Small renal cell carcinoma: MRI with pathologic correlation

Diagnostic Accuracy of MRI for Detection of Papillary Renal Cell Carcinoma: A Systematic Review and Meta-Analysis

OBJECTIVE

The objective of our study was to perform a systematic review and meta-analysis of the diagnostic performance of MRI in differentiation of papillary renal cell carcinoma (RCC) from other renal masses.

MATERIALS AND METHODS

We performed searches of three electronic databases for studies that used MRI techniques to differentiate papillary RCC from other renal lesions. Methodologic quality was assessed, and diagnostic test accuracy was summarized using bivariate random-effects modeling or with construction of a summary ROC (SROC) curve.

RESULTS

Thirteen studies involving 275 papillary RCC lesions and 758 other renal masses met the inclusion criteria. Resulting summary estimates for the performance of MRI to differentiate papillary RCC from other renal lesions were a sensitivity of 79.6% (95% CI, 62.3-90.2%) and specificity of 88.1% (95% CI, 80.1-93.1%). In subgroup analysis, quantitative pooling of seven studies using enhancement in the corticomedullary phase resulted in a sensitivity of 85.6% (95% CI, 67.8-94.4%), specificity of 91.7% (95% CI, 76.0-97.5%), and area under the SROC curve of 0.894. Four studies used tumor appearance on T2-weighted imaging to detect papillary RCC, and results showed a pooled sensitivity of 89.9% (95% CI, 73.0-96.7%) and specificity of 84.9% (95% CI, 69.0-93.4%). Three studies used signal loss on T1-weighted in-phase imaging to detect papillary RCC but marked heterogeneity precluded pooling.

CONCLUSION

Meta-analysis supports moderate sensitivity and excellent specificity of quantitative enhancement in the corticomedullary phase for differentiating papillary RCC from other tumors. The accuracy of combining enhancement and T2 signal-intensity characteristics merits further evaluation as a potential aid for management decisions.

Renal tumors with low signal intensities on T2-weighted MR image: radiologic-pathologic correlation

Accurate characterization of renal masses is essential for ensuring appropriate management. Low T2 signal intensity is a common feature of papillary renal cell carcinoma and fat-poor angiomyolipoma. Nonetheless, other types of renal cell carcinoma, oncocytoma, hemangioma, lymphoma, leiomyoma, and urothelial cell carcinoma also can show low signal intensities on T2-weighted imaging (T2WI). Histopathologic features that can lead to low T2 signal intensities in renal tumors include smooth muscle component, papillary architecture, a high nucleus-to-cytoplasm ratio, and hemorrhage. To establish an appropriate differential diagnosis for renal tumors on MRI, it is necessary to understand the relationship between the MR signal intensities and the histopathologic and morphologic features, in addition to contrast enhancement patterns and diffusion characteristics of the tumors.

Multimodality Imaging Characteristics of the Common Renal Cell Carcinoma Subtypes: An Analysis of 544 Pathologically Proven Tumors

Objectives:

The objective of this study was to define the characteristic imaging appearances of the common renal cell carcinoma (RCC) subtypes.

Materials and Methods:

The Institutional Review Board approval was obtained for this HIPAA-compliant retrospective study, and informed consent was waived. 520 patients (336 men, 184 women; age range, 22–88 years) underwent preoperative cross-sectional imaging of 544 RCCs from 2008 to 2013. The imaging appearances of the RCCs and clinical information were reviewed. Data analysis was performed using parametric and nonparametric statistics, descriptive statistics, and receiver operating characteristic analysis.

Results:

The RCC subtypes showed significant differences (P < 0.001) in several imaging parameters such as tumor margins, tumor consistency, tumor homogeneity, the presence of a central stellate scar, T2 signal intensity, and the degree of tumor enhancement. Low T2 signal intensity on magnetic resonance imaging (MRI) allowed differentiation of papillary RCC from clear cell and chromophobe RCCs with 90.9% sensitivity and 93.1% specificity. A tumor-to-cortex ratio ≥1 on the corticomedullary phase had 98% specificity for clear cell RCC.

Conclusion:

The T2 signal intensity of the tumor on MRI and its degree of enhancement are useful imaging parameters for discriminating between the RCC subtypes while gross morphological findings offer additional value in RCC profiling.

Small (< 4 cm) Renal Tumors With Predominantly Low Signal Intensity on T2-Weighted Images: Differentiation of Minimal-Fat Angiomyolipoma From Renal Cell Carcinoma

OBJECTIVE

The purpose of this study was to retrospectively investigate the utility of multiparametric MRI in differentiating minimal-fat angiomyolipoma (AML) from renal cell carcinoma (RCC) in small renal tumors with predominantly low signal intensity on T2-weighted MR images.

MATERIALS AND METHODS

Fifty-six patients with pathologically identified renal tumors (1-4 cm) with predominantly low signal intensity on T2-weighted images without visible fat on unenhanced CT images were enrolled. Clinical and MRI variables (tumor-to-renal cortex signal intensity [SI] ratio on T2-weighted images [T2 ratio], apparent diffusion coefficient [ADC], and SI index) on chemical-shift images were evaluated.

