Clear cell sarcoma of the kidney
Clear cell sarcoma (CCS) of the kidney are a rare mesenchymal tumor that account for ~5% of primary renal neoplasms in pediatric population 1.
CCS is the second most common primary malignant renal neoplasm after Wilms tumor, with an annual incidence of 20 cases in the United States 2,3. The mean age of diagnosis is 3 years 2, although it is very rare before the age of 6 months 3,4. Males are noticed to be affected more with a M:F = 2:1 1.
CCS usually presents with a palpable abdominal mass; with hematuria and bone pain being less common.
CCS appears as a large solid mass, usually unilateral and unifocal, replacing most of the kidney or centered in the medulla 1. The cut surface appears gelatinous due to abundance of extracellular mucopolysaccharides. Hemorrhage and necrosis are frequent finding (70%) 2.
Histologically, nine subtypes have been described 1. Most of these, however, will show some of the classic features of the tumor microscopically, consisting of cords or nests of cells surrounded by delicate branching cellular fibrovascular septa akin to chicken wire.
Although the margins of the tumor appear well defined grossly, they demonstrate infiltration in to adjacent renal parenchyma with entrapment of the tubules on high power field microscopy. The entrapped tubules may become extensively dilated, giving the apparent cysts seen on gross tumor inspection 2.
These tumors usually enhance heterogeneously and to a lesser extent than the adjacent kideny, with non enhancing foci representing hemorrhage and necrosis 5. They often cross the midline. Calcification is uncommon 5.
CCS usually appears low to intermediate on T1 weighted images and high signal on T2WI with cystic areas.
Treatment and prognosis
CCS has worse prognosis compared to Wilms tumors, especially in those younger than 12 months of age 3. The mainstay treatment is radical nephrectomy with lymph node dissection. Relapse rate is high (20-40% of patients) 4.