Scalp
anatomy in hair
restoration
In order to minimize post surgery complications and to obtain
superior hair transplants, it is necessary for the hair transplant
surgeons to have a thorough understanding of the anatomy of the
scalp.
When a cross section of the scalp is examined the following can
be observed:
1. Skin - forms the first layer consisting of the epidermis and
the dermis. The scalp skin is always thicker than the skin from
rest of the body. It contains sebaceous glands, sweat glands and
hair follicles and ranges from 3mm thick in the front to 8 m thick
on the back of the head.
2. Subcutaneous layer - forms the second layer comprising of
a rich network of arteries and veins. The fat in the subcutaneous
layer is compartmentalized by fibrous partitions. When this layer
is wounded, as it is when the donor strip of hair follicles skin
is cut from the back of the scalp, it often results in a hemorrhage.
This is because the blood arteries are attached to the dermis
and the fibrous septa, making it difficult for them to shrink
back to position. To avoid hemorrhage in hair transplant surgery,
surgeons usually suture the wound immediately while applying some
pressure to stop the blood from coming out of the cut arteries.
The carotid artery supplies blood to the scalp and runs along
the periphery of the head branching out into a network covering
all parts of head. The depth at which these arteries run is critical
in the surgeon’s point of view.
Similar to blood vasculature, nerve supply is also peripheral
forming a network that traverses the entire scalp. Hence the surgeon
needs to be very cautious while working on the peripheral layers.
Since the nerves are affected less in the centre of the scalp
during surgery, this region is the most often operated upon site.
That is one of the reasons why anesthetists are extra careful
when it comes to administering nerve blocks.
3. Galea aponeurotica - forms the third layer of the scalp. This
layer is always found in association with the muscles on the head.
The associated muscles are found behind the ears, in the neck
region and the forehead. This makes the scalp skin tight and closer
to the skullcap. When we contract the forehead muscles, our eyebrows
move up and the forehead wrinkles. The layer is not continuous
and in some areas such as beneath the eyelids, a subaponeurotic
space is present. When there is any head injury, many patients
have a black eye because blood streams down into this space.
The galea is 1-2 mm thick, dense, non elastic fibrous sheet and
is bound to the subcutaneous layer firmly. Except in congenital
defects, the galea is well developed in most individuals. Because
it is bound to the subcutaneous layer firmly, dissection of this
layer is difficult and results in heavy blood loss. Its non elastic
nature helps in protection while some surgeons find this a hinderance
in scalp surgery. This property was used to develop a technique
called galeotomy, but the main disadvantage of trauma to the subcutaneous
layer and heavy bleeding has resulted in practically no takers
for the technique.
4. Subgaleal space – forms the fourth layer. It is made
of a loosely bound fibroareolar tissue [fibrous connective tissue]
and has no vasculature. When the fibroareolar layer is underdeveloped,
the scalp is said to be tight and when we place our fingers on
our scalp and move it on the head, we can feel the movement of
the scalp above the pericranium. Subgaleal space is very important
from the surgical point of view. The subgaleal space extends to
the musculature of the head and blends with it.
So the area of scalp that has the subgaleal space is made of
5 layers viz. skin, subcutaneous layer, galea, subgalea and pericranium.
When the subgaleal space blends with the ear, forehead and nuchal
muscles, the scalp is only three layered, viz skin, subcutaneous
and deep fascia which is a band of fibrous connective tissue binding
the muscles together. This difference in scalp anatomy is very
important to plan surgeries. The five layered region can be subjected
to wide excisions since it can glide over the pericranium while
the same is much more restricted in the three layer regions. The
scalp is also differentiated into areas based on the tension patterns
which are described as Langer’s lines. These lines play
a major role in deciding the width of the surgical excisions.
5. Pericranium – forms the fifth layer of the scalp and
is just above the skull. It is a dense fibrous sheet varying in
its width on different parts of the skull based on the location
and is bound to the galea aponeurotica loosely separated by the
subgaleal space. It can hold sutures even when a significant amount
of tension is applied.
The importance of studying scalp anatomy
The knowledge of scalp
anatomy is of use to medical professionals for a variety of reasons.
There are many conditions occurring
on the head that need surgical correction. These include removal
of benign and malignant tumors, burn injuries, and congenital
malformations, apart from hair restoration procedures. Hence the
study is not limited to hair restoration surgeons, but has application
in plastic, neurological, dermatological and craniofacial surgeries
and each of these groups of surgeons view the scalp differently
depending on their professional priorities. Hence a general anatomy
of the scalp can be of appreciable use in minimizing all unintended
complications.
When one looks at the skin, we see wrinkles or lines oriented
in certain directions. These lines form due to the arrangement
of collagen bundles in the dermis
and along these lines are present the lines of minimum tension. In the hands,
legs and the scalp, these lines run longitudinally and in the neck and the
torso they are circumferential. The orientation of the lines is important
for excision procedures. When the excisions are made along the lines, there
is minimal scarring and the wounds heal faster. This is one of the reasons
why elliptical strips of hair are harvested from the occipital region (the
back) of the scalp while in the crown or other regions of the head, the excisions
must be vertical.
The laxity of the scalp is another important aspect during surgery. When the
scalp moves considerably well on the cranium, after a surgical procedure,
such scalps are easier to close with sutures and require very little or practically
no undermining and stretching of the skin. This scalp property is very useful
to surgeons as the post surgery complications and trauma of surrounding tissues
are minimal.
Elasticity and laxity of the scalp are independent of each other. When the
Langer’s lines are drawn on the head, we can see that the lines are
vertical from the front of the head to the back are vertical and when it comes
to the occipital region they become horizontal. In the occipital region the
nuchal line is present. Until just above the nuchal line, the scalp has five
layers and hence wide strips of donor hair can be harvested superior to the
nucha. But below the nuchal line the subgaleal layer blends with the muscles
and hence only three layers of the scalp are present. Hence donor harvesting
in this area is highly restricted.
How much can the skin stretch?
The stretchability of the skin depends on elastin and collagen
in the skin. The skin can be expanded up to 100% after which the
skin looses its elasticity irreversibly. Hence when the surgeon
has to stretch the skin for wound closure, he usually does not
undermine the closure so that some elasticity can be recovered.
When a patient undergoes a series of scalp excisions he experiences
irreversible damage and is referred to as stretch atrophy and
is very common in extensive hair transplantation procedures. Depending
on the scalp characteristics with emphasis on laxity, undermining
of tissues must be undertaken with proper judgment. Less undermining
is more beneficial as compared to heavy undermining.
The scalp anatomy studies may throw some light on the closing
patterns of the wounds as well. Other than skin to skin suturing,
a structured layered suturing may be beneficial in wound closure
and healing.
Scalp anatomy in hair restoration references
- Seery GE. Surgical
anatomy of the scalp. Dermatol Surg. 2002 Jul;28(7):581-7. PMID:
12135510
- Seery GE. Scalp surgery: anatomic
and biomechanical considerations. Dermatol Surg. 2001 Sep;27(9):827-34.
PMID: 11553172
- Parsley WM. Natural hair patterns.
Facial Plast Surg Clin North Am. 2004 May;12(2):167-80. PMID:
15135127
|
