Hibernomas are characterized by rearrangements of chromosome bands 11q13-21

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.

CD10 (neprilysin) expression: a potential adjunct in the distinction of hibernoma from morphologic mimics

Although the morphologic diagnosis of hibernoma is usually straightforward, some hibernomas have atypical morphologic features, mimicking atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDLs). In addition, the multivacuolated brown fat cells may be mistaken for lipoblasts by pathologists, especially those without significant soft tissue tumor exposure. Thus, we continue to receive in consultation cases of hibernoma sent for MDM2 fluorescence in situ hybridization testing to exclude ALT/WDL. Testing hibernomas for MDM2 amplification, however, adds cost and delays the final diagnosis. Recently, we have noted expression of neprilysin (CD10, CALLA), a zinc-dependent metalloproteinase involved in the inactivation of various peptide hormones, in brown fat cells, and wished to explore the potential utility of this widely available, inexpensive ancillary test in the differential diagnosis of hibernoma. Formalin-fixed, paraffin-embedded tissue sections from well-characterized cases of hibernoma (n = 48), brown fat (n = 21), ALTs/WDLs (n = 17), pleomorphic liposarcomas (PLPSs) (n = 6), lipomas (n = 5), and fat necrosis (n = 5) were immunostained for CD10, using a commercially available antibody and routine laboratory protocols. CD10 expression was evaluated in both adipocytes and in surrounding stromal cells. The hibernomas occurred in 28 men and 20 women, ranging from 11 to 76 years of age and involved the extremities (n = 25), pelvis (n = 7), abdomen/pelvis/retroperitoneum (n = 7), head and neck region (n = 6), back (n = 2), and chest (n = 1). All showed diffuse, strong CD10 expression in multivacuolated brown fat cells and in the majority of adjacent univacuolated fat cells. Brown adipose tissue from various anatomic structures showed an identical pattern of immunoreactivity. In contrast, CD10 expression was present in the adipocytes of only 3 of 17 (18%) ALTs/WDLs and was absent in lipomas and fat necrosis. Lipoblasts expressed CD10 in 3 PLPSs. Expression of CD10 by surrounding fibroblastic stromal cells was more widespread, present in 13 hibernomas, 10 ALTs/WDLs, 1 instance of fat necrosis, 6 PLPSs, and 4 examples of brown fat. We conclude that immunohistochemistry for CD10 may represent a useful, rapid and inexpensive ancillary test in the differential diagnosis of hibernoma from potential morphologic mimics, especially when morphologic features favor hibernoma. CD10 expression in adipocytes, however, should be rigorously distinguished from fibroblastic stromal cell CD10 expression, a nonspecific finding.

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.

A Twenty-Four-Year-Old Woman with Left Flank Lipoma-Like Hibernoma

A 24-year-old woman presented with a 5-month history of a left flank mass that was painful on palpation. Magnetic resonance imaging revealed a 10.0 × 6.0 × 2.5 cm mass consistent with lipoma. A fatty lobulated mass was excised and subjected to H&E staining and immunohistochemical analyses. The specimen consisted of mature univacuolated adipocytic cells, with intermixed multivacuolated eosinophilic granular cells. No atypia or hyperchromasia was identified. Most of the cells were S100 positive and Ki-67 immunonegative. A diagnosis of a lipoma-like hibernoma was rendered. Hibernomas are rare benign lipomatous tumors that show differentiation toward brown fat. The lipoma-like hibernoma subtype is rare and can be misdiagnosed as atypical lipoma or well-differentiated liposarcoma. Here we describe an example of this rare tumor.

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.

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.

Hibernoma--two patients with a rare lipoid soft-tissue tumour

Background

Hibernomas are rare benign soft-tissue tumours arising from brown fat tissue. Although imaging characteristics are not specific certain imaging features, common locations and patient demographics may suggest hibernoma as a differential diagnosis.

