Brian R. Herts

Management of the Incidental Renal Mass

Despite substantial advances in the imaging-based diagnosis of renal masses, the increased detection of incidental renal masses with cross-sectional imaging poses problems to the radiologist and referring physician. Most incidental renal masses can be diagnosed with confidence and either ignored or treated without further testing. However, some renal masses, particularly small ones, remain indeterminate and require a management strategy that is both medically appropriate and practical. In this article, the literature will be reviewed and an approach to the diagnosis and management of the incidental renal mass will be suggested. Management recommendations, derived from data regarding the probability of malignancy in cystic and solid renal masses, are provided for two types of patients, those in the general population and those with limited life expectancy or co-morbidity. The Bosniak classification is used to guide the management of cystic masses, with observation reserved for selected patients, and the presumption of benignity recommended for simple-appearing cystic masses smaller than 1 cm. Among solid renal masses, a more aggressive overall approach is taken. However, additional imaging, and in selected patients, percutaneous biopsy, is recommended to diagnose benign neoplasms. Although additional studies are needed to establish risks and benefits, observation of solid masses may be considered in selected patients. Minimally invasive treatments of renal cancer (including percutaneous ablation) show promise but at the same time challenge the radiologist to review the approach to the incidental renal mass.

Prospective Evaluation of Fine Needle Aspiration of Small, Solid Renal Masses: Accuracy and Morbidity

OBJECTIVES To determine the accuracy and clinical utility of fine needle aspiration (FNA) of small, solid renal masses. METHODS A total of 25 patients with small (less than 5.0 cm), solid, clinically localized renal masses were prospectively identified and evaluated with computed tomography guided FNA with analysis for presence of malignant cells and determination of nuclear grade. The final pathologic findings were used for comparison in each case. All patients had renal cell carcinoma and were managed with radical or partial nephrectomy; 3 had low-grade lesions (Fuhrmans grade 1/4), 2 had high-grade lesions (Fuhrmans grade 4/4), and all other patients had intermediate-grade lesions (Fuhrmans grade 2/4 or 3/4) on final histopathologic assessment. RESULTS Overall, 10 aspirations yielded diagnostic malignant cells, and 9 were read as rare as rare atypical cells suspicious for malignancy. The remainder were negative (n = 6). Correlation with final nuclear grade was observed in eight instances and discordance in two instances. Subcapsular hematomas were observed at the time of surgery in 10 patients, but in no instance was the operation adversely affected. CONCLUSIONS The diagnostic yield of FNA of small, solid renal masses appears to be too low to justify the potential morbidity of the procedure.

3-DIMENSIONAL VOLUME RENDERED COMPUTERIZED TOMOGRAPHY FOR PREOPERATIVE EVALUATION AND INTRAOPERATIVE TREATMENT OF PATIENTS UNDERGOING NEPHRON SPARING SURGERY

