A rare case of hibernoma in the posterior thigh of an elderly patient: A surgical case report

Abstract

Introduction and importance

Hibernoma is a rare benign adipose tumor that arises from brown fat. Often misdiagnosed as liposarcoma, hibernomas require biopsy and histopathological examination for accurate diagnosis. This case report presents an unusual instance of hibernoma located in the posterior thigh of an elderly patient, emphasizing the diagnostic challenges and surgical management involved.

Case presentation

We report the case of Mrs. F.D., a 70-year-old woman with a history of ovarian cyst surgery 17 years prior, who presented with a mass in the posterior left thigh. The mass had been developing over two years and was hard, painless, and measured 7 × 12 cm. Initial imaging suggested liposarcoma; however, an MRI revealed a 9 × 19 cm mass with heterogeneous tissue characteristics. A surgical biopsy confirmed the diagnosis of hibernoma. The tumor was excised completely, and histological examination showed typical features of hibernoma.

Clinical discussion

Hibernomas, although rare, should be considered in the differential diagnosis of soft tissue masses. Imaging techniques such as MRI are essential, but definitive diagnosis relies on histopathology. Surgical excision is the treatment of choice, requiring meticulous technique to manage the hypervascular nature of the tumor.

Conclusion

This case underscores the importance of considering hibernoma in differential diagnoses and highlights the role of biopsy for accurate diagnosis. Complete surgical excision is crucial to prevent recurrence. Further research is needed to better understand the pathogenesis and optimal management of hibernomas.

Highlights

• •This case report documents a rare occurrence of hibernoma in the posterior thigh of an elderly patient, emphasizing the diagnostic challenges and importance of differential diagnosis from more aggressive tumors such as liposarcoma.
• •Highlights the clinical presentation of hibernoma, typically manifesting as a painless, slow-growing mass, which can be mistaken for other soft tissue tumors.
• •Illustrates the essential role of advanced imaging techniques, including MRI, in differentiating hibernoma from other soft tissue masses and guiding the surgical approach.
• •Details the surgical excision of the hibernoma, focusing on the necessity of complete removal to prevent recurrence and the management of the tumor's hypervascular nature.
• •Provides valuable insights into the histopathological features of hibernoma, characterized by multivacuolated cells with eosinophilic cytoplasm, crucial for confirming the diagnosis.
• •Contributes to the limited literature on hibernoma, especially in atypical presentations, and underscores the need for heightened clinical awareness and careful diagnostic evaluation in similar cases.

1. Introduction

Hibernoma is a rare benign tumor originating from brown adipose tissue, most commonly found in regions where brown fat is typically present. These tumors are predominantly observed in adults, with a higher incidence in the third to fifth decades of life, but can occur at any age. Due to their rarity and clinical presentation, hibernomas are frequently misdiagnosed as liposarcomas, leading to unnecessary alarm and extensive diagnostic procedures [1].

The clinical manifestation of hibernomas varies depending on their size and location. Patients often present with a painless, slow-growing mass that may go unnoticed for years. Imaging studies, including MRI and CT scans, are essential in differentiating hibernomas from other soft tissue tumors. CT scans, in particular, play a crucial role by providing detailed images of internal structures and helping to assess the vascularization and tissue characteristics of hibernomas. CT scans can reveal well-defined masses with specific fatty densities, thereby aiding in the precise differentiation from other lipomatous tumors such as liposarcomas. However, definitive diagnosis relies on histopathological examination following a biopsy [2].

This case report describes an unusual presentation of hibernoma in the posterior thigh of an elderly patient. The diagnosis was initially confounded with liposarcoma due to overlapping imaging characteristics. A thorough anatomical and pathological analysis was crucial in confirming the benign nature of the tumor and guiding the subsequent surgical management. This case underscores the importance of considering hibernoma in the differential diagnosis of soft tissue masses in elderly patients and highlights the role of biopsy in establishing an accurate diagnosis.

Our objective is to provide insights into the clinical presentation, diagnostic challenges, and surgical management of hibernoma, emphasizing the importance of awareness among clinicians to prevent misdiagnosis and ensure appropriate therapeutic strategies.

2. Methods

This case report outlines the assessment, diagnosis, and surgical management of an elderly patient with a hibernoma in the posterior thigh. The patient was treated at a specialized orthopedic center.