RESULTS

The ADC was significantly lower in RCC than in minimal-fat AML (p = 0.001). The T2 ratio and signal intensity index were not significantly different between RCC (p = 0.31) and minimal-fat AML (p = 0.74). Multivariate analysis showed that ADC (odds ratio [OR], 0.01; p = 0.02) and male sex (OR, 46.7; p < 0.001) were the independent predictors of RCC. For differentiating minimal-fat AML from RCC, the ROC AUC of ADC was 0.781. When ADC and sex were combined, the AUC significantly increased to 0.937 with a cutoff value of 1.129 × 10^-3 mm²/s. For making the diagnosis of minimal-fat AML if the ADC was greater than the threshold, sensitivity was 89.7% and specificity was 88.2% (p = 0.02).

CONCLUSION

In small renal tumors with predominantly low SI on T2-weighted images, ADC is useful for differentiating minimal-fat AML from RCC. Combining ADC with male sex increases the accuracy of RCC prediction.

Diagnostic modalities

The incidental detection of small renal masses on imaging undertaken to evaluate unrelated symptoms or conditions is an increasingly common occurrence. Accurate imaging characterisation is fundamental to determining optimum patient management. The goals of imaging small renal masses include determining whether a lesion is solid or cystic, if there are signs of biological aggressiveness and whether the lesion is likely benign or malignant. The current imaging practices and the evidence supporting the use of different imaging modalities for the characterisation of small renal masses are discussed. CT remains the primary imaging modality and is able to classify most masses into surgical or non-surgical lesions. MRI and contrast enhanced ultrasound are most often employed to problem solve in lesions deemed indeterminate on contrast enhanced CT or for patients in which CECT is contraindicated. Percutaneous biopsy should be considered in lesions that remain indeterminate after initial imaging investigations. Given the central role of imaging in the management of small renal masses, all multidisciplinary team members involved in renal cancer care should have an understanding of the performance of the different imaging modalities.

Kidney, Ureter, and Bladder Biopsy

Percutaneous urologic biopsy is a safe and effective technique and can comprise a significant proportion of the daily workload of the interventional radiologist. This article discusses the indications and rationale for the performance of renal, ureter, and bladder biopsy as well as the approach to performing such biopsies, pitfalls, and potential complications.

A case of tubulocystic carcinoma of the kidney with aggressive features

Tubulocystic carcinoma of the kidney is rare and typically indolent. Our case involved an aggressive tubulocystic carcinoma as well as the radiological confirmation of its relation to papillary renal cell carcinoma. A 46-year-old male presented with renal multiloculated cysts with a solid part. On computed tomography and magnetic resonance imaging, the solid part showed the characteristics of papillary renal cell carcinoma. Contrast enhancement of the solid part was fluffy and sparse because of the coexistence of cysts. Perirenal fat invasion resulted in exophytic cysts, and renal-hilar cystic lymph node metastasis existed. The histopathological diagnosis was tubulocystic carcinoma associated with areas of papillary renal cell carcinoma and poorly differentiated carcinoma with metastasis. Our case suggests that the solid part enhancement of tubulocystic carcinoma tends to be fluffy and sparse, and exophytic cysts and cystic lymph nodes may show radiologically aggressive findings.

Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management

Angiomyolipoma is the most common benign solid renal neoplasm observed in clinical practice. Once thought to be a hamartoma and almost always diagnosed by the imaged-based detection of fat, angiomyolipomas are now known to consist of a heterogeneous group of neoplasms. Although all are considered perivascular epithelioid cell tumors, many display different pathology, imaging features, and clinical behavior. The importance of understanding this group of neoplasms is emphasized by the fact that many types of angiomyolipoma contain little to no fat, and despite being benign, sometimes escape a pre-operative diagnosis. These types of angiomyolipomas can all be considered when encountering a renal mass that is both hyperattenuating relative to renal parenchyma on unenhanced CT and T2-hypointense, features that reflect their predominant smooth muscle component. We review recent developments and provide a radiological classification of angiomyolipomas that helps physicians understand the various types and learn how to both diagnose and manage them.

Breast cancer metastatic to the kidney with renal vein involvement

The common sites of breast cancer metastases include bones, lung, brain, and liver. Renal metastasis from the breast is rare. We report a case of breast cancer metastatic to the kidney with extension into the renal vein. A 40-year-old woman had undergone left mastectomy for breast cancer at the age of 38. A gastric tumor, which was later proved to be metastasis from breast cancer, was detected by endoscopy. Computed tomography performed for further examination of the gastric tumor revealed a large left renal tumor with extension into the left renal vein. It mimicked a primary renal tumor. Percutaneous biopsy of the renal tumor confirmed metastasis from breast cancer. Surgical intervention of the stomach and the kidney was avoided, and she was treated with systemic chemotherapy. Breast cancer metastatic to the kidney may present a solitary renal mass with extension into the renal vein, which mimics a primary renal tumor.

A synchronous hepatocellular carcinoma and renal cell carcinoma treated with radio-frequency ablation

Radio-frequency ablation (RFA) is a curative treatment for hepatocellular carcinoma (HCC). Percutaneous RFA has been shown to be beneficial for patients with small renal cell carcinoma (RCC) lacking indications for resection. We experienced the case of a 53-year-old male who had conditions that suggested HCC, RCC, and alcoholic liver cirrhosis. Abdominal contrast-enhanced computed tomography (CT) and magnetic resonance image showed liver cirrhosis with 2.8 cm ill-defined mass in segment 2 of the liver and 1.9 cm hypervascular mass in the left kidney. These findings were compatible with the double primary cancers of HCC and RCC. Transarterial chemoembolization (TACE) was performed to treat the HCC. After the TACE, a focal lipiodol uptake defect was noticed on a follow up CT images and loco-regional treatment was recommended. Therefore, we performed RFAs to treat HCC and RCC. There was no evidence of recurrence in the follow up image after 1 month.

