Hibernomas are usually located in the interscapular region, but may also be encountered in the cervical, thigh or axillary areas. Intra thoracic, intramuscular, abdominal and retroperitoneal lesions have also been described, as well as exceptional locations such as the uterus, breast, popliteal area, cranium, pericardium [1] or mediastinum. Lesions may be multiple or bilateral, are painless, but may cause symptoms related to their mass effect [2] or to their secretory activity, as they are known to sometimes produce steroid hormones. They are usually described as slow growing (but fast growth is also possible) and firm or rubbery and are mostly encountered in adults in their thirties, and differential diagnosis with lipomas and liposarcomas must be taken into consideration, given that clinical presentations of the three pathological entities often overlap [3] [4]. Once the diagnosis of hibernoma is established, the physician does not need to be concerned about malignant transformation or metastasis [5]. However, recurrence is possible, although very rare.

• Stridor

  Otherwise patient have no stridor, no fever and able to perform his routine activities with limited movement of his left shoulder due to pain. [scireslit.com]

• Left Flank Pain

  A 51-year-old woman presenting with recurrent left flank pain was diagnosed with left kidney stone. Abdomen ultrasound and i.v. pyelografy showed pyelic stone of 2 cm without other pathologies of the urinary tract. [ncbi.nlm.nih.gov]

• Pelvic Mass

  On clinical examination, a large solid pelvic mass was found and pelvic ultrasound was requested. [ijri.org]

• Neck Mass

  We report a case of a patient with an asymptomatic neck mass that initially presented for evaluation of hoarseness. Imaging and complete surgical excision of the mass were performed and revealed hibernoma. [ncbi.nlm.nih.gov]

  The physical examination was unremarkable except for large swelling of the left side of the neck (Panel A), which caused limited mobility of the neck. The neck mass was firm, mobile, and nontender. [nejm.org]

  The most common sites of these tumors have been the back and thighs; head and neck involvement has been rare. We describe the case of a 54-year-old woman who presented with a 1-year history of a large, asymptomatic, lateral neck mass. [entjournal.com]

The first step in diagnosing a hibernoma after the clinical suspicion is raised is to perform imaging procedures. A radiography of the affected region will show no bone erosion or calcification. Echography describes hyperechoic tissue, while Doppler imaging highlights the presence of enlarged vessels. Computer tomography scanning describes well vascularized, well circumscribed, heterogeneous, diffusely septated lesions with a possibly incomplete peripheral capsule. Hibernoma signal intensity in magnetic resonance imaging is variable [6], usually high, but slightly inferior to that of subcutaneous tissue [5]. The degree of homogeneity is variable [7]. This method shows diffuse gadolinium enhancement of an otherwise isointense or mildly hypointense tissue formation. Myxoid hibernomas, being richer in water have higher signal intensity on magnetic resonance imaging scans [8]. Fluorodeoxyglucose positron emission tomography shows important radiotracer capture [9] due to the fact that hibernomas contain numerous mitochondria and are metabolically very active. Scintigraphy also reveals high radiotracer uptake with 99mTc-tetrofosmin, 123I-meta-iodobenzylguanidine and 99mTc-methoxyisobutylisonitrile administration. If an angiography is considered to be necessary, it may reveal, besides intense vascularization, the presence of internal arterio-venous shunting [10] which is important information prior to excision.

If clinical and imaging differential diagnosis cannot exclude a malignancy, excision is imperative. Analysis of the surgical specimen reveals a light brown to gray mass of tissue surrounded by a thin capsule [11]. Microscopic examination reveals high -number of mature, multivacuolated or uni vacuolar adipocytes intersecting with brown fat, intense vascularization, and few adipocyte atypia. Tumors may, however, be more or less well differentiated. Immunohistochemical analysis shows a positive cluster of differentiation (CD) 68 and negative CD 34.

In cases where cytogenic analysis reveals the presence of a 11q13 translocation, liposarcoma is improbable [12]. Rearrangements in the 11q13-21 region can be detected using metaphase fluorescent in situ hybridization.

