By Y. Jensgar. Southern Oregon State College.
Then the sheath and catheter are moved along their long axis as a single unit from septum to lateral freewall and the catheter torqued either clockwise (posterior groove) or counterclockwise (anterior groove) within the sheath order apcalis sx on line amex treatment of erectile dysfunction in unani medicine. Access to left lateral pathways in larger patients sometimes requires exchange of the typical Mullins-type transseptal sheath for one of a variety of specialized sheaths that are now available (see below) purchase apcalis sx 20 mg amex erectile dysfunction otc treatment. The top two cine frames show the catheter retrograde through the aortic valve purchase cheapest apcalis sx erectile dysfunction va rating, but a failed attempt to place the catheter through the mitral valve on top of the mitral annulus. The transseptal approach was then used (bottom two frames) and was successful with the catheter in position very close to, but slightly different from, the retrograde mitral approach. Note, the hockey stick appearance of the catheter tip (arrow) using the transseptal approach. However, the overall results and complications from the transseptal and retrograde techniques are similar. Right Freewall Pathways Right posterior and right posterior paraseptal pathways almost always can be approached from the right femoral vein with a deflectable-tipped catheter placed above the tricuspid valve. For right lateral pathways, most operators find the use of a long vascular sheath (see below) very important to enhance catheter stability and improve access. Posterior Septal Pathways For left-sided pathways, the retrograde aortic technique can be used with an attempt to deflect the catheter tip under the mitral valve near the aortic annulus. Alternatively, a transseptal approach can be used by extending the catheter all the way around the mitral annulus to the area of the septum. Regardless of approach, one must be aware of the small size and close proximity of the coronary arteries in this region. Consequently, some operators now perform preablation coronary angiograms for any pathway near the posterior septum to evaluate the proximity of the ablation site to a small coronary artery. This issue is particularly important for small children and infants, who have smaller coronary arteries and shorter distances from the ablation sites to the coronary artery (183). However, the most important advance we have found for these pathways is the use of cryoablation (101,106,186,187,188,189). Thus, cryoablation is probably the therapy of choice for septal pathways in the pediatric patient. Use of Long Vascular Sheaths The approach to left and right freewall pathways in particular can often be improved by use of one of a variety of long sheaths, including 6-, 7-, and 8-Fr straight and specially designed sheaths. The presence of the sheath provides catheter stability, markedly improves torque transmission from the catheter handle to the tip of the catheter, and allows for coaxial steering of the catheter tip (5). These characteristics may be critical for the atrial approach on either the right or left side, even when a patent foramen ovale is present. These sheaths seem to be most helpful for right freewall pathways, but are designed for use in every right- and left-sided location. Without temperature monitoring, the delivered power is likely to be too high or too low. With temperature monitoring, the delivered power may vary dramatically in an individual patient between individual applications, depending on catheter tip location and stability, both of which are affected by respiratory activity. Consequently, when general anesthesia is used, asking the anesthetist to hold respiration in either expiration or inspiration can markedly reduce catheter movement, improving the accuracy and effectiveness of the ablation application while reducing the possibility for catheter dislodgement. When cryoablation is used, the system may be used in either the mapping or ablation mode, as described above. Following creation of a successful lesion, patients are usually observed in the electrophysiology laboratory for 30 to 60 minutes, after which repeat electrophysiologic testing is performed, sometimes with and without an infusion of isoproterenol. Overall initial success rates for pathway ablation were about 94%, with results varying significantly by locations (left freewall 98%, right freewall 90%, left septal 88%, right septal 89%). Fluoroscopy times can be long compared to other pediatric catheterization procedures, but have generally decreased over time (21,197). High variance in the difficulty of individual procedures, combined with the variability of observations between investigators, probably attest to a large number of poorly defined factors P. However, the overall high success rates, sometimes requiring a second procedure, also indicate that these factors can be overcome. The schematic diagram reveals pathway locations as identified by successful radiofrequency ablation site. Note that four pathways were located outside of the typical posteroseptal location. A through D show representative angiograms of catheter-electrode positions in four locations. In panel A, the large tipped ablation catheter approaches from the inferior vena cava. Its final position is in the mouth of the coronary sinus, near the ostium of the middle coronary vein (posteroseptal