Assessment and characterisation of common renal masses with CT and MRI

Multifaceted Imaging of Renal Lesions With an Emphasis on Cross-Sectional Imaging

Introduction Renal lesions are common findings encountered in cross-sectional imaging. Ultrasonography (USG), computed tomography (CT), and magnetic resonance imaging (MRI) are available modalities for evaluating renal lesions. The Bosniak classification system aids in classifying a renal lesion into a particular category based on various imaging characteristics on contrast-enhanced CT (CECT).  Materials and methods The CT report archives were searched for the keyword 'Bosniak' lesions, and six illustrative cases were selected to be included in the review. Results Six cases under Bosniak categories I to IV were included in the review. Operative follow-ups were added in cases where patients underwent surgery. Discussion We have reviewed the imaging features of various renal lesions with cross-sectional modalities, namely CT and MRI, with special emphasis on the Bosniak classification system, including its amendments. Conclusion The Bosniak system is widely used to classify and characterize renal lesions. The authors have presented a scoping review of the features of renal lesions and the Bosniak system.

Virtual Non-Contrast Spectral CT in Renal Masses: Is It Time to Discard Conventional Unenhanced Phase?

Dual-layer Dual-Energy CT (dl-DECT) allows one to create virtual non-contrast (VNC) reconstructions from contrast-enhanced CT scans, with a consequent decrease of the radiation dose. This study aims to assess the reliability of VNC for the diagnostic evaluation of renal masses in comparison with true non-contrast (TNC) images. The study cohort included 100 renal masses in 40 patients who underwent dl-DECT between June and December 2021. Attenuation values and standard deviations were assessed through the drawing of regions of interest on TNC and VNC images reconstructed from corticomedullary and nephrographic phases. A Wilcoxon signed-rank test was performed in order to assess equivalence of data and Spearman's Rho correlation coefficient to evaluate correlations between each parameter. The diagnostic accuracy of VNC was estimated through the performance of receiver operating characteristic (ROC) curve analysis. Differences between attenuation values were, respectively, 74%, 18%, 5% and 3% (TNC-VNC_cort), and 74%, 15%, 9% and 2% (TNC-VNC_neph). The Wilcoxon signed-rank test demonstrated the equivalence of attenuation values between the TNC and VNC images. The diagnostic performance of VNC images in the depiction of kidney simple cysts remains high compared to TNC (VNC_cort-AUC: 0.896; VNC_neph-AUC: 0.901, TNC-AUC: 0.903). In conclusion, quantitative analysis of attenuation values showed a strong agreement between VNC and TNC images in the evaluation of renal masses.

A Rare Case of Bilateral Renal Abscess from Staphylococcal Infection in a Young Healthy Patient

Bilateral renal abscess is a rare infectious disease. Most patients have some risk factors for comorbidities, such as diabetes or an abnormal urinary tract, causing abscess formation. The incidence of the disease is infrequent in young healthy adults. Here, we report a case of a previously healthy non-diabetic young man who presented with abdominal pain with a high-grade fever. With clinically persistent abdominal pain, computerized tomography of the whole abdomen was done. The result showed bilateral renal abscess. The culture from the abscess reported Staphylococcus aureus. The patient's clinical abdominal pain and fever resolved after receiving antibiotics for 4 weeks.

Lexicon for renal mass terms at CT and MRI: a consensus of the society of abdominal radiology disease-focused panel on renal cell carcinoma

PURPOSE

There is substantial variation in the radiologic terms used to characterize renal masses, leading to ambiguity and inconsistency in clinical radiology reports and research studies. The purpose of this study was to develop a standardized lexicon to describe renal masses at CT and MRI.

MATERIALS AND METHODS

This multi-institutional, prospective, quality improvement project was exempt from IRB oversight. Thirteen radiologists belonging to the Society of Abdominal Radiology (SAR) disease-focused panel on renal cell carcinoma representing nine academic institutions participated in a modified Delphi process to create a lexicon of terms used to describe imaging features of renal masses at CT and MRI. In the first round, members voted on terms to be included and proposed definitions; subsequent voting rounds and a teleconference established consensus. One non-voting member developed the questionnaire and consolidated responses. Consensus was defined as ≥ 80% agreement.

