Great Cerebral Vein Research Articles

CT angiography for brain death diagnosis.

Lack of cerebral circulation is an important confirmatory test for brain death (BD). Conventional angiography remains the standard imaging method, but CT angiography (CTA) is emerging as an alternative. France accepts BD diagnoses relying on a score based on lack of opacification of 7 intracerebral vessels in CTA images. The purpose of this study was to validate the efficiency of this score and to evaluate the sensitivity of a novel 4-point CTA score in confirming BD. A prospective multicentric study was conducted during 12 months with 105 patients referred for CTA to confirm a clinical diagnosis of BD. Clinical data were recorded. CTA images were interpreted first by local radiologists at the referent center, resulting in a 7-point score based on lack of opacification of the pericallosal and cortical segments of the middle cerebral arteries (MCAs), internal cerebral veins (ICVs), and 1 great cerebral vein per patient and, second, by a consensus panel of 3 expert radiologists, blinded to the initial scores, resulting in novel 4-point scores based on the lack of opacification of the cortical segments of the MCAs and ICVs. Injection of contrast medium did not alter renal function. With the initial 7-point score, sensitivity was 62.8%. With the simplified 4-point score, sensitivity was 85.7% and specificity was 100%. Opacification of ICVs was absent in 98.1% of patients. Lack of opacification in the cortical segments of the MCAs and internal veins in CTA is efficient and reliable for confirming BD.

Junction between the great cerebral vein and the straight sinus: An anatomical, immunohistochemical, and ultrastructural study on 25 human brain cadaveric dissections

The cerebral venous system is poorly understood, and best appreciated under macroscopic anatomical considerations. We present an anatomical and immunohistochemical studies to better define the morphological characteristics of the junction between the great cerebral vein and the straight sinus. Twenty-five cadaveric specimens from the anatomy laboratory of the University Victor Segalen of Bordeaux were studied. The observation of the venous junctions with the straight sinus was performed under an operating microscope. The smooth muscular actin immunohistochemical staining was performed for 18 veno-sinosal junctions. Five venous junctions were observed using an electron microscope. We observed 3 different anatomic aspects: type 1 was a junction with a small elevation in its floor and a posterior thickening (14 cases); type 2 was a junction with an outgrowth on the floor like a cornice (7 cases); and type 3 was a junction presenting a nodule. Microscopic study of type 1 and 2 junctions showed a positive coloration to orceine attesting the presence of elastic fibers. Immunohistochemistry revealed the presence of smooth muscular actin and S 100 protein attesting the presence of smooth muscular fibers and nervous fibers. We observed in the ultrastructural study, a morphological progression of the endothelium. The venous orifice of the great cerebral vein into the straight sinus could be anatomically assimilated as a true "sphincter." Its function in the regulation of the cerebral blood flow needs further exploration.

Splenium Infarct Due to Cerebral Venous Thrombosis

A21-YEAR-OLD WOMAN was delivered of a neonate 10 days earlier with the use of epidural anesthesia without complications. A few hours post partum, she developed postural headache that was subsequently treated with a blood patch; this resulted in modest improvement. She returned a week later with worsening right-sided throbbing headache that was exacerbated by head movement and associated with severe photophobia and nausea. She had no noteworthy medical history and was not taking any medications. Findings from neurological examination were normal without alexia, agraphia, hemineglect, or papilledema. Results of laboratory studies revealed normal electrolyte and glucose values. Magnetic resonance imaging of the head demonstrated a focal lesion of the splenium of the corpus callosum with an increased diffusion-weighted image (Figure, A) and a corresponding decreased signal on apparent diffusion coefficient map (Figure, B) consistent with an ischemic etiology. Magnetic resonance venography revealed partial superior sagittal sinus and complete right transverse sinus thrombosis (Figure, C). Subsequently, the patient was started on anticoagulation with resolution of headache in the next few days. Lesions of the splenium of the corpus callosum are usually seen in association with malnutrition or alcohol abuse, infections, disturbance in electrolytes, neoplasms, and, most commonly, seizures. 1 The exact underlying pathophysiology of splenium lesions is not fully understood. They may represent nonspecific end points of different disease processes that lead to vasogenic edema. Proposed mechanisms after secondary generalized seizures include transient vasogenic edema due to the excessive activity of commissural projections disturbing energy metabolism and ionic transport. 2 Other possibilities include fluid-balance systems, namely, arginine-vasopression, by either anticonvulsant toxicity or rapid withdrawal in individuals with vitamin deficiency especially with low folate levels. 3 The ovoid splenium lesion seen in our patient was likely ischemic in nature as supported by the presence of cerebral venous thrombosis and an increased diffusion-weighted image signal with a corresponding decreased apparent diffusion coefficient signal. The lesion is likely caused by the occlusion of either the dorsal vein of the corpus callosum that drained into the great cerebral vein of Galen or the distal