pathway). In panel D, the large tip catheter positioned in the coronary sinus was used for mapping only. A deflectable tipped catheter with a “dumb-bell” shaped electrode was used for ablation, and was positioned using a transseptal approach from the inferior vena cava to the posterior mitral annulus (left posterior pathway). Variable location of accessory pathways associated with the permanent form of junctional reciprocating tachycardia and confirmation with radiofrequency ablation. As with initial success, recurrence also varied by pathway location, varying from 4. Although these rates may be higher than in other reports from single centers or uncontrolled registries, they are the only data from a prospectively controlled trial in children and the subjects have the broadest center representation of any prospective ablation trial. Thus, these recurrence rates may be the most accurate representation of what can be expected in the average pediatric ablation center. Although these characteristics make the technique undesirable for most children and adolescents, a small number of successful fast pathway ablations were reported in pediatric patients without significant complications (21,60). Initially, most operators would identify the slow pathway by the presence of a small electrical potential from a presumably discrete slow pathway potential as an indicator of an appropriate catheter position for ablation (206), while others have found this slow pathway potential to have very poor specificity (209). Application of cryoenergy at the slow pathway does not lead to junctional acceleration as does heating. Consequently, the technique with cryoablation focuses more on elimination of slow pathway conduction with only transient changes to fast pathway conduction as procedural endpoints (105,106). The technique involves the simultaneous collection of anatomic points and atrial electrogram amplitudes. A voltage map of the triangle of Koch and contiguous regions is created after data collection is complete. Typically, islands or strips of low to medium voltage areas are noted adjacent to areas with higher voltage, which may be near the base of the fast pathway. There may be multiple such low-voltage areas, representing multiple areas of slow pathway conduction, and each a potential area for ablation applications. Because slow pathway modification already has a nearly 100% success rate, the technique is unlikely to statistically improve success rates; so the rationale is that more precise delineation of the target (slow pathway(s)) will yield fewer applications, a shorter procedure time and enhance safety. There is limited experience using the same technique in pediatric patients (211,212). However, this recommendation occurred before the availability of cryotherapy which will likely be modifying factor when the guidelines are updated. Jude Medical) within the right atrium, geometry of the triangle of Koch was created and simultaneously multiple atrial voltage amplitude data points were automatically collected from the region during sinus rhythm (210,211,212). A, B, and D show a lateral view (see torso reference upper right corner) with the green His catheter, yellow coronary sinus catheter, orange right ventricle catheter.
Mitral Arcade This is a rare entity buy apcalis sx pills in toronto erectile dysfunction main causes, however one that has a significant impact on outcome (Videos 43 buy apcalis sx 20mg otc impotence statistics. The morphologic and echocardiographic features are of muscularization of the chordal apparatus order apcalis sx without prescription erectile dysfunction over the counter, such that it is difficult to differentiate between the leaflets, chordae, and their supporting papillary muscles (Fig. The functional result is often regurgitation which is due to a tethered valve with deficient zones of leaflet coaptation. This lesion usually presents early on in life and invariably results in a poor outcome (28,29). The upper left hand image is a three-dimensional echocardiogram seen from the left atrium, with the cleft being indicated by the black arrow. The upper right hand picture is the same case, but viewed from the left ventricular aspect. The lower two images are from the same case, with the left one showing the papillary muscle distribution and the right one the two-dimensional appearance of the cleft. Cleft Mitral Valve This involves the anterior or aortic leaflet of the mitral valve and varies in degree with some hearts having a complete cleft, whereas in others it involves only the tip of the leaflet (Videos 43. The cleft points toward the left ventricular outflow tract, which differentiates it from that seen in an atrioventricular septal defect (30,31,32,33,34,35) (Fig. The supporting papillary muscles are in the normal location (36), which differs from an atrioventricular septal defect where the posterior muscle is rotated laterally. In other cases, the edges of the cleft are supported by chordae without evidence of associated mitral valve regurgitation (Fig. The chordae invariably insert into the crest of the interventricular septum, while in other cases they may straddle an anterior ventricular septal defect. The degree of mitral valve regurgitation is usually dictated by the extent of the cleft, with greater regurgitation in those where the cleft extends along the whole length of the anterior leaflet. While two-dimensional echocardiography is helpful in