RESULTS

Of 37 proposed terms, 6 had consensus to be excluded. Consensus for inclusion was reached for 30 of 31 terms (13/14 basic imaging terms, 8/8 CT terms, 6/6 MRI terms and 3/3 miscellaneous terms). Despite substantial initial disagreement about definitions of 'renal mass,' 'necrosis,' 'fat,' and 'restricted diffusion' in the first round, consensus for all was eventually reached. Disagreement remained for the definition of 'solid mass.'

CONCLUSIONS

A modified Delphi method produced a lexicon of preferred terms and definitions to be used in the description of renal masses at CT and MRI. This lexicon should improve clarity and consistency of radiology reports and research related to renal masses.

Complicated pyelonephritis associated with chronic renal stone disease

Purpose

This article reviews imaging manifestations of complicated pyelonephritis associated with chronic renal stones disease, in particular xanthogranulomatous pyelonephritis (XGP) and emphysematous pyelonephritis (EPN), as potential mimics of other renal diseases and malignances and provides helpful tips and differentiating features that may alert the radiologist to suspect a diagnosis of infection.

Materials and methods

A retrospective review of the records from 6 adult patients (5 females and 1 male, mean age 72,3 years) with diagnosis of XGP associated with chronic nephrolithiasis and 7 adult patients (6 females and 1 male, mean age 59,3 years) with diagnosis of EPN associated with chronic nephrolithiasis from January 2010 to January 2020 was carried out. Computed tomography urography (CTU) with at least an unenhanced scan, and the parenchymal and excretory phases after contrast medium administration performed at our Teaching Hospital were included. When available images related to conventional radiography, ultrasound (US) and magnetic resonance imaging of the same patients, the comparison with CTU images was carried out.

Conclusion

A possible diagnosis of XGP or EPN must always be taken into account when a pyelonephritis is associated with untreated kidney stones, especially whenever clinical presentation is atypical, current therapy is not effective and imaging shows features of dubious interpretation. Due to their rarity and atypical presentation, a multidisciplinary approach is required and an expert radiologist represents a key figure in the multidisciplinary team as he can help to differentiate between benign and malignant lesions and thus avoid unnecessary radical surgical procedures.

Use of quantitative T2 mapping for the assessment of renal cell carcinomas: first results

Background

Correct staging and grading of patients with clear cell renal cell carcinoma (cRCC) is of clinical relevance for the prediction of operability and for individualized patient management. As partial or radial resection with postoperative tumor grading currently remain the methods of choice for the classification of cRCC, non-invasive preoperative alternatives to differentiate lower grade from higher grade cRCC would be beneficial.

Methods

This institutional-review-board approved cross-sectional study included twenty-seven patients (8 women, mean age ± SD, 61.3 ± 14.2) with histopathologically confirmed cRCC, graded according to the International Society of Urological Pathology (ISUP). A native, balanced steady-state free precession T2 mapping sequence (TrueFISP) was performed at 1.5 T. Quantitative T2 values were measured with circular 2D ROIs in the solid tumor portion and also in the normal renal parenchyma (cortex and medulla). To estimate the optimal cut-off T2 value for identifying lower grade cRCC, a Receiver Operating Characteristic Curve (ROC) analysis was performed and sensitivity and specificity were calculated. Students’ t-tests were used to evaluate the differences in mean values for continuous variables, while intergroup differences were tested for significance with two-tailed Mann-Whitney-U tests.

Results

There were significant differences between the T2 values for lower grade (ISUP 1–2) and higher grade (ISUP 3–4) cRCC (p < 0.001), with higher T2 values for lower grade cRCC compared to higher grade cRCC. The sensitivity and specificity for the differentiation of lower grade from higher grade tumors were 83.3% (95% CI: 0.59–0.96) and 88.9% (95% CI: 0.52–1.00), respectively, using a threshold value of ≥110 ms. Intraobserver/interobserver agreement for T2 measurements was excellent/substantial.

Conclusions

Native T2 mapping based on a balanced steady-state free precession MR sequence might support an image-based distinction between lower and higher grade cRCC in a two-tier-system and could be a helpful addition to multiparametric imaging.

Electronic supplementary material

The online version of this article (10.1186/s40644-019-0222-8) contains supplementary material, which is available to authorized users.

