Summary
Description
Hibernoma is a rare tumor is that is thought to arise from remnants of fetal adipose tissue.
People and Age
The average age of patients with hibernoma is 38 years. Slightly more men than women are affected.
Symptoms and Presentation
Patients with hibernoma present with a mass.
Brief description of the xray
Hibernoma is not visible on x-ray.
Brief desc of tx
Complete surgical removal of hibernoma is curative.
Tumor Name
Tumor Type
Benign or Malignant
Body region
Most Common Bones
Complete Information on this Tumor
Introduction and Definition
This rare, benign tumor is thought to arise from remnants of a fetal adipose tissue, or brown fat. It is also known as Lipoma of embryonic fat or Fetal lipoma. For this reason, it may occur where fetal or brown adipose tissue persists in adult life, such as the interscapular region. In actuality, the most common location for this tumor is in areas where brown fat is absent, suggesting that this tumor does not in fact always arise from remnants of fetal fat. Brown fat is present in hibernating animals such as bears. Most fat is a white fat.
Incidence and Demographics
This benign tumor comprises approximately 1.6% of all benign lipomatous tumors. Both men and women can be affected, from age to to age 75 years. The peak age at diagnosis is 38 years. Approximately 3/5 of patients are men. The most common anatomic location in one series was the thigh -50 cases, followed by the shoulder -20 cases, back-17 cases, neck-16 cases, chest-11 cases, arm-11 cases, and abdominal cavity-10 cases. (Am J Surg Pathol. 2001 Jun;25(6):809-14.)
Symptoms and Presentation
This tumor is typically asymptomatic and presents as a fleshy painless mass, with size at presentation ranging from 1 to 24 cm, with an average size of 9.3 cm. The tumor may be present from one month to 10 years, or may be an incidental finding.
X-Ray Appearance and Advanced Imaging Findings
Radiographic findings are variable. Lipomas and hybernomas may be seen as low density areas on plain radiographs, but MRI is a better imaging modality.
MRI Findings
On MRI, this lesion appears as a well-defined, heterogeneous mass, with slightly or significantly hypo-intense signal uptake relative to normal surrounding fat on T1 weighted images. T1 weighted images show prominent thin bands of low signal intensity. These lesions are distinct from lipoma on MRI, but have features suggestive of lipomatous origin. These lesions cannot be separated from malignant lipomatous tumors by MRI alone. This leads to potential misinterpretation and potential inappropriate treatment. Carefully planned biopsy will resolve the confusion. Beware false positive findings and confusion with liposarcoma on 18F-FDG PET/CT in hibernoma, which increase the potential for inappropriate treatment.
CT Findings
A well-defined mass of low attenuation, typical of fat attenuation. May vary depending on hemosiderin content. CT cannot distinguish this tumor from low-grade liposarcoma.
Laboratory Findings
no relevant laboratory findings
Differential Diagnosis
lipoma, low-grade liposarcoma, soft tissue sarcoma
Preferred Biopsy Technique for this Tumor
Open
Histopathology findings
Several variants of hibernoma have been defined. The subtypes include typical, myxoid, spindle cell, and lipoma-like. Typical type cases account for 85% of the tumors.
Treatment Options for this Tumor
Complete surgical removal with a marginal margin, and 100% negative margin is sufficient. Wide margin is not required. Intra-regional margins have been reported to lead to recurrence.Recurrence is rare and metastasis has not been reported.
Preferred Margin for this Tumor
marginal
Outcomes of Treatment and Prognosis
After complete removal, recurrence is not expected and patients are expected to do well. Incomplete removal may result in persistence or regrowth of the inadequately resected portion. Metastasis has not been reported and is not expected.
Special and Unusual Features
A brown fat, also called brown adipose tissue, is present in newborn humans and in hibernating mammals. In babies and hibernating mammals, the function of brown fat is to generate body heat. In human babies, brown fat is located on the back, along the upper half of the spine and around the shoulders. Brown fat is highly specialized for heat production. Mitochondria contained within the cells of brown fat contain iron and give the fat a brown appearance. In addition, Brown fat contains more capillaries and uses more oxygen than normal white fat.
Suggested Reading and Reference
The International Journal of Biochemistry & Cell Biology
Volume 30, Issue 1, 19 March 1998, Pages 7-11
Volume 30, Issue 1, 19 March 1998, Pages 7-11
