The scalp comprises five layers, each of which can be remembered using the mnemonic SCALP: Skin, subCutaneous tissue, Aponeurotic layer, Loose areolar tissue, Pericranium. The aponeurotic layer is also known as the galea and connects the frontalis and occipitalis muscles. It is also contiguous with the superficial musculoaponeurotic system (SMAS) of the face and neck. It should be approximated during closure of scalp wounds as it provides deep support to the repair. The terms subgaleal fascia and innominate fascia are used interchangeably with the term loose areolar layer which provides scalp mobility rather than strength. It is at this layer that most injuries are sustained and it is described as the scalping plane. Skin thickness varies from 3 to 8 mm according to anatomic location on the scalp and provides additional strength to the repair. The pericranium is the deepest layer and is tightly adherent to the calvarium. It tends to be thin and can easily tear. Therefore, approximation does not add to the strength of a scalp repair. Skin comprises the dermis and the epidermis. Overall thickness varies from 3 to 8 mm according to anatomic location on the scalp, and placement of sutures or clips through the skin provides additional strength to the repair and reapproximates the wound edges, but does not represent the most strength (Fig. 39.1).1–3 Fig. 39.1 Anatomic layers of the scalp. Skin Subcutaneous tissue Aponeurotic layer Loose areolar tissue Pericranium Cranium: External table Diploic space Internal table Epidural space Dura mater Subdural space
2. Tolhurst DE, Carstens MH, Greco RJ, Hurwitz DJ. The surgical anatomy of the scalp. Plast Reconstr Surg 1991;87(4):603– 612, discussion 613–614
3. Williams PL, Warwick R, eds. Gray’s Anatomy. 36th British ed. Philadelphia: WB Saunders; 1980 VASCULARITY OF THE SCALP 2. Which one of the following statements is correct regarding the blood supply to the scalp? artery. The scalp derives its blood supply from both the internal and external carotid systems. It is divided into four zones: anterior, posterior, lateral, and posterolateral. Each zone has its own blood supply, with collateralization between zones. This is clinically relevant with respect to scalp reconstruction using local flaps and replantation. The anterior scalp is supplied by the supraorbital and supratrochlear vessels. These derive from the internal carotid vessels (not the external carotid vessels). The supratrochlear vessels lie medial (not lateral) to the supraorbital vessels. The posterior territory is supplied by the occipital vessels and perforators from the splenius capitis and trapezius, but it is not the largest territory. The largest is the lateral territory, which is supplied by the superficial temporal arteries. A lesser occipital artery does not exist. The greater and lesser occipital nerves supply sensation to the occipital territory. The posterolateral scalp is the smallest territory and is supplied by the posterior auricular artery.1–4 Knowledge of the impressive collateral circulation has been clinically proven with successful near-total scalp replantation based on a single anastomosed artery and vein such as the superficial temporal vessels. Although this can be enough to supply the scalp, multiple anastomoses are still advocated by many where technically possible (Fig. 39.2).5 Fig. 39.2 Innervation and vascular anatomy of the scalp. VASCULARITY Supratrochlear nerve (V1) Supratrochlear artery Supraorbital nerve (V1) Supraorbital artery Posterior auricular artery Occipital artery Superficial temporal artery Zygomaticotemporal nerve (V2) Auriculotemporal nerve (V3) Lesser Occipital nerve (V3) Greater Occipital nerve (C2,C3) Occipital nerve (C3)
The biomechanics of the skin and different viscoelastic properties of the scalp layers can be used to assist in closure of scalp defects. Tissue creep and stress relaxation are terms used to describe the viscoelastic properties of skin that enable on-table closure of tight wounds and also apply to tissue expansion techniques. The two terms are often confused but have different meanings. Stress relaxation occurs when a force is applied to the skin that causes it to stretch to a given length. After a short amount of time, the load required to achieve the desired length or stretch reduces. In contrast, creep occurs when the force applied remains constant and this causes a continued stretch over time. Skin can be placed under tension intraoperatively by either placing temporary sutures or using skin hooks to partially close the wound. The skin has more stretch or elasticity than the underlying galea. Therefore, multiple perpendicular incisions or scores to the undersurface of the galea can significantly increase the amount of stretch within this layer. Simple undermining can also be helpful to close some defects because this allows redistribution of the available skin.1