Management of small renal masses: An interventional radiologist's perspective

Renal cell carcinoma is relatively common malignancy. Its imaging features are often non-specific and can present a diagnostic dilemma for clinicians. Historically, all patients with a renal mass underwent radical nephrectomy. Advances in technology have allowed for an increase in partial nephrectomies and percutaneous ablations. This essay briefly describes some of the imaging findings of renal cell carcinoma and several of its mimics followed by an in-depth review of procedural management with a particular focus on recent advancements.

Magnetic resonance imaging (MRI) of the renal sinus

This article presents methods to improve MR imaging approach of disorders of the renal sinus which are relatively uncommon and can be technically challenging. Multi-planar Single-shot T2-weighted (T2W) Fast Spin-Echo sequences are recommended to optimally assess anatomic relations of disease. Multi-planar 3D-T1W Gradient Recalled Echo imaging before and after Gadolinium administration depicts the presence and type of enhancement and relation to arterial, venous, and collecting system structures. To improve urographic phase MRI, concentrated Gadolinium in the collecting systems should be diluted. Diffusion-Weighted Imaging (DWI) should be performed before Gadolinium administration to minimize T2* effects. Renal sinus cysts are common but can occasionally be confused for dilated collecting system or calyceal diverticula, with the latter communicating with the collecting system and filling on urographic phase imaging. Vascular lesions (e.g., aneurysm, fistulas) may mimic cystic (or solid) lesions on non-enhanced MRI but can be suspected by noting similar signal intensity to the blood pool and diagnosis can be confirmed with MR angiogram/venogram. Multilocular cystic nephroma commonly extends to the renal sinus, however, to date are indistinguishable from cystic renal cell carcinoma (RCC). Solid hilar tumors are most commonly RCC and urothelial cell carcinoma (UCC). Hilar RCC are heterogeneous, hypervascular with epicenter in the renal cortex compared to UCC which are centered in the collecting system, homogeneously hypovascular, and show profound restricted diffusion. Diagnosis of renal sinus invasion in RCC is critically important as it is the most common imaging cause of pre-operative under-staging of disease. Fat is a normal component of the renal sinus; however, amount of sinus fat correlates with cardiovascular disease and is also seen in lipomatosis. Fat-containing hilar lesions include lipomas, angiomyolipomas, and less commonly other tumors which engulf sinus fat. Mesenchymal hilar tumors are rare. MR imaging diagnosis is generally not possible, although anatomic relations should be described to guide diagnosis by percutaneous biopsy or surgery.

Comparison of MDCT, MRI and MRI with diffusion-weighted imaging in evaluation of focal renal lesions: The defender, challenger, and winner!

Purpose:

To compare the diagnostic performance of multidetector computed tomography (MDCT), magnetic resonance imaging (MRI), and MRI with diffusion-weighted imaging (DWI) in the characterization of focal renal lesions. We also compared MDCT and MRI in the staging of renal cell carcinoma (RCC).

Materials and Methods:

One hundred and twenty adult patients underwent MDCT (40-row and 128-row scanners), MRI (at 1.5 T), and DWI (at b-values of 0 and 500 s/mm²) for characterization of 225 renal lesions. There were 65 malignant neoplasms (44 RCCs), 25 benign neoplasms, 25 abscesses, 45 pseudotumors, 15 hemorrhagic cysts, and 50 benign cysts. A composite gold standard including histology, typical imaging criteria, and follow-up imaging was employed. To determine the diagnostic performance of imaging modalities, area-under-curve (AUC) was calculated by receiver-operating-characteristic analysis and compared. Fisher's exact test was used to compare the diagnostic accuracies and confidence levels with MDCT, MRI, and MRI + DWI. Cross-tabulation was used to assess the precision of MDCT and MRI in RCC staging.

Results:

AUC for MDCT (0.834) and MRI (0.841) in the classification of benign and malignant lesions were within corresponding 95% confidence interval (CI) (P = 0.88) whereas MRI + DWI had significantly better performance (AUC 0.968, P = 0.0002 and 0.0004, respectively). Both CT and MRI had low specificity (66.9% and 68.8%, respectively), which increased substantially with DWI (93.8%) owing to correct diagnosis of pseudotumors. MRI was superior to CT in diagnosing necrotic RCC and hemorrhagic cysts. MRI + DWI had the highest accuracy (94.2%) in assigning the definitive diagnosis and 97.6% lesions were diagnosed with very high confidence, significantly better than CT and MRI. Both CT and MRI had the same accuracy (86.1%) in RCC staging and evaluation of intravascular thrombi.

