So this kind of brings us to our very last
category of the categories of AKI - urinary obstruction.
So this really is going to be caused
by obstruction of the outflow of urine
anywhere from the
renal pelvis to the urethra.
And the renal failure that we see
caused by this can either be acute
or it can be subacute if it occurs over time.
When we think about the different causes of
obstructive uropathy, they include calculi or stones
particularly if I have a stone or a patient has a stone
at the ureteropelvic junction in a solitary kidney
obstructing outflow of urine
that's gonna result in AKI.
Or think about a patient who
might have bilateral stones
And not only do they have little stones,
they have these big staghorn calculi
that take up the entire renal pelvis, that
can really obstruct the outflow of urine
So that can result in an AKI.
And when we have stone disease, we can see
it in younger patients as well as older patients.
We can also have anatomic abnormalities
most commonly seen in children.
So children who have problems with
the positioning of the urethral valves,
people who are born with congenital strictures or adults
who develop that over time because of a traumatic injury,
and then people who have stenosis of the
ureteral vesicle or the ureteropelvic junction
Again, that just means that
there's an area of narrowing
where the ureter anastomoses with the bladder
or the ureter is connected to the renal pelvis.
Now the most common and what we saw in
our case is benign prostatic hyperplasia or BPH.
This is most common in
men over the age of 50.
Another is urethral
stricture as we talked about.
And then finally, malignancy.
So malignancy which will include
malignancies of the prostate, the bladder
or any kind of extrarenal pelvic
neoplasms that end up compressing
the outflow of urine
essentially from those ureters.
Okay, so if our patients
presents with obstructive uropathy,
what can we do in order
to make that diagnosis?
Again, we're gonna be diligent detectives, we're
gonna do a very thorough history and chart review.
If our patient has BPH, we're really gonna
ask them about lower urinary tract symptoms.
That means do they have
hesitancy when they're voiding?
Do they have dribbling?
Do they have double voiding, feeling like
they've voided, but then have to void again?
That means that they
have incomplete emptying
and that's a very big sign or
symptoms that this patient has BPH.
In a patient who might be presenting with
stones, they could present with flank pain
depending on where that
stone is located,
or they can have gross hematuria, again
as that stone kind of traverses that ureter
or in the bladder even
you can develop hematuria.
And then of course, for people who have
malignancies that are compressing the ureters
then it's gonna be important to
look for that history of malignancy.
Physical exam can be helpful as
well in terms of diagnosing our patients.
For BPH, it would be important to do a digital
rectal exam to palpate for an enlarged prostate,
In patients who have stones, we might want
to do percussion at our costovertebral angle
to see if our patient has tenderness.
And then in the case of malignancy, it's always
important to do a thorough abdominal exam
to really palpate for any abdominal
mass in the pelvic and abdominal region.
Imaging is probably one of the most important parts
in diagnosing post-renal or obstructive uropathy.
And our imaging modality of choice
is going to be renal ultrasound.
Here we can look for
things like hydronephrosis.
As seen in the image over here, you
can see on ultrasound we have a kidney
with a very dilated renal pelvis
and a very big boggy renal cortex.
That's from essentially reflux of
urine back into that kidney, enlarging it.
If our patient is presenting with a stone, it'd be
important to get a CT of the abdomen and pelvis
without radiocontrast which will highlight
the stone - so very easy to see calculi.
We can also see pelvic
masses if we want to use contrast
although we'd want to avoid
that in our patients who have AKI.
On laboratory evaluation, that high BUN to creatinine
ratio is gonna be more reflective of post-renal.
Again, if you think about what's happening,
you have obstruction of urine outflow,
so you have stasis of
urine within that tubule
so plenty of opportunity to
absorb urea during that time period.
And again if I'm looking at that
urinary sediment, it's oftentimes bland.
There's no cellular
elements, there's no cast.
In the case of nephrolithiasis or stones, I
may be lucky enough to see some crystals
but they're not always present.
So how do we treat our patients once
they present with obstructive uropathy?
So for BPH, we can actually do a urinary catheter
inserted into the bladder for decompression
We can also remove medications that
precipitated the obstruction to begin with.
Remember our patient, he took a cold
medication which was an alpha-agonist.
So that increases tone of that bladder.
Next we absolutely want to ensure our patients are
off-medications that it can do things like that.
And there's also medical and
surgical therapy for prostate.
Right, so we're gonna give
your patients alpha-blockers.
And we can have our
urology colleagues get involved
and they can definitively
cure our patients with BPH.
For stones, we can remove the stone and that's
when I typically get my urology colleague involved
where they can do a percutaneous nephrolithotomy
or they can do shockwave lithotripsy.
We'll be talking a little bit more
about that in our nephrolithiasis chapter.
We can also have our urology
colleagues place a ureteral stent
from that renal pelvis
all the way to the bladder
which helps to keep that ureter open and
allows free passage of stones into the urine.
And finally, we can get our
interventional radiology colleagues involved
to place a percutaneous nephrostomy
as shown in this image over here.
So essentially, our IR colleagues will
place the catheter directly into the renal pelvis
which completely obviates the
obstruction and allows free passage of urine.