Dr. Alderson is a Fellow in the Department of Radiology; Dr. Hilton is a Clinical Professor of Radiology, Co-Chief, CT Section, Department of Radiology; and Dr. Papanicolaou is Professor of Radiology and Co-Chief, CT Section, at the Hospital of the University of Pennsylvania, Philadelphia, PA.
Imaging of the upper urinary tract has traditionally been the purview
of intravenous (IV) urography, but over the last decade, computed
tomography urography (CTU) has become the modality of choice in imaging
the urinary tract. With few exceptions, most notably that of the
unenhanced CT performed for acute flank pain and stone disease, many
urological symptoms and conditions are now investigated with CTU.
Continuing improvements in the spatial resolution and speed of newer CT
scanners, combined with advanced multiplanar and volume-rendered image
reconstruction, have made CTU a comprehensive examination whereby the
kidneys and upper collecting system, ureters, and urinary bladder can be
evaluated in one setting.
Indications for CTU continue to evolve.
Conditions commonly referred for CTU include urinary calculus disease,
hematuria, flank and abdominal pain, suspected renal or urothelial
neoplasm, a variety of inflammatory conditions, and congenital anomalies
of the kidneys and ureters. Experience with patients who have undergone
cystectomy with urinary diversion, most often for treatment of bladder
carcinoma,continues to increase, and CTU is commonly used for
surveillance of the urothelium in at-risk patients. Currently, CT
urographic evaluation of the urinary bladder generally is not considered
accurate enough to exclude small superficial urothelial tumors, and
cystoscopy is indicated for complete bladder evaluation. The ability to
biopsy and resect lesions are added benefits of cystoscopy.
American Urological Association Best Practices Policy guidelines
recommend IV or CT urography as the initial imaging test for patients
with asymptomatic microscopic hematuria.1 Likewise, the American College of Radiology rated CTU as the most appropriate imaging procedure in the evaluation of hematuria.1 Furthermore, extraurinary findings, some of them clinically important, can be found in a percentage of patients undergoing CTU.1
Contraindications to CTU are generally limited to those patients who
cannot receive iodinated contrast because of renal insufficiency, prior
severe reaction, or pregnancy.
Most CTU protocols are triphasic examinations that include noncontrast, enhanced, and delayed images.1-3 Noncontrast
images extending from the top of the kidneys through the bladder are
obtained to evaluate for calculi, fat-containing lesions and parenchymal
calcifications, and to provide baseline attenuation for assessment of
lesion enhancement. Intravenous contrast is administered and, following a
90- to 100-sec delay, scanning of the abdomen and pelvis is performed
during the nephrographic phase. Homogeneous enhancement of the kidneys
during the nephrographic phase optimizes small renal mass detection. The
final acquisition is during the excretory phase after a 12- to 15-min
delay, when there is opacification and distention of the collecting
systems, ureters, and bladder. Excretory images allow for evaluation of
the urothelium. While diagnostic unenhanced and nephrographic
acquisitions are relatively easy to obtain, optimal opacification and
distention of the ureters during the excretory phase can be more
problematic. Suboptimal distention of the ureters and intermittent
peristaltic waves may result in limited visualization of one or more
segments. A variety of techniques have been proposed to improve
visualization, including oral and IV hydration, diuretic administration,
use of a compression belt, prone positioning, and a log-rolling prior to
the excretory acquisition.1,3-7
As an alternative to
the triphasic single bolus CTU technique, the split contrast bolus
technique has been designed whereby the contrast is given as 2 boluses
before a single enhanced-scan is acquired.1 The aimed
cumulative effect is that the earlier smaller bolus provides excretory
information, while the second, larger bolus provides information on
vascular anatomy and the renal parenchyma. The benefit of this protocol
is the elimination of an additional acquisition, resulting in a
decreased radiation dose; the disadvantage is less reliable
opacification of the ureters. While the ideal protocol is not agreed
upon, many centers hydrate patients prior to contrast administration
(oral and/or IV route) and inject furosemide IV at contrast injection.