Conclusions:

Characterization of renal lesions was most accurate with MRI + DWI. The latter is also the most suitable modality in diagnosing pseudotumors and evaluating patients with renal dysfunction. CT and MRI were equivalent in RCC staging.

The safety and efficacy of MPR-CTU combined with precise intraoperative ultrasonography guided flexible ureteroscope in the treatment of renal cystic disease

The safety and efficacy of multi-planar reconstruction (MPR) image post-processing technique-computed tomography (CT) urography (CTU) combined with precise intraoperative ultrasonography guided flexible ureteroscope in renal cyst incision and drainage in the treatment of cystic diseases of kidney were evaluated. A total of 68 patients were randomly divided into control and observation group (n=34). All the patients were treated with renal cyst incision and drainage under flexible ureteroscope. The control group was under ultrasound guidance. The observation group was combined with MPR-CTU, the safety and efficacy was compared. There was no significant difference between the two groups in the success rate and the time of cyst treatment (P>0.05). The incidence of intraoperative and postoperative complications of the observation group was significantly lower than that of the control group. After 1 month follow-up, the total effective rate of the observation group was significantly higher than that of the control group, the difference was statistically significant (P<0.05). Conclusion MPR-CTU technique combined with intraoperative ultrasonography to guide cyst incision and drainage under flexible ureteroscope for renal cystic disease has a high safety and efficacy, and it is worthy of clinical application.

Magnetic Resonance Imaging and the Use in Small Renal Masses

The incidence of small renal masses (SRM) has been increasing, and this is mainly attributed to the incidental finding of such masses on imaging performed in asymptomatic patients. Consequently, this calls for careful evaluation and management of these masses to determine their nature and need for treatment. This article reviews current literature regarding the evaluation and management of SRM. It focuses on the specific use of MRI in the diagnosis and management of SRM. A Medline review of the literature was performed from 1996 to the present time. Computed tomography (CT) imaging has been the investigation of choice for evaluating SRM. However, some remain difficult to determine their malignant or benign nature and remain indeterminate. In such cases, further imaging with magnetic resonance imaging (MRI) can be performed to evaluate the mass in more detail. It can also be used where CT is contraindicated and where active surveillance is the treatment of choice and radiation exposure is a concern. MRI is a useful tool in evaluating an indeterminate small renal mass. Accurate diagnosis and management of SRM require close collaboration between a urologist and radiologist to identify potentially malignant tumours to subsequently reduce mortality from renal cell cancer.

Unusual benign solid neoplasms of the kidney: cross-sectional imaging findings

Kidney neoplasms are common diseases with varying prognoses depending on the subtype of the tumor. The most common solid lesion of the kidney is renal cell carcinoma, and the treatment is typically surgical removal. With increasing use of cross-sectional imaging in the last two decades, the detection of renal lesions has significantly increased, especially in asymptomatic patients who are scanned for other reasons. In this article, we present the imaging findings of rare solid benign primary kidney neoplasms including renal leiomyoma, reninoma, carcinoid tumor, metanephric adenoma, solitary fibrous tumor of the kidney, lipomatous hemangiopericytoma of the kidney, renal schwannoma, inflammatory myofibroblastic tumor of the kidney, extramedullary hematopoiesis in the kidney, and extranodal renal Rosai-Dorfman disease. Accurate preoperative or prebiopsy diagnoses of these lesions are unusual; however, informed radiologists may sometimes be able to favorably change the patient management and treatment.

[Quantitative perfusion imaging in magnetic resonance imaging]

CLINICAL/METHODICAL ISSUE

Magnetic resonance imaging (MRI) is recognized for its superior tissue contrast while being non-invasive and free of ionizing radiation. Due to the development of new scanner hardware and fast imaging techniques during the last decades, access to tissue and organ functions became possible. One of these functional imaging techniques is perfusion imaging with which tissue perfusion and capillary permeability can be determined from dynamic imaging data.

STANDARD RADIOLOGICAL METHODS

Perfusion imaging by MRI can be performed by two approaches, arterial spin labeling (ASL) and dynamic contrast-enhanced (DCE) MRI. While the first method uses magnetically labelled water protons in arterial blood as an endogenous tracer, the latter involves the injection of a contrast agent, usually gadolinium (Gd), as a tracer for calculating hemodynamic parameters.

