A 33-year-old white woman presented with a several-month history of a slowly enlarging, freely movable, firm in consistence, dorsal mass.
A 33-year-old white woman presented with a several-month history of a slowly enlarging, freely movable, firm in consistence, dorsal mass. Computed tomography showed the lesion interposed between the trapezius and dorsal muscles, with tissue attenuation intermediate between that of fat and skeletal muscle.Magnetic resonance imaging revealed a well-circumscribed mass, measuring 11 cm in maximum dimension. On T1-weighted images the overall signal of the mass was between that of muscle and subcutaneous fat. T2-weighted image with fat saturation showed multiple foci of high T2 signal in mass. At operation a fairly well circumscribed tumor was present below the trapezius muscle. A complete resection was performed and convalescence was uneventful. The tumor was encapsulated, firm, and presented a uniform tan-brown appearance on section. Histologically, fibrous tissue septa traversed the tumor, dividing it in variously sized nodules. There were granular, eosinophilic, and multilocular fat cells, making the diagnosis of a hibernoma.
Hibernoma is a rare, benign soft tissue tumor of brown fat. The lesion was named for its similarity to the brown adipose tissue encountered in the organs of hibernating animals, and was first described by Merkel in 1906, who named it a "pseudolipoma". Gery coined the term hibernoma in 1914 because of its resemblance to the brown fat in hibernating animals, and approximately 100 cases have been reported to date. Hibernoma has also been referred to as lipoma of immature adipose tissue, lipoma of embryonic fat, and fetal lipoma, terms that have been proposed by some authors because brown fat bears a close resemblance to immature white adipose tissue. Brown adipose tissue, the function of which is to promote non shivering thermo genesis in hibernating animals and in the newborn, is present in the fetus and gradually is replaced by white adipose tissue with advancing postnatal ages. It persists, however, in varying amounts throughout adult life and may be found in the neck, axilla, mediastinum, and periaortic and perirenal zones. In the fetus, brown fat has also been identified in the interscapular area, posterior abdominal wall, suprailiac and peripancreatic adipose tissue, and near autonomic ganglia, in addition to the sites described in adults. Gross pathologic inspection demonstrates a well-demarcated, encapsulated soft, greasy to rubbery, brown to yellow lobulated mass. These masses usually measure 5–10 cm in diameter, although there have been reports of hibernomas reaching 20 cm in size. At microscopy, univacuolar or multivacuolar adipocytes are commonly interspersed among granular to eosinophilic cells of hibernoma, resulting in a lipoma with hibernoma like areas. There is marked hypervascularity, which combines with abundant mitochondria to give hibernomas their brown colour. The marked hipervascularity of a hibernoma, both microscopically, and angiographically, is typical and in sharp contrast to mature adult fat. Hibernoma usually manifests as a slowly growing, painless soft-tissue mass in the third and forth decade of life, with a slight female predominance. The mass is typically mobile and pliable and may feel warm at physical examination secondary to its hipervascularity. Radiography may show a radiolucent mass with no osseous abnormalities or mineralization. Sonography demonstrates a well-circumscribed hyperechoic mass, and Doppler imaging may show hipervascularity. CT shows a well-defined lesion with tissue attenuation intermediate between that of fat and skeletal muscle, usually enhancing after intravenous contrast administration. At MR, lesions are heterogeneous with signal intensity similar, but not identical to that of fat. T1 weighted images show predominantly intermediate-signal mass isointense or slightly hypointense to subcutaneous fat, but hyperintense to normal muscle. On T2 weighted images the mass is isointense to subcutaneous fat and may show multiple foci of high signal intensity. Hibernoma enhances following gadolinium administration using fat-supressed T1-weighted images. The differential diagnosis with liposarcoma is almost impossible and the definite diagnosis is normally made after histopathologic examination.
Hibernoma
This case involves a 33-year-old female patient presenting with a gradually enlarging mass in the back. The mass is relatively firm and exhibits good mobility. Based on the provided CT and MRI images, the findings are as follows:
Considering the patient’s clinical presentation (slow growth, relatively firm texture, mild mobility) alongside the imaging features (fat-based density and signal with abundant vascular supply), the following differential diagnoses should be taken into account:
Based on the patient’s age, the slow-growing nature of the lesion, clinical findings of a relatively soft and mobile mass, and the CT/MRI findings demonstrating fatty components with a high vascular supply, the most likely diagnosis is:
Hibernoma.
Since lipoma-like lesions are often indistinguishable from liposarcoma and other malignant entities on imaging, definitive confirmation relies on histopathological examination. The decision to continue conservative observation or proceed with surgical intervention should be guided by the patient’s symptoms, tumor size, and pathological outcomes.
Disclaimer: This report is based solely on the available information and is intended for reference only. It should not replace in-person consultation or professional medical advice. If there are further concerns or if symptoms worsen, please seek medical attention promptly.
Hibernoma