the diagnosis, it does not permit a complete evaluation of the extent of the cleft: three-dimensional echocardiography does. Imaging the mitral valve from the left atrial or left ventricular aspect provides a complete assessment of the extent of the cleft, the supporting apparatus and the commissures. The site and degree of regurgitation can be determined by an en face view of the valve using color Doppler. Parachute Mitral Valve Although cases exist with a solitary papillary muscle, the initial description by Shone (26) included hearts with a dominant papillary muscle which supported most of the chordal apparatus and a smaller secondary rudimentary muscle. The presence of a parachute mitral valve does not infer stenosis or regurgitation, as medium term data would suggest that many require no intervention (37). In general it is the associated leaflet dysplasia and chordal tethering which result in valve failure. This entity is readily recognized by two-dimensional echocardiography, however its three-dimensional counterpart permits a more detailed assessment of the valve leaflets and chordal apparatus. Double Orifice Mitral Valve This entity is seen more frequently in hearts with an atrioventricular septal defect, however is occasionally encountered in an otherwise normal heart (Videos 43. In this setting it is more common for each orifice to be supported by chordal apparatus and papillary muscle (Fig. This may be discovered as an incidental finding during an echocardiogram for another reason, while in other cases one of the functional orifices is regurgitant. These valves are rarely stenotic and in most cases never require any intervention. In general this entity is readily recognized by both two- and three-dimensional echocardiography. In some instances one of the orifices is imperforate, and the supporting tension apparatus can be appreciated from the left ventricular aspect (Fig. B: These images are from a double orifice mitral valve with an imperforate anterior orifice. The two-dimensional echo images on the left show the large posterior orifice and what appears to be a large separate anterior papillary muscle. The upper right hand panel is a three-dimensional image from below and shows the main orifice indicated by the asterisk, and the tension apparatus that supports the imperforate anterior orifice. The lower right hand panel views the mitral valve from above and shows the imperforate anterior orifice indicated by the black arrow. There is significant mitral valve regurgitation which is seen in the right hand color Doppler panel. The left hand panel shows the thickened leaflets, but the precise mechanism is unclear. The image on the left shows the two atrioventricular valves from above during systole, while the one on the right shows the mitral valve from below. The Mitral Valve in Congenitally Corrected Transposition of the Great Arteries Although the major atrioventricular valve pathology involves the morphologic tricuspid valve, abnormalities of the mitral valve are encountered fairly frequently (41). It is important to recognize these abnormalities, as they can have a profound effect on outcome when a double switch or atrial switch and Rastelli pathway is chosen. There may be mitral valve leaflet dysplasia, multiple papillary muscles, an associated cleft, or a straddling mitral valve (Fig. Three-dimensional echocardiography provides superior evaluation of the morphologic mitral valve. The cleft, shortened chordae, and multiple papillary muscles are readily identified. In some cases the valve is competent at presentation, however when an anatomical repair is performed, the mitral valve is unable to accommodate the associated systemic pressure. Unlike the normal mitral valve which can cope with left ventricular dilation in the setting of normal left ventricular function many of these valves cannot due to the pathologic abnormalities mentioned above. Straddling of the Mitral Valve This is an important lesion to identify and invariably occurs in hearts with an abnormal ventriculoarterial connection, in particular ventriculoarterial discordance or double outlet right ventricle with an anterior aorta. The aortic or anterior leaflet is always involved with chordal apparatus from that leaflet having variable attachments within the right ventricle. In some instances they insert into the crest of the interventricular septum while in others they insert into a papillary muscle on the proximal or distal interventricular septum (Fig. Of note there is invariably an associated cleft in the mital valve with an eccentric orifice, pointing more toward the ventricular septal defect. The mitral valve is usually competent due to the chordal support, however recognition is important, because if the chordae are inadvertantly cut during repair, the valve will become regurgitant. Although two- dimensional echocardiography has superior temporal resolution making identification of fine chordal structures more accurate, inferior spatial resolution can impede precise location of the abnormal chordae. As the mitral valve and its straddling chords insert in an anterior location, they are readily identified in a full volume data set obtained from the parasternal long-axis view. Precise location of the straddling mitral valve at its site of insertion is important, as this dictates whether a biventricular or single ventricle operative pathway is followed (42).