PERFORMANCE

Studies have demonstrated the potential of perfusion MRI for diagnostics and also for therapy monitoring.

ACHIEVEMENTS

The utilization and application of perfusion MRI are still restricted to specialized centers, such as university hospitals. A broad application of the technique has not yet been implemented.

PRACTICAL RECOMMENDATIONS

The MRI perfusion technique is a valuable tool that might come broadly available after implementation of standards on European and international levels. Such efforts are being promoted by the respective professional bodies.

Diagnostic value of strain elastography for differentiation between renal cell carcinoma and transitional cell carcinoma of kidney

PURPOSE

The objective of our study was to prospectively evaluate the diagnostic performance of strain elastography for differentiation between renal cell carcinomas (RCCs) and transitional cell carcinomas (TCCs) of kidney.

METHODS

A total of 99 consecutive patients who were referred to our hospital because of a newly diagnosed solid renal mass suspicious for malignancy on radiological screenings were evaluated with sonography, including strain elastography. Strain elastography was used to compare the stiffness of the renal masses and renal cortex. The ratio of strain in a renal mass and nearby renal cortex was defined as the strain index value. Mean strain index values for RCCs and TCCs were compared, and mean strain index values between histological subtypes of RCC were also compared.

RESULTS

Although TCCs were smaller than RCCs (p < 0.001), there were no significant differences in gender distribution and mean age of the patients, and mean probe-tumor distance between RCC and TCC. The mean strain index value ±SD for TCC (5.18 ± 1.12) was significantly higher than the value for RCC (4.04 ± 0.72; p < 0.001). Mean strain index value for papillary cell carcinomas (4.09 ± 0.45) was slightly higher than that for clear cell carcinomas (3.85 ± 0.78): however, the difference was not statistically significant (p = 0.51).

CONCLUSIONS

Strain elastography can be used as a valuable imaging technique for preoperative differentiation between RCC and TCC of kidney.

An Incidental Renal Oncocytoma: 18F-Choline PET/MRI

PET/MRI is a new hybrid imaging modality and has the potential to become a powerful imaging tool. It is currently one of the most active areas of research in diagnostic imaging. The characterisation of an incidental renal lesion can be difficult. In particular, the differentiation of an oncocytoma from other solid renal lesions such as renal cell carcinoma (RCC) represents a diagnostic challenge. We describe the detection of an incidental renal oncocytoma in a 79-year gentleman who underwent a re-staging ¹⁸F-Choline PET/MRI following a rise in PSA values (4.07, nadir 1.3).

Comparison between computed tomography multislice and high-field magnetic resonance in the diagnostic evaluation of patients with renal masses

BACKGROUND

Renal masses are a common finding in diagnostic imaging; these lesions usually are solid or cystic, benign or malignant, and the correct diagnosis may be difficult. The aim of our study was the comparison of multi-slice computed tomography (MSCT) and high-field magnetic resonance (MR) in the diagnostic evaluation of renal masses.

METHODS

We studied 29 patients, 16 men and 13 women aged 8-85 years (mean 61±17 years) with histo-cytological diagnosis of renal masses (n=31), of which the majority (74%; n=23) was represented by malignant lesions [renal cell carcinoma (Ca) =16, chromophobe renal cell Ca =2, squamous cell Ca =1, urothelial Ca =2, lymphoma =1, Wilms tumor =1]; the remaining 8 masses (26%) were benign (pyelonephritis =2, simple cyst =1, hematic cyst =1, lipoma =1 and oncocytoma =3). All patients underwent MSCT and MR (3.0 Tesla) before and after contrast injection; the images were evaluated in double-blind by two expert radiologists. The results of the images were then compared with the histo-cytological data to calculate the values of diagnostic accuracy for both methods in the identification and characterization of renal masses. The benign or malignant nature of the lesions was established according to the regularity of the margins, presence or absence of significant contrast enhancement, infiltration of perirenal fat and vascular invasion. The concordance of the results of the two imaging techniques was then calculated using the coefficient Kappa Cohen.

