The course of the prevertebral segment of the vertebral artery: anatomy and clinical significance

BACKGROUND

The so called "pretransverse or prevertebral segment" of the vertebral artery is defined from its origin at the subclavian artery to its entry into the respective transverse foramen. In surgery, angiography, and in all noninvasive procedures it is of great importance to know the exact details of the course and the origin of this segment of the vessel as well as in which percentages real abnormalities can be found.

METHODS

The VI segment of the vertebral artery was investigated both in anatomic preparations and clinical studies. A total of 402 vertebral arteries were evaluated (70 anatomic preparations in different forms, 181 patients, 95 angiographies of the aortic arch, and 86 color coded doppler sonographies).

RESULTS

A contorted course was found in 157 (39%) cases. The plane of tortuosities demonstrated by the respective vessels was found to be horizontal in 40 (44.9%) cases, sagittal in 30 (33.7%) cases, and frontal in 19 (21.4%) cases. In 51 (32.5%) cases the contorted pathway was on the right side, and in 106 (68%) cases, on the left. A hypoplasia was found in 16 (10%) cases--11 (4.8%) right and 5 (2.2%) left. We further differentiated the convexity lying either medially or laterally in the transverse or frontal plane, or oriented dorsally or ventral in the sagittal plane. The exact location of the origin of the artery on the circumference of the subclavian artery (47% cranial, 44% dorsal, 3% ventral, 6% caudal) and also the average values of length and diameter are described. No significant differences between tortuous and nontortuous vessels were found with respect to length and diameter. A real abnormality of the origin of the vertebral artery was found in 8 (3.5%) cases.

CONCLUSIONS

The described morphologic variations and frequencies of the VI segment of the vertebral artery have clinical applications in a wide field of pathologies in that region. To know about these findings seems to be very important not only in diagnosis (angiography, color coded doppler sonography) but also in their surgical and endovascular treatment.

Rotational vertebral artery occlusion: a mechanism of vertebrobasilar insufficiency

OBJECTIVE

Symptomatic dynamic changes in blood flow secondary to vertebral artery compression with rotational head motion are evaluated in a series of patients as a cause for posterior circulation transient ischemic attacks. These cases are classic examples of rotational vertebral artery occlusion and allow for the discussion of the anatomic basis, angiographic features, and treatment options.

ILLUSTRATIVE CASES

In our series, symptoms of vertebrobasilar insufficiency were reproducible with rotational head movement. Compression of the vertebral artery was demonstrated angiographically. The correct site of occlusion of the vertebral artery was apparent only by dynamic angiography with progressive head rotation. All of the patients presented in the illustrative cases had occlusion at the C2 level; however, one patient had been previously misdiagnosed and another had an additional site of occlusion. The anatomic course of the vertebral artery is described in addition to the sites of rotational occlusion.

CONCLUSION

Rotational vertebral occlusion is an important cause of vertebrobasilar symptoms, which may lead to permanent neurological deficit if left undiagnosed. Dynamic angiography is the established method of diagnosis. Great care must be taken to avoid misdiagnosing the site of occlusion or missing a second occlusive site. For this reason, it is crucial to have a thorough understanding of the anatomic course of the vertebral artery and the muscular and tendinous insertions, which may cause rotational occlusion. The decision for treatment must be based on the site of occlusion as well as the assessment of the patient as a surgical candidate. A review of the literature reveals that surgical treatment is effective and must be considered to avoid further morbidity.

The influence of the blunting of the apex on the flow in a vertebro-basilar junction model

The apex of human vertebro-basilar junctions can be sharp-edged or blunted. In the present study, the effect of blunted apex on the flow in vertebro-basilar junction models is investigated. We compared the flow phenomena in a series of junction models with blunted apices and confluence angles 45, 85, and 125 deg with the flow phenomena in a series of junction models with sharp-edged apices and the same range of confluence angles, studied in a previous paper (Ravensbergen et al., 1996b). The blunting of the apex appears to have an effect on the size of the local recirculation area near the apex and the prevailing low velocities. Large recirculation areas are found in the models with blunted apices, especially in those with small confluence angles. In addition, the blunting of the apex has no influence on the flow further downstream, nor on the structure and strength of the secondary flow field. Furthermore, a blunted apex appears to be a geometric risk factor for atherosclerosis. This supports the hypotheses that recirculation areas and low wall shear stress influence the development of atherosclerotic plaques.

