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in this radiology tutorial we going to learn how to recognize left atrial
enlargement in chest radiographs. while assessment of cardia chamber size and
function is most practically assessed with echocardiography,
the sheer number of chest x-rays performed means that it remains important
to be able to confidently identify left atrial enlargement on radiography.
as you can see, this patient has received a mitral valve replacement
but the effects of their prior mitral disease on the left atrium remain
evident. we're going to compare with this normal chest x-ray. You will hopefully
recall that the right heart border is formed by the right atrium,
inferior border by the right ventricle,
and the left border primarily by the left ventricle.
The left atrium is located posteriorly
and only the atrial appendage component is visible on a normal frontal
projection.
however when the atrium becomes enlarged it's right aspect may become directly
visible as an extra shadow paralleling the right heart border.
this is known as the double density sign or the double right heart border sign
of left atrial enlargement.
if we look at this normal CT for correlation
you can see the posterior location of the left atrium,
here is the left ventricle,
the right ventricle,
and the right atrium where there is mixing of contrast arriving from the SVC with
non-opacified blood from the IVC.
the edge interface between the right atrium and the air within the right middle lobe is
responsible for the normal heart border seen on frontal radiographs.
as you can see left atrium does not project out into the lung
and therefore will not be visible on frontal radiography.
if we switch to this patient
who has mild left atrial enlargement due to the presence of an atrial myxoma,
we can see how the atrium begins to project laterally into the lung as it
enlarges. This creates a discreet edge interface visible one frontal radiographs
and explains the origin of the double density sign.
if the double density sign is present, then the obligue left atrial measurement
can be taken between the outer edge of the atrium to the midpoint of the left
main bronchus.
a distance of greater than seven centimeters
confirms left atrial enlargement.
the main bronchi themselves can also be used to assess left atrial enlargement.
as the left atrium dilates it causes splaying or widening of the carina.
an angle of greater than ninety degrees is considered a sign of left atrial
enlargement.
as you can see in our normal patient, the carinal angle is nowhere near ninety
degrees.
the final sign of left atrial enlargement we will be discussing on the frontal
radiograph
is bulging of the left atrial appendage.
normally the left atrial appendage contributes to a flat
or slightly concave upper aspect of the left heart border.
when enlarged however,
the left atrial appendage creates a discreet convex bump.
for completeness here is what's left atrial enlargement looks like on a lateral
radiograph.
the left atrium forms the posterior heart border.
here is our normal case
and here's a case of gross left atrial enlargement
which bulges posteriorly.
for further illustration
here again is our patient with left atrial enlargement due to a myxoma.
so hopefully now you'll be able to confidently identify left atrial enlargement on
chest radiographs by looking for the double density sign, an oblique
measurement greater than seven centimeters, a carinal angle greater than ninety degrees,
and convexity of the left atrial appendage.
you can read more and see additional cases on Radiopaedia.org.
and don't forget to check out the other video tutorials in our chest x-ray series.