hibernoma is a very rare fatty tumor that originates from remaining brown fat after one 's fetal stage .
fetal brown tissue is known to be found from pelvic limb , scapular region , axilla , collum , abdominal etc . , and observed from a mass , gradually increasing in size .
so far , there was hardly a case of a malignant tumor , and it is established as a ground rule to treat such conditions by a total resection of affected parts .
the following study reports about hibernoma that developed from a patient with a history of neurilemmoma and discussion of literature .
a 49-year - old man presented with a mass on his back which had been growing for several months . a year ago , he had his previous visit with symptoms of a stiff shoulder on his right scapular region that had last for a few months . at that time
, he underwent chest x - ray and thoracic mri and discovered a paraspinal mass on the right side of third thoracic vertebra .
1 ) after being diagnosed as neurilemmoma from a biopsy , and was observed for external proceedings without any abnormal findings . when neurilemmoma was first discovered , there was a mass found from the right back , yet the size was small and mri showed no hints of invasive remark .
the patient visited our hospital for further workup after the size of the mass increased gradually .
clinically , the oval - shaped mass on the patient 's back was visible to the naked eye .
the size was approximately 1273 cm , and there were no other abnormal findings such as change of color , ecchymosis , fossula formation etc . during a physical exam , there was local heat sense found around the mass , but there were no tenderness , or any neurologic abnormal findings such as motor paralysis or hypoesthesia . for a detailed examination of the mass ,
a thoracic mri was performed . from the result , a mass with an approximate size of 1273 cm was found within the right paraspinal muscle , with a clear margin .
it was lobulated , and appeared to be stronglyheterogenous from both t1 , t2 myelogram . in the operating room
after the incision , the vertical center from the sixth cervical vertebra to the fourth thoracic vertebra was desquamated to the subcutaneous tissues by skin incision .
the mass was yellowish brown , located at the intersection where the connection part of cervical vertebrae and thoracic vertebrae , and surrounded by numerous blood vessels .
being careful not to injure any neurovascular structures around the mass , a resection of the entire mass was performed , followed by scrupulous hemostasis .
the mass was 13.66.02.2 cm in size , and appeared to be encapsulated with irregular borders of yellow and brown colors.there were no hemorrhage or necrosis , and the cross - section of the mass was observed to be multi - lobulated ( fig .
histologically , it was a typical hibernoma , where polygonal and multivacuolated adipose cells , along with abundant granular cytoplasm , were divided into minute reticulin fiber septum and arranged into a form of lobules ( fig .
4 ) thoracic tomography performed after the operation showed only a small amount of undercurrent body fluid , without other specific findings such as tumor remnants .
the operated area did not have peculiar symptoms or infection , and the patient is now outpatient observation after discharge without particular complications .
the following hibernoma was accompanied by the history of neurilemmoma , and since several studies in the past reported related chromosome abnormality to these two types of tumor , additional chromosome test was carried out for checkup ; the result appeared to be normal without any abnormal findings .
hibernoma is a benign tumor that originates from remnants of brown fat tissue . because its cells resembled the cells of hibernating animals , gery first used the term " hibernoma " in 1914 .
from then , hibernoma has been a rare type of tumor , reported by only around 160 cases globally , and 10 cases nationally2,4 ) .
it commonly develops in one 's adolescence or twenties , and slightly appears more in women than in men1 ) . due to the vascular activity of the mass , the skin that covers
when diagnosing hibernoma , mri , angiography , and needle biopsy play an important role : it shows lower signal than subcutaneous fat at t1 weighted mri , increased heterogenous signal in t2 weighted mri , noticeably increased build - up from gadolinium imaging1 ) , and a distinguished image from a typical fat mass on fat suppression imaging because of its uncontrolled fat .
mri can be helpful in checking the size of the mass , vessel conditions , or any permeated parts in terms of radiation beforethe operation .
however , it is hard to actually diagnose through radiation results alone , because other tumors including fibroma , neural fibroma , polymorphic lipoma , and positive lipoblastoma display the same findings as hibernoma . at lipoma and hibernoma 's mri
, lipoma shows equivalent signal strength while hibernoma 's signal is presented with dysplasia on the inner parts due to its vascular fiber structure .
hibernoma is not composed of one particular structure , but a mixture of traditional lipoma and hibernoma component , two complex tumors are integrated as one .
if the composition of brown fat is higher than the other , it displays lower signal in t1 image and higher signal in t2 image1,8 ) .
because hibernoma shows strengthened vessel structure due to the copious blood distribution , it can be easily distinguished from the mass that has low blood vessel distribution , including simple lipoma , fibroma , neural fibroma and etc , yet it still requires a specialized method to distinguished it from liposarcoma . knowing the vessel distributionaround the surrounding area can be helpful before planning resection7 ) .
although definite diagnosis before the operation is possible via needle biopsy in most cases , it is recommended to avoid needle biopsy if there are too many vessels formed around the mass , which may result in excessive bleeding9 ) . in this case , the mass was a painless tumor according to the physical exam , only with a slight heat sensation around the mass area .
mri findings showed clear difference from a simple lipoma , which has similar signal strength to subcutaneous fat tissue , and seen from heterogenous aspects and high vessel distribution , the tumor had to be distinguished from low grade liposarcoma and angiolipoma8 ) .
there was a case of malignant hibernoma in the past , but in most of cases , it can be treated sufficiently by resection alone , with few sequelae . however , in terms of abundant vessel distribution of hibernoma , sometimes it can be hard to remove the tumor entirely .
hematoma may result after operation , and resection alone can not totally eliminate the possibility of malignancy in terms of histology .
therefore , performing a total resection reduces the chance of the recurrence of tumor remnants . after the operation , extra procedure is required to prevent hemostasis .
if there is a nutrition vessel found , embolization of the vessel is required to minimize the bleeding that may occur during the actual operation4,5,6 ) . in 1994 , fredrik et al . presented seven case reports in total , including three previous case reports , about chromosome abnormalities occurring in hibernoma patients3 ) .
thus , it is generally thought that hibernoma patients have a structural abnormalityof chromosome 11 's long arm , including 11q13 .
also , numerous neurilemmoma are discovered in type 2 neurofibromatosis , caused by a problematic sex chromosome . for the following patient in this case
actual chromosome test results proved that this patient had a normal karyotype without unusual number of chromosomes or structural disorder .
this case report presents a case of hibernoma that occurred in a patient who previously had an operation for neurilemmoma .
it was a rare case of two tumors presenting at the same time , which is hard to find in previous literature .
after diagnosis , thepatient was treated with total resection of each tumor , and upon observation showed no post - op complications or sequelae .
one should keep in mind that if hibernoma is identified via imaging tests and biopsy in future cases , the tumor can be fully treated by total resection , and that excessive bleeding may occur due to surrounding blood vessels formed anew . such knowledge and guidelines will benefit in additional chromosome examination of a hibernoma patient , and diagnosis and additional data collection .
 hibernoma is a very rare , benign soft fatty tumor that derived from remnants of fetal brown tissue . 
 the following case of hibernoma break out occurred from a patient who had received surgical resection of neurilemmoma . 
 there has never been a case that reported about hibernoma accompanied by neurilemmoma . 
 it is anticipated that this experience would be helpful to other physicians who are interested in this rare type of tumor . 
INTRODUCTION
CASE REPORT
DISCUSSION
CONCLUSION