Helical CT of renal masses: the value of delayed scans

Discrimination of oncocytoma and chromophobe renal cell carcinoma using MRI

PURPOSE

We aimed to evaluate magnetic resonance imaging (MRI) features, including signal intensities, enhancement patterns and T2 signal intensity ratios to differentiate oncocytoma from chromophobe renal cell carcinoma (RCC).

METHODS

This retrospective study included 17 patients with oncocytoma and 33 patients with chromophobe RCC who underwent dynamic MRI. Two radiologists independently reviewed images blinded to pathology. Morphologic characteristics, T1 and T2 signal intensities were reviewed. T2 signal intensities, wash-in, wash-out values, T2 signal intensity ratios were calculated. Sensitivity and specificity analyses were performed.

RESULTS

Mean ages of patients with oncocytoma and chromophobe RCC were 61.0±11.6 and 58.5±14.0 years, respectively. Mean tumor size was 60.6±47.3 mm for oncocytoma, 61.7±45.9 mm for chromophobe RCC. Qualitative imaging findings in conventional MRI have no distinctive feature in discrimination of two tumors. Regarding signal intensity ratios, oncocytomas were higher than chromophobe RCCs. Renal oncocytomas showed higher signal intensity ratios and wash-in values than chromophobe RCCs in all phases. Fast spin-echo T2 signal intensities were higher in oncocytomas than chromophobe RCCs.

CONCLUSION

Signal intensity ratios, fast spin-echo T2 signal intensities and wash-in values constitute diagnostic parameters for discriminating between oncoytomas and chromophobes. In the excretory phase of dynamic enhanced images, oncocytomas have higher signal intensity ratio than chromophobe RCC and high wash-in values strongly imply a diagnosis of renal oncocytoma.

Optimization of scan delay for multi-phase computed tomography by using bolus tracking in normal canine kidney

This study was performed to optimize scan delays for canine kidney by using a bolus-tracking technique. In six beagle dogs, computed tomography (CT) of the kidney was performed three times in each dog with different scan delays after a bolus-tracking trigger of 100 Hounsfield units (HU) of aortic enhancement. Delays were 5, 20, 35, and 50 sec for the first scan, 10, 25, 40, and 55 sec for the second scan, and 15, 30, 45, and 60 sec for the third scan. The renal artery-to-vein contrast difference peaked at 5 sec, and the renal cortex-to-medulla contrast difference peaked at 10 sec. The renal cortex-to-medulla contrast difference approached zero at a scan delay of 30 sec after the bolus trigger. For the injection protocol used in this study, the optimal scan delay times for renal arterial, corticomedullary, and nephrographic phases were 5, 10, and 30 sec after triggering at 100 HU of aortic enhancement using the bolus-tracking technique. The bolus-tracking technique is useful in multi-phase renal CT study as it compensates for different transit times to the kidney among different animals, requires a small dose of contrast media, and does not require additional patient radiation exposure.

[Modern imaging of renal tumors - application in diagnostics and therapy. Characterization, operation planning and therapy monitoring of renal lesions]

This article elucidates the various tools used for the diagnostics and characterization of renal lesions. The advantages and limitations of ultrasound, contrast-enhanced ultrasound (CEUS), computed tomography (CT) and magnetic resonance imaging (MRI) are presented and discussed. In addition, modern imaging features of CT and MRI, such as iodine quantification in CT as well as diffusion-weighted and perfusion imaging in MRI are presented. Lastly, recent developments in standardized reporting of renal tumors regarding the intraoperative surgical risk are presented.

