Anatomy of the Scalp

The scalp consists of five distinct anatomic layers. Listed from the most superficial to the deepest, these layers include: (1) the skin with its characteristic thick dermis; (2) the subcutaneous tissue; (3) the relatively rigid galea aponeurotica, which is continuous with the superficial musculoaponeurotic system, frontalis, occipitalis, and superficial temporal fascia; (4) underlying areolar tissue; and (5) skull periosteum.

The relatively poor fixation of the galea to the underlying periosteum of the skull provides little resistance to shear injuries, resulting in large flaps or “scalping” injuries. This layer’s resultant potential space also provides little resistance to hematoma or abscess formation. As a result, extensive fluid collections related to scalp injury tend to accumulate in the subgaleal plane.

The rich vascular supply of the scalp receives vascular contribution from the internal and external carotid arteries. The forehead and anterior scalp are mainly supplied by terminal branches of the ophthalmic artery, which is a branch of the internal carotid artery: the supratrochlear and supraorbital arteries. The supratrochlear vessels arise 1.6 to 2.3 cm from the midline, which is usually located at the medial border of the eyebrow.¹² The supraorbital vessels arise through the supraorbital notch which is located 2.4 to 2.9 cm from the midline.¹³ The external carotid artery provides three branches to the scalp. The terminal branch of the external carotid artery, the superficial temporal artery, ascends anterior to the helix within the superficial temporal fascia and it supplies the temporal and parietal region. The posterior auricular artery ascends between the auricle and mastoid process and supplies blood to the scalp posterior to the auricle. The occipital artery, which supplies blood to the back of the scalp, pierces the fascia connecting the cranial attachment of the sternocleidomastoid and trapezius muscle, and ascends at a mean distance of 4.2 cm from the midline of the external occipital protuberance.¹⁴

In the subcutaneous layer, there is an abundant communication of vessels, which can result in significant blood loss when the scalp is lacerated.

Planning Scalp Incisions

The single most important means of preventing or minimizing wound healing complications of the scalp is the thoughtful planning of the initial scalp incision. Because the current treatment of malignant brain tumors commonly requires repeated craniotomies, scarring and a loss of tissue elasticity can be predictably anticipated. Soft tissue is frequently further compromised by external beam radiation, resulting in scalp wound breakdown, failure to heal, or skin necrosis. Therefore, in anticipation of such compromised wound healing, the initial operative incision should be placed so as to maximize blood flow to the healing incision, and to allow for alternate salvage maneuvers in the event of wound breakdown. Generally, linear scalp incisions that run parallel to the major arteries of the scalp are preferred over traditional U-shaped craniotomy flaps. Such linear incisions are well perfused, heal favorably, and offer broader surgical options in the event of wound breakdown.¹⁵ Ideally, the scalp incision lies adjacent to, rather than directly over, underlying anticipated cranial osteotomies, microplates, and screws, to avoid hardware exposure and infection of the craniotomy bone segments in the event of minor incisional dehiscence.

Lacerations of the Scalp

Scalp wounds should always be inspected for underlying fractures. Because the scalp has a rich vascular supply, lacerations may result in significant blood loss, particularly in children. The large diameter of the scalp vessels often requires that they be individually clamped and ligated for control. Bleeding from a scalp wound can be controlled emergently until definitive care is provided with temporary pressure dressings, Raney clip placement of the wound edges, or an over-and-over continuous stitch with large sutures.

The rich intercommunicating blood supply of the scalp is such that one set of superficial temporal vessels alone may nourish the entire scalp. This rich vascularity allows the survival of large, narrow-pedicled avulsion flaps that would never survive anywhere else on the body. For that reason, almost all traumatic scalp flaps should be appropriately cleansed, minimally debrided, and anatomically replaced. Only the hair adjacent to the lacerated edges needs to be shaved to allow easier suture placement and removal. The subgaleal space is drained with a closed suction drainage system before the scalp is closed in layers. In general, the galea and the dermis are closed with 2-0 or 3-0 absorbable sutures before the skin is closed with running or interrupted 3-0 or 4-0 nylon sutures.

Wounds with Tissue Loss

The management of scalp wounds with soft-tissue loss is determined by the amount of soft tissue lost and the type of tissue exposed. Even relatively small scalp defects can present a reconstructive challenge. The inherent inelasticity of the galea aponeurotica contributes to a property known as “stretch-back,” the tendency for the scalp to contract back toward its original state.¹⁶ Stretch-back leads to increased tension and ischemia across the healing incision, with sequelae ranging from alopecia and widened scars, to nonhealing wounds and tissue necrosis. The convex curvature of the cranium also complicates scalp closures, requiring additional flap length to achieve the desired tissue advancement. Finally, although local scalp flaps provide the best cosmetic outcome, hair-bearing scalp is a limited resource, and one that can be further depleted by pre-existing scars across the axial blood supply.