Imaging management of incidentally detected small renal masses

Both imaging and intervention play an increasingly important role in the management of renal masses in general and renal cancer in particular. Indeed, radiologists are often the first to detect and diagnose renal cancer, and now with the burgeoning role of percutaneous ablation, they are often the treating physicians. Renal mass management begins with imaging, and although most can be diagnosed with a high degree of certainty using imaging, some remain indeterminate and require biopsy or observation, now referred to as active surveillance. Although active surveillance strategies have been employed for indeterminate renal masses that have a reasonable chance of being benign, recent data suggest that some renal cancers can undergo active surveillance safely. This article reviews the current imaging-based diagnostic evaluation of incidentally detected small renal masses, the burgeoning role of percutaneous biopsy, and how both imaging and biopsy are used to help select which patients need treatment and which can undergo active surveillance.

Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management

Angiomyolipoma is the most common benign solid renal neoplasm observed in clinical practice. Once thought to be a hamartoma and almost always diagnosed by the imaged-based detection of fat, angiomyolipomas are now known to consist of a heterogeneous group of neoplasms. Although all are considered perivascular epithelioid cell tumors, many display different pathology, imaging features, and clinical behavior. The importance of understanding this group of neoplasms is emphasized by the fact that many types of angiomyolipoma contain little to no fat, and despite being benign, sometimes escape a pre-operative diagnosis. These types of angiomyolipomas can all be considered when encountering a renal mass that is both hyperattenuating relative to renal parenchyma on unenhanced CT and T2-hypointense, features that reflect their predominant smooth muscle component. We review recent developments and provide a radiological classification of angiomyolipomas that helps physicians understand the various types and learn how to both diagnose and manage them.

Characteristic MRI findings of sarcomatoid renal cell carcinoma dedifferentiated from clear cell renal carcinoma: radiological-pathological correlation

PURPOSE

To evaluate MRI findings of sarcomatoid renal cell carcinoma (SRCC).

MATERIAL AND METHODS

Eleven patients with pathologically proven SRCC dedifferentiated from clear cell renal carcinoma (CCRC) underwent preoperative renal MRI. The MRI findings were compared with histological findings. On MRI, the following findings were evaluated: the presence and distribution of areas showing heterogeneous iso to high signal intensity (SI) on T2-weighted images (T2HIA) and conspicuously low SI areas (T2LIA) compared to normal renal cortex, areas showing high SI on T1-weighted images and unenhanced areas on dynamic contrast-enhanced images, disruption of pseudocapsule, and the SIs of T2HIA and T2LIA on diffusion-weighted imaging (DWI). The apparent diffusion coefficient (ADC) values and SI ratios to muscle on dynamic contrast-enhanced imaging (DCE) were compared between T2HIA and T2LIA using the t test.

RESULTS

The distribution of T2HIA and T2LIA was as follows: a mixed pattern alone in five, nodular T2LIA pattern alone in one, both mixed and nodular T2LIA patterns in four, and a separated pattern in one. Disruption of the pseudocapsule was seen in all cases. The imaging findings suggesting intratumoral hemorrhage and necrosis were seen in 18% and 63%, respectively. The SIs of T2HIA and T2LIA were low intermediate and high on DWI, respectively. T2LIA and T2HIA corresponded to the components of SRCC with abundant fibrosis and CCRC, respectively. T2LIA showed significantly lower enhancement at all DCE phases and a lower ADC value than T2HIA.

CONCLUSION

The presence of T2LIA corresponding to the area showing a hypovascular nature and markedly restricted diffusion might be characteristic findings of SRCC. Intratumoral hemorrhage and necrosis were seen, but they were not specific findings.

Evaluating hemorrhage in renal cell carcinoma using susceptibility weighted imaging

Background

Intratumoral hemorrhage is a frequent occurrence in renal cell carcinoma and is an indicator of tumor subtype. We hypothesize that susceptibility weighted imaging (SWI) is sensitive to hemorrhage in renal cell carcinoma and can give a more diagnostic image when compared to conventional imaging techniques.

Materials and Methods

A retrospective review of 32 patients with clear cell renal cell carcinoma was evaluated. All patients underwent magnetic resonance imaging (MRI) and 22 out of 32 patients also underwent a computed tomography (CT) scan. Hemorrhage was classified into 3 different categories according to shape and distribution. Histopathology was obtained from all masses by radical nephrectomy. The ability to detect the presence of hemorrhage using CT, non-contrast conventional MRI and SWI was evaluated, and the patterns of hemorrhage were compared.

Results

Using pathologic results as the gold standard, the sensitivities of non-contrast conventional MRI, SWI and CT in detecting hemorrhage in clear cell renal cell carcinoma were 65.6%, 100% and 22.7%, respectively. Accuracy of non-contrast conventional MRI and SWI in evaluating hemorrhagic patterns were 31.3% and 100%, respectively.

Conclusion

These results demonstrate that SWI can better reveal hemorrhage and characterize the pattern more accurately than either non-contrast conventional MRI or CT. This suggests that SWI is the technique of choice for detecting hemorrhagic lesions in patients with renal cancer.

