Published online January 16, 2004, 10.1148/rg.e20
RadioGraphics 2004;24:e20
© RSNA, 2004
Multi-Detector Row CT of the Kidneys and Urinary Tract: Techniques and Applications in the Diagnosis of Benign Diseases1
Sheila Sheth, MD and
Elliot K. Fishman, MD
1 From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, 600 N Wolfe St, Baltimore, Md 21287. Presented as an educational exhibit at the 2002 RSNA scientific assembly. Received April 18, 2003, revision requested August 12, final revision received and accepted November 28. Address correspondence to S.S. (e-mail: ssheth@jhmi.edu).
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Abstract
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Multi–detector row helical computed tomography (CT) offers considerable advantages in evaluation of the urinary tract. It has the potential to become the single imaging modality used for comprehensive evaluation and treatment planning of most conditions affecting the kidneys and urinary tract, making conventional diagnostic techniques such as intravenous urography and angiography nearly obsolete. This article illustrates important selected applications of multidetector CT in the evaluation of benign conditions of the kidneys and upper urinary tract, including evaluation of the renal arterial and venous anatomy in preparation for surgery, diagnosis of renal artery stenosis and aneurysms, assessment of the renal veins, imaging of inflammatory and infectious renal diseases and evaluation of selected benign pathologic processes of the urinary tract.
© RSNA, 2004
Index Terms: Aneurysm, renal, 961.73 • Computed tomography (CT), technology, 80.1211 • Kidney, CT, 81.12115 • Kidney, infection, 81.21 • Kidney, transplantation, 81.455 • Renal arteries, CT, 961.12115 • Renal arteries, stenosis or obstruction, 961.72
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Multi-Detector Row Helical CT
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Multi–detector row computed tomography (CT) is the latest improvement in helical CT technology, in which simultaneous activation of multiple detector rows positioned along the z axis allows acquisition of interweaving helical sections.
Advantages of Multidetector CT
Multidetector CT technology allows faster data acquisition times (average of 2.6 times faster for four–detector row CT) compared with single-detector CT, without any loss of image quality. Rapid data acquisition times are possible because of short gantry rotation intervals combined with multiple detectors providing increased coverage along the z axis (1). This combination, along with short interscan delays, allows image acquisitions in multiple phases of renal parenchymal enhancement and contrast material excretion in the collecting system after administration of a single bolus of intravenous contrast material (2). Timing of the contrast material bolus can thus be optimized to evaluate the arterial and venous supply of the kidney as well as the renal parenchyma and collecting system.
Another advantage of multidetector CT is improved z-axis spatial resolution. In multidetector CT, the user selects a specific beam collimation but does not need to choose a particular section thickness in advance (3). This parameter can be implemented after completion of data acquisition. Thinner collimation improves the quality of three-dimensional (3D) data sets and allows generation of exquisite 3D images of the renal arteries and veins, comparable with conventional angiograms and venograms. Three-dimensional reformations of the collecting system can potentially obviate conventional urography.
Challenges Posed by Multidetector CT
The benefits of multidetector CT outlined above also pose significant challenges that need to be understood. These challenges include selection of optimal imaging sequences, controlling radiation exposure to the patient, and efficiently managing the large amount of data generated.
Tailoring the Examination to the Clinical Indication
It is fundamental to carefully select the appropriate imaging sequence to evaluate a specific clinical indication and to choose the phase or combination of phases that is most appropriate (Table 1). This becomes critical to minimize radiation exposure to the patient and "image overload" to the radiologist (4). As important, significant abnormalities can be obscured or become less conspicuous if the timing is not optimal. The specific scanning protocols we use are outlined for each indication.
Phases of Contrast Enhancement in the Kidney and Collecting System
Four distinct phases of renal enhancement can be imaged depending on acquisition time (Fig 1). The timing of these phases varies with the speed of intravenous contrast material injection. We routinely inject 100–120 mL of nonionic contrast medium in a large antecubital vein at a rate of 3 mL/sec. The patients are given 500–750 mL of water to drink over a 15–20 minute period before the start of the examination.
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Figure 1a. Phases of renal enhancement at multidetector CT. (a) Unenhanced axial CT at level of renal hilum. (b) Late arterial phase axial CT at level of renal hilum. There is good opacification of the left renal artery (black arrow) and vein (white arrow). (c) Nephrographic phase axial CT at level of renal hilum. (d) Excretory phase axial CT at level of renal hilum.
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Figure 1b. Phases of renal enhancement at multidetector CT. (a) Unenhanced axial CT at level of renal hilum. (b) Late arterial phase axial CT at level of renal hilum. There is good opacification of the left renal artery (black arrow) and vein (white arrow). (c) Nephrographic phase axial CT at level of renal hilum. (d) Excretory phase axial CT at level of renal hilum.
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Figure 1c. Phases of renal enhancement at multidetector CT. (a) Unenhanced axial CT at level of renal hilum. (b) Late arterial phase axial CT at level of renal hilum. There is good opacification of the left renal artery (black arrow) and vein (white arrow). (c) Nephrographic phase axial CT at level of renal hilum. (d) Excretory phase axial CT at level of renal hilum.