Three-dimensional magnetization-prepared time-of-flight MR angiography of the carotid and vertebral arteries

Three-dimensional magnetization-prepared (MP) MR angiography (MRA) was applied to the carotid and vertebral arteries by using ECG triggering, a slab selective RF inversion pulse, centric phase encoding and acquisition during diastole. Both theoretically and experimentally, the MP MRA sequence was shown to perform well in cases where there was substantial blood replenishment during the inversion time TI (>330 ms). In comparison with standard, ungated, steady-state 3D time-of-flight MRA in 13 consecutive volunteers, the MP MRA images demonstrated better background suppression with less artifact and generally had more uniform vessel depiction. The MP MRA sequence was generally superior for portraying vessels exhibiting high pulsatility such as the carotid siphon. However, in distal vessels with slow flow and incomplete blood replenishment, the MP MRA technique was inferior due to increased loss of vessel signal. The reasons for this increased signal loss are identified and improvements to the MP MRA sequence are suggested.

The suboccipital cavernous sinus

The authors studied the microsurgical anatomy of the suboccipital region, concentrating on the third segment (V3) of the vertebral artery (VA), which extends from the transverse foramen of the axis to the dural penetration of the VA, paying particular attention to its loops, branches, supporting fibrous rings, adjacent nerves, and surrounding venous structures. Ten cadaver heads (20 sides) were fixed in formalin, their blood vessels were perfused with colored silicone rubber, and they were dissected under magnification. The authors subdivided the V3 into two parts, the horizontal (V3h) and the vertical (V3v), and studied the anatomical structures topographically, from the superficial to the deep tissues. In two additional specimens, serial histological sections were acquired through the V3 and its encircling elements to elucidate their cross-sectional anatomy. Measurements of surgically and clinically important features were obtained with the aid of an operating microscope. This study reveals an astonishing anatomical resemblance between the suboccipital complex and the cavernous sinus, as follows: venous cushioning; anatomical properties of the V3 and those of the petrous-cavernous internal carotid artery (ICA), namely their loops, branches, supporting fibrous rings, and periarterial autonomic neural plexus; adjacent nerves; and skull base locations. Likewise, a review of the literature showed a related embryological development and functional and pathological features, as well as similar transitional patterns in the arterial walls of the V3 and the petrous-cavernous ICA. Hence, due to its similarity to the cavernous sinus, this suboccipital complex is here named the "suboccipital cavernous sinus." Its role in physiological and pathological conditions as they pertain to various clinical and surgical implications is also discussed.

Magnetic resonance angiographic analysis of atlanto-axial rotation: anatomic bases of compression of the vertebral arteries

The aim of this study was to identify the functional anatomic factors involved in the maintenance or disturbance of flow in the vertebral aa. during atlanto-axial rotation. Fourteen healthy volunteers were studied by magnetic resonance angiography (MRA) by a three-dimensional sequence in phase contrast centered on the vertebral aa. at the level of the cranio-cervical junction before and after left rotation of the head. A decrease in the signal intensity of the arterial flow was sought for. The results were compared to the posterolateral development of the loop of the vertebral a. in its atlanto-axial segment in neutral position, and to the measurement of the angular opening between the atlas and axis in dynamic position. Seven subjects also had a three-dimensional CT study (3D CT) of the bony relations of C1 and C2 after rotation. In 4 subjects a disturbance of flow in the right vertebral a. was observed in the transverse foramen of C2. This occurred when two factors were combined: an under-developed atlanto-axial arterial loop and a C1-C2 angle exceeding 35 degrees in maximal rotation. In the other subjects a well-developed arterial loop and/or a C1-C2 angle of less than 35 degrees in maximal rotation were factors preserving the arterial flow. The risk factor associated with the C1-C2 angle seemed correlated in 3D CT with loss of the usual asymmetric character of rotation. A clinical application is reported with a case combining chronic rotational dysfunction of the cranio-cervical junction as shown by 3D CT and complete compression of the vertebral a. in MRA, confirmed by conventional angiography. A knowledge of this physiopathologic mechanism allows clinical detection and evaluation of the risk of any effect of pathology of the cranio-cervical junction on the vertebral a.

