teratoid wilms tumor , a rare variant of nephroblastoma , has a predominance of heterologous elements . to date
less than 30 cases of teratoid wilms tumor have been reported in the literature.[13 ] there is only one case in the literature , which has the squamous epithelial component comprising 70% of the tumor .
we describe a case in which the squamous epithelium with keratin cysts comprised majority ( about 75% ) of tumor mass . metastasis is seldom reported in teratoid wilms .
a -2-year - old boy presented with palpable mass on the right side of abdomen for 2 months . physical examination revealed a firm mass that was palpable in the lumber region .
contrast - enhanced computed tomography ( cect ) scan showed large hetrodense lesion in the right lumber region measuring 17 cm  8 cm  7 cm .
the right lung showed nodular opacities in posterior and lateral basal segments of about 0.5 cm in diameter suggestive of metastasis .
cect scan done after 6 weeks of chemotherapy showed little change in the size of tumor and the patient underwent nephrectomy .
grossly , nephrectomy specimen measured 17 cm  8 cm  6 cm that was soft in consistency .
the cut section was predominantly solid and pale grey with areas of cystic change , necrosis , and hemorrhage .
a thin segment of normal kidney was seen compressed at periphery [ figure 1 ] .
gross - predominantly cystic appearance of teratoid kidney microscopically , the tumor showed classical triphasic pattern with blastemal , epithelial , and mesenchymal components without anaplasia ; about 75% of the tumor revealed areas of squamous differentiation with keratin pearl formation but without adnexal structures [ figures 2 and 3 ] .
there were also small foci of mature adipose tissue and glial tissue [ figure 4 ] .
wilms tumor is an embryonic tumor typically composed of variable admixture of blastematous , epithelial and stromal components .
wilms tumor can include heterologous elements in addition to these components and variend et al in 1984 , coined the term teratoid wilms tumor for them .
. defined teratoid wilms as a tumor that contains hetrologous elements comprising more than 50% of the tumor mass . to date , less than 30 cases of teratoid wilms tumors have been reported.[13 ] the pathogenesis of this entity is still debated ; it is likely that it originates from totipotent primitive metanephric blastema .
the variable presence of intracellular matrix proteins may influence the presence , extent , and diversity of hetrologous differentiation .
the teratoid elements seen frequently are skeletal muscle , smooth muscle , adipose tissue , glial tissue , cartilage , bone , and are generally assumed to represent aberrant mesenchymal differentiation .
there is only one case of teratoid wilms in the literature , reported by karaka i et al , which had squamous epithelial component comprising 70% of the tumour .
we report a case that showed the familiar triphasic pattern of nephroblastoma along with the extensive squamous epithelial components constituting about 75% of the tumor .
the differential diagnosis of teratoid wilms is intrarenal teratoma , metastatic germ cell tumor , and retroperitoneal infiltration of teratoma . in our case ,
classical triphasic pattern of wilms tumour was seen and there was no attempt to form the adnexal structures or organogenesis thus ruling out intrarenal teratoma . also , the presence of normal testis excluded the possibility of metastatic testicular germ cell tumor .
renal capsule was also free of tumor so retroperitoneal infiltration of teratoma was also ruled out . although it is reported that teratoid wilms tumor is not usually aggressive or has metastatic potential .
the case reported by karaka et al , which had extensive squamous areas , died of metastasis .
whether the squamous differentiation is associated with higher stage at presentation remains to be seen .
the treatment of teratoid wilms tumor has not yet been established because of its rarity and varying tumor components .
both surgeons and pathologists should be aware that the treatment of this rare variant should be focused on total surgical removal of the tumor .
 teratoid wilms tumor is an unusual histological variant of nephroblastoma with predominant heterologous component . 
 frequently present components include adipose tissue , glial tissue , muscle , cartilage or bone . 
 the presence of squamous epithelial component on the other hand is rarely reported . 
 we describe a case of unilateral teratoid wilms tumor in a 2-year - old boy with lung metastasis . in this case 
 , tumor showed the familiar triphasic histologic pattern of nephroblastoma along with extensive squamous epithelial component . 
INTRODUCTION
CASE REPORT
DISCUSSION