Renal angiomyoadenomatous tumour: Imaging features

Renal angiomyoadenomatous tumour is a rare, recently described neoplasm with a distinctive histological appearance. Although reported in the pathology literature, to our knowledge, no prior reports have described its imaging appearance. We describe the computed tomography and magnetic resonance imaging features of an incidentally detected renal angiomyoadenomatous tumour that appeared as a well-marginated, solid T2-hypointense enhancing mass, in a 50-year-old woman. It is indistinguishable from a variety of benign and malignant renal neoplasms.

Mucinous tubular and spindle cell carcinoma of the kidney: imaging features

This article describes the features on sonography, computed tomography (CT) and magnetic resonance imaging (MRI) of mucinous tubular and spindle cell carcinoma of the kidney. Six pathologically proven cases of mucinous tubular and spindle cell carcinoma of the kidney were identified (5 females, 1 male); all patients underwent preoperative imaging. The mean age of the patients was 58.5 years. Thirteen imaging studies were available for review: 2 sonograms, 1 unenhanced CT scan, 5 contrast-enhanced CT scans, 1 unenhanced magnetic resonance imaging (MRI) examination, and 4 contrast-enhanced MRI examinations. Two abdominal radiologists evaluated all images retrospectively on a PACS workstation using a standardized data collection sheet until consensus was reached. All mucinous tubular and spindle cell carcinomas presented as well-marginated, small (mean 2.6 cm, range 1.9-3.2 cm) predominantly solid masses. No intratumoral fat or calcification was identified. Unenhanced CT and MRI appearances were variable as was the degree of enhancement following intravenous contrast material administration. There was no evidence of perinephric extension, renal vein involvement or metastatic disease in any of the cases. The radiological appearance of mucinous tubular and spindle cell carcinoma is diverse and therefore indistinguishable from the more common subtypes of renal cell carcinoma.

Small renal mass: what the urologist needs to know for treatment planning and assessment of treatment results

OBJECTIVE

Small renal mass is a new distinct clinical entity. Detection of these tumors has increased with increased use of imaging.

CONCLUSION

We know that a proportion of these tumors are not renal cell carcinoma, and imaging-guided biopsy is being increasingly used for treatment planning. The objectives of this review are to provide an update on our current understanding of the biology of small renal masses and to review approaches to the diagnosis and treatment of these lesions.

Misdiagnosis of clear cell renal cell carcinoma

Clear cell renal cell carcinoma (RCC) represents the most common histological subtype of malignant kidney tumors. Based on symptoms alone, clear cell RCC is indistinguishable from other histological classes of RCC unless the tumor is present in the context of an RCC syndrome. Histopathological examination is, therefore, important to accurately identify clear cell RCC. Clear cell RCCs have characteristic morphological criteria; these tumors can be easily identified upon typical presentation, but diagnosis can be challenging when tumor cell pattern is unusual or when availability of tissue samples is limited. In this Review, the clinical, radiological and pathological characteristics of clear cell RCCs are described, as well as the potential tumors that can be confused with clear cell RCC and need to be considered in the differential diagnoses. Finally, the importance of an accurate diagnosis is highlighted in the context of the increasing use of preoperative tissue sampling and the prevalence of clear cell tumors associated with hereditary syndromes, which could have different therapeutic and prognostic implications for patients and their families.

Value of T2-weighted MR imaging in differentiating low-fat renal angiomyolipomas from other renal tumors

BACKGROUND

Accurate preoperative diagnosis of fat scanty angiomyolipomas is an important clinical issue. By evaluating the low signal intensity of angiomyolipomas in MR T2-weighted images the diagnostic accuracy can be elevated.

PURPOSE

To retrospectively assess the usefulness of T2-weighted MR imaging for differentiating low-fat angiomyolipomas (AMLs) from other renal tumors.

MATERIAL AND METHODS

We retrospectively evaluated 71 patients with surgically proven renal masses (10 AMLs, 57 renal cell carcinomas [RCCs], and four oncocytomas), all of which showed no visible fat as well as gradual enhancement patterns on contrast-enhanced CT. Signal intensity was measured in each renal mass and in the spleen on T2-weighted images, and each signal intensity ratio (SIR) was calculated; SIR values were then compared in the AML and non-AML groups. Receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic performance of the two parameters for differentiating the two groups.

RESULTS

The SIR values (77 ± 24% vs. 162 ± 79%, p = 0.002) were significantly lower in the AML than in the non-AML group. The area under the ROC curve was 0.926 for SIR. The sensitivity and specificity in the diagnosis of AMLs were 90% and 90.2%, using SIR cut-off of 92.5%.

CONCLUSION

Signal intensity measurements on T2-weighted MR images can differentiate AML from non-AML in the kidney.

Renal mass sampling: an enlightened perspective

Renal mass sampling (RMS) can be carried out by core biopsy or fine needle aspiration with each presenting potential advantages and limitations. The literature about RMS is confounded by a lack of standardized techniques, ambiguous terminology, imprecise definitions of accuracy, substantial rates of non-informative biopsies, and recurrent diagnostic challenges with respect to eosinophilic neoplasms. Despite these concerns, RMS has an expanding role in the evaluation and treatment of renal masses, in order to stratify biological aggressiveness and guide management that can range from surgery to active surveillance. Non-informative biopsies can be managed with surgical excision or repeat biopsy, with the latter showing encouraging results in recent studies. We propose a new classification in which all biopsies are categorized as non-informative versus informative, with the latter being subclassified as confirmed accurate, presumed accurate or confirmed inaccurate. This terminology will facilitate the comparison of results from various studies and stimulate progress. Incorporation of novel biomarkers and molecular fingerprinting into RMS protocols will likely allow for more rational management of patients with renal masses in the near future.