Case presentation

We report on two 48-year-old male patients with hibernoma. The tumour presented with local swelling of the inguinal region in the first patient and was an incidental imaging finding in the second patient. Imaging included magnetic resonance imaging in both patients and computed tomography as well as ¹⁸ F-fluorodeoxyglucose positron emission tomography-computed tomography in the second patient. In both cases histological diagnosis was initially based on excisional and needle core biopsy, respectively. Complete surgical resection confirmed the diagnosis of hibernoma thereafter.

Conclusion

In soft tissue tumours with fatty components hibernoma may be included into the differential diagnosis. Because of the risk of sampling errors in hibernoma-like tissue components of myxoid and well-differentiated liposarcoma, complete resection is mandatory. This article also reviews the current imaging literature of hibernomas.

[Adipocytic tumors]

Adipocytic tumors are the most common mesenchymal neoplasms, liposarcoma accounting for approximately 20% of soft tissue sarcomas. The differential diagnosis between benign and malignant tumors is often problematic and represents a significant proportion of consultation cases. The goal of this article is to review liposarcoma subtypes, the main benign adipocytic neoplasms: lipoblastoma, hibernoma, spindle/pleomorphic cell lipoma, chondroid lipoma, as well as non adipocytic neoplasms with a lipomatous component such as lipomatous solitary fibrous tumor, emphasizing on practical differential diagnosis issues, and immunohistochemical and molecular tools allowing their resolution.

MEN1 Syndrome and Hibernoma: An Uncommonly Recognised Association?

MEN1 syndrome is known to classically result in parathyroid, pituitary, and pancreatic islet cell tumours. However, the potential association of MEN1 syndrome with hibernoma, a benign tumour with differentiation towards brown fat, is far less well known, despite their genetic profile both being linked to deletion of the MEN1 gene. Herein, we describe a case with its key radiological and pathological findings.

Laryngeal hibernoma: case series of a rare tumor

BACKGROUND

Hibernomas are rare, benign tumors of brown adipose tissue uncommonly found in the head and neck.

METHODS

A review of the English-language literature was conducted for this study. We present a series of 2 laryngeal hibernomas treated with transoral laser microsurgical resection at a tertiary referral center over a period of 18 years.

RESULTS

Only 2 cases of laryngeal hibernoma have been previously described in the literature. Two additional cases were encountered at our institution. Preoperative imaging demonstrated a well-circumscribed neoplasm with fat density compatible with lipoma, but internal heterogeneity and vascularity seen in the context of liposarcoma. Transoral laser microsurgical resection was successfully performed in each case.

CONCLUSION

Despite unique radiographic features, hibernomas are difficult to distinguish from well-differentiated liposarcoma and lipoma variants without pathologic correlation. Complete surgical resection is indicated. In our experience, transoral laser microsurgical excision of laryngeal hibernomas is a safe, effective treatment modality with little associated morbidity.

Hibernoma in the thoracic back muscle accompanied by neurilemmoma

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.

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.

Massive abdominal wall hibernoma: case report and literature review of a rare soft-tissue tumor

BACKGROUND

Hibernoma is a rare benign tumor arising from remnants of fetal brown adipose tissue. This tumor was first described by Merkel in 1906. The brown fat is a specialized form of fat found in the hibernating and nonhibernating animals such as rats, cats, monkeys, rabbits, and humans.

CASE PRESENTATION

A 27-year-old man presented with a painless, enlarging, anterior abdominal wall mass, which, upon core-needle biopsy, was found to be hibernoma. This was evaluated with abdominal computed tomography, which showed a heterogeneous mass that contained fat. At operation, the entire mass measuring 30x25x6 cm lying below the external oblique muscle was excised with a cuff of normal tissue.

CONCLUSION

Hibernoma is a rare, slow-growing benign soft tissue tumor composed of brown fat that is successfully treated by complete excision while preserving all related vital structures. Unlike lipoma, hibernoma is well vascularized and therefore good hemostasis must be achieved at surgery to prevent postoperative bleeding or hematoma. No case of recurrence has been previously reported.