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Figure 1d. Phases of renal enhancement at multidetector CT. (a) Unenhanced axial CT at level of renal hilum. (b) Late arterial phase axial CT at level of renal hilum. There is good opacification of the left renal artery (black arrow) and vein (white arrow). (c) Nephrographic phase axial CT at level of renal hilum. (d) Excretory phase axial CT at level of renal hilum.
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The arterial phase is a short phase that occurs about 15–25 seconds after the start of intravenous contrast medium injection and is marked by maximum opacification of the renal arteries. The renal veins also usually opacify in the late arterial phase.
The corticomedullary (angionephrographic) phase starts at about 30–40 seconds after the start of contrast medium injection. There is intense enhancement of the renal cortex due to preferential arterial flow to the cortex and glomerular filtration of the contrast material, while the medulla remains relatively less enhanced. This is also the best phase for maximum opacification of the renal veins.
The nephrographic phase begins at 80–120 seconds after the start of contrast medium injection. Tubular filtration of contrast material produces homogeneous enhancement of the renal parenchyma. This is the best phase for detection of subtle parenchymal lesions.
The excretory or urographic phase starts at 180 seconds (3 minutes) after the start of contrast medium injection. Excretion of the contrast material allows opacification of the calyces, renal pelvises, and ureters, while the intensity of the nephrogram progressively declines. We routinely acquire excretory phase images at 4–5 minutes to ensure opacification of the ureters.
In many instances, a precontrast image acquisition series is mandatory to detect calcification and stones or to assess initial attenuation of indeterminate renal lesions to be able to define their enhancement patterns.
Radiation Dose to the Patient
One of the main drawbacks of multidetector CT is the increased risk of potentially substantial radiation exposure to patients, compared with that of single-detector CT. Because of the geometry of multidetector scanners, as the width of the section exceeds the scan width, a penumbra of radiation extends beyond the field of useful energy, resulting in gratuitous radiation to the patient. This is particularly problematic when thin sections are used. The problem is compounded by the ability, and therefore temptation, to acquire multiple-phase images. As each additional imaging sequence increases the effective radiation dose to the patient, it becomes incumbent on the radiologist monitoring studies to carefully choose protocols tailored to answer the clinical question while minimizing radiation exposure to the patient (5)
Image Management and Postprocessing Techniques
As eloquently emphasized by Rubin (6), a paradigm shift needs to be embraced to handle the "data explosion" generated with multidetector CT. Film is rapidly becoming obsolete. Efficient interactive workstations designed both to handle the large number of axial images and to allow generation of reconstructed images simulating the conventional angiograms or urograms that clinicians are familiar with are essential (6). For optimal work flow, thicker 5-mm images are sent to the picture archiving and communication (PACS) station for interpretation of axial images. For 3D reconstruction, the volumetric data set reconstructed at 0.75–1 mm with overlapping sections is transferred to a free-standing Onyx Infinite Reality workstation (Silicon Graphics, Mountain View, Calif) equipped with 3D Virtuoso software (Siemens Medical Systems, Erlangen, Germany). The volume data set can be edited in real time, and the source images can be reviewed when necessary. In our department, as a rule, the radiologist interactively reviews the volumetric data sets and generates appropriate images that are then reviewed with the referring physician and printed. The length of time required for generating relevant images varies with the experience of the radiologist and the complexity of the case, but it is generally less than 5 minutes after an initial learning curve.
Several reconstruction techniques including maximum-intensity projection (MIP), multiplanar reconstruction, and volume rendering have been shown to be effective. With MIP, the maximum voxel intensity along a line of viewer projection in a given volume is displayed. High attenuation structures such as contrast material–filled vessels and the collecting system are nicely displayed in images resembling angiograms or urograms. Two disadvantages of MIP are the need for editing and high-density material such as calcium obscuring the area of interest. Multiplanar reconstruction demonstrates all structures within a predefined plane. However, since most structures of interest do not lie within a single plane, this technique is limited in the visualization of renal vasculature unless curved planar reformation is used. Volume rendering is the most versatile reconstruction technique, as it uses the information provided in the entire data set by assigning a specific degree of opacity to each attenuation value within the volume of interest. It also allows the viewer to interact with the data sets in real time, obviating complex editing (7,8). Thus, anatomic structures with varying degrees of opacity (eg, blood vessels, renal parenchyma, collecting system) can be visualized simultaneously. The main drawback of volume rendering is the need for more powerful computers and expensive workstations.
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CT Angiography of the Renal Arteries
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The main applications of CT angiography include evaluation of potential renal donors, evaluation of suspected renal artery stenosis or aneurysms, and demonstration and location of crossing vessels prior to pyeloplasty for ureteropelvic junction obstruction (9).
