(I) Important bony landmarks of the cranial region
The head is bounded by the superior orbital rim, the superior edge of the zygomatic arch, and the line from the superior edge of the external auditory meatus to the mastoid process, and is divided into the posterior upper cranial part and the anterior lower facial part. The bony landmarks of the skull are of great clinical significance for understanding the corresponding intracranial structures, especially the important functional parts of the brain tissue, so as to avoid or reduce the damage as much as possible when performing cranio-cerebral surgery.
1.Brow arch superciliaryarch: It is an arch-shaped elevation located above the supraorbital rim, where eyebrow hairs grow on the skin surface. The superciliary arch is located on the lower edge of the frontal lobe of the brain.
2, interbrow glaballa: located at the midpoint between the two brow arches.
3, frontal node frontaltuber: the most prominent part of the frontal bone outside. The deep side is suitable for the frontal gyrus of the brain.
4, zygomaticarch: by the zygomatic bone of the temporal prominence and the zygomatic prominence of the temporal bone together, the upper edge of the flat zygomatic arch, which corresponds to the lower edge of the frontal temporal lobe of the cerebral hemisphere. The semilunar midpoint between the lower edge of the zygomatic arch and the mandibular notch is the entry point for occlusal nerve closure and maxillary and mandibular nerve block anesthesia.
5.Pterygoid point pterion: It is located about 3 or 8 cm above the midpoint of zygomatic arch, and is the confluence of frontal, parietal, pterygoid and temporal bones, most of which are “H”-shaped and a few are “N”-shaped. The inner surface of the pterygoid point has the anterior branch of the middle meningeal artery passing through, when this place suffers a violent blow, the fracture fragment can injure this artery and form an epidural hematoma.
6.Star point: located at both sides of the posterior part of the skull, it is the intersection of the occipital, parietal and temporal bones behind and above the mastoid root. It is equivalent to 1.5cm above the upper edge of the external auditory meatus and the occipital ridge, and about 3.5cm after the center of the external auditory canal. The star point is at the point where the transverse sinus turns into the sigmoid sinus.
7.Papillary mastoidprocess: It is located at the posterior part of the earlobe. The inner surface of the posterior part of the mastoid process is the sigmoid sinus groove, which accommodates the sigmoid sinus.
8.Externaloccipitalprotuberance：Located outside the occipital bone in the middle of the bulge, its inner surface is the sinus sink. Below the externaloccipitalprotuberance there are occipital conduction vessels. This vessel is often dilated when the intracranial pressure is increased. If a median incision is made along the external occipital bulge during posterior craniotomy, care should be taken not to injure the occipital vessels and sinus sink to avoid hemorrhage.
9.Superiornuchalline: It is a bow-shaped bone peak that extends from the occipital ridge to both sides, and its deep surface is the transverse sinus.
10, brebma point: also known as the frontal vertex point, from the eyebrow to 13cm back, for the coronal suture and sagittal suture confluence, so also known as the coronal sagittal point. Neonatal fontanel is located at this point. Bulging fontanelle is. Signs of increased intracranial pressure.
11, herringbone point lambda: also known as the parieto-occipital point, is located about 6cm above the occipital ridge, the intersection of the sagittal and herringbone sutures. The posterior fontanelle of newborns is located at this point.
(B) Projection of important intracranial structures on the body surface
1.Main marker lines: The projection of important intracranial structures is often based on six marker lines.
(1) Lower horizontal line: the line from the lower edge of the orbit to the upper edge of the external auditory meatus.
(2) Upper transverse line: a line drawn backward from the superior orbital rim parallel to the lower transverse line.
(3) Sagittal line: the line between the eyebrows and the external occipital ridge.
(4) Anterior vertical line: a line perpendicular to the upper and lower horizontal lines through the midpoint of the zygomatic arch.
(5) Middle vertical line: a line parallel to the anterior vertical line is made upward through the midpoint of the mandibular condyle.
(6) Posterior vertical line: A line parallel to the anterior and middle vertical lines is made via the posterior edge of the mastoid root.
