Metastatic Malignant Mixed Tumor of Renal Pelvis

Eric Richard Handley, MD - Case Coordinator
Sidney Uttam Jain, MD - Radiology Discussion
Priscilla S Chang, MD, PhD - Pathology Discussion
Steven E Seltzer, MD - Attending Radiologist

January 26, 2004

Presentation

Imaging Findings

A contrast-enhanced CT of the chest (figure 1) shows a filling defect in the IVC. The defect is at the level just below the renal veins, below the right kidney. A non-enhanced chest CT obtained three months later (figure 2) is fairly unremarkable. Non-contrast images obtained seven months after the first CT (figures 3 and 4) are related to a biopsy (note the overlying mesh). There is a contour abnormality in the infralateral cortex of the left kidney. The lesion is slightly hypointense compared to the surrounding tissue. The history indicates that the mass developed within a period of two months.

Differential Diagnosis

Diagnosis

Discussion

The left nephrectomy specimen incorporates a 4.5-cm, tan-white infiltrating mass that abuts the renal pelvis. The patient’s history indicates that an 8.5-cm mass was resected from the left calf one year prior to this surgery (second gross image). At that time, the resection margins were positive. Histology of the kidney specimen shows a highly pleomorphic collection of tumor cells, a high rate of mitosis, and extensive areas of necrosis. This fairly nonspecific appearance simply indicates a high-grade sarcoma. The purple area, however, is a myxoid chondroid matrix; this is characteristic of a mixed tumor. Like the original primary tumor, this metastatic lesion stained positive for S-100 and a variety of keratins.

Radiology Discussion

Solid renal masses can original in the parenchyma, mesenchyma, or renal pelvis, or may be secondary tumors. Parenchymal tumors include renal cell carcinoma, Wilms tumor (in children), and adenoma. Renal cell carcinoma (RCC) typically demonstrates heterogeneous enhancement and can also be cystic (2-5% of cases). The tumor can invade the renal vein or inferior vena cava, sometimes causing blockage. This mass can also undergo sarcomatoid degeneration, becoming a high-grade spindle cell sarcoma. Wilms tumor affects young children (2-3 years old). Calcifications are uncommon. Like RCC, the tumor can invade the RV and IVC. Nephroblastomatosis is a precursor to Wilms tumor characterized by multiple, diffuse nephrogenic rests (low density on CT). Adenoma is a low-grade adenocarcinoma with a very low potential for metastasis. It is most often detected at autopsy. Oncocytoma is a benign proximal tubular adenoma that is radiographically indistinguishable from renal cell carcinoma. Mesoblastic nephroma , also known as fetal renal hamartoma, is the most common renal tumor in the neonate.Mesenchymal tumors include angiomyolipoma (hamartomas characterized by the presence of fat; may bleed), malignant fibro histocytoma (MFH), spindle-cell sarcoma, synovial cell sarcoma, hemangioma, and juxtaglomerular tumor. A juxtaglomerular tumor is also known as a reninoma. These small, hypovascular masses release renin, which causes hypertension, hypernatremia, and hypokalemia. Juxtaglomerular tumor sould be ruled out in young adults presenting with hypertension.

Tumors of the renal pelvis include transitional cell carcinoma, squamous cell carcinoma, and various benign masses: papilloma, angioma, fibroma, myoma, and polyp. Secondary tumors include lymphoma and metastases. The kidneys have no lymphatic tissues, so there is essentially no primary lymphoma. Secondary lymphoma in the renal tissue can present as a “ball” (expansile) or a “bean” (infiltrative) shape. Common metastases include primary cancers of the lung, breast, and colon, as well as melanoma and lymphoma; it is rare for sarcoma to metastasize to the kidneys.

References

Moch H et al. Primary renal synovial sarcoma. A new entity in the morphological spectrum of spindle cell renal tumors. Pathologe. 2003 Oct; 24(6): 466-72.

Weissleder et al. Primer of Diagnostic Imaging. Mosby. 1997.

Dahnert. Radiology Review Manual. Williams and Wilkins. 1991.

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