Technique and Scanning Protocol
The diagnostic accuracy of CT angiography of the renal arteries is greatly influenced by the selection of scanning parameters. The following principles should be applied to obtain high-quality image data (10): A bolus of 120–150 mL of contrast material (300–350 mg of iodine per milliliter) is injected at a rate of at least 3 mL/sec through a large-bore intravenous line. The images are acquired during the arterial plateau of contrast enhancement. The scanning protocol is further tailored to the precise clinical indication. In evaluation of potential renal donors, the scan area starts above the origin of the superior mesenteric artery and extends to the bifurcation of the common iliac arteries to include potential accessory renal arteries. Images are acquired in the arterial and venous phases of enhancement to display arterial and venous anatomy. This is followed by a scout urogram obtained at 4–5 minutes. In cases of suspected renal artery stenosis, unenhanced CT images are obtained. Only arterial phase images are necessary to locate the renal arteries in order to minimize coverage and optimize collimation. Thin collimation with 4 x 1-mm detectors and 1.25-mm section collimation and an overlapping reconstruction interval of 1 mm generate high-quality 3D images. Even higher-quality reconstructions can be achieved with the new 16-detector scanners. Postprocessing techniques include MIP and volume rendering. Table 2 presents the multidetector CT protocols for a renal donor for two different scanners.
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Evaluation of Potential Renal Donors
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Many recent articles have demonstrated the benefits of helical CT in the evaluation of potential renal donors (11–17. When properly performed, this single technique allows delineation of the size, number, and course of the renal arteries and veins, evaluation of the renal parenchyma and collecting system, and diagnosis of unsuspected conditions that preclude organ donation. CT angiography has been shown to depict 100% of main renal arteries and veins (11) and thus has replaced the previously used combination of intravenous urography and renal arteriography at considerable savings of cost and time. Alternatively, MR angiography is an effective technique for demonstrating renal vascular anatomy in these patients, although it may be slightly less sensitive (90% vs 93% in one series) for depicting small accessory renal arteries (11).
To determine if a potential donor is a suitable candidate and to choose the kidney to be harvested, the transplant surgeon must know the number of renal arteries for each kidney and be aware of the presence of prehilar arterial branching and potential variants in the number and course of the renal veins (12,13). The widespread use of laparoscopic surgical techniques, with their limited field of view, makes precise preoperative planning ever more crucial in avoiding potentially disastrous surprises.
Only approximately 70%–75% of subjects display classical renal arterial anatomy (Fig 2). Accessory renal arteries do not preclude laparoscopic nephrectomy but require modification of surgical technique and may lengthen procedure time (14). Multiple renal arteries are present in about one-third of kidneys. Accessory renal arteries arise from the aorta or the iliac arteries, and those supplying the polar regions tend to be smaller then the main arteries (Fig 3, Movie 1). The sensitivity of CT angiography in the detection of accessory renal arteries has been reported as approaching 77% with single-detector CT (15). These small accessory vessels were the most common source of error in one large study involving 154 renal donors (16). Expected improvement with use of multidetector CT was confirmed in a recently published series with 74 consecutive subjects. Fourteen of 18 accessory arteries found at surgery were detected preoperatively. Compared with surgical findings, the accuracy of multidetector CT in defining the number of renal arteries was 93% (17).
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Figure 3a. Multiple renal arteries in a 57-year-old potential renal donor. Two left renal arteries (arrows) are nicely depicted in the MIP image (a) as well as in the coronal volume-rendered image (b).
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Figure 3b. Multiple renal arteries in a 57-year-old potential renal donor. Two left renal arteries (arrows) are nicely depicted in the MIP image (a) as well as in the coronal volume-rendered image (b).
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The presence of prehilar branching of the renal artery should be reported, and measurement of the distance between the aorta and the first branch is helpful to the surgeon for planning the arterial anastomosis (Movie 2).
Approximately 15% of healthy subjects have more then one renal vein. Multiple renal veins and circumaortic and retroaortic left renal veins or bifid renal veins are easily demonstrated with multidetector CT (13) (Fig 4). Unusual location or size of lumbar, adrenal and gonadal veins should be reported to avoid potentially life-threatening hemorrhage during renal harvest.
Evaluation of the collecting system is important in detecting unexpected anatomic variants or urolithiasis and is traditionally performed with intravenous pyelography. We have found that a single scout image obtained at the completion of the imaging study of the collecting system provides sufficient information while limiting radiation dose to the patient (Fig 5).
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Diagnosis of Renal Artery Stenosis
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Renal artery stenosis is a surgically curable cause of refractory or accelerating hypertension. Because of its rarity (it has a prevalence of 1%–5%), noninvasive imaging plays an important role in screening high-risk patients. Atherosclerosis is responsible for approximately 60%–70% of cases and affects the origin or the proximal portion of the renal artery. Fibromuscular dysplasia, neurofibromatosis, Takayasu arteritis, and radiation are rare causes of renovascular hypertension.
Several studies that used single-detector helical CT have shown a sensitivity of 88%–92% and a specificity of 83%–98% in the diagnosis of a flow-limiting renal artery stenosis of 70% or greater (18,19). Those numbers are expected to improve with multidetector CT because of higher z-axis resolution, which allows near-isotropic imaging. Significantly, the demonstration of normal renal arteries has a negative predictive value of 95% in excluding renovascular hypertension (20).
The diagnosis of renal artery stenosis requires meticulous technique. The axial source images are reconstructed at 5 mm and sent to the workstation. Paraaxial and paracoronal images are reconstructed along the axis of the renal arteries, and the diameter of the maximum luminal narrowing is compared with the diameter of the normal portion of the artery.
