Subcutaneous tissue is the deepest layer of the skin. It lies under the dermis and above the muscle. It is made mostly of fat, also called adipose tissue. Your report may also call it the subcutis, subcutaneous fat, or hypodermis.
Subcutaneous tissue is a normal part of the body, not a diagnosis. Pathology reports mention it to describe how deep a finding extends or where a growth is located. This article explains what subcutaneous tissue is made of and why it appears in your pathology report.
What does subcutaneous tissue do?
Subcutaneous tissue has several jobs:
- Cushioning. The fat protects the muscles, bones, and organs underneath from bumps and pressure.
- Insulation. The fat helps keep the body warm.
- Energy storage. The body stores energy as fat and can use it when needed.
- Connecting the skin. Subcutaneous tissue attaches the skin to the tissue underneath while still allowing movement.
The thickness of the subcutaneous tissue varies from person to person and across the body. It is very thin on the eyelids and much thicker on the abdomen and buttocks.
What does subcutaneous tissue look like under the microscope?
Under the microscope, subcutaneous tissue is made of large, round fat cells. Each fat cell contains a single drop of fat, which looks clear on the slide because the fat dissolves during processing. The fat cells are grouped into small clusters called lobules.
Thin bands of fibrous tissue separate the lobules. These bands, called septa, carry the blood vessels and nerves that supply the skin.
Why is subcutaneous tissue mentioned in a pathology report?
Pathology reports mention subcutaneous tissue for several reasons:
- To describe how deep a skin cancer extends. Most skin cancers start near the surface. When a cancer grows through the dermis into the subcutaneous tissue, it has grown deeply. For some skin cancers, this depth affects the stage and the treatment plan.
- To describe tumors that grow in the fat. Many tumors start in the subcutaneous tissue itself. The most common is a lipoma, a noncancerous fat tumor. Others include an angiolipoma and a spindle cell lipoma.
- To describe tumors that spread into the fat. Dermatofibrosarcoma protuberans (DFSP) often grows from the dermis into the subcutaneous tissue. It can extend well beyond what can be seen or felt.
- To describe changes in the fat. Injury to the fat can cause fat necrosis, in which fat cells break down and form a firm lump. Inflammation of the fat is called panniculitis.
- To describe the deep margin. When skin is removed, the bottom edge often includes subcutaneous tissue. Your report may say whether a tumor reaches this deep margin.
Questions to ask your doctor
- Did the tumor extend into the subcutaneous tissue?
- Does the depth of the tumor affect my stage or treatment?
- Did the tumor start in the fat, or grow into it from the skin?
- Was the deep margin free of tumor?
- Is the growth noncancerous or cancerous?
- Do I need any further surgery or follow-up?
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