2.Surface projection of important intracranial structures.
(1) Longitudinal fissure of the brain: equivalent to the sagittal position.
(2) Central sulcus: it is on the line between the intersection of the anterior vertical line and the superior transverse line and the intersection of the posterior vertical line and the sagittal line, which is equivalent to the section between the posterior vertical line and the middle vertical line, and the lower end of this section is 5~5,5cm above the temporomandibular joint.
(3) Lateral sulcus: it corresponds to the equivocation of the intersection angle between the central sulcus projection line and the superior transverse line.
In clinical surgery, the most simple and practical way to determine the projection line of the lateral sulcus and the central sulcus is to set the sagittal line between the eyebrows and the occipital ridge, the wing point at 4 cm above the midpoint of the zygomatic arch (about 2 fingers), the line 2 cm after the midpoint of the wing point to the sagittal line (50%) is the projection line of the central sulcus of the brain, and the line from the wing point to the first three-quarters of the sagittal line (75%) is the projection line of the lateral sulcus of the brain. projection line.
(4) Parieto-occipital sulcus: A line 1.25-2.25 cm long is drawn laterally from about 1.25 cm above the herringbone point, and this line is the projection of the parieto-occipital sulcus on the body surface.
(5) Central anterior gyrus: It is located within the first 1,5 cm of the central sulcus projection line. The projection of the left precentral gyrus is located slightly above the intersection of the anterior vertical line and the superior transverse line.
(6) Postcentral gyrus: It is located within 1.5 cm posterior to the projection line of the central sulcus.
(7) Inferior cerebral border: starting from about 1, 25 cm above the root of the nose outward, along the superior orbital border posteriorly, through the superior border of the zygomatic arch and the superior border of the external auditory meatus to the line of the external occipital bulge.
(8) Middle meningeal artery: The projection of the main trunk of the middle meningeal artery, from the intersection of the inferior transverse line and the anterior vertical line ending about 2 cm above the midpoint of the zygomatic arch, is divided into two branches, anterior and posterior. The anterior branch goes upward to the intersection of the superior transverse line and the anterior vertical line, that is, the wing point, and then goes upward to the cranial vault; the posterior branch goes through the intersection of the superior transverse line and the middle vertical line, and then goes upward diagonally to the herringbone point. The branches of the middle meningeal artery sometimes have variants. To investigate the anterior branch, the drilling site is at the intersection of two lines 4 or 5 cm from the posterior edge of the zygomatic process of the frontal bone and the superior edge of the zygomatic arch; to investigate the posterior branch, it is carried out 2 or 5 above the external auditory meatus.
(9) Superior sagittal sinus: equivalent to the position of the sagittal line.
(10) Sinus sink: located on the deep side of the external occipital ridge.
(11) Transverse sinus: it corresponds to the deep surface of the superior collateral line.
Second, the hierarchical structure of the top of the skull features
The cranial part is composed of cranial vault, cranial base and cranial cavity. The cranial vault is divided into frontoparietal occipital area and temporal area, and includes its deep surface of the cranial vault bones.
(A) frontoparietal-occipital area
1.Realm: The front is the supraorbital rim, the back is the extraoccipital ridge and the supratrochlear line, and both sides are bounded by the supratrochlear line and the temporal area.
2.Level: The soft tissues covering this area are divided into five layers from superficial to deep, in order: skin, superficial fascia, capillary tendon membrane and cranial parietal muscle (frontal and occipital muscles), loose connective tissue under the tendon membrane and cranial epicranium. Among them, the three superficial layers are closely connected and it is difficult to separate them individually, therefore, they are often called “scalp” together. The deeper two layers are loosely connected and can be easily separated.
(1) Skin skin: The skin in this area is thick and dense, and has two distinctive features: first, it contains a large number of hair follicles, sweat glands and sebaceous glands, and is a good site for boils or sebaceous cysts; second, it has abundant blood vessels, and bleeds a lot when traumatized, but the wound heals quickly. The hair root obliquely crosses the dermis to reach the superficial fascia and is attached to the hair follicle. The surgical incision should be made in the same direction as the hair to reduce the damage to the hair follicle.
