Descriptive Anatomy of the Different Layers Covering the Cranium

A great deal of work has been carried out on the scalp [3, 8, 9, 12]. What follows is a description of the various layers as they appear on dissection.

The scalp is made up of the skin, sub-cutaneous tissue and the galeal aponeurosis.

The skin and subcutaneous tissue are extremely thick, representing one of the special features of the scalp. The vessels and nerves are found at the lower surface of the sub-cutaneous adipose tissue.

The innermost border of this sheet is delineated by the epicranium or galeal aponeurosis. The terms epicranium or superficial musculoaponeur-otic fascia are used to designate what is routinely referred to as the galea. Strictly speaking, the galea corresponds to the aponeurotic compartment of the fascia which incorporates a series of paired muscles (the frontal, auricular and occipital muscles) as well as an aponeurotic sheet. This sheet

Scalp Incision

Fig. 1. Left lateral view of the scalp in a cadaver specimen following skin incision and colored latex injection, (a) The galeal aponeurosis (GA) has been incised at the level of the frontalis muscle (FM) and has been turned with the skin and subcutaneus tissue (SST). The pericranium (P) is identified, (b) The pericranium (P) has been turned. The 3 layers can be identified: skin and subcutaneus tissue (SST), the galeal aponeurosis (GA) and the pericranium (P). (c) Periosteum (P) resection with exposure of the fascia temporalis (FT)

Fig. 1. Left lateral view of the scalp in a cadaver specimen following skin incision and colored latex injection, (a) The galeal aponeurosis (GA) has been incised at the level of the frontalis muscle (FM) and has been turned with the skin and subcutaneus tissue (SST). The pericranium (P) is identified, (b) The pericranium (P) has been turned. The 3 layers can be identified: skin and subcutaneus tissue (SST), the galeal aponeurosis (GA) and the pericranium (P). (c) Periosteum (P) resection with exposure of the fascia temporalis (FT)

extends from the frontal region back to the occiput, and from the vertex to the zygomatic arches. In front, it continues into the face. It is difficult to separate the galea from the sub-cutaneous fatty sheet because of the many arterial ramifications which originate in the vascular network of the galea and travel outwards. It is a dictum that when the galea moves, the skin and the fatty tissue moves with it [3, 12]. The lateral extension of the galea is sometimes called the temporoparietal fascia, and it is over this that the superficial temporal artery runs. This sheet is less dense. The frontal muscles arise in the galea and are inserted deep in the dermis. They are separated from one another by an extension of this fascia. The occipital muscles originate at the superior nuchal line and are inserted in the galea. The auricular muscles are very thin and are difficult to separate out by dissection.

The periosteum of the skull—also referred to as the pericranium—is a thin, fibrous sheet which is only loosely attached to the bone apart from along the sutures. It is easily lifted off the bone. It is conventionally said that the periosteum of the skull is continued at the temporal region by the aponeurosis of the temporal muscle (the temporalis fascia). This continues on down to attach at the zygomatic arch. The temporalis fascia is particularly strongly attached to the galeal aponeurosis. Thus, the temporalis muscle is situated between its fascia externally and bone internally. Blood and trophicity are supplied to this muscle by the deep temporal arteries which run across the muscle's internal surface.

Between the galea and the periosteum of the skull or the pericranium is found a tissue layer at which the scalp can be detached, namely the layer of subaponeurotic areolar connective tissue.

In the light of these anatomical considerations, it can be seen that the classic galeal flap described in the surgery of the anterior cranial base is, in reality, a periosteal flap.

In conclusion, in practical terms the surgeon needs to bear in mind that there are four successive layers between the skin and the periosteum of the skull:

- skin and subcutaneous tissue

- galeal aponeurosis (epicranium)

- subaponeurotic areolar connective tissue

- periosteum (pericranium)

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  • NANCY
    What tissue layers are under the scalp?
    7 months ago

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