5. Karibe J, Minabe T. Vascular consideration in repair of total scalp avulsion. BMJ Case Rep 2017, October 24;2017: bcr2017220605 SCALP INNERVATION 3. Which one of the following statements is correct regarding scalp innervation? The supraorbital nerve has superficial and deep divisions. The superficial component supplies sensation to the forehead anterior to the hairline. The deep component supplies sensation posterior to the hairline. This has clinical relevance in brow-lift procedures, bicoronal cranial flaps, and trauma in which the nerves may be damaged, leaving an area of paresthesia. The zygomaticofacial nerve derives from the maxillary division (not the ophthalmic division) of the trigeminal nerve. It supplies a region of skin lateral to the brow. The auriculotemporal nerve derives from the mandibular division of the trigeminal nerve and supplies the lateral scalp. The greater and lesser occipital nerves supply the occipital territory, but it is the greater occipital nerve that emerges from the semispinalis 3 cm below the occipital protuberance. The facial nerve supplies the scalp muscles. The trigeminal nerve supplies the muscles of mastication and the tensor tympani (see Fig. 39.2).1–5
The parietal scalp has a high degree of mobility, which facilitates closure with direct suturing or local flap reconstruction. Bone exposure is less common because the temporalis muscle and fascia provide an additional layer of soft tissue cover anteriorly. Local flaps are at risk of changing the orientation of hair and affecting the hairline or sideburn. The parietal scalp is supplied by the superficial temporal artery, the terminal branch of the external carotid artery. The superficial temporal artery is unlikely to be the vascular supply to flaps used in reconstruction of this area because it is likely to have been sacrificed already. Because of the excellent mobility of local tissues, distant tissue use is limited.1–4
The pinwheel flap is a type of local flap that uses three or four advancing triangular flaps which are arranged around a circular defect (Fig. 39.4). Bare skull Galeal scoring Occipital vessels Skin graft Galea Pericranium remains Fig. 39.3 Orticochea three-flap technique. (Adapted from Arnold PG, Rangarathnam CS. Multiple-flap scalp reconstruction: Orticochea revisited. Plast Reconstr Surg 69:607, 1982.) Fig. 39.4 The pinwheel flap for circular scalp defect closure. (Adapted from Lee S, Rafii AA, Sykes J. Advances in scalp reconstruction. Curr Opin Otolaryngol Head Neck Surg 14:249–253, 2006.) It may be particularly useful in small defects less than 2 cm2 on the vertex to recreate a whorl pattern at the patient’s crown while disguising the remaining scars within the hair. It can be used in other sites on the scalp including nonhair-bearing areas but is probably less useful as the long flap limbs result in more noticeable scars.1,2
Split calvarial bone graft is useful for reconstructing bony defects of the scalp as it has the same contour and can be harvested from the same operative site. Grafts are either taken full-thickness then split, or harvested at the level of the diploic space. The parietal region is the preferred donor site for calvarial bone harvest because it is thickest and minimizes risk of damage to dura or dural venous sinuses. Most split calvarial grafts are nonvascularized, and have a good take; however, it is possible to harvest a vascularized graft. This is based on the superficial temporal vessels by maintaining attachment to the superficial temporal fascia and pericranium.1–3
Small defects of the anterior scalp can often be closed directly with undermining of surrounding tissues. This avoids the need for a skin graft which will leave a bald patch and a contour defect at the surgical site. A scalp rotation flap is usually preserved for larger defects following triangulation of the defect (Fig. 39.5). Small defects can be left to heal by secondary intention but are best for nonhair-bearing regions of the scalp such as the forehead when there is a deep layer of vascularized tissue covering bone. Bilaminate neodermis reconstruction (Integra) can be a useful adjunct when reconstructing scalp defects, as it adds tissue depth, but in this situation it would not provide any benefit.1–6 Line of maximal tension Backcut Burow’s triangle Fig. 39.5 Rotation flaps can be useful in the scalp with triangulation of the defect. Flaps should be designed large to allow tissue redistribution without the need for a graft.