(2) Superficial fascia superficialfascia: It is composed of dense connective tissue and adipose tissue with many thick and vertical fibrous bundles, which make the skin and capillary tendon membrane closely connected and separate this layer into many small compartments, which are filled with fat and have blood vessels and nerves penetrating inside. In case of infection, the exudate does not spread easily, so the swelling is limited and the nerve endings can be compressed early to cause severe pain. In addition, the walls of the vessels in the lattice are closely fixed by the surrounding connective tissue, so it is not easy to contract and close the vessels by themselves when they are injured, so there is more bleeding, and compression or suturing is often needed to stop the bleeding.
(3) cap-like tendon membrane epicranialaponeurosis: it is a thick and tough tendon membrane, which is attached to the frontal belly of the occipital frontal muscle in front and the occipital belly in the back, protruding backward in the middle and attached to the occipital ramus, serving as the starting point of the supratrochlear muscle and the preauricular muscle on both sides, and gradually becoming thinner, continuing in the superficial temporal fascia and attached to the zygomatic arch, just like a cap fastened to the head.
The frontal belly of the occipital frontalis muscle ends at the skin under the frontalis, and some fibers are mixed with the orbicularis oculi muscle; the posterior side is connected with the membranous tendon membrane slightly in front of the coronal suture, which produces transverse lines on the frontalis when contracted.
The occipital ventral part of the occipital frontalis muscle starts from the lateral part of the superior collar line, travels forward and ends at the posterior edge of the capitate tendon membrane, which pulls the scalp backward when contracting.
The capitate tendon membrane is closely connected to the skin by the fibrous septum of the superficial fascia, and the three layers of skin, superficial fascia and capitate tendon membrane are clinically referred to as the scalp. Scalp trauma, such as not injured capillary tendon membrane, the wound is not obvious; such as capillary tendon membrane at the same time, due to the contraction and pull of the frontal occipital muscle, then the wound is split, especially the transverse wound is more. When suturing the scalp, this layer must be sutured in order to reduce the tension of the skin, which is conducive to wound healing and hemostasis.
(4) Subaponeurotic space: It is a thin layer of loose connective tissue located between the capitellar tendon membrane and the skull periosteum. This space is extensive, reaching anteriorly to the supraorbital rim, posteriorly to the superior collar line, and on both sides to the zygomatic arch. The scalp is loosely connected to the cranial epicranium by this layer, so it is highly mobile, and the flap can be turned up by this gap during craniotomy, and the scalp avulsion is also mostly separated along this layer. In case of bleeding or septicemia in the subtenoid space, it can spread rapidly to the entire cranial vault and form a large hematoma, and the scar can appear at the root of the nose and under the skin of the upper lid. The veins in this gap are connected to the cranial plate vein and the intracranial dural venous sinus via the infundibulum, and if infection occurs, it can be followed by cranial osteomyelitis or spread intracranially via the above pathways, so this layer is clinically considered to be the “dangerousarea” of the top of the skull.
(5) Cranial epicranium pericranium: It is composed of dense connective tissue and is connected to the surface of the skull by a small amount of connective tissue, both of which can be easily peeled off. However, the pericranium is closely attached to the cranial suture and penetrates deeply into the suture, becoming the pericranial membrane and fusing with the outer layer of the dura mater inside the skull. Therefore, a subperiosteal hematoma, which is often confined to a single skull bone, is easily distinguished from a subtenoid hematoma. In severe scalp avulsion injuries, the scalp may be avulsed along with part of the periosteum.
The extracranial membrane is less nutritive to the cranial bone. It does not affect the growth of the skull after detachment.
(B) Temporal area
1.Realm: It is located on both sides of the cranial vault, between the upper line and the upper edge of the zygomatic arch, in front to the frontal eminence of the zygomatic bone and the zygomatic eminence of the frontal bone, and in the back to the base of the mastoid process and the external auditory meatus.