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.

Concomitant deletions of tumor suppressor genes MEN1 and AIP are essential for the pathogenesis of the brown fat tumor hibernoma

Hibernomas are benign tumors with morphological features resembling brown fat. They consistently display cytogenetic rearrangements, typically translocations, involving chromosome band 11q13. Here we demonstrate that these aberrations are associated with concomitant deletions of AIP and MEN1, tumor suppressor genes that are located 3 Mb apart and that underlie the hereditary syndromes pituitary adenoma predisposition and multiple endocrine neoplasia type I. MEN1 and AIP displayed a low expression in hibernomas whereas the expression of genes up-regulated in brown fat--PPARA, PPARG, PPARGC1A, and UCP1--was high. Thus, loss of MEN1 and AIP is likely to be pathogenetically essential for hibernoma development. Simultaneous loss of two tumor suppressor genes has not previously been shown to result from a neoplasia-associated translocation. Furthermore, in contrast to the prevailing assumption that benign tumors harbor relatively few genetic aberrations, the present analyses demonstrate that a considerable number of chromosome breaks are involved in the pathogenesis of hibernoma.

C11orf95-MKL2 is the resulting fusion oncogene of t(11;16)(q13;p13) in chondroid lipoma

Chondroid lipoma, a rare benign adipose tissue tumor, may histologically resemble myxoid liposarcoma or extraskeletal myxoid chondrosarcoma, but is genetically distinct. In this study, an identical reciprocal translocation, t(11;16)(q13;p13), was identified in three chondroid lipomas, a finding consistent with previously isolated reports. A fluorescence in situ hybridization (FISH)-based positional cloning strategy using a series of bacterial artificial chromosome (BAC) probe combinations designed to narrow the 16p13 breakpoint revealed MKL2 as the candidate gene. Subsequent 5' RACE studies demonstrated C11orf95 as the MKL2 fusion gene partner. MKL/myocardin-like 2 (MKL2) encodes myocardin-related transcription factor B in a megakaryoblastic leukemia gene family, and C11orf95 (chromosome 11 open reading frame 95) is a hypothetical protein. Sequencing analysis of reverse transcription-polymerse chain reaction (RT-PCR) generated transcripts from all three chondroid lipomas defined the fusion as occurring between exons 5 and 9 of C11orf95 and MKL2, respectively. Dual-color breakpoint spanning probe sets custom-designed for recognition of the translocation event in interphase cells confirmed the anticipated rearrangements of the C11orf95 and MKL2 loci in all cases. The FISH and RT-PCR assays developed in this study can serve as diagnostic adjuncts for the identification of this novel C11orf95-MKL2 fusion oncogene in chondroid lipoma.

Assessment of the clinical and molecular impact of different cytogenetic subgroups in a series of 272 lipomas with abnormal karyotype

Conventional lipomas harbor karyotypic changes that could be subdivided into four, usually mutually exclusive, categories: rearrangement, in particular through translocations, of chromosome bands 12q13-15, resulting in deregulation of the HMGA2 gene, loss of material from or rearrangement of chromosome 13, supernumerary ring or giant marker chromosomes, and aberrations of chromosome band 6p21. In the present study, 272 conventional lipomas, two-thirds of them deep-seated, with acquired clonal chromosome changes were assessed with regard to karyotypic and clinical features. A nonrandom distribution of breakpoints and imbalances could be confirmed, with 83% of the cases harboring one or more of the previously known cytogenetic hallmarks. Correlation with clinical features revealed that lipomas with rings/giant markers were larger, occurred in older patients, were more often deep-seated, and seemed to have an increased tendency to recur locally, compared with tumors with other chromosome aberrations. The possible involvement of the HMGA2 gene in cases that did not show any of the characteristic cytogenetic changes was further evaluated by locus-specific metaphase fluorescence in situ hybridization (FISH) and RT-PCR, revealing infrequent cryptic disruption of the gene but abundant expression of full length or truncated transcripts. By FISH, we could also show that breakpoints in bands 10q22-23 do not affect the MYST4 gene, whereas breakpoints in 6p21 or 8q11-12 occasionally target the HMGA1 or PLAG1 genes, respectively, also in conventional lipomas.

