Anatomy clinical correlates: Skull, face and scalp

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Introduction0:00–0:36

The head is one of the most complex parts of our body. Besides having an abundance of muscles, nerves and blood vessels, it protects our brain and houses various facial structures.
In this video, we’ll go through a variety of conditions that can affect the skull, face, and scalp. This might not be the easiest subject to learn about, but you’ll see that it’s nothing to get a headache over!
First, let’s discuss the bones of the skull that make up the cranial vault, which as a group are also called the calvaria.
We’ll start from the very beginning of their development. See, the flat bones that make up the skulls of neonates have gaps between them and these gaps are covered by fibrous membranes.

Fontanelle0:36–2:11

These membrane-covered gaps between the bones are called fontanelles. The anterior fontanelle is a large diamond-shaped area found at the junction of the sagittal suture, coronal sutures and frontal suture.
In adults, this point where the sutures eventually come together is called the bregma. The anterior fontanelle is bordered by the frontal bone anteriorly and two parietal bones posteriorly.
By 18 months of age, the bones fuse together and the anterior fontanelle closes. The posterior fontanelle is a triangular shaped membrane found at the junction of the lambdoid sutures and sagittal suture.
In adults, this point is called the lambda. The posterior fontanelle is bordered by the two parietal bones anteriorly and the occipital bone posteriorly.
The posterior fontanelle usually closes during the first few months of life and is no longer palpable by the end of the first year.By palpating fontanelles before they close, bone growth and development of the skull can be assessed.
How fontanelles look is also important from a clinical standpoint. For example, a depressed fontanelle can indicate dehydration, while a bulging fontanelle can signal increased intracranial pressure.Now, let’s move on to bone fractures, and to start let's remember an intersection of the skull called the pterion.

Epidural hematoma2:11–3:42

This is where the frontal, parietal, temporal, and sphenoid bones meet. Now, immediately deep to the pterion is a branch of the maxillary artery called the middle meningeal artery and its branches.
So if an individual receives a hard blow to the area of the pterion; this can then fracture these bones right at that weak spot where they all meet.
The fracture can then damage the middle meningeal artery, causing significant intracranial bleeding. Specifically, the bleeding occurs between the outer endosteal or periosteal layer of the dura mater, and the bone.
Bleeding in this layer leads to the formation of an epidural hematoma. The typical presentation of an epidural hematoma is the individual may initially lose consciousness, which can be followed by a lucid period where they may act completely normal even though the bleed is getting worse.
Eventually, the individual will eventually show signs of elevated intracranial pressure such as headache, vomiting, and decreasing mental status.
Diagnosis requires a CT scan, which shows a biconvex, or lentiform, hyperdense mass between the endosteal or periosteal layer of the dura mater and the bone of the calvarium which does not cross suture lines.
Now, when it comes to injuries to the facial bones, some of the more common fractures are orbital blowout fractures. These can occur with motor vehicle crashes, a direct blow to the eye region, or with certain sports injuries, where in each case, an external force is applied to the orbit and its contents.

Orbital blowout fractures3:42–5:15

Since the orbit is a closed space, this external force increases the pressure within the orbit which then leads to a fracture of its thinnest part, usually the orbital floor, which is made up mainly by the maxilla and the zygomatic bone.
Since the maxillary sinus is right below the orbit, the contents of the orbit may be forced through the fractured floor and into the sinus.
Usually, the inferior rectus and the inferior oblique muscles are the structures that are forced into the maxillary sinus.
This can cause limited movement of the affected eye, which presents as double vision when the individual looks upwards. A branch of the maxillary nerve called the infraorbital nerve, which travels through the orbit along its floor and emerges beneath it through the infraorbital foramen, can also be damaged.
This can cause numbness in the lower eyelid, cheek, nose, upper lip, and upper gingiva. The best way to diagnose an orbital floor fracture is with a CT scan, which can show the fractured bone as well as the herniation of orbital contents into the maxillary sinus.

Quiz5:15–5:30

Okay, time for a quick break! Can you identify the anterior and posterior fontanelle on this image?
Also, what can a depressed fontanelle signal? Now let’s switch gears and discuss the danger triangle of the face, which refers to the area from the upper lip to the bridge of the nose.

