Despite the improved simplicity of this process over the years, however, a number of factors can affect the results, including hydration and body temperature, so it still needs some care when taking the test to ensure that the results are accurate.Hydrostatic weighingConsidered one of the more accurate methods of measuring body fat, this technique involves complete submersion of a person in water, with special equipment to measure the persons weight while submerged. This weight is then compared with "dry weight" as recorded outside the water to determine overall body density. As fat is less dense than muscle, careful application of this technique can provide a reasonably close estimate of fat content in the body. This technique does, however, require expensive specialized equipment and trained professionals to administer it properly.Dual-energy X-ray absorptiometry (DEXA)Originally developed to measure bone density, DEXA imaging is also used to precisely determine body fat content by using the density of various body tissues to identify which portions of the body are fat. This test is generally considered very accurate, but requires a great deal of expensive medical equipment and trained professionals to perform.The most common method for discussing this subject and the one used primarily by researchers and advisory institutions is BMI. Definitions of what is considered overweight vary by ethnicity. The current definition proposed by the US National Institutes of Health (NIH) and the World Health Organization (WHO) designates whites, Hispanics and blacks with a BMI of 25 or more as overweight.
Myxoid variant: Loose, basophilic matrix, with thick fibrous septa, and foamy histiocytes
Lipoma-like variant: Univacuolated lipocytes, with only isolated hibernoma cells
Spindle cell variant: Spindle cell lipoma combined with hibernoma

Histochemistry
Oil Red O-positive droplets of cytoplasmic lipid can be seen in most cases

Immunohistochemistry
The neoplastic cells are S100 protein positive (approximately 80%), and show membrane and vacuole CD31 immunoreactivity. Uncoupling protein 1 (UCP1), a unique brown fat mitochondrial protein, is also positive. Cytogenetics
There are structural rearrangements of 11q13-21, which are considered most characteristic. This alteration can be detected by metaphase fluorescent in situ hybridization (FISH). MEN1 gene (11q13.1) is most frequently deleted, while GARP gene (11q13.5) may also be involved. Cytology
The fine needle aspiration smears show small, round, brown fat-like cells, with uniform, small cytoplasmic vacuoles and regular, small, round nuclei. There is usually a rich vascular background of branching capillaries. It is not uncommon to also have mature fat cells. Differential diagnoses
It is important to separate hiberoma from adult rhabdomyoma, a granular cell tumor and a true liposarcoma. Classification
This lesion has been called a fetal lipoma, lipoma of embryonic fat or a lipoma of immature fat. Management
Complete surgical excision is the treatment of choice, associated with an excellent long term clinical outcome. Epidemiology
The tumor is rare, affecting adults in the 4th decade most commonly. Patients are usually younger than those who present with a lipoma. There is a slight male predominance. Hibernoma are most commonly identified in the subcutaneous and muscle tissue of the head and neck region (shoulders, neck, scapular), followed by thigh, back, chest, abdomen, and arms.