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  Table of Contents    
CASE REPORT  
Year : 2019  |  Volume : 62  |  Issue : 3  |  Page : 461-463
Hibernoma: A missed diagnosis!!


Department of Laboratory Medicine and Radiodiagnosis, Command Hospital (Air Force), Bangalore, Karnataka, India

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Date of Web Publication26-Jul-2019
 

   Abstract 


Hibernoma is a rare, benign soft tissue tumor described in <200 case reports/case series. It is slow-growing, painless, and commonly mistaken for lipoma or liposarcoma. Histopathological diagnosis is must for confirmation. Total excision is the treatment of choice. We present a rare case of hibernoma of thigh, which was initially misdiagnosed as atypical lipomatous tumor/well-differentiated liposarcoma on imaging, which turned out to be a hibernoma on histopathological examination.

Keywords: Brown fat, hibernoma, lipomatous tumour

How to cite this article:
Patil SD, Sheik AR, Tewari V, Mutreja D. Hibernoma: A missed diagnosis!!. Indian J Pathol Microbiol 2019;62:461-3

How to cite this URL:
Patil SD, Sheik AR, Tewari V, Mutreja D. Hibernoma: A missed diagnosis!!. Indian J Pathol Microbiol [serial online] 2019 [cited 2019 Aug 21];62:461-3. Available from: http://www.ijpmonline.org/text.asp?2019/62/3/461/263489





   Introduction Top


Hibernoma is a rare, benign soft tissue tumor originating from brown fat.[1] It is a slow-growing, painless tumor that accounts for 1.6% of benign lipomatous tumors and 1.1% of all adipocytic tumors.[2] Grey coined the term “hibernoma” because of its resemblance to brown fat of hibernating animals.[3],[4] Furlong et al. have reported 170 cases of hibernoma in an Armed Forces Institute of Pathology study.[5] This article describes a rare case of hibernoma thigh.


   Case History Top


A 39-year-old lady presented with complaints of a slowly growing painless swelling on anterior aspect of right thigh. There was no history of trauma or similar swelling elsewhere. The patient does not have any comorbidities or any other significant past history. Physical examination revealed a solitary, round, soft, nontender mass, located on anterior aspect of thigh. Laboratory examination was normal. (Hb 13.2 g/dl, total leukocyte count 10,700/mm3, DLC-N60L35E03M02, fasting blood sugar level of 89 mg/dl, serum creatinine of 0.9 mg/dl). Ultrasonography (USG) revealed a well-circumscribed hyperechoic lesion in the anterior compartment of thigh. Magnetic resonance imaging (MRI) of thigh [Figure 1] revealed a well-circumscribed oval lesion within the vastus intermedius muscle of thigh. It showed fat signal on noncontrast images and heterogenous postcontrast enhancement. There were no areas of hemorrhage or necrosis or prominent vascular channels within this lesion. No infiltration into the surrounding muscle, bone, or vascular structures seen. On the basis of MRI findings, a diagnosis of atypical lipomatous tumor/well-differentiated liposarcoma (WDLPS) was made. Further patient underwent incisional biopsy. Histopathology from the studied sections revealed encapsulated, lobulated, soft and greasy mass with yellowish to patchy red-brown cut surface. Microscopy [Figure 2] revealed hibernoma cells as large multivacuolated fat cells with eccentric nucleus and abundant granular to vacuolated cytoplasm. The patient underwent complete resection of the tumor and remained symptom free during 2-year follow-up with no signs of recurrence.
Figure 1: T2 coronal, T1 axial, T1 fat saturated pre- and postcontrast MRI of thigh showing a heterogeneously enhancing hyperintense oval lesion in vastus medialis muscle

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Figure 2: Hematoxylin and eosin stained sections of tumor (10×, 40× views): hibernoma cells – large cell with eccentric nuclei and abundant granular cytoplasm

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   Discussion Top


Hibernoma is a rare adipocytic tumor and forms approximately 1.1% of all adipocytic tumors.[2] Its occurrence in third to fourth decade of life contrasts with other fatty tissue tumors such as liposarcomas that occur in fourth to seventh decade.[2],[3],[4] Literature review reveals a slight female preponderance.[3],[4],[6] Hibernoma originates from brown fat. Brown fat forms 5% of body weight in fetus and neonates. Progressively, it decreases over a period of time and in adults it persists in neck, mediastinum, axilla, periadrenal, and perirenal areas.[2],[4] The most common reported sites of hibernoma are interscapular region, axilla, neck, thigh, mediastinum, and retroperitoneum.[1],[2],[4] The other rarely reported sites are scalp, buttock, popliteal fossa, scrotum, intracranial, intraspinal, and periureteric.[2],[4],[7] Atypical lipomatous tumors are commonly seen in extremities, whereas WDLPSs are seen in retroperitoneum and mediastinum. Hibernomas are usually asymptomatic and present as slow-growing painless mass. Large tumors may be symptomatic due to pressure effect on adjacent organs. Majority of the hibernomas are subcutaneous and only 10% are intramuscular.[2] They do not have malignant potential. They are usually mistaken for other fat containing tumors on clinical examination and imaging.

