Hibernoma: distinctive light and electron microscopic features and relationship to brown adipose tissue

Breast hibernoma in a male patient: a rare case report and review of the literature

Hibernomas are uncommon, benign, lipomatous tumours of brown fat. Although hibernomas may arise from any region where brown fat exists, common locations include thigh, shoulder, back and neck. We report a rare finding of a breast hibernoma in a 43-year-old male. The patient was managed surgically with an excision of the breast mass. This report will outline the pathology and clinical findings of breast hibernomas and review of the literature.

Brown adipose tissue human biomarkers: Which one fits best? A narrative review

Adipose tissue (AT) is an endocrine metabolically dynamic active tissue that plays a central role in the systemic energy balance and metabolic regulation. Brown AT represents approximately 1% of adult human AT, with an energy-burning function that uses fat to create heat. Brown AT activity was measured using 18F-fluorodeoxyglucose positron emission tomography/computed tomography. It has been shown that cold exposure could promote brown AT activation. However, many factors, such as aging and body mass index, may interfere with this activity. Many authors have discussed the role of factors specifically secreted by the AT in response to cold exposure. The aim of this review is to properly understand the effects of cold on AT and biomarkers and their possible application in rehabilitation medicine. A comprehensive literature review was performed to identify published studies regarding biomarkers of cold effects on Brown AT searching the following databases: PubMed, Science Direct, and Web of Science, from 2012 to 2022. After evaluation of the inclusion and exclusion criteria, 9 studies were included in this review. We reported the overall influence of cold exposure on brown AT activity, its related biomarkers, and metabolism, demonstrating that the therapeutic role of cold exposure needs to be better standardized. From our data, it is important to design proper clinical trials because most cold applied protocols lack a common and homogeneous methodology.

Intraosseous hibernoma: Two case reports and a review of the literature

Intraosseous hibernomas are exceedingly rare tumors with only 35 cases reported worldwide. They are composed of vestigial brown adipose tissue and require biopsy and pathologic analysis for definitive diagnosis. Given their propensity to mimic more insidious malignant neoplasms, early and accurate identification may spare the patient both anxiety and invasive therapeutic interventions. In this report, we present two cases of intraosseous hibernomas and provide a review of current literature to further characterize the clinical, radiographic, and histopathologic parameters of these lesions. Clinicians should consider the diagnosis of intraosseous hibernoma when evaluating patients with characteristic presentations as it may be more prevalent than currently reported.

Liposarcoma With Hibernoma-like Histology: A Clinicopathologic Study of 16 Cases

Hibernoma is an uncommon benign tumor of brown fat cells that consistently expresses uncoupling protein 1 (UCP1). Herein, we clinicopathologically characterized 16 liposarcomas, for which histology, at least focally, closely resembled that of hibernoma, including sheets of brown fat-like, finely multivacuolated-to-eosinophilic tumor cells with no or minimal nuclear atypia. The cohort consisted of 4 well-differentiated liposarcomas (WDLSs), 6 dedifferentiated liposarcomas with a concomitant WDLS component, and 6 myxoid liposarcomas (MLSs). For all dedifferentiated liposarcoma cases, hibernoma-like histology was present only in the WDLS component. All tumors presented as large, deep-seated masses. Hibernoma-like histology resembled the pale cell, mixed cell, eosinophilic cell, or spindle cell subtypes of hibernoma, and it was a focal observation, with conventional liposarcoma histology coexisting in all cases. However, a few biopsy samples were predominated by hibernoma-like patterns, and 1 case was initially interpreted as hibernoma. Hibernoma-like components in WDLS immunohistochemically coexpressed MDM2 and CDK4 in most cases and harboredMDM2amplification in tested cases, whereas half of the cases expressed UCP1. The hibernoma-like components of MLS expressed DDIT3, andDDIT3rearrangements were present in the tested cases, whereas only negative or equivocal UCP1 expression was observed. In summary, WDLS and MLS focally demonstrate hibernoma-like histology on rare occasions. These elements are neoplastic, and some such areas in WDLS likely represent true brown fat differentiation, as supported by UCP1 expression. This pattern requires recognition to avoid the misdiagnosis as hibernoma, especially in biopsies. A careful search for classic liposarcoma histology and additional work-ups for the MDM2/CDK4 or DDIT3 status will be helpful for an accurate diagnosis.

