Scalp - Layers

Layers

It is usually described as having five layers, which can conveniently be remembered as a mnemonic:

• S: The skin on the head from which head hair grows. It contains numerous sabaeceous glands and hair follicles
• C: Connective tissue. A thin layer of fat and fibrous tissue lies beneath the skin.
• A: The aponeurosis called epicranial aponeurosis (or galea aponeurotica) is the next layer. It is a tough layer of dense fibrous tissue which runs from the frontalis muscle anteriorly to the occipitalis posteriorly.
• L: The loose areolar connective tissue layer provides an easy plane of separation between the upper three layers and the pericranium. In scalping the scalp is torn off through this layer. It also provides a plane of access in craniofacial surgery and neurosurgery. This layer is sometimes referred to as the "danger zone" because of the ease by which infectious agents can spread through it to emissary veins which then drain into the cranium. The loose areolar tissue in this layer is made up of random collagen I bundles, collagen III. It contains the major blood vessels of the scalp, which bleed profusely upon injury, partly due to the absence of venous valves found in the circulation below the neck. It will also be rich in glycosaminoglycans (GAGs) and will be constituted of more matrix than fibers.
• P: The pericranium is the periosteum of the skull bones and provides nutrition to the bone and the capacity for repair. It may be lifted from the bone to allow removal of bone windows (craniotomy).

The clinically important layer is the aponeurosis. Scalp lacerations through this layer mean that the "anchoring" of the superficial layers is lost and gaping of the wound occurs; this requires suturing. This can be achieved with simple or vertical mattress sutures using a non-absorbable material, which are subsequently removed at around days 7-10.