URO-Radiology
by
Dr Clarence Lei Chang Moh, FRCS Urol
Consultant Urologist
email:
clarencelei@gmail.com
Urology
imaging is an essential component of the assessment and management of
urological disorders. However, the
history is still important as a working diagnosis can be made in majority of
cases. The urinary tract is also mainly
retroperitoneal and in early stages of urological disorders, there are a few
clinical signs. Urological imaging is
important to delineate anatomy and to have some idea of the function. The important parts of the anatomy include
the kidney, bladder and prostate as well as the entire urothelial system. Twenty five percent of the cardiac output
goes to the kidneys and therefore, angiography is important in specific
situations.
Urological
imaging consists of the following:
(1)
Ultrasound of the urinary tract – kidney, ureter (upper and lower),
bladder, prostate, posterior urethra.
Ultrasound is not optimal for the mid ureter & anterior
urethra. It does not give much direct
assessment of function although a ureteric jet seen in the bladder from the
ureteric orifice gives some idea of the function of that side of the urinary
tract.
(2)
Plain x-rays – KUB
(kidney, ureter, bladder).
(3)
IVU, Intravenous urogram.
(4)
CTU, Computerised tomographic urography; plain CTU is useful to
diagnose stones & is imaging of choice
in an acute situation.
(5)
CTU with contrast; this would be essential to investigate cases of haematuria to
see any abnormal vascularity of the urinary tract.
(6)
Radio isotope
scans so as to see the
perfusion and excretion of each part of the urinary tract. This would be useful to see the differential
function, especially with a view of nephrectomy.
(7)
Angiography either
direct or CTA. In an elective situation, it is useful to
work up patients for donor nephrectomy so as to preferentially harvest the
kidney with a single renal artery. In
emergency situations, it can be used for selective embolisation of a bleeder.
(8)
MRI, magnetic resonance imaging is useful for specific
situations. This is however quite
dependent on technology and expertise.
Hazards
of Urological Imaging
Radiation
exposure has a teratogenic effect, esp during first trimester
of pregnancy. Radio contrast toxicity is
a significant factor to consider. Therefore, ultrasound, plain x-ray or plain
CT is usually preferred. There is a definite radiocontrast associated
mortality, possibly around 1 in 40,000 (depending on contrast type). For patients who have history of allergy,
they should be pre-medicated with Prednisolone 40 mg 12 hours and 2 hours
before the study. When radio contrast
studies are used, there should be ready facilities for emergency
resuscitation. In addition to
radio contrast allergy, radio contrast is also
nephrotoxic.
Therefore, the serum creatinine (or preferably eGFR) should be assessed
before the contrast study. For patients
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Nephrogenic
systemic fibrosis is also a
progressive disorder which occurs up to 5% of patients who are exposed to
gadolinium, used in MRI.
Ultrasound
is almost like a stethoscope for many doctors, especially urologists. It is
often available in the clinic, emergency room, ward and operating theatre. The kidneys are readily suitable for
ultrasound. The ultrasound can pick up hydronephrosis, cysts, stones and
masses. Fluid would appear as
hypoechoic and may be due to hydronephrosis or cysts. For the occasional patients where
differentiation is difficult, a plain CTU would be useful. The upper ureter and lower ureter can be
imaged readily if they are dilated due to any obstruction eg stone. The bladder is readily seen by ultrasound to
assess the bladder volume, stones,
bladder tumour, bladder wall thickness and any intraprostatic protrusion of the
prostate (IPP).
However, the IVU would give a better view of the
collecting system. Where stone treatment
is contemplated, an IVU would usually be required to see the relation between
the stone and the collecting system.
Occasionally, calcification seen on ultrasound may not be in the
collecting system or may be in a calyceal diverticulum. For stones in the mid ureter, a CTU (IVU if
CTU not readily available) may be necessary to identify the stone. IVU would also be necessary to look for
urothelial tumours, although a CTU with contrast gives more idea about the
vascularity of the lesion.