Imaging renal cell carcinoma with ultrasonography, CT and MRI

The increased use of abdominal imaging techniques for a variety of indications has contributed to more-frequent detection of renal cell carcinoma (RCC). Ultrasonography has been used to characterize the solid versus cystic nature of renal masses. This modality has limitations, however, in further characterization of solid tumors and in staging of malignancy, although contrast-enhanced ultrasonography has shown promise. Cross-sectional imaging with multiplanar reconstruction capability via CT or MRI has become the standard-bearer in the diagnosis, staging and surveillance of renal cancers. The use of specific protocols and the exploitation of different imaging characteristics of RCC subtypes, including variations in contrast agent timing, MRI weighting and digital subtraction, have contributed to this diagnostic capability. Cystic renal masses are a special case, evaluation of which can require multiple imaging modalities. Rigorous evaluation of these lesions can provide information that is crucial to prediction of the likelihood of malignancy. Such imaging is not without risk, however, as radiation from frequent CT imaging has been implicated in the development of secondary malignancies, and contrast agents for CT and MRI can pose risks, particularly in patients with compromised renal function.

Imaging and management of the incidentally discovered renal mass

Improvements in imaging technology and the expanding use of imaging have led to a rapid increase in the discovery of incidental renal lesions. These can present both the radiologist and the referring clinician with diagnostic dilemmas. This article addresses the most frequently encountered lesions and provides a framework for the diagnostic and management pathways for both solid and cystic lesions.

Biopsy of renal masses: when and why

Percutaneous image-guided biopsy of renal masses is a safe and accurate procedure. Although once reserved for the diagnosis of unresectable renal cell carcinoma, metastases, lymphoma, and infection, today percutaneous image-guided biopsy has an expanded role. There is increasing awareness that a substantial proportion of small, solid renal masses are benign neoplasms. Although imaging can be used to diagnose most of them, some are incorrectly believed to represent renal cell carcinoma and unnecessary surgery may be performed. Based largely on advances in cytological techniques, percutaneous biopsy can be now be used to diagnose benign neoplasms and thus prevent them from being treated unnecessarily. Concurrent advances in percutaneous ablation have also promoted its use. As a result, there are 8 established indications for percutaneous biopsy, and reason to believe that the number of indications will expand further in the future.

Renal cell carcinoma: t1 and t2 signal intensity characteristics of papillary and clear cell types correlated with pathology

OBJECTIVE

The objective of our study was to describe the T1 and T2 signal intensity characteristics of papillary renal cell carcinoma (RCC) and clear cell RCC with pathologic correlation.

MATERIALS AND METHODS

Of 539 RCCs, 49 tumors (21 papillary RCCs and 28 clear cell RCCs) in 45 patients were examined with MRI. Two radiologists retrospectively and independently assessed each tumor's T1 and T2 signal intensity qualitatively and quantitatively (i.e., the signal intensity [SI] ratio [tumor SI / renal cortex SI]). Of the 49 tumors, 37 (76%) were assessed for pathology features including tumor architecture and the presence of hemosiderin, ferritin, necrosis, and fibrosis. MRI findings and pathology features were correlated. Statistical methods included summary statistics and Wilcoxon's rank sum test for signal intensity, contingency tables for assessing reader agreement, concordance rate between the two readers with 95% CIs, and Fisher's exact test for independence, all stratified by RCC type.

RESULTS

Papillary RCCs and clear cell RCCs had a similar appearance and signal intensity ratio on T1-weighted images. On T2-weighted images, most papillary RCCs were hypointense (reader 1, 13/21; reader 2, 14/21), with an average mean signal intensity ratio for both readers of 0.67 +/- 0.2, and none was hyperintense, whereas most clear cell RCCs were hyperintense (reader 1, 21/28; reader 2, 17/28), with an average mean signal intensity ratio for both readers of 1.41 +/- 0.4 (p < 0.05). A tumor T2 signal intensity ratio of < or = 0.66 had a specificity of 100% and sensitivity of 54% for papillary RCC. Most T2 hypointense tumors exhibited predominant papillary architecture; most T2 hyperintense tumors had a predominant nested architecture (p < 0.05).

CONCLUSION

On T2-weighted images, most papillary RCCs are hypointense and clear cell RCCs, hyperintense. The T2 hypointense appearance of papillary RCCs correlated with a predominant papillary architecture at pathology.

Radiologic evaluation of small renal masses (I): pretreatment management

When characterizing a small renal mass (SRM), the main question to be answered is whether the mass represents a surgical or nonsurgical lesion or, in some cases, if followup studies are a reasonable option. Is this a task for a urologist or a radiologist? It is obvious that in the increasing clinical scenario where this decision has to be made, both specialists ought to work together. This paper will focus on the principles, indications, and limitations of ultrasound, CT, and MRI to characterize an SRM in 2008 with a detailed review of relevant literature. Special emphasis has been placed on aspects regarding the bidirectional information between radiologists and urologists needed to achieve the best radiological approach to an SRM.

Differentiation of pathologic subtypes of papillary renal cell carcinoma on CT

OBJECTIVE

We reviewed the CT findings of the subtypes of papillary renal cell carcinoma (RCC), which behave differently clinicopathologically.