Femoral nerve compression caused by a hibernoma in the right thigh: a case report and literature review

BACKGROUND

A hibernoma, also known as a brown fat tumor, is a rare benign soft tissue tumor, which originates from brown adipose tissue remaining in the fetus after the gestational period. It is often detected in adult men, presenting as a painless slow-growing mass. Hibernomas of the thigh have been reported; however, motor and sensory disorders caused by the tumors compressing the femoral nerve have not been reported. We report a case of a histopathologically proven hibernoma that induced femoral mononeuropathy.

CASE PRESENTATION

A 26-year-old man was admitted to the hospital due to a mass, approximately 11.0 × 9.0 × 4.0 cm in size, that had developed 5 years ago in the anterolateral aspect of the proximal thigh. Furthermore, he had a history of hypoesthesia 1 month prior to his admission. He had signs and symptoms of both a motor and sensory disorder, involving the anterior aspect of the right thigh and the medial aspect of the calf, along the distribution of the femoral nerve. During surgery, the femoral nerve was found to be compressed by the giant tumor. The resultant symptoms probably caused the patient to seek medical care. Marginal resection of the mass was performed by careful dissection, and the branches of the femoral nerve were spared. Histopathology examination showed findings suggestive of a hibernoma. At the 4-month follow-up, no femoral nerve compression was evident, and local tumor recurrence or metastasis was not found.

CONCLUSIONS

Asymptomatic hibernomas do not require treatment; however, in cases of hibernomas with apparent symptoms, complete marginal surgical excision at an early stage is a treatment option because it is associated with a low risk of postoperative tumor recurrence.

Adipocytic tumors in Children: A contemporary review

Adipocytic neoplasms in the pediatric population demonstrate a different histologic spectrum and frequency than in adults. The vast majority of these tumors are benign, with lipoma being the most common entity. The identification of signature cytogenetic and molecular alterations for certain lesions, such as PLAG1 gene rearrangement in lipoblastoma and FUS-DDIT3 fusion in myxoid liposarcoma, has been helpful in approaching these neoplasms and aiding in confirming the diagnosis. Furthermore, it is important for pathologists to recognize that adipocytic neoplasms may be associated with different syndromes with potential impact in managing such patients. This review provides a summary of the clinical pictures, histologic characteristics, molecular alterations, differential diagnoses, and syndromic associations of the commonly encountered fatty tumors in children.

Intraosseous Hibernoma: A Rare and Unique Intraosseous Lesion

Background

Hibernoma is a rare benign tumor of adults that is composed of multivacuolated adipocytes resembling brown fat cells. Hibernoma typically occurs in soft tissue, and intraosseous examples are very rare. Intraosseous hibernomas can radiologically mimic metastatic carcinoma and other tumorous conditions.

Methods

To collect the intraosseous hibernomas, we searched the pathologic database and reviewed the hematoxylin and eosin (H&E)–stained slides of bone biopsy samples performed to differentiate radiologically abnormal bone lesions from 2006 to 2016. A total of six intraosseous hibernoma cases were collected, and clinical and radiological information was verified from electronic medical records. H&E slide review and immunohistochemical staining for CD68, pan-cytokeratin, and S-100 protein were performed.

Results

Magnetic resonance imaging of intraosseous hibernomas showed low signal intensity with slightly hyperintense foci on T1 and intermediate to high signal intensity on T2 weighted images. Intraosseous hibernomas appeared as heterogeneous sclerotic lesions with trabecular thickening on computed tomography scans and revealed mild hypermetabolism on positron emission tomography scans. Histopathologically, the bone marrow space was replaced by sheets of multivacuolated, foamy adipocytes resembling brown fat cells, without destruction of bone trabeculae. In immunohistochemical analysis, the tumor cells were negative for CD68 and pan-cytokeratin and positive for S-100 protein.

Conclusions

Intraosseous hibernoma is very rare. This tumor can be overlooked due to its rarity and resemblance to bone marrow fat. Pathologists need to be aware of this entity to avoid misdiagnosis of this rare lesion.

