Arterial vascularization of the human thalamus: extra-parenchymal arterial groups.

The problem of the arterial vascularization of the human thalamus has been debated at length. Anatomical references concerning the thalamic arterial groups are contradictory and complex, preventing any solid application in practice. It is, therefore, difficult to produce reliable anatomical radio-clinical correlation. In this work, 12 adult human cerebellums (24 hemispheres) were dissected after intra-vascular injection. With care for clarification and standardization, the extra-parenchymal thalamic arteries were classified in six groups: pre-mamillary artery, perforating thalamic arteries, thalamo-geniculate arteries, perforating branches of the postero-medial, postero-lateral and anterior choroidal arteries. Variations in the pre-mamillary artery were rare. The origin of the perforating thalamic artery was unilateral in two of three cases. The origin of the thalamo-geniculate arteries arose between the posterior cerebral artery (53%) and the posterior choroidal arteries (43%). The postero-median choroidal artery was most often single and usually gave the perforating branches for the medial aspect of the thalamus. The postero-lateral choroidal artery was frequently multiple and essentially gave the perforating branches for the superior aspect of the thalamus. The pulvinarian branches most often rose from the postero-lateral choroidal arteries (two thirds of cases) and more rarely from the postero-median choroidal arteries (one third of cases). The anterior choroidal artery is a source of thalamic vascularization by its cisternal branches running towards the lateral thalamus. It can also participate in the vascularization of the pulvinar by the plexiform branches crossing the temporal horn of the lateral ventricle. This study has allowed definition of the intra-parenchymatous arterial map of the thalamus. This mapping is essential for producing anatomical radio-clinical correlations which are pertinent for therapeutic decisions.

High resolution MRI of the deep brain vascular anatomy at 8 Tesla: susceptibility-based enhancement of the venous structures.

PURPOSE: The purpose of this work was to describe the deep vascular anatomy of the human brain using high resolution MR gradient echo imaging at 8 T. METHOD: Gradient echo images were acquired from the human head using a transverse electromagnetic resonator operating in quadrature and tuned to 340 MHz. Typical acquisition parameters were as follows: matrix = 1,024 x 1,024, flip angle = 45 degrees, TR = 750 ms, TE = 17 ms, FOV = 20 cm, slice thickness = 2 mm. This resulted in an in-plane resolution of approximately 200 microm. Images were analyzed, and vascular structures were identified on the basis of location and course. RESULTS: High resolution ultra high field magnetic resonance imaging (UHFMRI) enabled the visualization of many small vessels deep within the brain. These vessels were typically detected as signal voids, and the majority represented veins. The prevalence of the venous vasculature was attributed largely to the magnetic susceptibility of deoxyhemoglobin. It was possible to identify venous structures expected to measure below 100 microm in size. Perforating venous drainage within the deep gray structures was identified along with their parent vessels. The course of arterial perforators was more difficult to follow and not as readily identified as their venous counterparts. CONCLUSION: The application of high resolution gradient echo methods in UHFMRI provides a unique detailed view of particularly the deep venous vasculature of the human brain.

Consequences of the anatomy of deep venous outflow from the brain.

The deep venous system is best defined as the entire territory served by the great vein of Galen and the basal veins. This comprises not only the choroid plexuses and the deep grey matter of the thalamus and striatum, but also the periventricular white matter and corpus callosum, hippocampus and the cortical areas of the limbic lobe including the cingulate and parahippocampal gyri, the visual cortex, the diencephalon and rostral brain stem, and part of the cerebellum. The superficial venous system comprises the remaining neocortex (with the cortex of the entire convexity) together with a layer of subcortical white matter, separated from the periventricular white matter by a venous watershed. Outflow towards the great vein of Galen and straight sinus can be substituted by collateral channels towards the basal vein. The basal vein in turn is connected not only to the great vein of Galen, but also to the superior petrosal sinus (via the lateral mesencephalic vein), and in the adult configuration to the cavernous sinus and pterygoid plexus (via the deep and superficial sylvian veins). Evidence from pathological anatomy indicates that the venous watershed exists not only in the white matter of the hemispheres, but between the entire territories of the deep and superficial venous systems. Because of their anastomotic interconnections, only simultaneous obstruction of veins of Galen and basal veins wil effectively obstruct deep venous outflow. This can occur in the tentorial incisura, from swelling or displacement of the midbrain due to brain oedema, haematoma or tumour. Complete obstruction of great vein of Galen and basal veins leads to rapid death. In patients who survive incomplete obstruction, various combinations of damage to parts of the deep venous territory exist. This is possible because very many tributaries of the deep system unite below and sometimes above the tentorial incisura. The hallmarks these varying deep venous obstructions have in common are sparing of the subcortical white matter of the convexity, and cortical involvement limited to the limbic lobe and visual cortex. Obstruction of cerebral venous outflow explains many pathological phenomena. Treatment must aim at relieving this obstacle to blood flow.