Interpretation of renal artery stenosis studies is fraught with several potential difficulties. Because the renal arteries run parallel or oblique to the scan plane, direct measurement of the residual lumen diameter on axial images is not possible and the degree of stenosis can only be estimated (21). Accurate evaluation of the renal arteries can be potentially tedious and time-consuming. Interactive review of all images on a workstation and 3D display of the data are a necessity. Although both MIP and volume-rendering techniques have similar sensitivities for identifying flow-limiting stenosis, volume rendering has the advantage of being able to display calcified atherosclerotic plaques and the lumen at the same time (Fig 6).
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Figure 6. Right renal artery stenosis in a 65-year-old patient with evidence of right renal infarct at prior examination. Coronal volume-rendered image nicely demonstrates an 80% stenosis in the proximal right renal artery caused by a partially calcified plaque (white arrow). There is a large infarct involving the upper pole of the right kidney (black arrows).
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Although optimal technique can show main renal artery lesions in nearly all patients, the presence of a stenosis in small (2-mm diameter or less) accessory arteries remains an important pitfall and is one of the main causes of false-negative results (22).
In addition to direct evidence of renal artery stenosis, there are several important indirect corroborative signs: poststenotic dilatation, found to be 85% predictive of significant stenosis (18) (Fig 7); the finding of a small kidney with a smooth contour; thinning of the renal cortex; and the presence of a delayed and prolonged nephrogram (20).
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Figure 7a. Renal artery stenosis in a 52-year-old woman with hypertension. (a) Axial volume-rendered image in the arterial phase shows a tight stenosis at the origin of the right renal artery (arrow) with poststenotic dilatation. (b) Preangioplasty angiogram confirms the findings.
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Figure 7b. Renal artery stenosis in a 52-year-old woman with hypertension. (a) Axial volume-rendered image in the arterial phase shows a tight stenosis at the origin of the right renal artery (arrow) with poststenotic dilatation. (b) Preangioplasty angiogram confirms the findings.
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Similar CT technique has also been successfully used to check patency of renal artery stents (Fig 8) (23,24).
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Figure 8. Left renal artery stent in a 60-year-old man who was successfully treated for renovascular hypertension. Coronal volume-rendered image nicely demonstrates the stent at the origin of the left renal artery (arrow). The left renal artery beyond the stent is clearly patent.
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Renal Artery Aneurysms
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Atherosclerosis is the most common cause of renal artery aneurysms. Other causes include pregnancy, fibromuscular dysplasia, and neurofibromatosis. Pseudoaneurysms are usually posttraumatic, iatrogenic, or inflammatory (25) (Figs 9, 10).
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Figure 9a. Multiple left renal artery aneurysms in a 57-year-old woman. (a) Coronal MIP image shows three small aneurysms of the distal left renal artery (arrows). (b) Coronal volume-rendered image.
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Figure 9b. Multiple left renal artery aneurysms in a 57-year-old woman. (a) Coronal MIP image shows three small aneurysms of the distal left renal artery (arrows). (b) Coronal volume-rendered image.
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Figure 10. Pseudoaneurysm of a renal artery branch in a 72-year-old man with a history of partial nephrectomy of the right kidney for renal cell carcinoma. Coronal MIP image shows a pseudoaneurysm arising from a renal artery branch at the resection site. A large renal cell carcinoma replaces the lower pole of the left kidney.
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Diagnosis of Crossing Vessels in Ureteropelvic Junction Obstruction
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Vessels crossing a ureteropelvic junction obstruction contribute to the degree of hydronephrosis in up to 46% of these patients (Fig 11). Demonstration of these vessels and their location anterior or posterior to the obstruction facilitates surgical planning and limits potentially serious complications.
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Figure 11a. Crossing vessel in a patient with ureteropelvic junction obstruction. Coronal volume-rendered images from anterior (a) and posterior (b) show a lower pole artery (arrow) to the left kidney crossing a dilated renal pelvis.
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Figure 11b. Crossing vessel in a patient with ureteropelvic junction obstruction. Coronal volume-rendered images from anterior (a) and posterior (b) show a lower pole artery (arrow) to the left kidney crossing a dilated renal pelvis.
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Multidetector CT Evaluation of the Renal Veins
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Although specific evaluation of the renal veins is of paramount importance in patients with suspected renal cell carcinoma, bland thrombosis of a renal vein often presents with nonspecific symptoms such as hematuria or flank pain. Maximum opacification of the renal veins occurs during the corticomedullary phase of renal enhancement, which coincides with the portal venous inflow phase routinely used for abdominal CT imaging (9).
Patients with underlying acute renal vein thrombosis often present with flank pain, hematuria, and nephrotic syndrome (26). Although acute membranous glomerulonephritis is the most common cause of bland renal vein thrombosis, other risk factors include systemic lupus, diabetes, sepsis, and severe dehydration, particularly in children and the elderly (25,27).
In the acute phase, bland renal vein thrombosis is easily recognized: The affected kidney is enlarged, with a delayed and prolonged nephrogram due to a decrease in glomerular filtration and tubular compression caused by the interstitial edema. The renal vein is distended and filled with low-attenuation clot (Fig 12). Delayed images may be helpful to confirm the presence of thrombus and exclude a false-positive finding caused by mixing of poorly opacified blood from the lower extremities (25).
