Textbook of Catheter-Based Cardiovascular Interventions pp 1249-1268 | Cite as
Venous Structures of the Brain
The variability of encephalic venous drainage frequently causes some insecurity when interpreting the venous phase of an angiographic study, computed tomography, or magnetic resonance venograms. There is, however, a pattern that, once understood, gives a global overview for each individual and helps to differentiate between abnormality and variability. On the other hand, the location of both deep and superficial venous structures also determines anatomical limits that offer specific landmarks for neurosurgical and neuroradiological procedures.
This chapter provides a practical guide for reviewing and evaluating the basic features of the venous structures of the brain.
KeywordsCerebral Cerebellar Veins Anatomy Embryology Dural sinus Pial vein Pioarachnoidal vein Primary head sinus Emissary vein Tentorial sinus Falcine sinus
72.1 Introduction: General Venous Anatomy
The aim of this chapter is to provide a practical approach to evaluation of the venous anatomical configuration of a specific patient. This book is centered both in «know that» (theory) and «know how» (practice); thus, venous descriptions are followed by practical cases in which the venous anatomy can be evaluated by the reader. The way to perform the practical aspect is to cover up the picture on the left-hand side and then analyze the right-hand picture to see what you know. A more complete text referring to basic embryological aspects is found in the chapter «Encephalic venous drainage: understanding anatomy and pathology from a developmental approach» in the book Panvascular Medicine .
Dural sinuses and pial veins, recognizing the different location and characteristics of these channels and their walls
Superficial and deep drainage, understanding not only different territories, but also the clinical implications of the paucity of large venous interconnections in drainage of deep structures (basal ganglia, thalamus, and central structures)
Supratentorial and infratentorial veins, as the venous drainage of two compartments is quite easy to individualize thanks to the physical separation provided by the tentorium
72.2 Dural Venous Sinuses
The dural venous sinuses are unique vascular structures that lie within the tissue of the fibrous cranial dura mater. The cranial dura mater is composed of two layers, inner and outer. The endocranium (outer dural lamina) serves as the internal periosteum of the skull and is continuous with the outer periosteum through the various formina of the skull. The inner dural lamina is less vascular.
The largest venous sinuses represent endothelial-lined separations between the two layers of the dura mater. These separations are located primarily in the junctions and free edges of the major dural folds (e.g., the falx cerebri and the tentorium cerebelli) .
Embryologically, the meninx primitiva is initially composed of a relatively uniform cellular mesh around the developing encephalon that differentiates into three meningeal layers in embryos of around 10–16 mm crown–rump length (CRL). Light microscopy distinction between arteries and veins, even in very young embryos, lies in the fact that no muscular cells surround the endothelial layer. As Padget notes, expansion of the neural tissue separates the dural and pial layers of venous channels. Consequently, the numerous anastomoses traversing the primitive pia-arachnoid begin to decrease, leaving a few pia-arachnoidal veins that become connected by longitudinal anastomoses succeeded by transverse anastomoses between them; thus, initiating formation of the pial venous plexus and definitive veins .
Developmental remarks are added through the text as italicized paragraphs, whenever embryological or foetal features have been considered interesting.
72.2.1 The Superior Sagittal Sinus
The superior sagittal sinus (SSS) is contained within the dura at the junction of the falx and its attachment to the cranial vault; it has a roughly triangular cross-section. Extending from the foramen cecum anteriorly to the torcular herophili, its diameter progressively increases from anterior to posterior. The more anterior veins enter the sinus nearly at right angles, whereas posterior veins follow a course obliquely forward, entering into the sinus in a direction opposite the current of blood.
Early studies (1960s and 1970s) reported streaming or laminar flow in the SSS in some cases, as recognized from venous phase angiography. Bilateral simultaneous internal carotid angiography results in more complete opacification of the dural sinuses, and was recommended as a particularly useful technique in the evaluation of partial occlusions of the SSS in old texts, such as the 1974 chapter by Hacker . Irregular flow in the SSS may be related to either the entrance of blood coming from unopacified veins or to the presence of septi or dural membranes . Veins of the medial and lateral aspect of the hemisphere drain into the SSS. In the parietal region, several lateral superior cerebral veins may merge into two or three main trunks or into a single trunk known as the vein of Trolard or superior anastomotic vein. This vein, present in about one-third of patients, may anastomose to connect the SSS with the middle cerebral vein, leading to cavernous sinus region drainage, or with the vein of Labbé, leading to the transverse sinus.
