Книги по МРТ КТ на английском языке / Neurovascular anatomy in interventional neuroradiology Krings et al 2015

The longitudinal veins are divided into a midline and a lateral group. The midline veins run as an anastomotic venous channel composed of the median anterior pontomesencephalic vein, the median anterior pontine vein, and the median anterior medullary vein, which is continuous with the anterior spinal vein. The venous blood flow can run cranially to the posterior communicating vein or the peduncular veins or caudally toward the spinal veins. The lateral veins are the lateral anterior pontomesencephalic, mesencephalic, and medullary veins, which anastomose with each other and the midline veins. A particularly important vein in this group is the lateral mesencephalic vein, which connects the basal vein of Rosenthal with the lateral brainstem veins and the vein of the medullary fissure. When the basal vein of Rosenthal is discontinuous, the anterior segment will drain posteriorly to the infratentorial veins via the lateral mesencephalic vein. In addition, in patients with a vein of Galen malformation, the lower part of the epsilon sign seen in lateral angiograms represents the lateral mesencephalic vein, which serves as a collateral venous drainage route between the deep venous system and the extracranial veins.

and tentorial sinuses posteriorly, and to the superior petrosal sinus via the petrosal vein laterally. Small bridging veins between the brainstem veins and the cavernous sinus can also be rarely seen in angiography.

38.2.5 The Persistent Occipital Sinus

Of the three embryologic meningeal venous plexuses, the posterior plexus undergoes the fewest changes, simply extending to become the occipital sinus by the 50-mm stage. It serves as a connection between the torcular and the marginal sinus (at the level of the foramen magnum) and is continuous with the dorsal internal vertebral venous plexus. The occipital sinus is often prominent in the newborn and slowly decreases in size as the jugular bulb maturation occurs during the first year of life.

The presence of an occipital sinus can explain the combination of a hypoplastic transverse sinus with a normal-sized or even large jugular bulb, as the occipital sinus will use the jugular bulb to drain.

38.2.4 Bridging Veins

The bridging veins cross-connect the subarachnoid and subdural spaces to reach the dural venous sinuses. These bridging veins collect into the vein of Galen superiorly, to the torcular

38.3 Clinical Impact, Additional

Information and Cases

See Fig. 38.2, Fig. 38.3, Fig. 38.4, Fig. 38.5, Fig. 38.6,Fig. 38.7, and Fig. 38.8.

Pearls and Pitfalls

●The posterior fossa structures drain toward three main collecting structures, depending on the surface. The anterior (petrosal) surface drains mainly to the superior petrosal sinus. The superior (tentorial) surface drains to the vein of Galen. The posterior-inferior (suboccipital) surface drains to the torcular and the transverse sinus.

●The venous configuration explains the posterior fossa venous congestion in dural fistulas involving the transverse sinus and torcular.

●The infratentorial veins anastomose with the vein of Rosenthal via the pontomesencephalic vein and the lateral mesencephalic vein. These anastomoses explain the posterior fossa drainage of certain carotid-cavernous fistulas.

●Small bridging veins can exist between the brainstem veins and the cavernous sinus.

Further Reading

[1]Huang YP, Wolf BS. The veins of the posterior fossa—superior or galenic draining group. Am J Roentgenol Radium Ther Nucl Med 1965; 95: 808–821

[2]Huang YP, Wolf BS, Antin SP, Okudera T. The veins of the posterior fossa—an- terior or petrosal draining group. Am J Roentgenol Radium Ther Nucl Med 1968; 104: 36–56

[3]Lasjaunias P, Berenstein A, ter Brugge KG. Surgical Neuroangiography. Vol. 1. 2nd ed. Berlin: Springer; 2006

[4]Rhoton AL, Jr. The posterior fossa veins. Neurosurgery 2000; 47 Suppl: S69– S92

39.1 Case Description

39.1.1 Clinical Presentation

A 24-year-old female patient complained about progressive weakness in her left leg. When she was seen, she was unable to stand on her left leg without support. Sensation, bladder, and bowel functions were not disturbed. There was evidence of hyperreflexia in her left ankle and knee with clonus and an upgoing left plantar reflex. She had a left-sided skin discoloration on her lower thoracic region that had been there since birth.

39.1.2 Radiologic Studies

See Fig. 39.1, Fig. 39.2.

39.1.3 Diagnosis

Spinal arteriovenous metameric syndrome (Cobb syndrome or juvenile spinal arteriovenous malformation) at T12.

39.2 Anatomy

The blood supply to a given metamere (which consists of the vertebral body, the paraspinal muscles, the dura, nerve root, and spinal cord) is derived from segmental arteries. These segmental arteries are present in the fetus for each of the 31 spinal segments. This segmental supply remains preserved in the thoracic and lumbar regions via the intercostal or lumbar arteries. In the upper thoracic region, several segmental arteries coalesce to form a common feeder, which is the supreme intercostal artery. In the cervical region, this vascular rearrangement is even more obvious: on each side, three longitudinal anastomotic arteries are established as potential sources of spinal blood supply; namely, the vertebral artery, the deep cervical artery, and the ascending cervical artery.