PURPOSE Computerized tomography (CT) is the diagnostic and staging modality of choice for renal neoplasms. Existing imaging modalities are limited by a 2-dimensional (D) format. Recent advances in computer technology now allow the production of high quality 3-D images from helical CT. Nephron sparing surgery requires a detailed understanding of renal anatomy. Preoperative evaluation must delineate the relationship of the tumor to adjacent normal structures and demonstrate the vascular supply to the tumor for the surgeon to conserve as much normal parenchyma as possible. We propose that helical CT combined with 3-D volume rendering provides all of the information required for preoperative evaluation and intraoperative management of nephron sparing surgery cases. We prospectively evaluated the role of 3-D volume rendering CT in 60 patients undergoing nephron sparing surgery for renal cell carcinoma at the Cleveland Clinic Foundation. MATERIALS AND METHODS Triphasic spiral CT was performed preoperatively in 60 consecutive patients undergoing nephron sparing surgery for renal neoplasms. A 3 to 5-minute videotape was prepared using volume rendering software which demonstrated the position of the kidney, location and depth of extension of the tumor(s), renal artery(ies) and vein(s), and relationship of the tumor to the collecting system. These videotapes were viewed by a radiologist and urologist in the operating room at surgery, and immediately correlated with surgical findings. Corresponding renal arteriograms of 19 patients were retrospectively compared to 3-D volume rendering CT and operative findings. RESULTS A total of 97 renal masses were identified in 60 cases evaluated with 3-D volume rendering CT before nephron sparing surgery. There were no complications related to the 3-D protocol and 3-D rendering was successful in all patients. The number and location of lesions identified by 3-D volume rendering CT were accurate in all cases, while enhancement and diagnostic characteristics were consistent with pathological findings in 95 of 97 tumors (98%). Of 77 renal arteries identified at surgery 74 were detected by 3-D volume rendering CT (96%). Helical CT missed 3 small accessory arteries, including 1 in a cross fused ectopic kidney. All major venous branches and anomalies were identified, including 3 circumaortic left renal veins. Of 69 renal veins identified at surgery 64 were detected by 3-D volume rendering CT (93%). All 5 renal veins missed by CT were small, short, duplicated right branches of the main renal vein. Renal fusion and malrotation anomalies were correctly identified in all 4 patients. CONCLUSIONS The 3-D volume rendering CT accurately depicts the renal parenchymal and vascular anatomy in a format familiar to most surgeons. The data integrate essential information from angiography, venography, excretory urography and conventional 2-D CT into a single imaging modality, and can obviate the need for more invasive imaging. Additionally, the use of videotape in an intraoperative setting provides concise, accurate and immediate 3-D information to the surgeon, and it has become the preferred means of data display for these procedures at our center.

Contrast-to-Noise Ratio and Low-Contrast Object Resolution on Full- and Low-Dose MDCT: SAFIRE Versus Filtered Back Projection in a Low-Contrast Object Phantom and in the Liver

OBJECTIVE The purpose of this article is to evaluate the effect of sinogram-affirmed iterative reconstruction (SAFIRE) on contrast-to-noise ratio (CNR) compared with filtered back projection (FBP) and to determine whether SAFIRE improves low-contrast object detection or conspicuity in a low-contrast object phantom and in the liver on full- and low-dose examinations. SUBJECTS AND METHODS A low-contrast object phantom was scanned at 100%, 70%, 50%, and 30% dose using a single-source made of a dual-source MDCT scanner, with the raw data reconstructed with SAFIRE and FBP. Unenhanced liver CT scans in 22 patients were performed using a dual-source MDCT. The raw data from both tubes (100% dose) were reconstructed using FBP, and data from one tube (50% dose) were reconstructed using both FBP and SAFIRE. CNR was measured in the phantom and in the liver. Noise, contrast, and CNR were compared using paired Student t tests. Six readers assessed sphere detection and conspicuity in the phantom and liver-inferior vena cava conspicuity in the patient data. The phantom and patient data were assessed using multiple-variable logistic regression. RESULTS The phantom at 70% and 50% doses with SAFIRE had decreased noise and increased CNR compared with the 100% dose with FBP. In the liver, the mean CNR improvement at 50% dose with SAFIRE compared with FBP was 31.4% and 88% at 100% and 50% doses, respectively (p < 0.001). Sphere object detection and conspicuity improved with SAFIRE (p < 0.001). However, smaller spheres were obscured on both FBP and SAFIRE images at lower doses. Liver-vessel conspicuity improved with SAFIRE over 50%-dose FBP in 67.4% of cases (p < 0.001), and versus 100%-dose FBP, improved in 38.6% of cases (p = 0.085). As a predictor for detection, CNR alone had a discriminatory ability (c-index, 0.970) similar to that of the model that analyzed dose, lesion size, attenuation difference, and reconstruction technique (c-index, 0.978). CONCLUSION Lower dose scans reconstructed with SAFIRE have a higher CNR. The ability of SAFIRE to improve low-contrast object detection and conspicuity depends on the radiation dose level. At low radiation doses, low-contrast objects are invisible, regardless of reconstruction technique.