2.Levels: The soft tissues in this area also have five layers from superficial to deep, in order: skin, superficial fascia, temporal fascia, temporalis muscle and cranial epicranium.
(1) Skin: The skin in the anterior part of the temporal region is thin and mobile, so the longitudinal or transverse incision is easy to close during surgery and the scar is not obvious after healing.
(2) Superficial fascia: It contains less fatty tissue and fibrous septa. There are superficial temporal vessels and auriculotemporal nerve in front of the auricle, and there are posterior auricular vessels and small occipital nerve behind the auricle, which travel along the temporal area in a radial pattern from bottom to top towards the frontoparietal occipital area. When craniotomy is performed via this area, the base of the flap should be below, including both the above-mentioned vessels and nerves, to ensure the survival and sensation of the flap.
(3) Temporal fascial temporalfascia.
(1) Superficial temporal fascia: It is a continuation of the capitellar tendon membrane, which is weaker and tapers downward to continue with the deep temporal fascia. The preauricular and supratrochlear muscles start from the membranous fascia, the postauricular muscle starts from above the mastoid root, and all three muscles end at the root of the ear.
(2) Deep temporal fascia: The upper part is attached to the superior temporal line, and the lower part is divided into two deep and shallow layers attached to the inner and outer sides of the zygomatic arch, with fat and blood vessels between the two layers, through which the middle temporal artery (from the superior collar artery) and the middle temporal vein pass. Since this fascia is very dense, the hard fascial edge can be felt by the fingers when examining the wound and may be mistaken for a cranial injury.
(4) Temporal muscle temporalmuscle: fan-shaped, starting from the temporal fossa and the deep surface of the temporal fascia, the anterior muscle fibers are vertical downward, the posterior muscle fibers are almost horizontal forward, and the muscle fibers are gradually concentrated, passing through the deep surface of the zygomatic arch and ending at the coronoid process of the mandible. After partial removal of temporal bone scales by temporal craniotomy, temporal muscle and temporal fascia have the role of protecting meninges and brain tissues, so the temporal approach is often used for open and closed epidural hematoma removal and subtalar decompression of temporal muscle. There are deep temporal vessels and nerves in the deep temporal muscle, the deep temporal artery from the maxillary artery and the deep temporal nerve from the mandibular nerve, which innervate the temporal muscle.
(5) Periosteal periosteum: It is thin and close to the skull surface, thus subperiosteal hematoma rarely occurs in this area. Between the periosteum and the temporal muscle, it contains a large amount of adipose tissue, which is called sub-temporal fascial lax connective tissue, and is connected to the inferior temporal space through the deep surface of the zygomatic arch, and then forward to be continuous with the buccal fat body of the face. Therefore, if there is bleeding or inflammation in the sub-temporal fascial loose connective tissue, it can spread down to the face and form a deep facial hematoma or abscess, while facial inflammation, such as odontogenic infection, can also spread to the sub-temporal fascial loose connective tissue.
(iii) Blood vessels and nerves in the top of the skull
The blood vessels and nerves of the cranial region travel within the superficial fascia and can be divided into the preauricular and postauricular groups.
1.Vessels in the top of the skull: there are three pairs in the preauricular group and two pairs in the postauricular group.
(1) Supratrochlear artery and vein supratrochleara, &v: about 2cm from the median line. supratrochlear artery is one of the terminal branches of the ophthalmic artery and travels with the supratrochlear nerve around the frontal notch to the frontal area.
(2) Supraorbital artery and vein supraorbitala, &v: about 2,5 cm from the midline. supraorbital artery is a branch of the ophthalmic artery, which accompanies the supraorbital nerve and travels in the orbit between the levator muscle and the supraorbital wall, to the supraorbital foramen (incision) and around the supraorbital rim to the frontal area. The two groups of arteries and nerves are often accompanied by the supraorbital artery on the medial side of the supraorbital nerve and the supraorbital artery on the lateral side of the supraorbital nerve.
