renal angiomyolipoma ( aml ) is an infrequent tumor that , in most cases , follows a benign course and has clearly defined radiological and histological characteristics .
we present a case of giant renal aml , which is the heaviest ever reported , encountered in a tertiary care hospital in india .
a 49-year - old lady , a native of afghanistan , presented with a 3-year history of steadily increasing abdominal girth and bloating sensation in the abdomen .
she underwent investigation in another institute and was found to have a huge abdominal mass .
review of contrast enhanced computed tomography ( cect ) scans of abdomen revealed a large fat containing tumor measuring 40 cm  24 cm  10 cm ( < 20 hounsfield units ) , replacing the left kidney and displacing the rest of the abdominal contents toward the other side of the midline [ figure 1 ] .
there was absence of enhancement , inhomogeneity , necrosis , or calcification ruling out the possibility of malignancy .
a provisional diagnosis of benign renal neoplasm , possibly aml causing pressure effects was made .
hence , cect scan of the head was done , which excluded any lesion suggestive of tuberous sclerosis ( ts ) [ figure 2 ] and decision of to perform nephrectomy was taken .
49-year - old lady with complaints of bloating sensation in the abdomen and a steadily increasing abdominal girth , which was subsequently diagnosed as angiomyolipoma of left kidney .
contrast enhanced computed tomography scan axial section film of abdomen reveals a lipomatous neoplasm 40 cm  24 cm  10 cm in dimension ( hu
< 20 hu ) replacing the entire left kidney , while displacing the rest of the abdominal contents ( arrows ) toward the other side of the midline .
49-year - old lady with complaints of bloating sensation in the abdomen and a steadily increasing abdominal girth , which was subsequently diagnosed as angiomyolipoma of left kidney .
contrast enhanced computed tomography scan axial section films of the head reveals no lesion suggestive of tuberous sclerosis .
under intubated general anaesthesia , an abdominal midline incision was made extending from xiphisternum to just above pubic symphysis .
simple nephrectomy was performed with intact tumor retrieval and minimal blood loss , without necessitating any blood transfusion .
the recovered surgical specimen measured 39 cm  25 cm  9 cm and weighed 7500 g with compressed renal hilar vessels and ureter [ figure 3 ] .
grossly , it was well- circumscribed and with a glistening yellow (  fatty  ) appearance .
histopathological examination of the specimen revealed majority of the cells were mature adipocytes associated with thick - walled blood vessels and a few epithelioid stromal cells .
there was a pattern with typical fat and perivascular epithelioid cells arranged around a blood vessel , suggesting it to be aml [ figure 4 ] .
immuno - histochemical staining of the tissue by beta - hydroxy beta - methylbutyric acid-45 ( hmb-45 ) ( a melanosome - associated protein ) indicated the presence of epithelioid component [ figure 5 ] .
49-year - old lady with complaints of bloating sensation in the abdomen and a steadily increasing abdominal girth which was subsequently diagnosed as angiomyolipoma ( aml ) of left kidney .
excised specimen shows a giant aml 39 cm  25 cm  9 cm in dimension and weighing 7500 g , replacing the whole kidney .
renal hilar vessels and ureter are compressed , and emerging out of the mass . 49-year - old lady with complaints of bloating sensation in the abdomen and a steadily increasing abdominal girth , which was subsequently diagnosed as angiomyolipoma of left kidney .
histopathology slide of the excised mass shows admixture of tortuous thick - walled blood vessels ( arrows ) , sheets of mature adipose tissue ( f ) and bundles of smooth muscle fibres ( m ) ( stain used hematoxylin and eosin , 100 ) .
49-year - old lady with complaints of bloating sensation in the abdomen and a steadily increasing abdominal girth , which was subsequently diagnosed as angiomyolipoma of left kidney .
photomicrograph ( x40 ) of immunohistochemical stained specimen shows mature adipocytes ( arrow heads ) and strong staining of the epithelioid cells with the beta - hydroxy beta - methylbutyric acid-45 ( arrows ) .
the patient recovery was uneventful and she was discharged from the hospital on the 5 post - operative day . at 6 months post - operative follow - up
aml is a benign hamartous lesion consisting of varying amounts of mature adipose tissue , smooth muscle , and thick - walled vessels .
renal aml are benign tumors known to occur sporadically and in association with genetic syndromes like ts and lymphangioleiomyomatosis . however ,
in our patient there were no clinical or radiological signs suggestive of any systemic syndrome . according to vitaly et al .