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.

Deep-seated, well differentiated lipomatous tumors of the chest wall and extremities: the role of cytogenetics in classification and prognostication

BACKGROUND

Intramuscular lipomas and atypical lipomatous tumors (ALT) are common deep-seated lipomatous tumors of the chest wall and extremities. Distinguishing between these two entities can be difficult based on histologic analysis alone. However, the cytogenetic profiles of ALT and intramuscular lipomas are distinct. Correct classification is important, because aggressive local disease recurrence occurs more frequently in patients with ALT than in patients with intramuscular lipoma. The authors examined their single institutional experience and correlated their classification with clinical features and outcome.

METHODS

In the current study, 106 patients with deep-seated, well differentiated adipose tumors of the chest wall and extremities were classified as having ALT or intramuscular lipoma using a combined approach of histology and cytogenetics, if available. The classification was correlated with clinicopathologic features and follow-up data.

RESULTS

Fifty-five patients were classified as having intramuscular lipoma and 51 were classified as having ALT. Classification did not correlate with age and gender (P = 0.28 and P = 0.96, respectively). Intramuscular lipomas were smaller than ALTs (P < 0.0001), but there was significant overlap between the 2 groups. ALT occurred preferentially in the lower extremity (P < 0.0009). Four percent of patients with intramuscular lipomas and 27% of patients with ALTs developed local disease recurrence (P = 0.0006). Disease recurrence did not correlate with patient age at diagnosis, patient gender, tumor size, and tumor location (P = 0.45, P = 0.26, P = 0.49, and P = 0.28, respectively). Within the subset of patients with ALTs, disease recurrence did not correlate with patient age at diagnosis, patient gender, or tumor location (P = 0.38, P = 0.54, and P = 0.86, respectively).

CONCLUSIONS

Classification of deep-seated, well differentiated lipomatous tumors of the extremities and chest wall using a combined approach of histology and cytogenetics correlated well with biologic behavior/disease recurrence. This combined approach is advocated to better stratify patients for treatment purposes and follow-up.

11q13 alterations in two cases of hibernoma: large heterozygous deletions and rearrangement breakpoints near GARP in 11q13.5

Hibernomas are rare, benign tumors with a histological appearance resembling that of brown adipose tissue. The diagnosis of hibernomas may be difficult because some of them contain only a small number of the characteristic multivacuolated fat cells and can be mistakenly classified as well-differentiated liposarcomas. Cytogenetic information has been reported for 10 cases, showing that these tumors are characterized by structural rearrangements involving 11q13. Previous fluorescence in situ hybridization (FISH) studies revealed consistent and sometimes cryptic losses of the MEN1 region in 11q13.1. Here, we describe the molecular cytogenetic analysis of two new hibernoma cases. Both tumors showed complex rearrangements, simultaneously including translocations, inversions, and deletions affecting the pair of chromosomes 11. The translocation partners were chromosome 5 in one case and chromosomes 16 and 22 in the other case. The 11q13 region was concomitantly rearranged on both chromosomes 11. FISH studies revealed large heterozygous deletions within the 11q13 band, from 11q13.1 to 11q13.5. Genes such as PYGM, MEN1, CCND1, FGF3, ARIX, and GARP were deleted, showing that the size of the 11q13 altered region was larger than previously reported. Furthermore, both tumors had breakpoints in 11q13.5, one of them in the immediate proximity of the GARP gene. Our results suggest that rearrangements of GARP or a neighboring gene may be important for the pathogenesis of hibernomas.