(3) Superficial temporal arteries and veins superficialtemporala, &v,: accompanying the auriculotemporal nerve, penetrating the superior border of the parotid gland and crossing the zygomatic arch to reach the temporal region. The superficial temporal artery is one of the two terminal branches of the external carotid artery, which starts from the posterior aspect of the mandibular neck and travels superiorly on the deep surface of the parotid gland and in front of the auriculotemporal nerve, and the pulsation of this artery can be palpated in front of the ear screen. About 2-3 cm above the zygomatic arch, the superficial temporal artery divides into a frontal branch and a parietal branch. The frontal branch is thicker, with an outer diameter of about 1, 8 mm, and usually travels obliquely forward and upward at an angle of 15 to 900 anterior to the vertical line, to the supraorbital angle or near the frontal nodes and upward to the cranial vault, sending 2 to 5 frontal parietal branches posteriorly and superiorly during the stroke, distributed in the cranial vault, with a distribution area of about 99 cm2, and more than one of these branches has a diameter of more than 1, 0 cm2 (82%). The external diameter of the parietal branch is about 1.7 mm, with a posterior inclination of about 300 to the vertical line, posteriorly and superiorly to the parietal node, and the branches are distributed in the cranial vault, with a distribution area of about 53 cm2. The superficial temporal artery has a constant position, a large diameter, and a large expansibility, and is the ideal artery for supplying blood when the internal carotid artery system is ischemic for intracranial and external arterial anastomosis.
The superficial temporal veins converge into the posterior mandibular veins.
(4) Posterior auricular artery and vein posteriorauriculara, &v: The posterior auricular artery is small and starts from the external carotid artery on the deep side of the parotid gland, and travels along the posterior ventral superior edge of the diastasis muscle to the posterior and superior side of the auricle, and is distributed on the lateral surface of the auricle and its posterior and superior skin. Because of its small caliber, this artery is not suitable for intracranial and extracranial anastomosis, but it has more anastomoses with the superficial temporal artery and occipital artery, and is the axial vessel of the free flap in the posterior region of the ear, as well as the complementary vessel of the full frontal flap. The postauricular vein converges into the external jugular vein.
(5) Occipital artery and vein occipitala, &v,: Occipital artery is thick, starting from the external carotid artery, running posteriorly along the inferior margin of the posterior ventral part of the diastasis, passing through the occipital artery sulcus of the temporalis mastoid to the collar, and finally at the superior collar line, penetrating the oblique muscle and deep fascia lateral to the great occipital nerve, and distributing in the skin of the occipital area. The external diameter of the occipital artery is >1.1 mm, and the body projection is 2-3 cm below the external occipital ridge and 3-4 cm from the midline. Because of the constant position of the occipital artery and the thicker diameter of both the trunk and branches, the occipital artery is often chosen to anastomose with the posterior inferior cerebellar artery in cases of vertebrobasilar artery ischemia. The occipital artery is richly anastomosed with the contralateral homonymous artery, superficial temporal artery and posterior auricular artery, and the outer diameter of the anastomosis point is 0.3-0.6 mm or more in 60% of cases, so the occipital scalp can also be used as the donor area for free flap graft. The occipital vein converges into the external jugular vein. The occipital nerve is thick, and is a cutaneous branch of the posterior branch of the 2nd cervical nerve, which penetrates the oblique tendon membrane and deep fascia about 2 or 5 cm lateral to the lateral occipital bulge, and then travels with the occipital artery toward the cranial vault and distributes over most of the skin behind the head. The occipital artery is lateral to the occipital nerve, and there is a certain distance between the two.
The blood vessels of the cranial vault all travel radially from the peripheral part to the cranial vault, so when craniotomy is made here, the tip of the flap should be below, and the tip of the flap should be where the blood vessels and nerve trunk are located to ensure the nutrition of the flap. The general scalp incision should be radiolucent to avoid damage to the vascular nerve trunk. The arteries of the cranial vault have extensive anastomoses, not only between the left and right sides, but also between the internal and external carotid artery systems, so that the scalp is not easily necrotic in the event of a large tear. Similarly, when the scalp bleeds due to injury, circumferential compression should be made to stop the bleeding.