The vertebral artery is a chain of intersegmental anastomoses that connects the cervical segmental arteries, each of which is able to supply a cervical segment, with the most prominent being the arcade of the dens. In the upper cervical region, potential sources of metameric blood supply are via anastomoses

Fig. 39.2 Spinal angiography in the anteroposterior view in early (a) and late (b) arterial phases after injection into the left T12 segmental artery reveals the paravertebral AVM with arteriovenous shunting along the segmental artery supplying the skin, paravertebral muscles, and vertebral body, as well as the origin of a dorsolateral radiculopial artery (arrow) that supplies a spinal cord AVM. The concurrence of arteriovenous malformations affecting multiple compartments of the same metamere gave rise to the term spinal arteriovenous metameric syndrome.

to the external carotid artery, mainly the occipital artery (namely, the C1 and C2 anastomoses; see Case 4) and the ascending pharyngeal artery (namely, the hypoglossal artery, which anastomoses with the C3 collateral of the vertebral artery via the odontoid arterial arch that supplies the dens; see Case 30). In the sacral and lower lumbar region, sacral arteries and the iliolumbar artery (which often supply the L5 level) derived from the internal iliac arteries are the most important supply to the caudal spine.

In general, the segmental arteries supply all the tissues on one side of a given metamere, with the exception of the spinal cord. Because of its embryological origin, each metamere is centered at the level of the vertebral disk, and therefore, each vertebra is supplied by two consecutive segmental arteries on both sides that anastomose extensively both across the midline and between levels above and below. The latter is formed by an extraspinal longitudinal system that connects the neighboring segmental arteries longitudinally. The vessels course on the lateral aspect of the vertebra or transverse process. This system is highly developed in the cervical region, where the vertebral artery and the deep cervical and ascending cervical arteries form the most e ective chain of longitudinal anastomoses ( Fig. 39.3).

Fig. 39.3 After injection into the left ascending cervical artery, the rich anastomotic network is well visualized. The anterior spinal artery (black arrow) is supplied by multiple radiculomedullary arteries (white arrows) that demonstrate retrograde filing to the contralateral vertebral and deep cervical arteries. The vertebral artery gives rise to the arcade of the dens (thin double arrows) at the C3 level.

In addition to this extraspinal system, an intraspinal extradural system is present that constitutes a transverse anastomosis but also has longitudinal interconnections. The retrocorporeal and prelaminar arteries are the relevant vessels for the supply of bone and dura and interconnect with neighboring and contralateral segmental arteries. These anastomoses provide an excellent collateral circulation, and it is for this reason that numerous segmental arteries can be visualized by injection of one segmental artery ( Fig. 39.3). The extensive network of extraand intraspinal anastomoses protects the spinal cord against ischemia related to segmental arterial occlusion ( Fig. 39.4).

The segmental arteries course along the vertebral body posteriorly, supplying the periphery of the vertebral body by perforating arteries. While the muscular branch runs further posteriorly to the segmental muscles, the spinal branch of the segmental artery enters the vertebral canal through the intervertebral foramen and regularly divides into three branches: an anterior and posterior artery of the vertebral canal that supplies the bony spinal column and a radicular artery that supplies the dura and nerve root at every segmental level.

Fig. 39.4 At various and unpredictable levels, the anterior spinal artery is reinforced by additional metameric arterial supply. In this young patient with suspected AVM, injection of the right Th4 artery in early

(a) and late (b) arterial phases demonstrates the anterior spinal artery and its division into a superior and inferior branch (small black asterisk in a). In addition, the retrograde filling of additional feeders both superior and inferior to Th4 (white arrows) is visualized. Via an extensive collateral supply with longitudinal and transversel paravertebral anastomoses, and through the anastomotic network of the vasocorona (small black arrows), additional radiculopial arteries can be seen (black arrows). The level of the injected segmental artery can be deduced from the extensive vertebral blush (white asterisk).

39.3 Clinical Impact, Additional

Information and Cases

Knowledge of the segmental supply of the spinal cord helps with understanding the nature of the disease encountered in the index case: a metameric disease that a ects not only the spinal cord but also muscle, bone, and skin supplied by the affected vessel. Understanding the regional vascular anatomy also helps to classify di erent vascular shunts, depending on the feeding artery, thereby subdi erentiating spinal vascular malformations into paravertebral, radicular, dural, and pial arteriovenous malformations ( Fig. 39.5).

During postnatal development, a “pruning” process of the cord supply takes place that leads to regression of the number of cord-supplying arteries from the segmental arteries. This process explains why there is not necessarily cord supply from every single segmental level. Identification of cord supply is, however, of paramount importance when embarking on embolization of shunts that are fed by the radiculomeningeal arteries (such as the dural arteriovenous fistulae of the spine) or on preoperative devascularization of hypervascularized tumor metastases to the spine, because, from the segmental level that has to be embolized, vessels may arise that supply the cord ( Fig. 39.6; Fig. 39.7;

Fig. 39.8).

