CHAPTER 15: Scalp, Skull, and Meninges

ANATOMY OF THE SCALP

BIG PICTURE

The scalp consists of five layers of tissue (from superficial to deep): skin, subcutaneous connective tissue, muscular aponeurosis, loose connective tissue, and pericranium.

LAYERS OF THE SCALP

The layers of the scalp can best be remembered by the acronym “SCALP,” with each letter representing the tissue layer associated with it (Figure 15-1A).

• Skin. Contains sweat and sebaceous glands and usually numerous hair follicles.

• Connective tissue. Composed of dense collagenous connective tissue and contains the arteries, veins, and nerves supplying the scalp.

  • Scalp lacerations bleed profusely because the severed arteries do not contract when they are cut because the vessel lumens are held open by this dense connective tissue.

• Aponeurosis. Consists of the frontalis muscle connected to the occipitalis muscle via an aponeurosis known as the galea aponeurotica. The galea continues into the temples, investing the auricular muscles, and terminates by attaching to the mastoid processes and the zygomatic arch.

  • If this aponeurosis is lacerated in the coronal plane the frontalis and occipitalis muscles contract in opposite directions and may result in a large gaping wound.

• Loose connective tissue. Forms a subaponeurotic layer containing emissary veins.

  • Considered a danger area because infection within this layer can spread easily in all directions. For example, blood in this area easily spreads into the eyelids resulting in “black-eyes.” Additionally, blood can course into the cranial cavity via emissary veins.

• Pericranium. Is the periosteum over the external surface of the skull; knits into the sutures.

INNERVATION OF THE SCALP

The scalp receives its cutaneous innervation as follows (Figure 15-1B):

• Posterior region of the scalp. Lesser occipital and greater occipital nerve branches (C2 spinal nerve level).

• Anterior region of the scalp. Supraorbital and supratrochlear nerves (ophthalmic division of the trigeminal nerve; CN V-1).

• Lateral region of the scalp. Maxillary (CN V-2) and mandibular (CN V-3) divisions of the trigeminal nerve (the zygomaticotemporal and auriculotemporal nerves, respectively).

ARTERIAL SUPPLY OF THE SCALP

The scalp receives a rich arterial supply via external and internal carotid branches (Figure 15-1C).

• External carotid artery. Branches include the occipital, posterior auricular, and superficial temporal arteries.

• Internal carotid artery. Branches include the supraorbital and supratrochlear arteries.

Scalp arterial anastomoses. Scalp lacerations often bleed profusely because arteries bleed from both ends of the laceration due to the abundant anastomose. Additionally, it is important to wear a hat in the winter because a lot of body heat is lost through the rich arterial network in the scalp.▼