All medical procedures, including clinical evaluation, imaging, surgical intervention, and follow-up care, were conducted in accordance with established protocols at this center. The presentation of this case report adheres to the SCARE 2023 guidelines: updating consensus Surgical Case Report (SCARE) guidelines, ensuring a high standard of reporting in surgical case reports [20].

3. Case presentation

A 70-year-old woman, with a history of ovarian cyst surgery 17 years ago, presented with a mass in the posterior region of her left thigh that had been developing over a period of two years. She was afebrile and her general condition was preserved.

3.1. Clinical examination

Upon clinical examination, the mass was found to be hard, measuring approximately 7 × 12 cm, mobile relative to the superficial plane, but fixed relative to the deep plane. It was painless on palpation and exhibited collateral venous circulation without associated adenopathy or distal neurovascular compromise.

3.2. Imaging studies

• •Radiography: A standard radiograph centered on the mass showed no abnormalities.
• •Ultrasound: Soft tissue ultrasound revealed a heterogeneous, well-vascularized mass with a fatty appearance, raising suspicion for a liposarcoma.
• •MRI: MRI showed a 9 × 19 cm mass with heterogeneous tissue characteristics, areas of necrosis, and hemorrhagic foci. The tumor displaced the vascular bundle medially, exhibited a hypo-intense signal in T1, and a hyper-intense signal in T2 and on the fat-saturation sequence. Gadolinium enhancement was observed, particularly on the fat-saturation sequences (Fig. 1).

Fig. 1.

MRI section showing the tumor.

3.3. Diagnostic procedures

A surgical biopsy via a posterior approach was performed. The anatomo-pathological study confirmed the diagnosis of hibernoma.

3.4. Surgical treatment

The treatment involved excision of the tumor, removing the old scar tissue. The mass was brownish, richly vascularized, with a feeding pedicle. The tumor's intimate limits were related to the great sciatic nerve but did not encompass it (Fig. 2).

Fig. 2.

Per-operative image of the tumor and the great sciatic nerve.

3.5. Pathological findings

The anatomical-pathological examination of the excised mass revealed a yellowish, firm, and homogeneous formation with areas of mucoid reorganization. Histological examination showed adipose proliferation with predominantly monomorphic round or oval cells with eosinophilic multivacuolated cytoplasm. The nuclei were small, round, and central without atypia. Following the histological examination, an immunohistochemical study was performed to further confirm the diagnosis. The tumor cells were positive for S-100 protein, which is consistent with hibernoma (Fig. 3).

Fig. 3.

Post-operative image of the tumor.

4. Discussion

Hibernoma is a rare benign adipose tumor accounting for approximately 1.6 % of all adipose tumors [1]. It originates from immature fat cells (pre-adipocytes) derived from brown fat, which is predominantly present in the fetus [2]. In newborns, brown fat diminishes significantly by the second month of life. In adults, remnants are mainly found in areas such as the peri-esophagus, axillary fossa, posterior neck region, and scapulothoracic space [3,4].

Typically, hibernomas present between the ages of 20 and 40 years [5]. However, in this case, the patient's age and the tumor's location in the posterior thigh make it atypical. Another interesting aspect of our article is the tumor's hypervascular nature, which requires meticulous surgical technique to manage intraoperative bleeding. Clinically, hibernomas manifest as masses with a firmer consistency compared to lipomas [5]. These tumors are generally painless and exhibit a slow progression, often without any systemic symptoms. Doppler ultrasound typically reveals a homogeneous, encapsulated, hyperechoic, and richly vascularized mass [5].

Magnetic Resonance Imaging (MRI) is crucial for further characterization. Hibernomas appear as hyperintense on both T1 and T2-weighted sequences, with homogeneous patches of hypointensity within the tumor. Gadolinium-enhanced sequences show an increase in density, confirming the vascular nature of the mass [6]. Histological examination is necessary for definitive diagnosis, revealing a mix of multivacuolated round cells with central nuclei and eosinophilic cytoplasm [7]. Following histological examination, immunohistochemical studies were conducted, confirming the diagnosis with positive staining for S-100 protein, which is typical for hibernomas.

Differentiating hibernomas from other adipose tumors such as lipomas and liposarcomas is essential. Lipomas are the most common benign adipose tumors, characterized by mature white fat cells with a thin fibrous capsule. They typically present as soft, mobile, and painless masses. Unlike hibernomas, lipomas are hypovascular and do not show the brown fat characteristics on imaging or histology.

