Renal MDCT

CT of the urinary tract revisited

Computed tomography (CT) of the abdomen is usually appropriate for the initial imaging of many urinary tract diseases, due to its wide availability, fast scanning and acquisition of thin slices and isotropic data, that allow the creation of multiplanar reformatted and three-dimensional reconstructed images of excellent anatomic details. Non-enhanced CT remains the standard imaging modality for assessing renal colic. The technique allows the detection of nearly all types of urinary calculi and the estimation of stone burden. CT is the primary diagnostic tool for the characterization of an indeterminate renal mass, including both cystic and solid tumors. It is also the modality of choice for staging a primary renal tumor. Urolithiasis and urinary tract malignancies represent the main urogenic causes of hematuria. CT urography (CTU) improves the visualization of both the upper and lower urinary tract and is recommended for the investigation of gross hematuria and microscopic hematuria, in patients with predisposing factors for urologic malignancies. CTU is highly accurate in the detection and staging of upper tract urothelial malignancies. CT represents the most commonly used technique for the detection and staging of bladder carcinoma and the diagnostic efficacy of CT staging improves with more advanced disease. Nevertheless, it has limited accuracy in differentiating non-muscle invasive bladder carcinoma from muscle-invasive bladder carcinoma. In this review, clinical indications and the optimal imaging technique for CT of the urinary tract is reviewed. The CT features of common urologic diseases, including ureterolithiasis, renal tumors and urothelial carcinomas are discussed.

Imaging Advances in Urolithiasis

The prevalence of urinary stones in the United States has been described as 1 in 11 persons reporting a history of stones. Imaging plays a crucial role in diagnosis, management, and follow-up for these patients and imaging technology over the last 100 years has advanced as the disease prevalence has increased. CT remains the gold standard for imaging urolithiasis and changes in this technology, with the addition of multidetector CT and dual-energy CT, as well as the changes in utilization of CT, have decreased the radiation dose encountered by patients and allowed for improved stone detection. The use of digital tomography has been introduced for follow-up of recurrent stone formers offering the potential to lower radiation exposure over the course of a patient's lifelong treatment. However, there is still a demand for improved imaging techniques to detect smaller stones and stones in larger patients at lower radiation doses as well as the continued need for the judicious use of all imaging modalities for healthcare cost containment and patient safety.

MDCT of blunt renal trauma: imaging findings and therapeutic implications

Objectives

To show the wide spectrum of computed tomography (CT) findings in blunt renal trauma and to correlate them with consequent therapeutic implications.

Methods

This article is the result of a literature review and our personal experience in a level II trauma centre. Here we describe, discuss and illustrate the possible CT findings in blunt renal trauma, and we correlate them with the American Association for the Surgery of Trauma (AAST) classification and their therapeutic implications.

Results

CT findings following blunt renal trauma can be grouped into 15 main categories, 12 of them directly correlated with the AAST classification and 3 of them not mentioned in it. Non-operative management, which includes the “watchful waiting” approach, endourological treatments and endovascular treatments, is nowadays widely adopted in blunt renal trauma, and surgery is limited to haemodynamically unstable patients and a minority of haemodynamically stable patients.

Conclusions

The interpretation of CT findings in blunt renal trauma may be improved and made faster by the knowledge of their therapeutic consequences.

Teaching Points

• The majority of blunt renal injuries do not require surgical treatment.

• CT findings in blunt renal injury must be evaluated considering their therapeutic consequences.

• Some CT findings in blunt renal trauma are not included in the AAST classification.

[Contrast-enhanced sonography for blunt force abdominal trauma]

With the introduction of second generation ultrasound contrast agents, contrast-enhanced ultrasound (CEUS) has become available as an adjunct to the conventional FAST (focused assessment with sonography in trauma) protocol and B-mode sonography of the abdomen after blunt force abdominal trauma. Results from several controlled studies indicate excellent diagnostic accuracy of CEUS for the exclusion of clinically relevant parenchymal injuries after blunt force abdominal trauma. Particularly in younger, hemodynamically stable patients this technique could contribute to a reliable exclusion of parenchymal injuries without the use of ionizing radiation. This report provides details on the technical performance of CEUS, shows examples of typical CEUS findings after blunt abdominal trauma and summarizes the current clinical evidence regarding the use of CEUS after blunt abdominal trauma.