The rich collateral network that is present in between the

segmental arteries also explains why a proximal ligation embolization of dural arteriovenous shunts will not be successful, as other dural branches will take over the supply to the shunt with time if the liquid embolic agent does not reach the proximal “foot” of the vein ( Fig. 39.9).

Fig. 39.8 Spinal angiograms in two different patients (a,b) who both harbor a spinal dural arteriovenous fistula and who have additional supply to the cord (anterior spinal artery, white arrows) arising from the same level as the supply to the fistula. Identification of the additional cord supply is paramount to avoid inadvertent embolization into the cord supplying vessels.

Pearls and Pitfalls

●The segmental artery gives rise at each level to vertebral, muscular, and paraspinal branches and to a radicular artery that supplies the meninges of the nerve root sleeve, as well as the nerve root itself.

●Supply to the cord may arise from this segmental artery and has to be identified before embolizing lesions like dural arteriovenous fistulas, paravertebral shunts, or hypervascularized tumors.

●The rich anastomotic network between segmental arteries may lead to inadvertent embolization of neighboring segmental arteries, especially when using liquid embolic material with high penetration capabilities.

Knowledge of the existence of these anastomoses is important when employing liquid embolic agents that slowly polymerize and that may, therefore, open anastomoses, leading to inadvertent occlusion of distant segmental arteries and their daughter vessels.

Fig. 39.9 Injection into the right T7 segmental artery (a) revealed a dural arteriovenous shunt fed by the radiculomeningeal artery (short arrow), with the shunting zone (long arrow) underneath the pedicle of T7. On the T7 injection, a descending dural branch (small arrow) was noted that anastomosed to the ascending dural branch that arose from the right T8 segmental artery (b). This case demonstrates the rich collateral supply to the dura that is the cause for delayed reopening of dural arteriovenous fistulae in cases of proximal ligation of the feeding artery.

Further Reading

[1]Geibprasert S, Pereira V, Krings T et al. Dural arteriovenous shunts: a new classification of craniospinal epidural venous anatomical bases and clinical correlations. Stroke 2008; 39: 2783–2794

[2]Krings T, Mull M, Gilsbach JM, Thron A. Spinal vascular malformations. Eur Radiol 2005; 15: 267–278

[3]Thron AK. Vascular Anatomy of the Spinal Cord: Neuroradiological Investigations and Clinical Syndromes. Vienna: Springer; 1988

40.1 Case Description

40.1.1 Clinical Presentation

A previously healthy 58-year-old male patient had an acute onset of quadriplegia and sensory loss in his upper and lower limbs, severe headaches, and progressive respiratory dysfunction that required intubation.

40.1.2 Radiologic Studies

See Fig. 40.1, Fig. 40.2, and Fig. 40.3.

40.1.3 Diagnosis

Spinal perimedullary arteriovenous fistula arising from an unfused segment of the anterior spinal artery.

40.2 Anatomy and Embryology

Although in the embryo each radicular artery gives rise to a radiculomedullary artery to supply the spinal cord, in postnatal life, the number of radicular arteries supplying the spinal cord is reduced after a transformation and fusion process. At a few unpredictable segmental levels, the radicular artery has a persistent supply to the cord that reaches either the anterior surface via the ventral nerve root or the posterolateral surface via the dorsal nerve root to form and supply the superficial spinal cord arteries. Two to 14 (on average, six) anterior radiculomedullary arteries persist as the result of this “pruning process” of the feeding vessels. The posterior radiculomedullary arteries

are reduced less drastically, mostly to between 11 and 16 vessels.

Several nomenclatures and classifications have been used to describe spinal cord arteries, which may lead to some confusion. The original classification is based on where the spinal cord arteries run (i.e., on the posterior, posterolateral, or anterior surface of the spinal cord, thereby constituting the posterior or posterolateral arteries and the anterior spinal artery). A classification proposed by Lasjaunias di erentiates three types of spinal radicular arteries according to their region of supply: radicular, radiculopial, and radiculomedullary.

The spinal radicular artery is a small branch, present at every segmental level, that supplies the nerve root as well as the adjacent dura. The radiculopial arteries supply the nerve root and the dorsolateral superficial pial system (via the posterior radicular artery). The radiculomedullary arteries supply the nerve root, the superficial pial system, and the medulla (via the anterior radicular artery). This classification o ers advantages for the interventional neuroradiologist when compared with the classical di erentiation because it stresses the importance of the anterior supply for the gray matter of the spinal cord parenchyma. Because the anterior spinal artery has radicular, radiculopial, and medullary supply and the radiculopial posterolateral arteries may have some medullary supply (i.e., part of the posterior horns), this classification may, however, result in misunderstandings. This is why we proposed recently the following slight modification to the classification to overcome the anatomical confusions: Radicular arteries are vessels that supply the nerve root and the dura mater but do not supply the spinal cord. These arteries are present on every single segmental level, whereas the following two types may or may not be present at a given segmental level.