Scalp & Temple Reconstruction Techniques After Mohs Surgery

The scalp consists of five distinct layers, conveniently remembered by the SCALP mnemonic. Skin is the thickest on the body (3-8 mm), densely populated with hair follicles and sebaceous glands. Connective tissue is a fibrofatty layer containing the major scalp vasculature (superficial temporal, supraorbital, supratrochlear, occipital, and posterior auricular arteries). The Aponeurosis (galea aponeurotica) is a tough fibrous sheet connecting the frontalis muscle anteriorly to the occipitalis muscle posteriorly. This inelastic layer is the primary reason scalp wounds resist closure and is the key structure that must be scored or released to gain tissue mobility. Loose areolar tissue is the avascular glide plane between the galea and the pericranium. This plane allows the scalp to move freely over the calvarium and is the preferred undermining plane for scalp reconstruction. Pericranium is the periosteal layer adherent to the outer table of the skull. Intact pericranium is the minimum wound bed needed to support a skin graft. Without pericranium, the exposed calvarium cannot accept a graft and requires alternative strategies. The scalp receives blood supply from five paired arteries: the superficial temporal artery (STA), supraorbital artery (SOA), supratrochlear artery (STO), occipital artery (OA), and posterior auricular artery (PAA). These arteries anastomose freely, making the scalp one of the most vascularly reliable regions in the body. Flap survival rates on the scalp exceed 98% due to this rich anastomotic network. Sensory innervation comes from multiple sources: the supraorbital and supratrochlear nerves (anterior scalp), auriculotemporal nerve (temporal region), lesser occipital nerve (lateral posterior scalp), and greater occipital nerve (posterior scalp). Wound healing on the scalp differs from facial skin in several ways: hair-bearing skin heals with less visible scarring when scars are oriented parallel to hair follicle direction, but alopecia along the scar line is common and expected. Second-intention healing on the scalp is generally poor cosmetically and very slow due to the tight, inelastic tissue.

Scalp defects after Mohs surgery require a systematic approach based on defect diameter, depth (whether pericranium is intact), and location on the scalp. The reconstruction ladder for the scalp differs from other facial sites because of the limited tissue elasticity. Primary closure is feasible for smaller defects but requires far more undermining per centimeter of defect than on any other facial subunit. The following algorithm provides a size-based framework, but patient factors such as prior surgery, radiation history, anticoagulation status, and cosmetic expectations must also guide the decision.

Primary closure of scalp defects depends entirely on adequate undermining and tension relief. The subgaleal plane is the standard undermining plane for scalp reconstruction. Dissection in this avascular loose areolar tissue layer is rapid and nearly bloodless, and it preserves the blood supply to the overlying scalp flap (which runs in the connective tissue layer above the galea). For defects up to 2 cm, undermine at least 3-4 cm beyond the wound edge in all directions. If tension persists after undermining, galeal scoring is the next maneuver. Galeal scoring involves making parallel incisions through the full thickness of the galea aponeurotica perpendicular to the direction of closure, spaced 1-2 cm apart. Each scoring incision releases 0.5-1.0 cm of additional tissue length. Scoring can be performed on the undersurface of the flap (safer, as the blood supply runs superficial to the galea) or on the wound bed side. Buried tension-relieving sutures are placed through the galea using 2-0 or 3-0 braided absorbable suture (Vicryl). These galeal sutures bear the primary closing tension and are the most important sutures in scalp closure. The galea has excellent holding strength and distributes tension across the wound. Skin staples or interrupted nylon sutures are used for the skin layer. Staples are preferred by many surgeons for scalp closure because they are fast, produce minimal tissue reaction in hair-bearing skin, and are easily removed. Drain placement (Penrose or closed suction) should be considered for closures with extensive undermining to prevent hematoma formation.

