- Email: [email protected]
Diagnosis of Medullary Sponge Kidney by Computed Tomographic Urography
Diagnosis of Medullary Sponge Kidney by Computed Tomographic Urography Anna M. Maw, MA,1 Alec J. Megibow, MD, MPH, FACR,1,2 Michael Grasso, MD,3 and David S. Goldfarb, MD, FASN1,3,4 The diagnosis of medullary sponge kidney traditionally was established by means of intravenous pyelography. Beginning in the mid-1990s, intravenous pyelography rapidly was supplanted by computed axial tomography as the preferred imaging study for evaluating patients with renal stone disease. Conventional computed tomographic imaging has not been satisfactory for diagnosing medullary sponge kidney. The introduction of multidetector-row computed tomography in 1999 allowed radiologists to acquire images composed of elements allowing the creation of high-resolution 3-dimensional displays. Computed tomographic urography is an imaging technique that provides both cross-sectional displays and images of the contrast-filled renal collecting systems, ureters, and urinary bladder that are the equivalent of intravenous pyelography. We report a case of medullary sponge kidney diagnosed by means of 3-dimensional multidetector-row computed tomographic urography. Am J Kidney Dis 50:146-150. © 2007 by the National Kidney Foundation, Inc. INDEX WORDS: Kidney/abnormalities; nephrocalcinosis; urography; kidney calculi; tomography, spiral computed.
T
he diagnosis of medullary sponge kidney (MSK) traditionally was established by means of intravenous pyelography (IVP). The diagnosis of MSK is based on visualization of dilated collecting tubules that may or may not contain calculi. IVP shows the classic appearance, described as a “papillary blush” or “paint brush.” This appearance is the direct result of pooling of contrast material within the dilated collecting tubules located within the tips of the renal papilla. The disease may affect one, both, or only portions of the kidneys. Beginning in the mid-1990s, IVP rapidly was supplanted by computed axial tomography (CT) as the preferred imaging study for evaluating patients with renal stone disease.1 Conventional computed tomographic imaging has not been satisfactory for diagnosing MSK; thus, it was considered possible that the diagnosis would virtually disapFrom the 1New York University School of Medicine; 2 Department of Radiology, New York University School of Medicine; 3Department of Urology, St Vincents Hospital; and 4Nephrology Section, New York Harbor VA Medical Center, New York, NY. Received November 25, 2006. Accepted in revised form March 27, 2007. Originally published online as doi: 10.1053/j.ajkd.2007.03.020 on May 15, 2007. Address correspondence to David S. Goldfarb, MD, FASN, Nephrology Section/111G, New York DVAMC, 423 E. 23 St, New York, NY 10010. E-mail: [email protected] © 2007 by the National Kidney Foundation, Inc. 0272-6386/07/5001-0018$32.00/0 doi:10.1053/j.ajkd.2007.03.020 146
pear.2 Although neither the absolute sensitivity nor specificity of IVP for MSK was established, resolution for details of the collecting system is greater for IVP than for conventional CT. Even a recent case report showed IVP findings without referring to the infrequency with which IVP is now performed.3 The introduction of multidetector-row CT (MDCT) in 1999 allowed radiologists to acquire images composed of elements allowing the creation of high-resolution 3-dimensional (3D) displays. Computed tomographic urography is an imaging technique that provides both cross-sectional displays and images of the contrast-filled renal collecting systems, ureters, and urinary bladder that are the equivalent of IVP. We report a case of MSK diagnosed by means of 3D multidetector-row computed tomographic urography. CASE REPORT A 56-year-old woman presented to her internist with symptoms consistent with cystitis. Urinary tract infection was diagnosed, and the patient was treated with a 5-day course of trimethoprim-sulfamethoxazole. Despite this, her symptoms progressed to include intermittent hematuria, fever, and left flank pain. She was referred to a urologist approximately 2 weeks after the initial onset of symptoms. The patient’s medical and surgical history included a single episode of pneumonia earlier that year and 3 previous surgical procedures: simple hysterectomy for fibroids, appendectomy, and lumbar diskectomy. The patient had no other history of genitourinary problems. She reported a diet high in animal protein and few dairy products. Her father had nephrolithiasis, but the cause and composition of his stones was not known. No other family members, including her
American Journal of Kidney Diseases, Vol 50, No 1 (July), 2007: pp 146-150
CT Urography for Medullary Sponge Kidney
147
Figure 1. Representative images from the first phase of a multidetector-row computed tomographic urogram show bilateral nonobstructing intrarenal calculi (arrows). Similarsized calculi could be seen scattered throughout both kidneys.