Renal Function Assessment in the Era of Chronic Kidney Disease: Renewed Emphasis on Renal Function Centered Patient Care

PURPOSE Chronic kidney disease is more common than previously appreciated and it is now established as a major independent contributor to mortality. Serum creatinine is known to be an inaccurate reflection of the presence or development of chronic kidney disease. Since urologists frequently treat patients with coexistent chronic kidney disease, we reviewed the merits and limitations of the current methods to estimate renal function, and recent data indicating the importance of optimizing renal function during treatment. MATERIALS AND METHODS A comprehensive literature review was performed to evaluate the laboratory, computational and imaging techniques for renal function estimation. RESULTS Approximately 30% of elderly patients with normal serum creatinine (1.4 mg/dl or less) have chronic kidney disease based on an estimated glomerular filtration rate of less than 60 ml per minute per 1.73 m(2). The National Kidney Foundation currently recommends using a creatinine based estimate of glomerular filtration rate (eg Modification of Diet in Renal Disease formula) and has advocated a standardized classification for chronic kidney disease. Chronic kidney disease has been independently related to morbid cardiac events and all cause mortality in a dose dependent fashion, even after controlling for a variety of potentially confounding factors such as hypertension and diabetes. Many urological interventions can precipitate or exacerbate chronic kidney disease, most notably radical nephrectomy which is greatly overused. CONCLUSIONS Practicing urologists should be cognizant of current methodologies to diagnose chronic kidney disease and its profound implications. Estimation of renal function is better using a serum creatinine based formula than individual serum creatinine values. Treatment goals should not be limited to avoidance of dialysis, but should also include greater efforts to optimize renal function in all patients and early referral for nephrological consultation.

Effect of Altering Automatic Exposure Control Settings and Quality Reference mAs on Radiation Dose, Image Quality, and Diagnostic Efficacy in MDCT Enterography of Active Inflammatory Crohn's Disease

OBJECTIVE The purpose of our study was to determine whether the MDCT enterography dose can be reduced by changing automatic exposure control (AEC) setting and quality reference milliampere-seconds (mAs) without altering subjective image quality or efficacy in active inflammatory Crohns disease. SUBJECTS AND METHODS This is a prospective study of 2,310 MDCT enterography procedures performed using 16- and 64-MDCT in three cohorts (original, intermediate, and final dose levels). For 16-MDCT, the original and intermediate dose level quality reference mAs was 200, and weight-based (1 pound [0.45 kg] = 1 mAs) for the final dose level. For 64-MDCT, the original dose level quality reference mAs was 260; the mAs was 220 for intermediate and weight-based for the final dose level. For the intermediate and final dose levels, AEC was changed from strong to weak increase for obese and weak to strong decrease for slim patients. Demographic data and volume CT dose index (CTDI(vol)) were analyzed. Three readers evaluated the cases for image quality and efficacy differentiating normal from active inflammatory Crohns disease. RESULTS For 16-MDCT, CTDI(vol) decreased from 12.82 to 10.14 mGy and 10.14 to 8.7 mGy between original to intermediate and intermediate to final dose levels. For 64-MDCT, the CTDI(vol) decreased from 15.72 to 11.42 mGy and 11.42 to 9.25 mGy between original to intermediate and intermediate to final dose levels. Images were rated suboptimal or nondiagnostic more often in the intermediate dose level (p < 0.05) but not in the final. There was no reduction in diagnostic efficacy as measured by area under the ROC curve (p > 0.1443 except for one comparison with one reader). CONCLUSION Substantial dose reduction can be achieved using weight-based quality reference mAs and altering AEC settings without affecting diagnostic efficacy in active inflammatory Crohns disease of the terminal ileum. However, subjective image quality can be compromised at these dose settings, depending on radiologist preference.