CONCLUSION

The CT features of the two pathologic subtypes of papillary RCC differ, probably reflecting their different pathologic features. Type 1 tumors have more distinct margins than type 2 tumors and have homogeneous density. Although type 2 tumors in the early stages show findings similar to those of type 1 tumors, they are at more advanced stages on the whole, with CT features showing indistinct margins, frequent centripetal infiltration, and tumor thrombi in all pT3b cases. Radiologists should be familiar with the CT features of papillary RCC that suggest different pathologic behaviors, such as tumor stage, tumor proliferation, and microvascular or vascular invasion.

Hyperattenuating renal masses: etiologies, pathogenesis, and imaging evaluation

Some renal masses have higher attenuation than the surrounding renal parenchyma at computed tomography (CT). Their hyperattenuation is usually the result of proteinaceous fluid or densely packed cells. Most hyperattenuating renal masses are benign hemorrhagic or proteinaceous cysts. However, solid enhancing hyperattenuating renal masses may have malignant as well as benign causes. Possible malignant causes include renal cell carcinoma and lymphoma; benign causes include angiomyolipoma with minimal fat. It is important to identify the cause of a hyperattenuating renal mass so as to avoid unnecessary surgical resection or ablation. CT may be useful for diagnosing benign hyperattenuating renal cysts, hematomas, and vascular anomalies that appear masslike. However, some solid, enhancing, hyperattenuating masses cannot be diagnosed confidently with CT alone: Small (< or = 3-cm-diameter), homogeneously enhancing, hyperattenuating renal masses depicted on CT images may be either benign angiomyolipomas with minimal fat or renal cell carcinomas. Magnetic resonance (MR) imaging may be helpful for differentiating between angiomyolipomas with minimal fat and clear cell renal cell carcinomas; however, differentiation between angiomyolipomas with minimal fat and papillary renal cell carcinomas often is not possible on the basis of MR imaging. In such cases, a percutaneous biopsy may be useful for diagnosis. If the results of MR imaging and percutaneous biopsy are not definitive, surgery is warranted.

Segmental disorders of the nephron: histopathological and imaging perspective

Recent advances in molecular genetics and immunocytochemistry have clarified the cell of origin in many renal disorders. Several renal disorders are thought to involve specific segments of the nephron. Renin-secreting tumours arise from juxtaglomerular cells. Clear cell and papillary renal cell carcinoma (RCC) recapitulate the epithelium of the proximal tubules. Oncocytoma and chromophobe RCC differentiate towards Type A and Type B intercalated cells of the cortical collecting duct, respectively. Medullary collecting ducts are the target sites for the development of autosomal recessive polycystic kidney disease, collecting duct carcinoma and medullary carcinoma. Renal papillae are susceptible to unique changes such as necrosis or papillitis. The purpose of our article is threefold: to illustrate the imaging findings of renal disorders that show segmental involvement of the nephron, to describe proximal and distal nephron disorders and to correlate imaging findings of some entities with histopathological features.

Common and uncommon histologic subtypes of renal cell carcinoma: imaging spectrum with pathologic correlation

Renal cell carcinoma (RCC) is a cause of significant morbidity and mortality, with an estimated 35,000 new cases and 12,480 deaths in the United States in 2003. Recent advances in imaging technology, pathology, urology, and oncology permit early diagnosis of RCC and facilitate optimal management. The 2004 World Health Organization classification for renal neoplasms recognizes several distinct histologic subtypes of RCC. These subtypes include clear cell RCC, papillary RCC, chromophobe RCC, hereditary cancer syndromes, multilocular cystic RCC, collecting duct carcinoma, medullary carcinoma, mucinous tubular and spindle cell carcinoma, neuroblastoma-associated RCC, Xp11.2 translocation-TFE3 carcinoma, and unclassified lesions. Different histologic subtypes of RCC have characteristic histomorphologic and biologic profiles. Clear cell RCC is the most common subtype and has a less favorable prognosis (stage for stage) than do papillary RCC and chromophobe RCC. Collecting duct carcinoma and renal medullary carcinoma are associated with aggressive clinical behavior and a poor prognosis.

Renal Masses in the Adult Patient: The Role of Percutaneous Biopsy

Although percutaneous renal mass biopsy with cross-sectional imaging guidance has long been considered to be safe and accurate, there have been recent advances in imaging, interventional, and cytologic techniques that have increased the role of percutaneous biopsy in the diagnosis of renal masses. Today, biopsy plays a fundamental role in the care of patients with a renal mass. Biopsy results are used to confirm the diagnosis of renal cancers, metastases, and infections, and there is increasing evidence to suggest that biopsy can help subtype and grade many primary renal cancers. Because a considerable fraction of small solid renal masses are benign and do not need treatment, there is an increasing need to diagnose them. Biopsy after a full imaging work-up can help prevent unnecessary and potentially morbid surgical and ablation procedures in a substantial number of patients. Although more data are needed to understand the overall accuracy of biopsy for the diagnosis of benign lesions, many can be diagnosed with the aid of biopsy findings. This article reviews reported experience with percutaneous renal mass biopsy, discusses the technical factors that contribute to results, and details seven specific clinical settings that should prompt the clinician to consider percutaneous biopsy when encountering a renal mass.

