Fatty layer of subcutaneous tissue

The fatty layer of subcutaneous tissue (Panniculus adiposus), is the superficial layer of the subcutaneous tissue (superficial fascia) located between the dermis and the deep (membranous) layer of the superficial fascia. It is composed primarily of loose areolar connective tissue interspersed with varying amounts of adipose (fat) tissue, organized into lobules separated by fibrous septa.

Key Characteristics

• Location: It lies immediately deep to the skin (dermis) and superficial to the membranous layer of the superficial fascia (Scarpa's fascia in the abdomen).

• Composition: Predominantly adipocytes arranged in lobules, supported by a framework of connective tissue septa containing blood vessels, lymphatics, and nerves. The septa (retinacula cutis) anchor the skin to deeper structures and provide structural support.

• Thickness: Highly variable depending on body region, sex, age, and nutritional status. It is thickest over the abdomen, buttocks, and thighs, and thinnest (or virtually absent) over the eyelids, penis, and scrotum.

Functions

• Insulation: Acts as a thermal barrier, helping to regulate body temperature.

• Energy storage: Serves as a major depot for triglyceride storage and metabolic energy reserve.

• Mechanical protection: Provides cushioning against external trauma to deeper structures.

• Mobility: Allows the skin to glide over underlying deep fascia, muscles, and bones.

• Neurovascular conduit: Contains cutaneous nerves, superficial veins (e.g., the great saphenous vein), and lymphatic vessels that traverse this layer.

Clinical Relevance

This layer is the target of liposuction procedures, the site of subcutaneous injections (e.g., insulin, heparin), and the plane through which many superficial surgical dissections are performed. Pathological conditions affecting this layer include panniculitis (inflammation of the subcutaneous fat), lipomas, and cellulitis. In abdominal surgery, the distinction between the fatty layer (Camper's fascia) and the deeper membranous layer (Scarpa's fascia) is important, as Scarpa's fascia can hold sutures for wound closure while the fatty layer generally cannot.