Key points

Introduction

Penile skin loss may occur after a variety of disease processes. Reconstructive options are tailored to the defect. When skin is missing, skin grafting can achieve the goal of reconstructing like with like.

Even urologists who do not specialize in reconstruction may be called on to give their advice in complex cases, especially after necrotizing genital infections. Although they are experts in general reconstructive principles, plastic surgeons may not be aware of the unique anatomic and functional factors in penile and genital reconstruction; collaborative efforts are often necessary.

Introduction

Penile skin loss may occur after a variety of disease processes. Reconstructive options are tailored to the defect. When skin is missing, skin grafting can achieve the goal of reconstructing like with like.

Even urologists who do not specialize in reconstruction may be called on to give their advice in complex cases, especially after necrotizing genital infections. Although they are experts in general reconstructive principles, plastic surgeons may not be aware of the unique anatomic and functional factors in penile and genital reconstruction; collaborative efforts are often necessary.

Indications for penile skin grafting

Several disease processes may cause actual or functional loss of penile skin, and skin grafting is often necessary to reconstruct these wounds. The most common problems include necrotizing infections of genital skin (ie, Fournier gangrene), lichen sclerosus, trauma, and burns. Resection of penile cancer or genital lymphedema may require removal of skin from the penis, leading to a need for replacement. A circumcision sometimes results in too much skin removal and the need for a skin graft. In addition, reoperative repair of hypospadias or penile urethral stricture may use oral mucosal or skin grafting.

Skin anatomy

Skin has many roles, most importantly serving as a barrier to the outside world. The skin has 3 layers: the epidermis, the dermis, and the hypodermis or subcutaneous layer ( Fig. 1 ). The epidermis, the most superficial layer, produces and maintains the stratum corneum, the waterproof outermost barrier of the skin. The epidermis also contains important specialized cells such as melanocytes, immune cells, and sensory cells.

Layers of the skin.

( From Fang RC, Mustoe TA. Structure and function of the skin. In: Guyuron B, Eriksson E, Persing JA, editors. Plastic surgery: indications and practice. Philadelphia: Saunders Elsevier; 2009; with permission.)

The dermis makes up the remaining 90% to 95% of the total skin thickness and provides a collagen matrix to support the epidermis. The skin appendages, such as hair follicles, sweat glands, and sebaceous glands are found in the dermis. The hair follicle has multipotent bulb cells that are important in reepithelialization of a wound.

Terminology

A skin graft is skin that is removed from one anatomic location, without a blood supply, and transplanted to a new site. Engraftment is the process of revascularization and healing of the graft. Skin grafts are commonly categorized in terms of the depth of the graft. A full-thickness skin graft is comprised of all the dermis and epidermis. This graft is harvested at the interface of the dermis and hypodermis (see Fig. 1 ). The thickness of this graft is determined by the anatomic site from which is it is harvested. For example, a full-thickness skin graft obtained from the prepuce is thinner than a graft harvested from the back. In the case of a full-thickness skin graft, the donor site is closed primarily. In contrast, a split-thickness skin graft comprises the epidermis and only a portion of the dermis. It is harvested with a dermatome, an instrument that shaves a sheet of skin of controlled width and thickness.

Differences between split-thickness and full-thickness skin grafts

There is more dermis in a full-thickness skin graft than in a split-thickness skin graft, so there are some important distinctions in the behavior and potential use of both types of grafts ( Table 1 ). Because split-thickness skin grafts are thinner and have less tissue, they have less metabolic demand from the wound bed, and thus have better survival or take. In contrast, a full-thickness skin graft is thicker and, as such, has greater metabolic demand. Survival of a full-thickness skin graft is more uncertain and it requires a well-vascularized recipient site.

Full-thickness skin grafts display significantly more primary contraction than split-thickness skin grafts. Primary contraction is the recoil that occurs immediately after a skin graft is harvested and is directly related to the amount of elastin present in the dermis. A full-thickness skin graft can lose up to 40% of its surface area from primary contraction. These rates are lower with grafts that have less dermis. For example, a thin split-thickness skin graft only loses 10% of its surface area from primary contraction.

Over time, full-thickness skin grafts have a tendency to resist the significant problem of secondary contraction, the contraction of a skin graft after healing. Myofibroblasts within the graft are primarily responsible for secondary contraction. The use of thicker skin grafts, with more dermis, helps to prevent this type of contraction. Once secondary contraction ends, full-thickness skin grafts tend to stretch and grow with an individual, whereas split-thickness skin grafts tend not to expand as well.

Another important distinction between full-thickness skin grafts and split-thickness skin grafts is the durability of the graft. Once again, this difference is directly related to the thickness of the dermal layer. Thicker grafts are better able to resist friction and trauma.

