Lecture Notes: Anatomy of the Scalp

Overview

• The scalp is the soft tissue covering the vault of the skull.
• It extends from the superciliary arches (eyebrows) anteriorly to the external occipital protuberance and superior nuchal lines posteriorly.
• Laterally, it continues inferiorly to the zygomatic arch.
• The scalp is composed of several layers that can be remembered using the acronym SCALP:
  • S: Skin
  • C: Connective Tissue (dense)
  • A: Aponeurotic Layer
  • L: Loose Connective Tissue
  • P: Pericranium

Layers of the Scalp

Skin

• Thick and hairy, except over the forehead.
• Firmly attached to epicranial aponeurosis through dense connective tissue.
• Contains numerous hair follicles, sebaceous glands, and sweat glands.
• Common site for sebaceous cysts.

Dense Connective Tissue

• Also known as superficial fascia, it binds the skin to the underlying occipitofrontalis and its aponeurosis.
• Contains the scalp's blood vessels and nerves, which are held open by the dense tissue when cut, leading to profuse bleeding.

Aponeurotic Layer

• Contains the occipitofrontalis muscle with its frontal and occipital bellies and the epicranial aponeurosis (galea aponeurotica).
• Responsible for moving the scalp, wrinkling the forehead, and raising the eyebrows.
• Innervated by branches of the facial nerve (CN VII).
• Scalp wounds do not gape unless the aponeurosis is cut transversely.

Loose Connective Tissue

• Allows for movement of the scalp over the calvaria.
• Can localize infections and facilitate their spread due to its loose nature.
• Contains emissary veins that can lead to intracranial infections, making it a "dangerous layer."

Pericranium

• The periosteum on the outer surface of the calvaria, loosely attached except at suture lines.
• Known for forming a "safety valve hematoma" when blood pools in the fourth layer.

Clinical Correlations

• Scalp Bleeding: Due to the open nature of vessels in the dense connective tissue layer, scalp cuts can bleed profusely.
• Black Eye: Blood can track forward into the eyelids due to lack of anterior bony attachment, causing hematoma after head injuries.
• Safety Valve Hematoma: Blood from intracranial hemorrhage can accumulate in the sub-aponeurotic space after certain fractures.
• Cephalhematoma: A subperiosteal collection of blood, often in the parietal region, bounded by suture lines.
• Caput Succedaneum: Subcutaneous edema over the presenting part of the head at delivery, most common birth trauma of the scalp.

Summary

• The scalp is a complex structure with multiple layers, each with unique functions and clinical implications.
• Understanding the anatomy and potential complications associated with each layer is critical in clinical practice.