|Year : 2013 | Volume
| Issue : 1 | Page : 75-77
Lipoma-like variant of hibernoma in anterior abdominal wall: A rare occurrence
Meena Patil, Manjiri Karandikar
Department of Pathology, B. V. D. U. Medical College, Pune, Maharashtra, India
|Date of Web Publication||17-Aug-2013|
Department of Pathology, Flat No. 8, Surya Apt., Kohinoor Colony, Sahakarnagar No. 2, Pune - 411 009
Source of Support: None, Conflict of Interest: None
Hibernoma is an uncommon benign tumor arising from the remnants of the fetal brown fat. We report a case of a 55 year old male with history of swelling over anterior abdominal wall on right side. Till 2009, 170 cases have been reported. As abdominal wall is rare site of its occurrence, we report this case.
Keywords: Anterior abdominal wall, Benign, Brown fat, Fetal, Hibernoma
|How to cite this article:|
Patil M, Karandikar M. Lipoma-like variant of hibernoma in anterior abdominal wall: A rare occurrence. J Med Soc 2013;27:75-7
| Introduction|| |
The term hibernoma was first used by Gery in 1914, since the histology looked like brown fat of hibernating animals. Brown fat in humans occurs in only a few anatomic areas. In infants it is found in the interscapular area, the axilla, mediastinum, neck, post. abdominal wall, and about the kidneys, adrenals and pancreas. In adults brown fat persists in the neck, axilla, mediastinum and periadrenal and perirenal areas. Hibernoma is a rare benign neoplasm which occur chiefly in adults. The peak incidence of hibernoma is during the third decade of life; in contrast to other fatty tumors which usually occur within the 4 th to 7 th decades of life. It is slightly more predominant in males than in females. Malignancy in hibernoma has not been reported. 
| Case Report|| |
A 55-year male presented with a swelling over anterior abdominal wall on right side since one month. It was gradually increasing in size and was approximately 20 × 10 cm. There was a vague lumpy feel in the same area for the last 2-3 years.
On clinical examination, the skin over swelling was normal. There was no scar. Mass was soft, freely mobile and not fixed to underlying muscle. There was no history of trauma.
FNAC of the mass was done and was reported as lipoma.
Elective resection was done and the mass was excised from the right sided anterior abdominal wall in the region of iliac fossa and hypogastrium. A large, lobulated tumor mass measuring 18 × 12 × 5 cm. was resected. External as well as cut surfaces showed greyish brown appearance, with a few areas of golden yellow color [Figure 1].
Microscopically a capsulated tumor mass comprised of tumor cells was arranged in lobules. The cells are polygonal and had granular, eosinophilic cytoplasm with distinct cell membranes. The nuclei were centrally placed. Univacuolated lipocytes and multivacuolated lipoblasts were also seen intermixed with these cells [Figure 2] and [Figure 3].
|Figure 2: Hibernoma- Polygonal cells showing granular, eosinophilic cytoplasm with central nucleus and increased vascularity (H and E, ×100)|
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|Figure 3: Hibernoma- Polygonal cells showing granular, eosinophilic cytoplasm with central nucleus and few vacuolated cells (H and E, ×100)|
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The diagnosis of lipoma-like variant of hibernoma was offered on the basis of gross and microscopic features.
| Discussion|| |
In a human body, two types of fatty tissue are present - brown fat and white fat. The brown fat was described for the first time by Gales in 1670. This tissue participates in the regulation of the metabolism and in thermogenesis. It is more abundant in the animals that hibernate, but is also seen in animals that do not hibernate. In humans it diminishes after the eighth week of gestation.
It is mainly seen in newborns, infants and children, although small quantities persist in all ages. In the adults, it constitutes 1% of the corporal mass. These remains are usually located in the interscapular, inguinal and axillary regions. 
