Scalp and Calvarial Reconstruction

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