Liposarcomas, on the other hand, are malignant adipose tumors and present a greater diagnostic challenge due to their varied appearance. They often exhibit heterogeneous signals on MRI, with areas of necrosis and hemorrhage, which can mimic hibernomas. However, liposarcomas usually show more aggressive features such as rapid growth, invasion of surrounding tissues, and potential metastasis. Histologically, liposarcomas can be differentiated by the presence of atypical lipoblasts and a higher mitotic rate.

Other tumors with lipid components that need to be differentiated from hibernomas include angiolipomas, spindle cell lipomas, and pleomorphic lipomas. Angiolipomas are characterized by their vascular components and often present as painful lesions. Spindle cell lipomas and pleomorphic lipomas have distinct histological features with spindle-shaped cells and a mix of cell types, respectively, which help in their identification.

Chromosomal alterations have been implicated in hibernoma pathogenesis. Specifically, abnormalities in the q13 region of chromosome 11 near the multiple endocrine neoplasia type 1 (MEN 1) gene have been noted. Homozygous deletions of the MEN 1 tumor suppressor gene were found in a subset of cases, although a direct association with MEN 1 syndrome is not established. Cytogenetic studies suggest genetic rearrangements, including translocations involving the 11q13 region near the CNGB gene, playing a potential role in hibernoma development [8,9].

Hibernomas are classified histologically into four types: typical, lipoma-like, myxoid, and spindle cell hibernomas [11,12]. Differential diagnoses include angiolipoma, spindle cell lipoma, pleomorphic lipoma, lipoblastoma, elastofibroma, liposarcoma, clear cell sarcoma, and alveolar soft part sarcoma [[12], [13], [14], [15], [16]]. If the tumor had been malignant, the management approach would have included a combination of wide surgical excision with clear margins, possible adjuvant radiation therapy, and chemotherapy depending on the histological subtype of the sarcoma. Comprehensive staging with imaging and possibly PET scans would be essential to assess for metastasis and guide the treatment plan.

Surgical excision is the treatment of choice and must include the complete removal of the tumor along with its capsule to prevent recurrence [17,18]. Given the hypervascular nature of hibernomas, meticulous hemostasis is essential during surgery. Although the risk of malignant transformation is low, it is not negligible, with a solitary case reported in the literature [19].

5. Conclusion

This case report highlights the rarity and diagnostic challenges of hibernoma, particularly when it presents in atypical locations such as the posterior thigh in elderly patients. Despite its benign nature, hibernoma can be easily mistaken for more aggressive tumors like liposarcoma due to overlapping clinical and imaging features. This underscores the importance of thorough histopathological examination to achieve an accurate diagnosis.

Surgical excision remains the definitive treatment for hibernoma, necessitating complete removal of the tumor along with its capsule to prevent recurrence. The hypervascularity of the tumor requires meticulous surgical technique to ensure proper hemostasis. Although the risk of malignant transformation is low, vigilance is necessary given the potential for such rare occurrences.

This case contributes to the limited literature on hibernomas, especially in atypical presentations, and emphasizes the need for heightened clinical awareness and careful diagnostic evaluation. Further research is warranted to better understand the pathogenesis and optimal management strategies for hibernoma, thereby improving patient outcomes.

Consent

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Ethical approval

At our university hospital: CHU Ibn Rochd of Casablanca, it is established policy that case reports focusing on non-experimental medical or surgical treatment do not require ethical consent beyond the patient's informed consent prior to publication. This policy reflects our commitment to upholding ethical standards while recognizing the educational and informational value of sharing clinical experiences. Patient confidentiality and respect for their rights remain paramount; thus, informed consent is diligently obtained before any case details are published. This approach ensures that our case reports, while contributing valuable insights to the medical community, adhere strictly to ethical guidelines and respect patient autonomy

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contribution

All authors have contributed equally to all parts of the elaboration of this case series.

Guarantor

The grantors for this case series are the first author doctor Mohammed Bouhouche and the corresponding author doctor Lamris Mohamed Amine.

Provenance and peer review

Not commissioned, externally peer reviewed.

Conflict of interest statement

For all the authors, there's no financial or personal relationships with people or organosations that could inappropriately influence our work.