Hibernomas are rare benign soft tissue tumors derived from brown fat, while tumors arising from white adipose tissue as lipoma are among the most common soft tissue lesions. Hibernomas are slow growing, painless, soft, mobile neoplasms, which recur if incompletely resected. They are among the rarest, with only 170 cases reported till 2009 (AFIP series). This tumor was first described by Merkel in 1906. The term hibernoma was proposed in 1914 by Grey because of its morphologic similarity to the cells of the so-called hibernating animals. 
Microscopically, Furlong and colleagues described four morphologic variants of hibernoma:
In their review of 170 cases of hibernoma the authors found about 7% cases of lipoma-like variant of hibernoma, while spindle cell variant was therarest. ,
- Lobular type: The most common (typical) displays a distinct lobular pattern and is composed of cells that show varying degrees of differentiation ranging from uniform, round to ovoid, granular, eosinophilic cells with a distinct cellular membrane to multivacuolated cells with multiple small, oil-red-O positive lipid droplets and centrally placed nuclei
- Myxoid variant: Loose, basophilic matrix with thick fibrous septa and foamy histiocytes
- Lipoma-like variant: Composed predominantly of univacuolated lipocytes with only occasional cells showing hibernomatous features
- Spindle cell variant: Very rarely, the cells take on a spindle cell morphology. Common at neck and scalp. ,
For all subtypes, the vascular supply is considerably more prominent in hibernomas than in lipomas. In fact, the distinct brown color of hibernoma is due to the prominent vascularity and abundant mitochondria in the cytoplasm of the cells. 
These lesions usually stain strongly for S-100 protein. Rarely, the cells stain for CD-34, although this seems limited to the spindle cell variant. 
Hibernomas share a characteristic cytogenic aberration with other benign lipomatous tumors., Structural rearrangements of 11q13-21 are most common. Recent studies implicate involvement of the GARP gene on 11q13.5. 
The following entities should be considered when confirming the diagnosis of hibernoma. The points to differentiate them from hibernoma are given below:
- Adult rhabdomyoma: These are composed of similar eosinophilic cells, but its cells are larger and contain considerable amounts of glycogen and on careful search, crystals and cross-striations are also found. 
- Granular cell tumor: Superficial resemblance to hibernoma, but distinguished by the complete absence of the intracellular Oil red O- positive lipid vacuoles. Both are S-100 protein positive. 
- Atypical lipomatous tumor: Well-differentiated liposarcoma: Rarely superficial. Cells with atypical nuclei. Prominent 'chicken wire' vascular pattern. Hyperchromatic stromal cells, bizzare, multinucleated cells helps us in differentiating from ahibernoma. 
| Conclusion|| |
Hibernoma is a rare benign tumor. Lipoma-like variant of hibernoma is one of the rare types and is likely to be missed. Careful examination of gross specimen of an adipose tissue tumor and making a special effort to look for the cells of brown fat may result in the rise in number of cases. Presence of hibernoma in the anterior abdominal wall has not been reported to the best of our knowledge. Whereas majority of cases of hibernoma get detected in 3 rd to 4 th decade of life, our patient was in the 6 th decade of life. The site of occurrence, patient's age at presentation and the uncommon subtype of hibernoma prompted us to publish this case.
| References|| |
|1.||Mustafa KO, Metin KA. Hibernoma: A Case Report and Discussion of a Rare Tumor. Turk J Med Sci 2001;25:175-6. |
|2.||Carvajal J, Fernandez P, Albeniz L, González ML, Orellana JG, Cerquella CM. Axillary Hibernoma: An unusual benign soft-tissue tumor. Internet J of Surg 2009:22,1 ISSN: 1528-8242. |
|3.||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. |
|4.||Enzinger FM. Weiss SW. Soft tissue tumours. 5 th ed. Mosby Elsevier: Philadelphia, USA; 2008. p. 466-70. |
|5.||Reis-Filho JS, Cruz J, de Valbueva CR, Schmitt FC. Lipoma-like hibernoma: An atypical lipoma/well-differentiated liposarcoma mimicker. J Bras Patol Med-Lab 2002;38:4. |
[Figure 1], [Figure 2], [Figure 3]