For
congenital lesions, CTU or MRU would give a better definition of the urinary
tract, in particular, duplex urinary tracts with ectopic insertion, as a cause of incontinence. The characteristics of the lesion on ultrasound
(echogenicity) or CT (attenuation) would be give an idea of the underlying
pathology e.g. fat in an angiomyolipoma would appear hyperechoic on ultrasound
and a low attenuation on CT scan.
CT
is better to assess the retroperitoneum e.g. lymphadenopathy from tumours or
any tumours as a cause of ureteric obstruction. It would also give a better
view of the extent of infiltration and the vascularity of any renal
tumour.
Diuretic
studies are important when assessing patients with hydronephrosis. Hydronephrosis may be obstructive,
refluxing or non-refluxing and non-obstructive. When the hydronephrotic system is full,
IV Lasix will cause an increase of the distension if the system is
obstructed.
Radio
isotope scans allow the perfusion, excretion of different parts of the urinary
tract to be monitored with a count of its radiation. It can also give a differential function of
each kidney. This information is
important if a nephrectomy is to be considered.
If a diseased but good functioning kidney is removed, the patient may
end up with dialysis.
Direct
urography consists of the following:
(1)
Urethrogram, retrograde.
(2)
Bladder cystogram,
micturiting cystourethrogram, MCU to see the various grades of reflux
and also to see the urethra. In neonates
with bilateral hydronephrosis, the MCU is likely to show up a posterior
urethral valve (PUV).
(3)
Pelvis, retrograde
pyelogram, RPG, antegrade pyelogram, APG (the
latter requires a puncture of the kidney).
Bacteria
maybe introduced, with risk of sepsis.
Retrograde studies would usually have to be done with the use of a
cystoscope. The urologist would ensure radiation protection for himself and the
staff in the operating theatre.
Interventional
uro-radiology may be performed
by the radiologist or the urologist. For patients with ureteric obstruction by
stone or tumour, the kidney function can be preserved with a percutaneous
nephrostomy (PCN) or ureteric stenting.
Ureteric stenting can be performed by the antegrade or retrograde
technique. Puncture of the kidney may be
performed with the help of ultrasound or fluoroscopy or combination of
both. Where there are stones in the
kidney, the urologist can proceed to dilate the percutaneous tract and do PCNL,
percutaneous nephrolithotripsy. There
are structures which can be damaged by a PCN, namely, the kidney, renal
vessels, renal collecting system and the nearby organs, namely the colon and
the pleura.
Angiography is performed by direct puncture of the blood vessels or by
CTA. Generally, CTA has taken over the
role of direct angiography as it is less invasive. Angiography is useful for assessment of donor
kidneys so that the kidney with the single renal artery is preferentially
harvested for transplantation. For
patients with haematuria after trauma or PCNL, the affected bleeding vessel can
often be embolised as a therapy for the bleeding. This is usually performed by the
interventional radiologist in the fluoroscopy suite.
Transrectal
ultrasound, TRUS is an important
modality of patients with LUTS, lower urinary tract symptoms and prostate
cancer. It is a relatively non invasive
technique used in the urology clinic.
TRUS can look at the prostate size, prostate capsule, any prostate
nodules (hypoechoic more likely to be cancerous), seminal vesicle invasion and
also to look for urethral stones.
Prostate biopsies are also now routinely done in the urology clinic
under TRUS guidance, taking 6 to 12 cores under local anaesthetic.
In
most medical centres, CT with CTA is a standard emergency investigation where
there is suspicion of trauma to the urinary tract. It gives the maximal
information in the shortest possible time and it is also useful to look for
concomitant injuries in the abdomen.
SUMMARY: Urology imaging is an
important component for the management of most urological conditions. Depending on the clinical problems, the least
invasive & cost effective imaging is used.
24th December 2008, 2 Oct 2013
