multicystic dysplastic kidney ( mcdk ) is a relatively common developmental anomaly in infants and children , and its overall prognosis is good in older children . although mcdk is grossly " cystic " in appearance , it is not one of the inherited renal cystic diseases , but a kind of renal dysplasia , in which cystic elements are found along with immature , undifferentiated , primitive tissue ( 1 ) . in contrast , a malignant rhabdoid tumor of the kidney ( mrtk ) is one of the most lethal neoplasms of early life , and the mortality rate exceeds 80% ( 2 ) . mrtk usually arises from perihilar renal parenchyma and infiltrates into the medulla , renal sinus , and collecting system . the recurrence rate is high , and the tumor tends to metastasize to the lung , liver , and brain ( 2 , 3 ) . there have been some reports concerning mrtk and mcdk presenting individually and mcdk presenting with wilms tumor ( 4 ) . however , a combined case of these two diseases has not been reported to date . therefore , the authors present a case of mrtk combined with mcdk in a 5-yr - old girl with a literature review . a 5-yr - old girl who was previously diagnosed with mcdk at birth by abdominal sonography presented with a huge palpable mass on the right side of her abdomen . no symptoms were noted until a huge mass was palpated two weeks prior to presentation . abdominal sonography and computed tomography ( ct ) were performed , and they revealed an increased cystic lesion extensively replacing the right kidney and a newly - developed amorphous portion in the cystic lesion , compared to the previous radiologic findings at birth ( fig . the cut surface showed numerous cystic and semisolid masses in the cortex and medulla ( fig . some of the neoplastic cells had eccentric nuclei and large , round , eosinophilic cytoplasmic inclusions . in the remaining parenchyma the tumor cells were non - cohesive , large , round - to - polygonal cells with vesicular nuclei and prominent nucleoli ( fig . the immunohistochemical stains of the rhabdoid tumor cells were positive for cytokeratin , vimentin , ini1 , and epithelial membrane antigen and negative for desmin and smooth muscle actin ( fig . ultrastructurally , the tumor cells had poorly formed intercellular junctions , a fair amount of mitochondria , and were filled with lipid droplets ( not shown ) . generally , kidney abnormalities are classified by quantity , location , morphology , differentiation , and genetic disorder . among them one in 4,300 live births is estimated to have unilateral mcdk ( 6 ) , and few occur in syndromes of multiple malformations . in contrast , mrtk is a rare malignant tumor of the kidney , and it accounts for about 2 - 3% of kidney tumors ( 3 ) . mrtk also tends to occur in young infants and is one of the most lethal neoplasms in early life ( 7 ) . before 1981 , investigators thought mrtk was a kind of wilms tumor ; however , haas et al . they reviewed 111 cases of rhabdoid tumors of the kidney by analyzing microscopic findings , immunohistochemical stains , and electron microscopic findings of the cases . unlike with a wilms tumor , they found that some of the tumor cells originated from primitive cells . some investigators suggested that mrtk might originate from widely - distributed precursor cells or neuroepithelial cells ( 7 ) . there has not been a report about a case of mcdk presenting concurrently with mrtk with an examination of the cause of their coexistence and their pathophysiology to date . embryologically , dysplastic kidney disease , which is induced by a metanephron abnormality , is irreversible , and the severity of disease and affected areas are varied ( 5 ) . mcdk is a common disease in infants , yet the pathophysiology of mcdk is not well understood . one hypothesis is that mcdk results from an abnormal induction of the metanephric blastema by the ureteric bud ( 5 ) . embryologically , mcdk may result from abnormal renal morphogenesis , likely due to abnormalities of developmentally expressed genes ( 1 ) . until now , pax2 , bcl2 , and galectin-3 genes were thought to be related with the occurrence of mcdk , and chromosome t(6:19)(p21:q13.1 ) abnormality - induced cytogenetic change ( 8) . those genes are associated with oncogenesis and their high level of expression can accelerate the proliferation of dysplastic cysts , which causes some patients ' multicystic dysplastic kidney to continue to propagate ( 8 , 9 ) . on the other hand , about 15% of mrtks they arise embryologically from the stromal cell , mesenchymal cell , neuroectodermal cell , or germ cell . it is reported that genetically 90% of rhabdoid tumors have a 22q11.2 chromosomal translocation , and a mutation or deletion of smarcb1 , hsnf5/iml , and ddt1 genes ( 10 ) . according the theory of pathogenesis , the two kinds of disease are probably related to stem cell mutation . distinctions should be made among mcdk , wilms tumor , mrtk with a cystic pattern , and other diseases affecting the kidney . the pathologic findings in this case revealed a typical mcdk that coincided with embryonic tubules , glomeruloid structures , and immature cartilage . in addition , immunohistochemical stains were positive for cytokeratin , epithelial membrane antigen , and vimentin , but negative for smooth muscle actin . therefore , it was diagnosed as mcdk coexistent with mrtk ( 11 ) . by electron microscopy , tumor cells of usual cases of mrtk form sheetlike patterns , have poorly formed intercellular junctions , abundant mitochondria , and lipid droplets in the cytoplasm , especially prominent aggregates of filaments . however , in this case , the cytoplasm did not have prominent aggregates of filaments . therefore , the diagnosis of mrtk should be given only after thorough investigations by light microscopy , immunohistochemical stains , and electron microscopy . age is a highly significant prognostic factor , and the younger the patient , the better the prognosis . subjects older than five years are less responsive to chemotherapy , suggesting a poor prognosis ( 12 ) . however , when the disease is combined with hypertension or a malignant tumor , the patient is more likely to have a poor prognosis ( 13 ) . after being diagnosed with mcdk , the patient needs regular follow - up to ensure that the cystic tumor is regressing or to uncover any evidence that a new neoplasm is developing . until now , there have already been reports of mcdk simultaneously occurring with renal cell carcinoma , mesothelioma , and wilms tumor ( 14 ) . the prognosis of mrtk is related to the stage , lymph node metastasis , sex , nuclear diameter , and other factors . in this case , because the patient was 5 yr old , the tumor was stage i , and the cells had a medium nuclear size ( 2 - 4 m ) , according to the mrtk prognosis markers , the patient might have belonged to the favorable prognostic group . it is difficult to evaluate the patient 's prognosis when there are two different diseases present at the same time . hence , a prognosis should be related to the more serious disease , if two diseases occur simultaneously . in conclusion , the authors believe that this case , mcdk combined with mrtk found in an infant , is the first of its kind to be reported , and we consider that this occurrence can become a new disease entity in infantile renal disease in the future . according to the literature , finally , early development of one could have affected the course of the other . by reviewing more cases and studies , pathogenetic and prognostic evidence of mcdk combined with mrtk
multicystic dysplastic kidney ( mcdk ) is a relatively common developmental anomaly in infants and children and has a good prognosis . 
 in contrast , a malignant rhabdoid tumor of the kidney ( mrtk ) is one of the most lethal neoplasms of early life . 
 however , the presentation of such a lethal tumor combined with multicystic dysplasia has not been reported to date . in this report 
 , we describe a case of mrtk in a 5-yr - old girl who also had multicystic dysplasia . 
 she was previously diagnosed with mcdk at birth due to a huge palpable mass on the right side of the abdomen . 
 the right kidney was extensively replaced by numerous grossly dilated , variable - sized cysts . 
 microscopically , the tumor cells show a diffusely infiltrative growth pattern , which revealed large non - cohesive , round - to - polygonal tumor cells with vesicular nuclei . 
 some tumor cells had eccentric nuclei and large , round , eosinophilic cytoplasmic inclusions . 
 there were metanephrons present , with the central ureteric bud and peripheral branches surrounded by condensing mesenchyma , immature glomeruli , and metaplastic cartilage in the adjacent parenchyma . 
 to our knowledge , this is the first combined case of the two aforementioned diseases and this case may , in fact , suggest a new disease entity .