 Welcome back to our MedSmarter question of the week where we're taking a smarter approach to preparing future physicians. Before we get started, if you'll take just a quick minute and click that like button and also subscribe and turn the bell on so that you'll be notified when we post new videos. Let's get into a renal question today. As always, we start with the last sentence of the vignette and then read the rest. Which of the following is the most likely location of the lesion causing the patient's renal failure? A 25-year-old man is beginning chemotherapy for leukemia when he develops severe intermittent left flank pain that later migrates to the pelvis. Three days later, the patient's creatinine levels rise and he is diagnosed with acute renal failure. His fina, or fractional excretion of sodium, is greater than 4% with a urine osmolality of less than 350 mls per kilogram. Blood and urine cultures are negative for bacteria and eosinophilia. An abdominal radiograph fails to locate any pathology, which of the following is the most likely location of the lesion causing the patient's renal failure. So before we get to the answer choices, let's look over some important things here. So the patient is undergoing chemotherapy, so that's something that's very important to know here. And he developed left flank pain that migrated to the pelvis. Later on, our creatinine levels rose, diagnosed with acute renal failure. His fina was greater than 4%, urine osmolality less than 350 mls, and then our bacterial cultures were negative for bacteria and eosinophilia. And then also our abdominal radiograph gave us a negative result. So take a minute, read the question again, and then from these answer choices, put in the comment box below what you think is the correct answer. So we're going to have to make a decision between a lesion in one of these five locations causing these problems. So is this in the urethra, the spleen, the kidney tubules, the interstitium of the kidney, or the glomeruli? Well, going back over that this is a patient that's on chemotherapy, that gives me the likely possibility that we're dealing with something that is a side effect of that chemotherapy. So chemotherapy causes these cancer cells to lice pretty quickly, so we have something called tumor lysis syndrome. My guess is this is probably what we're dealing with, this tumor lysis syndrome. So what's happening is all those cells that are dying quickly and they're releasing their toxic contents around, so that can be causing problems with the kidneys. A lot of times we do see some stones associated with tumor lysis syndrome, and that seems to be pretty equivalent to what we're dealing with here. So we have left flank pain, that could be a kidney stone, then it migrates the pelvis, maybe that kidney stone was moving down, it was causing the pain in the ureters and then it got into the bladder, and the pain in the pelvis tells me it's probably more than likely somewhere along the urethral tract there. So therefore, looking at these answer choices, I would already rule out an interstitium of the kidney problem, glomeruli probably not correct either. The kidney tubules, not going to be an option because we're talking about pelvic pain here, and then spleen that's going to be out after we talked about pain that has now moved into the pelvis. So that leaves us with urethra as our only option in our final answer. And that is correct, the urethra is the location of what's causing this patient's renal failure. So what we're seeing here is, as we said, tumor lysis syndrome. So these leukemia cells are being liced, all of their contents, which includes potassium, uric acid, phosphate, and all other different types of chemicals and compounds are being released into the body. The kidneys are taking those and filtering them out and dumping them into the urine. What's happening here is, specifically with this, uric acid is going to be so concentrated that it will actually form kidney stones within the pelvis there of the kidney. And then when they start to move south down the ureters, they're causing those pain. In this particular situation, the fina here, we said is greater than 4%, that is a consistent number with post-renal failure. So post-renal failure is going to be something beyond the kidneys that are causing problems. And it's also likely here that this kidney stone passed through the ureters and then went into the urethra where we had that pelvic pain. Now you might be a little bit confused because this says that the abdominal radiograph fails to locate any pathology. And a lot of times we can see stones on an x-ray. The problem is that these are more than likely going to be uric acid stones, not calcium stones. If they are calcium stones, we can see them on x-ray. However, uric acid stones are radio-lucent and we can't see those on our x-ray films. If you found this material helpful for your studying, please like and consider subscribing to the channel. Also, share this video so that more people can benefit from it like you have.