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 .