The primary aim in this case is to fully remove the nevus and provide soft tissue cover while retaining a full head of hair. Two approaches to the management of congenital nevi on the scalp are serial excision or excision and tissue expansion. Serial excision is best suited to smaller defects that can be excised within three or four sessions. A defect of 30% is best treated with tissue expansion and local flap closure. Defects up to 50% of the hair-bearing scalp can be closed with tissue expansion and avoid bald patches. A transposition flap and skin graft would create a large bald area and would not be aesthetically pleasing. Free tissue transfer would be reserved for near-total scalp defects, particularly where bone is exposed. The Orticochea flap is not well suited to vertex defects because the location does not allow a large third flap to cover the donor defect.1–6
Several algorithms have been developed for scalp reconstruction. However, as with most reconstructions, the selection requires common sense and is based on each patient’s needs. The goals are to reconstruct like with like tissue and to minimize deformity and alopecia. It is not always necessary to reconstruct the calvarium, provided that soft tissue cover is adequate. In this case, a simple and reliable approach is recommended due to the patient’s frailty and the relatively small defect size. Although split skin graft cannot be usually placed directly onto bone, in the setting of burred calvarium it can be. The combined use of bilaminate neodermis reconstruction (Integra, LifeSciences, Plainsboro, NJ) and split skin grafting has been shown to be reliable for scalp defects like the one described, and may be as effective as a local flap option. It involves a two-stage approach with Integra placed at the first stage and graft placed at the second. It is well recommended in elderly patients as in this case for defects with exposed bone. It can add soft tissue bulk and contour with low rates of morbidity and short operative time.1,2 Full-thickness skin grafting is generally not advised on full-thickness scalp defects as the chances of graft take are low even with burring. A skin and galea transposition flap leaving pericranium behind to accept a split skin graft is a reasonable alternative to Integra but is more likely to require a longer operative time and a general anesthetic which would ideally be avoided in this patient. Neither tissue expansion nor free tissue transfer would be warranted in this scenario, although both can be offered to elderly patients if their underlying medical health is good enough to withstand the impact of surgery.3
The gold standard for near-total scalp reconstruction is free tissue transfer and the two most popular flaps for this are the latissimus dorsi and anterolateral thigh flaps. Of the two, the latissimus dorsi is generally preferred and harvested as a muscle-only flap because muscle flaps atrophy and contour well to the skull over time. The downside is that a large area requires split skin grafting and if they thin to excess, bone exposure can occur. Muscle flaps are also preferred in the setting of radiation. The other benefit of the latissimus dorsi is that the donor site can be closed directly and a long pedicle is standard to facilitate reach into the neck vessels. The radial forearm can be used for scalp reconstruction as it too has a long pedicle, but it will leave a major defect in the forearm which will require grafting if used for a large scalp defect as in this case. Tissue expansion would not work well here as there is little left to expand. Furthermore, immediate reconstruction is required. Integra and split skin grafting is best reserved for smaller defects in patients where free tissue transfer is contraindicated. The Orticochea flap is classically described for occipital scalp reconstruction. This flap is not well suited to large defects involving the vertex or near-total defects as there are no flaps to raise and reconstruct with.1–3
Scalp replantation of larger defects should be attempted in most traumatic amputations of the scalp providing the soft tissues to be replanted are in a reasonable condition to do so. For example, this should be avoided where there has been a severe shearing force, in association with an extended warm ischemia time, and in situations where there are other life- or limb-threatening injuries that may preclude this. There is actually a body of evidence to support replantation of the scalp following avulsion. One study of 20 patients who had replantation showed 100% survival in 16 patients, that is, 80% of cases.1 Another systematic review which included 90 scalp replant cases found that overall success was above 70%.2 It would be unlikely that more than one arterial anastomosis would be required due to the blood supply of the scalp, as there is extensive collateralization of the vascular territories within the scalp, so replantation can be reliably based on single arterial and venous anastomoses. Despite this some surgeons still recommend use of additional vascular anastomoses if possible.3
Polyetheretherketone, or PEEK, has become a popular choice for reconstruction in the head and neck where complex shapes need reconstruction. It is advantageous because computer aided design based on CT imaging can be undertaken before surgery so that a custom implant is ready for immediate use after tumor resection. This increases accuracy of reconstruction and reduces intraoperative time, which would otherwise be needed to shape the construct. PEEK also has other advantages such as strength, durability, thermal conductivity, cost effectiveness, and radiolucency.1 However, tissue integration is still inferior to autologous bone which, in principle, remains the gold standard for reconstruction of bony defects. Autologous bone reconstruction for the cranium is generally nonvascularized with either split calvarial or rib graft being used. Free tissue transfer is less commonly used for the cranium but scapula bone may be well suited to create complex structures with relatively thin bone and a long vascular pedicle. It also has the advantage that soft tissue can be transferred with the harvested bone as a chimeric flap. However, shaping of bone, whether it is vascularized or nonvascularized, will add time to the surgical procedure, particularly for more complex shaped defects. Of the alloplastic options for calvarial reconstruction, methylmethacrylate, titanium mesh, and hydroxyapatite all have a role to play. Methylmethacrylate has good strength and biocompatibility but can have poor integration and be prone to infection. Titanium mesh is easy to mold, inert, and fairly rigid. Hydroxyapetite is best used as an adjunct to refine scalp contour, for example, to fill craniotomy drill hole defects.2,3