Danger triangle5:30–6:33

Blood from this area drains through the facial vein. Usually, blood from the facial vein drains down into the internal jugular vein.
However, the reason it’s called the “danger” triangle is that the facial vein has no valves, so blood can flow through other draining branches upwards and can communicate with the cavernous sinus.
One way that happens is by draining through the superior ophthalmic vein and ultimately into the cavernous sinus. Alternatively, it can drain through the inferior ophthalmic veins and then into the pterygoid venous plexus which then ends up connecting into the cavernous sinus.
This means that any infection from the danger triangle, like an abscess, or cellulitis, can cause thrombophlebitis of the facial vein, which can then spread and cause intracranial infection to places such as the cavernous sinus.
Finally, let’s discuss some clinical correlates related to the scalp, starting with injuries that occur during birth and delivery.

Scalp injuries6:33–9:30

Injuries to the scalp are usually caused by passing through the birth canal, or iatrogenically through the use of vacuum extraction.
The most superficial injury is called caput succedaneum, which is a fancy way to say “scalp swelling” caused by venous congestion that leads to fluid collecting right beneath the skin.
The swelling is superficial to the pericranium, which is the periosteum that covers the skull, so it is not limited by the suture lines that the pericranium is anchored to and can thus spread freely along the scalp.
This condition is not harmful to the newborn, and the swelling is often mild, resolving on its own within a few days. Another type of injury that can occur to the scalp at birth is a subgaleal hemorrhage, which is a serious condition caused by strong traction that pulls the scalp away from the bone.
This leads to a rupture of emissary veins which connect the veins of the scalp to the dural venous sinuses within the skull.
Bleeding occurs in the loose connective tissue that lies superficial to the pericranium and deep to the galea aponeurotica, also known as the epicranial aponeurosis.
Since there is no strong connective tissue, or sutures to limit the bleeding, it can spread through the entire scalp, and even into the neck.
A subgaleal hemorrhage can progress over 2 to 3 days and cause substantial blood loss. The deepest type of scalp injury at birth is a cephalohematoma, which is caused by rupture of emissary veins right below the pericranium or periosteum layer of the bone.
Now, the pericranium is attached to the underlying bones and therefore this bleeding can only spread over one bone up to the suture lines that surround it.
It presents as a firm swelling on one side of the head, limited by suture lines, and so it does not spread all over the calvaria.
A cephalohematoma usually resolves on its own within two to three weeks. Finally, in adults, the most common type of scalp injury is a scalp laceration, which can cause profuse, potentially fatal bleeding if left untreated due to the numerous anastomoses between the arteries of the scalp.
Now, when there is a deep laceration to the scalp in the coronal direction involving the tense connective tissue of the galea aponeurotica, this laceration can be gaping and is held open by the occipital and frontal muscle bellies of the occipitofrontalis muscle.
In contrast to deep scalp lacerations which will gape, superficial scalp wounds will not gape because it won't be under tension from the muscle bellies.
Keep in mind all scalp wounds will need careful examination to see if they need sutures or staples for closure. Okay, time for a quick break!

Quiz9:30–9:40

Can you label these three different types of scalp bleeds?All right, as a quick recap, fontanelles are gaps between cranial bones spanned by fibrous membranes.

Review9:40–11:19

The anterior fontanelle is bordered by the frontal bone and two parietal bones, and it closes by 18 months of age. The posterior fontanelle is bordered by the two parietal bones and the occipital bone, and it closes by the end of the first year of life.
A depressed fontanelle can indicate dehydration, while a bulging one can signal increased intracranial pressure. Fractures of the pterion can damage the middle meningeal artery or its branches, causing an epidural hematoma.
Clinically, an epidural hematoma presents with initial loss of consciousness, followed by a lucid period, after which mental status decreases.
Diagnosis requires a head CT. Orbital floor fractures can cause herniation of the inferior rectus and the inferior oblique muscles into the maxillary sinus, as well as damage to the infraorbital nerve.
The danger triangle of the face includes the area from the upper lip to the bridge of the nose, which is drained by the facial vein.
The facial vein is valveless and is connected to the cavernous sinus, so any infection from the danger triangle can spread to the cavernous sinus.
Types of scalp injuries at birth include caput succedaneum, subgaleal hemorrhages and cephalohematomas. Scalp lacerations can be deep which will gape, or superficial which do not gape.