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The scalp consists of five layers of tissue. The five layers, from superficial to deep, are skin, subcutaneous connective tissue, a muscular aponeurotic layer, a loose connective tissue layer, and the pericranium.
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The layers of the scalp can best be remembered by the acronym “SCALP,” with each letter of the word representing the tissue layer associated with it Figure 15-1A.
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- Skin. The skin of the scalp contains sweat and sebaceous glands and usually numerous hair follicles.
- Connective tissue. The tissue between the skin and the aponeurotic layers is composed of dense collagenous connective tissue and contains the arteries, veins and nerves supplying the scalp.
- Aponeurosis. The superficial musculoaponeurotic system of the scalp consists of the occipitofrontalis muscle and its investing fascia. This fascia is specialized to form a tendinous epicranial 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. The frontalis muscle is instrumental in movements of the eyebrows and forehead and is an important muscle of facial expression are innervated by the facial nerve, cranial nerve (CN) VII.
- Loose connective tissue. A sponge-like layer of loose connective tissue forms a subaponeurotic compartment that enables free movement of the top three scalp layers across the pericranium. It also contains the emissary veins.
- Pericranium. The pericranium is the periosteum over the external surface of the skull where the fibrous tissue knits into the sutures.
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Understanding the structure of the scalp is important when treating patients with scalp wounds. Superficial scalp wounds do not gape because of the strength of the underlying aponeurosis, which holds the margins of the wound together. However, if the aponeurosis is lacerated in the coronal plane, deep scalp wounds gape because of the contraction of the frontalis and occipitalis muscles, which contract in opposite directions. This aponeurotic layer of the scalp is often tightened during cosmetic surgery (e.g., “facelifts”) to help reduce wrinkles in the face and forehead.
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Injury to the fourth layer of the scalp (loose connective tissue) is dangerous because infection can potentially spread from the scalp through emissary veins into the cranial cavity. In addition, an infection or fluid can enter the eyelids because the frontalis muscle inserts into the skin and subcutaneous tissue (not to bone), resulting in ecchymosis, or “black-eyes.”
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Innervation of the Scalp
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The scalp receives its cutaneous innervation as follows (Figure 15-1B):
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- Posterior region of the scalp. Innervated by ...