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.