children, had a history of related genitourinary or metabolic problems. On physical examination, the patient was 5 feet 3 inches tall (134.6 cm) and weighed 142 lbs (64.5 kg). She was afebrile, blood pressure was 130/90 mm Hg, and pulse was 92 beats/min. She had no flank or suprapubic tenderness at the time of the examination. Serum chemistry test results were unremarkable, with blood urea nitrogen level of 23 mg/dL (8.2 mmol/L), creatinine level of 0.6 mg/dL (53 mol/L), and white blood cell count of 8.3 ⫻ 103 /L (8 ⫻ 109/L). Urinalysis was dippositive for leukocytes, blood, and protein with pH of 5.0. Microscopic examination showed white blood cells, red blood cells, and bacterial rods. Urine culture was positive for
Escherichia coli, and an appropriate course of levofloxacin was prescribed. A multidetector-row computed tomographic urogram immediately was obtained. A 3-phase acquisition (unenhanced through the kidneys, abdominal/pelvic acquisition ⬃90 seconds after intravenous administration of low-osmolality contrast medium in the nephrographic phase, and abdominal/ pelvic acquisition 8 minutes later in the urographic phase) was obtained on a 16-detector row MDCT scanner (Siemens Sensation 16; Siemens Medical Systems, Forchiem, Germany). Each acquisition was obtained using a 16 ⫻ 0.75-mm detector configuration, allowing the creation of images composed of 1 mm near isotropic voxels. The 1-mm images acquired from the urographic phase were transferred to a 3D
Figure 2. Contrastenhanced maximum intensity projection 3-dimensional image from multidetector-row computed tomographic urogram shows characteristic papillary blush (arrows) associated with scattered calculi within the dilated collecting tubules. The computed tomographic demonstration is equivalent to the well-documented intravenous pyelography findings.
148
Maw et al
workstation (Leonardo; Siemens Medical Systems). This workstation is equipped with 3D software allowing the production of high-resolution volume-rendered and maximum intensity projection images. Because contrast fills the pelvicalyceal system, ureter, and bladder, the resultant images simulate traditional IVP images. The unenhanced images showed multiple bilateral nonobstructing intrarenal calculi (Fig 1). 3D volume-rendered and maximum intensity projection images showed the papillary blush and abnormal collecting ducts, some of which contained calculi characteristic of MSK (Fig 2). Normal maximum intensity projection renderings from a multidetector-row computed tomographic urogram offer excellent visualization of the pelvicalyceal system, ureters, and bladder and showed no papillary blush (Fig 3). A traditional IVP of a different patient with MSK is shown for comparison (Fig 4). A follow-up renal sonogram was obtained that showed increased echogenicity of medullary pyramids and varying degrees of caliectasis, findings consistent with MSK.
DISCUSSION
This is the first report, to our knowledge, of MSK diagnosed by means of 3D volume-rendered imaging acquired during the urographic
Figure 3. Normal maximum intensity projection rendering from multidetector-row computed tomographic urogram. There is no papillary blush, but excellent visualization of the pelvicalyceal system, ureters, and bladder. Data are filtered to enhance only structures (in this case, the pelvicalyceal system) of clinical and diagnostic relevance.
phase of a multidetector computed tomographic urogram. Demonstration of characteristic findings, like those seen on IVP, establishes the presence of MSK in an individual patient and are considered diagnostic. Diagnostic findings include papillary blush in mild cases and linear striations (“paint brush”) and papillary bouquets in more severe cases. These findings are the direct result of pooling of contrast in the dilated collecting ducts in the renal papilla. In most cases, involvement is bilateral; however, findings may be unilateral or even involve a single papilla.2,4 Medullary nephrocalcinosis, an associated finding, may or may not be present. A large proportion of patients with MSK are asymptomatic and therefore remain undiagnosed. Alternatively, the condition is diagnosed when IVP is performed for flank pain or diagnosed incidentally when IVP is performed for indications other than renal colic. The relative infrequency of IVP performance today has led some to speculate that the diagnosis would disappear.2 Although the prevalence in the general population is unknown, 12% to 20% of calcium stone formers carry this diagnosis, and the diagnosis is made in 1 in every 200 IVPs.5 Computed tomographic urography is ideally suited to the evaluation of patients with hematuria. Noncontrast MDCT is significantly more sensitive to urinary calculi than plain films. The combination of unenhanced and nephrographic phase images can evaluate whether a cortical mass enhances, and the urographic phase can visualize the pelvicalyceal system, ureters, and bladder, enabling the detection of small irregularities of the urothelium.6-11 Older reports suggested that IVP was more sensitive and specific than conventional single-slice axial CT or ultrasonography at detecting MSK; however, the sensitivity of single-slice contrastenhanced CT for MSK is limited because display of the pelvicalyceal system is suboptimal in the axial plane. The ability of radiologists to create high-resolution computed tomographic urographic images can overcome this limitation and further diminish the importance of IVP to make this diagnosis. In addition, MDCT is widely available and has contraindications identical to IVP; namely, a history of severe
CT Urography for Medullary Sponge Kidney
149
Figure 4. Severe bilateral medullary sponge kidney in a different patient by means of conventional intravenous pyelography. The collecting tubules are dilated, producing a blush-like appearance. There is bilateral cortical loss. Dense calcifications are present bilaterally within distended collecting tubules.
