Deep facial region and internal cranial base
The topographical anatomy of cranial structures is closely related to the adjacent deep facial region. In this space, the maxillary artery (a. maxillaris) gives off deep temporal arteries that supply the tissues of the temporal fossa. Innervation of this zone is provided by branches of the mandibular nerve (n. mandibularis), which is the third branch of the trigeminal nerve. Lymphatic drainage from these structures is directed to the deep parotid lymph nodes (nodi lymphatici parotideae profundi), embedded directly within the thickness of the salivary gland of the same name.
On the internal surface of the cranial bones (specifically, the squamous part of the temporal bone and the greater wing of the sphenoid bone), the middle meningeal artery (a. meningea media) forms a dense network of branches. Beneath the dura mater in this zone lie the frontal, parietal, and temporal lobes of the brain. The borders between them are formed by critical sulci: the central (Rolandic) and lateral (Sylvian) sulci.
The clinical significance of these anatomical relationships is immense. In cranial trauma, injury to the trunk or branches of the a. meningea media frequently leads to the formation of life-threatening epidural and subdural hematomas. To precisely determine the trepanation site for arresting hemorrhage, surgeons utilize a specialized projection scheme.
Construction of lines according to the Kroenlein scheme
The Kroenlein scheme of craniocephalic topography is a geometric grid that the physician plots on the patient's head to locate desired brain regions. Construction begins by drawing the baseline guidelines:
- Median sagittal line: drawn strictly along the center of the cranial vault from the glabella (glabella) to the external occipital protuberance (protuberantia occipitalis externa).
- Main lower horizontal: connects the infraorbital margin to the upper margin of the external acoustic meatus.
- Upper horizontal: drawn parallel to the lower line, passing through the supraorbital margin.
Three perpendiculars (verticals) are erected perpendicular to the two resulting horizontals:
- Anterior vertical: passes through the midpoint of the zygomatic arch.
- Middle vertical: constructed through the midpoint of the mandibular condylar process.
- Posterior vertical: dropped along the posterior boundary of the mastoid process base.
Projections of sulci and meningeal vessels
The intersection points of the drawn lines serve as precise landmarks for localizing anatomical formations hidden beneath the bones of the cranial vault.
- Central (Rolandic) sulcus (sulcus centralis): to locate its projection, connect with a line the intersection point of the posterior vertical with the median sagittal line and the intersection point of the anterior vertical with the upper horizontal.
- Lateral (Sylvian) sulcus (sulcus lateralis): projected as the bisector of the angle formed between the projection of the central sulcus and the upper horizontal. This sulcus occupies the segment strictly between the anterior and posterior verticals.
- Trunk of the a. meningea media: localized at the intersection point of the anterior vertical with the lower horizontal. Anatomically, this landmark is located at the upper margin of the zygomatic arch, 2.0–2.5 cm posterior to the frontal process of the zygomatic bone.
- Frontal branch of the a. meningea media (r. frontalis a. meningeae mediae): projected at the intersection of the anterior vertical with the upper horizontal.
- Parietal branch of the a. meningea media (r. parietalis a. meningeae mediae): determined at the intersection of the posterior vertical with the upper horizontal.
Additional projections according to Kroenlein-Bryussova
In the expanded modification of the Kroenlein-Bryussova scheme, the positions of the cerebral gyri and major blood vessels are also accounted for. The critical functional zones are localized around the central sulcus: anterior to it lies the precentral gyrus (gyrus precentralis), and posterior to it lies the postcentral gyrus (gyrus postcentralis).
The scheme allows for projecting the course of the neck vessels and the base of the brain: the common carotid artery (a. carotis communis), which divides into the internal (a. carotis interna) and external (a. carotis externa) carotid arteries. In the posterior cranial fossa, the course of the vertebral artery (a. vertebralis), transitioning into the unpaired basilar artery (a. basilaris), is taken into account.
Additionally, the coordinate system allows determining the projection of the intracranial cavernous sinus (sinus cavernosus) and the arteries directly supplying the brain tissue: the anterior cerebral artery (a. cerebri anterior), middle cerebral artery (a. cerebri media), and posterior cerebral artery (a. cerebri posterior).
Briefly: answers to topical questions
Through which opening does the middle meningeal artery enter the cranial cavity?
