Bilateral mammary hibernoma mimicking breast carcinoma: a diagnostic challenge

Abstract

We describe a 68-year-old postmenopausal woman who presented with a history of rapidly enlarging lumps in both breasts. Though the breast lumps appeared suspicious on ultrasonography, the core biopsy was reported to be benign. In view of the clinical and radiological suspicion of malignancy, she underwent a diagnostic excision of both the lumps, the histopathology was consistent with mammary hibernoma. To the best of the authors’ knowledge, this is the first report of a bilateral mammary hibernoma in an elderly postmenopausal woman. Given the clinical presentation, it is important to differentiate mammary hibernoma from carcinoma breast, which is a more common condition in this age group. However, preoperative diagnosis is challenging in view of the lack of definitive radiological and histological features. Although benign, hibernoma may have a propensity for local recurrence and, therefore, complete surgical excision remains the mainstay of treatment.

Background

The global burden of breast cancer is on the rise and in India, it is now the second most commonly diagnosed cancer in women.¹ Among the nonmodifiable risk factors for breast carcinoma, advanced age and delayed menopause are considered to play a prominent role.^{2 3} At the onset of menopause, the glandular tissue in the breast undergoes involution and gets replaced by stroma and fatty tissue.⁴ The significance of clinical breast examination in the diagnosis of various breast lesions cannot be over emphasised.⁵ Mammography and ultrasound aid in confirmation of the lesion once clinical diagnosis is established.⁶ The ‘triple’ test that comprises clinical, radiological and pathological examination further increases the diagnostic accuracy.⁷ The spectrum of benign breast diseases includes fibrocystic changes, periductal fibrosis, hamartomas, lipomas, phyllodes tumour and neurofibroma.⁸ Often, benign breast lesions can mimic malignancy on clinical and radiological evaluation.⁹ Core biopsy, although accurate, can be misleading if not sampled from the representative area further leading to diagnostic difficulties.¹⁰

In the current report, we describe a 68-year-old woman who presented with rapidly progressive lumps in both breasts. The clinical and radiological features were suggestive of carcinoma. However, following a diagnostic wide local excision, the lesions were reported to be mammary hibernoma. To the best of the authors’ knowledge, there have been no prior reports of bilateral mammary hibernoma mimicking a malignancy in an elderly postmenopausal woman. The clinical features, diagnostic challenges and management are discussed with a relevant review of literature.

Consent was obtained from the patient for her case to be reported.

Case report

A 68-year-old woman presented with a history of a mass in the left breast for 1 month. It was small to begin with but rapidly increased in size over the next 2 weeks. She did not report pain, nipple discharge or skin changes. She attained menarche at 12 years of age and had normal menstrual cycles till the age of 50 when she attained menopause. She has three children who were breastfed for 2 years each and her age at the first childbirth was 22 years. She had not taken any oral contraceptive pills or hormonal therapy. There was no history of Breats Cancer gene (BRCA) -associated cancers in her family.

On examination, there was a mass in the upper quadrant of the left breast measuring 8×5 cm. It was firm in consistency with irregular surface and restricted mobility. It was not fixed to the underlying pectoral muscles, chest wall or the overlying skin. There was a single, 1×1 cm, mobile, nontender left axillary node. The right breast and axilla were normal.

Investigations

With a clinical suspicion of a left breast carcinoma (cT3N1M0), she was further evaluated. Ultrasound of the breast revealed an encapsulated but irregular lesion in the left breast with increased vascularity. Although mammogram is the recommended imaging modality for the evaluation of a breast lump, it was not performed in this patient due to the lack of availability at our centre. The closest available facility was 4 hours away, and in view of the current pandemic with restrictions imposed due to the lockdown, it was not possible to avail the same. A core biopsy from the lesion showed stromal fibrosis with no nuclear atypia or increased mitosis. Although the core biopsy was negative for malignancy, in view of a high clinical and radiological suspicion, she was offered a diagnostic excision. Coincidently, during the waiting period for surgery, the patient noticed a similar lump in the right breast. It was in the upper quadrant measuring 3×2 cm with irregular surface, firm consistency and restricted mobility. There were no axillary nodes palpable in the right axilla.

Treatment

Following a discussion with the family, she consented to undergo wide local excision of bilateral breast lumps. Intraoperatively the lesions appeared fibrotic with surrounding desmoplastic reaction; however, there was no infiltration into the underlying muscles (figure 1). Her postoperative period was uneventful, and she was subsequently discharged.

