Spinal dysraphism at MR urography: initial experience

PURPOSE: To prospectively evaluate the role of magnetic resonance (MR) urography in the radiologic assessment of patients with spinal dysraphism. MATERIALS AND METHODS: Fourteen patients with spinal dysraphism were referred for MR urography with half-Fourier rapid acquisition with relaxation enhancement (RARE) (repetition time msec/echo time msec = 11.9/95) and RARE (2,800/1,100) sequences on a 1.5-T MR machine. Six patients did not tolerate MR urography owing to claustrophobia (n = 4) or flexion deformities (n = 2), giving a final success rate of 57% (eight patients). Two patients had a single kidney (one after nephrectomy, one with a crossed-fused ectopic kidney). Images were jointly assessed by two radiologists and compared with excretory urographic studies. The signal intensity ratio and contrast-to-noise ratio were also calculated. RESULTS: Visualization of the kidneys, pelvicaliceal system, and ureters was better with half-Fourier RARE than with RARE imaging, whereas visualization of the bladder was comparable with both sequences. The mean signal intensity ratios for half-Fourier RARE and RARE sequences, respectively, were 16.2 +/- 3.65 and 19.2 +/- 3.65 (P =. 58, factorial analysis of variance model), whereas the mean contrast-to-noise ratios were 55.4 +/- 5.16 and 47.8 +/- 5.16 (P =. 34). Cortical scarring was depicted more clearly at MR urography than at excretory urography, whereas a renal calculus seen at excretory urography was not detected at MR urography. CONCLUSION: MR urography was feasible in 57% of patients with spinal dysraphism and is a safe, accurate method of evaluating the upper urinary tract.     

MR-Urographie: Prinzipien, Untersuchungstechniken, Indikationen

MR urography is an evolving and promising technique in the evaluation of the urinary tract. MR urography is currently considered the method of choice for imaging of the renal parenchyma and the collecting systems in patients who cannot undergo routine radiographic studies such as pregnant women, pediatric patients, patients allergic to iodinated contrast agents, or patients with impaired renal function.The future development of MR urography in terms of functional, cellular, and molecular imaging is presently the subject of research. The ability of MR imaging to provide quantitative functional information (e.g., on blood flow, perfusion, glomerular filtration rate, and excretion as well as urine drainage) in addition to morphologic assessment of the parenchyma and the collecting system could lead to a single, "all-in-one approach" examination technique.     

Funktionelle und morphologische MR-Bildgebung des oberen Harntrakts im Kindesalter

MR imaging is being increasingly used for the diagnosis of congenital urinary tract obstruction. The following conditions have to be fulfilled to provide an MR urography technique which is useful for the pediatric age group: (1) the combination of morphology and function, (2) a high-resolution morphological image, (3) a morphological image independent of kidney function, (4) reliable determination of split renal function and (5) of urinary excretion. This is best accomplished with a combination of a T1-weighted fast GE sequence post-contrast and a heavily T2-weighted 3D IR-TSE sequence. Selected sequence parameters are important for optimization as well as for a correct functional assessment. Then MR urography is superior to the conventional methods of excretory urography, ultrasound, and scintigraphy in the morphological depiction of the urinary tract even of complex malformations as well as in a detailed functional assessment. In particular, this method is useful in the situation of complicated duplex kidneys, dystopic kidneys, unclear morphology, or discrepant former results and perioperative assessment. The main advantages are avoiding radiation and obtaining a simultaneous functional-morphological diagnosis.     

MR-Bildgebung der Nieren Neue Ansätze in der Diagnostik*

AIM: New diagnostic strategies for evaluation of the kidney by fast MR imaging techniques. MATERIAL AND METHODS: A comprehensive morphologic and functional evaluation of the kidney is proposed using fast MR imaging of renal morphology, multiphase 3D gadolinium MR angiography, MR urography and MR flow measurements. A single MR examination is designed to grade renovascular disease and assess the hemodynamic and functional significance, detect and characterize renal lesions and evaluate the urinary tract. RESULTS: The combined analysis of morphologic and functional data allows reliable assessment of renal artery stenosis, benign and malignant renal masses and diseases of the renal collecting system and ureters, as well as congenital abnormalities in good agreement to the results of conventional imaging modalities. The improved tissue contrast and additional functional information compensates for the disadvantage of a lower spatial resolution. CONCLUSION: Combined morphologic and functional MR examination represents a reliable, non-invasive and cost-effective alternative imaging modality for comprehensive diagnostic evaluation of renal disease.     

