Topographic anatomy of the neurocranium

Boundaries and divisions of the head

The human head is anatomically divided into two major parts: the cerebral and facial parts. The line separating them originates at the supraorbital margin, runs along the zygomatic bone and zygomatic arch, and ends at the external acoustic meatus. All anatomical structures located above and posterior to this boundary form the cerebral part, while tissues anterior and inferior belong to the facial part.

The general boundary of the head runs along the margin and angle of the mandible, extends to the apex of the mastoid process, and then follows the superior nuchal line (linea nuchae superior) to the external occipital protuberance (protuberantia occipitalis externa, or inion), symmetrically passing to the opposite side.

Important landmarks are used for precise skeletotopy. In the normal position of the head, the lowest point of the orbital opening and the highest point of the external acoustic meatus lie in the same horizontal plane.

The cerebral part itself is further subdivided into the vault (fornix) (fornix) and the base (basis) (basis). The boundary between them passes through the frontonasal suture, the supraorbital margin, the upper margin of the zygomatic arch (corresponding to the crista infratemporalis of the sphenoid bone), the base of the mastoid process, the superior nuchal line, and the protuberantia occipitalis externa.

Topography of the frontoparietooccipital region

On the cranial vault (fornix cranii), paired regions (temporal, mastoid regions) and unpaired regions (frontal, parietal, occipital) are distinguished. The first three unpaired zones are combined into a single frontoparietooccipital region, as they are characterized by a similar anatomical structure.

Boundaries of the combined region:

• Anteriorly: the supraorbital margin of the frontal bone and the glabella.
• Posteriorly: the superior nuchal line.
• Laterally: the superior temporal line.

Layer-by-layer Structure

The tissues of the frontoparietooccipital region have a distinct multi-layered structure that determines the specifics of trauma and inflammation:

1. Skin: immobile, dense, hair-covered, containing a large number of sebaceous and sweat glands.
2. Subcutaneous adipose tissue: well-developed, honeycomb-like in structure due to fibrous septa connecting the skin to the underlying aponeurosis. The main neurovascular bundles run precisely within this layer.
3. Musculo-aponeurotic layer: formed by the occipitofrontalis muscle (m. occipitofrontalis) and the epicranial aponeurosis, or galea aponeurotica (galea aponeurotica). The aponeurosis is weakly connected to the periosteum, but firmly fixed to the skin and subcutaneous tissue. This tissue triad is peeled off as a single block during surgeries or trauma (characteristic of 'scalp' wounds).
4. Subaponeurotic tissue: very loose tissue lacking septa. Inflammatory processes in this layer spread rapidly and become diffuse in nature.
5. Periosteum: loosely connected to the bones throughout, except along the suture lines, where the attachment becomes very tight.
6. Subperiosteal tissue: well-developed. Abscesses forming here (subperiosteal abscesses) cannot cross the cranial suture lines and remain confined within the boundaries of a single bone.
7. Bones of the cranial vault: classified as flat bones and consist of a strong outer table, spongy substance (diploe containing emissary veins), and a brittle inner ('vitreous') table. In the frontal bone, beneath the outer table, lies the pneumatized frontal sinus (sinus frontalis) lined with mucous membrane.
8. Dura mater (dura mater): closely adheres to the internal surfaces of the cranial bones. It consists of two layers and forms venous sinuses for blood drainage from the brain.

Projection of vessels and nerves

The arrest of massive hemorrhage on the head is achieved by compressing vessels against the bones; therefore, knowing the exact projections within the subcutaneous tissue is critically important:

• In the anterior region (orbital area): the supraorbital vessels and nerve (a., v. et n. supraorbitalis) emerge from the orbit, passing over the supraorbital margin at the junction of its inner and middle thirds (the nerve lies medial to the vessels). The supratrochlear bundle (a., v. et n. supratrochlearis) is projected at the intersection of the supraorbital margin with a vertical line from the medial angle of the eye fissure. The temporal branch of the facial nerve (ramus temporalis nervi facialis) heads toward this zone to the frontal belly of the occipitofrontalis muscle.
• In the lateral region (temporal area): the superficial temporal artery (a. temporalis superficialis) together with the auriculotemporal nerve (n. auriculotemporalis) ascends vertically anterior to the tragus (tragus). The posterior auricular vessels and nerve (a., v. et n. auriculares posteriores) are projected posteriorly and parallel to the attachment site of the auricle.
• In the posterior region (occipital area): the occipital artery (a. occipitalis) and the accompanying greater occipital nerve (n. occipitalis major) are projected at the midpoint of the distance between the external occipital protuberance and the posterior margin of the mastoid process base. The sensory lesser occipital nerve (n. occipitalis minor) runs laterally.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Topographical anatomy of the paired regions of the cranial vault (temporal and mastoid regions)
• Internal and external surfaces of the cranial base
• Dural venous sinuses and diploic veins
• Innervation sources of the fronto-parieto-occipital region skin

Other topics in the section "Topographic Anatomy of the Head"

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