Along the late embryological and early fetal period, plexal structures can be recognized in the dural anlage corresponding to the location of the SSS, but not yet as a definite single channel in the midline. The partial convergence of these venous channels joining in a single global venous structure may explain the presence of septi in the SSS, as well as the fact that some cortical veins drain in lacunae close to the sinus instead of directly to the sinus itself.
72.2.2 Torcular Herophili
The SSS drains into the torcular herophili, a confluent also connecting both lateral sinuses, the straight sinus and, in some instances, a medial occipital sinus. The junction of the SSS locates frequently at the right side of the torcular, draining the venous flow preferentially toward the right transverse sinus. On the other hand, drainage of the straight sinus locates more often at the left side of the torcular, flowing more toward the left transverse sinus.
72.2.3 Lateral Sinuses
The description by Knott, in 1881, is interesting to read because it discusses the conceptions of Vesalius, Galen, and Pacchioni regarding blood flow and anatomy . He explains about the lateral sinus: «it commences at the internal protuberance of the os occipitis and, taking at first a horizontal course, passes outwards along the transverse part of the linea cruciata on the corresponding side. On leaving the occipital bone, it passes over the inner surface of the mastoid portion of the temporal bone, to groove the occipital a second time on the upper surface of its jugular process. Bending into the jugular foramen, it there joins the inferior petrosal and marginal sinuses to form the internal jugular vein.» Knott also remarks that the transverse portion of the sinus presents the outline of a triangular prism as it lies between the layers of the tentorium cerebelli, but adopts a semicircular shape in its remaining part. The diameter of the lateral sinus averages 8–10 mm and is frequently asymmetrical and larger than the right lateral sinus (see embryological note for the torcular).
From a developmental point of view, the sigmoid sinus and jugular vein are the remnants of the original primary head sinus of the embryo, while the transverse sinus corresponds to a secondary anastomosis, using the trunk and the plexus located at the prosencephalic and mesencephalic portion of the embryo. Padget  states that the main initial pioarachnoidal veins draining the metencephalon and the myelencephalon remain in the adult as the superior petrosal sinus and inferior petrosal sinus, respectively. A review of embryological development brings some questions to this conception. For example, why do these two sinuses remain connected to the cavernous sinus, which Padget considers to be a remnant of the primary head sinus? A study centered on this question is underway.
The posterior temporal and occipital regions are mainly drained toward the transverse sinus. A major trunk can frequently be recognized, extending from the sylvian fissure backward and downward to the transverse sinus, known as the vein of Labbé (a mnemonic for distinguishing the vein of Labbé from the Trolard vein is «Labbé-lateral»).
Veins draining the lateral and inferior surfaces of the temporal and occipital lobes. Frequently those veins of the inferior surface of the cerebral hemisphere enter the tentorium and are embedded in the tentorium for some millimeters.
Veins draining the superolateral aspect of the cerebellar hemisphere, also joining the transverse sinus through tentorial sinuses.
The superior petrosal sinus.
Emissary veins communicating with scalp veins by way of mastoid and condiloid veins.
Venous injections in fetuses show multiple venous structures in the tentorium. In fact, in the embryological period the tentorium takes part of the loose mesenchyma that is the meninx primitiva, where most of the plexal veins course and connect.
From a neurosurgical perspective, the location of a point on the inferior lateral aspect of the temporal lobe has been highlighted. The point is the confluence of veins that drain the inferior and lateral aspects of the temporal and occipital lobes. As described in a review by Krisht et al. , such a venous confluent could be identified in 90% of 15 cadaveric brains studied. The veins converged into a venous point of the transverse sinus prior to its junction with the sigmoid sinus, located at the transverse–sigmoid junction region within a 1.5–2 cm span.
