The scalp

There are five layers to the scalp: skin, dense connective tissue, galea aponeurotica, loose connective tissue and pen-cranium (Fig. 35.1). The scalp receives a rich vascular supply. This arises from both the external and internal carotid arteries with the vessels lying in the dense connective tissue layer. The anterior scalp is supplied by the supratrochlear and supraorbital arteries, and branches of the internal carotid via the ophthalmic artery. The lateral and posterior scalp is supplied by the superficial temporal, posterior auricular and occipital arteries, and branches of the external carotid. The sensory nerves run with the arteries and are derived from the trigeminal nerve at the front and sides. The posterior aspect is supplied by the greater and lesser occipital nerves with motor supply to the occipitofrontalis muscle by the facial nerve. Venous drainage of the face and anterior scalp is via the facial vein. The lateral and posterior aspects are drained by the external jugular vein and the vertebral venous plexus, respectively. The veins of the scalp and face communicate directly with the intracranial venous sinuses via emissary veins, hence infections in the nasal region have the potential to cause cavernous sinus thrombosis. Lymph drainage from the scalp is to the preauricular and occipital lymph nodes.

The walls of the vessels in the dense connective layer are bound, preventing ready retraction when divided. Wounds to the scalp therefore bleed copiously. When the underlying cranium is intact, it is a safe and simple measure to arrest haemorrhage by compression against bone until haemostasis is achieved by suturing the wound. In the presence of a penetrating wound to the scalp, it is mandatory to exclude a fracture radiologically. If no fracture is present, it is safe to explore the wound, so that foreign bodies and debris may be removed, the wound débrided and the scalp closed. This is done in layers with a resorbable suture to the galea and a nonabsorbable suture to the skin.

The scalp heals readily and therefore it is often possible for skin of questionable viability to be left in place without becoming necrotic. When a scalp wound results in loss of tissue the limiting factor to closure is often the inflexibility of the galea. By performing release incisions in the galea, a moderate-sized defect may be closed. However, when large areas of scalp are missing, more extensive rotational flaps are required. Skin grafts will only take on a layer of intact pericranium.

The loose areolar tissue under the galea aponeurotica is a dangerous zone for infections. Pus can spread freely in this layer and reach the intracranial sinuses through the emissary veins. Abscesses and haematomas under the pericranium are limited to the area of one bone because the pericranium is firmly adherent to the sutures between the skull bones. In infants, blood loss into this layer can often be underestimated leading to cardiovascular decompensation. Osteomyelitis of the skull is associated with a subperiosteal swelling and oede­ma of the scalp referred to as Port’s puffy tumour (Fig. 35.27). This is now a rare condition but because of the possibility of intracranial sepsis, should be aggressively investigated and treated.

Lesions that occur on the head may be identical to those occurring in the skin elsewhere (Fig. 35.2a and b). Therefore any mobile lesion occurring within the skin should be inspected, investigated and treated using the usual diagnostic criteria. However, when lesions occur in the midline or appear to be more deeply connected within the layers of the scalp, then it is mandatory that more extensive radiological investigations [ideally computerised tomography (CT) or magnetic resonance imaging (MRI)] be performed to exclude any intracranial extension.