Reliability of Computed Tomographic Angiography in the Diagnosis of Brain Death

Objective This study examined the validity of cerebral computed tomographic (CT) angiography in the diagnosis of brain death (BD) compared with conventional cerebral angiography. Methods This prospective, monocentric study was performed over a 24-month period and included 43 patients, at least 18 years of age, with clinical criteria of BD. All patients underwent cerebral CT angiography and then cerebral angiography. To confirm BD, the CT scan had to show the absence of perfusion of A2 anterior cerebral artery segments (A2-ACA), M4 middle cerebral artery segments (M4-MCA), P2 posterior cerebral artery segments (P2-PCA), basilar artery, internal cerebral veins, and finally the great cerebral vein. Cerebral angiography showed cerebral blood flow arrest at the level of the foramen magnum for posterior circulation and carotid siphon for anterior circulation. Results For 30 patients, BD was confirmed by both examinations. For 13 patients, cerebral angiography confirmed BD, whereas CT angiography still showed cerebral perfusion; the divergence rate was 30.2%. Conclusions CT angiography seems to be a promising exam to confirm BD. However, the divergence with cerebral angiography is significant mainly concerning A2-ACA, which are proximal. It may be possible to only use the absence of opacification of M4-MCA, P2-PCA, basilar artery, and venous blood return to remain in conformity with the French law. In all cases, the international medical community should obtain a consensus for the interpretation of CT angiography to use it extensively as a complementary exam for BD.

Parinaud′s syndrome in a patient with thalamic infarction due to cerebral venous thrombosis

Dear Editor, The dorsal midbrain syndrome, characterized by upward gaze paralysis, convergence-retraction nystagmus and light-near dissociation owes its eponym to the French ophthalmologist, Henri Parinaud. Pineal tumors, intrinsic midbrain lesions and hydrocephalus or aqueductal enlargement compressing the posterior commissure are frequently implicated causes. We report a patient with thrombosis of the deep cerebral venous system (CVT) who presented with Parinaud's syndrome. Isolated eye signs are seldom discussed in CVT and Parinaud's syndrome has not been described. A diagnosis of "benign" intracranial hypertension (BIH) was proffered in a 30-year-old man with blurred vision, papilledema and normal brain magnetic resonance imaging (MRI). Lumbar puncture tapped clear cerebrospinal fluid (CSF) under opening pressure of 350 mmH2O; CSF analysis was normal. Obtaining no relief, he was referred for re-evaluation. Visual acuity was 20/20 and perimetry mapped full visual fields without blind spot enlargement. Bilateral papilledema and convergence-retraction nystagmus was noted; equal pupils constricted well during accommodation but sluggishly to light. Upgaze was absent, eyelids retracted on looking up (Collier's sign), downward saccades and pursuit were normal. Neurological examination was otherwise unremarkable. The lesion was clinically localized to the dorsal mesencephalon and MRI was repeated [Fig. 1]. Cerebral venogram revealed unilateral posterior thalamic infarction with thrombosis involving multiple cerebral venous sinuses [Fig. 2]. The third ventricle and aqueduct were not enlarged.Figure 1: T2 weighted axial MR image depicting altered hyperintense signal involving the right thalamus. The signal was hypointense on T1 and suggests infarction. To the right, a T2 weighted sagittal MR image shows a hyperintense signal replacing the normal flow void in the great cerebral vein of Galen (arrowhead), straight sinus, torcula (short arrow) and superior sagittal sinus (long arrow)Figure 2: MR venogram sagittal view shows absent flow in superior sagittal, straight, lateral and sigmoid sinuses and poor filling of the deep venous systemPremotor structures mediating vertical gaze lie in the periaqueductal paramedian nuclei of the midbrain reticular formation. The nuclei responsible are the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), posterior commissure and its nucleus, nucleus of Darkschewitsch and interstitial nucleus of Cajal (INC). Medium-lead burst neurons in riMLF generate vertical saccades1 while INC controls vertical slow movements and gaze integration. The posterior commissure is particularly important in mediating upward gaze. Although typically caused by bilateral involvement, upgaze paresis may result from unilateral midbrain lesions that disrupt posterior commissural connections.2 Intracranial hypertension could arguably cause upgaze palsy and papilledema even before ventricular dilatation is apparent.3 However, gaze palsy developed despite cerebral decongestant measures and persisted after CSF pressure had normalized. Our subject had venous thalamic infarction without obvious midbrain involvement but vertical gaze disturbances could result from concomitant undetected microinfarcts in dorsal mesencephalic structures that share a common vascular supply.45 Arterial thalamic infarcts may be associated with upgaze paresis, probably because of interruption of supranuclear pathways mediating vertical gaze.5 Patients with venous thalamic infarction are often obtunded and isolated eye signs are rarely reported. Thrombosis involving dural venous sinuses and deep cerebral veins may masquerade as BIH. MRI with venography is the technique of choice to diagnose CVT but may miss partial or early disease as described here. Thrombosis appears as absent flow void on spin-echo images and lack of signal in angiographic images. Decreased signal on T2 weighted imaging in early CVT may be confused with normal flow void and imaging at intermediate field strengths becomes necessary. We emphasize caution in diagnosing BIH when ocular motility disturbances are present and advocate repeated scanning directed by a high index of clinical suspicion.

