BRAIN VASCULARIZATION
Blood is pumped from the left ventricle of the heart to the aortic arch and thence to the common carotid arteries and anterior circulation of the brain (internal carotid, middle cerebral, and anterior cerebral arteries), and to the subclavian arteri art eries es and pos poster terior ior cir circul culati ation on of the br brain ain (ve (verte rtebra bral, l, bas basila ilar, r, and posterior cerebral arteries). The anterior circulation supplies the eyes, basal ganglia, part of the hypothalamus, the frontal and parietal lobes, and a large portion of the temporal lobes, while the post posterior erior circulation circulation supplies the brain stem, cerebellum, cerebellum, inner ear, occipital lobes, the thalamus, part of the hypothalamus, and a smaller portion of the temporal lobes. Venous blood from the supercial and deep cerebral veins (p. 1 !) drains via the dural venous sinuses into the internal "ugular veins and thence into the the superior vena cava and right atrium. The e#tracranial and intracranial portions of the blood supply of the brain as well as that of the spinal cord will be detailed further in the following paragraphs. Carotid Arteries: Extracranial Portion The brachiocephalic trun$ arises from the aortic arch arch behind the manubrium of the sternum and bifurcates bifurcates at the level of the sternoclavicular "oint to form the right subclavian and common carotid arteries. The left common carotid artery (usually ad"acent to the brachiocephalic trun$) and subclavian artery arise directly from the aortic arch. The common carotid carotid artery on either side bifurcates at the level of the thyroid cartilage to form the internal and e#ternal carotid arteries% these arteries lie parallel and ad"acent to each other after the bifurcation, with the e#ternal carotid artery lying medial. & dilatation of the common carotid artery at its bifurcation is called the carotid sinus. The e#ternal carotid artery gives o! the superior thyroid, lingual, facial, and ma#illary arteries anteriorly, the ascending pharyngeal artery medially, and the occipital and posterior auricular arteries posteriorly. The ma#illary and supercial temporal arteries are its terminal branches. The middle meningeal artery is an important branch of the ma#illary artery.
The internal carotid artery gives o! no e#tracranial branches. 'ts cervical portion runs lateral or dorsolateral to the e#ternal carotid artery, then dorsomedially along the wall of the pharyn# (parapharyngeal space) in front of the transverse processes of the rst three cervical vertebrae, and nally curves medially toward the carotid foramen.
Carotid Arteries: Intracranialortion The internal carotid artery ('&) passes through the base of the s$ull in the carotid canal, which lies within the petrous part of the temporal bone. 't runs upward about 1 cm, then turns anteromedially and courses toward the petrous ape#, where it emerges from the temporal bone to enter the cavernous sinus. ithin the sinus, the '& runs along the lateral surface of the body of the sphenoid bone (* segment of the '&), then turns anteriorly and passes lateral to the sella turcica along the lateral wall of the sphenoid bone (segment +). 't then bends sharply bac$ on itself under the root of the anterior clinoid process, so that it points posteriorly (segment , carotid bend). &fter emerging from the cavernous sinus, it penetrates the dura mater medial to the anterior clinoid process and passes under the optic nerve (cisternal segment, segment -). 't then ascends in the subarachnoid space (segment 1) till it reaches the circle of illis, the site of its terminal bifurcation. egments , +, and * of the '& constitute its infraclinoid segment, segments 1 and - its supraclinoid segment. egments -, , and + together ma$e up the carotid siphon. The ophthalmic artery arises from the carotid bend and runs in the optic canal inferior to the optic nerve. /ne of its ocular branches, the central retinal artery, passes together with the optic nerve to the retina, where it can be seen by ophthalmoscopy. 0edial to the clinoid process, the posterior communicating artery arises from the posterior wall of the internal carotid artery, passes posteriorly in pro#imity to the oculomotor nerve, and then "oins the posterior cerebral artery. The anterior choroidal artery usually arises from the '& and rarely from the middle cerebral artery. 't crosses under the optic tract, passes laterally to the crus cerebri
and lateral geniculate body, and enters the inferior horn of the lateral ventricle, where it "oins the tela choroidea.
The anterior and middle cerebral arteries are the terminal branches of the internal carotid artery.They originate at the '& bifurcation, located in the circle of illis at the level of the anterior clinoid process, between the optic chiasm and the temporal pole.
