Interactive Transcript
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I'm Dr. P, back discussing pediatric renal
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3 00:00:04,210 --> 00:00:06,529 masses and their differential diagnosis.
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I have on the left a gradient echo TR about 100
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to 150, so longer than usual, very short TE.
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So a type of, uh, spoiled gradient echo in phase.
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And on the right, I've got a T2
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spin echo without fat suppression.
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So the fact that this portion of the kidney and
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capsule are very dark on the T2, but not very bright
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on the T1, suggests and supports the diagnosis
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of a capsular bleed or hemorrhage, which is going
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to push you towards and away from some lesions.
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On the bottom, we've got a more solid
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appearing renal mass, multi lobulated,
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but nothing in the opposite kidney.
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Let's scroll it to be sure, because that's
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one of our most important search patterns.
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And we can see an adrenal gland on the left, The
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adrenal gland on the right, not so prominent,
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because neuroblastoma we'd want to exclude, but our
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lesion is in the inferior pole of the kidney, so
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neuroblastoma not a strong consideration, especially
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with sparing in the region of the right adrenal
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gland, which we'll see better in the axial projection.
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Lack of crossing of the midline.
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Lack of skeletal metastases.
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And then we know that neuroblastoma
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calcifies more often than Wilms tumor.
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But that's a very important
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differential diagnostic consideration.
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Let's scroll in and out of the lesion.
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And we really get into a more
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solid component of the lesion.
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And we're seeing foci of hemorrhage within the lesion.
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There were some scant calcifications
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seen on CT which occur about the midline.
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15 percent of the time, but I want to emphasize
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that age is the most important consideration
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when formulating a differential diagnosis, and
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Wilms tumor is the most likely diagnosis in the
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pediatric population, especially under age 5 or 10.
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Now, renal vein invasion is also important.
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A strong, uh, differential diagnostic separator.
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Here is your inferior vena
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cava with flow void on the T2.
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And I like the T2 for this purpose.
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I don't need contrast, uh, to clear the renal vein.
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The renal vein is compressed, but it is not
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invaded, even though the tumor is right next to it.
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Perhaps a little nubbin.
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Right there is just starting to enter the renal vein.
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But remember, you can get renal vein
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invasion with renal cell carcinoma.
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And this is the second most
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common renal tumor of childhood.
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Renal cell carcinoma becomes more common than
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Wilms tumor during the second decade of life.
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And Wilms tumor can occur in fetuses and neonates.
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But in this age group, congenital mesoblastic
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nephroma, and we'll use the abbreviation
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CMN from here on out, is more likely.
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Now, there are some other less common renal tumors
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that occur in young children, and they're generally
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indistinguishable from Wilms tumor at imaging alone.
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But, there may be some features that
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suggest one diagnosis over the other.
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One of these is clear cell sarcoma, also known
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as CCSK, clear cell sarcoma of the kidney.
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These also show early skeletal metastases,
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and our skeleton is nice and clean.
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And, um, the skeleton is not a common
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site early on for Wilms tumor.
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Another one is the rhabdoid tumor.
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Now this has an established association with
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brain tumors, especially in the posterior fossa.
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I haven't shown you any.
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In addition, the finding of subcapsular hemorrhage,
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which we do have in this case, suggests rhabdoid tumor,
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but still, Wilms tumor is so much more common that
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we would still favor the diagnosis of Wilms tumor.
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An additional important differential diagnostic
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consideration in a child is pyelonephritis.
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Now yes, pyelonephritis is a hyperemic state, but
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it's still not as vascular as the main kidney.
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Here's the renal parenchyma.
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So if we were to enhance pyelonephritis, we
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might see a cold area, and it might be, uh,
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striated or triangular, not cold, but less
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vascular than the rest of the renal parenchyma.
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So, you might have an episode of nephritis that is
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hypovascular relative to the normal renal parenchyma.
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And that is a little confusing because
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the kidney is quite a vascular organ.
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Another consideration would be a renal abscess.
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Now, in a renal abscess, you're
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going to get usually a single cavity.
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Occasionally, a cavity can be multiloculated.
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It's going to be pretty bright
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on the T2-weighted image, although sometimes in the
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center of an abscess, it'll be a little bit darker due
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to the peroxidases that cause, that cause shortening
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of T2 relaxivity, a so-called paramagnetic phenomenon.
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But probably the most helpful thing is the child has
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flank pain, a fever, and white cells in the urine.
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So, real basic, basic stuff is going to give you the
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right tip-off to the diagnosis of a renal infection.
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Although Wilms tumor is the most common
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pediatric renal tumor, and I'll say it again
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and again for you board takers, it can be
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indistinguishable from cellular, uh, CMN at imaging.
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CMN is more common in young infants.
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On the other hand, if there are bilateral
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tumors, venous invasion, or pulmonary metastases,
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which Wilms is prone to do, then Wilms is
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overwhelmingly a more likely diagnosis.
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How about CCSK?
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We've already talked briefly about
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clear cell sarcoma of the kidney.
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Um, this is similar to the cellular
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subtype of CMN with multiple cystic foci,
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but CMN is more common in young infants.
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Another very rare condition is known as
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ORTI, or ossifying renal tumor of infancy.
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ORTI typically demonstrates calcified osteoid matrix.
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If we, uh, take away our color here for a minute and
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go back to our areas of low signal intensity.
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Osteoid matrix doesn't look like this.
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It's cloudy.
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It's irregular.
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It may be a little whirly or
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swirly, but not popcorn-like.
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This is blood.
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So, you wouldn't want to confuse
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this with the osteoid matrix of ORTI.
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And then we come back to the all-important
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neuroblastoma at the very beginning where we said
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that we like our neuroblastoma to arise from somewhere
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high near the adrenal gland and invade the
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kidney rather than come directly from the kidney.
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And we've also given you some other key
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features to differentiate neuroblastoma
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from Wilms tumor in this five-year-old.
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Let's move on, shall we?
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Dr. P out.
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