Introduction

Rhabdoid tumor of the kidney (RTK) is extremely rare accounting for 1.5 to 3.7% of pediatric renal tumors. RTK is extremely aggressive leading to the worst outcomes seen in this tumor group with an overall survival ranging from 22 to 33% at four to five years. RTK was first described as a distinct tumor from Wilms tumor by Haas and colleagues in 1981 [1]. They called it rhabdoid tumor because histologically the cells resemble rhabdomyoblasts. Rhabdoid tumors can occur in multiple locations including the central nervous system and extracranial sites. Among extracranial sites, the kidney accounts for 48% of cases, the liver for 13% and the rest occurring in the soft tissues of the head, neck, trunk and extremities [2]. Several studies have shown that survival is uniformly poor and is not site dependent [3][4].

see also Pediatric Renal Tumors

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Rhabdoid Tumor of the Kidney

Accounting for two percent of renal tumors, malignant rhabdoid tumor of the kidney (RTK) occurs in young infants and is the most aggressive and lethal pediatric renal tumor. Grossly these tumors are unencapsulated and invasive with characteristic involvement of the perihilar renal parenchyma. Histologically, rhabdoid tumors are characterized by monomorphous, discohesive, rounded to polygonal cells with acidophilic cytoplasm and eccentric nuclei containing prominent large “owl eye” nucleoli reminiscent of skeletal muscle but lacking its cytoplasmic striations, ultrastructural features and immunochemical markers [5]. Ultrastructural examination suggests a neuroectodermal origin [1]. These tumors are notable for the occurrence of second primary neuroglial tumors resembling medulloblastoma in the midline of the brain [6]. A deletion of 22q11-12 has been described in both renal and extrarenal rhabdoid tumors [7]. All renal tumors except RTK show nuclear positivity for immunohistochemical staining for the wild type INI-1 protein while in renal and extra renal rhabdoid tumors this is absent [8].