Bosniak Category IIF and III Cystic Renal Lesions: Outcomes and Associations

PURPOSE To evaluate clinical outcomes, pathologic subtypes, metastatic disease rate, and clinical features associated with malignancy in Bosniak category IIF and III cystic renal lesions. MATERIALS AND METHODS This retrospective study was institutional review board approved and HIPAA compliant. Informed consent was waived. Radiology and hospital information systems were searched for Bosniak IIF and Bosniak III lesions in computed tomographic (CT) reports from January 1, 1994 to August 31, 2009. Patients 18 years and older with unenhanced and contrast material-enhanced CT results and with lesions either surgically resected or with 1 year or more of surveillance were included. Data recorded were history of renal cell carcinoma, number of renal lesions, presence of a coexistent solid renal mass, surgical pathologic findings, and presence of metastatic disease from a renal malignancy. Sixty-two patients with 69 Bosniak IIF lesions and 131 patients with 144 Bosniak III lesions were identified. Proportions from independent groups were compared by using the Fisher exact test; continuous variables were compared by using a two-tailed two-sample t test or a Wilcoxon two-sample test. RESULTS The malignancy rate of resected Bosniak IIF lesions was 25% (four of 16) and that for Bosniak III lesions was 54% (58 of 107) (P = .03). Thirteen percent (nine of 69) of Bosniak IIF lesions progressed at follow-up, and 50% (four of eight) of these resected cysts were malignant. History of primary renal malignancy, coexisting Bosniak category IV lesion and/or solid renal mass, and multiplicity of Bosniak III lesions were each associated with an increased malignancy rate in Bosniak III lesions. No patients developed locally advanced or metastatic disease from a Bosniak IIF or III lesion. CONCLUSION Although the malignancy rate in surgically excised Bosniak IIF and Bosniak III cystic renal lesions was 25% and 54%, respectively, in our study, the malignancy rate was higher in patients with a history of primary renal malignancy or coexisting Bosniak IV lesion and/or solid renal neoplasm.

Correlation Between Loss of Renal Function and Loss of Renal Volume After Partial Nephrectomy for Tumor in a Solitary Kidney

PURPOSE We assessed the correlation between reduced renal function and parenchymal volume following partial nephrectomy. MATERIALS AND METHODS In 21 of 42 patients with tumors in a solitary kidney who were enrolled in a study measuring function before and after surgery underwent computerized tomography, and measurement of the glomerular filtration rate and estimated glomerular filtration rate (the latter at baseline and 2 to 6 months) before and after surgery. A segmentation algorithm was used to measure renal parenchymal volume. The percent of renal parenchymal volume loss was correlated with the percent loss in glomerular filtration rate using the Pearson correlation coefficient. RESULTS Mean +/- SD net preoperative volume was 284 +/- 67 cc (range 179 to 413) and mean net postoperative volume was 240 +/- 61 cc (range 119 to 346) with an absolute functional volume loss of between 5 and 160 cc. The average percent of parenchymal volume loss was 15% (range -2% to 47%). The mean loss of the measured glomerular filtration rate 3 days postoperatively was 33.9% (range -70.7% to 74.4%) and the estimated glomerular filtration rate 2 to 6 months postoperatively was 19.7 % (-6.0% to 45.5%). There was a low degree of correlation between the percent volume loss and the percent measured glomerular filtration rate loss at 3 days (r = 0.28, p = 0.22). However, there was a moderate degree of correlation between the percent volume loss and the percent estimated glomerular filtration rate loss at 2 to 6 months (r = 0.48, p = 0.03). CONCLUSIONS In patients with partial nephrectomy the renal parenchymal volume loss correlates best with the renal function loss several months after surgery. Estimates of volume loss may be useful for predicting postoperative renal function when planning partial nephrectomy in patients with a solitary kidney.