Microsurgical anatomy of the venous drainage of the mesencephalodiencephalic junction.

The veins draining the posterior wall of the third ventricle and its adjacent structures and the posterior part of the midbrain have been the most neglected of the intracranial vascular structures in both the anatomic and neurosurgical literature. During our dissections of the pineal region and the quadrigeminal cistern, we did not always encounter topographic anatomy as described in previous articles. The purpose of this study is to describe the topographic anatomy and normal variations of the specific veins that drain the collicular plate and the pineal body and their adjacent structures with a view to better defining neurosurgical approaches to the pineal region. The deep cerebral veins draining the pineal body, the collicular plate, and their surrounding neural structures were examined on both sides of 25 adult cadaveric brains. In all specimens, the carotid and vertebral arteries and the jugular veins were perfused with red or blue silicone, respectively, to facilitate dissection under x3 to x40 magnification. The venous plexus on the dorsal aspect of the collicular plate drains via collicular veins according to three different patterns. These types of drainage are closely related to the existence or absence of the basal vein on one or both sides. The veins draining the superior and inferior aspects of the pineal body form a superior and an inferior pineal vein that usually drain into the internal or great cerebral vein.

Galen and his anatomic eponym: vein of Galen.

Galen or Galenus was born at Pergamum (now Bergama in Turkey) in 129 A.D., and died in the year 200 A.D. He was a 2nd century Greek philosopher-physician who switched to the medical profession after his father dreamt of this calling for his son. Galen's training and experiences brought him to Alexandria and Rome and he rose quickly to fame with public demonstrations of anatomical and surgical skills. He became physician to emperor Marcus Aurelius and the emperor's ambitious son, Commodus. He wrote prodigiously and was able to preserve his medical research in 22 volumes of printed text, representing half of all Greek medical literature that is available to us today. The structures, the great cerebral vein and the communicating branch of the internal laryngeal nerve, bear his eponym.

Autonomic nerves terminating on smooth muscle cells of vessels in the pineal organ of various mammals.

The significance of autonomic nerves reaching the pincal organ was already investigated in connection to the innervation of pinealocytes and mediating light information from the retina for periodic melatonin secretion. In earlier works we found that some autonomic nerve fibers are not secretomotor but terminate on arteriolar smooth muscle cells in the pineal organ of the mink (Mustela vison). Studying in serial sections the pineal organ of the mink and 15 other mammalian species in the present work, we investigated whether similar axons of vasomotor-type are generally present in the wall of pineal vessels, further, whether they reach the organ via the conarian nerves or via periarterial plexuses. In all species investigated, axons of perivasal nerve bundles were found to form terminal enlargements on the smooth muscle layer of pineal arterioles. The neuromuscular endings contain several synaptic and some granular vesicles. Axon terminals are also present around pineal veins. In serial sections, we found that the so-called conarian autonomic nerves reach the pineal organ alongside pineal veins draining into the great internal cerebral vein. Similar nerves present near arteries of the arachnoid enter the pineal meningeal capsule and septa by arterioles, both perivenous and periarterial nerves form terminals of vasomotor-type. The arteriomotor and venomotor regulation of the tone of the vessels of the pineal organ may serve the vascular support for circadian and circannual periodic changes in metabolic activity of the pineal tissue.

