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so in this lecture we will be discussing
extra luminal air this is also known as
free air which you may have heard being
discussed so where are the different
locations of extra luminal air it can be
intraperitoneal it can be
retroperitoneal it can be air within the
bowel wall or it can be air within the
biliary system so free intraperitoneal
air is also called pneumoperitoneum free
retroperitoneal air is also called
pneumo retroperitoneum retroperitoneal
free air is rarely the result of blunt
or penetrating trauma post-surgical free
air is normal and can be seen for a
maximum of about seven days post-surgery
so if the patient is not a post surgical
patient and they don't have
retroperitoneal air due to trauma then
this is actually a surgical emergency
any route pneumoperitoneum or
retroperitoneum is a surgical emergency
because it represents perforation of a
loop of bowel free air is best evaluated
on CT but it can be seen on radiographs
and it really it should not be missed so
it's important to know what free air
looks like on a radiograph what are some
radiographic signs of nua peritoneum
you can see air under the diaphragm and
that's really only seen in the upright
position you can see both sides of the
bowel wall this is called rig'lar sign
and this can be seen in any position and
you can see visualization of the
falciform ligament which is also called
the football sign and this is seen most
often in the supine position just a
reminder that when two structures of the
same density are next to each other they
cannot be differentiated on a radiograph
do you remember the name of the sign
this is called a silhouette sign so free
air under the diaphragm you can see on
this upright chest x-ray that there is
free air under the right hemidiaphragm
and you can see this because of the
adjacent soft tissue density which is
liver
down here so adjacent to the soft tissue
density of the liver when you have any
bit of air you can see the air you can
also differentiate it from the adjacent
lung because you can see the line right
here which represents diaphragm
this has really seen only on an upright
view because gravity will raise the air
superiorly and place it under the
diaphragm you can also do a left lateral
decubitus film and this is done in
patients who cannot stand up or sit
upright and it raises the air to the
right side adjacent to the liver so
again you see here this is a patient
that's lying on their left side down
this is the left side here are the ribs
so this is the patient's chest and then
here is free air right adjacent to the
soft tissue density of the liver the
Rigler sign at is visualization of both
sides of the bowel wall this is an
important sign that's seen in free air
and the bowel wall is normally not seen
because it's adjacent to surrounding
soft tissue density of the same density
so the bowel wall adjacent to say the
liver will appear to be of the same
density and you normally wouldn't see
the bell wall however if you have air on
both sides of it you now can see the
bell wall so this is an example of the
Rigler sign you can see this is from
free intraperitoneal air due to a
perforated gastric ulcer and you can see
here this represents the bowel wall and
you can see air within the bowel and
then you can see air outside of the
bowel so this is an important sign
representing free air let's just review
what the falciform ligament is it's
actually a portion of the peritoneum
extending from the anterior surface of
the liver to the anterior abdominal wall
so right here it contains the
obliterated umbilical vein which is
called the ligamentum Terry's so let's
take a look at this case which relates
to the falciform ligament what do you
see on here
so this right here is the falciform
ligament you can see it extending all
the way down from top to bottom and then
you can see multiple loops of bowel with
valve wall visible or the regular sign
this is a CT image of the same patient
you can see the falciform ligament
attaching to the anterior abdominal wall
and then you can see Freire on both
sides of the falciform ligament so this
is an example of the football sign you
can also see scattered foci of free air
surrounding the liver here as well as
over here
in the left side of the abdomen so this
is an example again of the football sign
and another important sign to remember
with free air this is seen best on a
supine radiograph let's take a look at
this image is this the Rigler sign that
you're looking at
so this is actually a pitfall an
important pitfall not to not to make a
mistake for you don't want to miss take
multiple dilated loops of a bell that
are adjacent to each other and consider
that free air so this is a patient that
has multiple dilated loops of bowel
probably a small bowel obstruction and
you can see bowel wall adjacent to this
air within the bowel so you would think
that this could represent the Rigler
sign if there's any kind of confusion
the next step would be to perform a CT
to see if there really is free air or
whether this represents a small bowel
obstruction so what are some
radiographic science of pneumo
retroperitoneum again this is free air
within the retroperitoneal space so air
will actually outline the
retroperitoneal structures such as the
psoas muscles or the kidneys and it may
Traverse the diaphragmatic hiatus and go
up into the chest causing
pneumomediastinum this is an example of
retroperitoneal iere outlining the IVC
and it also outlines a portion of the
aorta so this right here is the location
of the IVC you can see free air
surrounding that and you can see free
air here retroperitoneal II surrounding
the aorta as well and up in the left
upper abdomen
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