Multicystic dysplasia and crossed renal ectopia

Multicystic renal dysplasia in a crossed fused or nonfused ectopic kidney is a rare occurrence that produces unusual imaging findings. In four such cases in neonates, three presented with a palpable abdominal mass and one was discovered in utero with maternal sonography. In three cases, sonography showed a multicystic mass, contiguous with the lower pole of the orthotopic kidney. In the fourth infant, a crossed, tiny dysplastic kidney was not visualized, but its markedly dilated ectopic ureter was seen traversing the spine on CT. Ureteropelvic junction obstruction was present in the three fused orthotopic kidneys. The characteristic imaging findings of multicystic dysplasia and crossed renal ectopia include a multicystic mass of variable size that is contiguous with the lower pole of a hydronephrotic, malrotated kidney; ureteral displacement and/or dilatation; and contralateral absence of the kidney and its renal artery.     

Feasibility of MR urography in neonates and infants with anomalies of the upper urinary tract

The aim of this study was to evaluate the feasibility and diagnostic potential of dynamic MR urography (MRU) in neonates and infants with sonographically detected abnormalities of the upper urinary tract. Thirty infants (age range 5 days to 3 years, mean age 7.9 months; male:female: 22:8) underwent MRU using T2 and contrast-enhanced dynamic T1-weighted sequences. The results were compared with the findings of ultrasound ( n=30), intravenous urography (IVU, n=19) and/or scintigraphy ( n=25) based on the criteria suggestive of obstructive uropathy. Oral sedation was sufficient to perform MRU with diagnostic quality in 20 of 21 patients younger than 1 year; 9 older patients needed intravenous sedation. Diagnosis of the 66 renal units (58 kidneys, 29 successful examinations) included normal systems (contralateral units), duplex systems, vesico-ureteral reflux, obstructive megaureter, ureteropelvic junction obstruction and accompanying renal parenchymal disease, with complex pathology in 10 patients. Magnetic resonance urography demonstrated anatomy better than IVU, particularly the renal parenchyma, (ectopic) ureters, and poorly functioning dilated systems. Magnetic resonance urography was superior to US in showing ureteral pathology. Tiny cysts in dysplastic kidneys were better seen by US. Gadolinium-enhanced dynamic MRU allowed accurate assessment of obstruction applying IVU criteria. Here MRU matched IVU results, and most of the scintigraphic findings. Magnetic resonance urography can be performed in young infants with diagnostic quality using oral sedation. Magnetic resonance urography correctly depicts anatomy and allows assessment of the urinary tract better than US and IVU, with additional functional information. Magnetic resonance urography thus has the potential to replace IVU for many indications.     

磁共振尿路成像诊断儿童先天性肾发育不良

目的 探讨磁共振尿路成像(MR urography,MRU)在诊断儿童先天性肾脏发育不良中的应用价值. 方法 对患有先天性肾发育不良并患肾无功能的13例患儿采用常规MRI平扫及MRU(重T_2加权半傅立叶采集单次激发快速自旋回波序列)检查. 结果 13例病例中,常规MRI检查有1例发育不良并异位于盆腔内的小肾未被检出;在MRU原始图像上有1例位于脊柱旁肾窝下方的发育不良的小肾未被发现;MRU MIP重建图像可清晰显示出多房性囊性发育不良的肾脏,对单纯性肾盂呈杵状改变的肾脏显示不佳.全部病例及其伴发病变均被常规MRI结合MRU原始图像、MRU MIP重建图像正确诊断.结论常规MRI结合MRU对诊断儿童先天性肾发育不良有重要价值.     

