Hibernoma of the axillary region: a rare benign adipocytic tumor

Abstract

Hibernoma is a rare benign tumor considered to arise from remnants of fetal brown adipose tissue. It tends to occur in sites where brown fat persists beyond fetal life, such as the interscapular region, but can occur in sites where brown fat is usually absent in adults. Clinicallywell, hibernomas are slow-growing, asymptomatic tumors. However, unlike lipomas, MRI findings sometimes mislead clinicians to diagnose a malignant neoplasm. We describe a 63-year-old male with an axillary hibernoma involving the brachial neurovascular bundles and mimicking a well-differentiated liposarcoma, from which it should be distinguished.

An unusual presentation of a rare benign tumor in the head and neck: A review of hibernomas

“…Hibernomas are rare, slow‐growing, benign tumors comprised of multivacuolate brown adipocytes . Tumors composed of brown adipose tissue were first described by Merkel in 1906, and later termed “hibernomas” by Gery in 1914 . Hibernomas typically occur in the third or fourth decade of life as mobile, nontender, asymptomatic masses, with a slight female preponderance .…”

“…Patients typically present when the hibernoma becomes large enough to compress surrounding structures. Hibernomas are found, from most commonly to least commonly, on the thighs, torso, upper extremities, and the head and neck . It is difficult to distinguish a hibernoma from a malignant tumor by clinical exam alone.…”

“…A magnetic resonance imaging (MRI) scan may be more useful in diagnosing hibernomas, as increased signals on both T1‐ and T2‐weighted images may better characterize these masses; however, on T1, a hibernoma may be less intense than the surrounding subcutaneous fat . Nonlipoma subtypes tend to be heterogeneous, hypo‐ or isointense on MRI, with hypervascularity, and may interfere with identification of a hibernoma . Suppressing fat on MRI with intense gadolinium enhancement, particularly in areas of low signal, may identify any vasculature present in a hibernoma .…”

“…4 Tumors composed of brown adipose tissue were first described by Merkel in 1906, and later termed "hibernomas" by Gery in 1914. 5 Hibernomas typically occur in the third or fourth decade of life as mobile, nontender, asymptomatic masses, with a slight female preponderance. 2 Patients typically present when the hibernoma becomes large enough to compress surrounding structures.…”

Human adipose dynamics and metabolic health

“…150 Hibernomas most frequently occurs in people in their thirties and affects females more often than males. 151 The tumors are well encapsulated, soft, and mobile, and they are highly vascularized and composed of a mixture of brown and white adipocytes. A typical hibernoma contains more than 70% of brown adipocytes––the color varying from tan to brown.…”