Clear cell sarcoma of the kidney

Clear cell sarcomas of the kidney are a rare mesenchymal renal tumour that account for ~5% of primary renal neoplasms in the paediatric population ¹. 

Epidemiology

Clear cell sarcoma (CCS) of the is the second most common primary malignant renal neoplasm after Wilms tumour, 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 an M:F = 2:1 ¹. 

Clinical presentation

CCS usually presents with a palpable abdominal mass; with haematuria and bone pain being less common. 

Pathology

CCS appears as a large solid mass, usually unilateral and unifocal, replacing most of the kidney or centred in the medulla ¹. The cut surface appears gelatinous due to the abundance of extracellular mucopolysaccharides. Haemorrhage and necrosis are frequent findings (70%) ². 

Histologically, nine subtypes have been described ¹. Most of these, however, will show some of the classic features of the tumour microscopically, consisting of cords or nests of cells surrounded by delicate branching cellular fibrovascular septa akin to chicken wire. 

Although the margins of the tumour appear well defined grossly, they demonstrate infiltration into 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 tumour inspection ². 

Radiographic features

CT

These tumours usually enhance heterogeneously and to a lesser extent than the adjacent kidney, with non-enhancing foci representing haemorrhage and necrosis ⁵. They often cross the midline. Calcification is uncommon ⁵. 

MRI

CCS usuallyUsually appears as

• T1: low to intermediate on T1 weighted images andsignal
• T2: high signal on T2WI with cystic areas. 

Treatment and prognosis

CCS has a worse prognosis compared to Wilms tumours, 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. 

Due to their rarity, there is no standard treatment for CCS. Treatment may consist of surgical resection, chemotherapy, and/or radiotherapy ⁶.

Differential diagnosis

The imaging appearances for CCS are non-specific and can be very similar to other primary renal neoplasms, especially Wilms tumour which is much more common. Finding of bone metastasis could suggest CCS rather than Wilms tumour ¹.