Angiotensin II regulates choroid plexus blood flow by interacting with the sympathetic nervous system and nitric oxide.

Blood flow to the rat choroid plexus has minimal variability when plasma angiotensin II (AII) concentration is changed within a broad range of levels. We tested the hypothesis that a complex interplay of the vasoconstrictor and vasodilator AII actions in choroidal tissue results in small net changes in choroidal blood flow. Blood flow was measured with 123I- or 125I-N-isopropyl-p-iodoamphetamine. AII was infused intravenously (i.v.) at 30 (moderate dose) and 300 ng kg-1 min-1 (high dose), which respectively decreased (15%) and did not change choroidal blood flow. To determine whether AII regulates choroidal blood flow by interacting with the sympathetic nervous system, rats were given phentolamine (1 mg kg-1, i.v.). This alpha-adrenoceptor antagonist by itself did not alter blood flow; however, it attenuated the blood flow-lowering effect of moderate AII dose. Phentolamine also unmasked the vasodilator AII actions at high peptide concentration. beta-Adrenoceptor blockade, with propranolol (1 mg kg-1, i.v.), reduced blood flow (18-20%) and increased vascular resistance (23-26%). During beta-adrenoceptor blockade, a further decrease in blood flow (15-21%) and increase in vascular resistance (23%) was noted when high AII dose was administered. The direct vasoconstrictor effect of AII at moderate dose on choroidal vasculature was examined in rats subjected to chronic bilateral superior cervical ganglionectomy. In these animals, AII decreased blood flow (24%) and increased vascular resistance (24%). To find out whether the hemodynamic AII actions in choroidal tissue are mediated by nitric oxide (NO), Nomega-nitro-l-arginine methyl ester (l-NAME) was used. l-NAME (0.1 mg kg-1, i.v.) by itself did not alter blood flow; however, in l-NAME-treated rats high AII dose lowered blood flow (25-32%) and increased vascular resistance (30-43%). We conclude that the vasoconstrictor AII actions involve a direct peptide effect on the choroidal vascular bed, and the AII-mediated potentiation of sympathetic activity, which results in the activation of alpha-adrenoceptors. The AII-mediated stimulation of sympathetic nerves also results in the beta-adrenoceptor-dependent relaxation of choroidal blood vessels. In addition, choroidal vasodilatory actions of AII are NO-mediated.

Extent and location of cerebral infarcts on multiplanar MR images: correlation with distribution of perforating arteries on cerebral angiograms and on cadaveric microangiograms.

The basal gray matter in the cerebrum is supplied by different anatomical groups of perforating arteries, including striate, thalamic, and choroidal arteries. In this pictorial essay we illustrate multiplanar MR imaging of infarctions in those regions and correlate their appearances with cerebral angiographic findings of the same patients when available. We also correlate the extent and location of infarctions on multiplanar MR images with the anatomical distributions of perforating arteries seen on microangiograms of unrelated cadavers. Information conveyed from this correlation will increase understanding of patterns of basal cerebral infarction shown on cross-sectional imaging.

A developmental analysis of differences in the uptake of [123I]isopropyliodoamphetamine versus 99mTc-pertechnetate by the choroid plexus and brain.

The uptake of intravascular [123I]isopropyliodoamphetamine (IMP) and 99mTc-pertechnetate into choroid plexus (CP) and brain (frontal cortex) was studied by an indicator fractionation method applied to immature, ketamine-anesthetized Sprague-Dawley rats (1.5, 2, and 3 wk). Assessment of the rate and extent of uptake of these indicators provides functional information (eg blood flow; transport) about various regions of the developing CNS. IMP uptake by lateral ventricle CP was 1.15 ml/g/min in 1.5-wk-old infant rats and gradually increased to 3.9 mg/g/min by adulthood (7-8 wk) (P < 0.05); over the same postnatal period, 99mTc uptake went from 2.82 to 3.18 ml/g/min. IMP uptake by cortex was 0.39 and 0.99 ml/g/min in infants and adults, respectively (P < 0.05); however, 99mTc uptake by cortex was only 0.07 +/- 0.01 ml/g/min at all ages, reflecting early development of blood-brain barrier (BBB) to pertechnetate. Overall, our findings indicated a progressive increase with age in the rate of uptake of IMP by CP and brain; and that 99mTc penetration into CP was relatively constant and substantially greater than into cortex at all developmental stages. Thus the nature of uptake of IMP, relative to 99mTc, was markedly different at the blood-cerebrospinal fluid barrier (i.e., CP) vs. the blood-brain barrier.

