So before we delve in to the many abnormalities that can be found
within the abdominal x-ray, let's review first some of the normal findings
on an abdominal film on a normal approach.
So most abdominal imaging and diagnosis involves the use of ultrasound, CT, or MRI.
However, radiographs are often used as a quick first step
to help you decide what further imaging is needed next if any.
So what can be evaluated on abdominal plain films?
The bowel gas pattern is a very important thing.
You can always evaluate for free air
which is something that you really don't wanna miss.
Abnormal calcifications can be seen on abdominal radiographs
or abnormal masses. So these are the 4 major points
that you wanna keep in mind
when you're taking a look at an abdominal radiograph.
So let's come up with a general approach.
As with all of radiology, it's important to have a standard approach
so that you make sure that you look at every aspect of the film.
So what I do is I start off with the lung bases,
even though we're performing an abdominal film
often times a patient may have an abnormality at the lung base
that you don't wanna miss
I then look for free air because this is a finding that you really don't wanna miss
on an abdominal plain film. Next, I look at the bowel gas pattern
and then I evaluate the solid organs.
I then look for any abnormal soft tissue masses, any abnormal calcifications,
and lastly I take a look at all of the bony structures.
So before we look at the abdominal normal anatomy on a radiograph,
let's just review what normal abdominal anatomy looks like on a diagram.
So a large part of the upper abdomen is encompassed by the liver.
It's essentially seen on the right upper abdomen
but it also extends over to the left upper abdomen.
Adjacent to it is the spleen and often times on a radiograph
you can see the outline of both the spleen and the liver.
The gallbladder is usually not well seen on an abdominal plain film,
however, if it has calcifications in it such as gallstones that may be visualized.
And then the majority of the rest of the abdomen is encompassed by large bowel
which is seen peripherally and then small bowel which is usually seen centrally.
So let's review some radiographic anatomy.
So again, I start off by taking a look at the lung bases
and you can see them on every abdominal radiograph.
So you can see the diaphragm here on the right
and then you can see the left hemidiaphragm here
and just above it are the lung bases and a small portion of the heart.
In the left upper abdomen you can see the stomach bubble.
It usually has a little bit of air and then it has an air fluid level
which is, again, normal. You can see the outline of the liver,
primarily encompassing the right upper abdomen
and then you can see air within the large and small bowel.
In terms of bony structures, you can take a look at the iliac crest
which really should be included on every abdominal radiograph
and you can see the thoracic and lumbar spines.
So how can you differentiate between small and large on a radiograph?
When there's a bowel abnormality it's important to try and see
which bowel it's involving. So the small bowel is located centrally
and it has valvular markings called valvulae conniventes.
They cross the entire width of the small bowel
and they're spaced very close together.
They have the classic stacked coin appearance
so if you take a look at these stacks of coins the small bowel
actually looks very similar to that
and that's a very classic appearance of small bowel.
Large bowel on the other hand is usually located peripherally
and it contains haustra.
So the haustra either do not connect from one wall to the other
or they're spaced a lot wider apart than the valvulae conniventes are.
So if you take a look at this image here,
the haustra do actually go all the way from one end of the wall to the other.
However, they're not the typical stacked coin appearance
that you would expect from a small bowel, they are much wider apart.
This is another example of the large bowel
again seen predominantly in the periphery of the abdomen
and you can see air within small pieces of small bowel seen more centrally.
So how do you assess bowel gas pattern?
A normal bowel gas pattern in the small bowel
usually has about 2 or 3 air fluid levels.
It's normal to see air within the small bowel
and usually the bowel is not more than about 3 cm in diameter.
Large bowel on the other hand usually doesn't have air fluid levels
because a lot of the fluid is absorbed within the large bowel.
It does contain air and that's normal
and it can have a very variable diameter
so it's hard to rely on large bowel diameter to tell whether or not it's abnormal.
So let's take a look at this, this is the coned down view of the right upper abdomen.
You can see a somewhat modeled appearance here.
So what do you think that represents?
It doesn't follow the typical features of small or large bowel.
So this is an example of normal stool within the colon.
It appears as very small bubbles of gas that are partially solid
and they appear within the expected location of the colon.
So abdominal films can be performed in 3 different projections
and each one has different uses.
So typically, it's performed as an upright film.
Air is gravity dependent so it's very useful to evaluate for free air
so the air will rise up to the top and can often be seen
just underneath the diaphragm.
It's also used to evaluate for air fluid levels
which can indicate stasis and ileus or bowel obstruction.
So when the patient is standing upright,
again, the air will rise to the top of the bowel
and you can see the air fluid level
because the fluid will be at the bottom of the bowel.
Usually, these are obtained with the patient sitting
or ideally in the standing position.
A left lateral decubitus is usually used in patients that aren't able to stand upright.
So this is performed really as just a substitute for an upright film.
It also allows for evaluation of air fluid levels
and it allows for evaluation of free air so the patient lies on their left side down,
the right side is up and again air will rise to the top part of the body
and so you can see it adjacent to the liver on the right here.
Ideally, again it's performed on the left side down
because the liver forms a solid organ on the right
which allows you to see the difference between the air
and the density of the liver. If you perform it the other way,
you have a lot of bowel on the left side
and you may not see the difference between air
within the bowel and air outside of the bowel.
So supine film is also very commonly performed
and it's usually performed in addition to an upright or a decubitus.
This provides a general overview of the abdomen
and it's the one that's used to look for calcifications
or abnormal soft tissue masses.
This is obtained with the patient lying on their back
and it's really best when it's used again in conjunction with another examination,
either the upright or the decubitus.
So incidentally, this patient has a finding in their pelvis.
So what do you think this is?
This is actually an intrauterine device or an IUD.
It's used as a contraceptive device and this is very commonly seen in women.
This is a T-shape metallic structure which is why it appears so dense.
It's actually a little bit more dense than the surrounding bony structures.
So the take away points from this lecture I think
are that you really need to look for air fluid levels and free air within the abdomen.
Those are the 2 most important findings
and these are really best seen on an upright or a decubitus view.
Free air is mostly easily seen on these views as well
and it's a finding that you really don't wanna miss.
So hopefully, now that you have the background knowledge
of the abdominal anatomy, we can move on to discussing some pathology
and the appearance of pathology on an abdominal plain film.