Angiomyolipoma with Minimal Fat on MDCT: Can Counts of Negative-Attenuation Pixels Aid Diagnosis?

OBJECTIVE The purpose of this study was to determine whether counts of pixels with subzero attenuation on CT scans can aid in the diagnosis of renal angiomyolipoma with minimal fat. MATERIALS AND METHODS Of 33 angiomyolipomas identified among 719 renal masses resected from 702 patients over 4 years, 15 masses in 15 patients were prospectively diagnosed on the basis of the presence of fat at MDCT. The 18 patients with minimal-fat angiomyolipoma and a matched (age, sex, tumor size) cohort of patients with renal cell carcinoma were included in this study. Three radiologists independently counted the number of pixels with attenuation less than -10, -20, and -30 HU. Receiver operating characteristic analysis of the number of pixels at each cutoff was used to calculate sensitivity, specificity, and positive predictive value with the following criteria: 1, more than 10 pixels less than -20 HU; 2, more than 20 pixels less than -20 HU; 3, more than 5 pixels less than -30 HU. RESULTS Using criterion 1, reader A identified six angiomyolipomas; reader B, five; and reader C, two. The combined sensitivity was 24%; specificity, 98%; and positive predictive value, 69%. Using criterion 2, reader A identified three angiomyolipomas; reader B, four; and reader C, two. The combined sensitivity was 17%; specificity, 100%; and positive predictive value, 100%. Using criterion 3, reader A identified four angiomyolipomas; reader B, four; and reader C, two. The combined sensitivity was 18%; specificity, 100%; and positive predictive value, 100%. CONCLUSION CT findings of more than 20 pixels with attenuation less than -20 HU and more than 5 pixels with attenuation less than -30 HU have a positive predictive value of 100% in detection of angiomyolipoma, but most angiomyolipomas with minimal fat cannot be reliably identified on the basis of an absolute pixel count.

Urinary Calculi: Radiation Dose Reduction of 50% and 75% at CT—Effect on Sensitivity

PURPOSE To retrospectively determine the effect of 50% and 75% dose reduction on sensitivity and specificity of computed tomography (CT) for the detection of urinary calculi. MATERIALS AND METHODS This HIPAA compliant study was institutional review board approved; informed consent was waived. Raw CT data from 47 consecutive patients (24 male patients, 23 female patients; mean age, 46.0 years) who underwent unenhanced CT for flank pain were collected. Original CT examinations were performed by utilizing an automated dose modulation algorithm. Reconstructions of raw CT data were performed at 100%, 50%, and 25% of the original tube current by using simulation software; tube currents averaged 177, 88, and 44 mA, respectively. All reconstructed examinations were randomized and evaluated by two radiologists blinded to the presence, number, location, and size of calculi. The opinion of an unblinded radiologist who separately reviewed the original examination and report and the electronic medical record served as the reference standard. One hundred eight calculi (85 renal, 21 ureteral, and two in the bladder) were present in 32 of 47 patients. Calculus diameter ranged from 0.14 to 1.32 cm (mean, 0.34 cm). The decrease in sensitivity was assessed between doses and was independently evaluated for all calculi and separately for calculi greater than 3 mm in diameter by using the McNemar test, adjusted for clustered data. RESULTS For all calculi, the blinded readers demonstrated combined sensitivities of 91.7%, 83.3%, and 67.1% for the 100%, 50%, and 25% tube current reconstructions, respectively. For stones greater than 3 mm, combined sensitivities were 97.7%, 93.0%, and 91.9%, respectively, for the 100%, 50%, and 25% reconstructions. There was no significant difference between the 100% examinations and the 50% and 25% reconstructions for detection of stones greater than 3 mm (P = .106 and .099, respectively). CONCLUSION There were no significant differences between the 100% examinations and the 50% and 25% examinations for the detection of calculi greater than 3 mm.