Staging, surveillance, and evaluation of response to therapy in renal cell carcinoma: role of MDCT

Renal cell carcinoma is the most common malignant renal tumor in the adults. Significant advances have been made in the management of localized and advanced renal cell carcinoma. Surgery is the standard of care and accurate pre-operative staging based on imaging is critical in guiding appropriate patient management. Besides staging, imaging plays a key role in the post-operative surveillance and evaluation of response to systemic therapies. Both CT and MR are useful in the staging and follow up of renal cell carcinoma, but CT is more commonly used due to its lower costs and wider availability. In this article, we discuss and illustrate the role of multi-detector CT in pre-operative staging, post-operative surveillance, and evaluation of response to systemic therapy in renal cell carcinoma.

MDCT urography with high-volume low-concentration i.v. contrast material, peroral hydration, i.v. furosemide, and i.v. saline: qualitative and quantitative assessment in 100 consecutive patients

OBJECTIVE

The purpose of this study is to qualitatively and quantitatively assess MDCT urography performed with a high volume of low-concentration (240 mg I/mL) i.v. contrast agent supplemented with peroral hydration, i.v. furosemide, and i.v. saline.

MATERIALS AND METHODS

This retrospective evaluation of 100 consecutive normal MDCT urograms was performed for clinical indication of hematuria; patients (76 men and 24 women) were 27-90 years old (mean [± SD] age, 60 ± 15 years). Three radiologists evaluated the degree of opacification across six urinary tract segments (for a total of 1200 measurements per radiologist) on a 4-point scale (0-3). One radiologist measured the maximum short-axis diameter of the proximal, mid, and distal ureters in each patient. Mean opacification scores were calculated for each segment. Radiologist agreement was assessed by kappa coefficient and Spearman rank correlation. Ureteral diameter was correlated to degree of opacification using the Jonckheere-Terpstra trend test. A comparison with published studies using similar scoring methods was undertaken.

RESULTS

Of 1200 measured ureteral segments, a total of 24 among the three radiologists were reported as nonopacified. The mean opacification scores ranged from 2.63 ± 0.8 to 3.00 ± 0.8. Calculated kappa coefficients are indicative of substantial agreement (> 0.61). The mean maximal ureteral diameters were 5.44 ± 1.10, 6.32 ± 1.54, and 5.32 ± 1.55 mm for the proximal, mid, and distal ureters, respectively. For all three radiologists, the mean opacification scores increased as distention increased. The Spearman correlation and corresponding p value (p < 0.001) for the association between the distention with the opacification scores show significant correlation. The opacification scores and ureteral distention exceeded published results.

CONCLUSION

An MDCT urography technique using high-volume low-concentration i.v. contrast, oral and i.v. hydration, and i.v. diuretic reliably optimizes urinary tract opacification and distention. A positive correlation was found between ureteral distention and opacification.

Small renal oncocytomas: differentiation with multiphase CT

OBJECTIVES

To evaluate characteristic imaging findings of tumor attenuation in multiphase computed tomography (CT) between renal oncocytomas and clear-cell renal cell carcinoma (ccRCC) of small tumor size (≤5 cm).

METHODS

We retrospectively identified 20 patients with complete four-phase CT with either histologically confirmed small renal oncocytoma (N=10) or ccRCC (N=10) who underwent subsequent total or partial nephrectomy. Exclusion criteria for RCC were non-clear-cell components in histology and a tumor diameter>5 cm. The relative attenuation of solid renal lesions and normal renal cortex was determined in the unenhanced, corticomedullary, nephrographic and excretory phase. Statistical comparison was carried out by Wilcoxon Rank Sum Test.

RESULTS

Mean tumor size of renal oncocytomas was 2.8±0.4 cm (1.2-5) and of ccRCC 2.5±0.2 cm (1.7-4.4; p=0.57). All lesions were homogenous without extended areas of necroses. In the nephrographic phase, the difference of attenuation between renal cortex and tumor lesion was highest in both entities (oncocytoma, 48.1±5.2 HU; ccRCC, 67.5±12.1) but not between entities (p=0.30). In the corticomedullary phase, renal oncocytomas showed greater isodensity to the normal renal cortex (13.9±4.3 HU) compared to clear-cell RCC (51.5±5.0 HU; p=0.003). No further significant differences were found for the unenhanced and excretory phase.