allergic reaction to iodinated contrast media or renal failure. In addition, although it is more expensive than IVP (⬃$500 versus $150), MDCT provides significantly more information, in part by inclusion of the other abdominal organs. Although there is no specific therapy for patients with MSK, establishing the diagnosis has clinical value because it identifies a given patient as being at high risk of stone formation and recurrent urinary tract infection. Gambaro et al2 recently recommended that IVP continue to be a necessary step in the workup of recurrent calcium stone formation for this reason. In the current era, we believe well-performed computed tomographic urography may be the best available imaging technique. Although contrast is not routinely required for computed tomographic evaluation of renal colic or stones, urologists often continue to prefer a study with contrast, particularly if urological intervention is planned. Current estimates of radiation dose to patients undergoing computed tomographic urography suggest a 1.5-fold increase in exposure compared with IVP.11 However, current MDCT technology allows the performance of studies using a variety of dose-reducing technologies. Implementation of these techniques could decrease the dose to one equivalent to high-quality IVP. This case shows that 3D volume-rendered imaging acquired during the urographic phase of
a multidetector computed tomographic urogram can establish the diagnosis of MSK. The current literature suggests that single-slice helical CT, ultrasonography, and magnetic resonance imaging are not able to detect findings specific to MSK.12-14 However, computed tomographic urography with 3D volume-rendered imaging is comparable to IVP for the diagnosis of MSK. Considering the high resolution of this technique and its wide availability, it seems likely that clinicians involved in the management of patients with urinary tract disease will be able to rely on this technique to establish the diagnosis of MSK. ACKNOWLEDGEMENTS Support: None. Financial Disclosure: None.
REFERENCES 1. Amis ES: Epitaph for the urogram. Radiology 213:639640, 1999 2. Gambaro G, Feltrin GP, Lupo A, Bonfante L, D’Angelo A, Antonello A: Medullary sponge kidney (Lenarduzzi– Cacchi–Ricci disease). A Padua Medical School discovery in the 1930s. Kidney Int 69:663-670, 2006 3. Lee S, Jang YB, Kang KP, Kim W, Park SK: Medullary sponge kidney. Kidney Int 70:979, 2006 4. Elkin M, Bernstein J: Cystic diseases of the kidney. Clin Radiol 20:65-82, 1969 5. Yagisawa T, Kobayashi C, Hayashi T, Yoshida A, Toma H: Contributory metabolic factors in the development of nephrolithiasis in patients with medullary sponge kidney. Am J Kidney Dis 37:1140-1143, 2001
150 6. Sheth S, Fishman EK: Multi-detector row CT of the kidneys and urinary tract: Techniques and applications in the diagnosis of benign diseases. Radiographics 24:e20, 2004 7. Vrtiska TJ: Quantitation of stone burden imaging advances. Urol Res 33:398-402, 2005 8. Caoili EM, Cohan RH, Korobkin M, et al: Urinary tract abnormalities: Initial experience with multi-detector row CT urography. Radiology 222:353-360, 2002 9. Kawamoto S, Horton KM, Fishman EK: Computed tomography urography with 16-channel multidetector computed tomography: a pictorial review. J Comput Assist Tomogr 28:581-587, 2004 10. Raptopoulos V, McNamara A: Improved pelvicalyceal visualization with multidetector computed tomogra-
Maw et al phy urography; Comparison with helical computed tomography. Eur Radiol 15:1834-1840, 2005 11. Nawfel RD, Judy PF, Schleipman AR, Silverman SG: Patient radiation dose at CT urography and conventional urography. Radiology 232:126-132, 2004 12. Ginalski JM, Schnyder P, Portmann L, Jaeger P: Medullary sponge kidney on axial computed tomography: Comparison with excretory urography. Eur J Radiol 12:104-107, 1991 13. Schepens D, Verswijvel G, Kuypers D, Vanrenterghem Y: Renal cortical nephrocalcinosis. Nephrol Dial Transplant 15:1080-1082, 2000 14. Lang EK, Macchia RJ, Thomas R, et al: Improved detection of renal pathologic features on multiphasic helical CT compared with IVU in patients presenting with microscopic hematuria. Urology 61:528-532, 2003