Figure 1.

Intraop image of the excised mass from the right breast.

Outcome

The pathology of both the specimens showed diffuse areas of fibrosis and sheets of adipose cells showing fine multivacuolation of the cytoplasm interspersed with cells showing univacuolation. These monovacuolated cells had eccentric nuclei. There was no nuclear atypia or increased mitosis. The surrounding breast parenchyma was normal. These pathological features were consistent with mammary hibernoma (figure 2). On a 3 months review, the patient had no clinical evidence of local recurrence.

Figure 2.

Microscopic image of the specimen.

Discussion

Hibernoma is an uncommon soft tissue neoplasm arising from brown fat. Brown fat has both endocrine and thermoregulatory functions in the fetal and neonatal period, the amount of brown fat decreasing with the advancing age.^{11 12} The reason for development of hibernoma in adults is poorly understood. Hibernoma can arise at any region where the brown fat persists, the common sites include soft tissues of the thigh, shoulder, back, neck, chest, arm and retroperitoneum.^{12 13} Most patients present with asymptomatic, slow-growing, large subcutaneous masses.¹⁴ The radiological findings of hibernoma can be nonspecific. They are typically described as a well-defined echoic mass with vascularity on ultrasonography.¹⁵ MRI is more accurate in characterising these lesions including the location, shape and internal architecture suggesting a lipomatous tumour.¹¹ Pathologically, they are lobulated, well circumscribed, partially encapsulated neoplasms with yellowish brown rubbery texture. They contain multivacuolated cells with eosinophilic granular cytoplasm, peripheral nuclei and do not exhibit any nuclear atypia or increased mitoses.¹⁶

Mammary hibernoma is an exceedingly rare clinical entity with less than 10 cases reported in English literature so far.^{13 16–20} Of the cases reported, all the patients have been in the premenopausal category with unilateral involvement. Our case is peculiar as the patient is an elderly postmenopausal woman. The progression of symptoms was atypical as the masses rapidly increased in size over a short period of time, mimicking a malignancy. Moreover, there was involvement of both breasts.

Ultrasonography in our patient showed an encapsulated, but irregular mass with increased vascularity. As the diagnosis of breast carcinoma was entertained, this patient warranted bilateral mammogram; however, as discussed earlier, this was not performed due to logistic reasons. Although MRI could have given a better characterisation of the lesion, hibernomas cannot be promptly excluded from other soft tissue benign or malignant tumours like lipomas, liposarcomas, angiomyolipoma and haemangiomas.^{11 13} The role of Fluorodeoxyglucose - Positron emission tomography (FDG -PET) CT in differentiating a hibernoma from malignancy is unclear and is postulated to give a false-positive interpretation.²¹ Hence, imaging can only aid in ruling out a carcinoma but cannot be a sole diagnostic modality for mammary hibernoma.

The role of a core biopsy in diagnosing breast carcinoma is well known. However, in ruling out borderline benign lesions, the predictivity value of core biopsy is less accurate.²² Moreover, a core biopsy cannot conclusively diagnose hibernoma as similar features can be present in atypical fatty tumours and in myxoid liposarcomas.²³ Hence, a surgical excision becomes mandatory to establish the diagnosis of a hibernoma. Consequently, most of the cases of hibernoma are diagnosed in retrospect following the pathological examination of the excised surgical specimen. The core biopsy in our patient showed features of stromal fibrosis without evidence of malignancy. An image-guided biopsy from a better representative area could have been considered as an option to further characterise the pathology with the aid of relevant tumour markers.

There is a controversy regarding the surgical management of hibernoma. While few authors report local recurrence following incomplete excision (due to the location of the tumour making them incompletely resectable), others report no local recurrence despite incomplete excision.^{12 24 25} Hibernomas do not have a malignant potential, and hence, there is no role of neoadjuvant or adjuvant chemo or hormonal therapy.²⁶ Therefore, in view of their benign nature and few reports of local recurrence following incomplete excision, most authors recommend complete excision as the treatment for hibernomas.15 16 23 27

Learning points.

• Mammary hibernoma is an exceedingly rare clinical entity arising from remnants of brown fat.

• Although rare, it can affect the elderly postmenopausal women and can present with atypical features such as rapidly growing breast lumps leading to a suspicion of carcinoma.

• The preoperative diagnosis is challenging due to inconsistent radiological and histological features.

• Hibernomas may have a propensity for local recurrence if incompletely excised and, therefore, complete excision is the treatment of choice.