It is also notable that the skin’s appendages, such as sweat and sebaceous glands, are present in the dermis. As such, full-thickness skin grafts have a greater ability to sweat or produce oil. However, this ability depends on the reinnervation of the glands, which can take several months to years. In the interim, it is important to keep skin grafts well moisturized to prevent drying, which can lead to fissuring of the grafted skin, especially for split-thickness skin grafts, which are lacking in these glands permanently.

Hair follicles are also present in the dermis, and full-thickness skin grafts show the hair growth pattern of the donor site. It is therefore important to make sure that full-thickness skin grafts used in penile reconstruction are obtained from a hairless area. Split-thickness skin grafts are generally hairless and thus are generally preferred on the penis.

In choosing a skin graft, donor site morbidity must also be considered. A full-thickness graft, by definition, leaves a full-thickness defect at the donor site, and large donor sites may be difficult to close or hide. Split-thickness grafts have the benefit of leaving a donor site that heals with only simple wound care. In addition, the thickness of dermis varies by anatomic site and with age. The dermis is thinner in children and with advancing age, and what may be a thick split-thickness graft in a young adult patient may leave a full-thickness wound in the elderly.

Choice of skin graft in penile reconstruction

The choice of graft thickness depends on the needs of the wound to be covered and the inherent compromises associated with graft thickness. A core principle of reconstructing tissue loss is to replace like with like, meaning choosing donor tissue that most closely replicates the native tissue in function and appearance. The skin of the penis is thin, hairless, and flexible. Because of the dramatic change in size of the penis with erection and the need for durability because of the tissue demands of sexual activity, full-thickness skin grafts seem to be the preferred choice in the replacement of penile skin. Although some prefer full-thickness grafts in penile skin replacement, in most cases it is best replaced by a split-thickness skin graft ( Fig. 2 ). A thick split-thickness skin graft offers the best combination of graft take and durability.

( A ) Patient with skin loss and buried penis from lichen sclerosus. ( B ) Patient after excision of scarred skin and split-thickness skin grafting to penis. ( C ) Patient 5 weeks after surgery. ( D ) Lateral thigh skin graft donor site 5 weeks after surgery.

In some cases, a full-thickness skin graft may be appropriate in penile reconstruction. The most common example is in urethral reconstruction. Although a detailed discussion of graft urethroplasty is outside the scope of this review, understanding the principles behind graft selection and the factors that determine success is essential. Urethral reconstruction calls for tissue that resists the stress of urine passage. At present, a full-thickness oral mucosal graft is the closest replacement tissue for the urethra. It is used extensively in staged reconstruction of urethral repairs and complex hypospadias. Meshed foreskin and split-thickness skin grafts used in staged urethral reconstruction have fallen from favor, especially as oral mucosal grafts have come into use. In some circumstances, the prepuce of an uncircumcised patient may be used to reconstruct penile skin elsewhere.

Normal skin graft healing

Engraftment involves removing tissue (skin or mucosa) from its native location and blood supply and transferring it to a recipient bed, where the transplanted tissue undergoes revascularization. Disruption of this process leads to graft failure.

The first phase of engraftment is known as plasmatic imbibition and lasts for 24 to 48 hours. During this time, the diffusion of nutrients, oxygen, and metabolic waste occurs passively back and forth across the concentration gradient from the graft to the wound bed. For the duration of the imbibition phase, the graft is without blood flow and appears white. Greater vascularity of the wound bed results in shorter graft ischemia time. Because it is composed of more tissue and has greater metabolic demand, a full-thickness skin graft can only tolerate this ischemia for about 3 days. However, a split-thickness skin graft is more forgiving because it has less metabolic demand. It can survive ischemia through imbibition for up to 5 days.

The next stage, inosculation, begins within 36 hours and involves the formation of anastomotic connections between host and graft vasculature. Skin grafts begin to have capillary refill during this phase. As blood flow begins, it is disorganized at first. As such, especially full-thickness skin grafts may appear slightly cyanotic at this time.

During the final phase of skin graft healing, revascularization, new vessels within the graft establish the definitive vasculature that will ensure the long-term survival of the graft. Whether the preexisting vessels in the graft act as conduits for ingrowth and become reendothelialized, or entirely new vessels form, or all of these occur, remains an area of ongoing research.

Over time, it is normal for skin grafts to become hyperpigmented or hypopigmented. Grafts that are harvested from the lower trunk and thighs have a tendency to darken or take on a yellow color as the graft matures, especially with skin grafts from the groin. Thinner skin grafts have a greater tendency to be hyperpigmented.

Skin grafts can reinnervate over time. The process of nerve ingrowth begins both from the wound bed and from the periphery of the skin graft, progressing inwards. This process can take more than 2 years. The extent of reinnervation depends on the presence of neurilemmal sheaths within the graft. The more dermis that is present in the graft, the better the likelihood of reinnervation. Thus, full-thickness skin grafts have better potential for reinnervation than thin split-thickness skin grafts.