Development of Hibernomas in Rats Dosed with Phentolamine Mesylate During the 24-Month Carcinogenicity Study

Phentolamine is a reversible competitive α-adrenergic antagonist with similar affinities for α1 and α2 receptors. It has a long history of safe clinical use, and was developed as a potential therapy for male erectile dysfunction because of its capacity to increase the arteriolar blood flow to the corpora cavernosa. Phentolamine mesylate was administered to rats by oral gavage at daily doses of 10, 50, and 150 mg/kg for 24 months. A dose-related increase in mortality, ascribed to an exaggerated pharmacologic effect, was seen at high doses. Systemic exposure as measured by plasma drug concentration increased with dose and duration of dosing and slight drug accumulation occurred, particularly in high-dose males. In the treated groups, 10 males and 1 female were diagnosed with hibernomas, neoplasms of brown adipose tissue, which appeared in the thoracic cavity or retroperitoneal area as circumscribed, tan to reddish-brown lobulated masses. Histologically, the masses were well circumscribed with variably sized lobules defined by a rich capillary network and consisted of closely apposed oval to polygonal cells with large amounts of cytoplasm and a centrally located nucleus. The cytoplasm's appearance varied from multivacuolated to univacuolated to granular eosinophilic. In a few cases, neoplastic emboli were observed in capsular vessels. Ultrastructurally, the neoplastic cells contained numerous mitochondria with transverse parallel cristae that occupied over 60% of the cytoplasm and lipid droplets. This study documents the previously unreported development of hibernomas in rats treated with phentolamine mesylate.

Round Cell Variant of Myxoid Liposarcoma in a Japanese Macaque (Macaca fuscata)

A 5-year-old, female, Japanese Macaque ( Macaca fuscata) was diagnosed with round cell variant of myxoid liposarcoma. At necropsy, multifocal to coalescing, reddish tan to white nodules, ranging from 0.5 to 1 cm in diameter, were noted throughout the omentum and retroperitoneum. Similar neoplastic nodules were also present in diaphragm, abdominal wall, and on hepatic capsule. Microscopically, neoplastic masses consisted of round to polyhedral cells, which had round, often eccentric nuclei and abundant eosinophilic granular and microvacuolated cytoplasm; Oil red O staining demonstrated large numbers of lipid droplets in the cytoplasm. Ultrastructurally, the cytoplasm of the tumor cells was packed with occasional lipid vacuoles and numerous enlarged mitochondria. Immunohistochemistry revealed tumor cells were positive for vimentin, while negative to cytokeratin, actin, and Factor VIII-related antigen. To the authors' knowledge, this is the first report of round-cell variant of myxoid liposarcoma in nonhuman primate.

Mammary Hibernoma: A Rare Entity

Hibernoma arising in the breast is rare and may present as an asymptomatic mass or may be detected by screening mammography. Four histologic types have been identified: typical, myxoid variant, spindle cell variant, and the lipoma-like variant. The most common "typical variant" is composed of pale to eosinophilic multivacuolated cells with interspersed univacuolar cells. Hibernomas are universally benign and are not known to recur or have an aggressive behavior, even in incompletely excised lesions. Hence, their clinical importance lies in distinguishing them from other benign and malignant breast neoplasms as well as inflammatory conditions that come into the histologic or radiologic differential. 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.

Hibernomas of the upper extremity: a case report and literature review

Hibernomas are rare, benign tumors of brown adipose tissue. While they have been found in a variety of locations, they are rare in the upper extremity and not previously described in the hand. Diagnosis is most often made histologically, and treatment consists of surgical resection. We present an unusual case of hibernoma in the hand treated with marginal excision, resulting in good function, cosmesis, and no recurrence.

Adipose tissue as an endocrine organ

Obesity is one of the most important health challenges faced by developed countries and is increasingly affecting adolescents and children. Obesity is also a considerable risk factor for the development of numerous other chronic diseases, such as insulin resistance, type 2 diabetes, heart disease and nonalcoholic fatty liver disease. The epidemic proportions of obesity and its numerous comorbidities are bringing into focus the highly complex and metabolically active adipose tissue. Adipose tissue is increasingly being considered as a functional endocrine organ. This article discusses the endocrine effects of adipose tissue during obesity and the systemic impact of this signaling.

Subconjunctival hibernoma in a dog

A 10-year-old, castrated male, German Shepherd mixed-breed dog was presented to Kansas State University Veterinary Health Center for evaluation of a subconjunctival swelling in the ventral fornix of the left orbit. The owner elected to pursue excision of the mass 2 years after initial consultation following a sudden change in the size and color of the lesion. An excisional biopsy was performed, and the mass along with its associated capsule were submitted to the Comparative Ocular Pathology Laboratory of Wisconsin for histopathologic evaluation, which confirmed the diagnosis of a hibernoma. Fourteen months following excision, the patient showed no evidence of tumor regrowth.

