Scalp and subscalp

The principal soft tissue cranial covering can be characterized by the mnemonic SCALP (Fig. 17.1). From superficial to deep these include the Skin (dermis and epidermis with hair and sebaceous glands); the Connective subcutaneous tissue (fibroadipose tissue, arteries, veins, lymphatics, and nerves); the Aponeurotica or galea (fascia connecting the frontal and occipital muscles); Loose avascular connective tissue between the aponeurotica and the pericranium; the Pericranium (vascularized periosteum adherent to the cranial bones) and the potential subperiosteal space. The subgaleal space extends from front to back, side to side, and to the soft tissue of the neck. The periosteum is tightly adherent to the skull surface, and the extension of fluid within the potential space between the periosteum and the outer table of the skull is generally restricted by the cranial sutures (1–3).

Cranium

The cranium, or skull, consists of the cranial vault and skull base (Fig. 17.2) (4–8). The cranial vault is formed from membranous ossification and is made up of bony plates, each of which is separated from the other by sutures and fontanels of connective tissue. The calvaria include an inner table, an intermediate diploic space and an outer table; the calvarial bones do not become separate plates until late infancy. The inner table grows only in response to brain growth, whereas the outer table primarily responds to external forces (e.g., molding, postural factors). The shape of the vault is determined by development of the cerebrum and by external factors. The sutures are remnants of the original membranous cerebral capsule and permit progressive ossification by direct osteoblastic activity during expansile brain growth (4, 6). The inner table is reshaped by the osteoclastic–osteoblastic cycle. The bony edges of the sutures are tapered with relatively straight inner table margins. Outer table interdigitations develop beyond the neonatal period.