large number of very thin section images allows for isotropic
presentation of the axially acquired data set in any chosen plane. Often
on a workstation, CT urograms are frequently reviewed utilizing
multiplanar reformations, maximum intensity projections (MIP), and
3-dimensional volume-rendered images. Curved planar reformations along
the length of the ureters are also often helpful. Not only do these
postprocessing techniques allow the radiologist to interact with the
data to more fully appreciate pathologic changes, but they also aid in
communicating findings to referring physicians. If desired, IVU-like
projectional images can be created for those more familiar with these
As 3 CT scans of the abdomen
and pelvis are performed in the examination, radiation dose to the
patient is of concern. One study reported a mean effective dose estimate
of 14.8 mSv +/- 90 for CTU, and 9.7 mSv +/- 3 for IVU.2 Another study reported that the total effective dose for a triphasic CTU ranges between 20.1 mSv and 66.3 mSv.8 Thus,
the total dose can be significantly higher than with IVU, and many
report radiation doses for CTU to be 1.5 to 2 times higher.1,2 To
limit the dose, the upper abdomen superior to the kidneys is excluded
on the unenhanced and excretory acquisitions. Additionally, radiation
reduction techniques, such as automated tube current modulation, can be
employed, whereby tube potential and tube current-time product are
automatically customized to each patient’s body habitus to limit
overexposure while maintaining image quality. A recent study evaluating
low-dose noncontrast CT for the evaluation of stone disease suggests
that significant dose reductions can be realized in certain patient
populations without sacrificing accuracy.9 Nonetheless, at
this time, most authors report radiation doses associated with CTU to be
greater than those with IVU, and continued refinement of patient
selection criteria and imaging protocols should be performed to avoid
Renal and urinary tract pathology
Renal parenchymal masses
variety of benign and malignant renal masses are well depicted by CTU,
particularly during the nephrographic phase. Noncontrast images are
essential in identifying calcification, macroscopic fat within a lesion,
and high attenuation of hemorrhagic or proteinaceous cystic lesions;
they provide the baseline attenuation necessary for assessment of
enhancement. In addition to simple and complicated/complex cysts, other
common masses include renal cell carcinoma and angiomyolipoma. Less
commonly encountered masses include renal lymphoma (primary or
secondary), fat-poor angiomyolipoma, multilocular cystic nephroma,
oncocytoma, and metastatic disease. A detailed description of the
radiographic features of each lesion is beyond the scope of this review.
Renal papillary/medullary abnormalities
necrosis is associated with analgesic overuse, sickle cell anemia,
diabetes, pyelonephritis, renal obstruction, and renal vein thrombosis.10(p89,p151),11(pt3,sec3,p46)
Identified on the excretory phase, papillary necrosis may have several
findings, including contrast-filled clefts in the medulla, contrast
collections within one or more papillae, or caliceal-filling defects
from sloughed papillae (Figure 1).10(p89,p151),11(pt3,sec3,p46)
Renal tubular ectasia is characterized by noncalcified cystic dilatation of the collecting tubules.10(p40) Patients
are frequently asymptomatic, but may have microhematuria. Classically
described as having a “paint brush” appearance, contrast opacifies the
dilated tubules, resulting in dense striations extending from the
papillary tips into the medulla.3,10(p40) Patients with
medullary sponge kidney disease, part of the spectrum of medullary
cystic diseases, have associated medullary nephrocalcinosis with or
without urolithiasis (Figure 2).
Collecting system (calyces, renal pelves, ureters)
calyces, renal pelves, and ureters may be affected by a variety of
inflammatory, traumatic, congenital, and neoplastic processes.
diverticula are incidental findings of little or no significance.
However, infrequently, they may contain stones and/or become obstructed,
causing flank pain, hematuria, or urosepsis. Small outpouchings of the
calyx are identified as contrast collections contiguous with a calyx
(Figure 3).10(p43,pp105–106) Stones within diverticula are best identified on noncontrast images.
subepithelial inflammatory cysts in the renal pelvis and/or ureter
characterize pyeloureteritis and ureteritis cystica, respectively.The
cysts appear as multiple smooth filling defects most commonly in the
proximal one-third of the ureter and are often seen in association with
chronic urinary tract infections or stones.6,10(pp191-192),11(pt3,sec4,p10)
Findings may be bilaterally symmetric or asymmetric or even
unilateral.Involvement of the bladder is termed cystitis cystica. The
radiolucent filling defects should be differentiated from multifocal
uroepithelial carcinoma, in which they are usually not as numerous.