Clinical, morphologic, and immunohistochemical features of canine orbital hibernomas

Hibernomas are uncommon benign tumors of brown fat that occur in humans and various animal species. They have not been observed in the orbit of dogs, humans, or other animals. Here we report clinical, light and electron microscopic, and immunohistochemical features of a series of 7 hibernomas arising in the orbital region of dogs. These neoplasms occurred in adult dogs with no breed predilection. The mean age of the affected dogs was 10.4 years (range, 8-13 years). All neoplasms presented as soft lobular masses composed of predominantly round or polygonal neoplastic cells with granular eosinophilic and vacuolated cytoplasm resembling adipocytes. The cytoplasm contained large numbers of pleomorphic mitochondria with dense matrices and indistinct cristae. Immunohistochemical evaluation confirmed positive labeling of neoplastic cells from all cases with uncoupling protein 1 (UCP-1) consistent with brown fat differentiation. Interestingly, rare neoplastic cells also expressed myogenin and myoD, possibly suggesting a common progenitor cell for neoplastic brown adipose and skeletal muscle cells.

Adipose and myxoid tumors of childhood and adolescence

Adipose and myxoid tumors in children are an unusual and challenging group of neoplasms that have some unique aspects in contrast to these tumors in adults. Less than 10% of soft tissue neoplasms in the 1st 2 decades of life have an adipose phenotype and most are benign. The most common are various types of lipoma and lipoblastoma. Liposarcoma in young patients is rare and has a distinctive distribution of histologic subtypes, including classic myxoid liposarcoma, and unusual variants, such as pleomorphic-myxoid liposarcoma. Pathologic examination enhanced by adjunct techniques, such as immunohistochemistry and cytogenetic or molecular genetic studies, is useful for classification of difficult cases. Myxoid tumors can overlap with adipose tumors and are included in this review because of the morphologic similarities and importance of diagnostic accuracy. This article reviews the clinicopathologic features of adipose and myxoid tumors with an emphasis on the unique aspects of these neoplasms in children and adolescents and the differential diagnosis.

Hibernomas: clinicopathological features, diagnosis, and treatment of 17 cases

Hibernomas are rare benign adipose tumors composed of brown fat cells with granular, multivacuolated cytoplasm admixed with white adipose tissue. They account for 1.6% of benign lipomatous tumors and approximately 1.1% of all adipocytic tumors. They are more common in the third and fourth decades of life. The most common location is the thigh, followed by the shoulder, back, and head and neck. Four histological types have been reported; abundant vascularity is characteristic, and atypias are rare. The treatment of choice for hibernomas is complete surgical excision. Metastases or malignant transformation have not been reported.This article presents a series of 17 patients with hibernomas diagnosed and treated at our institution from January 1986 to December 2009. Six men and 11 women (M:F, 1:2) had a mean age of 38 years (range, 10 months to 64 years). All patients underwent surgical treatment; 14 patients had marginal and 3 had wide excision. Adjuvants such as radiation therapy, chemotherapy, or embolization were not administered for any patient. The most common symptom was a painless palpable mass, followed by a tender or painful mass; in 2 patients, the tumor was an incidental finding. The duration of symptoms ranged from 1 month to 10 years (mean, 27 months). The most common location was the thigh, followed by the buttock, scapula, and neck. The most common histological variant was the typical variant followed by the lipoma-like variant. At a mean follow-up of 5 years (range, 1-9 years), local recurrences were not observed.

Pure hibernoma of the breast: insights about its origins

Hibernomas are rare benign tumors composed of cells reminiscent of brown adipose tissue. In the mammary gland, hibernomas are extraordinary rare, with only 4 cases reported previously. We report the fifth case in a 37-year-old woman who presented with a slowly growing mobile mass in her right breast. A 2.2 cm well-circumscribed lobulated mass was completely removed. The histopathologic analysis showed the full characteristics of the hibernoma. A review of the clinicopathologic features of hibernomas, its relation to brown adipose tissue in humans, and considerations about its histogenesis are made.