MR Imaging of papillary renal neoplasms: potential application for characterization of small renal masses

The purpose of our study was to evaluate the role of MRI in demonstrating the precise nature of papillary renal tumors (P RCC) and its potential application to select patients for partial surgery. Ninety-seven tumors less than or equal to 3 cm in size [55 papillary renal cell carcinoma - 42 clear cell renal carcinoma (CC RCC)] were preoperatively evaluated by MRI. Imaging findings were assessed with a special focus on the aspect of the tumoral process. Correlations were performed with pathologic staging after surgery. At pathology, 92 tumors were established to be staged p T1 and 5 were p T3 ( 3 cases of CC RCC and 2 cases of P RCC). Ninety-four percent of papillary tumors exhibited low signal intensity with homogeneous pattern on T2-weighted images. All clear cell carcinoma were hyperintense and heterogeneous on T2-weighted sequence. Enhancement was lower and delayed in the papillary type in comparison with the clear cell type. MRI is accurate enough to predict the 'histologic' nature of papillary renal carcinoma. It is an additional argument to propose that the tumor can be removed by partial surgery.

Are T2-weighted images necessary in renal mass characterization?

OBJECTIVE

To determine what role T2-weighted images play in characterizing renal masses.

METHODS

Forty-four pathologically proven renal masses (34 renal cell carcinomas, 8 oncocytomas, 1 metanephric adenoma, 1 angiomyolipoma without macroscopic fat) and 38 simple renal cysts were evaluated with T1- and T2-weighted images at 1.5T. Two independent and blinded readers initially characterized all masses using only the T1-weighed images (in- and opposed-phase chemical shift, unenhanced frequency-selective fat-suppressed, gadolinium-enhanced frequency-selective fat-suppressed and subtraction images) and placed each mass into one of three categories: nonsurgical, in need of follow-up, or surgical. The masses were then re-evaluated with the addition of the T2-weighted images. It was determined if the T2-weighted images changed the initial classification.

RESULTS

Forty-three of the 44 (98%) pathologically proven renal masses were characterized as a surgical mass using only the T1-weighted images. The remaining renal mass (a renal cell carcinoma) was characterized as a mass in which follow-up exams would be suggested. Thirty-eight of 38 (100%) simple renal cysts were correctly characterized using only the T1-weighted images. The T2-weighted images did not change the initial interpretation of the T1-weighted images in any of the cases.

CONCLUSION

The results of this study suggest that T2-weighted images are not necessary in the evaluation of all renal masses and are specifically not necessary in the differentiation of solid and cystic renal neoplasms from simple renal cysts.

Papillary renal carcinoma: Diagnostic approach by chemical shift gradient-echo and echo-planar MR imaging

PURPOSE

To elucidate whether MRI can detect fat in interstitial histiocytes and hemosiderin (Hs) deposition (both of which are histological characteristics of papillary renal carcinoma (RCpap)) within RCpap.

MATERIALS AND METHODS

Preoperative MR images of nine surgically confirmed RCpap and 57 clear cell renal carcinoma (RCcc) cases were retrospectively studied. Solid components of the lesions were evaluated. For fat detection, signal reduction on opposed-phase images of chemical shift MRI (CSI) was used. For Hs detection, signal reduction on echo-planar images or in-phase images of CSI was used. The prevalence of fat and Hs detection was compared between RCpap and RCcc.

RESULTS

In five of nine RCpap (54%), and 38 of 57 RCcc (67%), the presence of fat within the tumor was suggested by CSI (P = 0.71). Hs deposition within tumors was suggested by either EPI or CSI in nine of nine RCpap (100%), and 28 of 57 RCcc (51%) (P = 0.0036). Hs in RCpap was observed without or apart from necrosis or hemorrhage, whereas Hs in RCcc was located predominantly around necrosis.

CONCLUSION

Detecting intratumoral Hs by EPI or CSI, particularly that unrelated to necrosis or hemorrhage, may help differentiate RCpap from RCcc.

Imaging characteristics of papillary renal cell carcinoma by computed tomography scan and magnetic resonance imaging

AIM

To analyse the differences in the patterns between clear and papillary renal cell carcinomas using magnetic resonance imaging (MRI) and dual-phase helical computed tomography (CT).

METHODS

We examined seven patients with papillary renal cell carcinoma, and six with clear cell carcinoma. The highest attenuation value of tumors in the corticomedullary phase (CMP) and the excretory phase (EP) was measured using the observer-defined region of interest (ROI). MRI consisted of T1-weighted and T2-weighted spin-echo imaging.

RESULTS

All five tumors except for one with papillary renal cell carcinoma showed homogenous hypointensity, but all six tumors with clear cell carcinoma showed heterogeneous hyperintensity on their T2-weighted images. In the CMP, the mean CT numbers of the papillary renal cell carcinomas were significantly lower than those of the clear cell carcinomas. The mean enhancement of the papillary renal cell carcinomas in the CMP and the EP was significantly lower than that of the clear renal cell carcinomas. The mean CT numbers of the clear cell carcinomas in the CMP were markedly increased from those on the unenhanced CT; those in the EP were decreased gradually. But the mean CT numbers of the papillary renal cell carcinomas in the EP were still slightly more increased than those in the CMP. The enhancement patterns of the papillary renal cell carcinomas in the CMP and the EP were homogenous, but those of the clear cell carcinomas were heterogeneous.

CONCLUSIONS

We can speculate the differential diagnosis from clear to papillary renal cell carcinoma using MRI and dual-phase helical CT.