Like the anterior leaflet discount apcalis sx 20 mg with visa impotence journal, the posterior leaflet is supported by both papillary muscles cheap apcalis sx 20 mg amex impotence causes. The posterior leaflet frequently has a series of scallops which are supported by chordal structures (Fig cheapest apcalis sx erectile dysfunction brochure. B: This montage shows the normal papillary muscle arrangement of the mitral valve. The image on the left demonstrates the anterior papillary muscles with mitral chordal insertion. The image on the right shows the posterior papillary muscle (black arrow) and shows how it is blended in the posterior wall of the left ventricle. Three-dimensional echocardiography has provided the ability to assess not only the morphology, but the dynamic changes that are seen in the mitral valve. This technique emphasizes that the leaflets are not flat, but consist of a series of undulations which are in part related to the chordal attachments (13) (see Fig. There are several chordal support mechanisms that can be appreciated in pathologic specimens (19), as well as by real-time three-dimensional echocardiography. The strut chordae insert into the undersurface of the anterior leaflet and in part result in the appearance of a series of peaks and valleys in the anterior leaflet when seen in real-time from the left atrial view (Fig. These chordae run onto the belly of the leaflet, whereas the rough zone chordae insert into the tip of the anterior leaflet (Fig. The strut chordae are important in situations of ischemic mitral valve regurgitation where they are displaced, resulting in leaflet tethering and regurgitation (20). Next, there are commissural chords, which by definition, support the two mitral valve commissures, while the cleft chordae support the scallops of the posterior or mural leaflet. The zones of coaptation of the leaflets roll over each other, providing the maximum area of contact, which maintains valve competence. It is when pathologic processes disturb this relationship that regurgitation is seen. Pathologic specimens and surgical inspection, along with saline testing of the valve provide a suboptimal assessment of the functional nature of the mitral valve; three-dimensional echocardiography overcomes this limitation (21). The three-dimensional image from below show the thickened leaflets with shortened chordae. The image on the right is a two-dimensional Doppler and shows the turbulent jet through the valve. B: This montage is from a case with mitral valve stenosis due to thickened chordae, with virtual fusion of the anterior papillary muscle to the leaflets, as seen by the lower right hand three-dimensional echo. The upper left hand image shows the two-dimensional appearance of the anterior papillary muscle and leaflet. The restrictive functional orifice is clearly seen in the lower right hand panel (black arrow). The two papillary muscles are evenly placed such that they maintain constant tension on the leaflets throughout systole (Fig. The angle between the papillary muscle tips and the mitral annulus is about 70 to 80 degrees, as determined by three-dimensional echocardiography. This is achieved by the ability to map the coordinates of all of the components of the mitral valve througout the cardiac cylce and relate them to each other. This papillary muscle angle does not change throughout the cardiac cycle, despite the influence of ventricular contraction and torsion of the left ventricle. The chordae fan out as they insert into the leaflets, but the direction of pull on the leaflets is relatively vertical, avoiding tension on the leaflets. The papillary muscle morpholgy is also variable, in particular with regard to the number of heads. The papillary muscles are derived from left ventricular myocardium and blend in with the wall of the left ventricle, playing an important role in maintaining normal left ventricular function (Fig. Indeed if they are removed during valve replacement, then this results in left ventricular dysfunction (22). Mitral Valve Pathology: An Integrated Morphologic and Hemodynamic Approach Although it is tempting to divide pathology into regurgitant and stenotic lesions, this is artificial, since congenital mitral valve abnormalites can result in both. We will therefore describe the types of pathology and their echocardiographic appearances together. Mitral Valve Dysplasia and Hypoplasia In mitral valve dysplasia, the leaflets are thickened, the interchordal spaces obliterated and the papillary muscles deformed (7,23,24). The valve often shows global hypoplasia and is the most common lesion associated with isolated congenital mitral stenosis, though this may occur in conjunction with regurgitation ( Videos 43. Therefore, when viewed as a functional unit, the thickened leaflets and obliterated interchordal spaces result in tethering and deficient zones of coaptation. These features are readily appreciated by three-dimensional echocardiography, both from a left atrial and left ventricular view (Fig. As well, additional images can be obtained by cropping the heart from above, which demonstrate the mitral valve and its support apparatus. This is of particular value for imaging the chordal apparatus, as they are imaged in the axial plane which provides optimal resolution. The left ventricular view is of particular importance for imaging the commissures, because they are imaged more reliably from below that from the left atrial view. This is due to fact