they may present with bilateral aml at an early age in patients who have tuberous sclerosis , vonhippel - lindau syndrome and neurofibromatosis type 1 ( phakomatosis ) . with this in mind , we present a case which was initially diagnosed as a wilms tumor but was finally found to be a renal aml in a child without underlying phakomatosis .
a 12-year - girl was referred from another hospital with chief complaints of a lump in the left side of abdomen for the last 5 months .
the mass had progressively increased in size over a period of 5 months to involve most of her abdomen and produced significant abdominal distension .
an initial evaluation with ultrasonography and contrast - enhanced computed tomography ( cect ) of abdomen and chest at the referring center showed that it was a left renal mass .
subsequently , she was started on chemotherapy for wilms tumor with 3 drugs ( vincristine , doxorubicin and actinomycin d ) .
after receiving  week 6  of chemotherapy , she presented to us . at the time of presentation to us , she had a huge abdominal lump that was occupying the entire abdomen .
the size of the mass had decreased subjectively as per the patient herself by 25% after initiation of chemotherapy .
it was found to be having a variegated appearance arising from the lower pole of the left kidney and occupying almost the whole of abdomen .
we repeated the cect abdomen and chest which revealed a 21 cm  17 cm  12 cm solid mass with necrosis within it and this was arising from the left kidney [ figure 1 ] .
( a and b ) contrast - enhanced computed tomography scan images in the axial plane showing a large heterogeneous mass lesion arising from the left side of retroperitoneum replacing the entire left kidney .
the mass was displacing the bowel loops , aorta ( outlined arrow ) , and inferior vena cava ( arrow ) to the opposite side .
the right kidney ( * ) was normal and located in the right renal fossa there was no intravascular extension or lung metastasis .
fine - needle aspiration cytology ( fnac ) was performed , but the aspirate contained only blood . considering the rapid increase in size of the mass and the partial response to chemotherapy and the related necrosis ,
a repeat fnac was not ordered , and a working diagnosis of wilms tumor was kept .
the operative findings confirmed that the mass was arising from the lower pole of the left kidney , and it was occupying the entire abdomen and pushing the peritoneal contents to the right paracolic gutter [ figure 2a ] .
the specimen measured 27 cm  22 cm  18 cm and weighed 5.5 kg [ figure 2b ] . ( a ) intra - operative image showing the lump occupying almost the entire abdominal cavity with colon stretched over it and pushed to the right of the patient ( b ) the excised specimen showing that it arose predominantly from the middle and lower pole of the left kidney postoperative recovery was uneventful .
immunohistochemical analysis on the specimen showed negative pattern for wt-1 , mic-2 , desmin , nse , synaptophysin , s-100 andchromogranin .
there was a positive reaction towards hmb45 [ figure 3 ] and trace positivity towards vimentin .
she was evaluated and found not to be having any such features , and hence , she has been put on annual follow - up .
photomicrograph of the tumor shows features of anangiomyolipoma with a variable mixture of smooth muscle bundles ( thin arrow ) , blood vessels ( bold arrow ) , and adipose tissue ( star ) ( a and b : h and e , 40 and c : h and e , 200 ) .
focal immunopositivity for hydroxy beta - methyl butyric acid-45 was also noted ( parentheses ) ( d : hmb 45 , 200 )
the histologic picture resembles a hamartoma , but currently , they are considered as benign neoplasms .
there is a 4:1 female predominance and the mean age at presentation is around 40 years .
eighty percent of children with tuberous sclerosis develop these lesions by the age of 10 years . in children ,
the imaging characteristics of renal aml can vary considerably based on the amount and type of histologic elements present .
although fat is occasionally found even in wilms tumor , the diagnosis of renal aml is generally straight forward when correlated with other clinical features .
had described three cases of pediatric renal aml ( age range 1115 years ) that posed a diagnostic challenge . in all 3 cases ,
the misdiagnosis was attributed to the large size of the tumor with poor fat content , in an age group where renal aml is usually not common .
renal aml is the only benign renal tumor that can be categorically diagnosed by radiological studies alone . despite this , the imaging in our case did not indicate towards aml because of low - fat content .
lipopenic aml comprises only about 5% of all amls , and in this situation , the diagnosis can be difficult to clinch with radiology alone .
although 75%80% of the patients present before 5 years of age , the age range is quite wide , and cases have been reported even in adolescence and adults .
in fact , in the society of pediatric oncology ( siop ) 93 - 01 study , thirty patients out of 962 patients enrolled with wilms tumor were older than 16 years
. in the siop study , wilms tumor in children between 6 months to 16 years were diagnosed by means of radiological studies alone . with this background ,
the diagnosis of wilms tumor was initially considered in our patient . because the size of the mass had decreased on chemotherapy further made us to believe that this mass was in fact a wilms tumor .
typical cytological features described in conventional aml are admixture of adipocytes , smooth muscle cells , endothelial cells , foam cells , and giant histiocytes with a backdrop of inflammatory cells .
a fnac or needle biopsy before initiating chemotherapy probably would have been helpful in diagnosing it early .
tuberous sclerosis complex has been characterized by vogt 's triad , comprising mental retardation , adenoma sebaceum , and seizures .
renal amls in the setting of tuberous sclerosis may reach giant proportions although there is no consensus on when to term an aml as  giant . 
the largest reported case of bilateral renal aml measured 30 cm  21 cm  13 cm and 30 cm  18 cm  10 cm with a total tumor burden of 7843 g that resulted in respiratory failure .
our patient was later evaluated for any markers for phakomatosis but none were found . after reviewing the literature , it is our belief that our case has by far the largest pediatric sporadic aml reported in literature .
the largest sporadic renal aml reported till date weighed 7500 g in a 49-year - old lady .
management is conservative if the size of the lesion is < 4 cm but larger lesions need to be surgically removed .
nephron - sparing surgeries are advocated , especially in tuberous sclerosis patients in whom bilateral affliction may occur . in our case , the absence of a pre - operative diagnosis precluded a nephron - sparing approach although in the hindsight , renal preservation would have been a difficult technical proposition considering the size and extent of involvement of the kidney . to conclude , a rare case of giant sporadic pediatric renal aml has been reported that was mistaken for a wilms tumor .
this case highlights the importance of obtaining a tissue diagnosis before initiating chemotherapy , especially when the age of the patient is not in the standard age bracket for wilms tumor .
 renal angiomyolipoma ( aml ) is not commonly seen in the pediatric age group other than patients of tuberous sclerosis where in they can have renal amls within the first decade with bilateral in involvement . 
 diagnosis of renal aml can generally be made by the current radiological modalities in the appropriate clinical setting , but it can be mistaken for other tumors when it is large and has low - fat content . 
 herein we report a case of giant renal aml that was initially misdiagnosed as a wilms tumor in a 12-year - old girl . 