Acetylcholine levels and choline acetyltransferase activity in rat cerebrovascular bed after uni- or bilateral sphenopalatine ganglionectomy.

Endogenous acetylcholine (ACh) levels and choline acetyltransferase (ChAT) activity were measured in several vascular segments (major cerebral arteries, cortical pial vessels, and peripheral arteries) and nervous tissues [including the sphenopalatine ganglion (SPG)] in the rat. The effects of uni- or bilateral surgical ablation of the SPG, a putative origin of the cholinergic cerebrovascular innervation, were investigated on these two specific cholinergic markers at various postoperative times. ChAT activity and ACh levels were enriched in the cerebral as compared to the peripheral arteries. Among the cerebrovascular tissues tested, ACh levels were particularly high in the circle of Willis and the vertebrobasilar segments and, to a lesser extent, in the middle cerebral artery. Lower levels were found in the small pial vessels and choroid plexus. Overall, ChAT activity measured in different arterial beds paralleled the distribution of ACh. Following uni- or bilateral removal of the SPG, slight reductions (18-36%, statistically not significant) were observed in ChAT activity in rostral cerebral arteries and pial vessels overlying the frontal cortex. Similarly, bilateral ganglionectomy resulted in minor decreases (11-22%, not significant) in the cerebrovascular contents of ACh in these same vascular segments. These results clearly show that the SPG does not or only partly contributes to the cholinergic fibers that supply the cerebrovascular bed.

Microsurgical anatomy of the choroidal fissure.

The microsurgical anatomy of the choroidal fissure was examined in 25 cadaveric heads. The choroidal fissure, the site of attachment of the choroid plexus in the lateral ventricle, is located between the fornix and thalamus in the medial part of the lateral ventricle. The choroidal fissure is divided into three parts: (a) a body portion situated in the body of the lateral ventricle between the body of the fornix and the thalamus, (b) an atrial part located in the atrium of the lateral ventricle between the crus of the fornix and the pulvinar, and (c) a temporal part situated in the temporal horn between the fimbria of the fornix and the lower surface of the thalamus. The three parts of the fissure are the thinnest sites in the wall of the lateral ventricle bordering the basal cisterns and the roof of the third ventricle. Opening through the body portion of the choroidal fissure from the lateral ventricle exposes the velum interpositum and third ventricle. Opening through the temporal portion of the choroidal fissure from the temporal horn exposes the structures in the ambient and crural cisterns. Opening through the atrial portion of the fissure from the atrium exposes the quadrigeminal cistern, the pineal region, and the posterior portion of the ambient cistern. The neural, arterial, and venous relationships of each part of the fissure are reviewed. The operative approaches directed through each part of the fissure are also reviewed.

Anastomoses in the territory of the posterior cerebral arteries.

Anastomoses in the region of the posterior cerebral arteries were found in all of 40 brains examined. Anastomoses were channel-like, plexiform or combined. The former measured from 0.07 mm to 1.1 mm in diameter. They were most often found among the interpeduncular perforating vessels (71.2%), and between the branches of the posterior and anterior cerebral arteries (75.7%). The functional significance of the anastomoses is discussed.

[Amnesia in thalamic infarction]. / L'amnésie des infarctus thalamiques.

Restricted thalamic infarctions are in man a useful model for investigating the consequences of limited diencephalic lesions on memory and verbal or visual learning. Two new cases of amnesia with thalamo-sub-thalamic infarctions are presented, with a general review of the problem. The gathering of the different cases according to the vascular thalamic territories and, as a consequence, to nuclear or associative structures concerned, allows a better approach of the relations between amnesia and infarctions. Uni or bilateral anterior lesions are the cause of more important and pure memory deficits, posterior infarctions are more often associated to language involvement or spatial cognitive problems which interfere with memorizing.

[Ocular and head movements in infarctions of the thalamic region]. / La motricité oculaire et céphalique dans les infarctus de la région thalamique.

Oculomotor disorders in 22 infarctions in the thalamic region are recorded. Clinical examination and electro-oculography (17 cases) showed that paramedian thalamo-subthalamic lesions were responsible for clear deficits: upgaze paralysis and in some cases downgaze paralysis, partial paresis of the oculomotor nerve, deficits of lateral eye movements, myosis, paralysis of head flexion combined with downgaze paralysis. Postero-median choroid artery infarction was associated with upgaze paresis, slight deficit of lateral eye movements and myosis. Postero-lateral choroid artery infarction resulted in a partial visual field defect and in some cases, a contralateral hypometria; myosis was slight and inconstant. Infarctions of the internal capsule (anterior choroid artery, deep branches of the middle cerebral artery) were associated with a deficit of contralateral saccades. Ocular pursuit, when possible, was often saccadic, whatever the site of the infarction. This prevailed with gaze towards the lesion side.

