Lipoma-like hibernoma of the breast: A case report and literature review

Abstract

Hibernomas are uncommon and benign tumors made up of brown fat cells. These tumors are typically found in the thigh, axillae, shoulder, back, neck, thorax, arm, and retroperitoneum. There are 4 histological variants of hibernomas, including the typical pattern, myxoid, lipoma-like, and spindle cell variant. The lipoma-like variant is characterized by numerous univacuolated adipocytic cells with intermingled multivacuolated granular cells. It is worth noting that lipoma-like hibernoma in the breast is infrequent.

In this case, we present a 72-year-old woman with a history of moderately differentiated cholangiocarcinoma, obesity, and no family history of breast cancer. She consulted for a mass sensation in her right breast that had been present for a year. The mass was not painful and showed no inflammation or nipple discharge. Upon physical examination, a palpable 14 cm mass was identified, occupying the 2 internal quadrants and causing deformation of the surface of the right breast. Imaging studies indicated a solid mass in the lower-inner quadrant of the right breast, which was oval-shaped, well-defined, and displayed internal vascularization. Initially, a diagnosis of low-grade liposarcoma was considered, leading to a core needle biopsy guided by ultrasound. However, the histopathology study revealed a lipoma-like hibernoma, an exceedingly rare benign lesion. Lipoma-like hibernoma can present as a palpable mass or may be incidentally discovered. It should be considered in the differential diagnosis of any lesion containing fatty content. Imaging methods may suggest its presence, but histopathology confirms the diagnosis and its accuracy prevents needless overtreatment.

Introduction

Hibernomas are uncommon, benign neoplasms composed of brown fat cells derived from fetal remnants that persist into adulthood [1]. They are named due to their similarities with brown adipose tissue found in hibernating animals [2].

Brown fat has endocrine and thermoregulatory functions and is more prevalent in newborns. As individuals age, brown fat becomes involute and is replaced by white fat cells. In adulthood, deposits of brown fat persist around the kidneys, adrenal glands, aorta, mediastinum, and neck [3], [4], [5]. Hibernomas are generally found in the thigh, axilla, shoulder, back, neck, chest, arm, and retroperitoneum [6]. They have 4 histological variants, including the typical pattern (82%), myxoid (9%), lipoma-like (7%), and the spindle cell variant (2%) [7]; the lipoma-like variant exhibits numerous univacuolated adipocytes mixed with multivacuolated cells with granular aspect [7].

Notably, there have been only 5 documented cases of pure hibernomas in the literature. It is crucial to highlight that no cases of lipoma-like hibernoma in the breast have been reported, making this location extremely rare. Previous case reports have solely documented occurrences in anatomical areas like the thigh, left arm, and left flank. In this context, we present the case of a woman with a medical history of cholangiocarcinoma who developed a mass in her right breast. This mass was subsequently diagnosed through histology as a lipoma-like hibernoma.

Case report

A 72-year-old woman who had a history of obesity and hypertension was recently diagnosed with moderately differentiated cholangiocarcinoma, and had no family history of breast cancer presented with a painless mass in her right breast that had been there for a year. Notably, the patient could not recall her last breast imaging. Physical examination revealed no signs of inflammation or nipple discharge. Initially, she sought medical attention at another healthcare facility. Based on the clinical assessment, she underwent a breast ultrasound, which showed an image measuring 12 × 4 cm that appeared to be consistent with a lipoma (BI-RADS 1). Consequently, considering her existing medical condition, she was referred for further evaluation with breast magnetic resonance imaging (MRI) and chest computed tomography (CT).

Chest CT

A solid mass measuring 10 × 6 cm with a slightly higher density than fatty tissue was observed in the lower-inner quadrant of the right breast. It displayed an oval shape, well-defined borders, and internal vascularity (Fig. 1).

Fig. 1.

Chest computed tomography with contrast: A solid mass measuring 10 × 6 cm, with slight and heterogeneous postcontrast enhancement (White arrow), located in the lower inner quadrant of the right breast.

Breast MRI

The oval and well-defined mass exhibited signal intensity similar to subcutaneous cellular tissue in all imaging sequences. Gadolinium-based MRI contrast agent is administered intravenously; mild, delayed, and peripheral enhancement leads to initial suspicion of a low-grade liposarcoma (Fig. 2., Fig. 3, Fig. 4). Consequently, a core needle biopsy guided by ultrasound was performed (Fig. 5).