Ureteral pseudodiverticulosis (Figure 4) is associated with chronic
inflammation and urothelial neoplasms. Multiple small
contrast-containing outpouchings are evident on excretory images. The
significance of this finding is its reported association with an
increased risk of urothelial carcinoma. 10(p89,p151)
strictures may be the result of prior surgery or instrumentation, stone
passage, primary urothelial neoplasms, penetrating injuries, prior
radiation therapy, ischemia, retroperitoneal fibrosis, endometriosis,
metastatic tumor encasement, or an infectious disease (e.g.,
tuberculosis, schistosomiasis,etc.).10(pp92,96,183-184,201) CT
urography may diagnose the focal wall thickening at the site of the
stricture and demonstrate its cause. In contradistinction to malignant
strictures, benign strictures should be smoothly tapered with little
luminal irregularity. As a rule, proximal urinary tract dilation and
Traumatic injury to the ureter is most
frequently iatrogenic, but it may result from blunt or penetrating
traumatic injuries. Hematuria following traumatic injury may be an
initial clinical clue. Intramural hematomas appear as wall thickening
with stranding of the periureteral fat(Figure 5). There may be proximal
dilatation if the ureteral lumen is narrowed. Rupture or tear of the
ureter is identified on excretory imagesas excreted contrast accumulates
outside of the collecting system and ureter (Figures 6 and 7). It
should be noted, however, that the most reliable method to diagnose a
suspected ureteral tear is a retrograde pyelogram.
Fibroepithelial polyps are benign mesodermal tumors of the ureter composed of a fibrovascular core lined by normal urothelium.6
Commonly solitary and in the proximal ureter, the tumor is usually
identified as a smooth long filling defect that may be seen to move
between the different acquisitions if it is attached by a long stalk.6
Nonetheless, the polyp may not be easily differentiated from urothelial
malignancy and is therefore resected for pathological diagnosis.
of urothelial carcinoma is arguably the primary role of CT urography,
be it in patients with hematuria or those with a history of urothelial
tumors of the bladder requiring surveillance of the upper tracts.
Urothelial carcinoma, most commonly transitional cell carcinoma,most
commonly affects males older than 60.11(pt3,sec3,p103) Risk
factors include history of smoking, occupational exposure to certain
dyes and plastics, prior cyclophosphamide and other medication use, and
chronic infections, such as schistosomiasis.6,11(pt3,sec3,p104)
Patients may report hematuria or flank pain, or present with
obstructive uropathy. Various growth patterns have been described,
including predominantly pedunculated or intraluminal growth and sessile
with mural invasion.6,11(pt3,sec3,p103) Tumors may be
localized, spread extensively along the urothelium, or present as a
multifocal process throughout the urinary tract. If the tumor arises in
the calyces or renal pelvis, differentiation from a central renal cell
carcinoma may occasionally be difficult. Infiltrating urothelial
carcinoma tends to invade the renal sinus fat and renal parenchyma as a
soft tissue neoplasm of decreased attenuation compared to that of the
normal kidney, usually without a significant change in the renal contour
(Figure 8). If the tumor obstructs a calyx, the calyx may appear
irregular or amputated. Lesions frequently demonstrate enhancement in
the nephrographic phase and appear as filling defects (Figure 9) or as
an irregular luminal contour in the excretory phase. Urothelial
thickening often results from tumor spread.
Congenital anomalies of the kidneys and ureters
anomalies of the kidneys, including horseshoe kidney, renal ectopia
with or without crossed-fusion,hypertrophied column of Bertin, and renal
agenesis (sometimes with a genesis or cystic dilatation of the
ipsilateral seminal vesicle), are all well depicted by CT urography.10(pp29-48),11(pt3, sec3,pp6-15) Anomalous
kidneys may be complicated by duplicated ureters, stone disease,
vesicoureteral reflux, traumatic injury, and ureteropelvic junction
obstruction (Figure 10). CT urography is well suited to detect such
Congenital anomalies of the ureters include
complete and partial duplication, ectopic ureteral insertion, and
orthotopic or ectopic ureteroceles (Figure 11). Often, the ureter
draining the upper pole moiety of a duplicated system drains into an
ectopic ureterocele located inferomedial to the insertion of the lower
pole ureter. Classically, the ureterocele of the upper pole ureter
results in obstruction, while abnormal insertion of the lower pole
ureter results in vesicoureteral reflux (Weigert-Meyer rule).
Diseases of the urinary bladder
urography is useful in detecting and characterizing multiple bladder
abnormalities. Calculi within the bladder appear similar to those in the
upper tract and are easily seen on noncontrast images. Often, stones
are found at or near the ureterovesical junction, and it may be
necessary to differentiate a stone lodged in the distal ureter from one
that has passed into the bladder lumen and which is lying on the
dependent wall. In these situations, the patient can be placed in the
prone position and sections through the pelvis can be repeated. Stones
lodged at the ureterovesical junction will not change position, while
those free within the bladder will shift to the new dependent wall.
hematuria is the indication for imaging, particularly in the setting of
gross hematuria, intraluminal blood clots within the bladder usually
can be differentiated from urothelial tumors. Prior to contrast
administration, clots will be of soft tissue attenuation. After
intravenous contrast injection, clots do not enhance, whereas urothelial
tumors usually do.
