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I.
Imaging of nephrolithiasis, urinary tract infections and their
complications
II.
Julia R. Fielding, M.D. and Raj Pruthi, M.D.*
Dept. of Radiology and *Division of Urology
Univ. of North Carolina at Chapel Hill
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Key Points
III. ISSUES
1. Nephrolithiasis
A. What is the appropriate test for suspicion of obstructing ureteral stone?
B. How should stones be followed after treatment?
Special case: The pregnant patient
2. Urinary tract infections
A. When is imaging required in the adult female with urinary tract infection?
B. When is imaging required in the adult male with urinary tract infection?
C. How should imaging be performed in the child with a urinary tract
infection?
Special case: The neurogenic bladder
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IV. Key Points
Nephrolithiasis
1. Non contrast- enhanced helical CT with 5mm slice thickness is the test of choice
for the patient with a suspected obstructing ureteral stone. In the absence of an
available CT scanner, IVU or a combination of plain film and US should be
performed (MODERATE EVIDENCE)
2. Plain film should be used to follow the descent of stones along the ureter.
(MODERATE EVIDENCE)
3. For the pregnant patient with a suspected renal stone, there is insufficient
evidence to determine whether IVU or CT is the appropriate test when US is not
diagnostic (INSUFFICIENT EVIDENCE)
Urinary tract infection
1. Uncomplicated urinary tract infections in adult females, those without
systemic signs or symptoms, do not require imaging. (MODERATE
EVIDENCE)
2. Complicated urinary tract infections in adult females, those that occur in
combination with pregnancy or with symptoms that extend beyond 10 days
and evolve to include fever, chills and flank pain may require imaging to
exclude renal abscess. It is unclear what clinical finding should prompt
imaging and whether CT or US should be performed. (INSUFFICIENT
EVIDENCE).
3. Uncomplicated, isolated urinary tract infections in men are uncommon. It is
unclear when US or cystoscopy should be performed to exlude associated
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infection of the testis or epididymis and bladder cancer, respectively.
(INSUFFICIENT EVIDENCE)
4. Because of the high likelihood of vesicoureteral reflux in children with
urinary tract infections, US and VCUG should be performed in children with a
urinary tract infection (MODERATE EVIDENCE). At most academic
institutions in the United States, both US and VCUG are performed in boys
and girls to exclude hydronephrosis, significant renal scars and vesicoureteral
reflux. Nuclear medicine cystogram may be substituted for VCUG however
the currently used low dose fluoroscopy units and higher spatial resolution
make VCUG the more commonly used test.
5. Patients with neurogenic bladders often have colonized the urine with
pathogens. They may demonstrate few signs and symptoms when developing
a complicated infection. It is unclear when and what type of imaging should
be performed (INSUFFICIENT EVIDENCE).
Nephrolithiasis
Issue 1: What is the appropriate test for suspicion of obstructing ureteral stone?
Summary
Patients with clinical signs and symptoms of renal obstruction should undergo
unenhanced helical CT of the abdomen and pelvis. The accuracy of this test has been
shown to be higher than that of intravenous urography (IVU) and a combination of
ultrasound (US) and plain film in level 2 (moderate evidence) studies. In addition, CT is
quick to perform and interpret and does not require the administration of intravenous
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contrast medium. Findings on the CT scan can be used by the referring physician to
determine treatment. The drawbacks of the technique include cost and a relatively high
dose of ionizing radiation (30-40 mSV). When CT is not available either IVU or a
combination of plain film and sonography may be used.
Issue 2: How should stones be followed after treatment?
Summary
Because plain film has the highest spatial resolution of any imaging modality,
good contrast sensitivity, is inexpensive and delivers minimal radiation dose, it is at
present the best way to follow the passage of a stone down the ureter over time.
Special case: The pregnant patient
Summary
There is no compelling published evidence that IVU, plain film and sonography
or helical CT is the preferred test. In dealing with the pregnant patient, fetal age and
estimated radiation dose is of paramount importance. Pregnant patients routinely have
right hydronephrosis as the enlarging uterus turns slightly to the right, compressing the
ureter. CT, the most accurate test, delivers approximately 16mSv to the fetus. Two plain
films obtained prior to and post administration of intravenous contrast material deliver
significantly less radiation but may be more difficult to interpret because of the overlying
bony fetal parts and lateral deviation of the ureters. Dilation of the left ureter is thought
to be less common and the presence of left hydronephrosis with flank pain and or
hematuria is often enough clinical evidence for clinicians to begin treatment for stone
disease.
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Urinary tract infection
Issue 1: When is imaging required in the adult female with urinary tract infection?
Summary
Level 2 (moderate evidence) studies have revealed that IVU and US is of little value in
males or females in the diagnosis of uncomplicated urinary tract infections in which
symptoms are confined to the pelvis. In evaluating recurrent urinary tract infections, IVU
may be of some use, particularly when a structural abnormality of the urinary tract is
suspected. There is no compelling evidence to determine when and how imaging of
complicated urinary tract infections should be performed. Complicated infections include
those in which symptoms exceed 10 days, there is coexisting pregnancy, or symptoms
evolve to include fever, chills and flank pain.
Issue 2: When is imaging required in the adult male with urinary tract infection?
Summary
There is no compelling evidence to indicate the role of imaging in men with urinary tract
infections. Isolated urinary tract infections are uncommon. Associated disorders such as
orchitis, epididymitis, and prostate enlargement can be detected using US. It is possible
that IVU and other contrast studies may be of use when stones or strictures of the ureter
are suspected, however there is no compelling evidence to support this.
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Issue 3: When is imaging required in the child with a urinary tract infection?
Summary
During the first 6 years of life, 8% of all girls and 2% of all boys will have a
symptomatic urinary tract infection. The diagnosis is confirmed by the presence of
bacterial organisms and white blood cells in the urine. Diagnosis of pyelonephritis in
small children who cannot communicate the location of pain remains a challenge. In a
study of 919 girls undergoing a first imaging evaluation for UTI, Gelfand et al. found that
vesicureteral reflux was extremely uncommon in girls with a fever less than 38.5oC and
greater than 10 years of age. Because urinary tract infections can be associated with
vesicoureteral reflux, the standard imaging algorithm consists of a voiding fluoroscopic
or nuclear cystourethrogram and a renal US.
Special case: The neurogenic bladder
Summary
The neurogenic bladder fails to fill and empty on a regular basis due to
neuropathy. This may be due to a congenital anomaly such as myelomeningocele, trauma
to the spinal cord or pelvic nerves or ischemic neuropathy such as occurs in diabetes
mellitus. Because of stasis, the urine of many of these patients is colonized by bacterial
pathogens. Asymptomatic urinary tract infections are rarely treated. The difficulty arises
when a complicated infection occurs. Because of the neuropathy, affected patients may
not feel pain or distention of the bladder and the immune system may not respond
adequately leading to minimal symptoms.
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