Microsurgical anatomy of the great cerebral vein of Galen and its tributaries.

The deep cerebral veins may pose a major obstacle in operative approaches to deep-seated lesions, especially in the pineal region where multiple veins converge on the great cerebral vein of Galen. Because undesirable sequelae may occur from such surgery, the number of veins and branches to be sacrificed during these approaches should kept to a minimum. The purpose of this study was to examine venous drainage into the vein of Galen with a view to surgical approaches. If a vein hampering surgical access must be sacrificed, it can therefore be selected according to the smallest draining territory. The deep cerebral veins and their surrounding neural structures were examined in 50 cerebral hemispheres from 25 adult cadavers in which the arteries and veins had been perfused with red and blue silicone, respectively. Special consideration was given to the size and location of drainage of the vein of Galen and its tributaries. When a surgeon approaches the pineal region, several veins may hamper the access route. From posterior to anterior, these include the following: the superior vermian and the precentral or superior cerebellar veins, which drain into the posteroinferior aspect of the vein of Galen; and the tectal and pineal veins, which drain into its anterosuperior aspect. The internal occipital vein is the main vessel draining into the lateral aspect of the vein of Galen. It may be joined by the posterior pericallosal vein, and in that case has an extensive territory. To avoid intraoperative venous infarction, it is important to use angiography to determine the venous organization before surgery and to estimate the permeability and size of the branches of the deep venous system.

Transcranial color-coded duplex sonography of intracranial veins and sinuses in adults. Reference data from 130 volunteers.

Transcranial color-coded duplex sonography (TCCS) of intracranial veins and sinuses in adults is a new, emerging application of ultrasonographic imaging. This study reports a standardized examination protocol for venous TCCS and provides reference data for clinical application. In 130 healthy volunteers (mean age, 45.9+/-16.9 years; range, 14 to 77 years) the intracranial venous system was examined using frequency-based transtemporal TCCS. Identification rate, blood flow velocity, resistance index, and systolic/diastolic ratio were recorded for each examined venous vessel. Intracranial veins and sinuses show a low pulsatile forward flow with maximal systolic blood flow velocity up to 20 cm/s. Significant side differences of blood flow velocity in the paired venous structures could not be detected. Venous flow velocities decreased with age, whereas resistance indices and systolic/diastolic ratios increased. Women showed higher flow velocities than men. Mean identification rates for all age groups ranged from 70% to 90% for the deep middle cerebral vein, the basal cerebral vein, and the great cerebral vein of Galen. The straight sinus, the transverse sinus, and the rostral part of the superior sagittal sinus could be detected in 55% to 70% of cases. Detection rates were dependent on age and decreased as age increased. Venous TCCS can reliably image a significant part of the cerebral venous system. This method can provide information on venous hemodynamics in normal subjects and pathological cases.

Melatonin rhythms and pineal structure in a tropical bat, Anoura geoffroyi, that does not use photoperiod to regulate seasonal reproduction.

It has been hypothesized that pineal structure and function might differ between temperate zone and tropical species of mammals because of lower amplitudes of seasonal change in photoperiod and, in some areas, less seasonal climatic variation. Anoura geoffroyi produce a single offspring in November or December of each year on the Caribbean island of Trinidad, at 10 degrees N latitude in the deep tropics. Previous work has shown that this population lacks reproductive responses to photoperiod, and must be enforcing seasonal breeding using a non-photoperiodic cue. Anoura geoffroyi have a minute, thin, and rod-like pineal gland. Throughout much of its length, the pineal courses irregularly within the ventrolateral wall of the great cerebral vein. This intimate relationship may have functional implications. Despite having a very small pineal gland, this species produced a nocturnal rise in serum melatonin. Serum melatonin levels in most individuals were below or near undetectable levels during the light period and rose to a peak averaging 100 pg/ml in the last third of the dark period. Our results indicate that, although the pineal gland of A. geoffroyi is extremely small, serum melatonin levels are comparable to those of other mammals.