Renal transit time with MR urography in children

PURPOSE: To prospectively evaluate use of dynamic contrast material-enhanced magnetic resonance (MR) urography for measurement of renal transit time (RTT) of a contrast agent through the kidney and collecting system so as to identify obstructive uropathy in children. MATERIALS AND METHODS: One hundred twenty-six children suspected of having hydronephrosis were hydrated prior to undergoing both conventional and dynamic contrast-enhanced MR urography of the kidneys and urinary tract. A three-dimensional sequence was used to track passage of contrast agent through the kidneys. Time between the appearance of contrast material in the kidney and its appearance in the ureter at or below the level of the lower pole of the kidney was defined as RTT. Bland-Altman plots were used to quantify intra- and interobserver performance. In 30 children, a nuclear medicine renogram was also obtained, and the half-life of renal signal decay after furosemide administration was derived and compared with the MR imaging RTT by using receiver operating characteristic curves. RESULTS: On the basis of RTT, kidneys were classified as normal (RTT RTT 490 seconds). Inter- and intraobserver agreement indicated that the technique is both robust and reproducible. Receiver operating characteristic analysis for comparison of results of MR imaging and diuretic renal scintigraphy showed good agreement between the modalities, with a mean area under the curve of 0.90. CONCLUSION: When used in conjunction with morphologic images obtained in the same examination, RTT generally allowed normal kidneys to be differentiated from obstructed and partially obstructed kidneys.     

Computed tomography demonstration of renal dysplasia with a vaginal ectopic ureter

The diagnosis of renal dysplasia associated with a single vaginal ectopic ureter is often difficult, because the dysplastic kidney is usually not seen on excretory urography. A 17-year-old girl, whose affected kidney was accurately identified by computed tomography, is reported. Computed tomography is a useful technique for the diagnosis of renal dysplasia with a single vaginal ectopic ureter.     

Renal cystic diseases

Renal cystic disease comprises a mixed group of heritable, developmental, and acquired disorders. Because of their diverse etiology, histology, and clinical presentation, no single scheme of classification has gained acceptance. Conditions include autosomal dominant polycystic kidney disease, acquired renal cystic disease, medullary sponge kidney, autosomal recessive polycystic kidney disease, multicystic dysplastic kidney, medullary cystic disease, tuberous sclerosis, cysts of the renal sinus, and von Hippel-Lindau's disease. An awareness of the pathology of each cystic disease is helpful in the understanding of the corresponding radiological images. Imaging techniques used in evaluating renal cystic disease include intravenous urography, sonography, CT, MRI, nuclear medicine, and renal angiography. Many types of cystic disease show similar imaging features. Meticulous attention to subtle radiological findings is therefore essential for reaching a correct diagnosis. Imaging features requiring analysis include whether the cysts are unilateral or bilateral, renal size and functional status, cyst distribution in the kidneys, and the presence of hemorrhagic and calcified renal cysts, solid renal masses, renal sinus cysts, and cysts in adjacent organs. Radiological findings should be carefully correlated with clinical features such as patient age, family history, symptoms, physical findings, and renal functional status before a diagnosis is attempted. Received 10 October 1996; Revision received 30 January 1997; Accepted 4 February 1997     

Evaluation of children for liver transplantation: value of MR imaging and sonography