CONCLUSIONS

In this study, the maximum tumor-to-kidney contrast coincided with the nephrographic phase which was thus the most reliable for the detection of a renal lesion<5 cm. For lesion characterization, the corticomedullary phase was most useful for differentiating both entities. This finding is particularly important for the preoperative planning of a partial nephrectomy.

How not to miss or mischaracterize a renal cell carcinoma: protocols, pearls, and pitfalls

OBJECTIVE

MDCT protocol optimization for renal cell carcinoma requires attention to several data acquisition, reconstruction, and display parameters. Specifically, multiple acquisitions with varying coverage, careful timing of each contrast-enhanced phase, and use of 2D and 3D multiplanar displays are required. This article reviews these parameters, supplemented by experience-based pearls and pitfalls.

CONCLUSION

Proper data acquisition and utilization of postprocessing tools are essential to avoid missed diagnoses or misinterpretation when imaging renal cell carcinoma.

Multi-detector row CT of the kidney: Optimizing scan delays for bolus tracking techniques of arterial, corticomedullary, and nephrographic phases

PURPOSE

To determine optimal scan delays for renal arterial-, corticomedullary-, and nephrographic-phase imaging with multi-detector row computed tomography (MDCT) of the kidney using a bolus-tracking technique.

METHODS AND MATERIALS

One hundred and twenty-eight patients underwent three-phase CT scan of the kidney with eight-row MDCT after receiving 2 mL/kg of 300 mgI/mL contrast medium at 4 mL/s. Patients were prospectively randomized into three groups with different scan delays for the three scan phases (arterial, corticomedullary, and nephrographic) after bolus-tracking triggered at 50 HU of aortic contrast enhancement: group 1 (5, 20, 45 s); group 2 (10, 25, 50s); and group 3 (15, 30, 55 s). Mean CT values (HU) of the abdominal aorta, renal artery, renal vein, renal cortex, and renal medulla were measured; increases in CT values pre- to post-contrast were assessed as contrast enhancement. Renal artery-to-vein and renal cortex-to-medulla contrast differences were also assessed. Qualitative analysis was also performed.

RESULTS

Mean renal artery enhancement was 240-288 HU at 5-15s after the trigger and peaked at 10s (P<.001). Mean renal cortical enhancement was 195-217 HU at 10-30s and peaked at 25s (P<.01). Contrast enhancement in the renal medulla increased gradually and reached mean 145 HU at 55 s. Cortex-to-medulla contrast difference was high (110-140 HU) at 5-30s and decreased below 30 HU at 45 s after the trigger. Renal artery-to-vein contrast difference was high (121-125 HU) at 5-10s. Qualitative results correlated well with quantitative results.

CONCLUSION

For the injection protocol used in this study, optimal scan delays after the bolus-tracking trigger were 5-10 s for renal arterial, 15-25 s for corticomedullary, and 50-55 s for nephrographic phases.

Renal Oncocytoma on 1-11C acetate Positron Emission Tomography: Case Report and Literature Review

Renal oncocytomas are uncommon tumors of the renal collecting duct. Although generally benign, these tumors pose a diagnostic and therapeutic dilemma in that they can not be differentiated noninvasively from renal cell carcinomas. We report a 67-year-old man who underwent a clinical 1-11C acetate positron emission tomography (PET) scan for evaluation of possible metastatic prostate carcinoma. The study demonstrated a nodule at the inferior pole of the right kidney with more uptake than the remainder of the kidney. Correlation was made with MRI, which demonstrated that the nodule was solid, and enhanced after contrast agent administration. Upon resection, this nodule was determined to be an oncocytoma. To our knowledge, this marks the first report of the 1-11C acetate PET scan appearance of a renal oncocytoma Possible mechanisms for increased uptake include dysfunctional, but up-regulated oxidative phosphorylation or uptake through lipid biosynthesis pathways.