Clustering of deletions on chromosome 13 in benign and low-malignant lipomatous tumors

Deletions and structural rearrangements of the long arm of chromosome 13 are frequently observed in benign and low-malignant lipomatous tumors, but nothing is known about their molecular genetic consequences. We assessed the karyotypes of 40 new and 22 previously published cases (35 ordinary lipomas, 15 spindle cell/pleomorphic lipomas, 2 myxolipomas, 1 angiomyxolipoma and 9 atypical lipomatous tumors) with chromosome 13-abnormalities, and found bands 13q12-22 to be frequently affected. Twenty-seven cases with structural abnormalities within this region were selected for breakpoint and deletion mapping by metaphase fluorescence in situ hybridization (FISH), using a set of 20 probes. Deletions were found in 23 of 27 cases. The remaining 4 cases had seemingly balanced rearrangements. The breakpoints were scattered but clustered to band 13q14, and in all cases with unbalanced abnormalities, a limited region within band 13q14 was partially or completely deleted. A deletion within band 13q14 was found together with a breakpoint on the other homologue in 5 cases, 4 of which could be tested further with regard to the status of the retinoblastoma (RB1)-gene. In all 4 cases, only 1 copy of the gene was deleted. In addition to the breaks and deletions in the vicinity of the RB1-locus, several other regions of 13q were recurrently affected, e.g., in the vicinity of the hereditary breast cancer (BRCA2; 13q12)- and lipoma HMGIC fusion partner (LHFP; 13q13)- genes. Our findings strongly indicate that deletion of a limited region (approximately 2.5 Mbp) within 13q14, distal to the RB1-locus, is of importance in the development of a subset of lipomatous tumors.

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.

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.

Unique cytological features and chromosome aberrations in chondroid lipoma: a case report based on fine-needle aspiration cytology, histopathology, electron microscopy, chromosome banding, and molecular cytogenetics

Chondroid lipoma is a rare, benign tumor that may mimic soft-tissue sarcoma clinically. Its histopathologic features may resemble hibernoma, myxoid liposarcoma, myxoid chondrosarcoma, and other lipomatous or chondroid neoplasms. In this study, a chondroid lipoma was analyzed by fine-needle aspiration cytology, histopathology, electron microscopy, chromosome banding, and metaphase fluorescence in situ hybridization. The results demonstrate that chondroid lipoma exhibits a characteristic pattern by fine-needle aspiration cytology, including a mixture of benign adipose tissue with lipoblastlike cells, and chondroblastlike cells with a fibrochondroid matrix. Cytogenetically, a three-way rearrangement between chromosomes 1, 2, and 5 was found, together with an 11;16 translocation with a breakpoint in 11q13, approximately 1 Mb proximal to the MEN1 region shown to be rearranged frequently in hibernoma. The presence of a karyotype of low complexity, but without any of the genetic aberrations characteristic for other types of soft-tissue tumors, indicate that chondroid lipoma develops along a unique pathogenetic pathway.

Hibernomas are characterized by homozygous deletions in the multiple endocrine neoplasia type I region. Metaphase fluorescence in situ hybridization reveals complex rearrangements not detected by conventional cytogenetics

Hibernomas are benign tumors of brown fat, frequently characterized by aberrations of chromosome band 11q13. In this study, the chromosome 11 changes in five hibernomas were analyzed in detail by metaphase fluorescence in situ hybridization. In all cases, complex rearrangements leading to loss of chromosome 11 material were found. Deletions were present not only in those chromosomes that were shown to be rearranged by G-banding, but in four cases also in the ostensibly normal homologues, resulting in homozygous loss of several loci. Among these, the gene for multiple endocrine neoplasia type I (MEN1) was most frequently deleted. In addition to the MEN1 deletions, heterozygous loss of a second region, approximately 3 Mb distal to MEN1, was found in all five cases, adding to previous evidence for a second tumor suppressor locus in 11q13.

