Scalp
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Definition: it is formed by skin and subcutaneous
tissue that covers the bones of vault of the skull. It Extends of scalp
Anteriorly:
Supraorbital margin,
Laterally :
Superior temporal lines,
Posteriorly:
External occipital protuberance and highest and superior nuchal lines.
Layers of scalp
It contain five layers.
Superficial three
are intimately bound together and move as one unit.
The five layers from superficial to deep are:
1.
S- Skin: It is thick layer. It contains large number of hair
follicles and associated sebaceous glands. Thus, scalp is the commonest site of
sebaceous cysts.
2.
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. This layer contains large number of blood vessels and nerves which adherent to the fibrous network, so any injury
of this layer, if the blood vessels are
torn or cut, the walls are unable to retract and this causes profuse bleeding.
3.
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) which is a tendon like structure with
connect the occipitalis and frontalis muscles the two belly of
occipitofrontalis muscle . 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.
4.
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 is also known as the
‘dangerous layer of scalp’.
5.
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 tightly to the
endocranium via sutural ligaments.
Arterial supply of scalp
Scalp has a rich
blood supply from the branches of external and internal carotid arteries.
There are five
arteries on each side, three in front of the auricle and two behind the
auricle. The arteries are:
In
front of the auricle:
Supratrochlear and
Supraorbital (branches of internal carotid artery)
Superficial
temporal (branch of external carotid artery)
Behind the auricle:
Posterior auricular
and Occipital (branches of external carotid artery)
Venous Drainage
The venous drainage of the scalp
It 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.
Nerve supply of scalp
It receives cutaneous innervation from
branches of the trigeminal nerve or the cervical nerve roots.
Trigeminal Nerve
Supratrochlear
nerve – branch of the ophthalmic nerve (sensory nerve) , branch of trigeminal
nerve which supplies the anteromedial
forehead.
Supraorbital nerve
– branch of the ophthalmic nerve (sensory nerve) which supplies a large portion
of the scalp between the anterolateral forehead and the vertex.
Zygomaticotemporal
nerve (sensory nerve) – branch of the maxillary nerve, this supplies the
temple.
Auriculotemporal
nerve (sensory nerve) – branch of the mandibular nerve which supplies skin
anterosuperior to the auricle.
Cervical Nerves
Lesser occipital
nerve – derived from the anterior ramus (division) of C2 spinal nerve and
supplies the skin posterior to the ear
Greater occipital
nerve – derived from the posterior ramus (division) of C2 spinal nerve and
supplies the skin of the occipital region.
Great auricular
nerve – derived from the anterior rami of C2 and C3 spinal nerves and supplies
the skin posterior to the ear and over the angle of the mandible.
Third occipital
nerve – derived from the posterior ramus of C3 spinal nerve and supplies the
skin of the inferior occipital region.
Scalp on either
side of the midline is supplied by
Sensory nerves of
the scalp
|
IN FRONT OF
THE AURICLE |
BEHIND THE
AURICLE |
|
Supratrochlear (from ophthalmic division of trigeminal nerve |
Great 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 nerve |
Greater 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
|
MUSCLE |
LOCATION |
NERVE
SUPPLY |
|
Occipital bellies
of occipitofrontalis muscle |
Behind the auricle |
Posterior auricular
branch of facial nerve |
|
Frontal bellies of
occipitofrontalis muscle |
In front of the
auricle |
Temporal branch of
facial nerve |
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.
|
MUSCLE |
ORIGIN |
INSERTION |
NERVE SUPPLY |
ACTION |
|
Occipital bellies of occipitofrontalis muscle |
Lateral 2/3 rd of superior nuchal lines of occipital bone |
Into epicranial aponeurosis |
Posterior auricular branch of facial nerve |
Alternate contraction of occipitalis and frontalis move the scalp
backward and forward |
|
Frontal bellies of occipitofrontalis muscle |
Skin and subcutaneous tissue over the eyebrows and root of nose |
Into epicranial aponeurosis |
Temporal branch of facial nerve |
Frontal bellies raise the eyebrows as in surprise. |
Why deep transverse wounds of scalp
tend to gape, but not longitudinal wound?
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 longitudinally along the direction of fibers of the
aponeurosis which is directed antereoposteriorly, so it will not create large gape.
Why scalp wounds bleed profusely –
explain anatomically?
Deep lacerations to the scalp tend to bleed
profusely for several reasons.
These are:
1.
Rich Blood Supply and Adherent Blood Vessel
Walls: The scalp has a large
number of arteries, veins, and capillaries that provide blood to the tissues.
Compared to blood vessels in other parts of the body, these blood vessels in
the scalp are less mobile because they are embedded in the fibrous connective
tissue. A scalp wound prevents the arteries from properly retracting or
constricting, which results in prolonged bleeding.
2.
Occipitofrontalis Muscle: The muscle covering the top of the skull is
called the occipitofrontalis muscle, or epicranial aponeurosis. It is a thin,
broad muscle. It is divided into the frontal belly and the occipital belly,
which are joined by a central tendon. This muscle is in charge of making the
forehead wrinkled and lifting the eyebrows. Because of its adherence to the
scalp's epidermis, it may impede a wound's natural healing process, thereby
intensifying bleeding.
3.
Anastomoses: Numerous arterial anastomoses, or connections between arteries
that permit blood to flow from one vessel to another, are characteristics of
the scalp's blood supply. In the event of a compromised vascular, these
anastomoses offer alternative pathways for blood flow. Under normal
circumstances, this redundancy helps with tissue perfusion; nevertheless, when
a scalp injury occurs, it also leads to excessive bleeding.
Why 4th layer of scalp
(loose areolar tissue) is known as ‘dangerous layer of scalp’-explain
anatomically?
The sub-aponeurotic 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.
Why a blow on head may cause ‘Black
Eye”-explain anatomically?
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.
Why 4th layer of scalp known
as safety valve hematoma-explain anatomically?
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.
Explain anatomical basis of 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.
Explain anatomical basis of 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.
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