Diagnostic imaging plays a major role in the diagnosis and treatment of chronic liver disease in children. Decisions regarding the need for sclerotherapy, palliative shunts, and anatomic suitability for hepatic transplantation are based on the upper abdominal anatomy. Thirty-six children with various forms of chronic liver disease were referred for diagnostic imaging, including MR and sonography. Each study was evaluated independently without knowledge of the other examination. The first six patients were evaluated retrospectively and the last 30 patients prospectively. The size of the portal vein and inferior vena cava varied in this population, with excellent agreement between sonography and MR. A 2-mm portal vein was shown only on MR imaging in two patients, but MR missed a 3-mm portal vein. Portosystemic collateral vessels also were evaluated and noted to be detected more readily with MR imaging (64%) than with sonography (22%). In particular, paraumbilical veins were detected more often with MR (28% vs 6% by sonography). Associated or coexisting anomalies were relatively common in children with chronic liver disease (14%). These included polysplenia (two cases), preduodenal portal vein (one), unilateral dysplastic kidneys (two), ureteropelvic junction obstruction (one), and splenic (one) and renal (one) cysts. MR imaging was more sensitive than sonography for detection of abnormal anatomy in this group of patients and should be considered the pretransplantation imaging technique of choice in children with end-stage liver disease.     

Nierenfunktionsdiagnostik mittels Magnetresonanztomographie

Due to progress in the development of sequences and techniques magnetic resonance imaging (MRI) methods, such as functional MR urography (fMRU), arterial spin labeling (ASL), diffusion-weighted imaging (DWI), diffusion tension imaging (DTI) and blood oxygen level dependent MRI (BOLD-MRI) have become available for renal functional evaluation. In recent years research of these imaging techniques has demonstrated that they provide valid functional data with respect to renal perfusion, oxygenation and interstitial diffusion as well as glomerular filtration and the extent of an obstructive uropathy. Many pathophysiological renal processes, e.?g. in transplanted kidneys, in the setting of chronic kidney disease and in the diagnostics of renal tumors, can therefore be fully evaluated. The fMRU, which enables a reliable assessment of renal function combined with high-resolution morphological evaluation of the kidneys and the entire urinary tract, has already become an inherent component in the clinical setting, at least in specialized pediatric radiology centers. To establish the new imaging methods in the clinical routine, further technical improvements and large-scale prospective clinical studies are necessary to validate the determined functional parameters, to generate standard protocols and to unify and facilitate data post-processing.     

Diffusion-weighted MR imaging of kidneys in renal artery stenosis

OBJECTIVE: The purpose of our study was to evaluate perfusion and diffusion of kidneys in renal artery stenosis (RAS) and any correlation between stenosis and ADC values and whether this imaging modality may be a noninvasive complementary assessment technique to MR angiography before interventional procedures. MATERIALS AND METHODS: Twenty consecutive patients suspected of having renal artery stenosis were evaluated with renal MR angiography to exclude stenosis and were then included in the study. Transverse DW multisection echo-planar MR imaging was performed. In the transverse ADC map, rectangular regions of interest were placed in the cortex on 3 parts (upper, middle, and lower poles) in each kidney. ADCs of the kidneys were calculated separately for the low, average, and high b-values to enable differentiation of the relative influence of the perfusion fraction and true diffusion. The ADC values of 39 kidneys (13 with renal artery stenosis and 26 normal renal arteries) were compared, and the relationship between stenosis degree and ADC values was calculated. RESULTS: RAS was detected in 11 of 20 (55%) patients with MRA. Thirteen of 39 kidneys demonstrated RAS, and 26 were normal. The ADClow (1.9+/-0.2 versus 2.1+/-0.2; P=.020), ADCaverage (1.7+/-0.2 versus 1.9+/-0.1; P=.006), and ADChigh (1.8+/-0.2 versus 2.0+/-0.1; P=.012) values were significantly lower in patients with kidneys with arterial stenosis than that in patients with kidneys with normal arteries. Statistical analysis revealed that stenosis degree correlated strongly with ADClow (r=-.819; P=.001), ADCaverage (r=-.754; P=.003), and ADChigh (r=-.788; P=.001). The ADClow, ADCaverage, and ADChigh values were significantly lower in patients with kidneys with arterial stenosis than that in patients with kidneys with normal arteries. CONCLUSION: We think that DW MR imaging of kidneys with RAS can help determine the functional status of a renal artery stenosis.     