EFFECT OF HIGH FREQUENCY OSCILLATORY VENTILATION (HFOV) ON ARTERIAL AND VENOUS CEREBRAL BLOOD FLOW VELOCITIES IN NEONATES

The different ventilatory pattern of HFOV and conventional ventilation (IPPV) may differently affect cerebral hemodynamics in neonates. Using color Doppler sonography we measured left ventricular output (LVO), the mean blood flow velocity (BFV,cm/s) in the median cerebral artery (MCA) and in the great cerebral vein (GCV) in 10 critically ill neonates [GA 27 (25-37) wks, weight 980 530-2500) g, age a (1-36) d] during IPPV and 3 (2-18) h after initiating HFOV (Infant Star). Indication for HFOV: Air leak (n = 8), failure of IPPV (n = 2).RESULTS: Data are medain and range. MAP = mean airway pressure (mmHg) OI = oxygenation index (OI = FiO2 × MAP × 100 / paO2). * = p < 0.05.During IPPV, LVO was low and MCA-BFV normal compared to data of 54 stable ventilated (IPPV) preterm neonates [GA 28(23-35)wks; LVO: 248(212-316), mean MCA-BFV: 10(5-28)]. During HFOV the blood flow in the MCA was oscillating synchroneously with the oscillations of the ventilator and arterial cerebral BFV was increased in all infants (increased pCO2) compared to IPPV. Venous cerebral BFV however was decreased (up to 45%), possibly due to the increased PEEP during HFOV. CONCLUSION: HFOV affects cerebral hemodynamics and may cause cerebral congestion in neonates at risk of intracranial hemorrhage.

Vascular ontogeny of the septal region in rats

The development of the arterial and venous systems of the septum was studied in rat brains injected daily with India ink, from the 11th embryonic (E) until the first postnatal day. Arterial blood is supplied to the septum by the unpaired hemispheric artery, the stem and septal branches of which are to be recognized on the 14th and 15th embryonic days respectively. At earlier stages, e.g. on E12, a capillary network, the hemispheric plexus, can be seen between the two hemispheres contributing to the blood supply of the septum during the early phase (E14 to E18) of development. From E18 onwards, the arterial supply of the septum is derived only from direct branches of the hemispheric artery; one group of them being dorsal (infracallosal) and the other ventral (subcallosal). The venous drainage of the septum is bidirectional: 1) Veins of the ventral group leading to the interperioptic sinus are seen on E14. At first they collect blood only from a small rostral portion of the septum, but later their territory expands to include the anteroventral two-thirds of the septum. 2) The dorsal septal veins drain into the great cerebral vein (of Galen), or into the superior sagittal sinus directly. Initially, twigs run directly into the great cerebral vein. These later become the tributaries of the internal cerebral vein, which appears on E17 or E18. Until E18 this dorsally-directed drainage predominates, whereas at birth it becomes restricted to one third of the septum as a result of a gradual regression. The development of both arterial and venous circulations of the septum is complete at birth.

16 COLOR DOPPLER ECHOENCEPHALOGRAPHY

From January to December 1990, 100 color doppler echoencephalograms were obtained in 40 infants without cardiopulmonary affections and with a mean birth weight of 2940g (range 1760-3420 g), a mean gestational age of 37.2 weeks (range 34-40w). The examinations were performed using a real-time 2-D Doppler Scanner and a 3,75 MHz sector transducer. Serial scans were obtained in sagittal, coronal and axial plans. Detection rate of intracranial vessels was: internal carotid, anterior cerebral, pericallosal, basilar, vertebral artery (100%); callosomarginal artery (90%); frontopolar artery (82%); medial and lateral striate artery (17%); internal, great cerebral vein(GCV) and straight sinus (SS) (100%); superior sagittal sinus (69%); occipital sinus (39%). Flow mean velocity of GCV and SS was 6-10 and 15-24 cm/sec respectively. Usually vein curve has a continuous profile (therefore we can calculate only mean velocity) while sometimes, expecially in the biggest vein (SS), we observe particular aspects of vein flow similar to artery's one with a sort of systolic and diastolic phase. Probably this waving venous curve is within respiratory control becouse the “squeeze” of superior cava vein may induce an increase of vein flow velocity during inspiration.

Scanning electron microscopic study on pineal vascularization of the common tree shrew (Tupaia glis)

The detailed blood supply including microvascularization of pineal gland in the common tree shrew (Tupaia glis) was investigated using a vascular corrosion cast technique in conjunction with scanning electron microscopy. Adult common tree shrews of both sexes, divided into 3 groups, were injected with red latex, blue vinyl resin, and Batson's No. 17 plastic mixture for the studies of arterial supply, venous drainage, and microvasculature of the pineal gland, respectively. It was found that the pineal gland is a highly vascularized organ. It receives two to four branches from the medial posterior choroidal arteries. Two types of capillary arrangements, fan-like and network, are observed. As in the human, usually one and occasionally two pineal veins, draining directly into the great cerebral vein of Galen, are observed. A pineal portal system is not demonstrated.

