The expanded application of radiologic imaging resulted in an increased incidence of renal masses in the recent decade. Clinically, it is difficult to determine the malignant potential of the renal masses, thus resulting in complex management. Image-guided biopsies are the ongoing standard of care to identify molecular variance but are limited by tumor accessibility and heterogeneity. With the evolving importance of individualized cancer therapies, radiomics has displayed promising results in the identification of tumoral mutation status on routine imaging. This article discusses how magnetic resonance imaging features can guide a radiologist toward identifying renal mass characteristics.

Renal malignancies can be divided into cortical- and medullary-based tumors, the latter of which classically infiltrate the renal parenchyma by extending between nonneoplastic structures. Although high-grade cortical tumors can rarely exhibit the same growth pattern, the infiltrative morphology should elicit a differential diagnosis to be considered in each case. However, these diagnoses can be challenging to distinguish, especially on small renal biopsy samples.

To provide an overview of the clinical, gross, and microscopic findings; genetic and molecular alterations; and immunohistochemical evaluation of medullary-based renal tumors and other tumor types with overlapping morphologies and growth patterns.

Literature review and personal observations were used to compile the information in this review.

Collecting duct carcinoma is a prototypical medullary-based tumor, and although diagnostic criteria exist, it remains a diagnosis of exclusion, especially with ancillary techniques aiding the recognition of established as well as more recently described neoplasms. Other medullary-based malignancies included in the differential diagnosis include renal medullary carcinoma/renal cell carcinoma unclassified with medullary phenotype, fumarate hydratase-deficient renal cell carcinoma, and upper tract urothelial carcinoma. Moreover, other rare entities should be excluded, including metastatic carcinoma, lymphoma, and melanoma. In addition to potential prognostic differences, accurate diagnoses can have important surgical and clinical management implications.

Renal masses increasingly are found incidentally, largely due to the frequent use of medical imaging. Computed tomography (CT) and MR imaging are mainstays for renal mass characterization, presurgical planning of renal tumors, and surveillance after surgery or systemic therapy for advanced renal cell carcinomas. CT protocols should be tailored to different clinical indications, balancing diagnostic accuracy and radiation exposure. MR imaging protocols should take advantage of the improved soft tissue contrast for renal tumor diagnosis and staging. Optimized imaging protocols enable analysis of imaging features that help narrow the differential diagnoses and guide management in patients with renal masses.

Chronic viral hepatitis C (CHC) is a global health problem, being responsible for about 399 000 deaths worldwide, mostly from cirrhosis and hepatocellular carcinoma. Virus C infection has well known hepatic manifestations - cirrhosis and liver cancer - but the extrahepatic ones are responsible for up to 75% of morbidity in these patients. The well-known hepatitis C virus (HCV) lymphotropism is probably linked with the most frequent extrahepatic manifestations, mixed cryoglobulinemia and B-cell non-Hodgkin's lymphoma (BCNHL). We report a very rare entity, the case of an 82-year-old female with Child-Pugh class A viral C cirrhosis associated with a primary renal lymphoma (PRL). PRL is a non-Hodgkin's lymphoma (NHL) localized in the kidney, without any involvement of extrarenal lymphatic tissue. In addition to the case report, some relevant data from the literature were reviewed here.

Primary renal lymphoma (PRL) is a rare disease, with no more than 70 cases reported in the literature. The present study reports the case of a 70-year-old woman with PRL. The patient was asymptomatic, however, a mass on the right kidney was identified incidentally during routine physical examination. Computed tomography revealed a mass in the right kidney that was 3.6 cm in diameter. Subsequently, right nephrectomy was performed. The histological evaluation of the nephrectomy specimen showed diffuse large B-cell non-Hodgkin's lymphoma. The patient was treated with 6-8 cycles of a cyclophosphamide, epirubicin, vindesine and dexamethasone regimen. Follow-up examination performed after 2 months of treatment revealed no evidence of local recurrence. The present study also reviewed 49 cases of PRL that have been reported since 1989. It was found that a shorter survival time was experienced by patients with bilateral PRL (mean, 21 months) compared with unilateral PRL (mean, 68 months). A shorter survival time was also experienced by patients who were treated with chemotherapy only (mean, 15.8 months) compared with those who were treated with combination chemotherapy and surgery (mean, 49.4 months).

The kidneys and perinephric tissues can be affected by a variety of hematologic disorders, which usually occur in the setting of multisystem involvement. In many of these disorders, imaging is used to evaluate the extent of disease, guide biopsy, and/or monitor disease activity and patient response to therapy. Lymphoma, leukemia, and multiple myeloma commonly manifest as multiple parenchymal or perinephric lesions. Erdheim-Chester disease and Rosai-Dorfman disease, rare forms of multisystemic histiocytosis, are often identified as perinephric and periureteral masses. Renal abnormalities depicted at imaging in patients with sickle cell disease include renal enlargement, papillary necrosis, and renal medullary carcinoma. Sickle cell disease, along with other causes of intravascular hemolysis, can also lead to hemosiderosis of the renal cortex. Thrombosis of renal veins is sometimes seen in patients with coagulation disorders but more often occurs in association with certain malignancies and nephrotic syndrome. Immunoglobulin G4-related sclerosing disease is another multisystem process that often produces focal renal lesions, seen along with involvement of more characteristic organs such as the pancreas. Perinephric lesions with calcifications should raise the possibility of secondary amyloidosis, especially in patients with a history of lymphoma and multiple myeloma. Although the imaging patterns of renal and perinephric involvement are usually not specific for a single entity, and the same entity can manifest with different or overlapping patterns, familiarity with these patterns and key clinical and histopathologic features may help to narrow the differential diagnosis and determine the next step of care. (©)RSNA, 2016.

Primary renal lymphoma (PRL) is a rare disease which is often mistaken for renal cell carcinoma. In the present study, a 56-year-old man visited a clinic complaining of an intermittent fever and right flank pain. A computerized tomography examination revealed a hypoenhancing mass in his right kidney. Radical nephrectomy was conducted, and a diagnosis of diffuse large B-cell lymphoma was confirmed. The present case was determined to be a true PRL according to the results of a positron emission tomography examination and a bone marrow biopsy to rule out any lymphoma invasions apart from the right kidney.