns of pathology.

That's what clinical reasoning is all about.

It's a puzzle.

And the x -ray is one of the key pieces.

But only if you know how to read it.

Well, this has been an amazing deep dive.

A huge thank you to you, our listener, for studying along with us and decoding this with us.

We hope it makes that next gray film a little less intimidating.

It's always a pleasure.

Keep asking why.

From the Last Minute Lecture Team, thanks for joining us.

And we'll see you on the next deep dive.