Rotation flaps are the workhorse for medium to large scalp defects (2-8 cm). The scalp is ideally suited for rotation flaps because the rich vascular supply supports large flap arcs, and the convex surface of the calvarium provides a smooth glide plane for rotation. The arc of the rotation flap should be at least 4 times the diameter of the defect. For a 3 cm defect, the flap arc should measure at least 12 cm. This ratio is larger than for rotation flaps elsewhere on the body because of the scalp inelasticity. A back cut at the base of the flap increases rotational mobility but sacrifices some random-pattern blood supply. Keep back cuts short (1-2 cm) to minimize vascular compromise. The O-to-Z closure (also called double opposing rotation flaps) is a powerful technique for central scalp defects. Two rotation flaps are designed on opposite sides of the circular defect, converting the circle into a Z-shaped closure. This distributes tension bilaterally and avoids the dog-ear that can occur with a single rotation flap. For very large defects, bilateral rotation flaps or pinwheel flaps (3-4 rotation flaps arranged around the defect) provide maximum tissue recruitment. These designs can close defects up to 50% of the total scalp surface area. All rotation flaps on the scalp require undermining in the subgaleal plane, extending well beyond the flap margins. Galeal scoring on the flap undersurface further increases mobility.

Advancement flaps on the scalp are less commonly used than rotation flaps because the inelastic galea limits linear advancement. However, bilateral advancement flaps (H-plasty) and island pedicle advancement flaps have specific roles. The H-plasty creates two parallel advancement flaps on either side of the defect. Bilateral Burow triangles at each end of the parallel incisions allow the flaps to advance toward each other. On the scalp, H-plasty works best for elongated defects oriented along the anterior-posterior axis, where the bilateral advancement distributes tension laterally. Each advancement flap requires subgaleal undermining extending at least 3 cm beyond the flap edge, and galeal scoring may be necessary. Island pedicle advancement flaps rely on a subcutaneous pedicle (connective tissue and subdermal plexus) for blood supply. The flap is completely islanded from surrounding skin and advanced into the defect on its deep pedicle. On the scalp, island pedicle flaps are useful for defects near the hairline where hair-bearing tissue needs to be advanced into the defect to preserve the hairline contour. The key limitation is the advancement distance, which rarely exceeds 1-2 cm on the scalp without excessive tension.

Skin grafts are a reliable option for scalp defects when pericranium is intact. Full-thickness skin grafts (FTSG) placed on vascularized pericranium have graft take rates of 85-95%. The donor site should provide a good color and texture match; common choices include the supraclavicular fossa, preauricular skin, or upper inner arm. FTSG on the scalp creates a permanent alopecic patch, which may be acceptable in elderly or bald patients but is cosmetically limiting in younger patients with hair. Split-thickness skin grafts (STSG) have higher take rates (>95% on pericranium) but produce a depressed, shiny, alopecic patch with poor cosmetic outcomes. STSG is best reserved for patients who are poor surgical candidates or for very large defects where flap coverage is not feasible. When pericranium is absent but granulation tissue has formed over the outer cortex, STSG on granulation tissue is a viable option. Allow 4-6 weeks for adequate granulation before grafting. Bolster dressings or negative-pressure wound therapy improve graft take rates on the convex scalp surface. Tie-over bolster dressings should remain in place for 7-10 days. Negative-pressure wound therapy (wound VAC) at 75-125 mmHg continuous pressure for 5-7 days is an effective alternative to bolster dressings, particularly for larger grafts.