Imaging of renal lesions: evaluation of fast MRI and helical CT

The purpose of this study is to compare triphasic helical CT and fast MRI with respect to detection, characterization and staging of suspected renal masses. To achieve this triphasic helical CT (plain, corticonephrographic and tubulonephrographic phase) and MRI with fast T(1) weighted and T(2) weighted sequences were performed in 29 patients with a suspected renal lesion. Image quality, lesion characterization and lesion extent were assessed for both methods in all patients. The acquisition phase for CT and the image sequence for MRI offering the best image quality and best diagnostic information regarding renal parenchyma, renal vessels, detection of enlarged lymph nodes, and other abdominal organs were determined. Histologically confirmed renal cell carcinomas (n=18) were staged based on the Robson classification. Quantitative data were obtained from operator-defined regions of interest (ROIs) in all acquisition phases (CT) and all image sequences (MRI). For most criteria the rating of image quality for helical CT was generally higher as compared with fast MRI. CT and MRI detected all 24 histologically proven masses, while no false positive solid tumour was diagnosed with both imaging modalities. All three acquisition phases in CT and all applied image sequences in MRI were regarded as necessary in order to gain important diagnostic information. Altogether, 12 of 18 renal cell carcinomas (67%) were correctly staged by CT and MRI. Helical CT and fast MRI allow the correct detection and characterization of suspicious renal lesions. Both imaging modalities can be recommended for clinical routine application. Although the correct histological staging of renal cancer remains difficult for both imaging methods, both are excellent in providing the critical staging information needed before surgery. Helical CT offers a significantly shorter acquisition time to cover the entire abdomen.

Spoke-wheel pattern in renal oncocytoma seen on double-phase helical CT

Renal oncocytomas are benign, solid tumours of the kidney. An angiographic spoke-wheel pattern is known to be associated with oncocytomas, although it is not pathognomonic. On review of the literature, we found two reports of sonographic spoke-wheel appearance in oncocytomas. These were sufficiently characteristic to enable a confident preoperative diagnosis of oncocytoma. We present a case of a surgically proven oncocytoma with a distinct helical CT appearance, -commensurate with the angiographic and sonographic spoke-wheel appearance from which the diagnosis was suspected preoperatively.

Comparison of reliabilities of the delayed images of helical renal CT in detecting small renal masses

The reliabilities of the delayed images of helical computed tomography (CT) in detecting renal mass lesions of 30 mm or less in diameter was compared. Nephrographic, excretory and nephrographic+excretory phase images of all patients were evaluated separately to detect mass lesions of < or = 5 and 5-30 mm. There was not any statistically significant difference in the results of three groups. Nephrographic, excretory and nephrographic + excretory phase images are not different from or superior to each other in lesion detection.

Renal lymphoma: CT patterns with emphasis on helical CT

Renal lymphoma is most often seen in conjunction with multisystemic, disseminated lymphoma or as tumor recurrence. Renal lymphoma may also be seen in immunocompromised patients or, rarely, as primary disease. Computed tomography (CT) is the most sensitive, efficient, and comprehensive examination for evaluation of the kidneys in patients with suspected renal lymphoma. Helical CT in particular improves detection and characterization of lymphomatous renal involvement by optimizing contrast dynamics and data acquisition and is the current modality of choice for accurate staging of lymphoma. Typical CT patterns in renal lymphoma include single and multiple masses, invasion from contiguous retroperitoneal disease, perirenal disease, and diffuse renal infiltration. Atypical CT patterns may also be encountered and provide a diagnostic challenge. These include spontaneous hemorrhage, necrosis, heterogeneous attenuation, cystic transformation, and calcification. Solid renal masses including renal cell carcinoma and metastases are the most commonly encountered entities that mimic renal lymphoma at CT and require biopsy for definitive diagnosis. CT (particularly helical CT) is useful in the evaluation of patients with suspected renal lymphoma, and familiarity with the spectrum of findings in renal lymphoma is important for accurate diagnosis.