Anterior Cerebral Artery ACA! The && is the more medial of the two arteries arising from the '& bifurcation. 't ascends lateral to the anterior clinoid process and past the the optic nerve and optic chiasm, giving o! a small branch, the anterior communicating artery (&omm&), which crosses the midline to "oin the contralateral &&. The segment of && pro#imal to the origin of the &omm& is its precommunicating segment (segment &1). The &1 segments on either side and the &omm& together form the anterior half of the circle of illis. egment &1 gives o! an average of eight basal perforating arteries that enter the brain through the anterior perforated substance. The recurrent artery of eubner arises from the && near the origin of the &omm&, either from the distal part of &1 or from the pro#imal part of &-. The postcommunicating segment of the && (segments &- to &*) ascends between the frontal lobes and runs toward the occiput in the interhemispheric ssure, along the corpus callosum and below the free border of the fal# cerebri, as thepericallosalartery. egment&-,whichusually gives o! the frontopolar artery, ends where the artery turns forward to become apposed to the genu of the corpus callosum% segment & is the frontally conve# arch of the vessel along the genu. The&+and&*segmentsrunroughlyhori2ontally overthecallosalsurfaceandgiveo!supracallosal branches that run in a posterior direction. "istrib#tion$ The basal perforating arteries arising from &1 supply the ventral hypothalamus and a portion of the pituitary stal$. eubner3s artery supplies the head of the caudate nucleus, the rostral four4fths of the putamen, the globus pallidus, and the internal capsule. The blood supply of the inferior portion of the genu of the corpus callosum, and of the olfactory bulb, tract, and trigone, is variable. The &omm& gives o! a few small branches (anteromedial central branches) to the hypothalamus. Branches from the postcommunicating segment of the && supply the inferior surface of the frontal lobe (frontobasilar artery), the medial and parasagittal surfaces of the frontal lobe (callosomarginal artery), the paracentral lobule (paracentral artery), the medial and parasagittal surfaces of the parietal lobe (precuneal artery), and the corte# in the region of the parieto4occipital sulcus
(parieto4occipital
artery).
%iddle Cerebral Artery %CA! The 0& is the more lateral of the two arteries arising from the '& bifurcation. 'ts rst segment (01, sphenoidal segment) follows the anterior clinoid process for a distance of 1 to - cm. The 0& then turns laterally to enter the depths of the ylvian ssure (i.e., the ylvian cistern), where it lies on the surface of the insula and gives o! branches to it (0-, insular segment). 't bends bac$ sharply to travel along the surface of the operculum (0, opercular segment) and then nally emerges through the ylvian ssure onto the lateral conve#ity of the brain (0+and0*,terminalsegments). "istrib#tion$ mall branches of 01 (the thalamostriate and lenticulostriate arteries) supply the basal ganglia, the claustrum, and the internal, e#ternal, and e#treme capsules. 0and 0 branches supply the insula (insular arteries), lateral portions of the orbital and inferior frontal gyri (frontobasal artery), and the temporal operculum, including the transverse gyrus of eschl (temporal arteries). 0+ and 0* branches supply most of the corte# of the lateral cerebral conve#ity, including portions of the frontal lobe (arteries of the precentral and triangular sulci), the parietal lobe (anterior and posterior parietal arteries), and the temporal lobe (arteries of central and postcentral sulci). 'n particular, important cortical areas supplied by 0+ and 0* branches include the primary motor and sensory areas (precentral and postcentral gyri) and the language areas of Broca and ernic$e.
VERTEBRAL ARTERY
Extracranial Portion The vertebral artery arises from the arch of the subclavian artery at a point designated V5. The prevertebral or V1 segment e#tends from V5 to the foramen transversarium of the transverse process of 6. The transversarial or V- segment passes vertically through the foramina transversaria of 6 through -, accompanied by venous ple#uses and sympathetic nerves derived from the cervical ganglia. 't gives o! branches to the cervical nerves, vertebrae and intervertebral "oints, nec$ muscles, and cervical spinal cord. /ften, a prominent branch at the * level anastomoses with the anterior spinal artery. The V segment, also called the atlas (1) loop, runs laterally and then vertically to the foramen transversarium of 1, which it passes through, winds medially along the lateral mass of 1, pierces the posterior atlanto4occipital membrane behind the atlanto4 occipital "oint, and then enters the dura mater and arachnoid membrane at the level of the foramen magnum. The two vertebral arteries are une7ual in si2e in about 8*9 of persons, and one of them is e#tremely narrow (hypoplastic) in about 15 9, usually on the right side. Intracranial Portion The V+ segment of the vertebral artery lies entirely within the subarachnoid space. 't terminates at the "unction of the two vertebral arteries to form the basilar artery, at the level of the lower border of the pons. :ro#imal to the "unction, each vertebral artery gives o! a mediobasal branch% these two branches run for ca. - cm and then unite in the midline to form a single anterior spinal artery, which descends along the anterior surface of the medulla and spinal cord (see p. -). The posterior inferior cerebellar artery (:'&), which originates from the V+ segment at a highly variable level, curves around the inferior olive and e#tends dorsally through the root laments of the accessory nerve. 't then ascends behind the bers of the hypoglossus and vagus nerves, forms a loop on the posterior wall of the fourth ventricle, and gives o! terminal branches to the inferior surface of the cerebellar hemisphere, the tonsils, and the vermis. 't provides most of the blood supply to the dorsolateral medulla and the posteroinferior
surface of the cerebellum. The posterior spinal artery (there is one on each side) arises from either the vertebral artery or the :'&. The basilar artery runs in the prepontine cistern along the entire length of the pons and then bifurcates to form the posterior cerebral arteries. 'ts inferior portion is closely related to the abducens nerves, its superior portion to the oculomotor nerves. 'ts paramedian, short circumferential, and long circumferential branches supply the pons and the superior and middlecerebellarpeduncles. The anterior inferior cerebellar artery (&'&) arises from the lower third of the basilar artery. 't runs laterally and caudally toward the cerebellopontine angle, passes near the internal acoustic meatus, and reaches the ;occulus, where it gives o! terminal branches that supply the anteroinferior portion of the cerebellar corte# and part of the cerebellar nuclei. The &'& lies basal to the abducens nerve and ventromedial to the facial and auditory nerves in the cerebellopontine cistern. 't often gives rise to a labyrinthine branch that enters the internal aco#stic&eat#s. The superior cerebellar arteries (&) of both sides originate from the basilar trun$ "ust below its bifurcation.