T
he diagnosis of medullary sponge kidney (MSK) traditionally was established by means of intravenous pyelography (IVP). The diagnosis of MSK is based on visualization of dilated collecting tubules that may or may not contain calculi. IVP shows the classic appearance, described as a “papillary blush” or “paint brush.” This appearance is the direct result of pooling of contrast material within the dilated collecting tubules located within the tips of the renal papilla. The disease may affect one, both, or only portions of the kidneys. Beginning in the mid-1990s, IVP rapidly was supplanted by computed axial tomography (CT) as the preferred imaging study for evaluating patients with renal stone disease.1 Conventional computed tomographic imaging has not been satisfactory for diagnosing MSK; thus, it was considered possible that the diagnosis would virtually disapFrom the 1New York University School of Medicine; 2 Department of Radiology, New York University School of Medicine; 3Department of Urology, St Vincents Hospital; and 4Nephrology Section, New York Harbor VA Medical Center, New York, NY. Received November 25, 2006. Accepted in revised form March 27, 2007. Originally published online as doi: 10.1053/j.ajkd.2007.03.020 on May 15, 2007. Address correspondence to David S. Goldfarb, MD, FASN, Nephrology Section/111G, New York DVAMC, 423 E. 23 St, New York, NY 10010. E-mail: [email protected] © 2007 by the National Kidney Foundation, Inc. 0272-6386/07/5001-0018$32.00/0 doi:10.1053/j.ajkd.2007.03.020 146
pear.2 Although neither the absolute sensitivity nor specificity of IVP for MSK was established, resolution for details of the collecting system is greater for IVP than for conventional CT. Even a recent case report showed IVP findings without referring to the infrequency with which IVP is now performed.3 The introduction of multidetector-row CT (MDCT) in 1999 allowed radiologists to acquire images composed of elements allowing the creation of high-resolution 3-dimensional (3D) displays. Computed tomographic urography is an imaging technique that provides both cross-sectional displays and images of the contrast-filled renal collecting systems, ureters, and urinary bladder that are the equivalent of IVP. We report a case of MSK diagnosed by means of 3D multidetector-row computed tomographic urography. CASE REPORT A 56-year-old woman presented to her internist with symptoms consistent with cystitis. Urinary tract infection was diagnosed, and the patient was treated with a 5-day course of trimethoprim-sulfamethoxazole. Despite this, her symptoms progressed to include intermittent hematuria, fever, and left flank pain. She was referred to a urologist approximately 2 weeks after the initial onset of symptoms. The patient’s medical and surgical history included a single episode of pneumonia earlier that year and 3 previous surgical procedures: simple hysterectomy for fibroids, appendectomy, and lumbar diskectomy. The patient had no other history of genitourinary problems. She reported a diet high in animal protein and few dairy products. Her father had nephrolithiasis, but the cause and composition of his stones was not known. No other family members, including her
American Journal of Kidney Diseases, Vol 50, No 1 (July), 2007: pp 146-150
CT Urography for Medullary Sponge Kidney
147
Figure 1. Representative images from the first phase of a multidetector-row computed tomographic urogram show bilateral nonobstructing intrarenal calculi (arrows). Similarsized calculi could be seen scattered throughout both kidneys.
