A critical anatomic landmark in the mature male hairline is the frontal–temporal recession. This landmark is formed by the emergence of two convex lines making up the frontal and the temporal hairlines. Design of the frontal–temporal recession is critical to a natural result (Fig. 23.3). A hair restoration in which this rule has not been observed leads to an extremely unaesthetic appearance, especially in the mature adult. Young males usually do not have this recession, and this is one characteristic that distinguishes the child from the adult pattern. As baldness progresses, the frontal–temporal recession increases, forming an acute angle. Both women and children tend to have a continuous line between the frontal and temporal areas without this recession. Another important characteristic of a natural hairline is the transition from fine hair to more dense hair with a degree of irregularity along the margin. Natural hairlines are not straight and regular. Many of the unsatisfactory results in hair restoration demonstrate a fundamental lack of knowledge of these critical points. Other important factors are that the hair follicle sits about 3–3.5 mm below the surface of the scalp and that scalp thickness varies between 5.5 and 6.5 mm. These factors are important in considering the placement of the grafts in the scalp, the thickest layer of skin on the human body.

Fig. 23.3 (A) Preoperative and (B) postoperative appearance of a patient who had undergone hair transplantation in the frontal area in which the acute frontal–temporal angles were maintained, resulting in a normal-appearing recession. Maintenance of this recession is critical for a natural appearance.

Characteristics of hair

There are two primary types of normal adult hair. Vellus hair is soft, short, lightly pigmented or hypopigmented hair that can be almost invisible. It can be found over the entire body. On the scalp, it is primarily seen in the frontal area on the forehead, and it also makes up a large area of the bald scalp. Terminal hair is the coarser, long hair and is pigmented. Within the terminal hair group are subgroups, such as those on the scalp, pubic area, and eyebrows. As an individual who is destined to lose hair ages, the terminal hairs can be replaced by vellus hairs. It is usually a progressive evolution in which the terminal hairs are lost and the thinner, shorter hairs slowly replace them until it converts to a vellus-type pattern. This process continues until, eventually, baldness is evident in the area. It is an interesting phenomenon that biopsies, even of bald areas, show that hair follicles are present, but they are atrophic in nature and are no longer producing significant amounts of hair in these individuals.

There is great variation in all aspects of hair, which is determined in each individual on the basis of race, sex, and area of the scalp. There is also variation in thickness between races: whites have thinner hair than both blacks and Asians do. The shape of the hair also varies greatly. The differences correspond to cross-sectional characteristics. For example, wavy hair is oval on cross-section, whereas stiff or straight hair tends to be round. An important variable is the density of hair per square centimeter. The density of adult hair can vary between 200 and 400 hairs per square centimeter. In the presence of androgenic alopecia, the number of hairs drastically drops off. Large plug grafts, in which 20–60 hairs could be contained in each graft, often led to an unnatural appearance in many patients, resulting in cornrows. The transplantation of these grafts led to a clustering and unnatural look. Normally, one to three hairs emerge from a single orifice, and this fact is critical in obtaining a natural result in hair transplantation. Once this number is exceeded, that is, more than one to three hairs, there is the risk of a visible, unnatural result, especially along the frontal hairline.

The other critical variable is the angle at which the hairs exit the scalp normally. A violation of this principle also leads to an unnatural appearance. In the frontal area, the hair is angled forward; on the temporal and parietal areas, it tends to be angled slightly forward and downward. In the vertex, a spiral pattern is present; below the occipital area, the hairs are angled downward toward the neck. The two factors, thickness and density of hair per square centimeter, are important variables in the visual appearance of the hair. Whereas dark hair is effective in covering areas, fair hair is less effective. The converse is true, however, in designing a natural appearance. Blond or salt-and-pepper hair gives a more acceptable result when it is transplanted versus dark hair, especially in light-skinned individuals. This is especially obvious with dark plug grafts, in which thick hair clusters give a particularly unnatural result in contrast with light-colored skin.

Hair growth cycles

A discussion of the hair follicle cycles of growth and degeneration is relevant in considering hair restoration surgery. These cycles will have an impact on the time it takes for newly transplanted hair to begin to grow and also on the period necessary to see the final result.

There are essentially three cycles – anagen, catagen, and telogen. During the growth phase, referred to as anagen, the follicular cells are actively reproducing, and matrix keratinocytes are producing cells that differentiate into the different hair components. It is estimated that approximately 90% of the hair on the scalp is in the anagen phase, which lasts approximately 2–5 years. During the regression phase, called catagen, there is a degeneration of the keratinocytes, and special mesenchymal cells, referred to as dermal hair papillae, cluster and separate. This phase typically lasts 2–3 weeks (Fig. 23.4). The final resting phase, called telogen, lasts approximately 3 months. During the 3–4-month phase of telogen, the follicle is inactive and hair growth ceases. Approximately 10% of hairs are in telogen phase at any one time. In the telogen phase, the dermal papilla releases from its epidermal attachment, and eventually there is a reforming of a growing bulb. The old hair is shed, and as the cycle goes back to anagen, a new hair will come up and grow in this area. This information is relevant in discussing hair transplantation with patients. After the follicle has been transplanted, one usually sees a resting or telogen phase, and the patient should not expect any significant hair growth for 3–4 months. Although some of the hairs transplanted occasionally seem to continue to grow immediately after the surgical procedure, this can be misleading. This early growth frequently leads to a shedding of the hair shaft before the telogen phase. Therefore, the patient needs to wait several months before any significant hair growth is seen.

