Intraosseous hibernoma

Intraosseous hibernoma mimicking sclerotic bone metastasis-a case report

Intraosseous hibernoma is an uncommon presentation of brown adipose tissue benign tumors. Imaging differential diagnoses include bone island, sclerotic metastasis, lymphoma, hemangioma, and sclerotic myeloma. In this report, a 72-year-old patient presented with right hip pain following a fall injury, leading to an extensive diagnostic workup. Initial CT of the pelvis without contrast suggested potential sclerotic metastatic disease. MRI findings could not be definitive. Further assessment with CT-guided biopsy and S-100 immunohistochemical staining confirmed a rare diagnosis of intraosseous hibernoma. This case describes multimodality imaging characteristics of a rare intraosseous hibernoma with discussion of imaging features of differential diagnostic considerations of related benign and malignant bone lesions.

Intraosseous Hibernoma: A Rare Entity in Orthopedics With Peculiar Radiological Features

Intraosseous hibernoma is a rare benign bone tumor derived from brown fat. It is typically found in the axial skeleton and is more commonly observed in women. It can manifest as a painful lesion or may be incidentally discovered. Intraosseous hibernoma often presents as a sclerotic lesion, although it can also manifest as a lytic lesion. Due to its varied radiographic appearance, it should be considered in the differential diagnosis of bone lesions as it can mimic metastatic lesions as well as other sclerotic and lytic bone lesions. Therefore, obtaining a biopsy of the lesion is crucial for an accurate diagnosis. In this report, we present the clinical, radiological, and histopathological findings of two cases of intraosseous hibernoma and provide a concise overview based on a review of the literature.

Benign incidental do-not-touch bone lesions

Benign bone lesions may occasionally be incidentally detected on radiographs and are also increasingly found on CT or MRI performed for other clinical indications. Although mostly asymptomatic or associated with minor symptoms, these lesions may simulate true pathological lesions, causing problems in diagnosis. For instance, asymptomatic benign bone lesions can be misinterpreted as metastasis when incidentally encountered in a patient with known cancer. Recognising these entities as "do-not-touch" lesions helps avoid unnecessary further investigation or harmful intervention. In this review, we highlight three groups of bone incidentalomas found in adults, namely: osteolytic lesions, osteoblastic lesions, and bone protuberances. We aim to review the key imaging features of selected common and less common conditions in these three groups, so as to help radiologists confidently identify these benign do-not-touch lesions and to distinguish them from more sinister pathological lesions.

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.

Intraosseous hibernoma of the appendicular skeleton

Hibernomas are rare lipomatous tumors composed of brown adipocytes. The relative paucity of reported cases involving the bones accounts for the poor understanding of this entity, which is known to affect almost exclusively the axial skeleton. We present a case of intraosseous hibernoma of the humerus, which was found incidentally in a 52-year-old woman and initially misinterpreted as a cartilaginous tumor on magnetic resonance imaging (MRI). The lesion was unchanged in size and morphology at short interval follow-up but increased in size during follow-up over 6 years with an 11 mm increase in the largest diameter. Given the patient's concerns and lesion growth, curettage was performed. Pathology analysis revealed brown fat in keeping with the diagnosis of intraosseous hibernoma. Radiological and pathological findings and pitfalls are herein highlighted to enforce knowledge on this lesion rarely affecting the long bones. Radiologists should think of intraosseous hibernoma if they come across a sclerotic lesion on X-ray or computed tomography, which contains macroscopic fat and shows enhancement on contrast-enhanced MRI. In addition, an intraosseous hibernoma may be picked up incidentally on positron emission tomography-computed tomography due to high fluorodeoxyglucose avidity.

Miscellaneous Tumours of Bone

There are several tumors that do not easily fit into the specific classifications of primary bone tumors. These tumors include tumors of neural, adipocytic, smooth muscle lineage, and some of uncertain lineage. The pathologic features with recent updates of these tumors are discussed here.