PosteriorCerebral Artery (PCA)
The precommunicating segment of the :& (:1) e#tends from the basilar bifurcation to the origin of the posterior communicating artery (:omm&). 'ts course lies within the interpeduncular cistern, which is demarcated by the clivus and the two cerebral peduncles. The oculomotor nerve, after its emergence from the brain stem, runs between the :& and the superior cerebellar artery. The postcommunicating segment (:-) curves laterally and bac$ward around the crus cerebri and reaches the posterior surface of the midbrain at an intercollicular level. The precommunicating and postcommunicating segments are together referred to as the pars circularis of the :&. (<ernatively, the pars circularis may be divided into three segments= interpeduncular, ambient, and 7uadrigeminal= named after the cisterns they traverse.) >istal to the pars circularis of the :& is the pars terminalis, which divides above the tentorium and caudal to the lateral geniculate body to form its terminal branches, the medial and lateral occipital arteries. Pars circ#laris$ The precommunicating segment gives o! ne branches (posteromedial central arteries) that pierce the interpeduncular perforated substance to supply the anterior thalamus, the wall of the third ventricle, and the globus pallidus. The postcommunicating segment gives o! ne branches (posterolateral central arteries) to the cerebral peduncles, the posterior portion of the thalamus, the colliculi of the mid brain, the medial geniculate body, and the pineal body. ?urther branches supply the posterior portion of the thalamus (thalamic branches), the cerebral peduncle (peduncular branches), and the lateral geniculate body and choroid ple#us of the third and lateral ventricles (posterior choroidal branches). Pars ter&inalis$ /f the two terminal branches of this terminal portion of the :&, the lateral occipital artery (together with its temporal branches) supplies the uncus, the hippocampal gyrus, and the undersurface of the occipital lobe. The medial occipital artery passes under the splenium of the corpus callosum, giving o! branches that supply it (dorsal branch to the corpus callosum) as well as the cuneus and precuneus (parieto4occipital branch), the striate
corte# (calcarine branch), and the medial surfaces of the occipital and temporal lobes (occipitotemporal and temporal banches), including the parasagittal portion of the occipital lobe.
Cerebral Veins The supercial cerebral veins (cortical veins) carry blood from the outer 1@ cm of the brain surface to large drainage channels such as the superior and inferior sagittal sinuses, the great cerebral vein of Aalen, the straight sinus, and the tentorial veins. Thus, the cerebellar veins drain blood from the cerebellar surface into the superior vermian vein and thence into the great cerebral vein, straight sinus, and transverse sinuses. The deep cerebral veins (central veins) drain blood from the inner regions of the brain (hemispheric white matter, basal ganglia, corpus callosum, choroid ple#us) and from a few cortical areas as well. S#'er(cial cerebral )eins (cortical veins)$ The supercial cerebral veins are classied by their location as prefrontal, frontal, parietal, and occipital. <#cept for the occipital veins, which empty into the transverse sinus, these veins all travel over the cerebral conve#ity to "oin the superior sagittal sinus. They are termed bridging veins at their distal end, where they pierce the arachnoid membrane and bridge the subarachnoid space to "oin the sinus. The supercial middle cerebral vein (not shown) usually follows the posterior ramus of the ylvian ssure and the ssure itself to the cavernous sinus. The inferior cerebral veins drain into the cavernous sinus, superior petrosal sinus, and transverse sinus. The superior cerebral veins drain into the superiorsagittalsinus. "ee' cerebral )eins (central veins)$ The internal cerebral vein arises bilaterally at the level of the interventricular foramen (of 0onro). 't traverses the transverse cerebral ssure to a point "ust infe rior to the splenium of the corpus callosum. The venous angle at its "unction with the superior thalamostriate vein can be seen in a laterally pro"ected angiogram. The two internal cerebral veins "oin under the splenium to form the great cerebral vein (of Aalen), which receives the basal vein (of osenthal) and then empties into the straight sinus at the anterior tentorial edge at the level of the 7uadrigeminal plate. The basal vein of osenthal is formed by the union of the anterior cerebral vein, the deep middle cerebral vein, and the striate veins. 't passes posteromedial to the optic tract, curves around the cerebral, peduncle, and empties into the internal vein or the great cerebral vein posterior to the brain stem.