Exposed calvarium (outer cortex without pericranium) is the most challenging wound bed on the scalp. Bare cortical bone will not support granulation tissue formation and cannot accept a skin graft directly. The outer table of the calvarium must be modified to allow vascular ingrowth from the diploe (cancellous bone between the inner and outer tables). Several strategies address exposed calvarium. Outer cortex burring involves using a high-speed rotary burr or dermatome to remove the outer cortical table down to the bleeding diploe. The punctate bleeding from the diploe indicates adequate depth. Granulation tissue forms over the exposed diploe within 3-6 weeks, after which STSG can be applied. This is the most established technique with success rates of 80-90%. AlloDerm (acellular dermal matrix) can be placed directly on bare cortex and covered with a wound VAC. The dermal matrix provides a scaffold for cellular ingrowth and neovascularization. A skin graft is placed over the incorporated AlloDerm in a second stage, typically 3-4 weeks later. Negative-pressure wound therapy (wound VAC) alone on bare cortex can promote granulation tissue formation over 4-8 weeks without burring. This approach is slower but avoids the morbidity of outer cortex removal. Apply 75-125 mmHg continuous negative pressure with foam or gauze dressings changed every 48-72 hours. Local scalp flaps over bare calvarium are possible if the flap includes its own blood supply independent of the wound bed. Rotation flaps with pericranial attachment can bridge areas of exposed bone, with the flap surviving on its axial blood supply rather than the wound bed.

Hematoma is the most common complication after scalp reconstruction, occurring in 3-8% of cases. The rich vascularity that makes the scalp reliable for flaps also produces significant intraoperative and postoperative bleeding. The subgaleal space is a potential space that can accumulate large volumes of blood. Risk factors include anticoagulant or antiplatelet therapy, hypertension, and extensive undermining. Prevention involves meticulous hemostasis, drain placement for large flaps (Penrose or closed suction for 24-48 hours), and pressure dressings. Expanding hematomas require urgent evacuation to prevent flap compromise. Wound dehiscence occurs in 2-5% of scalp closures, most often due to excessive wound closure tension. The inelastic galea transmits tension directly to the skin edges. Inadequate galeal scoring or insufficient undermining are the usual causes. Dehiscence is managed with local wound care and secondary-intention healing or delayed re-closure once the wound has contracted. Alopecia along the scar line is expected and nearly universal. Wide scars and alopecia are more noticeable in patients with dark hair and less noticeable in patients with light, thin, or gray hair. Minimizing wound tension reduces scar width and associated alopecia. Hair transplantation into mature scars can be performed as a secondary procedure. Sensory loss after scalp reconstruction is common (30-50% of patients report temporary numbness) due to transection of sensory nerves during undermining. The supraorbital, supratrochlear, greater occipital, and lesser occipital nerves are most frequently affected. Sensation typically returns over 6-12 months through collateral nerve ingrowth, though some deficit may be permanent. Infection rates after scalp reconstruction are low (1-3%) due to the excellent blood supply. Standard perioperative antibiotics (cephalexin 500 mg four times daily for 5-7 days) are sufficient for most cases.

The temple is a distinct reconstructive zone that bridges the scalp and face, combining thin mobile skin with the dangerous course of the temporal branch of the facial nerve (CN VII). Temple skin is thinner than scalp skin and has moderate laxity, making primary closure and local flaps feasible for most defects. The superficial temporal artery (STA) runs through the temple and provides reliable blood supply for local flaps. Palpation of the STA anterior to the tragus helps orient the surgeon to the vascular anatomy. The temporal branch of CN VII is the primary danger in temple reconstruction. This nerve exits the parotid gland and crosses the zygomatic arch in or just deep to the superficial temporal fascia (temporoparietal fascia). Injury causes ipsilateral brow ptosis and loss of forehead animation, a conspicuous and often permanent deformity. The danger zone for the temporal branch lies within a triangle bounded by: the zygomatic arch inferiorly, a line from the tragus to the lateral brow anteriorly, and a line from the tragus to the highest forehead crease superiorly. Within this triangle, all undermining must be superficial, staying above the temporoparietal fascia in the subcutaneous fat. Deep undermining in this zone risks transecting the nerve. Above the superior temporal line (the bony ridge palpable at the lateral forehead), the temporal branch has entered the frontalis muscle, and deeper undermining in the subgaleal plane is safe. Reconstructive options for temple defects include primary closure (feasible up to 2-3 cm due to moderate skin laxity), rotation flaps from the forehead or scalp, transposition flaps, advancement flaps, and full-thickness skin grafts from the preauricular region. The preauricular FTSG provides an excellent color and texture match for temple defects.