Microsurgery of the third ventricle: Part I. Microsurgical anatomy.

The 3rd ventricle is one of the most surgically inaccessible areas in the brain. It is impossible to reach its cavity without incising some neural structures. Twenty-five cadaveric brains were examined in detail to evaluate the surgically important relationships of the walls of the 3rd ventricle. The routes through which the 3rd ventricle can be reached are (a) from above, through the foramen of Monro and the roof after entering the lateral ventricle through the corpus callosum or the cerebral cortex; (b) from anterior, through the lamina terminalis; (c) from below, through the floor if it has been stretched by tumor; and (d) from posterior, through the pineal region or from the posterior part of the lateral ventricle through the crus of the fornix. The posterior part of the circle of Willis and the basilar artery are intimately related to the floor, the anterior part of the circle of Willis and the anterior cerebral and anterior communicating arteries are related to the anterior wall, and the posterior cerebral artery supplies the posterior wall. The deep cerebral venous system is intimately related to the 3rd ventricle; the internal cerebral vein is related to the roof, and the basal vein is related to the floor. The junction of these veins with the great veins forms a formidable obstacle to the operative approach to the pineal gland and the posterior part of the 3rd ventricle.

Microsurgical anatomy of the pineal region.

Thirty cadaver brains were examined under X 6 to 16 magnification in order to define the microsurgical anatomy of the pineal region, particularly the relationship of the pineal body, posterior cerebral artery, superior cerebellar artery, vein of Galen, basal vein of Rosenthal, internal cerebral vein, straight sinus, bridging vein, the size of the tentorial notch, and the third and the fourth cranial nerves. The infratentorial and supratentorial approaches to the pineal region are compared from the viewpoint of microsurgical anatomy.

[Arteries of the thalamus in man. Choroidal arteries. I. Macroscopic study of individual variations. II. Systematization]. / Les artères du thalamus humain. Les artères choroïdiennes. I--Etude macroscopique des variations individuelles. II--Systématisation.

One may describe 4 types of individual dispositions for the postero-median choroideal and thalamic system: Type A with a single artery of anterior origin, type P with two consecutive arteries (a mesencephalothalamic artery and a posteromedian artery of posterior origin), type D with two parallel arteries and type O. One may also describe 4 types of individual dispositions for the postero-lateral choroideal and thalamic system. Type C is constituted by a single postero-lateral chorideal artery giving off thalamic branches. Type D comprises two arteries, a postero-lateral choroideal and a postero-lateral thalamic artery. According to the relative importance of the two arteries one may describe subtypes Dc, De and Dt. Type T is constituted by a single postero-lateral thalamic artery giving off choroideal branches. In type H hippocampothalamic arteries intervene. We also studied the variations of the ending point of the anterior choiroideal artery.

[Arteries of the thalamus in man. Choroidal arteries. III. Absence of the constituted thalamic territory of the anterior choroidal artery. IV. Arteries and thalamic territories of the choroidal and postero-median thalamic arterial system. V. Arteries and thalamic territories of the choroidal and postero-lateral thalamic arterial system]. / Les artères du thalamus humain. Les artères choroïdiennes. III.--Absence de territoire thalamique constitué de l'artère choroïdienne antérieure. IV.--Artères et territoires thalamiques du système artériel choroïdien et thalamique postéromédian. V.--Artères et territoires thalamiques du système artériel choroïdien et thalamique postérolatéral.

The anterior chor oideal artery cannot be considered as an arterial source for thalamic vascularization. Its territory is primarily pallidocapsular and reaches the thalamus only irregularly and superfically. 2. The posteromedian choroideal and thalamic system, in its infrathalamic portion, gives off lateral mesencephalosubthalamic, inferocentral (for the tips of the arcuate nucleus and the inferolateral part of the centre median nucleus), brachiopulvinarian and posterocentral arteries. In its suprathalamic portion it gives off medial pulvinarian and superomedian thalamic arteries. These arteries irriguate the major part of nucleus medialis and the nucleus anterior. 3. The posterolateral choroideal and thalamic system gives off lateral genicular arteries (for the lateral geniculate body), inferolateral pulvinarian and superolateral thalamic arteries. These arteries irriguate the dorsal part of the interal region of the thalamus.