Hey everybody this is Rishi Agarwal and in this video I'm gonna go over how I look at
a chest CT. This video is intended for radiology residents who are starting
out on their chest rotation but if you're a trainee in pulmonology or
in thoracic surgery you'll probably find some of this information useful as well.
Alright now the first thing that I look at before I even look at the CT is the scout image.
And the reason is a lot of times the scout image covers more than you'll see on the axial images,
so you might pick up something in the abdomen or in the neck on the acout that you won't see on the
axial chest CT images, so it's very important to look at the scout image on every patient.
The next thing I do is go to the soft tissues. So I'll pull up the soft tissues
and I'll start with the supraclavicular region and I'll usually make sure that
I'm on the right window and levels so I'm using the abdomen windows here because
I want to accentuate the difference between the fat and the soft tissues.
The first thing I look at is the thyroid gland. The thyroid gland is right here
and I'm making sure that it's not enlarged and that it doesn't have any nodules in it,
but you don't have to follow up every nodule. I use the ACR guidelines on
whether to follow up a nodule which is based on size and the age of the patient.
The next thing I do is look for lymph nodes. The the supraclavicular region can be tricky
because there are a lot of vessels that are coursing in and out of the area and you have
the scalene muscles which can be confused for lymph nodes so it's important to scroll up and
down and take your time in this area when you're starting out to make sure that if you're calling
a lymph node that it's a lymph node and not a muscle or a vessel. You can use your coronal
images to help you. So if you localized things with your coronal images then the vessels will
show up as vertically oriented structures and lymph nodes will show up more as nodules.
After looking at the supraclavicular region, I then look at the subpectoral and axillary regions,
also looking for enlarged lymph nodes. For example, there is a small lymph node right
there. I usually wouldn't measure a lymph node of this size but just for demonstration purposes,
what you want to do is take the long axis, so go from one end to the other end, and then take
a measurement that's orthogonal to the long axis. So it's actually too small right now;
it's really hard to do it on this small lymph node but like that that would be orthogonal
to the long axis. So this lymph node is 5.6 mm in size. That's probably actually an over
measurement but that's how you measure lymph nodes when you're starting out.
As you get more used to measuring lymph nodes then it's okay to just measure the
short axis straight away. For the axillary lymph nodes I use a measurement of 10 mm.
So 10 mm or greater means that that lymph node is enlarged and that's a general rule
for most of body imaging, chest, and abdomen you use a short axis of 10 mm as your cutoff.
Okay the next thing I look at is the internal mammary artery and vein region. This is the
internal mammary artery and that's the vein. I'm looking also for lymph nodes in this area.
This area is a little bit different from lymph nodes in other areas because I don't use my 10
mm cut-off for this area. Any lymph node really is abnormal but in general I use a cut-off of 4
mm for the internal mammary area to determine whether that lymph node is enlarged or not.
And then I scroll down, keep going down and I look at the lymph nodes
in the anterior diaphragmatic region here looking for enlarged lymph nodes. Here,
I do again use a 10 mm cutoff. And then I go all the way down to the last image and I look
at the area around the aorta and the esophagus so the paraesophageal and paraaortic area,
looking for lymph nodes. This is the azygos vein right here. And I scroll up until I reach the
subcarinal region which is right here. This is what a normal subcarinal lymph node looks like.
I then look at each hilum, so I follow each bronchus out and make sure that there are no
enlarged lymph nodes in either the right hilum or in the left hilum. Now I'll tell you that the
right hilum usually has a lymph node right here and that lymph node can be a little bit big. It
can be up to 9 or 10 mm and that's okay. This lymph node is 9 mm and that's okay usually that
lymph node is about that size and if you don't see any other abnormalities in the mediastinum,
like no other enlarged lymph nodes and you don't see anything in the lung that can be causing lymph
node enlargement in that right hilum, then I would just ignore that finding because I've
learned from experience that that lymph node can be normally 9 to 10 mm in size. Okay the
left hilar lymph nodes are not that size, those are reliably pretty small so if you see a 9 or 10
mm lymph node in the left hilum that's something that you should point out and that's abnormal.