Mediastinal hibernoma

A 46-year-old asymptomatic male was detected to have a posterior mediastinal mass on a routine check-up. He underwent thoracotomy to remove the mass, which was found to be a hibernoma. The mediastinum is an extremely rare site for an even rarer tumor like the hibernoma. An additional unique feature was the very large tumor size despite which the patient was asymptomatic. Imaging studies are not helpful in revealing its clinically indeterminate nature, hence a surgical specimen is necessary to establish the correct diagnosis. Total excision is advocated for cure, as there is no known malignant potential.

Constitutional balanced translocations in alveolar rhabdomyosarcoma

Chromosomal analysis of tumor tissue from two children with alveolar rhabdomyosarcoma revealed t(1;5)(q32;q31) and t(1;22)(q21;q11.2) in all metaphases examined, respectively. Peripheral blood lymphocytes carried the same cytogenetic abnormality as that of the tumor cells in both patients. Parental lymphocytes were karyotypically normal in the patient with t(1;22), indicating a de novo constitutional translocation, but t(1;5) was paternally inherited in the other patient. The presence of constitutional translocations in these two children might have contributed to the development of alveolar rhabdomyosarcoma.

Comparison of chromosomal patterns with clinical features in 165 lipomas: a report of the CHAMP study group

Soft tissue lipomatous tumors are morphologically heterogeneous. Various morphologic features are associated with specific chromosomal patterns and clinical features such as age, sex, and tumor site, location, and size. Simple lipomas are known to be karyotypically heterogeneous, but this has not been correlated with clinicopathological features. In 165 cases of solitary soft tissue lipoma, short-term cultures were analyzed cytogenetically. The karyotypes were divided into the following groups: normal karyotype; 12q13-15 aberrations; 6p rearrangements; 13q rearrangements, 8q11-13 aberrations; ring or giant marker chromosomes or both; other aberrations. The tumors were reexamined morphologically without knowledge of the karyotypic or clinical data. An abnormal chromosomal pattern was observed in 129 of 165 cases (78%): in 75 of 90 (83%) lipomas in the extremities and in 43 of 63 (68%) trunk wall lipomas. Chromosomal aberrations were present in 69 of 90 (77%) subcutaneous tumors and in 59 of 64 (80%) deep tumors. A normal karyotype was twice as frequent in tumors in patients under 30 years of age than in those from older individuals (6 of 16 vs. 30 of 149, 40% resp. 20%). Apart from the finding that normal karyotypes were more common in patients younger than 30 years, there was no significant association between cytogenetic pattern and patient sex or age or tumor localization, size, or depth. The pathogenetic basis and clinicopathologic relevance (if any) of the cytogenetic subtypes among benign lipomas remain unexplained.

Cervicomediastinal hibernoma

Hibernoma is a benign soft-tissue tumor, derived from the brown fat, that often presents as a painless, slow-growing mass. About 100 cases of hibernomas have been reported in the world literature. Seven cases of intrathoracic hibernoma are reported, of which only 1 was located in the mediastinal region. That tumor was an intramediastinal hibernoma with a cervicomediastinal location, which was excised through an extended left supraclavicular incision without the necessity to perform a sternotomy. No recurrence was evident after 18 months.

Combined morphologic and karyotypic study of 59 atypical lipomatous tumors. Evaluation of their relationship and differential diagnosis with other adipose tissue tumors (a report of the CHAMP Study Group)