Multidetector computed tomography with triple-bolus contrast medium administration protocol for preoperative anatomical and functional assessment of potential living renal donors

OBJECTIVE

To evaluate multidetector computed tomography (MDCT) with a triple-bolus contrast administration protocol for preoperative anatomical and functional assessment of living renal donors.

METHODS

Fifty-five potential living renal donors underwent MDCT of which 27 proceeded to donor nephrectomy. A triple-bolus contrast administration protocol was used for simultaneous acquisition of arterial, nephrographic, and excretory phases. MDCT images were independently reviewed in random order by two radiologists blinded to surgical anatomy findings. Diagnostic accuracy for anatomical variants was quantified by sensitivity and specificity. Differential renal function (DRF) was derived from MDCT for 54 patients and compared with technetium-99 m dimercaptosuccinic acid renography (Tc-99 m DMSA).

RESULTS

All triple-bolus MDCT examinations were technically adequate. Accessory renal arteries and veins were identified at surgery in 33% (n = 9/27) and 22% (n = 6/27) of donor kidneys. The mean difference between MDCT-derived DRF and DMSA was 0.8% (95% CI 0.1-1.6) with 95% limits of agreement of -4.6% (95% CI -3.3 to -5.9) to 6.3% (95% CI 5.0-7.6). MDCT delivered a mean (SD, range) radiation dose of 9.5 (3.6, 3.6-17.3) mSv.

CONCLUSION

MDCT with a triple-bolus contrast administration provides accurate anatomical and functional evaluation of living renal donors.

Imaging of advanced renal cell carcinoma

OBJECTIVES

To describe current radiological cross-sectional imaging in the detection and staging of advanced renal cell carcinoma (RCC), defined here as RCC reaching beyond the renal capsule, whether by immediate extension or by metastasis.

METHODS

Review and summary of current radiological and urological literature, including original articles and reviews, retrieved from the medical data base "PubMed".

RESULTS

Multi-detector-row computed tomography (MDCT) shows a sensitivity of up to 100% and specificity of about 90% for retroperitoneal disease, venous tumour thrombus, and metastasis, but limited accuracy for lymphadenopathy in RCC. Magnetic resonance imaging (MRI) is applied as a problem-solving modality, with particular strength in imaging metastasis to brain and bone. However, dynamic, contrast-enhanced- (DCE-) and arterial-spin-labelling (ASL-) MRI may help to monitor early response to angiogenesis inhibitor drugs. Ultrasonography (US) shows limited capability of identifying retroperitoneal disease, venous tumour thrombus extension, and metastasis. Positron Emission Tomography with 18-fluoro-desoxy-glucose (FDG-PET) demonstrates modest accuracy for metastasis of RCC, with positive studies being suspicious, while negative studies cannot reliably exclude disease.

CONCLUSIONS

MDCT represents the diagnostic mainstay for the detection and staging of RCC. In the wake of new systemic therapies for advanced RCC, including angiogenesis inhibitor drugs, monitoring treatment response may become a new task for cross-sectional imaging.

[Multi-detector computed tomography in non-traumatic urologic emergencies]

Today's modern multi-detector computer tomography (MDCT) with its fast gantry rotation enables scanning of large body volumes with high temporal and spatial resolution. The fast acquisition of data and subsequent data reconstruction enables multiphase protocols with short time gaps between consecutive scan series so that large numbers of scans within one respiratory pause are possible and even in cases of non-cooperative patients acceptable quality of image data is provided. The acquired thin-slice raw data with isotropic submillimeter voxels can be visualized with different reconstruction algorithms. The advantages of imaging for diagnostics in urologic emergencies are the excellent visualization of acute arterial and venous pathologies, detailed assessment of renal parenchyma and the precise depiction of the urinary tract. In non-trauma settings this enables detailed visualization of inflammatory diseases and differentiation of obstructive or post-therapeutic pathologies along the upper and lower urinary tract. Based on these MDCT findings adequate therapy planning and planning of interventional or surgical procedures can be carried out.

Advances in noninvasive methods for functional evaluation of renovascular disease

As the number of patients with newly diagnosed renal artery stenosis increases, so has the number of percutaneous transluminal renal-artery angioplasties in the last few years. Deciding the preferred treatment in the clinical setting is fraught with difficulties related to many factors, and there is limited evidence to support angioplasty/stent for any indication. These considerations emphasize the urgent need for improved noninvasive assessment of kidney function in patients with vascular disease. This review will attempt to summarize the available techniques that may potentially be used for measurement of renal function in this context.

