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Describe the layers of the scalp with their clinical importance.

Anatomy · 1st Professional — Pre-Clinical

Layers of the Scalp

The scalp covers the vault of the skull, from the supra-orbital margins in front to the external occipital protuberance and superior nuchal lines behind.

Letter	Layer	Features
S	Skin	Thick; hair-bearing; many sebaceous glands — hence sebaceous cysts are common
C	Connective tissue	Dense, vascular; the vessels are held open by fibrous septa
A	Aponeurosis (galea aponeurotica) with occipitofrontalis	The "scalp proper" — the first three layers are firmly united and move together
L	Loose areolar tissue	The dangerous layer; contains emissary veins
P	Pericranium	Periosteum; adherent at the sutures

WHY Each Layer Matters Clinically

Scalp wounds bleed profusely and do not close spontaneously, because the vessels in the dense second layer are held open by the fibrous septa; bleeding is controlled by pressure against the skull or by suturing
Wounds gape only if the aponeurosis is cut, since the frontal and occipital bellies then pull in opposite directions; a transverse cut therefore gapes, a sagittal one does not
The loose areolar layer is the "dangerous area" — infection and blood spread widely in it, and emissary veins carry infection to the intracranial venous sinuses, causing meningitis or sinus thrombosis
Black eye — blood in this layer tracks forward into the eyelids, as the occipitofrontalis has no bony attachment anteriorly
Collections stop at the nuchal lines and the zygomatic arches, because the aponeurosis is attached there

Blood Supply

Region	Arteries	Source
Front	Supratrochlear, supra-orbital	Internal carotid (via the ophthalmic artery)
Side	Superficial temporal, posterior auricular	External carotid
Back	Occipital	External carotid

The arteries anastomose freely across the midline and between the two carotid systems, which is why the scalp bleeds so freely and why an avulsed scalp flap often survives on a narrow pedicle
The vessels run in the second layer and pass upward from the periphery, so flaps are made with the base downward to preserve the supply

Nerve Supply

In front of the ear — branches of the trigeminal: supratrochlear, supra-orbital, zygomaticotemporal, auriculotemporal
Behind the ear — branches of the cervical nerves: lesser occipital (C2), greater occipital (C2), third occipital (C3), great auricular (C2, C3)
Lymphatics — there are no nodes in the scalp; it drains to the pre-auricular, post-auricular and occipital nodes, then to the deep cervical chain

Applied Aspects

Local anaesthesia of the scalp is achieved by a ring block, since the nerves all enter from the periphery
Sebaceous cysts are the commonest scalp swelling, arising from the skin layer; they are attached to the skin and cannot be moved separately from it
Cephalhaematoma is confined by the sutures and resolves spontaneously; a subgaleal haemorrhage crosses them and may be life-threatening
Caput succedaneum is oedema of the scalp itself, present at birth, crossing sutures and resolving within days — unlike a cephalhaematoma, which appears after birth
Scalp avulsion occurs at the loose areolar plane, since it is the plane of least resistance; replantation is often possible because of the rich anastomosis

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