The veins at the top of the skull are accompanied by the eponymous arteries and form a network of veins under the skin. In addition, there are ductal veins in the head that form the traffic between the extracranial veins and the intracranial dural venous sinuses. The conduit veins are.
① parietalemissaryv, which crosses the parietal foramen on both sides of the sagittal line behind the midpoint of the cranial vault and connects the superficial temporal veins with the superior sagittal sinus;
(ii) mastoidemissaryv, which passes through the mastoid foramen and connects the retroauricular vein, occipital vein and sigmoid sinus;
(iii) condylaremissaryv, which crosses the condylar canal and connects the inferior occipital plexus with the sinus sink; sometimes a single occipital vein crosses the external occipital bulge and connects the occipital vein with the sinus sink. There is no valve in the conduit vein, and the direction of venous blood flow is usually to the outside of the skull, but under certain circumstances, it can also flow backwards into the skull, so the intracranial and extracranial infections can spread directly to each other; minor scalp injuries, if not treated in time or improperly treated, can sometimes cause serious intracranial infections, such as venous sinus thrombosis and meningitis.
2.Nerves at the top of the skull
There are ten pairs of nerves on the top of the skull, five pairs in front of the ear and five pairs behind the ear, including one pair of motor nerves and four pairs of sensory nerves.
(1) Preauricular group
(1) Supratrochlear nerve supratrochlearn: a terminal branch of the frontal nerve emanating from the first ophthalmic nerve of the trigeminal nerve, which travels superiorly via the superior orbital rim at 2,0mm from the midline and is distributed in the skin near the midline.
(2) Supraorbital nerve supraorbitaln,: another terminal branch of the frontal nerve, reaches the forehead and cranial vault through the supraorbital notch to the skin at the herringbone suture, and also gives off a small branch to the frontal sinus.
Both the supraorbital nerve and the supraorbital nerve are branches of the ophthalmic nerve, so patients with trigeminal neuralgia have pressure pain at the medial and middle 1/3 of the supraorbital rim.
3) Zygomaticotemporalbranch of the zygomaticotemporal nerve: it is fine and originates in the orbit from the zygomatic branch of the maxillary nerve, which crosses the temporal fascia behind the frontal process of the zygomatic bone and distributes in the skin of the anterior part of the temporal region.
(4) Temporal branch of facial nerve, temporalbranchesoffacialn,: it comes out from above the anterior part of the parotid gland and sends out small branches to the frontalis muscle, supratrochlear muscle, preauricular muscle and the upper part of the orbicularis oculi muscle, and has an anastomotic branch connected with the zygomaticotemporal nerve of the trigeminal nerve.
(5) Auriculotemporal nerve auriculotemporaln,: it is a branch of the mandibular nerve of the third branch of the trigeminal nerve, and after issuing from the inferior temporal fossa, it passes out at the upper end of the parotid gland and travels up immediately in front of the auricle, distributing in the upper part of the auricle, the external auditory canal, the anterior part of the tympanic membrane and the skin of the temporal region and the lateral part of the head, and can be anesthetized with a local block in front of the foot of the auricle.
(2) Posterior auricular group
(1) The posteriorauricular nerve is a small branch of the facial nerve that emanates immediately after the stem mammary foramen, bends upward immediately behind the root of the ear, and is distributed in the occipital muscle, posterior auricular muscle and part of the supratrochlear muscle.
(2) The greatauricular nerve comes from the 2nd and 3rd mental scenes and distributes behind the auricle, behind the anterior part of the lower part of the auricle and the surface skin of the parotid gland.
(3) Lesser occipital nerve: it comes from the 2nd and 3rd cervical nerves and is a branch of the cervical plexus, distributing in the upper part of the neck, behind the auricle and the adjacent skin of the cranial vault.
(4) Greater occipital nerve greateroccipitaln: thick and large, it is a cutaneous branch of the posterior branch of the second cervical nerve, which penetrates the rhomboid muscle and deep fascia at a distance of about 2 or 5 cm from the lateral aspect of the occipital ridge and distributes over most of the skin at the back of the head. The occipital nerve can be closed one finger below the lateral occipital bulge and about 2 or 5 cm lateral to the lateral side.