that the normal mitral leaflets billow toward the left atrium, just as a parachute does when seen from the sky. With the addition of color Doppler, sites of mitral regurgitation can be identified and related to valve pathology (see Fig. It is possible to image the vena contracta, which represents the en face view of the regurgitant jet. The area of this jet correlates well with absolute volume regurgitation, providing a semiquantitative assessment of the degree of regurgitation (Fig. As well, it provides an accurate road map to the location of the regurgitation, providing vital information for the surgeon when planning repair. With the addition of pulsed or continuous wave Doppler the hemodynamic mean gradient can be determined. However, this is directly related to cardiac output, with an underestimation in states of low output. Unfortunately, in the majority of children, it is not possible to calculate a pressure half-time which can provide an absolute valve area in adults. Dysplasia of the Posterior or Mural Leaflet Occasionally, a young child is seen who has significant mitral valve regurgitation secondary to dysplasia of the posterior or mural leaflet (Videos 43. The regurgitant jet extends along the total length of the valve orifice and may respond to surgical repair by leaflet extension. Three- dimensional echocardiography provides optimal imaging of this entity, as well as an accurate assessment of the severity of regurgitation.
Associated with this visual loss was numbness and tingling in the right hand and fngers apcalis sx 20 mg without a prescription erectile dysfunction only with partner, drooping of the right side of the face purchase 20mg apcalis sx mastercard green tea causes erectile dysfunction, and signifcant diffculty in producing words order 20 mg apcalis sx with amex erectile dysfunction over 65. All of these symptoms occurred without warning and cleared completely within 20 minutes. The patient’s neurologic examination was normal, and the only positive fnding was a loud bruit over his left carotid artery. When deprived of blood fow for only 20 seconds, the Clinical brain is reduced to a state of unconsciousness; if cir- Connection culation is not reestablished in 4 to 5 minutes, this state is usually irreversible. This 750 mL is supplied by the two carotid consumes 20% (50 mL/min) of the total available arteries and the basilar artery, each contrib- oxygen. The total sumption demand an extensive yet smoothly func- intracranial blood volume is 100 to 150 mL tioning delivery system, the cerebrovascular system. The larger extracerebral vessels In primates, small discontinuities possess a readily identifable adventitial plexus of the media occur at the points of nerves, but autoregulation persists even after where larger intracranial arteries branch. Clinically, these so-called media gaps pathetic infuences on cerebrovascular tone are relate to the location of saccular aneurysms quite limited. Hypoxia or weak support progressively balloons to form hypercarbia or both result in cerebral vasodi- an aneurysm. The intracranial extracerebral vessels are con- tained within the subarachnoid space (Fig. Clinical As these vessels and their branches penetrate the Connection brain, they become intracerebral. A small peri- vascular extension of the subarachnoid space is Clinically, the effects of oxygen formed alongside these penetrating vessels. This and carbon dioxide on cerebro- Virchow-Robin space extends from the general vascular tone can be manipulated in patients subarachnoid space and gradually thins as the with elevated intracranial pressure. Disease processes in the sub- arachnoid space such as sub- arachnoid hemorrhage and meningitis may gain entrance into the brain tissue itself as they Intracranial arteries differ considerably in fll the perivascular spaces surrounding the histologic composition from those found else- penetrating vessels. The adventitia is thin and intravascular space and the brain is suggested by contains no paravascular supporting tissue, no the result of dyes (such as trypan blue) being external elastic lamina, and no vasa vasorum. Most of the Histologically, intracranial veins are thin- body tissues including the meninges are stained, walled structures consisting mostly of collagen but not the brain. The blood-brain barrier with minimal elastic tissue, little muscle, and selectively prevents the penetration of certain no valves. The The common carotid artery begins on the right tight junctions and nonfenestrated composition as the brachiocephalic trunk bifurcates into the of the capillary endothelium impede the passage common carotid and the subclavian arteries. The left common carotid artery branches from the arch of the aorta at its highest point. Each com- mon carotid artery lies within the carotid sheath, Clinical with the internal jugular vein lateral and the vagus Connection nerve dorsal (lying between the artery and vein). Similarly, in infants, the capillary endothelium is immature Clinical and fenestrated, allowing substances such as Connection bilirubin to enter. Elevation of bilirubin in the neonate may lead to staining in the basal gan- Clinically, the carotid bifurcation glia, thalamus, and ependyma, a condition is a common site of atheroscle- called kernicterus. This laterally (without branching) to enter the carotid condition occurs commonly with trauma and canal in the petrous portion of the temporal bone. The