This closeness offers a better understanding of one of the possible causes of pathologic arteriovenous connections in cases of dural fistulae: Any event breaking the wall between a dural artery and a neighboring dural sinus contained in the dural covering could lead to a vascular connection. There is also another interesting detail: Embryologically, virtually all large pial veins must travel inside the dural covering for some millimeters before draining their blood into the sinus. This explains the fact that multiple adult veins become surrounded by a dural covering before joining the sinus. When dealing with dural fistulae, it is not infrequent that the fistular point locates just at the wall of the sinus, even parallel to the sinus itself, but not directly in the sinus. Thus, the direction of the pathological fistula may flow either toward the sinus (Cognard type 1 or 2), when patent, or retrogradely toward a dilated pial vein (included in Cognard type 3 or 4 fistulae) without intervening flow inside the sinus, regardless of its proximity in the case of thrombosis of the neighboring sinus .
The Sigmoid Sinus
72.2.4 Occipital and Marginal Sinuses
The main venous structures draining the nervous system in the early embryologic period are plexual. An anterior plexus covers the prosencephalon, a medial plexus covers the romboencephalon, and a posterior plexus covers the myelencephalon. Later, the three plexuses become connected by anastomotic channels constituting the main venous dural structure. The marginal sinus is the remnant of the posterior plexus, being the occipital sinus anastomotic channels .
72.2.5 Inferior Sagittal Sinus
The inferior sagittal sinus courses above the corpus callosum in the free edge of the falx cerebri. It receives veins of the falx and veins that drain the roof of the corpus callosum, the cingulated gyrus, and the adjacent medial hemisphere. For a portion of its course, the inferior sagittal sinus may lie slightly above the free edge of the falx. Frequently, its most anterior aspect shows a hook shape where it receives a bunch of veins from the roof of the corpus callosum.
72.2.6 Straight Sinus
The straight sinus is located in a triangular space at the junction of the falx and both tentorial folds. It connects the deep venous system joined in the great vein of Galen and the torcular herophili. The straight sinus may receive veins of the neighboring parenchyma: the occipital lobes, or the cerebellum.
72.2.7 Cavernous Sinus
The cavernous sinus is located in the lateral aspect of the sphenoid body. The dura of the pituitary gland forms its medial wall. The dura of the pons forms the dorsal wall. The dura of the hypothalamus forms the lateral wall. The apex is formed by the superior orbital fissure. The floor is formed by the periosteum of the basisphenoid  with the foramen rotundum anteriorly. The lateral wall consists of two layers; the outer is formed by the dura propria of the temporal lobe and the inner layer consists of the nerve sheaths of the III, IV, and V cranial nerves. They are connected by the inner reticular layer, which is a loose connective tissue. The VI cranial nerve runs more medially, closer to the carotid artery.
72.2.8 Superior Petrosal Sinus
The superior petrosal sinus connects the cavernous sinus with the lateral sinus at its transverse–sigmoid junction, running along the superior tentorial margin. It is the main outlet for drainage of the anterior aspect of the cerebellum and lateral brainstem through the petrosal vein, and also receives supratentorial veins of the basal and medial aspect of the hemisphere.
The superior petrosal sinus is considered to be the embryological remnant of the metencephalic pioarachnoidal vein. As result of growth of the hemisphere, which enlarges the distance between the primitive veins covering the pial layer and the dural venous structures, most small veins fade and some larger veins remain. The few elongated and augmented veins that remain, and are directed laterally toward the parenchyma for some distance, are called pioarachnoidal veins. Padget  records that, in 10-mm CRL embryos, at least one pia-arachnoidal vein can usually be identified for each of the five regions of the brain: the telencephalon, the diencephalon, the mesencephalon, de metencephalon, and the myelencephalon.
72.2.9 Inferior Petrosal Sinus
The inferior petrosal sinus, located between the temporal bone and the clivus, connects the posteroinferior aspect of the cavernous sinus and the jugular bulb. The junction of the inferior petrosal sinus and the jugular vein lies lateral to the cranial nerves in the jugular fossa . It may receive tributaries from the lateral recess of the fourth ventricle, veins of the internal auditory region, and veins from the medulla oblongata.