Diverticula of the bladder are fairly common
and appear as focal outpouchings of the bladder wall contiguous with the
lumen. They maybe congenital, as in paraureteral (Hutch) and urachal
diverticula, or acquired. Calculi may form within a diverticulum because
of urinary stasis. Diverticula are also predisposed to infection and
development of urothelial tumors.
Urinary bladder rupture may be
seen in cases of pelvic trauma, although the recommended imaging method
to detect a urinary bladder rupture is a cystogram, using direct
instillation of contrast into the bladder and imaging with either
conventional radiography or CT. It is important to correctly identify
the type of bladder injury. Extraperitoneal rupture, the most common
type, is treated conservatively with Foley or suprapubic catheter
drainage. Intraperitoneal rupture requires immediate surgical repair.
Mixed type injuries also need to be correctly identified. CTU and/or CT
cystography can diagnose the type of bladder injury as well as posterior
urethral ruptures. Furthermore, CTU is used to diagnose fistulae
between the lower ureter or bladder and adjacent intestinal tract or
vagina. Patients with bladder catheters should have their catheters
clamped during the examination to achieve adequate bladder distention.
tumors of the bladder, similar to those involving the collecting system
or ureters, may have a variety of appearances. Superficial tumors may
be undetectable, which is one of the reasons why cystoscopy remains the
gold standard for evaluation of the bladder. Accumulating data, however,
indicates that CTU is reliable in detecting bladder cancer.13,14
More advanced tumors may be polypoid, sessile, or present as focal or
diffuse bladder wall thickening (Figure 12). Invasion into the
perivesical fat may be revealed as infiltration or irregular fat-bladder
Evaluation of the postoperative patient
or noninvasive tumors are often treated locally, with cystectomy
reserved for more advanced disease (muscle-invasive carcinomasor
recurrent, extensive superficial disease). Many surgical techniques are
available for urinary diversion following cystectomy and are created by
fashioning a section of bowel into a conduit or reservoir to which the
ureters can be anastomosed. Diversions may be formed utilizing an
isolated loop of ileum to form a conduit (Bricker, incontinent
diversion); a segment of colon to form a catheterizable reservoir
(continent diversion); or an orthotopic neobladder (Studer pouch,
continent) to which the urethra is anastomosed (Figure 13). These
diversions may be imaged on CTU.15 Complications related to
the surgery generally occur within the first 30 days and include
hematoma, abscess, conduit/reservoir anastomotic leak,hydronephrosis,
ischemia, and infection. The bowel anastomosis may leak, or a
postoperative ileus or bowel obstruction may occur. Late complications
include ureteral reflux with hydronephrosis, ureteral stricture, stone
formation, pouch necrosis, and tumor recurrence.
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- Nawfel RD, Judy PF, Schleipman AR, et al. Patient radiation dose at CT urography and conventional urography. Radiology. 2004;232: 126-132.
- Joffe SA, Servaes S, Okon S, et al. Multi-detector row CT urography in the evaluation of hematuria. Radiographics. 2003;23:1441-1456.
- Noroozian M, Cohan RH, Caoili EM, et al. Multislice CT urography: State of the art. Br J Radiol. 2004;77, Spec No 1:S74-S86.
- Nolte-Ernsting CC, Wildberger JE, Borchers H, et al. Multi-slice CT urography after diuretic injection: Initial results. Rofo. 2001;173:176-180.
- Kawashima A, Vrtiska TJ, LeRoy AJ, et al. CT urography. Radiographics. 2004;24 Suppl 1:S35-S54; discussion S55-S58.
S, Wang LL, Heiken JP, et al. Opacification of urinary bladder and
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TJ, Hartman RP, Kofler JM, et al. Spatial resolution and radiation dose
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Ciaschini MW, Remer EM, Baker ME, et al. Urinary calculi: Radiation
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- Silverman SG, Cohan RH, eds. In: CT Urography: An Atlas. 1st ed. Philadelphia, Pa: Lippincott Williams and Wilkins; 2007.
- Federle MP, Jeffrey RB, Desser TS, et al. In: Diagnostic Imaging: Abdomen. Salt Lake City: Amirsys; 2004.
- Wasserman NF, La Pointe S, Posalaky IP. Ureteral pseudodiverticulosis. Radiology. 1985;155:561-566.
- Sadow CA, Silverman SG, O’Leary MP, et al. Bladder cancer detection with CT urography in an academic medical center. Radiology. 2008;249:195-202.
- Park SB, Kim JK, Lee HJ, et al. Hematuria: Portal venous phase multi detector row CT of the bladder--a prospective study. Radiology. 2007;245:798-805.
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