, an estimated 20 - 30% of amls are found in patients with ts syndrome , which is an autosomal dominant disorder characterized by mental retardation , epilepsy , and adenoma sebaceum .
mean age at presentation is 30 years , and there is a 2:1 female - to - male predominance .
however , 70 - 80% of patients with aml who do not have ts , there is a more pronounced female predominance and most patients present later in life , during the fifth or sixth decade , as was in the present case .
although , renal aml in patients with ts can be associated with significant morbidity , mostly related to complications from bleeding , sporadic cases do occur mostly as incidental lesions .
the detection of sporadic cases has increased due to greater use of abdominal imaging for the evaluation of a wide variety of non - specific complaints .
occasionally , the increase in abdominal swelling or epigastric fullness may be the presenting feature , as in our case .
aml is the only benign renal tumor that is confidently diagnosed on cross - sectional imaging .
the presence of fat ( confirmed on non - enhanced thin - cut computed tomography by a value of 20 [ hu ] or less ) seen within a renal lesion on imaging is considered the diagnostic hallmark .
findings of more than 20 pixels with attenuation less than 20 hu and of more than 5 pixels with attenuation less than 30 hu have been shown to have a positive predictive value of 100% .
histopathologically , aml consists of mature adipocytes , thick - walled blood vessels , and epithelioid stromal cells in various proportions .
usually it displays as a pattern of typical fat and perivascular epithelioid cells arranged around a blood vessel .
positive immunoreactivity for hmb-45 , a monoclonal antibody raised against a melanoma - associated antigen , is characteristic for aml and can be used to differentiate this tumor from sarcoma and other tumors .
the indication for surgical treatment is usually a symptomatic aml or an incidental aml of size larger than 4 cm . in cases of bilateral lesions , as in ts ,
nephron - sparing surgery ( by either selective embolization or open or laparoscopic / robotic partial nephrectomy ) must be performed . in our case ,
the tumor was so large that there was no option but to excise the whole lesion in totality .
on review of cases in the literature , we find our case represents the heaviest aml ( 7500 g ) ever reported , both in ts and sporadic categories .
this giant lesion surpasses the aml mass weighing 6300 g in a case associated with ts reported by rossell barbar et al . , and the lesion ( weighing 3500 g each ) in the cases reported by tsutsumi et al . , and katz and poster .
the only other aml , which has dimensions larger than the present one ( 39 cm  25 cm  9 cm ) has been reported by katz and poster , where the mass measured 45 cm  20 cm  15 cm and weighed 3500 g ( weight less than 7500 g measured in the present case ) , and was associated with ts . thus the present case is the largest sporadic renal aml in size and heaviest renal aml in both syndromic and sporadic categories ever reported in the literature .
aml can be identified when on ct image more than 20 pixels show attenuation less than 20 hu and if more than 5 pixels show attenuation less than 30 hu .
histologically , aml lesions show a pattern of typical fat and perivascular epithelioid cells arranged around a blood vessel .
positive immuno - histochemical staining by hmb-45 ( a melanosome - associated protein ) for epithelioid component confirms the lesion as aml .
we present a case where the patient presented with a huge abdominal mass in the left kidney diagnosed as aml and was managed by left nephrectomy .
the giant tumor is the heaviest aml ever reported in the literature . at 6 months post - operative follow - up
 we present the imaging and histopathological characteristics of a giant renal angiomyolipoma ( aml ) in a 49-year - old female patient , who presented with bloating sensation in the abdomen and a steadily increasing abdominal girth for about 3 years . 
 contrast enhanced computed tomography ( cect ) scan films of abdomen revealed that a large fat containing tumor had replaced the left kidney while displacing the rest of the abdominal contents toward the other side of the midline . 
 intraoperatively the left kidney was completely replaced by a fat containing tumor . 
 the recovered surgical specimen measured 39 cm  25 cm  9 cm and weighed 7500 g. histopathological investigation with immuno - histochemical staining of the specimen with hydroxy beta - methylbutyric acid-45 confirmed this lesion as aml . 
 cect scan of the head did not show any lesion suggestive of tuberous sclerosis . 
 the giant tumor of the present case is the heaviest aml in both syndromic and sporadic categories and largest by dimensions as sporadic aml ever reported in the literature . 