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Figure 12a. Right renal vein thrombosis in a 46-year-old woman with Escherichia coli urinary tract infection and pyelonephritis. (a) Axial CT image in the corticomedullary phase shows an enlarged right kidney with delayed function. The renal parenchyma appears infiltrated by the inflammatory process and interstitial edema. There is lack of opacification of the right renal vein and the inferior vena cava (arrow). (b) Axial CT image in the corticomedullary phase at the upper pole of the right kidney shows a normal inferior vena cava (arrow) at that level. (c) Coronal reformation shows the right renal vein thrombus (arrow) extending into the inferior vena cava.
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Figure 12b. Right renal vein thrombosis in a 46-year-old woman with Escherichia coli urinary tract infection and pyelonephritis. (a) Axial CT image in the corticomedullary phase shows an enlarged right kidney with delayed function. The renal parenchyma appears infiltrated by the inflammatory process and interstitial edema. There is lack of opacification of the right renal vein and the inferior vena cava (arrow). (b) Axial CT image in the corticomedullary phase at the upper pole of the right kidney shows a normal inferior vena cava (arrow) at that level. (c) Coronal reformation shows the right renal vein thrombus (arrow) extending into the inferior vena cava.
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Figure 12c. Right renal vein thrombosis in a 46-year-old woman with Escherichia coli urinary tract infection and pyelonephritis. (a) Axial CT image in the corticomedullary phase shows an enlarged right kidney with delayed function. The renal parenchyma appears infiltrated by the inflammatory process and interstitial edema. There is lack of opacification of the right renal vein and the inferior vena cava (arrow). (b) Axial CT image in the corticomedullary phase at the upper pole of the right kidney shows a normal inferior vena cava (arrow) at that level. (c) Coronal reformation shows the right renal vein thrombus (arrow) extending into the inferior vena cava.
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Collateral veins and thickening of the Gerota fascia are indirect signs and can be seen in subacute or chronic cases (28).
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Multidetector CT of Renal Inflammatory Disease
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Technique
Inflammatory renal diseases are generally well depicted with conventional single-detector CT. With the increasing availability of multidetector CT, however, careful consideration needs to be paid to the timing of image acquisition because imaging too early or too late may actually obscure disease processes in the renal parenchyma or render their detection more difficult. Abnormalities in renal perfusion associated with acute pyelonephritis are best depicted during homogeneous enhancement of the renal parenchyma in the nephrographic phase. This phase appears to be more sensitive then the corticomedullary phase in the detection of subtle lesions, particularly if the medulla is predominantly affected (4,29) (Figs 13, 14). Delayed postcontrast images (some authors advocate that images be obtained up to 3 hours after contrast material injection) may be invaluable in detection of subtle areas of persistent nephrogram caused by vasospasm in regions of focal inflammation (30) (Fig 15). Unenhanced images are helpful in diagnosing an underlying abnormality such as a staghorn calculus or in detection of parenchymal gas or hemorrhage.
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Figure 13a. Left renal abscess in a 46-year-old man with a history of human immunodeficiency virus (HIV) infection, left flank pain, and fevers. (a) Axial CT image in the corticomedullary phase of enhancement does not show any abnormality. (b) Axial CT image in the late nephrographic phase. The hypoenhancing lesion in the left renal parenchyma is clearly demonstrated (arrow). This case illustrates the importance of tailoring image acquisitions to the clinical indication. This small lesion would have been missed in the corticomedullary phase image. A few milliliters of pus were aspirated from this lesion.
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Figure 13b. Left renal abscess in a 46-year-old man with a history of human immunodeficiency virus (HIV) infection, left flank pain, and fevers. (a) Axial CT image in the corticomedullary phase of enhancement does not show any abnormality. (b) Axial CT image in the late nephrographic phase. The hypoenhancing lesion in the left renal parenchyma is clearly demonstrated (arrow). This case illustrates the importance of tailoring image acquisitions to the clinical indication. This small lesion would have been missed in the corticomedullary phase image. A few milliliters of pus were aspirated from this lesion.
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Figure 14a. Acute pyelonephritis of the right kidney in a 32-year-old HIV-positive man. (a) Corticomedullary phase contrast-enhanced axial CT shows an almost normal-appearing right kidney. (b) Early excretory phase contrast-enhanced axial CT clearly shows multiple low-attenuation lesions (arrows) in the right renal parenchyma.
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Figure 14b. Acute pyelonephritis of the right kidney in a 32-year-old HIV-positive man. (a) Corticomedullary phase contrast-enhanced axial CT shows an almost normal-appearing right kidney. (b) Early excretory phase contrast-enhanced axial CT clearly shows multiple low-attenuation lesions (arrows) in the right renal parenchyma.
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Figure 15a. Acute pyelonephritis of the left kidney in a 46-year-old woman. (a) Corticomedullary phase contrast-enhanced axial CT shows a patchy striated nephrogram in the left kidney (arrows). (b) There are areas of persistent enhancement (arrows) in the early excretory phase, likely due to vasospasm.
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Figure 15b. Acute pyelonephritis of the left kidney in a 46-year-old woman. (a) Corticomedullary phase contrast-enhanced axial CT shows a patchy striated nephrogram in the left kidney (arrows). (b) There are areas of persistent enhancement (arrows) in the early excretory phase, likely due to vasospasm.