Imaging of the renal donor and transplant recipient

Renal transplant remains the mainstay of the treatment of end-stage renal disease. With improvement in management strategies and the diverse imaging options, the yearly survival of recipients with functional kidneys has improved significantly. This improved survival is attributed to factors such as immunosuppressive therapy planning in recipients, human leukocyte antigen matching, surgeon experience, and recipient's age. Transplantation offers the closest thing to a normal state if the transplanted kidney can replace the failed kidneys. Living-donor kidney transplants are playing a vital role in bridging the gap between decreased supply of, and increased demand for, kidneys for transplant. Early detection and characterization of complications in the recipient are of immense clinical relevance, allowing timely intervention to prevent graft failure.

Computed tomography of renal cell carcinoma in patients with terminal renal impairment

PURPOSE

An increased incidence of renal tumors has been observed in patients with end-stage-renal-disease (ESRD). The very strong association with acquired renal cystic disease (ACRD) and increased incidence of the renal tumors (conventional renal cell carcinoma (CRCC), papillary renal cell carcinoma (PRCC) or papillary renal cell adenoma (PRCA)) was reported. This study discusses the role of computed tomography (CT) in detecting renal tumors in patients with renal impairment: pre-dialysis, those receiving dialysis or with renal allograft transplants.

MATERIALS AND METHODS

Ten patients (nine male, one female) with renal cell tumors were enrolled into a retrospective study; two were new dialysis patients, three on long-term dialysis, and five were renal transplant recipients with history of dialysis. All patients underwent helical CT, a total of 11 procedures were performed. Sixteen-row detector system was used five times, and a 64-row detector system for the six examinations. All patients underwent nephrectomy of kidney with suspected tumor, 15 nephrectomies were performed, and 1 kidney was assessed during autopsy. CT findings were compared with macroscopic and microscopic assessments of the kidney specimen in 16 cases.

RESULTS

Very advanced renal parenchyma atrophy with small cysts corresponding to ESRD was found in nine patients, chronic pyelonephritis in remained one. A spontaneously ruptured tumor was detected incidentally in one case, patient died 2 years later. In the present study, 6.25% (1/16) were multiple PRCA, 12.5% (2/16) were solitary PRCC, 12.5% tumors (2/16) were solitary conventional renal cell carcinomas (CRCC's), 12.5% tumors (2/16) were multiple conventional renal cell carcinomas (CRCC's), 25% (4/16) were CRCC's combined with multiple papillary renal cell carcinomas with adenomas (PRCC's and PRCA's), and 25% (4/16) of the tumors were multiple PRCC's combined with PRCA's without coexisting CRCC's. Bilateral renal tumors were found in our study in 60% (6/10) confirmed in six cases, one kidney left on follow-up due to the small tumors.

CONCLUSIONS

With the use of a multi-detector row system, it is possible to detect smaller foci suspected to originate in multiple tumors, especially when up to 3-mm thin multi-planar reconstructions are used. Two cases demonstrated the possibility the development of RCC in impaired kidneys may start before dialysis initiation.

Assessment of the kidney tumor vascular supply by two-phase MDCT-angiography

PURPOSE

Current kidney surgery uses less invasive laparoscopic and nephron-sparring procedures. Thus, perfect imaging of the renal vasculature is essential for surgery planning. The aim of our retrospective study was to evaluate the accuracy of 16-detector-row CT-angiography in assessing the vascular anatomy of the kidney with a tumor.

SUBJECTS AND METHODS

Referred for computed tomography (CT) because of a suspected renal tumor, 50 consecutive patients (mean age 58.6 years; range 43-82) were enrolled into our retrospective study. All examinations were performed with 16x0.75 mm collimation after the intravenous application of 80 ml of a non-ionic contrast material. The imaging protocol contained two-phase scanning in the arterial and then in the venous phase. The vascular anatomy of the kidney with tumor was evaluated using volume rendered (VRT) and maximum intensity images (MIP). Findings were compared with the anatomy found during surgery.