• Soft Tissue Calcification

  It was well marginated and showed no soft tissue calcification or invasion of nearby structures. There was no enhancement with intravenous contrast. [healio.com]

The literature provides only a few treatment details regarding this variant. [ncbi.nlm.nih.gov]

(Review of lipoma and epidermal inclusion cysts including workup and treatment.) Bancroft, LW, Kransdorf, MJ, Peterson, JJ, O’Conner, MI. “Benign fatty tumors: classification, clinical course, imaging appearance, and treatment”. [clinicalpainadvisor.com]

This review discusses the clinical features, radiologic and histopathologic characteristics, ancillary studies, suggested pathogenesis, differential diagnosis, and treatment of and prognosis for these uncommon lesions. [ncbi.nlm.nih.gov]

[…] typically prominent; cytoplasm multivacuolated, oval, eosinophilic, granular LM DDx reaction to silicone implant Gross lobulated lesion, light-brown, usually extremities Site soft tissue - adipocytic lesions Clinical history young adults Prevalence uncommon Prognosis [librepathology.org]

There are multivacuolated cells and a cell with a central nucleus IMMUNOHISTOCHEMISTRY Positive • S100 • Oil red O • Sudan black Negative • CD 34 • P53 PROGNOSIS BIOLOGICAL BEHAVIOR • Hibernoma is benign and does not metastasize or convert to a malignancy [tumorsurgery.org]

He subsequently underwent dual time point FDG PET/CT imaging which revealed a significant rise in standard uptake value (SUV) within the lesion over time, favoring a malignant etiology. [ncbi.nlm.nih.gov]

Etiology The etiology involves clinically significant persistence of remnants of or accumulation of brown fat in regions where small amounts of brown fat normally persist as vestigial remnants. [clinicalpainadvisor.com]

Usually asymptomatic.[3] Epidemiology: Young adults. Gross Well-circumscribed. Lobulated and light-brown on sectioning. [librepathology.org]

Epidemiology[edit] The tumor is rare, affecting adults in the 4th decade most commonly. Patients are usually younger than those who present with a lipoma. There is a slight male predominance. [en.wikipedia.org]

Definition / general Lipoma containing prominent brown adipocytes that resembles normal brown fat as classic lipoma resembles white fat Epidemiology Rare (2% of lipomas) Mean age 26 - 38 years; 60% male Sites Most commonly in axilla, back, mediastinum [pathologyoutlines.com]

We describe the case of an intramuscular hibernoma and illustrate the pathophysiology of the observed hibernoma in relation to recent insights on physiological BAT. [ncbi.nlm.nih.gov]

Pathophysiology Pathophysiology involves cytogenic abnormalities of chromosomes 11q13-21 and 10q22, which can cause a deletion in the MEN-1 gene. Structural rearrangements involving the long arm of chromosome 11 are characteristic. [clinicalpainadvisor.com]

These tumors are by definition benign entities but, given their propensity for growth over time, they require complete extirpation to prevent recurrence. [ncbi.nlm.nih.gov]

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3. Lee J, Gupta A, Saifuddin A, et al. Hibernoma: MRI features in eight consecutive cases. Clin Radiol. 2006;61(12):1029–1034.
4. Dursun M, Agayev A, Bakir B, et al. CT and MR characteristics of hibernoma: six cases. Clin Imaging. 2008;32(1):42–47.
5. Murphey M, Carroll J, Flemming D, et al. From the archives of the AFIP: benign musculoskeletal lipomatous lesions. Radiographics. 2004;24(5):1433-1466.
6. Cypess A, Lehman S, Williams G, et al. Identification and Importance of Brown Adipose Tissue in Adult Humans. N Engl J Med. 2009;360:1509–1517.
7. Drevelegas A, Pilavaki M, Chourmouzi D. Lipomatous tumors of soft tissue: MR appearance with histological correlation. Eur J Radiol. 2004;50(3):257–267.
8. Ritchie D, Aniq H, Davies A, et al. Hibernoma—correlation of histopathology and magnetic-resonance-imaging features in 10 cases. Skeletal Radiol. 2006;35(8):579-589.
9. Chatterton B, Mensforth D, Coventry B, et al. Hibernoma: intense upstake seen on Tc-99m tetrofosmin and FDG positron emission tomographic scanning. Clin Nucl Med. 2002;27(5):369–370.
10. Angervall L, Nilsson L, Stener B. Microangiographic and histological studies in 2 cases of hibernoma. Cancer. 1964;17:685-692.
11. Lele M, Chundru S, Chaljub G, et al. Hibernoma. Arch Pathol Lab Med. 2002;126(8):975-978.
12. Mrózek K, Karakousis C, Bloomfield C. Band 11q13 is nonrandomly rearranged in hibernomas. Gen Chrom Cancer. 1994;9(2):145-147.