Localized cystic disease of the kidney

OBJECTIVE: Localized cystic disease of the kidney is a benign nonsurgical condition. Its imaging and clinical features are characterized and differentiated from autosomal dominant polycystic kidney disease, multilocular cystic nephroma, and cystic neoplasm. MATERIALS AND METHODS: Localized cystic disease was diagnosed in 18 patients on the basis of a review of imaging studies, clinical histories, and pathologic proof in four of the 18 patients. Average age at diagnosis was 54 years (age range, 24-83 years). Fifteen of the patients (83%) were men. CT was performed on 18 patients, sonography on nine, excretory urography on six, arteriography on four, and MR imaging on two. RESULTS: Localized cystic disease was unilateral in all patients and characterized by multiple cysts of various sizes separated by normal (or atrophic) renal tissue in a conglomerate mass suggestive of cystic neoplasm. In some patients, involvement of the entire kidney, which was suggestive of unilateral autosomal dominant polycystic kidney disease, was seen. No cysts were seen in the contralateral kidney in 14 patients, and only one or two scattered small cysts were present in four patients. Clinical presentations included hematuria, flank pain, palpable abdominal mass, and localized cystic disease as an incidental finding. None of the patients had a family history of autosomal dominant polycystic kidney disease. Ten patients underwent follow-up (follow-up range, 1-12 years); nine patients underwent imaging follow-up and one patient underwent clinical follow-up, which showed stability of disease. Four patients underwent nephrectomy for suspected renal neoplasm. CONCLUSION: Familiarity with localized cystic disease of the kidney and its imaging findings is important to avoid unnecessary surgery and to differentiate the disease from autosomal dominant polycystic kidney disease.     

Magnetic resonance imaging in the assessment of urologic disease: an all-in-one approach

The aim of this study was to evaluate an “all-in-one” MR procedure to examine the kidneys, the renal vascular supply and renal perfusion, and the urinary tract. In 64 patients (58 with urologic disease and 6 healthy volunteers), MR was performed including: (a) T1- and T2-weighted imaging; (b) 3D contrast-enhanced MR angiography (MRA), including the renal arteries, renal veins, as well as renal perfusion; and (c) 3D contrast-enhanced MR urography (MRU) in the coronal and sagittal plane. For the latter, low- and high-resolution images were compared. Prior to gadolinium injection, 0.1 mg/kg body weight of furosemide was administered intravenously. The results were compared with correlative imaging modalities (ultrasonography, intravenous urography, CT), ureterorenoscopy and/or surgical–pathologic findings. Visualization of the renal parenchyma, the vascular supply, and the collecting system was adequate in all cases, both in nondilated and in dilated systems and irrespective of the renal function. One infiltrating urothelial cancer was missed; there was one false-positive urothelial malignancy. Different MR techniques can be combined to establish an all-in-one imaging modality in the assessment of diseases which affect the kidneys and urinary tracts. Continuous refinement of the applied MR techniques and further improvements in spatial resolution is needed to expand the actual imaging possibilities and to create new tracts and challenges in the MR evaluation of urologic disease. Received: 27 September 1999; Revised: 20 January 2000; Accepted: 22 May 2000     

Kidneys in infants and children: evaluation with MR

Magnetic resonance (MR) imaging was performed in 58 children aged 1 day to 17 years. In 43 patients with suspected renal abnormalities, the results of MR were compared with those obtained by ultrasonography, computed tomography, or excretory urography. The remaining 15 children with no known renal disease were initially imaged to define the appearance on MR images of the normal kidneys according to the child's age. The signal intensity from hilar adipose tissue increased with age; corticomedullary differentiation was best seen in younger children. Compared with other imaging modalities, MR added useful information in evaluating the complications associated with renal failure and in patients with renal neoplasms. The use of MR in children with possible renal disease is limited, and the modality should be used as an adjunct to renal ultrasonography in a carefully selected group of patients.     