Surgical anatomy of the anterior cervical spine: the disc space, vertebral artery, and associated bony structures

OBJECTIVE

To elucidate the relationships between the neurovascular structures and surrounding bone, which are hidden from the surgeon by soft tissue, and to aid in avoiding nerve root and vertebral artery injury in anterior cervical spine surgery.

METHODS

Using six cadaveric spines, we measured important landmarks on the anterior surface of the spine, the bony housing protecting the neurovascular structures in the lateral disc space, and the changes that occur during the discectomy with interbody distraction of the vertebral bodies. The measurements included the distance between the medial borders of the longus colli muscle at the level of each interspace; the width and height of each disc space at the midline; the width and height of the costal process; the distances between the cranial tip of the uncinate process (UP) and the vertebral body (VB) above and from the tip of the UP to the vertebral artery; the anteroposterior diameter or the extent of the disc spaces in the midline; the height at the midpoint of the distracted disc space; the UP-VB distance in distraction; and the width of the visible nerve root.

RESULTS

The distance between the medial borders of the longus colli muscles increased in a rostral to caudal direction. The height of the UP was shortest at C4-C5 and greatest at C5-C6; the width was narrowest at C4-C5 and widest at C6-C7. The width of the costal process measured from the VB to the anterior tubercle was narrowest at C2-C3 and widest at C6-C7. The midpoint height of the costal process was smallest at C6-C7 and tallest at C4-C5 and C5-C6. The nondistracted UP-vertebral artery distance was the shortest at C2-C3 and longest at C4-C5. The nondistracted UP-VB distance averaged 1 mm at C2-C3 and C6-C7 and 1.5 mm at C4-C5. The height of the distracted disc space was shortest at C2-C3 and C6-C7. The UP-VB distance after distraction was greatest at C4-C5. Only at the C2-C3 interspace was the nerve always above the process. The vertebral artery entered the foramen transversarium of C6 in all the specimens.

CONCLUSION

Although avoiding unfortunate injury is not always possible, understanding the locations and relations among the anatomic features is the only safeguard against unwarranted damage.

Magnetic resonance angiography of the origins of the supraaortic arteries: comparison of single and double volume acquisition 3D time of flight

PURPOSE

The authors have optimized the technique of Magnetic Resonance Angiography (MR-angio) in the study of the origins of the supraaortic arteries.

METHODS

Twenty healthy volunteers, mean age 21.5, were studied with MR-angio of the origins of the supraaortic arteries; a 1 T superconductive magnet (Impact) with body coil was used. All the volunteers were studied using Time of flight (TOF), and two acquisition techniques: single volume FISP (fast imaging with steady-state precession) 3D TONE (titled optimized non-saturating excitation) and double volume FISP 3D TONE with 30% overlapping. The images were acquired on the axial plane following the positioning of three pre-saturation pulses.

RESULTS

Regarding the visualization of the different components of the origins of the supraaortic arteries, a statistical analysis was worked out using the Mann Whitney test (p < 0.05); there was no statistically significant difference between two techniques. Regarding the visualization of the various segments (origin, 1/3 proximal, 1/3 middle, 1/3 distal), although the double volume did on the one hand allow a better visualization of the more distal vascular components (statiscally significant difference), on the other it induced the presence of artefacts with decreased the quality of the image as a whole.

DISCUSSION

In our experience TOF 3D technique with TONE and single volume has well identified the origin of the vertebral arteries, while, in several cases, TOF 3D technique with TONE and double volume did not permit the visualization of the origin of the vertebral arteries due to the presence of the artefacts from overlapping.

CONCLUSION

From our experience we have established that the TOF 3D technique with TONE and single volume makes it possible to obtain MR-angio of a high diagnostic quality in a short time (10-15 mn).