children, had a history of related genitourinary or metabolic problems. On physical examination, the patient was 5 feet 3 inches tall (134.6 cm) and weighed 142 lbs (64.5 kg). She was afebrile, blood pressure was 130/90 mm Hg, and pulse was 92 beats/min. She had no flank or suprapubic tenderness at the time of the examination. Serum chemistry test results were unremarkable, with blood urea nitrogen level of 23 mg/dL (8.2 mmol/L), creatinine level of 0.6 mg/dL (53 mol/L), and white blood cell count of 8.3 ⫻ 103 /L (8 ⫻ 109/L). Urinalysis was dippositive for leukocytes, blood, and protein with pH of 5.0. Microscopic examination showed white blood cells, red blood cells, and bacterial rods. Urine culture was positive for
Escherichia coli, and an appropriate course of levofloxacin was prescribed. A multidetector-row computed tomographic urogram immediately was obtained. A 3-phase acquisition (unenhanced through the kidneys, abdominal/pelvic acquisition ⬃90 seconds after intravenous administration of low-osmolality contrast medium in the nephrographic phase, and abdominal/ pelvic acquisition 8 minutes later in the urographic phase) was obtained on a 16-detector row MDCT scanner (Siemens Sensation 16; Siemens Medical Systems, Forchiem, Germany). Each acquisition was obtained using a 16 ⫻ 0.75-mm detector configuration, allowing the creation of images composed of 1 mm near isotropic voxels. The 1-mm images acquired from the urographic phase were transferred to a 3D
Figure 2. Contrastenhanced maximum intensity projection 3-dimensional image from multidetector-row computed tomographic urogram shows characteristic papillary blush (arrows) associated with scattered calculi within the dilated collecting tubules. The computed tomographic demonstration is equivalent to the well-documented intravenous pyelography findings.
148
Maw et al
workstation (Leonardo; Siemens Medical Systems). This workstation is equipped with 3D software allowing the production of high-resolution volume-rendered and maximum intensity projection images. Because contrast fills the pelvicalyceal system, ureter, and bladder, the resultant images simulate traditional IVP images. The unenhanced images showed multiple bilateral nonobstructing intrarenal calculi (Fig 1). 3D volume-rendered and maximum intensity projection images showed the papillary blush and abnormal collecting ducts, some of which contained calculi characteristic of MSK (Fig 2). Normal maximum intensity projection renderings from a multidetector-row computed tomographic urogram offer excellent visualization of the pelvicalyceal system, ureters, and bladder and showed no papillary blush (Fig 3). A traditional IVP of a different patient with MSK is shown for comparison (Fig 4). A follow-up renal sonogram was obtained that showed increased echogenicity of medullary pyramids and varying degrees of caliectasis, findings consistent with MSK.
DISCUSSION
This is the first report, to our knowledge, of MSK diagnosed by means of 3D volume-rendered imaging acquired during the urographic
Figure 3. Normal maximum intensity projection rendering from multidetector-row computed tomographic urogram. There is no papillary blush, but excellent visualization of the pelvicalyceal system, ureters, and bladder. Data are filtered to enhance only structures (in this case, the pelvicalyceal system) of clinical and diagnostic relevance.
phase of a multidetector computed tomographic urogram. Demonstration of characteristic findings, like those seen on IVP, establishes the presence of MSK in an individual patient and are considered diagnostic. Diagnostic findings include papillary blush in mild cases and linear striations (“paint brush”) and papillary bouquets in more severe cases. These findings are the direct result of pooling of contrast in the dilated collecting ducts in the renal papilla. In most cases, involvement is bilateral; however, findings may be unilateral or even involve a single papilla.2,4 Medullary nephrocalcinosis, an associated finding, may or may not be present. A large proportion of patients with MSK are asymptomatic and therefore remain undiagnosed. Alternatively, the condition is diagnosed when IVP is performed for flank pain or diagnosed incidentally when IVP is performed for indications other than renal colic. The relative infrequency of IVP performance today has led some to speculate that the diagnosis would disappear.2 Although the prevalence in the general population is unknown, 12% to 20% of calcium stone formers carry this diagnosis, and the diagnosis is made in 1 in every 200 IVPs.5 Computed tomographic urography is ideally suited to the evaluation of patients with hematuria. Noncontrast MDCT is significantly more sensitive to urinary calculi than plain films. The combination of unenhanced and nephrographic phase images can evaluate whether a cortical mass enhances, and the urographic phase can visualize the pelvicalyceal system, ureters, and bladder, enabling the detection of small irregularities of the urothelium.6-11 Older reports suggested that IVP was more sensitive and specific than conventional single-slice axial CT or ultrasonography at detecting MSK; however, the sensitivity of single-slice contrastenhanced CT for MSK is limited because display of the pelvicalyceal system is suboptimal in the axial plane. The ability of radiologists to create high-resolution computed tomographic urographic images can overcome this limitation and further diminish the importance of IVP to make this diagnosis. In addition, MDCT is widely available and has contraindications identical to IVP; namely, a history of severe
CT Urography for Medullary Sponge Kidney
149
Figure 4. Severe bilateral medullary sponge kidney in a different patient by means of conventional intravenous pyelography. The collecting tubules are dilated, producing a blush-like appearance. There is bilateral cortical loss. Dense calcifications are present bilaterally within distended collecting tubules.
