Anatomy chapters
Danger area of the face and scalp
Why infection in the triangle around the nose and in the loose layer of the scalp can spread inside the skull, through valveless veins to the cavernous sinus and dural sinuses.
- The danger area of the face is the area around the nose and upper lip; its veins drain to the cavernous sinus.
- The danger area of the scalp is the loose areolar tissue (fourth layer), where emissary veins connect to the dural sinuses.
- Both are dangerous because the veins have no valves, so infection can spread inside the skull.
On this page
Overview
Two parts of the head are called "danger areas" because infection there can spread inside the skull.
- The danger area of the face: the triangle around the nose and upper lip.
- The danger area of the scalp: the loose areolar tissue, the fourth layer of the scalp.
In both, the key is veins with no valves that connect outside veins with the venous sinuses inside the skull.
Danger area of the face
The area is a triangle from the bridge of the nose to the corners of the mouth, including the upper lip, the nose and the cheek next to it.
Venous drainage of the face
The facial vein begins at the medial angle of the eye. It runs down and back across the face and drains into the internal jugular vein.
It connects with the cavernous sinus by two routes:
- Superior ophthalmic vein: links the start of the facial vein, at the medial angle of the eye, directly with the cavernous sinus.
- Deep facial vein and pterygoid venous plexus: the deep facial vein joins the facial vein to the pterygoid plexus, which drains to the cavernous sinus through small emissary veins.
The facial vein has no valves. If the muscles of the face squeeze it, or a clot blocks it, blood and infection can flow backwards into the cavernous sinus.
The facial vein connects to the cavernous sinus mainly via the ophthalmic veins and the pterygoid plexus, not directly.
Cavernous sinus thrombosis
How it happens: infection from a boil, pimple or abscess in the danger area (often after squeezing it), or from the sinuses, spreads along the veins and causes a clot in the cavernous sinus.
What you see:
- Fever and severe headache.
- Swollen eyelids and a bulging eye (proptosis), because the ophthalmic veins cannot drain.
- Paralysis of eye movements: the nerves III, IV and VI pass through or beside the sinus. The abducent nerve (VI) is usually affected first, because it lies free in the sinus.
- Numbness of the forehead and cheek (V1 and V2).
- Infection can spread to the other side through veins that link the two sinuses.
In cavernous sinus thrombosis the abducent nerve is usually the first to be affected: the eye cannot look outwards.
This was often fatal before antibiotics. It is still a medical emergency.
The scalp
The scalp has five layers.
S-C-A-L-P: Skin, Connective tissue (dense), Aponeurosis (epicranial), Loose areolar tissue, Pericranium.
| Layer | Features |
|---|---|
| Skin | Thick, hairy, many sebaceous glands |
| Dense Connective tissue | Contains the arteries, veins and nerves; holds vessel walls open |
| Epicranial Aponeurosis | Tendon sheet joining frontalis and occipitalis |
| Loose areolar tissue | Allows the top three layers to move; contains emissary veins |
| Pericranium | Periosteum on the outer surface of the skull |
The first three layers are tightly bound and move together as the scalp proper.
Why the scalp bleeds so much
The arteries run in the dense connective tissue layer, which holds their walls open. When cut, they cannot close by spasm, so even small wounds bleed heavily.
The scalp has a rich blood supply from both the internal and external carotid arteries, so scalp flaps heal well.
A scalp wound gapes only if the epicranial aponeurosis is cut across. A shallow wound above it does not gape.
Danger area of the scalp
The loose areolar tissue (fourth layer) is called the danger area because:
- Emissary veins pass through it. They have no valves and connect the veins of the scalp with the diploic veins of the skull bones and the dural venous sinuses inside the skull.
- Infection here can spread through these veins into the skull and cause meningitis, osteomyelitis of the skull bones or thrombosis of the venous sinuses.
- Pus or blood spreads easily in this loose layer over the whole vault.
The fourth layer (loose areolar tissue) is the danger area of the scalp because of its emissary veins.
Black eyes after a scalp injury
How it happens: blood collects in the loose areolar layer. In front, frontalis attaches to skin, not bone, so the blood can track forward into the eyelids.
What you see: bruising around both eyes a day or two after a head injury, even with no blow to the face.
Subaponeurotic haemorrhage in newborns
How it happens: bleeding into the loose areolar layer, for example after a vacuum-assisted delivery.
What you see: a boggy swelling that crosses the suture lines and can hold a lot of blood.
A cephalhaematoma lies under the pericranium, so it is limited by the sutures. A subaponeurotic bleed lies in the loose layer and crosses the sutures.
Questions ask why the danger area of the face is dangerous (valveless facial vein linked to the cavernous sinus), which nerve is first affected in cavernous sinus thrombosis, the five layers of the scalp, which layer is the danger area, and why scalp wounds bleed so much.
Quick revision
- Danger area of face: nose, upper lip, nearby cheek.
- Facial vein: no valves; links with the cavernous sinus via the superior ophthalmic vein and the pterygoid plexus.
- Cavernous sinus thrombosis: proptosis, eyelid swelling, eye muscle palsies; VI first.
- Scalp layers: skin, dense connective tissue, aponeurosis, loose areolar tissue, pericranium.
- Danger area of scalp: loose areolar tissue with emissary veins.
- Scalp bleeds heavily: vessels held open in the dense connective tissue.
Written by The House Job from standard anatomy references (Snell's Clinical Anatomy by Regions is the book named in the UHS PGET syllabus).
FAQ
What is the danger area of the face?
The triangle around the nose and upper lip, whose veins connect with the cavernous sinus.
Why is the loose areolar tissue of the scalp called the danger area?
It contains emissary veins that let infection spread into the skull and dural venous sinuses.
Which cranial nerve is first affected in cavernous sinus thrombosis?
The abducent nerve (VI).
Why do scalp wounds bleed so much?
The arteries are held open by the dense connective tissue layer and cannot constrict.