Regions of the head and border areas
The head is traditionally divided into two major regions based on the bony framework of the skull. The facial region (viscerocranium) includes the upper and lower jaws, zygomatic, nasal, and lacrimal bones; it houses the sensory organs and the initial segments of the respiratory and digestive tracts. The cranial vault / neurocranium (neurocranium) is formed by the frontal, parietal, occipital, temporal, sphenoid, and ethmoid bones. Its primary function is to protect the brain and its meninges.
The frontoparietooccipital region is of particular clinical importance. It combines the first three unpaired zones of the cranial vault due to their identical anatomical structure. Its boundaries are:
- Anteriorly: supraorbital margin of the frontal bone and glabella.
- Posteriorly: superior nuchal line.
- Laterally: superior temporal line.
Layered structure of the cranial vault
The tissues of the frontoparietooccipital region are arranged in a strict sequence, forming eight layers:
- Skin — thick, immobile, abundantly supplied with hair follicles, sebaceous, and sweat glands.
- Subcutaneous adipose tissue — has a cellular structure due to strong fibrous septa extending from the skin to the aponeurosis. The main neurovascular bundles (supraorbital, supratrochlear, temporal, occipital) pass here.
- Musculo-aponeurotic layer — includes the occipitofrontalis muscle (m. occipitofrontalis) and the epicranial aponeurosis (galea aponeurotica).
Surgical feature: the first three layers are tightly fused together. In severe trauma, they detach as a single piece, leading to specific "scalp avulsion" wounds.
- Subaponeurotic space — characterized by looseness and the absence of septa. Inflammation in this zone quickly becomes diffuse.
- Periosteum — loosely adheres to the bone everywhere except at the cranial sutures, where fixation is very rigid.
- Subperiosteal space — the site of subperiosteal abscess formation. Due to the tight fusion of the periosteum with the sutures, the abscess is always limited to the boundaries of one specific bone.
- Bones of the cranial vault — flat, consisting of a strong outer plate, spongy substance (diploë) containing veins, and a very fragile inner ("glassy") plate. The air-containing frontal sinus (sinus frontalis) is also hidden within the frontal bone.
- Dura mater (dura mater) — closely fused with the inner surface of the bones, consists of two leaves, and forms venous sinuses for blood outflow from the brain.
Specifics of cerebral circulation
The blood supply to the brain has a number of unique physiological features due to the enclosed space of the skull.
- Absence of pulsation and reserves: Inside the cranial vault, arteries do not pulsate. The pulse wave is damped due to the pronounced tortuosity of the vessels and the constant volume of the cranial contents. In addition, there are no arteriovenous anastomoses or "reserve" capillaries in the brain — the entire capillary network works continuously.
- Autoregulation and hyperemia: Blood flow increases locally in those areas of the brain that are actively working at the moment. The autoregulation system (myogenic and metabolic mechanisms) maintains stable brain nutrition regardless of fluctuations in systemic blood pressure.
- Relationship of pressures: Since the cranial vault is airtight, the total volume of its contents is constant. If intracranial pressure increases (e.g., due to a tumor), the body compensates by increasing systemic arterial pressure to maintain cerebral tissue perfusion.
Anatomy and pathophysiology of headache
Headache (cephalgia) is topographically defined as any uncomfortable sensation within the boundaries from the supraorbital arches to the occiput. Anything localized below the level of the eyebrows is classified as facial pain.
Paradoxically, the brain parenchyma itself lacks pain receptors. Extensive damage to the brain substance can be completely painless, manifesting only as pronounced neurological deficits.
Pain impulses are generated upon irritation of other structures: the dura mater, large arteries of the base of the brain, as well as the skin, muscles, tendons, and mucous membranes of the head. The trigeminal (n. trigeminus), glossopharyngeal (n. glossopharyngeus), vagus (n. vagus) nerves, and the upper two cervical spinal roots participate in the transmission of these signals.
To understand the nature of pus spread in the cranial vault tissue, remember: under the skin, pus is confined by cellular septa; under the aponeurosis, it spreads freely; under the periosteum, it is limited by the sutures of a single bone.
Class and exam questions
Why are soft tissue wounds of the cranial vault often avulsion wounds?
The skin, subcutaneous tissue, and epicranial aponeurosis are tightly connected by fibrous tracts into a single layer, which easily detaches from the underlying loose subaponeurotic tissue during trauma.
Can pus from the subperiosteal space of the parietal bone spread to the frontal bone?
No. The periosteum fuses very tightly with the bones in the area of the cranial sutures, so a subperiosteal abscess is always strictly limited to the boundaries of a single bone.
Why does systemic arterial pressure often rise in brain tumors?
The cranial vault is airtight. Tumor growth increases intracranial pressure, and in order to maintain adequate blood flow in the brain, the body is forced to compensatorily increase systemic blood pressure.
What else to study on this topic
- Topography and projection lines of the neurovascular bundles of the subcutaneous tissue of the cranial vault.
- Mechanisms of cerebral blood flow autoregulation (myogenic and metabolic).
- Classification of cephalgias: primary and secondary headaches.
- "Red flags" and mandatory parameters when taking a medical history in patients with headache.
- Structure of the cranial vault bones and the functional role of diploic veins.
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