Grossing and reporting of bone tumor specimens in surgical oncology: Rationale with current evidence and recent updates

Primary bone tumors, including sarcomas, are rare tumors and require a multidisciplinary approach, including inputs from a radiologist, pathologist, medical oncologist, and surgical and radiation oncologist, for optimal management. Over the years, there has been a paradigm shift toward the treatment of bone sarcomas, from radical resections to conservative surgical procedures, to achieve improved clinical and functional outcomes. This has led to receiving and processing various types of specimens in orthopedic oncopathology. Grossing and reporting of bone tumors require expertise. This review focuses upon the types of biopsies, grossing techniques of various specimens in orthopedic oncology and reporting, with rationale and recommendations from pathologists, actively involved in reporting and pursuing a special interest in bone tumors, based on current evidence. Furthermore, there is a section on some of the updates in the diagnosis of bone tumors, based on the recent fifth edition of the World Health Organization classification of tumors of soft tissues and bone.

The 2020 WHO Classification of Tumors of Bone: An Updated Review

Bone tumors are a rare and heterogeneous group of neoplasms that occur in the bone. The diversity and considerable morphologic overlap of bone tumors with other mesenchymal and nonmesenchymal bone lesions can complicate diagnosis. Accurate histologic diagnosis is crucial for appropriate management and prognostication. Since the publication of the fourth edition of the World Health Organization (WHO) classification of tumors of soft tissue and bone in 2013, significant advances have been made in our understanding of bone tumor molecular biology, classification, prognostication, and treatment. Detection of tumor-specific molecular alterations can facilitate the accurate diagnosis of histologically challenging cases. The fifth edition of the 2020 WHO classification of tumors of soft tissue and bone tumors provides an updated classification scheme and essential diagnostic criteria for bone tumors. Herein, we summarize these updates, focusing on major changes in each category of bone tumor, the newly described tumor entities and subtypes of existing tumor types, and newly described molecular and genetic data.

Sacral tumours and their mimics: pictorial review and diagnostic strategy

Sacral tumours encompass an extensive range of differential diagnosis. The clinical presentation is often non-specific, including neurological deficits and low back pain. Accurate diagnosis of sacral lesions is challenging and requires a comprehensive imaging strategy and robust knowledge on the imaging characteristics of different pathological processes. This review will provide an updated overview of the computed tomography (CT), magnetic resonance imaging (MRI), and integrated positron-emission tomography (PET)-CT features of some common and rare sacral tumours and their mimics. Several clinical scenarios with specific diagnostic considerations and treatment implications will be described.

Spinal Intraosseous Hibernoma: A Case Report and Review of Literature

Hibernoma is a rare benign tumor that arises from vestiges of brown fat. Spinal intraosseous hibernoma has only recently been described in the literature, and only 12 cases have been reported to date due to its extreme rarity. Here, we report the case of a patient who was incidentally diagnosed with an intraosseous hibernoma in the thoracic spine, following a diverse imaging work-up and pathologic confirmation. We correlate the clinical presentation and imaging features of our case with those of previously reported cases during our review of the literature.

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.

Intraosseous hibernoma: a rare adipocytic bone tumour

Hibernoma is a benign adipose tumour that contains foetal brown fat cells. We report a case of hibernoma arising in the left ischium of a 65-year-old female with a past history of ovarian carcinoma. The patient presented with a relatively short history of left sacral/hip pain. Radiologically, the lesion, which was large (5 cm) and sclerotic, had been stable for a number of years. Histologically, it was composed mainly of plump cells with foamy, multivacuolated cytoplasm. These cells showed no reaction for epithelial, melanoma or leucocyte markers but expressed FABP4/aP2 and S100, indicating that they were brown fat cells. There was no mitotic activity or nuclear pleomorphism and the lesion was diagnosed as a benign intraosseous hibernoma (IOH). IOH is a recently identified benign adipocytic lesion that presents typically as a sclerotic bone lesion. It has characteristic morphological and immunophenotypic features and should be regarded as a discrete primary bone tumour that needs to be distinguished from metastatic carcinoma/melanoma, chondrosarcoma and metabolic storage diseases containing numerous foamy macrophages.

Intraosseous Hibernoma in the Sacrum of an Adult

Hibernoma is an uncommon lipomatous tumor composed of brown adipose cells that until recently has only ever been described in soft tissue locations. This report describes the histological features of a discrete lesion in the sacrum of an 84-year-old lady. Biopsy of this lesion demonstrated that it consisted predominantly of multivacuolated lipocytes with a morphological and immunohistochemical profile consistent with brown fat cells. The lesion was diagnosed as an intraosseous hibernoma. This is the 16th report in the English literature of a hibernoma occurring outside of a soft tissue location.