(5) The third occipital nerve, the thirdoccipitaln, is a small cutaneous branch of the posterior branch of the third cervical nerve, which penetrates the oblique muscle and distributes in the upper part of the collar and the skin near the external occipital bulge.
The nerves of the cranial vault travel within the superficial fascia and coincide with each other, and the distribution areas overlap with each other, so local anesthesia blocking one nerve often does not have a satisfactory effect, and it is necessary to inject anesthetics in more places to expand the scope of the nerve block. At the same time, it should be noted that when local anesthesia is used, the anesthetic must be injected into the superficial fascia, because there are thick fiber bundles in the subcutaneous tissue, so the injection will feel a greater resistance. If it is mistakenly injected into the subtenon space, the anesthetic effect will not be achieved.
(D) Structural characteristics and clinical significance of the cranial cap bone
The cranial cap bone is a membranous bone during embryonic development, and it has not been completely ossified at birth.
The bones of the skullcap are flat bones. The frontal bone is in front and the occipital bone is in the back. Between the frontal and occipital bones are the left and right parietal bones. Both sides
A small part of the frontal bone is the large wing of the pterygoid bone; most of the posterior part is the squamous part of the temporal bone. When increased intracranial pressure occurs, the bony sutures may be slightly separated in pediatric patients. In adults, the bones of the skullcap are joined by the jagged cranial suture, which firmly unites the skull into a whole.
The thickness of the skull cap bone varies according to gender, age, individual and location. The average thickness of the skullcap in adults is about 5 mm, with the thickest part (occipital ridge) reaching 10 mm and the thinnest part (temporal area) being only 1 to 2 mm. Since the thickness of each part of the skullcap varies, care should be taken when drilling the skull. The thickness can be measured by X-ray or CT before surgery.
The cranial parietal bone is dome-shaped and has a certain degree of elasticity. It is often concentrated at one point when struck by external force, and the fracture line in adults is mostly centered on the point of force and radiates in all directions.
The adult fracture line is centered on the point of force and radiates in all directions. In children, the cranial vault is thin, soft and flexible, so depressed fractures often occur after trauma.
The skull cap bone is divided into three layers: outer plate, plate barrier and inner plate. The outer plate is thicker, with an average thickness of 1 to 2 mm, and is more tolerant to tension and has a smaller curvature than the inner plate. The inner plate is thinner, with an average thickness of about 0, 5 mm, and is also more fragile in texture, so it is called glass-like plate. Therefore, the outer plate can remain intact during trauma, while the inner plate is fractured. Or the outer plate is linearly fractured and the inner plate is comminuted. The fracture fragments can cause serious complications by puncturing intracranial vessels, venous sinuses, meninges and brain tissue.
The lamina cribrosa is the cancellous bone between the inner and outer plates that contains bone marrow and has a lamina cribrosa vein located in the lamina cribrosa canal. The lamina cribrosa canal is cracked on x-ray and can sometimes be mistaken for a fracture line, which should be distinguished. Because the lamellar vein is located in the bone, it cannot be ligated during surgery, and bone wax is often used to stop the bleeding.
The platysmal veins can be usually grouped into four groups.
(1) Frontal plate vein frontaldiploicvein is located in the frontal region and connects with the superior sagittal sinus and outwardly with the superior ophthalmic vein;
(ii) anterior temporal plate barrier vein anteriortemporaldiploicvein communicates with the pterygoid sinus and outwardly with the vein of the temporalis muscle;
(iii) The posteriortemporaldiploicvein is in the posterior temporal plate barrier from the top down to the mastoid and communicates with the transverse sinus;
The occipital diploicvein is located in the occipital region and communicates with the transverse sinus and outwardly with the occipital vein. In addition to the intracranial venous sinus, the platysmal vein is also connected to the veins of the soft tissues of the cranial vault, so it is also a way for extracranial infection to spread intracranially.