 I'm Dr. Stephen Pomeranz talking about pediatric renal masses. And I've got a five-year-old whose parents incidentally discovered an abdominal mass while playing with her child. On the left is a coronal T1 weighted image. In the middle, a coronal T2 weighted image. And on the far right, with exuberant fat suppression, is a sagittal T2 vaspe and echo image. Now if we do a little scrolling here, it is obvious that there is a large mass in the right mid-abdomen. And most of you would ascertain that this mass is associated with the right kidney. There are several components to the mass. There's a very low signal component on the T2 at the top. We see it here on the T1 weighted image, more gray. We've got a more solid appearance to the mass, inferiorly. And it is gray on the T1. It is light gray or slightly hyper intense on the T2. And then we see what looks like more familial renal parenchyma. If we go to the exuberant fat suppressed image, we see the renal parenchyma, portions of our solid mass, and this very low signal area that appears to surround the kidney, perhaps in the renal capsule. So on a five-year-old, what would you think of? Well, under age 10, you really have to think about Wilms Tumor, which we'll talk about in a minute in terms of demographics and commonality. That is a renal tumor. But the most important differential diagnostic consideration in a young patient, five years of age or younger, would be neuroblastoma. Neuroblastoma and Wilms Tumor occur in very young individuals. Under age 10, in fact, neuroblastoma around age two. And we'll see Wilms Tumor in a similar age range and a similar location. But neuroblastoma arises from the adrenal gland. So the fact that our mass is centered down below and we have this periurenal area up above that doesn't have a shape reminiscent at all of an adrenal lesion favors a Wilms Tumor. Also, when you're looking at a mass arising from the kidney, sometimes the claw sign is helpful. In other words, you have a mass, here's our mass right here. And the kidney is seen as a claw wrapping around the mass. And we do have that here. Here's our claw, as they say when you're playing with kids, the claw. So we've got that present here, which also favors this as a primary renal mass. Now rarely, Wilms Tumor can arise in extra adrenal sites. And determining the site of origin, we're starting basic basic, helps in developing an appropriate differential diagnosis, along with identifying the claw sign. And in the axial projection, and perhaps in the coronal projection, identifying the adrenal glands. Now features that would push you towards neuroblastoma rather than Wilms Tumor would include calcification. We'll see Wilms Tumor calcifies, but neuroblastoma much more commonly. About 85% of neuroblastomas calcify on CT versus about 15% of Wilms Tumor cases. Tumor entacement of vessels occurs in neuroblastoma versus displacement or invasion with Wilms Tumor. Let's see if we can spot a renal vein. And we can, right there, that renal vein is displaced. This one is not invaded, and it is not encased. So that favors the diagnosis of Wilms Tumor. Crossing of the midline, which we do not have here, also favors the diagnosis of neuroblastoma. Now you might have nodes, but that doesn't necessarily count as direct crossing. Let's go over to our sagittal projection and see if our solid tumor is crossing the midline. And it certainly doesn't look like it is. The spine also looks clean in terms of metastatic disease. Also, extension behind the aorta through neuroferamina into the spinal canal and skeletal metastases would all favor the diagnosis of neuroblastoma. Age is really critical, though, when you're forming a differential diagnosis for renal mass in a young child. Because in a young child, remember, those of you that are taking boards, that are residents, that are fellows, that are internists, that are pediatricians, that are new to MRI, Wilms Tumor is the most likely diagnosis. And renal vein invasion, which we don't have here, is highly suggestive of Wilms Tumor. Let's move on with our basic introduction to pediatric renal masses. In this case, a rising from the kidney, which is a Wilms Tumor.