Introduction
Scalp comprises the forehead and the hair-bearing regions. It extends from the supraorbital ridge anteriorly to the highest nuchal line posteriorly, while ears and zygomatic arches define its lateral borders. In surgical practice, the scalp refers to the hair-bearing region exclusively, separating forehead from the frontal hairline. Hair-bearing scalp represents an irreplaceable tissue unit with esthetic importance. Its reconstructive approach should adhere to the basic principle of the reconstructive ladder, while providing durable coverage to protect intracranial contents with esthetically pleasing contour. The reconstruction also needs to preserve hair-bearing patterns and avoid neighboring structure distortions. Hair restoration should be considered to refine postreconstruction esthetics.
Anatomy of the Scalp
Anatomical Layers
The acronym of scalp compositions is represented by its own capital letters, SCALP, representing Skin, Connective tissue (subcutaneous tissue), Aponeurosis (galea aponeurotica), Loss of connective tissue, and Pericranium. The skin of the scalp is the thickest in the body (3–7 mm), and the occipital region is its thickest portion. The scalp has the highest hair follicle density and is highly sebaceous. Connective tissue consists of adipose tissue and fibrous septa, allowing skin anchorage to galea aponeurotica. The aponeurosis layer is a broad and thin layer of tendinous sheet that unites the paired frontalis and occipitalis muscles. It extends bilaterally and fuses with the external auricular muscles. Its continuance forms temporoparietal fascia bilaterally, and the superficial musculoaponeurotic system (SMAS) of the face anteriorly. The tight and inelastic nature of the galeal layer provides the explanation of “tight” and “loose” portions of the scalp. The “loose” portion refers to the region where the galeal edges blend with the temporoparietal fascia and scalp musculatures, whereas the “tight” portion extends from the same edges towards the scalp vertex. Recognizing the tight and loose portion of the scalp facilitates the design of local flaps and placement of tissue expanders. Loose connective tissue (areolar tissue) connects the galeal layer to the pericranium while permitting union gliding of the galeal layer and above, allowing contraction movements of occipitofrontalis. Emissary veins (posterior condyloid, mastoid, occipital, and parietal emissary vein) penetrate through this layer, connecting the superficial venous system of the scalp to cranial diploic veins and intracranial venous sinuses. Pericranium is the periosteum of the cranial bones; it fuses bilaterally with the deep temporal fascia at the superior temporal crest, and extends interiorly as endosteum at the cranial sutures.
Arterial Supply
The rich arterial plexus supply to the scalp is formed by extensive arterial anastomoses from terminal branches of both internal and external carotid arteries. Posterolaterally, the arterial supply of the scalp derives from branches of the external carotid arteries, including a pair of occipital, posterior auricular, and superficial temporal arteries. Anteriorly, its blood supply derives from the internal carotid arteries, including a pair of supratrochlear and supraorbital arteries. The arteries are located at the deepest layer of the dermis in the connective tissue layer.
Venous Drainage
The veins of the scalp are located in the connective tissue layer accompanying their corresponding arteries. They form a complex venous network, anastomosing with each other and via emissary veins. The occipital vein drains into the suboccipital venous plexus around the semispinalis capitis muscle and continued into vertebral veins, or less commonly into the internal jugular vein. The posterior auricular vein drains the post-auricular region as well as receiving the mastoid emissary vein from the sigmoid sinus. It joins the retromandibular vein at its exit from the parotid gland, forming the external jugular vein. The superficial temporal vein courses with its artery until its union with the maxillary vein in the parotid gland, forming the retromandibular vein. Anteriorly, the supraorbital and supratrochlear veins accompany their respective arteries before uniting medial to the orbit. They are drained by the angular vein into the facial vein.
Lymphatic Drainage
The lymphatic system is located within the subdermal and subcutaneous level. There are no lymph nodes in the scalp. Posteriorly, the lymphatic channels drain into occipital and postauricular nodes. Anteriorly, it drains to the parotid gland, preauricular, submandibular, and upper cervical lymph nodes. The lymph eventually reaches the nodes of the deep cervical chain.
Nerve Supply
Motor Nerves
Anteriorly, frontalis is supplied by the ipsilateral frontal branch of the facial nerve. The frontal nerve exits the parotid gland approximately 2.5 cm anterior to the tragus, ascends on the periosteum of the zygomatic arch, then continues adherent to the deep surface of, and eventually within, the temporoparietal fascia towards a point approximately 1.5 cm lateral to the orbital rim. Pitanguy’s line is the most widely used landmark to estimate the course of the frontal nerve, and is defined by a line drawn from 0.5 cm inferior to the tragus to 1.5 cm superior and lateral the eyebrow. Posteriorly, the posterior auricular branch of the facial nerve supplies both occipitalis and extrinsic auricular muscles, which leaves the facial nerve before it enters the parotid.