MR urography findings of a duplicated ectopic ureter in an adult man

In this report we present the imaging findings in an adult male with a duplicated ectopic ureter which inserted into the prostatic urethra. The appearances at excretory urography, US, CT, and MR urography are described together with the potential pitfalls of the imaging techniques. Both US and MR urography accurately image the collecting system from the kidney to the point of distal ureteral insertion, and in our patient, MR urography provided similar information to US. Received: 20 July 1999; Revised: 21 December 1999; Accepted: 24 December 1999     

Imaging end-stage kidney disease in adults. Low-field MR imaging with magnetization transfer vs. ultrasonography

Purpose: To 1) assess the potential of magnetization transfer (MT)-weighted MR imaging to improve the often poor visibility of native kidneys in patients with a renal transplant; and 2) compare low-field MR imaging and ultrasonography (US) for imaging these fibrotic kidney remnants.Material and Methods: Seventy-two native kidneys of 36 patients were prospectively evaluated with US and MR. In low-field (0.1 T) MR imaging, T1-, T2- and MT-weighted sequences were used. MT-weighted images were compared with T2-weighted images in their ability to delineate the kidneys from their surroundings whereas US and MR were compared for detection of renal cysts and possible solid tumors.Results: MT-weighted images proved superior to conventional T2-weighted images in producing contrast between the kidney remnants and their fatty surroundings. Although US revealed a few small renal cysts that were not seen at MR images, no statistical difference was found between the two modalities in this respect.Conclusion: MT imaging, due to its unique protein-specific signal depression, offers significantly improved visualization and delineation of end-stage kidneys. US, because its better availability and cost-benefit ratio, remains the method-of-choice compared to low-field MR imaging in detecting cysts in multicystic kidneys. MR investigation is helpful in selected patients and may be used as an alternative.     

Functional, dynamic, and anatomic MR urography: feasibility and preliminary findings.

RATIONALE AND OBJECTIVES: The authors assessed the feasibility of using magnetic resonance (MR) urography to acquire functional, dynamic, and anatomic information in human subjects with normal and hydronephrotic kidneys. MATERIALS AND METHODS: In subjects known to have or suspected of having hydronephrosis, split renal filtration fractions were measured with a customized magnetization-prepared, inversion-prepared gradient-recalled echo sequence to determine the T1 of flowing blood in the inferior vena cava and aorta before and after contrast medium administration and in the renal veins and arteries after contrast medium administration. Multiple timed sets of coronal fast spoiled gradient-echo 70 degrees flip-angle images were acquired before and after contrast medium administration to derive MR renograms from changes in the signal intensity of the cortex and medulla. Precontrast T2-weighted images were obtained with a three-dimensional fast spoiled gradient-echo maximum intensity projection pulse sequence, and postcontrast T1 maximum intensity projection images were also obtained to depict the renal anatomy. RESULTS: Split filtration fraction differentiated normal from hydronephrotic kidneys. MR renograms depicted vascular, tubular, and ductal phases and differentiated between normal and hydronephrotic kidneys (P < .05, n = 20). Contrast medium dose correlated with the peak of the cortical signal intensity curves on the renogram (r = 0.7, P < .0005; n = 20). The sensitivities for the visual determination of hydronephrosis and unilateral delayed excretion of contrast material were both 100%, and the specificities were 64% and 85%, respectively. CONCLUSION: The preliminary findings show promise for the use of MR urography in the comprehensive assessment of renal function, dynamics, and anatomy.     

Magnetic resonance imaging in renal transplantation.

End stage renal disease is common and can result from a variety of diseases. The expense and morbidity of dialysis has made renal transplantation the preferred treatment when it is available. In the United States, 11,000 renal transplants are performed annually. Because of the limited supply of donor organs, every effort is made to salvage the transplanted kidney that has began to fail. Imaging modalities that are currently used to evaluate transplanted kidneys are ultrasound (US), computed tomography (CT), scintigraphy, intravenous urography (IVU), contrast angiography, and magnetic resonance imaging (MRI). MRI offers multiple advantages. MRI provides cross sectional and vascular information without the risks of ionizing radiation, iodinated contrast, or arterial catheterization. This article describes the role of MR imaging in renal transplantation, technical aspects of image acquisition, and MR findings of post-transplantation complications.