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Acute Pyelonephritis
Acute pyelonephritis is a suppurative inflammation of the renal interstitial tissue due to an ascending urinary tract infection, usually caused by Gram-negative bacteria. Although uncomplicated acute pyelonephritis is usually diagnosed and treated on the basis of clinical findings, CT is increasingly being requested for evaluation of poor response to treatment, for detection of potential complications, and for diagnosis of underlying predisposing factors. Patients with poorly controlled diabetes, HIV infection, and immunocompromised state are especially prone to developing complications such as a renal abscess or spread of infection to the perinephric space.
The CT abnormalities reflect the underlying histologic abnormalities: There is poor concentration of intravenous contrast material within the renal tubules secondary to tubular obstruction caused by inflammatory debris associated with interstitial edema and vasospam. This results in the characteristic CT findings that include the so-called "striated nephrogram," caused by hypo- and hyperattenuating, alternating wedge-shaped lesions, areas of poorly defined corticomedullary differentiation, and focal cortical or subcortical areas of decreased attenuation (Fig 14). Global or focal enlargement of the kidney, obliteration of the renal sinus fat, thickening of the pelvicalyceal wall, and focal calyceal obliteration are useful secondary signs.
Emphysematous Pyelonephritis
Emphysematous pyelonephritis is a rare life-threatening, fulminant necrotizing infection of the renal parenchyma caused by gas-forming organisms, predominantly E coli, Proteus species, or Klebsiella pneumoniae. It primarily affects patients with poorly controlled diabetes or severe immunosuppression. Immediate treatment with surgical debridement or percutaneous drainage is mandatory to reduce mortality. CT is invaluable for rapid diagnosis and for determination of the extent of infection and prognosis. Typical CT findings include extensive destruction of the renal parenchyma, with mottled or streaky regions of gas within the parenchyma (Fig 16). In one series of 38 patients, Wan and coauthors found that the presence of large renal or perinephric fluid collections containing loculated gas or gas predominantly in the collecting system was associated with a better outcome (31).
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Figure 16a. Emphysematous pyelonephritis in a 45-year-old woman with sepsis. Axial (a) unenhanced and (b) corticomedullary phase CT shows extensive intraparenchymal gas (arrows) in a poorly functioning enlarged left kidney. Gas bubbles extend into the perinephric space.
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Figure 16b. Emphysematous pyelonephritis in a 45-year-old woman with sepsis. Axial (a) unenhanced and (b) corticomedullary phase CT shows extensive intraparenchymal gas (arrows) in a poorly functioning enlarged left kidney. Gas bubbles extend into the perinephric space.
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Xanthogranulomatous Pyelonephritis
Xanthogranulomatous pyelonephritis is an uncommon chronic infection resulting from long-standing urinary obstruction by urolithiasis. It classically occurs in middle-aged women who often present with a history of recurrent urinary tract infections, flank pain, and low-grade fever. E coli and Proteus mirabilis are the most common infectious agents. The affected kidney is hydronephrotic and non- or poorly functioning. Histologic evaluation reveals extensive destruction of the renal parenchyma and infiltration with lipid-laden macrophages (32).
The combination of a precontrast sequence and nephrographic phase and delayed images produces typical CT findings of renal enlargement, staghorn calulus, poor or no renal function, and multiple round low-attenuation masses that represent the markedly hydronephrotic collecting system (Fig 17). Extension of the inflammatory process to the perinephric space and adjacent organs is common.
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Figure 17a. Xanthogranulomatous pyelonephritis in a 80-year-old woman with chronic pyuria. (a) Coronal unenhanced volume-rendered image shows a large staghorn calculus (arrow) in the left kidney. (b) Coronal volume-rendered image in early excretory phase shows, in addition to the staghorn calculus (arrow), marked hydronephrosis of the left kidney with poor function. Incidental multiple renal cysts are present in the right kidney.
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Figure 17b. Xanthogranulomatous pyelonephritis in a 80-year-old woman with chronic pyuria. (a) Coronal unenhanced volume-rendered image shows a large staghorn calculus (arrow) in the left kidney. (b) Coronal volume-rendered image in early excretory phase shows, in addition to the staghorn calculus (arrow), marked hydronephrosis of the left kidney with poor function. Incidental multiple renal cysts are present in the right kidney.
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Multidetector CT of the Upper Urinary Tract
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Since the advent of helical CT, this modality has largely replaced excretory urography in the evaluation of patients with renal colic. More recently, several authors have advocated "CT urography" for diagnosis of a variety of pathologic conditions of the urinary tract. The ability to acquire near-isotropic data sets in multiple phases offered by multidetector CT allows exquisite multiplanar and 3D reconstruction displays of the collecting system and the production of images similar to conventional urograms (Movie 3; Figs 18, 19). Although conventional intravenous urography offers excellent visualization of the lumen of the collecting system, an important potential advantage of CT urography is the ability to directly image abnormalities in the wall of the collecting system and in surrounding structures (4,33). This advantage of CT urography over conventional intravenous urography should be weighed against the risk of increased radiation exposure with the former technique. In one recent published study, 86 patients with microscopic hematuria and normal intravenous urograms were found to have subtle abnormalities at multiphasic CT urography (34). These pathologic conditions included benign lesions such as early papillary necrosis, medullary sponge kidney, pyelonephritis, and calculi, as well as small transitional-cell carcinomas.