Intraosseous hibernoma

We describe the imaging and pathological features of a rare case of sacral hibernoma that was discovered incidentally in a patient with low back pain. The benign-appearing, small intraosseous lesion in the sacrum was sclerotic on CT. MRI revealed that the lesion was heterogeneously hyperintense on T1W (lower in intensity than subcutaneous fat) and heterogeneously hypointense on fat-saturated T2W and STIR images. It showed mild heterogeneous enhancement on the post-contrast fat-saturated T1 MR images due to increased vascularity. A biopsy of the lesion was performed. The biopsy specimen demonstrated multivacuolated cells with immunohistochemical features of brown adipose tissue consistent with hibernoma.

A Case of Spontaneous Malignant Hibernoma in a Crl:CD(SD)IGS Rat

A firm, tan, well-circumscribed mass that measured 25 × 30 × 35 mm was observed in the thoracic cavity of a 53-week-old male Crl:CD(SD) IGS rat. Histologically, the mass was encapsulated by fibrous tissue and contained fibrovascular septae. Tumor cells were compactly arranged, and most were oval to polygonal in shape with multivacuolated cytoplasm and a centrally located nucleus. In some parts of the tumor, marked cellular atypia and frequent mitoses were evident. Vacuoles in cytoplasm were positive for oil red O. The tumor cells were characterized ultrastructurally by abundant, round to oval mitochondria with transverse closely-packed cristae. Tumor cells were immunohistochemically positive for uncoupling protein 1 (UCP-1). Several thrombi and hemorrhagic or necrotic foci were also observed within the tumor mass. Vascular invasion of the tumor capsule was observed; however, invasion of surrounding tissues or metastases were not observed. Based on the pathology findings, this case was diagnosed as a malignant hibernoma.

Pediatric hibernoma: a case review

We present an unusual case of supraclavicular benign hibernoma in a 12-year-old girl who presented with chest discomfort, night sweats, shortness of breath, fatigue, and pruritus. This is the first case of hibernoma being reported as symptomatic in the world literature. Symptoms persisted for 1 year till excision biopsy. Biopsy of supraclavicular lump revealed a hibernoma. Symptoms resolved within 2 months of excision and 1-year follow-up showed no recurrence of symptoms or supraclavicular swelling.

Subpleural Hibernoma

Here we report the case of a 41-year-old man with an asymptomatic, 5-cm, pleural-based mass excised by thoracoscopy. We also review the clinical, radiologic, and pathologic features of hibernomas.

Hibernoma: MRI features in eight consecutive cases

AIM

To describe the preoperative magnetic resonance imaging findings of eight histologically-proven cases of hibernoma.

MATERIALS AND METHODS

The site, size, and signal characteristics of eight consecutive hibernomas were retrospectively assessed on T1-weighted spin-echo and short T1 inversion recovery (STIR)/fat-saturated T2-weighted fast spin echo magnetic resonance images. Four patients also had gadolinium-enhanced fat-saturated T1-weighted spin echo imaging. Patient age and sex, and duration of symptoms were recorded.

RESULTS

Three female and five male patients with an average age 36 years (range 16-53 years) were included. Seven lesions occurred in the thigh, four in the anterior compartment and three in the posterior compartment. One lesion occurred superficial to the scapula. All cases demonstrated common magnetic resonance imaging findings of a well-defined, heterogeneous mass, slightly or clearly hypo-intense to subcutaneous fat on T1-weighted spin-echo images, with prominent thin low signal bands throughout the tumour. The lesions failed to fully suppress on STIR or fat-saturated T2-weighted images. Only one of the four contrast-enhanced studies demonstrated increased vascularity in the tumour.

CONCLUSION

The MRI findings of a lesion that is diffusely slightly hypointense to surrounding subcutaneous fat, should prompt the operator to consider hibernoma in the differential diagnosis.

A (9;11)(q34;q13) translocation in a hibernoma

The diagnosis of hibernoma has historically been made by histopathologic examination and finding of characteristic brown fat cells with granular multivacuolated cytoplasm. The diagnosis of hibernoma may be complicated, however, because seemingly diagnostic cells could be mistakenly identified as lipoblasts, leading to the erroneous diagnosis of well-differentiated liposarcoma. Cytogenetic alterations in lipomatous tumors are well established and could be used for diagnostic purposes. Previous cytogenetic abnormalities reported in hibernomas have included alteration of 11q13 region. Here, we present a case of a hibernoma with a novel cytogenetic alteration involving a reciprocal translocation between 9q and 11q that was useful in establishing the final diagnosis.