Initial imaging workup includes USG followed by computed tomography (CT) or MRI, 18-F-fluorodeoxyglucose position emission tomography (18F-FDG-PET), and angiography. USG shows a well-circumscribed hyperechoic mass. Doppler imaging may show hypervascularity within the tumor. CT scan shows a lobulated well-defined fat-attenuating mass with multiple septations and variable enhancement.[2] MRI shows an encapsulated, well-defined fat-containing mass. Presence of T1 hyperintense signal which is slightly less than the subcutaneous fat and incomplete fat suppression on fat saturated sequences may be a useful clue. They show diffuse postcontrast enhancement as compared to lipomas which do not show any enhancement.[2] Presence of thickened (>2 mm) irregular septa and nonfatty elements within the tumor can help to differentiate WDLPS from lipomas and hibernomas. 18F-FDG-PET helps to differentiate hibernoma from liposarcoma, as hibernomas have increased uptake.[2] Angiography may help in differentiating hypervascular hibernoma from hypovascular tumors such as lipoma.[4] Thus imaging cannot reliably diagnose hibernoma, and histopathological confirmation is essential as was in our case.

Macroscopically, hibernomas are well-circumscribed, encapsulated, lobulated soft greasy mass of usually 5–10 cm size. Cut surface reveals yellow to red brown appearance with rare areas of hemorrhage. Microscopic sections reveal encapsulated tumor comprising large multivacuolated cells and univacuolated cells. Multivacuolated cells have eccentric vesicular nucleus and characteristically fine granular, vacuolated cytoplasm. Abundant capillaries with lack of mitosis or atypia is a usual feature. Presence of atypia and lipoblasts helps to differentiate liposarcoma from lipoma and hibernoma. These adipocytic tumors can be reliably diagnosed with the help of molecular markers such as MDM-2, CDK-4, and p-16[8] [Table 1].
Table 1: Markers to differentiate lipomatous tumor

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Hibernoma is a rare benign brown fat tumor, which is usually misdiagnosed clinically and radiologically as lipoma or liposarcoma. Thus, hibernoma should always be considered as a differential for these lesions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Ulmar B, Trubrich A, Kappe T, Kocak T, Schulz C, Reichel H, et al. Large hibernoma of the proximal upper arm and the axilla-Literature review and case description of a very rare benign soft tissue tumor. Z Orthop Unfall 2016;154:591-4.  Back to cited text no. 1
    
2.
Mavrogenis AF, Coll-Mesa L. Soft tissue: Hibernomas. Atlas Genet Cytogenet Oncol Haematol 2013;17:60-74.  Back to cited text no. 2
    
3.
Kosem M, Karakok M. Hibernoma: A case report and discussion of a rare tumor. Turk J Med Sci 2001;25:175-6.  Back to cited text no. 3
    
4.
Saito M, Tsuji Y, Murata H, Kanemitsu K, Makinodan A, Ikeda T. Hibernoma of the right back. Orthopedics 2007;30:495-6.  Back to cited text no. 4
    
5.
Furlong MA, Fanburg-Smith JC, Miettinen M. The Morphologic spectrum of hibernoma: A clinicopathologic study of 170 cases. Am J Surg Pathol 2001;25:809-14.  Back to cited text no. 5
    
6.
Rigor VU, Goldstone SE, Jones J, Bernstein R, Gold MS, Weiner S. Hibernoma a case report and discussion of a rare tumor. Cancer 1986;57:2207-11.  Back to cited text no. 6
    
7.
Murphey MD, Carroll JF, Flemming DJ, Pope TL, Gannon FH, Kransdorf MJ. From the archives of the AFIP: Benign musculoskeletal lipomatous lesions. Radiographics 2004;24:1433-66.  Back to cited text no. 7
    
8.
Rouse RV. Atypical lipomatous tumour. [Internet]. Stanford medicine surgical pathology criteria 2013. Available from: http://surgpathcriteria.stanford.edu/softfat/atypical_lipomatous_tumor/differentialdiagnosis. [Last accessed on 2019 Jan 21] html  Back to cited text no. 8
    

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Correspondence Address:
Abdul R Sheik
Department of Radiology, CHAF, Bangalore, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/IJPM.IJPM_577_18

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