72.2.10 Sphenoparietal Sinus
72.2.11 Sphenopetrosal Sinus
Another alternative route taken by the SSV is called, in the adult, the sphenopetrosal sinus. Its trajectory borders the inferolateral aspect of the temporal lobe running along the lateral aspect of the middle cranial fossa, to drain into the transverse sinus. See drainage of the SSV (◘ Fig. 72.6).
72.2.12 Emissary Veins
Emissary veins are venous structures located in channels that traverse the cranial vault. They usually connect dural sinuses (or pial veins) to scalp venous structures. Emissary veins can help in planning surgical procedures by acting as landmarks indicating the location of the sinus below. These veins serve the important function of equalizing intracranial pressure and act as safety valves during cerebral congestion; however, they can also serve as pathways by which infections are carried into the cranial cavity
Emissary veins through the mastoid connecting to scalp veins are easily seen and conspicuous at embryological and early fetal stages, as well as in children.
72.3 Superficial Pial Supratentorial Drainage
Even though surface veins are quite variable, global patterns are recognized. Numerous reviews of these patterns can be found for each region and can help in avoiding venous damage or thrombosis during different neurosurgical approaches.
Vein of Trolard: This is a dominant hemispheric vein to the SSS for the central region.
Vein of Labbé: This is a dominant vein toward the transverse sinus for the temporoparietal region.
Superficial sylvian vein: For the frontal-temporal region; its most common outlet is the cavernous or paracavernous drainage.
Deep sylvian vein: For the fronto-temporo-insular basal region. This vein frequently drains toward the basal vein or the superior petrosal sinus.
The cortical surface is completely covered by a venous network, with various main outlet veins draining each cortical region. Surface pial venous evaluation relies on the drainage pattern in a global approach. Cortical veins can be named on the basis of the cortical region they drain. Frequently, a dominant vein receives tributaries from a broad territory, whereas other main draining veins of the hemisphere tend to be less conspicuous.
For the three large anastomotic veins, the vein of Labbé more frequently drains the temporal and inferior parietal region toward the lateral sinus in the transverse-sigmoid junction; the vein of Trolard is directed to the middle portion of the SSS; and the SSV drains the antero-lateral portion of the hemisphere toward the pterygoid plexus. Tanriverdi  found that the vein of Trolard frequently coursed at the level of the central region. He also found that the SSV was the predominant type on the right hemisphere, whereas the vein of Labbé tended to be predominant on the left hemisphere.
Rothon  differentiates between lateral and medial tentorial sinuses. The former receive veins from the basal temporal and occipital lobe surfaces and are located within the lateral part of the tentorium, coursing laterally to drain into the transverse sinus. The medial tentorial sinuses (receiving cerebellar veins), course medially to empty into the straight sinus or the junction of the straight and transverse sinuses.
Frontal Lobe: Lateral and medial ascending group of veins drain toward the SSS and the descending group join the SSV (most frequently at the sphenoparietal sinus–pterigoid plexus). Veins of the cingulum, corpus callosum, and caudal aspect of the medial frontal gyrus also join the inferior sagittal sinus and, in some instances, the anterior end of the basal vein of Rosenthal.
Parietal lobe: Lateral and medial ascending group of veins drain toward the SSS, and lateral descending veins to the transverse sinus and SSV. Medial descending veins (precuneus) also join the posterior pericallosal vein toward the vein of Galen complex.
Occipital lobe: Veins drain toward the SSS, the lateral sinus (frequently through a tentorial sinus), the straight sinus, and the vein of Galen for the medial aspect of the parietal lobe (cuneus).
- Basal temporoocipital region:
Fusiform gyrus: Veins drain toward the petrosal sinus and tentorial veins
Lingual and parahyppocampal gyrus: Veins drain toward the basal vein of Rosenthal.
Temporal lobe: Lateral veins drain toward the SSV, and caudolateral veins to the transverse sinus. With respect to the inferomedial aspect of the temporal lobe, the uncal, anterior hippocampal, and medial temporal veins empty into the basal vein of Rosenthal.
Sphenoparietal sinus: This drains into the cavernous sinus. The main trunk of the SSV may also be located in the dural wall of the cavernous sinus but not connected to it, named then the laterocavernous sinus . In this case, the drainage is directly to the pterigoid plexus.