Fig. 2.

(A) Breast MRI: Axial image, T1 sequence with fat saturation. (B) Axial image, postcontrast T1 sequence after 110 seconds presents mild, late, and peripheral enhancement. Despite being considered a benign mass, because it was a palpable mass with an increase in size, it was classified as BI-RADS 4, and a biopsy was indicated for its definitive characterization.

Fig. 3.

Oval mass measuring 8.1 × 7.3 × 11 cm (volume of 332 mL) (white arrow) is clearly defined in the right breast, displaying a consistent response akin to fat (yellow arrow) in various imaging sequences. (A) Coronal T1-weighted MRI, isointense mass to fat tissue. (B) Coronal T2-weighted MRI, isointense mass to fat tissue. (C) Axial STIR, isointense mass to fat tissue with some hyperintense areas.

Fig. 4.

Breast positive enhancement integral (PEI) color maps. (A) The mass presents slight peripheral enhancement. (B, C) Upward dynamic behavior in the peripheral section (Line and color-coded curve: Yellow), concerning the parenchyma (Line and color-coded curve: Orange) and center of the mass (Line and color-coded curve: Pink).

Fig. 5.

Breast ultrasound previous percutaneous image-guided core biopsy revealed a oval-shaped mass, exhibiting similar characteristics compared to the fatty tissue.

The histological study revealed mature adipose tissue with slight eosinophilia and cytoplasmic vacuolization without identified nuclear atypia or prominent capillaries, consistent with hibernoma lipoma-like (Fig. 6).

Fig. 6.

(A and B) H&E staining, 4x and 10x: The lesion is made up of polygonal brown fat cells, accompanied by stromal cells in the background. (C and D) H&E staining, 40x: Presence of fat and pale brown cells with eosinophilic characteristics, displaying multivacuolated granular cytoplasm and a small central nucleus.

Due to the benign nature of the findings, a conservative approach was chosen to prioritize the treatment of cholangiocarcinoma.

Therefore, the patient began chemotherapy with cisplatin plus gemcitabine, but unfortunately, her condition worsened after 5 months of treatment. The oncology team then switched to a combination of paclitaxel and gemcitabine. However, after 7 months, she succumbed to her pre-existing oncological condition.

Discussion

Hibernoma is a rare soft tissue tumor that originates in brown fat and represents 1.6% of all lipomatous neoplasms [1]. Its initial description dates back to 1906 when Merkel referred to it as a pseudo-lipoma [8]. The term “hibernoma” was introduced in 1914 by Gery, who noted the morphologic resemblance between these tumors and hibernating glands in animals [9]. Typically found in adults, hibernomas are most prevalent during the third decade of life and are more frequently seen in women [10]. These tumors are usually incidental findings, presenting as painless, mobile, firm, slow-growing, subcutaneous masses. Common sites for their occurrence include the axillae, neck, thorax, shoulders, and extremities [5].

Hibernomas can have 4 histologic variants, including the typical pattern (82%), myxoid (9%), lipoma-like (7%), and spindle cell variant (2%) [7]. The lipoma-like variant exhibits numerous univacuolated adipocytic cells with interspersed multivacuolated granular cells [7]. This less common lipoma-like hibernoma variant was identified in 7% of hibernomas within a comprehensive series of 170 tumors (12/170) [6]. In 2001, Furlong et al. described the typical histologic features of hibernomas, defining the 4 previously mentioned variants. They also highlighted that the lipoma-like subtype is the most challenging for pathologists due to occasional multivacuolated adipocytic cells that mimic lipoblasts [6,11]. Interestingly, 23% of referral pathologists considered this diagnosis when examining lipoma-like hibernomas [6]. However, lipoma-like hibernomas lack significant atypia, deeply scalloped nuclei of lipoblasts, nuclear hyperchromasia, and significant fibrous septa. Furthermore, cells within lipoma-like hibernomas exhibit sparsely eosinophilic finely multivacuolated cytoplasm and do not exhibit recurrence following complete excision. Unlike well-differentiated atypical lipomas/liposarcomas, lipoma-like hibernomas do not undergo dedifferentiation into more aggressive forms or metastasize [12].