Posterior *ossa$ The anterior, middle, and posterior veins of the posterior fossa drain into the great cerebral vein, the petrosal vein, and the tentorial and straight sinuses, respectively. Extracerebral Veins The e#tracerebral veins=most prominently, the dural venous sinuses= drain venous blood from the brain into the sigmoid sinuses and "ugular veins. The diploic veins drain into the e#tracranial veins of the scalp and the intracranial veins (dural venous sinuses). The emissary veins connect the sinuses, diploic veins, and supercial veins of the s$ull. 'nfections sometimes travel along the emissary veins from the e#tracranial to the intracranial compartment. The veins of the brain empty into the superior and inferior groups of dural venous sinuses. The sinuses of the superior group (the superior and inferior sagittal, straight, and occipital sinuses) "oin at the con;uence of the sinuses (torcular erophili), which drains into both transverse sinuses and thence into the sigmoid sinuses and internal "ugular veins. The sinuses of the inferior group (superior and inferior petrosal sinuses) "oin at the cavernous sinus, which drains into the sigmoid sinus and internal "ugular vein via the inferior petrosal sinus, or into the internal vertebral ple#us via
the basilar ple#us.
Craniocer)ical Veins &nastomotic channels connect the cutaneous veins of the two sides of the head. Venous blood from the facial, temporal, and frontal regions drains into the facial and retromandibular veins and thence into the internal "ugular vein. ome blood from the forehead drains via the nasofrontal, angular, and superior ophthalmic veins into the cavernous sinus. The
occipital vein carries blood from the posterior portion of the scalp into the deep cervical vein and thence into the e#ternal "ugular vein. Blood from the "ugular veins continues to the brachiocephalic vein, superior vena cava, and right atrium. The venous channels in the spinal canal and the transcranial emissary veins play no more than a minor role in venous drainage. The pterygoid ple#us lin$s the cavernous sinus, the facial vein, and the internal "ugular vein. The numerous anastomoses between the e#tracranial and intracranial venous systems provide a pathway for the spread of infection from the scalp or face to the intracranial compartment. ?or e#ample, periorbital infection may e#tend inward and produce septic thrombosis of the cavernous sinus. Cranial Veins The facial vein drains the venous blood from the face and anterior portion of the scalp. 't begins at the inner canthus as the angular vein and communicates with the cavernous sinus via the superior ophthalmic vein. Below the angle of the mandible, it merges with the retromandibular vein and branches of the superior thyroid and superior laryngeal veins. 't then drains into the internal "ugular vein in the carotid triangle. The veins of the temporal region, e#ternal ear, temporomandibular "oint, and lateral aspect of the face "oin in front of the ear to form the retromandibular vein, which either "oins the facial vein or drains directly into the internal "ugular vein. 'ts upper portion gives o! a prominent dorsocaudal branch that "oins the posterior auricular vein over the sternocleidomastoid muscle to communicate with the e#ternal "ugular vein. Venous blood from the posterior portion of the scalp and the mastoid and occipital emissary veins drains into the occipital vein, which anastomoses with the occipital venous ple#us and nally drains into the e#ternal "ugular vein. The pterygoid ple#us lies between the temporalis, medial pterygoid, and lateral pterygoid muscles and receives blood from deep portions of the face, the e#ternal ear, the parotid gland, and the cavernous sinus, which it carries by way of the ma#illary and retromandibular veins to The internal "ugular vein. Cer)ical Veins The deep cervical vein originates from the occipital vein and suboccipital ple#us. 't follows the course of the deep cervical artery and vertebral
artery to arrive at the brachiocephalic vein, which it "oins. The vertebral vein, which also originates from the occipital vein and suboccipital ple#us, envelops the vertebral artery li$e a net and accompanies it through the foramina transversaria of the cervical vertebrae, collecting blood along the way from the cervical spinal cord, meninges, and deep nec$ muscles through the vertebral venous ple#us, and nally "oining the brachiocephalic vein.
DAFTAR PUSTAKA
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Rohkamm Reinhard, Color Atlas of Neurology, 2004, Sande Germany, 10-21