A 28-year-old woman presented with a paraspinal mass on a conventional chest examination that was performed for suspected pneumonia.
A conventional radiograph of the chest showed a right-sided, ill-defined, paraspinal mass with scoliosis of the thoracic spine and rib deformities.
A CT scan demonstrated a solid paravertebral mass with inhomogeneous density. It contained fatty components slightly more dense than subcutaneous fat. Within the lesion multiple serpentine, enhancing structures were noted, representing blood vessels. The adjacent osseous structures were deformed, indicating slow growth. There was no mineralisation within the mass.
MR imaging confirmed fatty components with high signal intensity on both T1- and T2-weighted images, but not quite as high as subcutaneous fat. These components were not completely suppressed after fat suppression. Also, multiple streaky areas with signal intensity similar to muscle were visible. After intravenous contrast administration, slow inhomogeneous enhancement was seen within the lesion.
The patient refused surgery due to religious reasons. After 4 years there was almost no growth of the lesion.
Hibernomas are painless, slow-growing, benign, fatty lesions resembling brown fat. [1] They are most commonly found in the thigh, shoulder, back, neck, chest, arm and, occasionally, in the retroperitoneum. [1] These lesions are rare and often discovered in the 3rd and 4th decades of life. [2]
Macroscopically, the tumours have a yellow to brown colour and may contain hypertrophic vessels. [2] Typical hibernomas are composed of multivacuolated cells resembling brown fat with a small amount of univacuolated white fat cells, but other subtypes can show a higher myxoid content (myxoid type), higher white fat content (lipoma-like type), or display features of spindle cell lipoma (spindle cell type). [1]
The imaging characteristics of hibernomas depend on the histological composition of the lesion. Typical hibernomas are solid, non-mineralised lesions. Compared to subcutaneous fat, they are slightly more dense on CT and slightly less bright on T1- and T2-weighted MR images. Fat suppression may be incomplete, giving them a heterogeneous appearance. [2, 3, 4] Lesions are often intramuscular and do not invade surrounding structures. [4]
Hypervascularity with intratumoral hypertrophic vessels is a distinct feature. Core needle biopsy should, therefore, be avoided when a hibernoma is suspected. Fine needle aspiration in a less vascularised area is preferred. [2] Hypervascularity also causes moderate radiotracer accumulation on bone scintigraphy and intense uptake on F18-FDG PET, mimicking malignancy. [5, 6]
The differential diagnosis includes low-grade liposarcoma and angiolipoma, which, in contrast with typical hibernoma, contain areas of homogeneous, pure fat. [4, 7] Higher grade liposarcomas could also be considered, however, hibernomas show a more homogeneous internal structure. [4, 7] The branching vessels and flow voids seen in any type of hibernoma are usually not found in other lipomatous tumours, including liposarcoma. [2, 3, 7] Myxoid hibernoma is difficult to differentiate from other myxoid tumours on imaging alone. [1, 2]
Other differential diagnoses include a resolving haematoma, which regresses in time, and clear cell sarcoma of the soft tissues, which appears less bright on T1-weighted images. [8] In children and adolescents lipoblastoma can be also be considered.
Hibernomas do not metastasise or recur after resection. [9] Therefore, when the diagnosis is histologically confirmed, local excision can be considered. [7, 10]
TEACHING POINT:
When faced with a slow-growing, well-defined soft-tissue lesion that is located around the shoulder, chest and thighs, and contains prominent vessels and fatty components that are not exactly similar to subcutaneous fat, think of hibernoma as an alternative diagnosis to liposarcoma.
In our case, the lesion fulfilled these criteria. The diagnosis of hibernoma was confirmed by biopsy.
Hibernoma of the chest wall
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Based on the provided routine chest images (X-ray, CT, and MRI), a soft-tissue density or signal shadow can be observed in the right posterior thoracic region, adjacent to the paravertebral area. The specific findings are as follows:
Overall, the lesion exhibits typical fatty components, abundant internal vasculature, relatively heterogeneous signals, well-defined margins, and no bone destruction or significant involvement of adjacent tissues.
Considering the patient’s age and the presence of a fatty lesion located in the posterior thoracic region, the following are possible diagnoses or differential considerations:
Taking into account that the patient is a 28-year-old female, with a lesion composed of fatty elements but differing slightly from normal fat on CT and MRI, and with evidence of abundant vascular structures, together with biopsy confirmation, the final diagnosis is: Hibernoma.
Because hibernoma is a benign tumor, it typically grows slowly and does not metastasize. If the tumor continues to enlarge or causes local discomfort or compressive symptoms, local surgical excision is recommended. If it is asymptomatic and remains stable in size, the decision for surgery should be made in consultation with a specialist.
For patients who have undergone surgical resection, postoperative rehabilitation mainly targets maintaining and restoring the function of the thoracic and back muscles:
Throughout the exercise program, adhere to the FITT-VP principle (Frequency, Intensity, Time, Type, Volume, Progression), adjusting load and difficulty levels on an individual basis, and closely monitor the incision site and surrounding area. If there is notable pain, redness, swelling, or any other discomfort, please seek prompt medical evaluation.
This report provides reference analysis based on current imaging and clinical information and cannot substitute for in-person consultation or advice from a specialized physician. If you experience further discomfort or have additional concerns, please seek timely medical attention and consult with a specialist for an individualized treatment plan.
Hibernoma of the chest wall