Evaluation of the vestibular system by magnetic resonance angiography

This report describes the normal arterial patterns of the vestibulocerebellar regions visualized by magnetic resonance angiography. Variations in the vertebrobasilar arterial system are described, limitations in imaging are discussed, and collateral connections within the cerebellar vessels and the circle of Willis are reviewed. Clinical correlations are defined between the vestibular nuclei, the associated intraaxial tracts, and with specific posterior cerebral and brain stem arteries.

Origin of the anterior spinal artery

This investigation was designed to extend our present knowledge of the origin of the anterior spinal a. and is based on 80 brains of human cadavers. The anterior spinal a. is usually formed rostrally by the union of the anterior spinal branches from the intracranial segments of the vertebral aa. In this study, we observed three different locations of the origin of the anterior spinal a. Each type has different characteristics. A bilateral origin (type I) was present in 60 specimens (75%). This type could be further subdivided according to the caliber of the arteries, into the following subtypes: "balanced" (type Ia 42.5%), right-dominated (type Ib 17.5%), and left-dominated (type Ic 15%). A unilateral origin (type II) was found in 9 specimens (11.3%), and an origin in an intervertebral transverse anastomosis was demonstrated in 11 (13.8%). In all cases, the anterior spinal a. had an average caliber of 1.145 +/- 0.12 mm.

A morphological study on the V2 segment of the vertebral artery

Morphometric investigations on the V2 segment of the vertebral artery, showed that, it did not have a constant calibre during its course within the foramina transversaria. The vertebral artery, entering the foramina transversaria reduced its calibre and further continued to reduce until C3 level, above C3 it began to reincrease its calibre and at C1 level reached its largest calibre. Measurements on the muscular thickness, showed an increase as ascending through the foramina transversaria. The widening and narrowing of the vertebral artery within the foramina transversaria was attributed as tortious artery or congenital anomaly. This study showed that it was the normal anatomy of the artery within the foramina transversaria.

The location of the vertebral artery foramen and its relation to posterior lateral mass screw fixation

STUDY DESIGN

This study evaluated the anatomic relationship between the vertebral artery foramen and the posterior midpoint of the cervical lateral mass using cervical spine specimens.

OBJECTIVES

To determine quantitatively the location of the vertebral artery foramens from C3 to C6 and their relationship to the posterior midpoints of the lateral masses.

SUMMARY OF BACKGROUND DATA

Anatomic studies of the cervical nerve root and facet relative to lateral mass screw placement have been addressed. It is necessary to know the correct location of the vertebral artery foramen during lateral mass screw placement to minimize the risk of injury to the vertebral artery.

METHODS

Forty-three cervical spines from C3 to C6 were directly evaluated for this study. Anatomic evaluation included the dimension of the vertebral artery foramen and its projection on the posterior aspect of the lateral mass. The vertical distance from the posterior midpoint of the lateral mass to the posterior border of the vertebral artery foramen, and the angle between the parasagittal plane and the line connecting the posterior midpoint of the lateral mass with the lateral limit of the vertebral artery foramen, were also measured.

RESULTS

The vertical distances from the posterior midpoint of the lateral mass to the vertebral artery foramens at C3-C6 averaged from 9.3 to 12.2 mm for male and female specimens. The average angles medial to the sagittal plane, between the parasagittal plane and the line connecting the posterior midpoint of the lateral mass with the lateral limit of the vertebral artery foramen, from C3 to C5, were found to range from 6.0 degrees to 6.3 degrees for male specimens and from 5.3 degrees to 5.5 degrees for female specimens. At C6, the average angles lateral to the sagittal plane, between the parasagittal plane and the line connecting the posterior midpoint of the lateral mass with the lateral limit of the vertebral artery foramen, were 6.4 degrees for male specimens and 5.4 degrees for female specimens.

CONCLUSIONS

The present study indicated that there is no risk of damaging the vertebral artery if a screw is directed perpendicular to the posterior aspect of the lateral mass at C3-C5 and 10 degrees lateral to the sagittal plane at C6 starting at the midpoint of the lateral mass.