Sphenobasal (paracavernous) vein: The connection with the pterigoid plexus frequently exits the cranial vault through the foramen of Vesalius.
Sphenopetrosal vein or sphenolateral trajectory: In this case, the SSV remains in a lateral position, turning posteriorly toward the transverse sinus. Its course corresponds to the primitive tentorial sinus of the embryo.
72.4 Deep Venous Drainage
The main structures constituting the deep venous system are the internal cerebral vein, the basal vein of Rosenthal, and the great vein of Galen.
It has to be remembered that the venous drainage of the gyri is not only superficial. The so-called deep medullary veins (or veins of the white matter) traverse the white matter toward the ventricular wall. They converge in the subependymal veins, constituting a significant amount of the internal cerebral vein and the basal vein tributaries. Between the superficial medullary veins, which drain the white matter 1–2 cm below the gray matter toward the superficial venous sinuses, and the deep medullary veins converging to the deep venous system, the intracerebral anastomotic veins or transcerebral veins may connect both systems.
72.4.1 Internal Cerebral Vein
Structures adjacent to the ventricular wall (corpus callosum, caudate, lenticular, hippocampus, and deep hemispherical veins) mostly drain toward the internal cerebral vein.
The nomenclature of the smaller tributaries of the internal cerebral vein can vary between authors and, since the introduction of ventriculostomy as a habitual technique, much interest has arisen about their anatomy.
Most tributaries of the internal cerebral vein are subependymal, but the trunk of the internal cerebral vein courses between the layers of the tela choroidea of the third ventricle, entering the subarachnoid space of the transverse cerebral fissure where it is surrounded by the connective tissue of the velum interpositum.
From a developmental point of view, the subarachnoidal location of the internal cerebral vein is in consonance with its evolution. At the late embryological period, the cerebral cortical mantle is still thin, and the choroid plexus becomes progressively more developed. Being an essentially vascular structure, choroidal arteries and veins are between the larger vascular structures at this age (◘ Fig. 72.16).
The paired anterior choroidal vein becomes the internal cerebral vein in the adult. Because it is the main deep drainage for the choroid plexus, it becomes a constant vein and is found in virtually all cerebral angiograms, normally draining into the straight sinus, even though a falcine sinus can also be its outlet in cases of very primitive vein of Galen malformations.
72.4.2 The Basal Vein of Rosenthal
The basal vein of Rosenthal shows a variable length.
Padget  refers to the basal vein as a relatively new phylogenetic channel. An alternative interconnection of deep venous structures compensates for the elongation of the surface veins caused by expansion of the hemisphere. The basal vein is formed from elements of widely separated embryonic veins. This explains its frequent existence is somewhat fragmentary form.
The most anterior segment, striate of first segment , corresponds to the prepeduncular portion. It extends from the anterior perforated substance by union of the anterior cerebral, deep middle cerebral, and inferior striate veins. The posterior frontoorbital vein and olfactory veins also unite.
The second or peduncular segment begins at the most medial point of the basal vein anterior to the peduncle and finishes at the most lateral point in its turn around the cerebral peduncle. A peduncular vein may unite both basal veins on the midline representing the posterior part of the unconstant venous anastomotic circle at the base of the brain.
The third or posterior mesencephalic segment has a tegmental portion, around the mesencephalon, and a terminal portion finishing in the great vein of Galen at the quadrigeminal cistern.
Thalamic Venous Drainage
Superior: This is the largest, draining the superior and central part of the dorsal thalamus; it runs medially to drain into the vein of Galen or posterior part of the internal cerebral vein.
Anterior: This drains the anterior thalamus and runs anteriorly to join either the septal or the internal cerebral vein near the foramen of Monro.
Inferior and posterior: These veins are small in caliber and drain the inferomedial and inferolateral regions of the thalamus; they drain into the basal vein.
72.4.3 Great Vein of Galen
The great vein of Galen is the point of convergence for venous blood from all deep structures: internal cerebral vein, basal vein, inferior sagittal sinus, and the infratentorial venous channels as superior cerebellar and brainstem veins. The vein of Galen is the anterior portion of the straight sinus connecting this dural sinus with subarachnoidal veins.
