The scalp refers to the layers of skin and subcutaneous tissue that cover the bones of the cranial vault. In this article, we shall look at the anatomy of the scalp - its layers, neurovascular supply, and any clinical correlations.
The scalp consists of five layers. The first three layers are tightly bound together and move as a collective structure. The mnemonic 'SCALP' can be a useful way to remember the layers of the scalp: Skin, Dense Connective Tissue, Epicranial Aponeurosis, Loose Areolar Connective Tissue, and Periosteum.
The loose connective tissue layer is considered to be the danger area of the scalp. This is because it contains the emissary veins - these are valveless veins which connect the extracranial veins of the scalp to the intracranial dural venous sinuses. The emissary veins are a potential pathway for the spread of infection from the scalp to the intracranial space.
The scalp receives a rich arterial supply via the external carotid artery and the ophthalmic artery (a branch of the internal carotid). There are three branches of the external carotid artery involved:
Anteriorly and superiorly, the scalp receives additional supply from two branches of the ophthalmic artery - the supraorbital and supratrochlear arteries. These vessels accompany the supraorbital and supratrochlear nerves respectively.
The venous drainage of the scalp can be divided into superficial and deep components. The superficial drainage follows the arterial supply: superficial temporal, occipital, posterior auricular, supraorbital, and supratrochlear veins. The deep (temporal) region of the skull is drained by the pterygoid venous plexus. This is a large plexus of veins situated between the temporalis and lateral pterygoid muscles, and drains into the maxillary vein. Importantly, the veins of the scalp connect to the diploic veins of the skull via valveless emissary veins. This establishes a connection between the scalp and the dural venous sinuses.
The scalp receives cutaneous innervation from branches of the trigeminal nerve or the cervical nerve roots. The trigeminal nerve has three branches: supratrochlear nerve, supraorbital nerve, and zygomaticotemporal nerve.
The scalp is composed of several layers, each containing important structures. The blood vessels within the layer are highly adherent to the connective tissue, which prevents them from constricting fully if lacerated. This renders them unable to constrict fully and makes the scalp a common site of profuse bleeding. The layer beneath the skin of the scalp is the Epicranial Aponeurosis, which is a thin, tendon-like structure that connects the occipitalis and frontalis muscles. Below the Epicranial Aponeurosis is the Loose Areolar Connective Tissue, a thin connective tissue layer that separates the periosteum of the skull from the Epicranial Aponeurosis. This layer contains numerous blood vessels, including emissary veins which connect the veins of the scalp to the diploic veins and intracranial venous sinuses. The outer layer of the skull bones is called the Periosteum, which becomes continuous with the endosteum at the suture lines.
The Loose Areolar Connective Tissue layer is considered the danger area of the scalp due to the presence of the emissary veins. These are valveless veins which connect the extracranial veins of the scalp to the intracranial dural venous sinuses. Because these veins lack valves, they are a potential pathway for the spread of infection from the scalp to the intracranial space.
The scalp receives a rich arterial supply via the external carotid artery and the ophthalmic artery (a branch of the internal carotid). The external carotid artery has three branches which supply the scalp - the superficial temporal artery, the posterior auricular artery, and the occipital artery. Anteriorly and superiorly, the scalp receives additional supply from two branches of the ophthalmic artery - the supraorbital and supratrochlear arteries. These vessels accompany the supraorbital and supratrochlear nerves respectively.
The venous drainage of the scalp can be divided into superficial and deep components. The superficial drainage follows the arterial supply- superficial temporal, occipital, posterior auricular, supraorbital and supratrochlear veins. The deep (temporal) region of the skull is drained by the pterygoid venous plexus. This is a large plexus of veins situated between the temporalis and lateral pterygoid muscles, and drains into the maxillary vein. Importantly, the veins of the scalp connect to the diploic veins of the skull via valveless emissary veins. This establishes a connection between the scalp and the dural venous sinuses.
The scalp receives cutaneous innervation from branches of the trigeminal nerve or the cervical nerve roots.
Deep lacerations to the scalp tend to bleed profusely for several reasons. These are due to the pull of the occipitofrontalis muscle preventing the closure of the bleeding vessel and surrounding skin, the blood vessels adhered to dense connective tissue, preventing the vasoconstriction that normally occurs in response to damage, and the presence of many anastomoses of the artery of the scalp, which contribute to profuse bleeding.
The scalp is a complex structure composed of numerous layers and structures. A thorough understanding of its anatomy is essential for assessing and managing lacerations and other conditions of the scalp.