Local Advancement (Galeal Scoring)

The surface area of the scalp adjacent to the defect can be enlarged considerably by galeal scoring to allow closure by advancement of the wound edge. Each cut, which is made at 1-cm intervals in a parallel or crosshatch fashion, allows the scalp to be stretched approximately 4 to 6 mm. Galeotomies should be oriented perpendicular to the desired direction of advancement, and must be done carefully so as to avoid compromising the vascular supply to the scalp with incisions that are unnecessarily deep. This scoring maneuver requires a complete division of the substantial galeal layer (Fig. 139-1). Tissue loss of more than 1 to 2 cm may require extension of the laceration to allow greater undermining and scoring. Defects that are 3 cm in diameter can be routinely closed with this technique.

FIGURE 139-1 Scalp flaps can be enlarged considerably by galeal scoring. The galea is completely divided at 1-cm intervals. A, Defect before debridement. B, Defect after debridement. C, Appearance of galea before scoring. D, Appearance of galea after scoring. Note the increase in surface area. E, Resultant closure.

Skin Grafts

Wounds in which soft-tissue loss is so extensive that the skin edges cannot be approximated are closed with either skin grafts or flaps. Full-thickness skin grafts contain the epidermis and the complete thickness of dermis from the recipient area. Split-thickness grafts contain the epidermis and a variable thickness of the dermis. Grafts with a greater thickness of dermis contract less on the wound bed and provide more durable coverage. Thin grafts have the advantage of more rapid revascularization, so they are more likely to be successful. Thin grafts, however, tend to provide less durable coverage.

A skin graft may cover any scalp wound that has capillary circulation, which will ultimately provide a source of vascular ingrowth for that graft. For that reason, skull periosteum or any more superficial scalp layer will support a skin graft. Most scalp defects are closed with thin (0.010- to 0.014-inch thickness), “meshed” skin grafts.

Meshed grafts are those that are mechanically perforated in a grid pattern, which allows them to be expanded and to conform to irregular surfaces. The perforations also provide egress for wound drainage. The resultant improved graft bed contact optimizes conditions for graft take (Fig. 139-2). For scalp defects, meshed grafts should not be perforated and expanded more than 1.5 times their normal size unless donor skin is in short supply. A widely expanded graft is less desirable because larger open areas take longer to epithelialize and provide poorer protective coverage.

FIGURE 139-2 A meshed skin graft placed minimally expanded over a scalp wound. Note how perforations in the graft allow egress for drainage from the wound bed.

Skin grafts are most easily harvested with an electric dermatome. The upper lateral thigh has skin of sufficient thickness to allow uncomplicated healing of the donor site. Donor site scarring in this area is usually covered with clothing.

To ensure optimal graft-bed interface for graft take, the graft should be immobilized to the scalp recipient site. A tie-over stent dressing or a quilt dressing in which the overlying dressing is sutured to the intact wound edges is most often used to achieve this immobilization.

Several flap designs allow closure of scalp wounds with significant soft-tissue loss. However, the wound should not be enlarged considerably to close a large traumatic wound emergently; rather, if the periosteum remains, a split-thickness skin graft should be applied. When scalp with periosteum is lost, a closed wound is obtained most expeditiously if, at the time of presentation, the outer table is drilled down to find bleeding points that can provide a bed for a split-thickness skin graft take. A meshed, nonexpanded, split-thickness skin graft is placed immediately at the time of the drilling. An older, well-proven technique involves removing the outer table of the skull to expose the diploë and treating the wound with wet dressings for 5 to 7 days, at which time luxuriant granulation tissue usually forms. This granulation tissue readily accepts a skin graft.

Another method involves making small drill holes 1 cm apart through the outer table down into the diploë space. Usually, granulation tissue arises from these holes and grows over the exposed calvarium to coalesce and form a suitable bed for skin grafting.

Recently, multiple studies showed that vacuum-assisted closure devices hasten soft-tissue contraction as well as granulation tissue formation in various trunk and extremity wounds.¹⁷ In the scalp, two small studies demonstrated a possible role for the vacuum-assisted closure device. Molnar et al. treated four patients with exposed skull by removing the outer table, immediate application of a split thickness skin graft to the diploë and treatment of the wound with a vacuum-assisted closure device for 3 to 4 days. The author reported a 100% graft take without complications.¹⁸ In a another study, Umesh et al. reported a successful case report where the author closed a 10 × 12 cm wound with exposed dura by using the vacuum-assisted closure device over the dura for a period of 3 weeks and then grafting the granulated wound bed with a split thickness skin graft.¹⁹

Skin grafting directly onto bone is susceptible to breakdown after minimal trauma and leaves an area with alopecia and significant contour deformity. This problem can be corrected as a delayed reconstruction with advancement or rotational flaps after galeal scoring or with tissue expanders.

Flaps

Wounds with exposed vital structures or wounds that do not have exposed capillary circulation require flap coverage. Whereas skin grafts provide only thin coverage and depend on the wound bed for their revascularization and survival, flaps carry their own blood supply and provide soft-tissue bulk to the wound.

The two basic principles of flap coverage follow:¹ move available tissue with its intact circulation from an area of relative excess to the area of deficiency, and²