petrous segment is contained receive blood from the carotid and vertebral arter- within the carotid canal of the petrous portion of ies, respectively (Fig. This portion of the artery has circulatory systems are described: an anterior or several small branches to the inner ear. The cav- carotid system and a posterior or vertebral-basilar ernous segment is contained within the cavern- system. On the left, the cerebellar hemisphere and ventral part of the temporal lobe have been removed. It gives rise to the central artery of the ret- tentorial (which supplies the tentorium), the ina and eventually communicates freely with the inferior hypophysial (which supplies the poste- external carotid artery via its lacrimal, ethmoidal, rior lobe of the pituitary gland), and the cavern- supraorbital, supratrochlear, and nasal branches. Recurrent artery of Heubner Anterior cerebral artery Medial striate arteries Anterior communicating artery Lateral striate arteries Middle cerebral artery Superior hypophysial arteries Thalamogeniculate arteries Thalamoperforate Posterior cerebral artery arteries Anterior choroidal artery Superior cerebellar artery Pontine arteries Anterior inferior cerebellar artery Anterior spinal artery Figure 22-4 Perforation zones for major penetrating arteries on the base of the brain. Chapter 22 The Blood Supply of the Central Nervous System: Stroke 293 A-1 Segment. The A-1 segment begins at the Clinical carotid bifurcation and passes over the optic tract Connection and chiasm to reach the anterior communicating artery (Figs. Along The capillaries of these ves- its course, branches supply portions of the ante- sels aid in the formation of the rior hypothalamus. Anatomically, the anterior communicating artery is seldom a Anterior Choroidal Artery distinct vessel but more often constitutes a com- plex network or web of vessels. Small perforators The anterior choroidal artery usually arises from from the anterior communicating artery supply the internal carotid just proximal to its bifur- the genu of the corpus callosum, septum pellu- cation. The anterior choroidal artery crosses the optic tract and passes toward Clinical the medial surface of the temporal lobe (Figs. The penetrating branches of the anterior choroidal artery supply the hippocam- The anterior communicating artery pus, the amygdaloid nucleus, and the ventral forms an important potential source and entire retrolenticular part of the posterior of blood fow between the two hemispheres, limb of the internal capsule. In addi- anterior choroidal artery supplies the choroid tion, the anterior communicating artery is plexus of the inferior horn of the lateral ventricle another one of the frequent sites of saccular (Fig. It frontal branches to the superior frontal gyrus is the cerebral artery most often occluded. It ends as the paracentral artery to divided into a proximal (M-1) segment and a dis- the paracentral lobule. It passes posteriorly in close rela- or the lenticulostriate arteries, arise and supply tion to the corpus callosum, supplying penetrating the dorsal part of the head and the entire body vessels to the corpus callosum, septum pellucidum, of the caudate nucleus, most of the lentiform and fornix. Terminal branches include the precu- nucleus, and the internal capsule above the neal artery, which supplies the precuneus, and the level of the globus pallidus. Like the recurrent posterior callosal artery, which supplies the sple- artery of Heubner, these penetrating arteries run nium of the corpus callosum (Fig. Chapter 22 The Blood Supply of the Central Nervous System: Stroke 295 to penetrate the lateral two-thirds of the anterior angiographic shape of the superior and inferior perforated substance (Fig. The branches of both the superior and inferior trunks are named accord- ing to the region they supply. These include the Clinical precentral or prerolandic, the central or rolan- Connection dic, the postcentral or postrolandic, the anterior Clinically, the lenticulostriate ves- and posterior parietal, the angular, the posterior sels are the most common site of temporal, and the posterior occipital arteries. These trunks travel deep in the lateral (sylvian) fssure along A stroke in the cortical distribu- the insula. Generally, the superior involvement, global aphasia also results; with trunk supplies branches to the frontal and pari- nondominant hemisphere involvement, the etal lobes, and the inferior trunk supplies the neglect syndrome or amorphosynthesis results. The Postcentral artery Posterior parietal artery Angular artery Central artery Precentral artery r Middle cerebral artery Figure 22-6 Major arterial territories on the lateral surface of the hemisphere. This combination of The vertebral arteries are the frst branches of signs is the lateral medullary or Wallenberg the subclavian arteries. They then enter lary junction and travels in the shallow median the cranial cavity through the foramen magnum groove on the ventral surface of the pons to end ventral to the hypoglossal nerves, travel along at the midbrain. As the join to form the basilar artery near the pontomed- basilar artery travels along the pons, it supplies ullary junction (Figs. After entering the cranial cavity, each verte- These vessels penetrate the pons as paramedian, bral artery gives rise to a posterior spinal artery short circumferential, and long circumferential that descends along the posterolateral aspect of arteries (Fig.