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Subcutaneous tissue (scrotum)

Subcutaneous tissue, also called the hypodermis or superficial fascia, is the layer of connective tissue and fat located directly beneath the skin (dermis) and above the underlying muscles, bones, or fascia. It consists of adipose tissue, fibrous septa, blood vessels, lymphatics, and cutaneous nerves.

This layer provides insulation, mechanical protection, energy storage, and a conduit for vessels and nerves. Its thickness varies across the body, and it is clinically relevant in obesity, metabolic disease, infections, oncology, and reconstructive surgery.

Synonyms

  • Hypodermis

  • Superficial fascia

  • Subcutaneous fat layer

Composition and Layers

  • Superficial fatty layer (Camper’s fascia): Dominated by fat cells

  • Deeper membranous layer (Scarpa’s fascia, abdominal wall): Fibrous connective tissue

  • Fibrous septa: Strands connecting dermis to deep fascia, subdividing fat into lobules

  • Contained structures: Cutaneous vessels, lymphatics, and sensory nerves

Location and Relations

  • Present throughout the body beneath the dermis

  • Lies superficial to deep fascia, muscles, and bones

  • Thickest in buttocks, abdomen, and thighs; thinnest in eyelids, ear, and genitalia

  • Provides an anatomical plane for surgical dissection and spread of infection

Function

  • Cushioning and shock absorption

  • Thermal insulation

  • Energy storage in the form of adipose tissue

  • Conduit for vessels, lymphatics, and nerves

  • Skin mobility over deeper structures

Clinical Significance

  • Altered thickness in obesity and cachexia

  • Site for infections (cellulitis, necrotizing fasciitis)

  • Involved in edema and lymphedema

  • Important in surgical approaches, flap surgery, and grafting

  • Can harbor lipomas, liposarcomas, metastases, and inflammatory lesions

  • Used as an imaging marker for systemic diseases and nutritional status

MRI Appearance

T1-weighted images:

  • Subcutaneous fat appears bright (high signal intensity)

  • Fibrous septa appear dark linear strands

T2-weighted images:

  • Subcutaneous fat appears bright (high signal intensity)

  • Fibrous septa remain dark

  • Edema or inflammatory fluid appears even brighter than fat

STIR (Short Tau Inversion Recovery):

  • Fat signal suppressed → appears dark

  • Pathology (edema, infection, tumor infiltration) appears bright hyperintense

T1 Fat-Sat Post-Contrast:

  • Fat suppressed → appears dark

  • Lesions or inflammatory changes enhance (diffuse, nodular, or rim enhancement)

3D T2 SPACE / CISS:

  • Fat appears with moderately bright signal (but less intense than CSF)

  • Fibrous septa and fascia appear dark strands

CT Appearance

Non-Contrast CT:

  • Fat appears as low attenuation (-80 to -120 HU)

  • Fibrous septa and vessels appear as thin soft tissue density strands

  • Edema or infiltration increases attenuation (fat stranding)

Post-Contrast CT:

  • Fat does not enhance

  • Inflammatory or neoplastic tissue within subcutaneous layer enhances

  • Abscesses appear as low-density collections with rim enhancement

MRI images

Subcutaneous tissue of pelvis