Magnetic Resonance Imaging of the Kidney

High tissue contrast, multiplanar image capabilities, and tissue characterization render MR into an ideal imaging modality for effective evaluation of a wide range of renal disorders. It provides high details of anatomy and can suggest the composition of lesions. Improvements of MRI technology during the last years have made MRI increasingly attractive for body imaging. Fast imaging sequences and parallel imaging techniques have proved to be useful in minimizing artifacts from respiratory motion and magnetic susceptibility differences providing superior imaging quality. Additionally, the use of renally eliminated paramagnetic contrast agents permits assessment of parenchymal perfusion and visualization of the excretion of the contrast medium providing information on renal function.

Papillary renal cell carcinoma in allograft kidney

Papillary renal cell carcinoma is a subgroup of malignant renal epithelial neoplasms. Its occurrence in allograft transplanted kidney has not been debated in the literature. We report two pathologically proven cases and discuss the clinical hypothesis for such neoplasms and the aspect on MR images. The paramagnetic effect of the iron associated with an absence of signal coming from calcifications is a plausible explanation for this unusual hypo-intense appearance on T2-weighted sequence.

Abundant intracytoplasmic hemosiderin in both histiocytes and neoplastic cells: A diagnostic pitfall in fine-needle aspiration of cystic papillary renal-cell carcinoma

Benign renal tubular cells and renal-cell carcinomas (RCC) may have intracytoplasmic hemosiderin (ICH). The RCC subtype most commonly reported to contain ICH is papillary carcinoma (PRCC). PRCC, usually a low-grade neoplasm, may be associated with cystic degeneration, hemorrhage, and presence of abundant hemosiderin-laden macrophages (HLM). We report a case of PRCC with massive ICH and HLM that created a diagnostic challenge to differentiate from a hemorrhagic cyst. Review of 14 additional nephrectomy specimens with PRCC disclosed ICH in 3 cases. All had coexisting cystic change and hemorrhage. Preoperative FNA had been performed in one of these cases, and both ICH and HLM were found. Papillary epithelial cell features, however, were well-defined in this case. PRCC should be considered in the differential diagnosis of cystic renal lesions with hemosiderin-laden cells. Differentiation of HLM from neoplastic cells with massive ICH may be difficult, especially when epithelial fragments are scanty.

MR imaging of renal masses interpreted on CT to be suspicious

OBJECTIVE

Prior studies have shown that renal MR contrast enhancement improves the efficacy of mass and proximal vascular evaluation. This study assessed the usefulness of different sequences for characterization of masses that appeared suspicious on CT and for prediction of their potential for malignancy.

SUBJECTS AND METHODS

In a prospective manner 32 patients (age range, 26-78 years: average age, 54 years), each with at least one suspicious mass on CT, were examined with MR imaging. The following sequences were performed: conventional spin-echo with and without fat saturation, fast spin-echo, and dynamic gadopentetate dimeglumine-enhanced infusion using a 1.5-T superconducting magnet. Results were analyzed and compared with pathologic results after resection.

RESULTS

A total of 65 renal masses of average size 2.6 cm (range, 1-10 cm) were detected with dynamic MR imaging. Seventeen of the 65 masses were malignant. Of the 17 malignant masses, three did not enhance on dynamic MR imaging (because of hemorrhage). Sixteen of the 17 malignant masses were heterogeneous on T2-weighted images. Three enhancing masses contained fat and all were angiomyolipomas. Thirty-five of the 65 masses (four with hemorrhage) did not show enhancement, all of which were homogeneous on T2-weighted images and were proven to be cysts. Five masses resulted from infections and had heterogeneous T2 appearance. The remaining masses were three hematomas with hemorrhage, one column of Bertin, and one aneurysm.

CONCLUSION

Renal masses that are interpreted as suspicious on CT may lack MR enhancement because of hemorrhage effects; heterogeneity of their T2 appearance is thus critical in differentiating malignancy from benign disease. Odds-ratio calculations give an adjusted estimate of a 3.36-fold increase (95% confidence interval, 1.8-6.27) in the likelihood of malignancy when masses are heterogeneous on T2-weighted images and a 29-fold increase (95% confidence interval, 3.67-241.8) for predicting malignancy when enhancement is present.

Renal cell carcinoma: preoperative assessment for enucleative surgery with angiography, CT, and MRI

PURPOSE

Our purpose was to assess various imaging methods in detecting a pseudocapsule of renal cell carcinoma (RCC), which is critical for successful tumor enucleation.

METHOD

In 42 patients with histopathologically proven RCC, images obtained at angiography (n = 42), CT (n = 30), and MRI (n = 19) were investigated retrospectively. All patients underwent treatment (enucleation: n = 15; nephrectomy: n = 27). The imaging criteria for the presence of a pseudocapsule were as follows: a surrounding radiolucent rim on angiography, a low or high density rim on CT, and a low intensity rim on MRI. All images were retrospectively reviewed by three radiologists without knowledge of the clinical and histological findings.

RESULTS

Thirty-three of 42 RCCs showed a pseudocapsule on the surgical specimen. A pseudocapsule was detected in 67% of tumors (22/33) on angiography, 26% (6/23) on CT, 27% (4/15) on T1-weighted MRI, 93% (14/15) on T2-weighted MRI, 67% (8/12) on dynamic enhanced T1-weighted MRI, and 15% (2/13) on delayed enhanced T1-weighted MRI.

CONCLUSION

T2-weighted MR images are superior for visualizing a pseudocapsule of RCC and for providing reliable selection criteria for tumor enucleation.