RESULTS

For both identification and characterization of renal masses, MSCT and MR showed comparable values of diagnostic accuracy with a significant concordance (k=1); in particular, the diagnostic accuracy of MSCT/MR was 100%/100% for lesion identification, 90%/90% for lesion characterization in terms of benign or malignant nature, 97%/97% for the evaluation of lesion edges, 90%/90% for the assessment of lesion contrast enhancement, 93%/93% for the evaluation of peri-renal fat infiltration and 96%/96% for the evaluation of vascular infiltration. Only in three cases of oncocytoma the two imaging methods were both inaccurate for diagnosis of benignity classifying the lesions as probably malignant on the basis of the absence of central scar and of dynamic contrast enhancement pattern.

CONCLUSIONS

The results of our study show comparable diagnostic accuracy of computed tomography (CT) and MR for the identification and characterization of expansive renal lesions. High-field MR is, therefore, a valid alternative to MSCT in the evaluation of renal masses avoiding exposure to ionizing radiation.

Utility of semiquantitative strain elastography for differentiation between benign and malignant solid renal masses

OBJECTIVES

The aim of this study was to determine the role of semiquantitative strain elastography for differentiation of benign and malignant solid renal masses.

METHODS

Seventy-one patients with solid renal masses were prospectively examined with ultrasound elastography after grayscale sonography. Strain elastography was used to compare the stiffness of the renal masses and renal parenchyma. The ratio of strain in a renal mass and nearby renal parenchyma was defined as the strain index value. Mean strain index values for benign masses (n = 29; 24 angiomyolipomas and 5 oncocytomas) and malignant masses (n = 42; 34 renal cell carcinomas, 4 transitional cell carcinomas, 3 metastases, and 1 lymphoma) and mean strain index values for angiomyolipomas and renal cell carcinomas were compared.

RESULTS

There were no significant differences in the mean age of the patients, mean diameter of the masses, and mean probe-mass distance between benign and malignant groups. The mean strain index value ± SD for malignant masses (4.05 ± 2.17) was significantly higher than the value for benign masses (1.43 ± 0.94; P < .05). The mean strain index value for renal cell carcinomas (4.30 ± 2.27) was significantly higher than the value for angiomyolipomas (1.28 ± 1.01; P < .0001).

CONCLUSIONS

Strain elastography may be a useful imaging technique for differentiation between benign and malignant solid renal masses.

[Imaging renal cell carcinoma]

Renal cell carcinoma is the eighth most common malignancy in adults and the most common malignancy in the kidney. It is thus a very common disease for radiologists. This review aims to provide a general overview of the imaging techniques used to diagnose, characterize, and help plan the treatment of renal cell carcinoma as well as to review basic aspects related to staging, imaging-guided percutaneous treatment, and follow-up in the most common clinical scenarios.

Renal oncocytoma: contrast-enhanced sonographic features

OBJECTIVES

The purpose of this study was to illustrate the features of renal oncocytoma on contrast-enhanced sonography.

METHODS

Five cases of surgical pathologically proven renal oncocytoma were retrospectively reviewed and analyzed in this study. The 5 patients studied included 3 men and 2 women with a mean age of 52.3 years (range, 32-66 years). All patients underwent conventional and contrast-enhanced sonographic examinations before surgery. The sonographic features, enhancement pattern, and dynamic perfusion change of the tumors and renal parenchyma in vascular phases were evaluated and compared to computed tomography.

RESULTS

On grayscale sonography, renal oncocytomas appeared as solitary hypoechoic or isoechoic masses originating from the renal cortex measuring 2 to 6 cm with a well-defined margin. Color Doppler flow imaging showed rich blood flow signals in the periphery and striplike blood flow signals within the masses. On contrast-enhanced sonography, the features of these tumors included early enhancement, hyperenhancement, and fast wash-out compared to the adjacent renal cortex. There were irregular nonenhanced areas seen in the center of the masses (n = 3) and nonenhanced thin rims seen in the periphery (n = 5). Macroscopically, the well-marginated tumors were yellowish brown with a tender texture and were located in the renal cortex. Central irregularly shaped fibrous scars were seen in 3 tumors, consistent with nonenhanced areas on contrast-enhanced imaging.

CONCLUSIONS

Contrast-enhanced sonography can provide valuable hemodynamic information on renal oncocytoma, which may help in making a differential diagnosis of this benign renal tumor in clinical practice.