The inner diameter of human intracranial vertebral artery by color Doppler method

In 50 healthy subjects the internal diameter of the intracranial vertebral artery were measured by echocolor doppler method. The diameter of left vertebral a. was greater than that of the right in most subjects (58%); the mean left/right difference was statistically significant (p < 0.05). Analyzing men and women separately, the difference remained significant only in women (p < 0.05). A significant correlation was found between vertebral a. diameter and sex (p < 0.01). The vertebral a. diameter had a tendency to increase with age, that reached significance only for the left vertebral one. No significant correlation was found between body surface area and vertebral a. diameter.

The influence of the angle of confluence on the flow in a vertebro-basilar junction model

In earlier work, it was demonstrated that the flow in models of the vertebro-basilar junction is highly three-dimensional and the geometry exerts a strong influence on the hemodynamics. The morphology of the vertebro-basilar junction is very variable amongst individuals. In a study of 85 human vertebro-basilar junctions, the angle between the vertebral arteries varied between 10 and 160 degrees. To determine how the flow is influenced by this geometrical parameter, the flow is studied both experimentally, with laser Doppler velocimetry, and numerically, with a finite element package. A series of junction models is used with a range of confluence angles (45, 85 and 125 degrees). It appears that the angle of confluence has a strong influence on the structure and strength of the secondary flow field. The secondary velocities persist far downstream. Furthermore, near the apex, a region with low velocities is present. The larger the confluence angle is, the larger this region is, and even backflow may occur. In addition, the occurrence of atherosclerotic plaques in 85 human vertebro-basilar junctions is studied. Only one preferential location was found: the apex, the other plaques seem to be randomly distributed. The magnitude of the confluence angle of junctions with sharp-edged apices has a significant influence (p = 0.006) on the occurrence of a plaque at the apex. Apparently, a large confluence angle is a geometrical risk factor for atherosclerosis.

Vulnerability of vertebral artery in anterolateral decompression for cervical spondylosis

This study aimed to provide anatomic data for the location of the vertebral artery and offer an optimal approach for lateral cervical decompression that minimizes the risk of injury to the vertebral artery. Anatomically, there has been little study documenting the safe zone to prevent vertebral artery injury during the resection of the uncinate process or uncovertebral joint during the lateral decompression of the nerve root. The transverse foramen and its related parameters were measured on dry cervical spines from C3 to C7. The cadaveric cervical spines were dissected to determine a method for resection of the uncovertebral joint with decreased risk of vertebral artery laceration. The anteroposterior diameters of the transverse foramina gradually decreased from C6 to C3. The transverse diameters of the transverse foramina were smaller at C5. The interforaminal distance, width of the vertebrae, interuncinate distance, and the distance from the lateral tip of the uncinate process to the medial border of the transverse foramen became smaller in more cephalad vertebrae. After subtotal vertebrectomy and opening of the anterior walls of the transverse foramina, the resection of the uncovertebral joint and lateral decompression became easier and safer. Anatomic measurements obtained in this study indicate the vertebral artery to be at risk during decompression of the more cephalad vertebrae. The lateral decompression can be completed under direct vision with smaller rongeurs and curettes, rather than with high speed burr after deroofing the anterior walls of transverse foramina and retracting the vertebral artery laterally.

3D phase contrast EPI MR angiography of the carotid arteries

OBJECTIVE

Our goal was to compare 3D phase contrast (PC) echo planar imaging (EPI) MRA of the carotid and vertebral arteries with conventional 3D PC in volunteers and patients.

MATERIALS AND METHODS

The carotid arteries of 12 volunteers were imaged with conventional and EPI 3D PC sequences. The visibility for each of seven carotid and four vertebral segments was qualitatively assessed. Signal intensity and homogeneity determinations were performed on the source images. Three patients with known carotid artery disease were also imaged with the same protocol.

RESULTS

EPI reduced 3D PC data acquisition time from 459 to 32 s (factor of 15). Both techniques permitted full assessment of the common carotid artery, the bifurcation, as well as the proximal internal carotid artery (ICA), external carotid artery (ECA), and vertebral arteries. Visualization of the distal ICA/ECA and vertebral arteries was inferior with EPI compared with the conventional acquisition. In all patients, lesions as established by X-ray angiography were seen to equal advantage with both techniques.