Brown adipose tissue and bone

Brown adipose tissue (BAT) is capable of transforming chemically stored energy, in the form of triglycerides, into heat. Recent studies have shown that metabolically active BAT is present in a large proportion of adult humans, where its activity correlates with a favorable metabolic status. Hence, the tissue is now regarded as an interesting target for therapies against obesity and associated diseases such as type 2 diabetes, the hypothesis being that an induction of BAT would be beneficial for these disease states. Apart from the association between BAT activity and a healthier metabolic status, later studies have also shown a positive correlation between BAT volume and both bone cross-sectional area and bone mineral density, suggesting that BAT might stimulate bone anabolism. The aim of this review is to give the reader a brief overview of the BAT research field and to summarize and discuss recent findings regarding BAT being a potential player in bone metabolism.

Intraosseous hibernoma: case report and tumor characterization

Intraosseous hibernoma is a rare finding that has only recently come to light in the literature. We report a case of intraosseous hibernoma in the sacrum identified as an incidental finding in a 40 year-old female with chronic lower back pain. The tumor was characterized with all routine imaging modalities. In the review of the literature we correlate the imaging findings with previously reported cases. With increasing number of radiologic investigations it is expected to discover more intraosseous hibernomas and the radiologists should consider intraosseous hibernoma as differential diagnosis of the sclerotic bone lesion.

Rare case of a radiographically occult sacral lesion detected on MRI presenting with intractable back pain

We report the imaging findings and histopathology of a rare case of sacral hibernoma in a female presenting with right buttock pain while sitting. The lesion was occult on radiographs and CT scan. A small, rounded right S2 lesion was hypointense on T₁ weighted images and hyperintense on short tau inversion-recovery images. It demonstrated homogeneous contrast enhancement. The lesion was biopsied, and histopathology revealed an intraosseous hibernoma composed of brown fat cells. Intraosseous hibernomas are rare and demonstrate non-specific imaging findings requiring biopsy for diagnosis, although most hibernomas are incidental and asymptomatic. Initial treatment with microwave ablation and cementoplasty improved the patient’s symptoms temporarily but cementoplasty caused radicular symptoms, and eventually, cement removal, bone curettage, grafting and sacral nerve root decompression were required for symptom remission.

Intraosseous hibernoma: a case report and review of the literature

STUDY DESIGN

A case report and a literature review are presented.

OBJECTIVE

To describe and review the clinical presentation and characteristic imaging and pathology findings of intraosseous hibernoma.

SUMMARY OF BACKGROUND DATA

Hibernomas are lesions of brown fat. Brown fat is typically found in newborn mammals and is rich in mitochondria, thus enabling its role in thermoregulation. It represents a small proportion of adult fat and is distinct from the more common "white fat." Rarely does a hibernoma occur within bone. To the authors' knowledge, 5 cases in all have been reported in the literature.

METHODS

We report the first case to our knowledge of an intraosseous hibernoma occurring within the lumbar spine as well as a review of the literature.

RESULTS

Characteristic findings from magnetic resonance studies include variable T1W signal relative to skeletal muscle and hyperintense signal on fluid-sensitive imaging. Computed tomography has consistently demonstrated a sclerotic lesion with variable definition. Pathologic findings include sheets of multivacuolated cells with centrally placed nuclei and numerous tiny surrounding cytoplasmic vacuoles overlying bony trabeculae.

CONCLUSION

Our review of the literature demonstrates that intraosseous hibernoma is most likely an incidental finding with a predilection for the lower extremities in middle-aged females.

LEVEL OF EVIDENCE

4.

Intraosseous hibernoma: characterization of five cases and literature review

OBJECTIVE

To describe the imaging and histopathological findings and provide an overview of a recently described and rare cause of bone sclerosis.

MATERIALS AND METHODS

Five cases of intra-osseous hibernoma of bone that presented over the last year. The imaging and histopathology is reviewed.

