18. Renal Imaging Flashcards
what imaging modality is best for renal cysts?
ultrasound. kidney size helps prognosis
how early will hydronephrosis be evident on US after obstruction?
not evident for 1-2 days post-obstruction. takes a few days to develop
what imaging modality is usually preferred for diagnosing renal obstruction?
ultrasound
CT: contrast or non-contrast best for nephrolithiasis?
non-contrast. because contrast can obscure stones
what imaging modality can show early signs of renal obstruction?
contrast CT
what renal structures can contrast CT highlight in particular?
vascular structures
what’s one problem with CT contrast?
it is nephrotoxic. be careful particularly with patients who already have low renal function
generally, what 4 things are we evaluating the kidney for with imaging?
- obstruction w hydronephrosis
- stones
- renal masses
- renal vasculature
how does the CT contrast move through the kidney: what lights up first?
arteries –> cortex –> veins –> collecting systems
what is the appearance of urine with contrast CT?
dark unless contains contrast (contrast is bright white)
by comparing the kidneys over time with contrast (as the contrast goes through phases), what can you discern?
asymmetric function, whether one kidney has delayed function
if one kidney is processing contrast more slowly than the other, what are possible causes?
- decr GFR
- decr inflow of contrast due to prob with afferent arteriole
if kidney is stretched (collecting system enlarged( is the obstruction acute or chonic?
chronic (stretch takes time)
if something enhances (takes in contrast), what can we conclude? does that make us more or less concerned?
if it takes up contrast, then generally it receives blood flow and it’s “alive”. we care more about this type of mass than about one that is not taking up contrast.
if a mass does not enhance, what can we conclude?
no blood flow, just a cyst. water, essentially.
what criteria do we use to decide whether or not to biopsy?
Bosniak criteria. based on CT. don’t need to know details
Can we measure enhancement?
yes, it is definable, expressed as Hounsfield units. The number assigned increases with increased enhancement.
how does radio frequency ablation work?
little umbrella thing is inserted and deployed… basically cooks the area, then retracted. the tissue scars and is eventually resorbed.
what is a ‘stone protocol’ CT
non-contrast CT of kidneys, in order to identify stones in collecting system, ureters or bladder
with a big cyst or angiomyolipoma, what is one option for treatment?
these are not malignancies, but they can bleed… so insert a coil as far distally as possible to clot off vasculature that is feeding it.
what will a hematoma look like on CT?
roughly the same grey color as the muscle tissue. active bleeding looks a little lighter.
why would you get US of a kidney?
can see motion/flow on US using doppler (not on CT)
normal kidney on US: should there be urine in center?
no, that indicates hydronephrosis if you can see black fluid in the center of the kidney
how should the kidney and the liver compare on US, in terms of their shade?
they should be the same shade of grey
what is a physiologic cause of renal obstruction?
pregnancy
how can we use doppler/US to figure out if an obstruction is due to pregnancy or something else?
ureteral jets: if they are symmetrical, then the cause is preg
benefits of US as compared to CT?
cheap, no radiation, can see motion w doppler