Brown fatty tissue within the breast parenchyma is uncommon, but it can be observed in composite lesions that contain some brown fat content, such as adenohibernomas and hamartomas of the breast, or in pure lesions like hibernomas. However, only 5 cases of pure hibernoma have been reported in the literature (Table 1) [1,5,[13], [14], [15]]. It is worth noting that there have been no reported instances of lipoma-like hibernomas occurring in the breast. Case reports have only documented occurrences in anatomical regions such as the thigh, left arm, and left flank [11,12,16].

Table 1.

Summary.

Journal article	Medical history	Case	Diagnostic approach	Treatment
Gardner-Thorpe et al. [15].	Breastfeeding up to 3 months before.	29 y-old female	US Pathology	Surgical resection
Colville et al. [14].	Family history of breast cancer.	39 y-old female	Mammography US Biopsy	Conservative management
Martini et al. [5].	Ovarian cancer.	42 y-old female	US MRI PET-CT Biopsy	Conservative management
Padilla-Rodriguez [13].	Family history of breast cancer.	37 y-old female	US Pathology	Surgical resection
Neves et al. [1].	None	42 y-old female	Mammography US Biopsy	Partial mastectomy

MRI, magnetic resonance imaging; PET-CT, positron emission tomography and a computed tomography scan; US, Ultrasound.

Regarding imaging diagnosis, hibernomas typically appear as well-defined, echogenic masses with internal vascularity on ultrasound [5,17]. On plain CT, the lesion is generally well-demarcated, heterogeneous, and hypodense, often with some intratumoral septa. After administering a contrast medium, hibernomas usually exhibit diffuse enhancement [2]. In positron emission tomography and computed tomography (PET-CT) scans, breast hibernomas show hypermetabolic activity. On MRI, hibernomas have an intermediate intensity between muscle and subcutaneous fat due to their high mitochondrial content. Furthermore, they exhibit contrast medium-enhanced intensity due to their robust vascularization. In sequences utilizing fat suppression, a signal intensity decrease is attributed to their fat content [2,5,18]. The differential diagnosis for hibernomas includes fat necrosis, angiolipoma, giant cell tumor, rhabdomyosarcoma in children, and atypical lipoma/well-differentiated liposarcoma [2,7].

Angiographic studies reveal the tumor's high vascularity, which is a characteristic feature of hibernomas. Some articles propose a hyperintense mass in T1 with pronounced internal vascularization could indicate a hibernoma diagnosis [19]. However, distinguishing a hibernoma solely based on imaging findings from other benign or malignant lesions might not be feasible in most cases.

Therefore, a histological examination must confirm the hibernoma diagnosis and its specific variants. Brown fat adipocytes are multinucleated cells containing numerous mitochondria, and hibernomas are heavily vascularized [2,5]. Imaging also aids in planning hibernoma resection; MRI angiography enables clear identification of the tumor's blood supply, thereby enhancing the precision of surgical procedures. Additionally, the role of interventional radiology with intravascular embolization has been suggested as a treatment approach for these lesions. However, due to the rarity of this condition, limited studies support this therapeutic option [2].

Due to its benign nature, the typical approach to treating hibernoma involves local excision. In this case, considering the patient's medical history and treatment priorities, it was decided to focus on addressing the malignant neoplasm (cholangiocarcinoma) before considering any intervention for the breast mass. Conservative management has also been reported in the literature for breast hibernomas when malignancy is ruled out, and the lesion is asymptomatic [5,14].

Lipoma-like hibernoma is an extremely uncommon benign lesion. It might become noticeable as a detectable mass or be found accidentally, but it should be considered when evaluating any growth containing fatty tissue. While imaging techniques might provide suggestive indicators, they lack distinctiveness to distinguish it definitively from other growths, whether benign or malignant. Hence, the definitive diagnosis relies on histopathology, and an accurate diagnosis can avert unnecessary treatment. Unlike atypical lipomatous tumors, which often reappear and can progress to dedifferentiated liposarcoma, hibernomas are benign tumors that do not reappear following complete local removal.

Data sharing statement

The authors can provide the relevant anonymized patient-level data upon request.

Availability of data and materials

Not applicable.

Authors' contributions

DN: Project administration, writing, review & editing. ER: Conceptualization - writing - original draft. HE: Conceptualization - writing - original draft. LS: Review & editing. JM: Review, writing & editing.

Patient consent

We are pleased to inform you that we have obtained the written informed consent to publish our case report in Radiology Case Reports. This confirmation acknowledges that we had permission for the publication, adhering to the guidelines and principles of patient confidentiality and privacy.