RESULTS

Forty-seven patients underwent nephrectomy, with an advanced clinical stage (IV) found in the three remaining ones. Correct topography of the renal hilus, including a number of arteries and veins, and the anatomy of their branching, was described in 46 patients. A very small upper polar artery was overlooked in one patient. The accuracy for the only-arterial was 97.9% and only-venous anatomy was 100%. The parasitic vasculature of the tumor was discovered in 10 cases and all of them were confirmed by surgery (100% accuracy). Macroscopic intravenous spread of the tumor was discovered in two cases, but microscopic intravenous invasion was confirmed during histology of the kidney specimens in another two cases, the overall tumor staging accuracy reaching 95.7%.

CONCLUSION

Two-phase multidetector CT is a valuable tool for assessing vascular supply of the kidney before surgery due to the tumor and can fully replace catheter-based angiography.

MDCT urography: experience with a bi-phasic excretory phase examination protocol

The benefit of multidetector computed tomographic urography (MDCTU) for visualising early and late excretory phase (EP) upper urinary tract (UUT) opacification has been studied. UUT opacification was retrospectively evaluated in 45 bi-phasic four-row MDCTU examinations. The UUT was divided into intrarenal collecting system (IRCS), proximal, middle and distal ureter. Two independent readers rated opacification: 1, none; 2, partial; 3, complete. Numbers of segments and percentages of UUTs at each score were calculated for each EP and two EPs combined. Results of a single EP and of combined EPs were compared by Wilcoxon matched-pairs signed-ranks. IRCS and proximal ureter were at least partially opacified in each EP in >95%. The middle ureter was at least partially opacified in the early and late EP in 85% and 93%, respectively. The distal ureter was opacified in 65% (49/75) in the early EP and in 78% (59/75) in the late EP. Combining two EPs, non-opacified distal segments decreased to 9% (7/75). Significant improvement between a single EP and combining two EPs were found for the middle and distal ureter (P < 0.03). Bi-phasic MDCTU substantially improved opacification of the middle and distal ureter. IRCS and proximal ureter are reliably opacified with one EP.

Multidetector row computed tomography evaluation of potential living laparoscopic renal donors: the story so far

Renal transplantation is the treatment of choice for end-stage renal disease. Living related kidney donation is the major source of renal grafts due to limited availability of cadaveric kidneys. Open nephrectomy was used to harvest donor kidneys. However, the laparoscopic approach is associated with less postoperative pain and quick recovery. So, most centers now prefer a laparoscopic approach to explant donor kidneys. Laparoscopic approach is technically challenging due to limited operative visibility. Hence, accurate preoperative detection of renal arterial and venous anomalies is imperative to avoid inadvertent vascular injury and bleeding. The preoperative workup of renal donors includes clinical evaluation, laboratory tests, and imaging. Traditionally, the renal donors were evaluated with conventional imaging techniques, which included renal catheter angiography and intravenous urography. However, conventional imaging is invasive, expensive, and less accurate for evaluation of complex renal venous anomalies, small calculi, and diffuse or focal renal parenchymal lesions. The introduction of multidetector row computed tomography (MDCT) revolutionized the CT technology by enabling isotropic resolution with faster scan coverage in a single, short breath-hold. Consequently, MDCT has now replaced conventional imaging for comprehensive imaging of potential living renal donors. MDCT is a minimally invasive technique that can accurately detect urolithiasis, renal arterial and venous anomalies, renal parenchymal lesions, and urinary tract anomalies. Renal vascular anomalies detected by MDCT can help the surgeon in planning donor nephrectomy. MDCT with three-dimensional CT angiography enables accurate preoperative renal vascular mapping. This article reviews the role of MDCT in preoperative evaluation of potential laparoscopic renal donors.

MDCT urography: retrospective determination of optimal delay time after intravenous contrast administration

The optimal delay time after intravenous (i.v.) administration of contrast medium (CM) for opacification of the upper urinary tract (UUT) for multidetector computed tomography urography (MDCTU) was investigated. UUT opacification was retrospectively evaluated in 36 four-row MDCTU examinations. Single- (n=10) or dual-phase (n=26) MDCTU was performed with at least 5-min delay after i.v. CM. UUT was divided into four sections: intrarenal collecting system (IRCS), proximal, middle and distal ureter. Two independent readers rated UUT opacification: 1, none; 2, partial; 3, complete. Numbers and percentages of scores, and the 5%, 25%, 50%, 75% and 95% percentiles of delay time were calculated for each UUT section. After removing diseased segments, 344 segments were analysed. IRCS, proximal and middle ureter were completely opacified in 94% (81/86), 93% (80/86) and 77% (66/86) of cases, respectively. Median delay time was 15 min for complete opacification. The distal ureter was completely opacified in 37% (32/86) of cases and not opacified in 26% (22/86). Median delay time for complete opacification was 11 min with 25% and 75% percentiles of 10 and 16 min, respectively. At MDCTU, opacification of the IRCS, proximal and middle ureter was hardly sensitive to delay time. Delay times between 10 and 16 min were favourable in the distal ureter.