Characterization of the myxoid variant of hibernoma

Hibernomas are rare benign neoplasms composed of brown adipose tissue. Although they were first mentioned in the literature almost a century ago, relatively few reports have documented their range of pathological features. Multivacuolated fat cells with small, central nuclei are typical features of hibernomas. Based on the nature of the stroma and the appearance of the multivacuolated cells, 4 categories of hibernomas are described: typical, lipoma-like, myxoid, and spindle cell. The myxoid variant is very rare. In this report, we present and characterize the spectrum of morphological features of the myxoid variant of hibernoma by describing the case of a 45-year-old white man who was referred to our hospital for treatment of an ovoid mass in the posterior segment of the right deltoid region. Histopathologic examination of the resected specimen revealed a multilobulated, tan-yellow, variegated tumor with a rubbery consistency that was separated by thick fibrous septa with interspersed collections of foamy histiocytes. The mass was initially diagnosed as schwannoma with degenerative changes, but workup revealed a myxoid variant of hibernoma. This report highlights recent advances that may help confirm the diagnosis and explain the differential diagnosis of this rare tumor. This is one of only a few cases of a myxoid variant of hibernoma reported in the literature.

Hibernoma: a report of 2 unusual cases with a review of the literature

Hibernomas are rare neoplasms composed of brown adipose tissue. The behavior of these neoplasms has been described as uniformly benign in humans. The only recurrence cited in the English literature involved a sarcoma with hibernoma-like features, which was reported in abstract form. We present 2 cases of hibernoma, one that continued to grow following partial excision and another at an unusual site (anterior abdominal wall). Both of these tumors overexpressed p53 protein by immunohistochemistry, which was a novel finding. A review of the literature highlights recent advances that may help confirm the diagnosis and explain the biology of these rare tumors.

Fine-needle aspiration characteristics of hibernoma

BACKGROUND

Hibernoma is a rare, benign lipomatous tumor with features of brown fat. The preoperative diagnosis of hibernoma is difficult at times because its clinical, radiographic, and fine-needle aspiration (FNA) characteristics overlap with those of liposarcoma.

METHODS

The preoperative FNA findings of eight surgically excised hibernomas from seven patients (three men and four women, ages 24-60 years) were reviewed. The cytologic features were compared with the histologic features of the corresponding surgical specimens as well as lipomatous tumors and other lesions that may cause confusion in the differential diagnosis.

RESULTS

The FNA cytologic features of the hibernomas were found to correspond well with their histologic appearance. The FNA findings included small, round, brown fat-like cells with uniform, small cytoplasmic vacuoles and regular, small, round nuclei; delicate branching capillaries; and variable numbers of mature fat cells.

CONCLUSIONS

The FNA cytologic features of hibernoma are characteristic and useful in the preoperative investigation of lipomatous tumors, particularly with regard to excluding a diagnosis of liposarcoma.

The morphologic spectrum of hibernoma: a clinicopathologic study of 170 cases

Hibernoma, an uncommon tumor of brown fat, has been described only in a few case reports and small series. The authors reviewed 170 cases of hibernoma and evaluated the morphologic features and the behavior of this tumor. The records from the Soft Tissue Registry of the Armed Forces Institute of Pathology from 1970 were searched for cases coded as "hibernoma." Clinical information and available slides from 170 hibernomas were reviewed. Immunohistochemical staining for S-100 and CD34 was performed on select cases. Follow-up information was obtained from the patients' medical records, the patients' physicians, and the patients themselves. Of 170 patients with hibernoma, 99 were men and 71 were women. The tumor occurred most commonly in adults, with a mean age of 38.0 years (age range, 2-75 years). Nine tumors occurred in pediatric patients. The most common anatomic locations included the thigh (n = 50), shoulder (n = 20), back (n = 17), neck (n = 16), chest (n = 11), arm (n = 11), and abdominal cavity/retroperitoneum (n = 10). The average duration of the tumor was 30.6 months. Tumor size ranged from 1 to 24 cm with an average dimension of 9.3 cm. All tumors were composed partly or principally of coarsely multivacuolated fat cells with small, central nuclei and no atypia. Four morphologic variants of hibernoma were identified: typical, myxoid, spindle cell, and lipoma-like. "Typical" hibernoma (n = 140) included eosinophilic cell, pale cell, and mixed cell types based on the tinctorial quality of the hibernoma cells. The myxoid variant (n = 14) contained a loose basophilic matrix. Spindle cell hibernoma (n = 4) had features of spindle cell lipoma and hibernoma; all occurred in the neck or scalp. The lipoma-like variant (n = 12) contained only scattered hibernoma cells. Immunohistochemically, 17 of 20 cases (85%) were positive for S-100 protein. Only one hibernoma of 20, a spindle cell variant, was positive for CD34, whereas other hibernoma variants were negative. Follow-up was obtained for 66 cases (39%) over a mean period of 7.7 years (range, 6 months-28 years). None of the patients with follow-up had a recurrence or metastasis, including eight with intramuscular tumors. No patient died of disease. Hibernoma is a tumor found most often in adults and most commonly in the thigh, with several morphologic variants. It is a benign tumor that does not recur with complete excision. Hibernomas should not be confused with atypical lipomas or well-differentiated liposarcoma.

