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Left atrial enlargement on chest x-ray – radiology video tutorial

Left atrial enlargement on chest x-ray – radiology video tutorial


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.

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