CONCLUSION

EPI 3D PC MRA renders diagnostic images of the proximal carotid system. The considerable reduction in data acquisition time must be weighed against poorer image quality.

Microsurgical anatomy of the atlantal part of the vertebral artery

BACKGROUND

Microanatomy of the vertebral artery has been the subject of multiple studies. However, none of them has covered every aspect of microvascular anatomy of the atlantal part of the vertebral artery.

MATERIALS AND METHODS

Microsurgical anatomy of the atlantal part of the vertebral artery was studied in 14 cadaveric specimens. The artery was dissected using the standard microsurgical technique under operative microscope magnification. The atlantal part of the vertebral artery was divided into five segments: the foraminal, sagittal, transverse, medial condylar, and dural. The length of each segment was measured, as was the diameter of the artery. The branches of this part of the artery were identified and the distance between the point of dural entry of the artery and the midline of the atlanto-occipital dura was measured. Distance between the mastoid tip and the artery and the distance between the mastoid tip and the tip of C1 transverse process were measured.

RESULTS

Results of all measurements are summarized in tables and text. We discuss various anomalies, branches, and lesions of the vertebral artery and surgical approaches with new methods of managing diseases in this area.

The blood supply of the trigeminal nerve root, with special reference to the trigeminocerebellar artery

The vasculature of the 29 roots of the trigeminal nerve was examined after india ink and gelatin had been injected into the vertebrobasilar arterial system. The trigeminal arteries were most often noted to arise from the superolateral pontine branch of the basilar artery (89.66%), and from the peduncular cerebellar branch of the anterior inferior cerebellar artery (75.86%). The trigeminocerebellar artery supplied two roots (6.89%) of the trigeminal nerves. The number of trigeminal arteries ranged from two to six, and their diameters ranged from 100 to 510 microns. Anastomoses among them were seen in 37.93% of the cases. The arteries formed the vascular rings around 58.61% of the roots. The motor portion of the trigeminal nerve most often received blood from the superolateral pontine artery (79.31%). The same artery most commonly supplied the rostral part of the sensory portion, which corresponded to the ophthalmic division of the trigeminal nerve. The superolateral artery, together with the inferolateral pontine artery and the peduncular cerebellar branch of the anterior inferior cerebellar artery, irrigated the middle part of the sensory portion, which corresponded to the maxillary division. The caudal part of that portion, which corresponded to the mandibular division, was commonly perfused by the peduncular cerebellar branch of the anterior inferior cerebellar artery. In this article, we discuss the possible clinical significance of the anatomic data observed.

Variable-angle uniform signal excitation (VUSE) for three-dimensional time-of-flight MR angiography

A spatially asymmetric RF pulse that improves the uniformity of blood signal intensity and vascular contrast in three-dimensional (3D) MR angiography (MRA) is presented. The pulse, called variable-angle uniform signal excitation (VUSE), was designed to provide uniform signal response and improved contrast for blood flowing through a 3D imaging volume during a FLASH sequence. The VUSE excitation profile was optimized on the basis of the number of pulses seen by the blood, which varied with the velocity of through-plane flow, repetition time, and slab thickness with the maximum flip angle at the flow exit constrained at 90 degrees. The theoretical results show that the optimal RF pulse gives more uniformity for flow signal than does a linear ramp excitation profile or a Gaussian pulse combined with a presaturation pulse. After truncation and filtering of the VUSE pulse in the time domain, the general shape of the VUSE RF excitation profile is maintained, but the maximum flip angle is reduced. The arteries of the neck in a healthy volunteer were imaged with the VUSE pulse, a constant flip angle (flat) pulse, and a linear ramp pulse in flow-compensated 3D MRA sequences. The VUSE pulse produced the most uniform signal as evidenced by the lowest relative dispersion of signal along the left vertebral artery (18.0 versus 26.4 to 23.6 for the other studies). F-distribution tests also showed that the signal distribution obtained with the VUSE pulse in a 3D FLASH sequence was statistically different from that for the flat and the linear ramp pulses.

