Anatomy, Fascia Layers

Fascia is made up of sheets of connective tissue that is found below the skin. These tissues attach, stabilize, impart strength, maintain vessel patency, separate muscles, and enclose different organs. Traditionally, the word fascia was used primarily by surgeons to describe the dissectible tissue seen in the body encasing other organs, muscles, and bones. Recently, the definition has been broadened to include all collagenous based soft tissues in the body, including cells that create and maintain the extracellular matrix. The new definition also includes certain tendons, ligaments, bursae, endomysium, perimysium, and epimysium.

Classification System

Fascia can be classified as superficial, deep, visceral, or parietal and further classified according to anatomical location.

Superficial Fascia

Superficial fascia is found directly under the skin and superficial adipose layers. It can show stratification both grossly and microscopically. Traditionally, it is described as being made up of membranous layers with loosely packed interwoven collagen and elastic fibers.

1. Superficial fascia is thicker in the trunk than in the limbs and becomes thinner peripherally.

2. Superficial fascia layers can sometimes include muscle fibers to create all types of structures in the body. A few examples include the platysma muscle in the neck, the external anal sphincter, and the dartos fascia in the scrotum.

3. A subtype of superficial fascia in the abdomen is Scarpa’s fascia.

Deep Fascia

Deep fascia surrounds bones, muscles, nerves, and blood vessels. It is commonly has a more fibrous consistency and rich in hyaluronan as compared to the other subtypes. Deep fascia tends to be highly vascularized and contain well developed lymphatic channels. In some instances, deep fascia can even contain free encapsulated nerve endings, such as Ruffini and Pacinian corpuscles.

There are 2 subtypes of deep fascia:

Aponeurotic fascia

1. It forms into sheets of pearly-white fibrous tissue to attach muscles needing a wide area of attachment. Aponeurosis can thin into a tendon and become a point of origin or insertion for other muscles. Some examples of aponeurotic fascia include the fascia of limbs, thoracolumbar fascia, and rectus sheath.

2. It is the thicker of the 2 subtypes that are normally easily separated from the underlying muscle layer.

3. It is comprised of 2 to 3 parallel collagen fiber bundles.

Epimysial fascia

1. Also known as the epimysium, this is the connective tissue sheath surrounding skeletal muscle and can, in some cases, connect directly to the periosteum of bones.

2. Some major muscle groups enveloped in epimysium include muscles of the trunk, pectoralis major, trapezius, deltoid, and gluteus maximus.

3. It is the thinner of the 2 subtypes, on average, and is more tightly connected to the muscle via septa that penetrate the muscle layer.

Visceral Fascia

Visceral fascia surrounds organs in cavities like the abdomen, lung (pleura), and heart (pericardium).

Parietal Fascia

Parietal fascia is a general term for tissues that line the wall of a body cavity just outside of the parietal layer of serosa. The most commonly known parietal fascia is found in the pelvis.

In many places in the body, superficial and deep fascial layers are connected by fibrous septa and create a connection network that weaves in between fat lobules that make up the deep adipose tissue layer.