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Introduction

Scalp is the soft tissue that covers the vault of the skull. It extends:

  • Anteriorly: Supraorbital margin
  • Laterally : Superior temporal lines
  • Posteriorly: External occipital protuberance and superior nuchal lines.

 Enumerate the layers of Scalp.

The scalp consists of five layers. Superficial three are intimately bound together and move as one unit. The five layers from superficial to deep are:

  • S- Skin: It is thick and has large number of hair follicles and associated sebaceous glands. Therefore, scalp is the commonest site of sebaceous cysts.
  • C – Connective tissue (Superficial fascia) It is composed of dense connective tissue that binds the skin to the  underlying aponeurosis of occipitofrontalis muscle. Fibrous septa break up this layer into numerous small pockets containing lobules of fat. The named blood vessels and nerves of the scalp are located in this layer and the walls of the blood vessels are adherent to the fibrous network, therefore in case due to injury,  if the blood vessels are torn or cut, the walls are unable to retract and this causes profuse bleeding. 
  • A- Aponeurosis (Epicranial aponeurosis): It is composed of occipitofrontalis muscle and its aponeurosis. The aponeurosis of occipitofrontalis muscle is also called epicranial aponeurosis or galea aponeurotica (Latin: galea = helmet). The wounds of the scalp gape if epicranial aponeurosis is cut transversely because the aponeurosis is pulled in the anteroposterior direction by the tone of occipitofrontalis muscle.
  • L- Loose areolar tissue: It is made up of loose areolar tissue. It is traversed by emissary veins which connect the veins in the second layer of scalp with intracranial dural venous sinuses. It acts as a natural plane of cleavage during craniotomy. It is also known as the ‘dangerous layer of scalp’.
  • P –Pericranium: It is composed of the periosteum of bones of vault of skull. It is loosely connected to the underlying bones and can be easily stripped except at sutures, where it is connected to the endocranium via sutural ligaments.

Layers of scalp

Name the arteries  that supply Scalp.

Scalp has a rich blood supply from the branches of internal and external carotid arteries. There is rich anastomosis between the branches of  two sides and branches of internal and external carotid arteries of the same side.

There are five arteries on each side, three in front of the auricle and two behind the auricle. The arteries are:

 Three in front of the auricle:

  • Supratrochlear and Supraorbital (branches of internal carotid artery)
  • Superficial temporal (branch of external carotid artery)

Two behind the auricle:

  • Posterior auricular and Occipital (branches of external carotid artery)

arteries of scalp

Arteries of scalp

 Name the nerves  that innervate Scalp.

Scalp on either side of the midline is supplied by

  • 8 sensory nerves: 4 in front of the auricle and 4 behind the auricle.
  • 2 motor nerves1 in front of the auricle and 1 behind the auricle.

The nerves in front of the auricle are branches of the three subdivisions of trigeminal nerve ie. ophthalmic, maxillary and mandibular. Those behind the auricle arise from the second and third cervical nerves (C1 spinal nerve has no cutaneous branch).

Sensory nerves of the scalp

In front of the auricleBehind the auricle
Supratrochlear (from ophthalmic division of trigeminal nerveGreat auricular (from ventral rami of C2-C3 spinal nerves)
Supraorbital (from ophthalmic division of trigeminal nerve)Lesser occipital from ventral ramus of C2 spinal nerve)
Zygomaticotemporal (from maxillary division of trigeminal nerveGreater occipital (from dorsal ramus of C2 spinal nerve)
Auriculotemporal (from mandibular division of trigeminal nerve)Third occipital (from dorsal ramus of C3 spinal nerve)

Motor supply of Scalp

MuscleLocationNerve supply
Occipital bellies of occipitofrontalis muscleBehind the auriclePosterior auricular branch of facial nerve
Frontal bellies of occipitofrontalis muscleIn front of the auricleTemporal branch of facial nerve

scalp nerve supply

Write in a tabulated form the origin, insertion, action and nerve supply of  Occipitofrontalis Muscle.

 Occipitofrontalis muscle consists of a pair of occipital bellies (posteriorly) and a pair of frontal bellies (anteriorly). Both the parts are inserted into the intervening galea aponeurotica or epicranial  aponeurosis.

occipitofrontalis muscle

MuscleOriginInsertionNerve supplyAction
Occipital bellies of occipitofrontalis muscleLateral 2/3 rd of superior nuchal lines of occipital boneInto epicranial aponeurosisPosterior auricular branch of facial nerveAlternate contraction of occipitalis and frontalis move the scalp backward and forward
Frontal bellies of occipitofrontalis muscleSkin and subcutaneous tissue over the eyebrows and root of noseInto epicranial aponeurosisTemporal branch of facial nerveFrontal bellies raise the eyebrows as in surprise.

Applied Aspects

Deep transverse wounds of scalp tend to gape

 In deep wounds of scalp if the epicranial aponeurosis is cut transversly the wounds tend to gape because the aponeurosis is under tension in anteroposterior direction due to the tone of occipitofrontalis muscle. If the wound cuts the aponeurosis in antereoposterior direction, it will not gape.  

Scalp wounds bleed profusely

The scalp has rich blood supply and the walls of the blood vessels are adherent to the fibrous network as they pass in the second layer of the scalp. Therefore, when the blood vessels are torn or cut, they are unable to retract and cause profuse bleeding. 

Fourth layer of scalp (loose areolar tissue) is known as ‘dangerous layer of scalp’.

The subaponeurotic loose areolar connective tissue layer is known as dangerous layer of scalp because the blood and pus tend to collect in this layer and as it contains the emissary veins ( which connect veins of scalp to intracranial dural venous sinuses), the infection from this layer may travel readily along the emissary veins into the intracranial venous sinuses.

A blow on head may cause ‘Black Eye”

A  blow on head leads to collection of blood in the 4th layer  (loose areolar tissue) of scalp. The blood from this layer may gravitate into the eyelids because the frontalis muscle has no bony attachment. This leads to formation of hematoma and black discoloration of skin around the eyes few hours after the head injury resulting in a condition called ‘black eye’. The blood cannot pass laterally or posteriorly due to the attachment of  epicranial aponeurosis and occipitalis muscle to the superficial temporal lines and superior nuchal lines respectively.

Safety valve hematoma

In children the fracture of cranial vault may be accompanied by  torn dura mater and pericranium. In such cases the blood from intracranial hemorrhage escapes into the subaponeurotic/fourth layer of the scalp through the fracture lines. As a result, the signs of cerebral compression are not seen until the subaponeurotic space is completely full of blood. Because of this the collection of blood in the fourth layer is referred to as a safety valve hematoma.

Cephalhematoma

Accumulation of blood deep to the pericranium/periosteal layer of scalp due to injury is known as cephalhematoma. The swelling  is localized over the particular bone and takes the shape of the bone involved, because  the pericranium is loosely attached over the bones except at the sutural lines where it is connected to the endosteum via sutural ligaments. The hematoma is bound by suture lines  and the swelling has well-defined margins. Cephalhematoma is often seen in the parietal region. It may take 4-7 days to disappear.

Caput succedaneum: It is a collection of fluid in the loose areolar tissue/fourth layer of the scalp.  The swelling is diffuse, crosses the sutures and the midlne and is over the presenting part of the head at delivery.  It  occurs  due to obstruction of venous return of scalp during the passage of head via the birth canal. Usually the edema subsides in  24-48 hrs.

9 thoughts on “Scalp

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