Sensory Nerves
Sensory innervation of the scalp is provided by the trigeminal nerve, cervical spine nerves, and branches from the cervical plexus. Anteriorly, the scalp is supplied by the paired supratrochlear and supraorbital nerves; both arise from the ophthalmic division of the trigeminal nerve. The supratrochlear nerve courses with its artery and provides sensation to the conjunctiva, upper eyelid, nasal sidewall, medial forehead, frontal scalp, and its vertex. The supraorbital nerve travels with its artery, and divides into superficial and deep branches to provide sensation to the forehead and frontoparietal scalp. Laterally, the scalp is supplied by the zygomaticotemporal nerve and auriculotemporal nerve. They arise from maxillary and mandibular branches of the trigeminal nerve respectively. Posteriorly, the sensation of the scalp is supplied by the greater occipital nerve (posterior ramus of C2), lesser occipital nerve (anterior ramus of C2), and third occipital nerve (posterior ramus of C3).
Reconstructive Principles
Patient Evaluation and Examination
Holistic evaluation of the intrinsic and extrinsic patient factors is an integral part of surgical assessment. Multidisciplinary unit assessments for oncological resection and reconstruction are essential for patient outcome maximization. Collaboration with neurosurgeons may be necessary if further calvarial reconstruction is required. Patients’ baseline functions, medical comorbidities, history of cigarette smoking, immunocompetence status, histological and clinical staging of the malignant neoplasm, as well as history and planned chemoradiotherapy are to be explored in detail. Surgically, knowledge of previous incision, hair status, and the patient’s expectation are important factors of reconstruction design. Comprehensive understanding of the defect size, location, and nature of the defect (simple versus composite defect) facilitates surgical planning and choice of surgical technique.
Reconstruction Goals
The goals of scalp reconstruction are both functional and esthetic. The functional goal is to provide a durable, in some cases, sensate coverage for the protection of calvarium or alloplastic cranioplasty prosthesis in prevention of desiccation and infection. Esthetic goals include an esthetically placed incision, replacing “like with like,” adequate contouring, preservation of hairlines and their growth patterns, limits to postoperative alopecia, avoidance of neighboring structure distortion (anterior hairline, sideburns, eyebrow, upper eyelids, and auricles), and if appropriate, utilizing adjuvant hair transplantation to restore trauma and reconstruction-induced hair loss.
Reconstruction Options
Healing by Secondary Intention
The rich vascular network plexus of the scalp and its high-density skin appendages permit superior healing potential by secondary intention. This approach is most suitable for small wounds in patients who are intolerant of anesthesia or related donor site morbidity. Superficial partial-thickness wounds from abrasions or burns, after minimal debridement, can expect to heal adequately with simple but frequent dressing regimens. Deep partial-thickness wounds may heal sufficiently with dressing only, however, they may result in sparse hair growth and scar contracture. In small defects with an exposed outer table of the calvarium, granulation tissue can form secondarily if a moist environment is provided through adequate dressings. Becker et al presented their series of 205 patients with secondary intention healing of exposed scalp following Mohs surgery. The mean healing time in exposed calvarium with intact pericranium was 7 weeks, and the average time for bare calvarium to heal was 13 weeks.
Vacuum-assisted closure (VAC) dressing should be considered in large and complex scalp wounds in patients who are unsuitable for complex reconstruction. VAC therapy is believed to promote wound healing in the negative-pressure environment by increasing blood flow and stimulating granulation tissue formation, thus enhancing its healing by secondary intention. Marathe and Sniezek reported their experience in VAC dressing for scalp and calvarial defects with exposed dura. They achieved 25% reduction of defect size while gaining a granulation wound bed, successfully simplifying the complexity of scalp reconstruction options.
Primary Closure
The applicability of primary closure of scalp is tightly associated with defect size and location. Primary closure is generally attainable in most acute scalp defects up to 10 cm 2 in size. Primary closure of larger defects is possible in the “loose” area of the scalp where underlying muscles are located. Primary closure limits alopecia, provides good contouring, and allows monitor of tumor recurrence. In traumatic cases, limited debridement of hair-bearing scalp is advisable. Dual-layer closure allows the galeal layer to endure wound closure tension, allowing tension-free skin closure. Tension-free closure reduces scar widening and its associated alopecia. Surgical techniques commonly employed to facilitate primary closure in larger defects or tight areas of the scalp include undermining, galeal scoring, induction of mechanical creep, and stress relaxation of the skin. These techniques are also applicable during advancement and inset of local flaps.