Nonlinear excitation profiles for three-dimensional inflow MR angiography

An RF excitation pulse for three-dimensional (3D) time-of-flight (TOF) MR angiography (MRA) with a nonlinear excitation profile was numerically calculated under the condition of uniform vessel signal across the excitation volume (slab), and the superiority of the optform pulse as compared with conventional RF pulses and TONE pulses was demonstrated. For this purpose we acquired MRA of the lower leg and of the carotid and vertebral arteries in a 30-year-old healthy volunteer. Although the flow velocity ranges in these two anatomic locations are different by about a factor of 10, in both cases the corresponding optform pulse provided the best signal homogeneity at the highest level.

Comparison of left and right vertebral artery intracranial diameters

BACKGROUND

The vertebral artery is vulnerable to mechanical injury, especially in the region of the first and second cervical vertebrae, with resultant thrombus and/or emboli formation, often found at the vertebro-basilar junction. Such vascular injuries and associated neurological insults have been documented repeatedly in the literature as following cervical spine manipulation, when movements of the head and neck can cause compression and/or stretching of the vertebral artery and alterations in its blood flow. This has particular clinical relevance if a patient has a hypoplastic vertebral artery. Such persons may be considered at risk as regards vascular accidents following manipulation of the cervical spine. The aim of this study was to measure and compare the intracranial diameters of the left and right vertebral arteries in groups of black and white male and female South African subjects.

METHODS

Cadaver material from 58 specimens was processed for light microscopy, and measurements of inner (lumen only) and outer (lumen, tunica intima, and tunica media) diameters taken and compared, using the t-test.

RESULTS

Data analysis revealed a significant difference between the left and right vertebral artery intracranial diameters in the white female group only (N = 8).

CONCLUSIONS

Such a statistically significant difference implies a difference of biological importance and it is suggested that this particular group of subjects may be a high-risk group as regards vascular accidents following cervical spine manipulation.

Quadrant anatomy of the articular pillars (lateral cervical mass) of the cervical spine

Knowledge of the relevant anatomy is important when developing a strategy for introducing screws into the lateral masses to secure internal fixation devices. This paper defines key bony landmarks and their relationship to critical neurovascular structures and identifies a location for safe placement of cervical articular pillar (lateral mass) screws. Measurements of anatomical landmarks in 10 spines from human cadavers aged 61 to 85 years were made by caliper and a metric ruler. Landmarks were the lateral facet line, rostrocaudal line, medial facet line, intrafacet line, and medial facet line-vertebral artery line. The average distances and ranges were recorded. Such great variance existed in measurements from spine to spine and within the same spine as to render averages clinically unreliable. Dissection revealed that division of the articular pillar into four quadrants leaves one, the superior lateral quadrant, under which there are no neurovascular structures; this may be considered the "safe quadrant" for placement of posterior screws and plates.

The anterior operative approach to the cervical vertebral artery

BACKGROUND

Vertebral arterial trauma continues to be a perplexing diagnostic and therapeutic challenge. Operative management is often required despite improved radiologic interventions for these injuries. Accounts of the operative approaches to anterior cervical vertebral artery injuries have been limited.

STUDY DESIGN

We reviewed our experience with anterior cervical vertebral arterial trauma in 53 consecutive patients requiring operative management during a 14-year period. In seven patients, the vertebral arterial injury was identified at urgent surgical intervention either for an expanded cervical hematoma or active bleeding. The remaining injuries were identified by arteriographic investigation of penetrating cervical trauma. The injuries were equally distributed between the three anatomic zones of the anterior cervical vertebral artery. The general features of the operative approaches that were used to manage these injuries were the emphasis of the study.

RESULTS

The anterior approaches to patients with vertical arterial trauma were effective in controlling injuries in all cases. Proximal and distal ligation of the artery adjacent to the injury site was accomplished in 95 percent of the patients. Associated major cervical injuries in 43 percent of the patients (carotid artery, eight patients; pharyngoesophageal, six patients; and neurologic, nine patients) contributed to the postoperative morbidity rate and the overall mortality rate of 10 percent.