Then I continue up looking at the pararacheal region and the esophagus looking for enlarged
lymph nodes there up until I get to the thoracic inlet. Then I go back down looking
at the anterior mediastinum. Here I have some normal thymic tissue and I know it's
normal tissue because it is soft tissue interspersed with little bits of fat in
it so that means that this is normal, benign thymus and not a thymic mass or a lymph node.
Then I look at the heart and great vessels. So I usually measure them,
and I have the measuring tool open. So I usually measure the pulmonary artery right
here and it has to be orthogonal to the long axis, and that's 28. And I usually measure
the aorta about right there and that's 33. So you should follow your own institutional
guidelines regarding the threshold limits for the pulmonary artery and the aorta but I use about
30 mm for the pulmonary artery and 40 mm for the aorta. But you should poll your attendings
and see what numbers they use to determine whether or not these vessels are enlarged.
Since this is a chest CT with contrast,
I want to look inside of the pulmonary arteries following each lobar and segmental
artery out as best as I can to make sure that there are no filling defects in the
pulmonary arteries. Occasionally you will find incidental pulmonary emboli on these patients.
After I'm done with the great vessels, I look at the heart. First I start with the coronary
arteries to make sure that there's no coronary calcium. This is a patient who has contrast,
so it's a little bit harder to tell whether there's coronary calcium,
but you should definitely mention it if you see it.
And then I look at the heart itself, looking at each chamber making sure that it's not enlarged
and that there's no filling defects. The left atrial appendage is a common place
to get thrombus formation, but not all filling defects that you see on CT equate to thrombus.
You can get unopacified blood from eddy currents as well as trabeculation of the muscle causing
filling defects. The same is true of the right atrium. You can have unpacified blood coming in
from the IVC mixing in with the opacified blood from the SVC, and that can cause mixing artifact
in the right atrium. So it's important not to confuse mixing artifact with a filling defect.
While I'm looking at the left atrium, I'm also looking at the four pulmonary veins and making
sure that they're not stenosed or occluded which can occur after a pulmonary vein isolation and
other procedures. And then I'm done looking at the heart. After I'm done with the heart I look
at the pericardium to make sure that there's no effusion pericardial thickening or calcification.
Next I look at the pleural surfaces on soft tissue windows. Here I'm looking
mainly for pleural effusions, pleural nodules, thickening,
or pleural calcification. We'll have another chance to look at the pleura when we go to the
lung windows. I like to look at it first on soft-tissue windows before I move on.
After I'm done with the pleura, then I look at the abdomen. So the first thing I do in the abdomen
is look at the liver. It's really important when you're looking at the liver to narrow the windows,
because lesions in the liver can look like normal liver parenchyma, so if you narrow the windows you
will enhance that contrast between the abnormal lesions and the normal liver parenchyma. The
liver commonly has incidental small lesions like this which can be cysts or hemangiomas
or other benign lesions, and if the patient doesn't have any known malignancy or cirrhosis,
I tend to ignore those or I put them in the report and call them too small to characterize.
After looking at the liver I then look at the adrenal glands. The right adrenal gland,
right kidney, left kidney, left adrenal gland. Then I look at the spleen. Then I look at the
distal esophagus, then stomach. I'll follow that around to the duodenum then the pancreas
and then the gallbladder.
After looking at all of those organs, I then look for lymph nodes. So first, in this gastrohepatic
ligament region, then here in the splenic hilum, retroperitoneum, then in the liver hilum.
I then look at the bowel including the colon (the visualized portion) and the small bowel. OK,
so I think the abdomen is fine, so the next thing I do is look at the bones.