Fifty-nine cases of atypical lipomatous tumors (ALT) of soft tissue (atypical lipomas, well-differentiated liposarcomas) were studied morphologically and cytogenetically as part of an international collaborative study. Forty-nine cases were deeply seated (including retroperitoneum), and 10 were superficial. Clonal chromosomal abnormalities were found in 55 cases (93%). Supernumerary ring or giant marker chromosomes (RGCs), the sole consistent alteration, were found in 37 ALTs (63%). They were more common in tumors that were large (p < 0.001), deeply seated (p < 0.005), that contained lipoblasts (p < 0.05), and that had marked cytologic atypia (p < 0.05). In a relatively short follow-up period (average, 3 years), only three of 59 cases recurred, one resulting in the patient's death. All three cases had RGCs. Also, five of the six cases that underwent dedifferentiation had RGCs, indicating that RGCs are associated not only with low-grade malignant behavior (in the form of local recurrence) but also with the potential for tumor progression. When the karyotypic profile of ALT was compared with that of 233 other types of adipose tissue tumors similarly analyzed by the authors, a statistically highly significant correlation (p < 0.0001) was found between ALT and RGCs. These results support the existence of ALT as a distinct tumor subtype that is different from ordinary lipoma and from spindle or pleomorphic lipoma, albeit histogenetically closely related to them. It also supports the proposed pathogenetic link between ALT and dedifferentiated liposarcoma. The association between chromosomal and morphologic findings indicates the potential role of karyotypic analysis in the differential diagnosis of ALT with ordinary lipoma, spindle or pleomorphic lipoma, hibernoma, and myxoid liposarcoma.

Lipomatous tumours of soft tissues: an update

This review summarizes the clinicopathological features of recently characterized variants of lipomatous tumours of soft tissue, attempts to deal with some difficult conceptual issues relating to adipocytic neoplasms and aims to provide an update on cytogenetic aspects of fatty tumours. Myolipoma is a rare benign neoplasm, occurring most frequently in adults in the deep soft tissue of the abdomen or retroperitoneum, and is composed of irregularly admixed mature adipose and smooth muscle tissues. Chondroid lipoma represents an unusual benign lesion occurring mainly in adult females subcutaneously or in deep soft tissue; it is easily mistaken for myxoid liposarcoma or extraskeletal myxoid chondrosarcoma. Spindle-cell liposarcoma is a variant of well-differentiated liposarcoma quite commonly found in subcutaneous tissue of the shoulder region and upper limbs and is composed of relatively bland-appearing spindle cells mixed with a well-differentiated liposarcomatous component. Recently there has been considerable debate about classification of lipomatous tumours. The term atypical lipoma was proposed for a group of well-differentiated non-metastasizing liposarcomas arising in surgically amenable soft tissues and for deep-seated atypical adipocytic neoplasms that show variation in adipocytic size and atypical stromal cells but lack lipoblasts. However, these neoplasms recur repeatedly and may dedifferentiate and thereby acquire metastatic potential. We use the diagnosis atypical lipoma with caution and propose to use the terms well-differentiated liposarcoma and atypical lipoma interchangeably. The relationship between myxoid and round-cell liposarcoma, which constitutes the morphological spectrum of a single entity, has been clarified but there remain considerable problems in defining likely clinical behaviour. The recent advances in cytogenetic characterization and classification of lipomatous tumours, which is already proving to be of diagnostic importance, are reviewed, and the genetic importance of the distinct chromosomal translocation in myxoid/round cell liposarcoma is briefly discussed.

A new cytogenetic subgroup in lipomas: loss of chromosome 16 material in spindle cell and pleomorphic lipomas

Six spindle cell lipomas and two pleomorphic lipomas were analyzed cytogenetically. One spindle cell lipoma had a supernumerary ring chromosome as the sole anomaly. The other five spindle cell lipomas and both pleomorphic lipomas had hypodiploid stemlines with monosomy 16 or unbalanced aberrations leading to loss of 16q13-qter, a feature distinguishing these lipoma subtypes from other benign and borderline adipose tissue tumor histotypes. unbalanced aberrations of chromosomes 13 and 10 were found in five and three cases respectively; 13q12 was lost in all of these cases, whereas there was no common deleted segment in chromosome 10. No aberrations involving 12q13-15, which are frequent in typical lipomas, were found. Both pleomorphic lipomas, but none of the spindle cell lipomas, had hypotetraploid sidelines, multiple nonclonal aberrations, and telomeric associations. The present findings reveal a new cytogenetic/histopathological association in adipose tissue tumors.