Hibernoma—hibernomata in plural form—is a type of skin lesion or benign tumor that is composed of brown fat. It falls under the category of tumors called lipoma, and its main component is adipose tissue, also known as body fat. The term hibernoma comes from the brown fat resembling the fat found on some hibernating animals.

Alternative terms for this condition include lipoma of immature adipose tissue, fetal lipoma, and lipoma of embryonic fat. These terms refer to lipoma's origin in the fetus or embryo. It is more common in females than in males and tends to occur during adulthood. Hibernomata usually appear around the hips or on the back.

Hibernoma is sometimes called a cutaneous condition, since it affects the skin. More specifically, it is subcutaneous, since it occurs under the skin. Additionally, it can be split into certain types. Mediastinal hibernoma describes cases in which the tumor is found in the mediastinum, the region that separates the lungs from other organs such as the heart and esophagus. Another variant, cervical hibernoma, occurs in the cervix, which is the neck of the uterus.

The cells that comprise hibernomata condition are large, foamy and shaped like polyhedrons, or three-dimensional structures composed of polygons. Each cell is widened by several lipoid-filled vacuoles, which are small cavities in the cytoplasm. Lipomas are characterized by tumors created by adipose tissue. They are also known as the most common kind of soft tissue growth.

Hibernoma is one of the rarer types of lipoma, while superficial subcutaneous lipoma is the kind with the most incidents of occurrence. Other common types of lipoma include angiolipoma, which, unlike most lipomas, could be painful; spindle-cell lipoma, which tends to appear on the neck, shoulders and back of older men; and chondroid lipomas, which are characterized by a yellowish pigmentation.

No one knows the exact cause of hibernoma or other types of lipoma. Some medical researchers have suggested that lipomas in general are triggered by certain injuries or attribute their occurrence to genetics. These hypotheses, however, are hotly disputed.

Hibernoma, like most other types of lipoma, is deemed not harmful. This is because it is believed to be a benign tumor, which means that it lacks the ability to metastasize, or spread. Some medical researchers, however, believe that there is a chance that a hibernoma could turn into a malignant tumor, which denotes cancer. Surgical excision, or removal, is the traditional treatment for hibernomata.