Fig. 23.4 The cycles of hair growth.

Diagnosis/patient presentation

Types and patterns of baldness

The most common type of hair loss in both men and women is referred to as androgenic alopecia. The mechanism of androgenic alopecia is inherent in each individual hair follicle as it responds to external stimuli, essentially androgens. The progressive loss of hair is predetermined by genetic characteristics associated with these responsive scalp follicles. In regions of the scalp susceptible to androgenic alopecia, androgens reduce the growth rate, the hair shaft diameter, and the length of the anagen phase. The mode of action of androgens on the target cells occurs at the bulbar region of the follicle. Testosterone is converted to dihydrotestosterone (DHT) by 5 ox-reductase. DHT acts on the target cells, and as discussed in the section on the role and effectiveness of medications, below, it is on this mechanism that finasteride acts in attempting to reduce hair loss by blocking the formation of DHT. It appears that androgenic alopecia is under the control of a single dominant sex-linked autosomal gene. However, this may be influenced by other modifying factors, and there is probably a polygenic component to the expression of male-pattern hair loss. In most men with hair loss, the hair follicles in the frontal and crown regions of the scalp appear most likely to be affected by androgenic alopecia. Although there is considerable variation among ethnic groups as far as the average number of hairs, and also variation among the different hair colors, it is typical that the average individual with a relatively full head of hair has approximately 100 000–150 000 or more hairs growing from the scalp.

Hair loss in women is frequently of a diffuse nature, and thus, most women may not be ideal candidates for hair restoration. The pattern of hair loss, because of its diffuseness, often results in a lack of appropriate donor hair. However, there is a subgroup of women who demonstrate hair loss similar to the male pattern.³ The hair loss in these women frequently begins at the vertex and progresses anteriorly as they approach their 30s and 40s. The family history in these women is also compatible with a male-pattern type of hair loss, with many of the male and female family members reporting balding in both the vertex and superior portions of the scalp. It is this subgroup of women who may be the most appropriate candidates for hair transplantation because the posterior scalp area has adequate donor hair. The history these women give is fairly typical and is one of slow but progressive hair loss, and it is most evident on the superior scalp with good density on both sides and posteriorly. The other interesting characteristic in many of these women is that they maintain a low frontal hairline with a margin of hair anteriorly. This is unlike the male counterpart with progressive elevation of the frontal hairline and increasing temporal recession as the patient ages. Women with this primary type of alopecia characteristically will maintain that frontal hairline for life, and therefore transplantation needs to begin in this relatively low frontal area and progress posteriorly.

In many women, however, the cause of hair loss is secondary to numerous factors, such as surgery, metabolic disorders, chemotherapy stress, and autoimmune disease. This type of hair loss is often of an acute nature, and most of these patients are not candidates for transplantation. On occasion, in the patient who has had hair loss after chemotherapy, if enough time has transpired to allow recovery and there still has been no regrowth, transplantation may be appropriate. However, the take of the grafts has not been ideal in these patients. In many women, the cause of hair loss is secondary to cosmetic surgery, and the mechanism is traumatic hair loss.

Traumatic alopecia is primarily secondary to ischemia of the hair bulbs, although it can be secondary to direct tissue loss, as in postburn alopecia.⁴ Numerous factors can lead to this ischemia. Prolonged pressure on the scalp in a single area, such as in a patient who lies in a comatose position for hours at a time, can cause enough ischemia to the scalp that there can be hair loss without loss of the actual scalp soft tissues. In addition, patients undergoing prolonged surgical procedures under general anesthesia can sustain pressure in an isolated area of the scalp, leading to hair loss.

One of the most common causes of traumatic hair loss is aesthetic surgery of the face and scalp area. Temporal hair loss is probably the most common of this group. It may be due to damage of the hair bulb from a subcutaneous dissection in the temporal area or excess skin traction with resulting ischemia. This also is seen in patients undergoing a coronal forehead lift, with hair loss in the area of a coronal scar. In most of these patients, the alopecia is temporary, and hair will regrow after several months. In some patients, however, the hair loss is permanent, and hair transplantation may be appropriate.^5,⁶ In addition, the scar itself in the scalp or facial area may widen, and because of the absence of hair follicles within the widened scar, a visible area of hair loss is seen.

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