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Figure 18. Duplicated left renal collecting system in a 50-year-old woman with a possible left renal mass. Coronal volume-rendered image in the excretory phase shows a duplicated left renal collecting system and no renal mass.
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Figure 19. Normal collecting system and ureters in a 35-year-old man with acute flank pain. Coronal volume-rendered image in the excretory phase depicts the entire collecting system. Both ureters are seen along their entire course.
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Technique
In patients with hematuria, one of the major benefits of multidetector CT is the ability to image the renal parenchyma and collecting system, provided an appropriate scanning protocol is used. The ideal imaging sequence is still a matter of controversy in the literature, but most authors agree on some basic principles. Our protocol is outlined in Table 3. Some authors advocate the use of abdominal compression to achieve optimal distension of the upper collecting system, followed by compression-release images in the excretory phase (35). A compression-release scout image of the abdomen and pelvis may be more practical, allowing good visualization of the distal ureters and bladder while minimizing the radiation dose and limiting the number of images that need to be reviewed. We do not routinely use compression but encourage patients to ingest 1,000 mL of water over 15–20 minutes prior to the examination. This ensures optimal hydration and distention of the urinary bladder, sufficient to allow opacification of the calyces and ureters in most instances (Table 3). Three-dimensional data reconstructions with MIP, multiplanar reconstructions, and volume rendering are used to generate images simulating intravenous urography.
Examples
Although the exact role of CT urography is still under investigation, a variety of benign pathologic conditions of the urinary tract have been successfully depicted, as illustrated in the these examples (33,35,36) (Figs 20, 21).
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Figure 20. Reflux nephropathy of left kidney in a 40-year-old woman with a history of reflux and recurrent urinary tract infections. Coronal volume-rendered image of the left kidney and ureter in excretory phase shows blunting of the upper pole calyces with substantial loss of renal cortex (arrows). The lower pole calyx is dilated and there is loss of renal cortical thickness. A calculus obstructing the lower pole calyx was seen on the precontrast image (not shown). The left ureter is seen along its entire course and is normal.
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Figure 21a. Left ureteral stent in a 55-year-old woman with severe recurrent left flank pain. (a) Coronal volume-rendered image in the excretory phase shows the ureteral stent in the left ureter. There is no hydronephrosis or urine leak. (b) Coronal posteroanterior volume-rendered image.
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Figure 21b. Left ureteral stent in a 55-year-old woman with severe recurrent left flank pain. (a) Coronal volume-rendered image in the excretory phase shows the ureteral stent in the left ureter. There is no hydronephrosis or urine leak. (b) Coronal posteroanterior volume-rendered image.
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Footnotes
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Abbreviations: MIP = maximum-intensity projection, 3D = three-dimensional.
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References
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- Hu H, He HD, Foley WD, Fox SH. Four multi-detector-row helical CT: image quality and volume coverage speed. Radiology 2000; 215:55-62.[Abstract/Free Full Text]
- Foley WD. Special focus session: multidetector CT: abdominal visceral imaging. RadioGraphics 2002; 22:701-719.[Abstract/Free Full Text]
- Horton KM, Sheth S, Corl F, Fishman EK. Multidetector row CT: principles and clinical applications. Crit Rev Comput Tomogr 2002; 43:143-181.[Medline]
- Schreyer HH, Uggowitzer MM, Ruppert-Kohlmayr A. Helical CT of the urinary organs. Eur Radiol 2002; 12:575-591.[Medline]
- Baker SR. Musings at the beginning of the hyper-CT era. Abdom Imaging 2003; 28:110-114.[CrossRef][Medline]
- Rubin GD. 3-D imaging with multidetector CT. Eur J Radiol 2003; 45(suppl 1):S37-S41.
- Rubin GD. Techniques for performing multidetector-row computed tomographic angiography. Tech Vasc Interv Radiol 2001; 4:2-14.[Medline]
- Johnson PT, Halpern EJ, Kuszyk BS, et al. Renal artery stenosis: CT angiography—comparison of real-time volume-rendering and maximum intensity projection algorithms. Radiology 1999; 211:337-343.[Abstract/Free Full Text]
- Urban BA, Ratner LE, Fishman EK. Three-dimensional volume-rendered CT angiography of the renal arteries and veins: normal anatomy, variants, and clinical applications. RadioGraphics 2001; 21:373-386.[Abstract/Free Full Text]
- Lawler LP, Fishman EK. Three-dimensional CT angiography with multidetector CT data: study optimization, protocol design, and clinical applications in the abdomen. Crit Rev Comput Tomogr 2002; 43:77-141.[Medline]
- Rankin SC, Jan W, Koffman CG. Noninvasive imaging of living related kidney donors: evaluation with CT angiography and gadolinium-enhanced MR angiography. AJR Am J Roentgenol 2001; 177:349-355.[Abstract/Free Full Text]
- Herts BR, Coll DM, Lieber ML, Streem SB, Novick AC. Triphasic helical CT of the kidneys: contribution of vascular phase scanning in patients before urologic surgery. AJR Am J Roentgenol 1999; 173:1273-1277.[Abstract/Free Full Text]
- Rydberg J, Kopecky KK, Tann M, et al. Evaluation of prospective living renal donors for laparoscopic nephrectomy with multisection CT: the marriage of minimally invasive imaging with minimally invasive surgery. RadioGraphics 2001; 21:S223-S236.[Abstract/Free Full Text]
- Johnston T, Reddy K, Mastrangelo M, Lucas B, Ranjan D. Multiple renal arteries do not pose an impediment to the routine use of laparoscopic donor nephrectomy.. Clin Transplant 2001; 15(suppl 6):62-65.
