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Scalp antomy

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Scalp Anatomy

The scalp is the soft tissue covering of the cranial vault. It is a multilayered structure with important clinical implications for surgery, trauma management, and infection.

Extent

The scalp extends:
  • Anteriorly: from the supraorbital ridges
  • Posteriorly: to the external occipital protuberance / superior nuchal line
  • Laterally: down to the zygomatic arch and external acoustic meatus, blending with the temporalis fascia

The Five Layers (Mnemonic: SCALP)

Scalp layers cross-section showing all five layers, emissary vein, and venous sinus
LayerDetails
S - SkinThick, hair-bearing; contains sebaceous glands, hair follicles, and sweat glands. The densest hair follicle region of the body.
C - Connective tissue (Subcutaneous)Dense fibro-adipose tissue firmly tethered to both the skin above and the galea below by inelastic fibrous septa. Blood vessels run within this layer - this is the primary source of profuse bleeding in scalp wounds.
A - Aponeurosis (Galea aponeurotica)The epicranial aponeurosis, connecting the frontalis muscle anteriorly and occipitalis posteriorly. Inelastic and tough. Transection of the galea causes wounds to gape open. Clinically, the skin + subcutaneous tissue + galea are treated as a single outer layer.
L - Loose areolar tissue (Subaponeurotic)The "danger space." Contains emissary veins that drain through diploic channels into the intracranial venous sinuses. Allows infection to spread intracranially (osteomyelitis, meningitis, brain abscess). Permits the outer layers to slide freely over the skull - hematomas here spread widely.
P - Pericranium (Periosteum)Tightly adherent to the outer skull surface. Thin and flimsy - cannot be sutured. Continues into sutures of the skull as the endosteum.

Coronal Section with Deeper Relations

Coronal section through scalp showing epicranial aponeurosis, pericranium, skull layers, meninges, emissary vein, diploic vein, falx cerebri, and superior sagittal sinus
The emissary veins pass through foramina in the skull and connect the subaponeurotic venous plexus with the diploic veins of the skull and then the intracranial venous sinuses (e.g., the superior sagittal sinus).

Blood Supply

The scalp receives a dual arterial supply from both the internal and external carotid systems, creating a rich anastomotic network:
ArteryTerritoryOrigin
Supraorbital arteryForehead / anterior scalpInternal carotid (via ophthalmic a.)
Supratrochlear arteryMedial foreheadInternal carotid (via ophthalmic a.)
Superficial temporal arteryLateral scalp, temporal regionExternal carotid (terminal branch)
Posterior auricular arteryPosterior scalp above earExternal carotid
Occipital arteryPosterior scalpExternal carotid
The vessels run upward from the base of the scalp and lie within the subcutaneous (connective tissue) layer. Because they are tethered by the fibrous septa, cut vessels cannot retract - this is why scalp wounds bleed profusely and persistently. The dense anastomoses mean flaps and grafts have excellent viability even after pedicle ligation of individual branches.

Nerve Supply (Sensory)

NerveRegion suppliedOrigin
Supratrochlear nerveMedial forehead, anterior scalpV1 (ophthalmic division, CN V)
Supraorbital nerve (superficial + deep divisions)Forehead, vertex of scalpV1 (ophthalmic division, CN V)
Zygomaticotemporal nerveAnterior temporal regionV2 (maxillary division, CN V)
Auriculotemporal nerveLateral scalp, templeV3 (mandibular division, CN V)
Lesser occipital nerveLateral occipital scalpC2 (cervical plexus)
Greater occipital nervePosterior scalp (major supply)C2 dorsal ramus
Third occipital nerveLower occipital regionC3 dorsal ramus
The deep division of the supraorbital nerve runs between the galea and the periosteum, which is important during forehead dissection and flap elevation.

Motor Supply

The scalp musculature (frontalis, occipitalis) is innervated by CN VII (facial nerve):
  • Frontalis: temporal branch of facial nerve
  • Occipitalis: posterior auricular branch of facial nerve

Clinical Significance

  1. Profuse bleeding from lacerations: Vessels in the subcutaneous layer are tethered and cannot retract. Compression and early suturing (rather than vessel ligation) is the preferred hemostasis method.
  2. Gaping wounds = galea transection: A non-gaping scalp wound has an intact galea and can be closed superficially. A gaping wound means the galea is cut and must be separately sutured to achieve hemostasis and prevent infection spread.
  3. "Dangerous area" / subaponeurotic space: Infections, pus, or hematomas in this loose areolar layer can spread freely across the entire vault (from the orbital margin to the nuchal line). Emissary veins in this layer provide a route for intracranial spread.
  4. Temporal lacerations: Heal poorly because the temporalis fascia offers rigid resistance to the galea, making wide mobilization for closure difficult.
  5. Scalp avulsions: The loose areolar layer is the plane along which the outer three layers (skin + SQ tissue + galea) peel away from the skull in degloving injuries.
  6. Bruise migration: A subgaleal hematoma can track anteriorly into the orbit (giving periorbital bruising) or laterally behind the ear, appearing remote from the actual injury site.
Sources: Roberts and Hedges' Clinical Procedures in Emergency Medicine, p. 813-814 | P.C. Dikshit Textbook of Forensic Medicine and Toxicology, p. 192 | Scott-Brown's Otorhinolaryngology Head & Neck Surgery | Dermatology 2-Volume Set 5e
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