Case 353 - Discussion

Uploaded: 2009-09-25, Updated: 2009-09-25

 Clear Cell Sarcoma of Kidney (CCSK)

DEFINITION

• Malignant mesenchymal neoplasm

• Undifferentiated cells, abundant extracellular matrix, in cords and nests separated by a fine vascular network.

• A striking predilection to metastasize to bone, "bone metastasizing renal tumor of childhood."

CLINICAL FEATURES

• 5% of primary pediatric renal tumors;

• Peak age, 2 years.

• M:F>2:1.

GROSS FINDINGS

• Median weight, 500 - 600 g.

• Mostly within the renal medulla, irregular and sharply defined, unencapsulated.

• Homogeneous, light brown or gray, dense, firm texture. Some tumors soft and mucoid.

• Cysts often present .

MICROSCOPIC FINDINGS

• Undifferentiated plump cells arranged in nests or cords of 6-10 cells in width.

• "Chicken wire":  evenly dispersed, regularly branching small vessels separating cord cells.

• Cord cells:

  • Uniform in size, loosely spaced, and have indistinct cell borders. Rarely densely packed or overlapping.

  • Nuclei: finely dispersed chromatin, no prominent nucleoli or chromatin condensation. Frequent "empty"-appearing nuclei.

  • Focally the tumor cells may have condensed and acidophilic cytoplasm.

• Abundant extracellular, Alcian blue positive, mucopolysaccharide matrix.

• Tumor boarder: subtly infiltrating the normal renal parenchyma for short distances, nibbling into the adjacent renal parenchyma.

• Variants:

  • Myxoid pattern,: most common variant, diffuse accumulation of mucopolysaccharide matrix between cord and septal cells.

  • Sclerosing pattern (35%CCSKs): abundant acellular collagen, often limited to the region of cord cells.

  • Cellular pattern ( 25%): close spacing and overlapping of nuclei, decreased intercellular material.

  • Epithelioid pattern (13%):  most often mistaken diagnosis of nephroblastoma. Condensation of the cord cells in ribbons, tubules, rosettes, and trabeculae. The intervening vascular septa usually retained but not always conspicuous.

  • Spindle cell pattern (7%): both the septal and cord cells may have spindle cell features, reminiscent of other soft tissue tumors.

  • Palisading pattern (15%): alignment of spindle cell nuclei in parallel linear arrays, alternating with nuclear free zones.

  • Sinusoidal (pericytomatous) pattern: blood vessels distended, resembling a hemangiopericytoma.

IMMUNOHISTOCHEMISTRY STAINING

• Vimentin +

• Epithelial markers -

DIFFERENTIAL DIAGNOSES

TREATMENT AND PROGNOSIS

• Bone metastasis is the most common mode of relapse, other commonly metastatic sites are brain, lung, liver, and soft tissue.

• 6-year survival: 97% stage I; 75% stage II; 77% stage III; and 50% stage IV.

REFERENCES

• AFIP, tumor of the kidney, bladder and related urinary structures, series 4;