- Pozniak MA, Balison DJ, Lee Jr FT, Tambeaux RH, Uehling DT, Moon TD. CT angiography of potential renal transplant donors. RadioGraphics 1998; 18:565-587.[Abstract]
- Platt JF, Ellis JH, Korobkin M, Reige K. Helical CT evaluation of potential kidney donors: findings in 154 subjects. AJR Am J Roentgenol 1997; 169:1325-1330.[Abstract/Free Full Text]
- Kawamoto S, Montgomery RA, Lawler LP, Horton KM, Fishman EK. Multidetector CT angiography for preoperative evaluation of living laparoscopic kidney donors. AJR Am J Roentgenol 2003; 180:1633-1638.[Abstract/Free Full Text]
- Rubin GD, Dake MD, Napel S, et al. Spiral CT of renal artery stenosis: comparison of three-dimensional rendering techniques. Radiology 1994; 190:181-189.[Abstract/Free Full Text]
- Beregi JP, Elkohen M, Deklunder G, Artaud D, Coullet JM, Wattinne L. Helical CT angiography compared with arteriography in the detection of renal artery stenosis. AJR Am J Roentgenol 1996; 167:495-501.[Abstract/Free Full Text]
- Prokop M. Protocols and future directions in imaging of renal artery stenosis: CT angiography. J Comput Assist Tomogr 1999; 23(suppl 1):S101-S110.
- Kuszyk BS, Heath DG, Johnson PT, Eng J, Fishman EK. CT angiography with volume rendering for quantifying vascular stenoses: in vitro validation of accuracy. AJR Am J Roentgenol 1999; 173:449-455.[Abstract/Free Full Text]
- Rubin GD, Napel S. Helical CT angiography of renal artery stenosis. AJR Am J Roentgenol 1997; 168:1109-1111.[Medline]
- Behar JV, Nelson RC, Zidar JP, DeLong DM, Smith TP. Thin-section multidetector CT angiography of renal artery stents. AJR Am J Roentgenol 2002; 178:1155-1159.[Abstract/Free Full Text]
- Mallouhi A, Rieger M, Czermak B, Freund MC, Waldenberger P, Jaschke WR. Volume-rendered multidetector CT angiography: noninvasive follow-up of patients treated with renal artery stents. AJR Am J Roentgenol 2003; 180:233-239.[Abstract/Free Full Text]
- Kawashima A, Sandler CM, Ernst RD, Tamm EP, Goldman SM, Fishman EK. CT evaluation of renovascular disease. RadioGraphics 2000; 20:1321-1340.[Abstract/Free Full Text]
- Llach F. Thromboembolic complications in nephrotic syndrome: coagulation abnormalities, renal vein thrombosis, and other conditions. Postgrad Med 1984; 76:111–114, 116–118-121–123.
- Llach F, Papper S, Massry SG. The clinical spectrum of renal vein thrombosis: acute and chronic. Am J Med 1980; 69:819-827.[Medline]
- Wyatt SH, Urban BA, Fishman EK. Spiral CT of the kidneys: role in characterization of renal disease. I. Nonneoplastic disease. Crit Rev Diagn Imaging 1995; 36:1-37.
- Kawashima A, Sandler CM, Goldman SM. Imaging in acute renal infection. BJU Int 2000; 86(suppl 1):70-79.
- Dalla-Palma L, Pozzi-Mucelli F, Pozzi-Mucelli RS. Delayed CT findings in acute renal infection. Clin Radiol 1995; 50:364-370.[CrossRef][Medline]
- Wan YL, Lee TY, Bullard MJ, Tsai CC. Acute gas-producing bacterial renal infection: correlation between imaging findings and clinical outcome. Radiology 1996; 198:433-438.[Abstract/Free Full Text]
- Chuang CK, Lai MK, Chang PL, et al. Xanthogranulomatous pyelonephritis: experience in 36 cases. J Urol 1992; 147:333-336.[Medline]
- Caoili EM, Cohan RH, Korobkin M, et al. Urinary tract abnormalities: initial experience with multi-detector row CT urography. Radiology 2002; 222:353-360.[Abstract/Free Full Text]
- 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 2003; 61:528-532.[CrossRef][Medline]
- Chow LC, Sommer FG. Multidetector CT urography with abdominal compression and three-dimensional reconstruction. AJR Am J Roentgenol 2001; 177:849-855.[Free Full Text]
- O'Malley ME, Hahn PF, Yoder IC, Gazelle GS, McGovern FJ, Mueller PR. Comparison of excretory phase, helical computed tomography with intravenous urography in patients with painless haematuria. Clin Radiol 2003; 58:294-300.[CrossRef][Medline]
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Abstract
Multi-Detector Row Helical CT