So I'm gonna change the window put it on bone windows, go all the way to the bottom and start
looking at the vertebral bodies. So here on the axials, I am looking for sclerotic lesions,
lytic lesions, and it makes a big difference if you know that the patient has cancer because a
sclerotic lesion in a patient without cancer, if it's small, it's probably a bone Island.
Now if the patient has prostate cancer, then you might not just blow off small sclerotic
lesions as bone islands, you would probably call them suspicious for metastatic disease.
So after I've looked at the vertebral bodies, I look at the ribs. The ribs
can be tricky because they go in and out of the plane, so I usually take it one quadrant
at a time. So I'll look at the anterior right ribs first going from top to bottom,
looking for fractures or lytic lesions or sclerotic lesions. Then the right posterior ribs,
and I usually take that from the bottom up. And then I'll look at the left side,
the left anterior ribs, and then the left posterior ribs from the bottom up.
After looking at the ribs, I then look at each clavicle. So there's the left,
there's the right. Then I look at the sternum,
then the scapula. There's the right scapula, right humerus, left humerus, left scapula.
Then before moving on to the soft tissues, I look at the sagittal images. I want to make sure that
there are no compression deformities that I missed on the axials, so I look very closely at the
sagittal images, especially in the midline to make sure that there's no compression deformities or
any other abnormalities that I may have missed on the axial images. Okay so that covers the bones.
Then I move on to the soft tissues. So the first thing I do is look at the spinal canal. This is
a low-yield place. Rarely will you see anything in the central canal in these patients, but sometimes
you can see metastases or lymphoma here, and if you do see that then there are big consequences
to the patient. So even though it's low yield, it's an important place to look for abnormality.
Then I look at the anterior soft tissues including the muscles and the subcutaneous
fat. This is a male but he has a little bit of gynecomastia bilaterally. Then I look at
the posterior soft tissues including the subcutaneous fat and the muscles.
Okay so we've covered the bones and the soft tissues. Now it's time to look at the lungs.
So let's pull up the lung windows. I usually start with the airways. The first thing I do
is make sure that the trachea and the central airways are all clear. So I follow each airway
out to its lobar and segmental bronchi, and make sure that I don't see anything
in the airways. I have a video showing you the segmental anatomy on CT. So, if you don't know
the segmental anatomy it's really important to learn that because you want to make sure
that you can localize things in the lungs based on the segment that it's in not just the lobe.
Once I've cleared the airways then I look at the lungs. I do two different passes of the
lungs. The first is, I look at both lungs looking for big things like consolidations
or masses or large areas of ground glass opacity. This is sort of a macro search
for disease and I can tell already that this patient's lungs are basically normal.
The second pass that I do is more of a fine pass looking for lung nodules. This can be a tedious
process but with some practice you can get pretty fast at looking for lung nodules. The way I like
to do it is scroll down a couple then up one, scroll down a couple then up one. And I want
to keep the mouse moving so that I'm not staying on one image for too long because when you stay
on one image, any vessel can mimic a pulmonary nodule, but if you keep the image moving like
this going down two up one, down two up one, then you can look for nodules a lot easier because
they'll tend to pop out at you. The vessels look like vessels, and the nodules look like nodules.
I do this for each lung and I usually split it up into quadrants so I'll do
the right anterior lung and then the right posterior lung. Then the left posterior lung,
then the left anterior lung. Now if you have MIP images,
MIP images can be very helpful for looking for lung nodules. Without going too much into detail,
it makes the vessels look like branching long tubular opacities and it makes nodules
look like nodules. So if you have MIP images, then you can use those to look for nodules.
Or your institution might subscribe to other software packages that can help look for
nodules like lung CAD or vessel subtraction software. Alright after looking for nodules,
then my job is done. During this whole process, I've been dictating the abnormalities that I see.
And it would be at this time that I read my findings and summarize them in my impression.
Okay thanks a lot I hope this has been helpful for you and if you
have any questions please feel free to leave a comment below.