Skin Grafts, Adjuvant Techniques, Dermal Matrix and Dermal Substitutes
In the presence of a noninfected vascularized wound bed with intact pericranium, skin graft is an easy and quick solution for scalp defect reconstruction. It is a reliable technique and able to reconstruct medium to large defects. It shortens healing time and allows oncological surveillance. The major disadvantages of skin grafts are alopecia, contouring deficiency, and hypopigmentation. Split-thickness skin graft (STSG) is more commonly used than its full-thickness variant. In contrast to full-thickness skin graft (FTSG), STSG is suitable for medium to large defects, but creates greater contour deficiency and wound contracture. Donor site morbidity is considerably more significant in STSG than FTSG.
If bare calvarium is exposed, several adjuvant techniques can be utilized to convert a non-skin-graftable wound bed to a graftable defect. A large subgaleal, periosteal, and temporoparietal fascia flap can be raised, to either rotate or advance into the defect. These flaps enhance vascularity of the wound bed, allowing immediate skin grafting. Decortication of cranial outer table also coverts cranium into a graftable wound bed. These reconstructions, however, commonly result in unstable wounds and are subject to recurrent breakdowns and risk of subsequent infection. VAC dressing converts bare calvarium into a graftable wound bed by promoting granulation. Second-stage skin graft is thus achievable with prolonged VAC dressing application. Dermal matrix and dermal substitute simplified the complexity of scalp wound by its adherence to non-graftable structures such as calvarium. Onlay skin grafting to dermal matrix or dermal substitutes enhances the durability and pliability of the reconstruction, and lessens contour deformity when compared with skin grafting alone. They are, however, expensive and frequently require delayed skin grafting up to 3 weeks. Careful patient selection is thus imperative.
Skin graft is also used for secondary defect reconstruction after transposition or bipedicled flaps. In addition, skin graft can be utilized as temporary biological dressing prior to the definitive reconstruction. This concept is valuable in oncological cases when staged operation is planned and clearance of resection margin is being assessed.
Locoregional Flaps
Locoregional flaps are indicated when recruitment and advancement of neighboring tissue is inadequate for tension-free closure. Locoregional flaps are applicable to wide ranges of defect sizes, and are important options for complex scalp wound reconstructions, principally for those with exposed calvarium and alloplastic cranioplasty prosthesis. Utilizing local flaps adheres to the “replace like with like” principle of plastic surgery. Advantages are hair bearing, superior contouring, and color matching, and thus they are more esthetically pleasing. Successful local flap reconstruction requires familiarity with regional vascular anatomy, flap designs, judicious assessments of regional tissue pliability, and avoidance of neighboring tissue distortions. Based on the concepts of “tight” and “loose” portion of the scalp, the feasibility of using local flap is greater in the frontal, temporoparietal, and occipital region, in contrast to vertex of the scalp. General surgical pearls for successful local flap reconstruction include designing a large flap with a wide base, minimizing the number of flaps, and avoiding suture lines in critical areas. If skin grafting is planned, it should be designed to locate inconspicuously so it can be camouflaged with hairstyling. Importantly, resist the temptation of trimming the dog-ears as they will invariably settle. Revising the dog-ear on the scalp narrows the skin pedicle and reduces vascular supply and drainage.
Although a surfeit of locoregional techniques were described for scalp reconstruction, the workhorse options are variations of rotation and transposition flaps. In contrast, an advancement flap shares less success due to the innate inelasticity of the scalp. In a smaller defect, a random pattern fasciocutaneous flap can be reliably raised, and serves as an alternative option to skin graft. For medium and large scalp defects, designing a local flap based on the named vascular pedicles is preferred. A pinwheel flap consists of four small rotation flaps bordering the defect that are 90 degrees apart from each other. It is used for small circular defects of the scalp. Recent modification by Simsek and Eroglu extended its application to scalp defects up to 50 mm in size. It is an alternative choice if a large rotation flap is to be avoided.
A rotation flap is the classical solution for a scalp defect of up to 50 mm diameter ( Fig. 33.1 ). The flap is based on an axial pattern blood supply, incorporating at least one of the named arteries. Although the ideal flap circumference and defect width ratio is inconsistently described, an experimental study by Lo and Kimble demonstrated that the effect in decreasing tension becomes minimal once the flap circumference exceeds approximately 5 times. Meticulous reverse planning with careful attention to pivot point, blood supply, sensory supply, and defect/flap dimensions are critical. A transposition flap is used in medium to large scalp defect. As a transposition flap creates a secondary defect and requires skin grafting, it is typically reserved for large scalp defect reconstruction ( Fig. 33.2 ). Similar to the design of a rotation flap, it should be raised based on an axial pedicle with a wide skin paddle.