Even though veins that converge in the vein of Galen look physically distant in the embryo, the location of the pineal area later reveals itself as strategic. Telencephalic, diencephalic (basal ganglia), mesencephalic, and metencephalic (pontine and cerebellar) veins can converge in this point because of folding of the encephalon. The edge of the falco-tentorial incisure represents a kind of carrefour. The anterior choroidal veins (future internal cerebal veins) connect with the primordium of the vein of Galen and straight sinus in stages as early as 30 mm CRL. Anterior choroidal veins show a broad caliber and their location probably favors the central role taken by the adult internal cerebral vein in draining neighboring structures.
72.5 Posterior Fossa Veins
The traditional classification  relates cerebellar and brainstem veins to three main confluents: superior toward the vein of Galen, anterior toward the petrosal vein, and posterior toward the torcular or lateral sinuses. In fact, a fourth confluent can also be considered as caudal confluent to the inferior petrosal sinus, frequently being a minor contribution to the posterior fossa drainage. Rothon  considered these confluents to be bridging veins of the posterior fossa. In a neurosurgical approach, he divides the posterior fossa veins into four groups: superficial, deep, brainstem, and bridging veins. The superficial veins are divided on the basis of the three surfaces they drain: The tentorial surface is drained by the superior hemispheric and superior vermian vein. The inferior or suboccipital surface is drained by inferior hemispheric and inferior vermian veins. The petrosal surface is drained by anterior hemispheric veins. The deep veins course in the three fissures between the cerebellum and the brainstem and on the three cerebellar peduncles: veins of the cerebellomesenchephalic, cerebellopontine, and cerebellomedullary fissures and veins of the superior, middle, and inferior peduncles. The veins of the brainstem course transversely or longitudinally along the midbrain, pons, and medulla and are named on the basis of their location. These veins of the posterior fossa terminate as bridging veins that collect in the galenic, petrosal, and tentorial confluents.
72.5.1 Superior (Galenic) Confluent
The superior vermian vein is also quite constant but very variable. It may be a broad vessel draining culmen and declive and the superior aspect of the cerebellar hemispheres, or a small vein just for the culmen.
Brainstem Veins Toward the Galenic Confluent
In general, interconnected perpendicular veins cover the brainstem. These consist of longitudinal channels coursing anteriorly or laterally, remaining connected through transversal veins at different levels. A dominant lateromensencephalic vein directly joining the vein of Galen or the basal vein of Rosenthal is one of the frequent configurations of the lateral drainage for the mesencephalon and pons. Frequently, it is possible to identify an anterior mesencephalo-pontine (and/or medullar) vein outlining the anterior aspect of the brainstem. The petrosal vein (anterior confluent) is another venous outlet for brainstem veins.
72.5.2 Anterior (Petrosal) Confluent
Posterior fossa veins do anatomose and, in this way, drain in non-habitual confluents, and/or establish communications between confluents.
72.5.3 Posterior (Torcular) Confluent
At least one main hemispheric vein traveling close to the great horizontal fissure and receiving perpendicularly veins of the neighboring parenchyma
A dominant inferior vermian vein located paramedially
The cerebellar hemisphere may also be drained by more than one tentorial sinus. Part of the superior vermis may show veins joining the inferior vermian vein.
72.5.4 Inferior Confluent
72.6 Evaluation of Venous-Related Pathological Conditions
Anatomical location of the pathology. Evaluation of the habitual veins expected in this location. Is there any venous structure lacking?
Is the pathological condition showing any abnormal vein? Dilated or varicose? Stenotic? Can this venous anatomy be related to the adult drainage or does it maintain an embryological pattern?
Toward which collectors do the abnormal veins drain?
What do the rest of venous structures look like? Are any lacking, or thrombosed?
Does this drainage interfere with any other encephalic drainage? Slow flow? Reversed flow? Dilated medullary veins?
In view of the veins involved in the pathology, is there any unexpected artery to take into account?
With this information about venous behavior, is there any other feature to review in magnetic resonance imaging (edema), clinical course, neuropsychological exam, EEG, etc.?
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