allergic reaction to iodinated contrast media or renal failure. In addition, although it is more expensive than IVP (⬃$500 versus $150), MDCT provides significantly more information, in part by inclusion of the other abdominal organs. Although there is no specific therapy for patients with MSK, establishing the diagnosis has clinical value because it identifies a given patient as being at high risk of stone formation and recurrent urinary tract infection. Gambaro et al2 recently recommended that IVP continue to be a necessary step in the workup of recurrent calcium stone formation for this reason. In the current era, we believe well-performed computed tomographic urography may be the best available imaging technique. Although contrast is not routinely required for computed tomographic evaluation of renal colic or stones, urologists often continue to prefer a study with contrast, particularly if urological intervention is planned. Current estimates of radiation dose to patients undergoing computed tomographic urography suggest a 1.5-fold increase in exposure compared with IVP.11 However, current MDCT technology allows the performance of studies using a variety of dose-reducing technologies. Implementation of these techniques could decrease the dose to one equivalent to high-quality IVP. This case shows that 3D volume-rendered imaging acquired during the urographic phase of
a multidetector computed tomographic urogram can establish the diagnosis of MSK. The current literature suggests that single-slice helical CT, ultrasonography, and magnetic resonance imaging are not able to detect findings specific to MSK.12-14 However, computed tomographic urography with 3D volume-rendered imaging is comparable to IVP for the diagnosis of MSK. Considering the high resolution of this technique and its wide availability, it seems likely that clinicians involved in the management of patients with urinary tract disease will be able to rely on this technique to establish the diagnosis of MSK. ACKNOWLEDGEMENTS Support: None. Financial Disclosure: None.
REFERENCES 1. Amis ES: Epitaph for the urogram. Radiology 213:639640, 1999 2. Gambaro G, Feltrin GP, Lupo A, Bonfante L, D’Angelo A, Antonello A: Medullary sponge kidney (Lenarduzzi– Cacchi–Ricci disease). A Padua Medical School discovery in the 1930s. Kidney Int 69:663-670, 2006 3. Lee S, Jang YB, Kang KP, Kim W, Park SK: Medullary sponge kidney. Kidney Int 70:979, 2006 4. Elkin M, Bernstein J: Cystic diseases of the kidney. Clin Radiol 20:65-82, 1969 5. Yagisawa T, Kobayashi C, Hayashi T, Yoshida A, Toma H: Contributory metabolic factors in the development of nephrolithiasis in patients with medullary sponge kidney. Am J Kidney Dis 37:1140-1143, 2001
150 6. Sheth S, Fishman EK: Multi-detector row CT of the kidneys and urinary tract: Techniques and applications in the diagnosis of benign diseases. Radiographics 24:e20, 2004 7. Vrtiska TJ: Quantitation of stone burden imaging advances. Urol Res 33:398-402, 2005 8. Caoili EM, Cohan RH, Korobkin M, et al: Urinary tract abnormalities: Initial experience with multi-detector row CT urography. Radiology 222:353-360, 2002 9. Kawamoto S, Horton KM, Fishman EK: Computed tomography urography with 16-channel multidetector computed tomography: a pictorial review. J Comput Assist Tomogr 28:581-587, 2004 10. Raptopoulos V, McNamara A: Improved pelvicalyceal visualization with multidetector computed tomogra-
Maw et al phy urography; Comparison with helical computed tomography. Eur Radiol 15:1834-1840, 2005 11. Nawfel RD, Judy PF, Schleipman AR, Silverman SG: Patient radiation dose at CT urography and conventional urography. Radiology 232:126-132, 2004 12. Ginalski JM, Schnyder P, Portmann L, Jaeger P: Medullary sponge kidney on axial computed tomography: Comparison with excretory urography. Eur J Radiol 12:104-107, 1991 13. Schepens D, Verswijvel G, Kuypers D, Vanrenterghem Y: Renal cortical nephrocalcinosis. Nephrol Dial Transplant 15:1080-1082, 2000 14. Lang EK, Macchia RJ, Thomas R, et al: Improved detection of renal pathologic features on multiphasic helical CT compared with IVU in patients presenting with microscopic hematuria. Urology 61:528-532, 2003