Alerts and Notices
SynopsisHibernomas, or pseudolipomas, are rare, benign soft tissue tumors derived from brown fat. The term hibernoma refers to the morphologic similarity of tumor cells to the brown adipose tissue (BAT) typically found in hibernating animals. BAT is present in newborns and is recognized as an important form of nonshivering thermogenesis in early life that significantly decreases in volume with age.
Hibernomas tend to present as painless, slow-growing masses that are firm, mobile, and nontender to palpation. They are well-defined, encapsulated, hypervascular lesions that typically range in diameter from 5-10 cm but may grow to larger than 20 cm. Hibernomas have no sex predilection and tend to occur in adults during middle age, although cases have been documented across ages. There are 4 distinct pathologic variants of hibernomas: typical, myxoid, spindle cell, and lipoma-like. Each variant can be found intermuscularly, intramuscularly, or subcutaneously. Variants are not readily distinguishable clinically or on imaging and require histology for distinction.
Hibernomas are not considered life-threatening and only manifest symptoms secondary to compression of adjacent structures. While often slow growing and asymptomatic, patients may present with rapid tumor growth, fever, and weight loss. There are no reported cases of malignant transformation, recurrence, or metastatic spread after complete excision. Accurate preoperative diagnosis is critical in reducing patient anxiety and guiding proper surgical and surveillance strategy.
There have been speculations about an association between hibernomas and multiple endocrine neoplasia type 1 (MEN1) as there have been a few case reports of hibernoma occurring in patients with MEN1.
D17.9 – Benign lipomatous neoplasm, unspecified
404064001 – Hibernoma
Differential Diagnosis & PitfallsBiopsy is necessary for identifying most of the differential diagnoses.
- Lipoma – Benign, slow-growing soft tissue tumor of white fat cells that often appears on the neck, trunk, extremities, and buttocks. Nontender, mobile, solitary or multiple, and usually occurs between the fourth and seventh decades of life.
- Liposarcoma – Malignant tumor of fat cells with potential to grow very large.
- Neurofibroma – This asymptomatic skin-colored or violaceous nodule can arise anywhere on the body, most commonly on the head, neck, and upper trunk. When compressed, the buttonhole sign is a strong diagnostic clue.
- Angiolipoma – This appears during the second and third decades of life as tender or painful subcutaneous swelling.
- Lymphoma – Patients often present with systemic symptoms (fever, night sweats, weight loss, etc) in addition to a growing mass.
- Rhabdomyoma – Benign tumor of striated muscle that occurs in children and adults.
- Rhabdomyosarcoma – Rare malignant tumor most commonly found on the head, neck, genitourinary tract, and extremities. Typically occurs in younger children and is associated with bone destruction visible on imaging.