Dose reduction in multidetector CT of the urinary tract. Studies in a phantom model

A novel ureter phantom was developed for investigations of image quality and dose in CT urography. The ureter phantom consisted of a water box (14 cm x 32 cm x 42 cm) with five parallel plastic tubes (diameter 2.7 mm) filled with different concentrations of contrast media (1.88-30 mg iodine/ml). CT density of the tubes and noise of the surrounding water were determined using two multidetector scanners (Philips MX8000 with four rows, Siemens Sensation 16 with 16 rows) with varying tube current-time product (15-100 mAs per slice), voltage (90 kV, 100 kV, 120 kV), pitch (0.875-1.75), and slice thickness (1 mm, 2 mm, 3.2 mm). Contrast-to-noise ratio as a parameter of image quality was correlated with dose (CTDI) and was compared with image evaluation by two radiologists. The CT densities of different concentrations of contrast media and contrast-to-noise ratio were significantly higher when low voltages (90 kV versus 120 kV, 100 kV versus 120 kV) were applied. Smaller slice thickness (1 mm versus 2 mm) did not change CT density but decreased contrast-to-noise ratio due to increased noise. Contrast phantom studies showed favourable effects of low tube voltage on image quality in the low dose range. This may facilitate substantial dose reduction in CT urography.

Multidetector CT of the kidney

The technological development of multidetector CT offers new possibilities for better imaging of organic structures that can be used in diagnosis of the kidney. The thinner slices allow a better spatial resolution, and slice fusion allows improved contrast resolution. The isotropic voxel has been realized in the latest 64-channel scanners. The image quality of arbitrarily reconstructed planes has arrived at the image quality of the scan plane. Faster scanning allows studies in different contrast phases, which is helpful for better discrimination of benign or malignant lesions especially in the highly vascularized kidney. Different phases of contrast uptake can be differentiated (arterial, cortico-medullary, nephrographic, and excretory phase). Multidetector CT brings along the risk of increased dose due to thinner slice collimation and overranging phenomena. Indications for CT investigation of the kidney include urolithiasis, tumor diagnosis and staging, renal trauma, and vascular disease. Even in children, special indications for CT of the kidney remain in polytrauma and tumor staging. Multidetector CT of the kidney has become a very valuable tool in urology, but a careful protocol strategy is mandatory.

Renal Multidector Row CT

Multidetector row CT is the most recent advance in CT technology. An increased number of detector rows and more powerful x-ray tubes result in faster scanning time, increased volume coverage, and improved spatial and temporal resolution. MDCT technology allows superior image quality, decreased examination time, and the ability to perform complex multiphase vascular and three-dimensional examinations.

Antegrade MDCT Pyelography for the Evaluation of Patients with Obstructed Urinary Tract

OBJECTIVE

The purpose of this study was to design an alternative imaging technique to CT urography in patients with high-grade urinary tract obstruction, with or without impaired renal function, that uses the superior resolution of MDCT and avoids IV contrast material administration.

CONCLUSION

Antegrade MDCT pyelography is an alternative imaging technique to CT urography in patients with high-grade urinary tract obstruction with or without impaired renal function. It enables accurate diagnosis of the level of obstruction, as well as its etiology, including nephroureterolithiasis, urothelial tumors, primary congenital megaureter, uretero-pelvic junction stenosis, ureteral edema, ureteral stricture, retroperitoneal fibrosis, and pelvic lymphadenopathy.

Multidetector row CT of the kidneys

In this article, the value of multiple detector-row computed tomography (MDCT) in renal applications is discussed, with emphasis on clinical uses. The superiority of application techniques of MDCT renders it one of the most distinguished modality in detection of congenital anomalies, tumors, transplants, trauma, and arterial diseases of the kidney.