The Lateral Perforating Branches of the Anterior and Middle Cerebral Arteries* HARRY A. KAPLAN, M.D. Division of Neurosurgery, Seton Hall College of Medicine, and Jersey City Medical Center, Jersey City, New Jersey T IS well known that aneurysms occur at rive state, anatomically the numerous gyra- the site of branching of the large vessels tions of the cell masses in their attempt to ac- I at the base of the brain. Two relatively commodate to the relatively small cranial common sites are in the region of the anterior cavity present a grossly different final form. communicating vessel and the site of branch- Nevertheless, anatomically the adult rostral ing of the main stem of the middle cerebral brain can be described by depicting the cere- artery. Unfortunately, these sites frequently bral hemispheres as dorsal overgrowths from are the location of important lateral perfora- the rostral segment of the neural tube ex- ting vessels which irrigate large cell masses panding in all directions to cover the rest of enclosing bands of traversing axone fiber the brain; the basal ganglia, the rostral base bundles, namely the internal capsule. Fre- segment of the neural tube from which the quently, the small perforating vessels are not hemispheres grow dorsally, as caudolateral well visualized at operation and damage to expansions about the diencephalon; and the them will, at times, produce severe neuro- white matter from the base of the brain as a logical deficits. These vessels can be well lateral outgrowth from the neural tube. The demonstrated in autopsy specimens of latero-caudal expansion from the midline of fresh brain by gross dissection and roent- the rostrally situated basal ganglia, there- genography, after injection of radiopaque fore, encloses a large group of white fibers substances2 In order to define the precise lo- between itself and the thalamus to produce cation of the lateral perforating vessels, it was thought helpful to present a brief over- all survey of certain vascular relationships to the brain. Anatomy The anatomieo-vascular relationship of the central nervous system follows a well organized pattern. The brain can be de- scribed as a multi-segment unit arbitrarily formed caudo-rostrally by 5 territories: the myelencephalon, metencephalon, mesen- cephalon, diencephalon, and telencephalon. In horizontal cross-section it can be de- scribed again as a multi-segment unit con- taining a central base, lateral base and dorsal supra-segmental portion (Fig. la and b). While functionally the adult human brain FIG. 1. Diagrams of basic design of the brain. (a) Later- can still be considered in terms of its primi- al view showing the various components of the brain in re]ation to its basic segmentation. (b) Cross-section of Received for publication October 13, 1964. primitive brain. (c) Dorsal view of rostral brain indicat- * Presented at meeting of the Harvey Cushing Soci- ing formation of the internal capsule by growth of the ety, Los Angeles, California, April ~1, 1964. basal ganglia lateral to the white matter. 305 306 Harry A. Kaplan sels which go to make up a "four-segment" vascular unit is similar in design. Each large vessel gives off first central perforators to the central base cells, then single, or at times multiple, lateral perforators to the lateral cell mass, and finally distal perforators to the supra-segmental cell mass on the dorsum of the neural tube. Using this overall basic pattern of the brain, it now can be seen that the lateral perforators of the anterior and middle cerebral arteries will irrigate pri- marily the most rostral ventro-lateral cell masses of the brain. The most rostral part of the lateral cell mass in the neural tube, the head of the caudate nucleus and rostro-mesial part of the putamen, is irrigated by the lateral perforat- ing vessel of the most distal segment of the Fro. ~. Diagrams of the brain vascular patterns. (a) Double "four-segment" units made up caudally of internal carotid artery, the anterior cerebral PIC--posterior inferior cerebellar artery; AIC--ante- artery. This lateral perforating branch from rior inferior cerebellar artery; SC--superior cerebellar the anterior cerebral artery is often referred artery; 1V[cs--mesencephalic artery; and rostrally of PC--posterior cerebral artery; ACh--anterior choroidal to as Heubner's artery. It usually arises from artery; 5IC--middle cerebral artery; and AC--anterior the lateral aspect of the anterior cerebral cerebral artery. ]CA--internal carotid artery; Bas-- vessel at about the level of the anterior com- basilar artery; V--vertebral artery. (b) Cross-section of basic brain showing perforating arteries arising from the municating artery, but actually may arise main cerebral arteries. One notes the central, lateral, from any site on the lateral aspect of the and distal perforating arteries arising from each main proximal portion of the anterior cerebral ar- cerebral artery. tery (Fig. 3). It passes caudo-laterally along- side, or dorsal to, the main proximal portion the internal capsule. The white matter from of the anterior cerebral artery. Heubner's ar- the overlying cerebral cortex (suprasegmen- tery then continues laterally to reach the tal portion of the telencephalon) which will rostro-mesial portion of the anterior perfor- enter into the formation of the internal cap- ated substance. At this site it begins to divide sule must, in order to exit from the neural and send perforating branches into the cere- tube, traverse the lateral basal cell masses bral substance immediately rostral to the and thus pass between the caudate nucleus perforating branches of the middle cerebral and the putamen (Fig. lc). artery. On entering the cerebral substance The vascular pattern of this primitive- the vessel courses rostro-mesially to irrigate type brain can be shown as a double "four- the most rostro-mesial portion of the lateral segment" unit (Fig. ~). The caudal "four- cell mass (Figs. 4 and 5). Its terminal segment" unit is made up proximo-distally branches supply the antero-mesial aspect of by the posterior inferior cerebellar, anterior the head of the caudate nucleus and adjoin- inferior cerebellar, superior cerebellar and ing putamen, part of the septal nucleus, and mesenccphalic arteries, all arising from the cells in the rostro-lateral area of the olfac- vei~tebro-basilar artery. The rostral "four- tory trigone. Fiber tracts lying in the do- segment" unit is made up of the posterior main of the ramifications of this vessel are cerebral (posterior communicating),2 an- the fronto-pontine fibers of the anterior terior choroidal, middle cerebral, and an- limb of the internal capsule, the intermediate terior cerebral arteries arising from the in- olfactory stria and fibers of the ventral por- ternal carotid artery. Each of the major yes- tion of the internal capsule passing through .