Hibernoma of the spermatic cord. The second reported case and literature review

A 23-year-old man was admitted with a 6-month history of a slow-growing mass in the left side of the scrotum. Echography revealed a mixed-density mass that was mainly fatty. The histopathological examination was considered typical of a hibernoma. To our knowledge this is the second case reported.

Abl expression in human fetal and adult tissues, tumours, and tumour microvessels

Abl kinases encoded by the abl oncogenes inhibit apoptosis without affecting cell proliferation. The aim of this study was to examine a wide range of normal fetal and adult human tissues and a variety of tumour types for Abl immunoreactivity. Sections from 193 paraffin blocks of normal fetal and adult tissues and 72 blocks from representative tumours were stained immunohistochemically using a polyclonal antibody to c-Abl/Bcr-Abl oncoprotein. Weak Abl immunoreactivity was observed in many adult tissues. Moderately intense or strong staining (cytoplasmic, nuclear or membranous) was consistently seen in hyaline cartilage, adipocytes, and ciliated epithelium. In fetal tissues, there was a broadly similar staining pattern, but Abl expression was also seen in muscle (all types) and occasionally in endothelial cells. The most intense staining was seen in sites of endochondral ossification and in the umbilical cord stroma. Negatively staining tissues included epidermis and squamous mucosa, lymph nodes, tonsil, spleen, hepatocytes, and adrenals. Most tumours showed focal or weak Abl immunoreactivity. The most intense staining was seen in chondrosarcoma, liposarcoma, and diffuse gastric (signet ring) adenocarcinoma. In the latter two tumour types, Abl expression was also observed in tumour microvessels. These results suggest that Abl not only functions as an apoptosis inhibitor, but also may have a role in connective tissue maturation and differentiation and in tumour growth and angiogenesis.

Scalp hibernoma: case report and literature review

Hibernomas are uncommon, benign neoplasms derived from the remnants of fetal brown adipose tissue. A review of the world literature revealed 105 cases, with the interscapular location the most common. Typically, hibernomas are asymptomatic and slow-growing. Adequate treatment usually consists of simple excision. We describe the second documented case of a scalp hibernoma.

Involvement of 10q22 and 11q13 in hibernoma

A hibernoma studied cytogenetically had the karyotype 46,XY,t(9;10;11)(q34;q22;q13),t(17;19) (q21.3;q13). The findings are discussed and compared with those of the previous case described in the literature.

Hibernoma in the parotid region

Hibernoma is a benign tumour, arising from vestigial remnants of brown adipose cells, which have persisted from embryonic life. Although it is a well recognized entity, it is an extremely rare tumour. Recent reports estimate 81 cases in the world literature, only seven being in the neck. To our knowledge, it has never been reported in the parotid region. We report such a case and discuss the historical background of a hibernoma, along with its pathological and clinical behaviour.

Metastatic hibernomas in transgenic mice expressing an alpha-amylase-SV40 T antigen hybrid gene

Mice transgenic for a hybrid gene containing the liver promoter of the mouse amylase gene (Amy-1a) fused to the SV40 tumor antigen coding region unexpected developed malignant brown adipose tissue tumors (malignant hibernomas). Expression of the alpha-amylase gene had previously been thought to be confined to the liver parotid, and pancreas; however, analysis of white and brown adipose tissue from nontransgenic mice revealed expression of the endogenous Amy-1a gene in these tissues. Gene constructs driven by the Amy-1a liver promoter thus provide a means of targeting gene expression to the adipocyte cell lineage in transgenic mice. Moreover the high frequency of metastases in the liver, lungs, spleen, heart, and adrenals of these mice provides an experimental system in which to study the development of disseminated malignancy.