hibernoma is a rare , benign , slow - growing tumor of brown fat origin the majority occurring in the extremities and the neck .
the presacral location is rare , although a few cases in the retroperitoneum have been described in the literature.[25 ] we describe a case of presacral hibernoma with radiologic - pathologic correlation .
the imaging findings are nonspecific but , given the rarity of this tumor , when there is a large well - defined heterogeneous retroperitoneal mass with dilated intratumoral vessels , the possibility of a hibernoma should be considered in the appropriate clinical setting .
a 36-year - old female presented with abdominal distention and dull , vague , left lower quadrant pain since 2 years .
a large solid pelvic mass was found and pelvic ultrasound was requested . on ultrasound , there was an ill - defined large heterogenous mass with increased vascularity seen posterior and superior to the uterus , with poor demarcation from the uterus and the left ovary .
the patient being unwilling for mri , ct scan of the pelvis was performed for further evaluation .
ct scan revealed a large presacral , heterogeneous , hypervascular mass , measuring approximately 10.6  10.0  5.8 cm and causing compression and displacement of the rectum anteriorly [ figure 1a  c ] .
this mass had multiple tortuous arterial and venous channels , with the dominant arterial supply being from branches of the inferior mesenteric artery ( i m a ) .
on microscopy , there were numerous multivacuolated adipose cells with eosinophilic cytoplasm and eccentric nuclei , consistent with hibernoma [ figure 3 ] .
noncontrast ( a ) and contrast - enhanced ( b ) axial ct scans through the pelvis demonstrate a large well - defined , heterogeneous , enhancing presacral mass ( arrows ) , with dilated tortuous vessels ( arrowheads ) .
sagittal reformatted contrast - enhanced image ( c ) demonstrates the mass pushing the rectum ( r ) and uterus ( ut ) anteriorly .
ub = urinary bladder prone , axial , plain ct scan through the pelvis , with the biopsy needle ( arrow ) in the presacral mass photomicroscopic image of the biopsy specimen shows numerous multivacuolated adipose cells , with eosinophilic cytoplasm and eccentric nuclei as the mass was hypervascular , preoperative embolization of this mass was clinically requested . on selective
i m a catheter angiogram , there were dilated vascular branches feeding this mass , with an early tumor blush , but no arteriovenous communication was seen [ figure 4a ] .
selective catheter angiogram of the inferior mesenteric artery ( i m a ) , ( a ) shows a feeding vessel ( arrow ) and early tumor blush ( arrowhead ) .
selective i m a angiogram , ( b ) after particle embolization of the feeding branch of the i m a shows the embolized feeding branch ( arrow ) with near complete loss of tumor blush ( arrowhead ) on gross examination , the mass was lobulated and well encapsulated , measuring 13.1  12.6  4.2 cm .
the cut surface was brownish yellow in color , with multiple coursing vessels and without any areas of hemorrhage or necrosis [ figure 5 ] . cut surface of the gross specimen shows the brownish - yellow color of the mass , with multiple vessels but without any areas of hemorrhage or necrosis
hibernoma is a rare , benign , slow - growing tumor of brown fat origin .
the tumor is named hibernoma due to its similarity to brown fat , which has a thermogenic role in hibernating animals .
the tumor was first termed as pseudolipoma by merkel in 1906 and subsequently renamed hibernoma by gery in 1914 .
the imaging features of this rare tumor have been mostly described for lesions occurring the extremities and neck region , with only six cases of retroperitoneal hibernoma described in the english literature.[125 ] to the best of our knowledge , this is the first case report of a presacral hibernoma , describing cross - sectional ct imaging and conventional catheter angiographic feature of this tumor with preoperative vascular embolization .
hibernoma is seen in the 20- to 50-year age - group , with a female preponderance .
however , a large series by the armed forces institute of pathology ( afip ) did show a slight male preponderance .
the intra - abdominal hibernoma , by itself , does not produce symptoms and as a result the tumor is often large at initial presentation , the large size of the tumor causing abdominal discomfort and mass effect on adjacent structures .
the usg findings of intra - abdominal hibernoma have not been described , but subcutaneous and intramuscular hibernomas are seen as well - defined heterogenous masses with variable echogenicity ; some may appear as hypoechoic masses , with increased vascularity on color doppler flow .
on ct scan , the hibernoma is seen as a large heterogeneous , well - circumscribed mass , with attenuation ranging between fat and muscle .
the heterogeneity of the hibernoma is attributed to the presence of varying amount of fat , muscle , and vessels . in our case ,
the mass demonstrated soft - tissue attenuation , without any definite fat attenuation or necrosis .
following intravenous contrast administration , the hibernoma shows heterogeneous enhancement , with hypertrophic branching intratumoral vessels as was seen in our case .
retroperitoneal hibernoma causes displacement of the adjacent organs and structures but no infiltration . on mri
, hibernoma demonstrates high signal intensity on t1w and t2w images ; however , the intensity is less than that of subcutaneous fat and there is incomplete fat suppression on fat - saturated pulse sequences .
the differential diagnosis of a large well - defined heterogenous retroperitoneal and/or presacral mass containing large intratumoral vessels could include liposarcoma , angiolipoma , and hemangiopericytoma .
liposarcoma are heterogenous soft - tissue masses with areas of necrosis , hemorrhage , and/or calcification , but without large intratumoral vessels .
also , in contrast to the slow - growing well - defined hibernoma , the liposarcoma has a poor margin , with infiltration into adjoining structures .
a mature teratoma classically presents as a complex mass containing fat , calcification , rarely a fat - fluid level , without intralesional vascularity .
angiolipoma and hemangiopericytoma may have increased vascularity ; however , none of these lesions show both increased signal intensity on t1w and t2w images and large branching intratumoral vessels . on angiography , hibernoma demonstrates dilated feeding vessels , typical tumor blush , and early venous return , as was seen in our case . in the past , angiography was performed for evaluating presurgical vascular anatomy and also to differentiate hibernoma from hypovascular lesions like lipomas and fibromas .
these days , ct and mri have superseded the role of conventional angiography in the diagnosis of such lesions . given the nonspecific features on imaging , histological diagnosis
is usually required for appropriate planning before surgery . despite the increased vascularity of this tumor , image - guided core biopsy
microscopically , hibernoma is composed of multivacuolated adipocytes with granular eosinophilic cytoplasm and eccentric nuclei , univacuolated cells with peripheral nuclei , and abundant capillaries .
 hibernoma is a rare benign tumor of brown fat origin . 
 it is found in locations where brown adipose tissue is present in the fetus . 
 these locations include the neck , axilla , thorax , and extremities . 
 retroperitoneal hibernoma is an extremely rare site of presentation . 
 we present a rare case of presacral hibernoma . 
 preoperative embolization of this highly vascular tumor was performed . to the best of our knowledge , 
 this is the first reported case of a presacral hibernoma in the english literature . 
Introduction
Case Report
Discussion