Deep venous drainage in great cerebral vein (vein of Galen) absence and malformations

We report two types of venous patterns associated with great cerebral vein (vein of Galen) absence or unavailability. Developmental venous anomalies or vein of Galen arteriovenous malformations (VGAM) serve as an illustrative material. A diencephalic pattern that collects the thalamo-striate veins into the tentorial sinus is recognized in most VGAM. A telencephalic arrangement connecting the striate veins with the rostral afferents to the basal vein is less frequent. Both patterns reproduce embryonic stages preceding the development of the great cerebral vein, thus confirming Raybaud's hypothesis that in VGAM the pouch is not the vein of Galen but the medial vein of the prosencephalon. The prognostic value of each pattern can then be appreciated and the therapeutic strategies rationalized; some unexplained complications of the venous approach for non selected VGAM can thus be avoided.

Anomalies of Central Nervous System in Infaney; Evaluation by Color Doppler Echoencephalography

We performed 78 color Doppler examinations to demonstrate intracranial vasculature in 61 infants; 30 cases with normal and 19 with abnormal central nervous system anatomy. Developmental abnormalities such as hydrocephalus, hydranencephaly, holoprosencephaly, absent corpus callosum, and Dandy-Walker syndrome were demonstrated. Serial scans were obtained in sagittal, coronal, and axial plains. Most of the major intracranial arteries and veins could be clearly demonstrated in real-time. In patients with hydrocephalus, color Doppler imaging demonstrated a widely streched and elevated sweep of the anterior cerebral arteries, straightening of the middle cerebral arteries by the enlarged ventricles. The internal cerebral veins, great cerebral vein, straight sinus were straighted and displaced posteriorly and inferiorly. In infants with absent corpus callosum, anterior cerebral arteries and their branches appeared to be wavy. However, in patients with developmental abnormalities, visualizations of the vasculature were relatively poor. In conclusion, the color Doppler examination is a useful and practical method of imaging of cerebral vessels in infants, because of its non-invasiveness and portability.

Intracranial vessels with color doppler echoencephalography in infants

A technique for imaging of the intracranial vessels in infants was described, which used high resolution, commercially available, color Doppler ultrasonography (real-time two-dimensional Doppler). On 12 normal infants, serial scans were obtained in sagittal, coronal, and axial plains. A large number of intracranial arteries and veins could be clearly demonstrated in real-time, including anterior cerebral artery, pericallosal artery, middle cerebral artery, posterior cerebral artery, basilar artery, communicating artery, internal cerebral vein, inferior and superior sagittal sinuses, great cerebral vein, straight sinus, occipital sinus and transverse sinus. In conclusion, color Doppler examination is useful in the detection of vessels in infants and in the measurement of intracranial blood flow velocity.

The blood vascular architecture of the rat pineal gland: a scanning electron microscopic study of corrosion casts.

The blood vascular bed of the rat pineal gland was reproduced through a low viscosity methacrylate casting medium and observed with a scanning electron microscope. The pineal gland was located in front of the confluens sinuum which was formed by the confluence of the left and right transverse sinuses and the superior sagittal and great cerebral veins. The pineal gland was found to contain a rich vascular network of freely anastomosing capillaries. This network received a few afferent arteries from the posterior cerebral arteries while emitting ten to fifteen efferent veins. Most of these efferent veins drained into the upper segment of the great cerebral vein; the remaining one or two efferent veins continued directly into the confluens sinuum. A marked constriction, probably representing a venous valve or valve-like projection, was observed in the opening area of the great cerebral vein. Circular constrictions, probably representing sphincters, were imprinted in the efferent vessels. No direct vascular connection was noted between the pineal gland and the nervous tissues or between the pineal gland and the choroid plexuses of the third and lateral ventricles.

Persistent embryonic veins in the arteriovenous malformation of the diencephalon.

The diencephalic arteriovenous malformation is produced by the posterior cerebral, posterior choroidal, and anterior choroidal arteries. The abnormal arterialised vessels seen in these malformation represent dorsal and ventral diencephalic veins. The drainage of the shunted blood is primarily into the transverse sinus. This is later diverted medially into the great cerebral vein, with the formation of the basal vein. The medial drainage, in keeping with the normal developmental pattern, is seen frequently. The presence and locations of angiomas are very variable and do not follow any predictable pattern.