The middle meningeal artery (a. meningea media) enters the cranial cavity through the foramen spinosum (foramen spinosum). It is a major branch of the maxillary artery (a. maxillaris). Along with the artery, the accompanying vein and the meningeal branch of the mandibular nerve (r. meningeus spinosus) pass through this opening. Within the cranial cavity, the vessel branches out on the squamous part of the temporal bone and the greater wing of the sphenoid bone, supplying most of the dura mater.
What branches does the middle meningeal artery give off?
The middle meningeal artery (a. meningea media) gives off a series of branches supplying the dura mater and adjacent structures. The main ones are:
- Frontal branch (r. frontalis) — runs along the outer surface of the dura mater.
- Parietal branch (r. parietalis) — also located on the outer surface of the dura mater.
Additional branches:
- Superior tympanic artery (a. tympanica superior) — to the mucosa of the tympanic cavity.
- Petrosal branch (r. petrosus) — to the canal for the greater petrosal nerve.
- Orbital branch (r. orbitalis) — to the orbit.
- Anastomotic branch with the lacrimal artery (r. anastomoticus cum a. lacrimali).
- Pterygomeningeal artery (a. pterygomeningea) — to the pterygoid muscles, auditory tube, and dura mater.
What soft tissue layers cover the bones of the cranial vault in the temporal region?
The bones of the cranial vault in the temporal region are covered by the following soft tissue layers (from superficial to deep):
- Skin — thin, retaining hair follicles in the posterior region.
- Subcutaneous tissue — contains the vestigial muscle (m. auricularis superior), neurovascular structures, and superficial temporal fascia.
- Temporal fascia (fascia temporalis) — appears as an aponeurosis, splitting into superficial and deep layers.
- Interaponeurotic fatty tissue — enclosed between the layers of the temporal fascia.
- Subaponeurotic cellular space — contains loose connective tissue.
- Temporalis muscle (m. temporalis).
- Deep cellular space — located beneath the muscle.
- Periosteum (periosteum) — covers the cranial bones.
Which nerves innervate the dura mater of the brain?
The dura mater of the brain is innervated by branches of the trigeminal, vagus, hypoglossal, and upper cervical spinal nerves.
Supratentorially (above the tentorium cerebelli), innervation is provided by branches of the trigeminal nerve (n. trigeminus):
- Tentorial branch (r. tentorii) — from the ophthalmic nerve.
- Meningeal branch (r. meningeus medius) — from the maxillary nerve.
- Meningeal branch (r. meningeus spinosus) — from the mandibular nerve.
Infratentorially (in the posterior cranial fossa), the dura is innervated by:
- Meningeal branches of the vagus nerve (n. vagus).
- Meningeal branches of the hypoglossal nerve (n. hypoglossus).
- Branches of spinal nerves — from the upper cervical segments.
Rule of verticals for the a. meningea media: The trunk lies inferiorly on the anterior vertical, the frontal branch superiorly on the anterior vertical, and the parietal branch superiorly on the posterior vertical.
Class and exam questions
Why is it necessary to know the projection of the middle meningeal artery?
Rupture of this artery during a cranial trauma causes rapid and dangerous epidural hematomas. Knowledge of its projection is essential for correctly selecting the trepanation burr hole site.
Where is the projection of the trunk of the a. meningea media located?
The trunk of the artery is projected at the intersection of the anterior vertical line (midpoint of the zygomatic arch) and the main lower horizontal line (line from the infraorbital margin to the upper margin of the external acoustic meatus).
How to construct the projection of the lateral (Sylvian) sulcus?
It is constructed as the bisector of the angle between the projection line of the central sulcus and the upper horizontal line, located on the segment between the anterior and posterior vertical lines.
What else to study on this topic
- Topography of the precentral and postcentral gyri (gyrus precentralis et postcentralis).
- Anatomy and branches of the a. cerebri anterior, a. cerebri media, and a. cerebri posterior on a diagram.
- Topography of the cavernous sinus (sinus cavernosus) and its connection with the vessels of the cranial base.
- Course of the vertebral and basilar arteries (a. vertebralis, a. basilaris) relative to bony landmarks.
- Blood supply and innervation of the deep facial region (branches of the a. maxillaris and n. mandibularis).
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