RESULTS

All cases were identified in asymptomatic middle-aged to elderly adults as incidental findings with bone sclerosis in the axial skeleton. MRI showed lesions that were T1 hypointense to subcutaneous fat and hyperintense to skeletal muscle and one showed contrast enhancement. Glucose avidity was demonstrated on FDGPET in both cases tested and isotope bone scan performed in three cases showed strong positivity in two, but uptake was inconspicuous in one case.

CONCLUSIONS

Intra-osseous hibernoma is a rare cause of sclerotic bone lesions, predominating in the axial skeleton of middle-aged and elderly adults. They have a non-aggressive appearance on CT and on MRI are T1 hypointense to subcutaneous fat and hyperintense to skeletal muscle. They are usually T2 hyperintense and may show peripheral contrast enhancement. They may show increased glucose avidity on FDGPET and may or may not be positive on isotope bone scans. We suspect that with ever-increasing use of a variety of imaging techniques, particularly in a setting of staging for malignant disease, more such cases will come to light. This diagnosis should be added to the differential diagnosis of sclerotic bone lesions.

Quantitative proton MR techniques for measuring fat

Accurate, precise and reliable techniques for the quantification of body and organ fat distributions are important tools in physiology research. They are critically needed in studies of obesity and diseases involving excess fat accumulation. Proton MR methods address this need by providing an array of relaxometry-based (T1, T2) and chemical shift-based approaches. These techniques can generate informative visualizations of regional and whole-body fat distributions, yield measurements of fat volumes within specific body depots and quantify fat accumulation in abdominal organs and muscles. MR methods are commonly used to investigate the role of fat in nutrition and metabolism, to measure the efficacy of short- and long-term dietary and exercise interventions, to study the implications of fat in organ steatosis and muscular dystrophies and to elucidate pathophysiological mechanisms in the context of obesity and its comorbidities. The purpose of this review is to provide a summary of mainstream MR strategies for fat quantification. The article succinctly describes the principles that differentiate water and fat proton signals, summarizes the advantages and limitations of various techniques and offers a few illustrative examples. The article also highlights recent efforts in the MR of brown adipose tissue and concludes by briefly discussing some future research directions.

MRI detection of brown adipose tissue with low fat content in newborns with hypothermia

PURPOSE

To report the observation of brown adipose tissue (BAT) with low fat content in neonates with hypoxic-ischemic encephalopathy (HIE) after they have undergone hypothermia therapy.

MATERIALS AND METHODS

The local ethics committee approved the imaging study. Ten HIE neonates (3 males, 7 females, age range: 2-3days) were studied on a 3-T MRI system using a low-flip-angle (3°) six-echo proton-density-weighted chemical-shift-encoded water-fat pulse sequence. Fat-signal fraction (FF) measurements of supraclavicular and interscapular (nape) BAT and adjacent subcutaneous white adipose tissues (WAT) were compared to those from five non-HIE neonates, two recruited for the present investigation and three from a previous study.

RESULTS

In HIE neonates, the FF range for the supraclavicular, interscapular, and subcutaneous regions was 10.3%-29.9%, 28.0%-57.9%, and 62.6%-88.0%, respectively. In non-HIE neonates, the values were 23.7%-42.2% (p=0.01), 45.4%-59.5% (p=0.06), and 67.8%-86.3% (p=0.38), respectively. On an individual basis, supraclavicular BAT FF was consistently the lowest, interscapular BAT values were higher, and subcutaneous WAT values were the highest (p<0.01).

CONCLUSION

We speculate that hypothermia therapy in HIE neonates likely promotes BAT-mediated non-shivering thermogenesis, which subsequently leads to a depletion of the tissue's intracellular fat stores. We believe that this is consequently reflected in lower FF values, particularly in the supraclavicular BAT depot, in contrast to non-HIE neonates.

Intraosseous hibernoma: a potential mimic of metastatic carcinoma

Intraosseous hibernoma is a rare benign bone tumor, with only 3 cases reported in English literature. In this report, we describe a 50-year-old woman with a history of stage IIB breast cancer and posterolateral right hip pain. Imaging studies showed a sclerotic lesion in the right ilium, which was biopsied and showed mildly thickened bone trabeculae and multivacuolated brown fat cells replacing the normal white fat and hematopoietic elements, diagnostic of intraosseous hibernoma.