Assessment of a bolus-tracking technique in helical renal CT to optimize nephrographic phase imaging

PURPOSE

To evaluate a bolus-tracking technique in helical computed tomography (CT) for identifying the onset of the nephrographic phase and to determine the effect of varying the volume and injection rate of contrast material on nephrographic phase onset.

MATERIALS AND METHODS

Seventy-five patients underwent bolus tracking of contrast material followed by helical renal CT. In 50 patients, 150 mL of 60% iodinated contrast material (iohexol or iothalamate meglumine) was injected at either 2 mL/sec (25 patients [group 1]) or 3 mL/sec (25 patients [group 2]). In 25 patients who had previously undergone nephrectomy, 100 mL of 60% iodinated contrast material was injected at 3 mL/sec (group 3). Nephrographic phase onset was determined by visually assessing the transition to a homogeneous nephrogram during a monitoring scan series starting 40 seconds after injection.

RESULTS

Nephrographic phase onset ranged from 60 to 136 seconds (mean, 89 seconds +/- 17 [+/- SD]). Statistically significant differences in mean onset times were observed among groups 1 (103 seconds +/- 12), 2 (91 seconds +/- 16), and 3 (75 seconds +/- 9) (P < .001). Multiple regression analysis showed patient age, contrast material volume, and injection rate to be independent predictors of nephrographic phase onset. Contrast material volume, patient age, and patient weight were independent predictors of the degree of renal enhancement.

CONCLUSION

Nephrographic phase onset is highly dependent on methods of contrast material administration and patient characteristics.

Urinary bladder pseudolesions on contrast-enhanced helical CT: frequency and clinical implications

OBJECTIVE

The goals of this study were to define the distinguishing characteristics and frequency of urinary bladder pseudolesions that are produced as opacified urine enters the bladder during contrast-enhanced helical CT of the abdomen and to evaluate the usefulness of delayed imaging in differentiating pseudolesions from true lesions.

SUBJECTS AND METHODS

Contrast-enhanced routine CT scans of 184 patients were obtained prospectively. For each patient, we also obtained 5-min delayed images of the bladder. The images were evaluated for apparent focal thickening or polypoid lesions involving the bladder wall, findings that may represent bladder neoplasia, without knowledge of the indications for the scan, the patient's clinical history, or the patient's diagnosis. Apparent lesions that were visible on routine images and entirely absent on delayed images were considered to be pseudolesions.

RESULTS

Apparent lesions were identified on 20 (10.9%+/-4.5% [limits of the 95% confidence interval]) of the routine CT scans. Using delayed images, the 21 apparent lesions in these 20 patients were resolved as 13 pseudolesions and eight true lesions. Pseudolesions were present in 6.5%+/-3.6% of patients.

CONCLUSION

Pseudolesions of the bladder that are indistinguishable from true lesions pose a significant clinical problem in routine contrast-enhanced helical CT of the abdomen. Delayed imaging of the bladder is useful in distinguishing pseudolesions from true lesions.

The diagnosis and management of small (< or = 3 cm) renal neoplasms: a commentary

Many renal cell carcinomas are discovered incidentally. This phenomenon is largely attributable to advances in renal imaging, particularly regarding CT, to the widespread use of cross-sectional imaging in the diagnosis of abdominal disease, and to growing experience with the detection and diagnosis of renal masses. Accompanying the apparent increasing prevalence of renal masses are several controversies that specifically concern small (< or = 3 cm) neoplasms, those that are of a size associated with relatively slow growth and a low risk of metastasis. Are some of these small neoplasms renal adenomas? What is their growth pattern, and of what significance is their enlargement? Are all small renal carcinomas truly "cancers"? And what are the implications for management of such lesions in an asymptomatic individual? These controversies are discussed in depth in the hope of stimulating further investigation of this complex problem.