CONCLUSIONS

The surgeon approaching vertebral arterial trauma should have a clear appreciation of the deep anterior cervical anatomy to expedite the operative management and avoid unnecessary complications related to a misdirected surgical dissection. The descriptions of the operative techniques used in this clinical experience can aid the surgeon in managing patients with vertebral vascular trauma.

Comparative anatomy of the baboon and the human cervical spine

STUDY DESIGN

The anatomy of baboon and human cervical spines were compared by measuring adult, cadaveric specimens.

OBJECTIVE

The objective of the study was to compare human and baboon cervical motion segments to determine whether the baboon provides a suitable model for spinal research.

SUMMARY OF BACKGROUND DATA

Several studies have examined the quantitative anatomy of the human cervical bones and ligaments. Several animal species have been used for cervical spine research; however, no studies have validated whether the animal models resemble the human cervical spine closely enough to provide generalizable data.

METHODS

Multiple morphologic parameters were measured directly from nine baboon and six human adult cadaveric cervical spine specimens. The bone structure and geometry of each of the seven cervical vertebrae were analyzed; the structure and histology of the ligaments were measured; and histomorphometry of the vertebrae was performed.

RESULTS

The architectural composition and geometry of individual cervical vertebrae of baboons and humans were similar at each level. The proportional relationship of bone and ligament structures in the two species was almost identical. There were, however, several differences: 1) The baboon spine was about half the size of the human spine; 2) its vertebral arteries were encased fully within the C1 lateral mass; 3) its uncovertebral joints were more prominent; 4) its vertebral endplates were more concave; 5) its pedicles were thinner; 6) its transverse processes were longer; and 7) its spinous processes were horizontal and nonbifid.

CONCLUSIONS

The geometry and anatomy of the baboon cervical spine closely resemble that of the human cervical spine. It therefore provides an excellent model for in vivo and in vitro research.

The piglet as a model for cerebral circulation: an angiographic study

The aim of this study was to further investigate the possibilities and limitations of the newborn piglet as a model for neonatal cerebral circulation and injury. The precerebral and cerebral circulation was visualized by aortic arch contrast injection and selective injections into internal carotid and vertebral arteries. Due to the well-developed collateral circulation, it is not possible to produce severe focal cerebral ischemia in the piglet by ligation of extracranial arteries. It is possible to produce a modified common carotid artery which supplies mainly intracerebral tissues and is accessible for continuous measurements of cerebral blood flow.

Vertebral artery location in relation to the vertebral body as determined by two-dimensional computed tomography evaluation

STUDY DESIGN

This study analyzed the precise two-dimensional location of the vertebral artery within cervical vertebrae as determined by measurements obtained from axial computed tomographic images of the cervical spine.

OBJECTIVE

To determine the margin of safety necessary to avoid vertebral artery laceration during central decompression and lateral nerve root decompression for cervical spinal stenosis.

SUMMARY OF BACKGROUND DATA

Laceration of the vertebral artery is a rare but potentially catastrophic complication of anterior decompressive surgery of the cervical spine.

METHODS

The mean, standard deviation, and 95% confidence interval of the mean of measurements localizing the vertebral artery within the vertebral body were calculated from 50 transaxial computed tomography images of each of the second through sixth cervical vertebrae.

RESULTS

Both the mean interforaminal distance (from 25.90 +/- 1.89 mm at C3 to 29.30 +/- 2.70 mm at C6) and the average distance of the posterior border of the foramen transversarium from the ventral border of the spinal canal (from 2.16 +/- 1.18 mm at C3 to 3.53 +/- 1.56 mm at C6) increased from C3 to C6.

CONCLUSIONS

According to our measurements, the risk of vertebral artery laceration is greater at more cephalad vertebrae during lateral extension of central decompressive procedures and lateral nerve root decompression. Because of the variability of these parameters between individuals, accurate individual preoperative localization of the vertebral arteries is recommended.

The far lateral/combined supra- and infratentorial approach. A human cadaveric prosection model for routes of access to the petroclival region and ventral brain stem

A far lateral approach to the ventral brain stem, lower clivus, and anterior foramen magnum is described. Methods for further exposure of the superior petroclival region by incorporating a subtemporal craniotomy and posterior petrosectomy are also demonstrated. Eight sequentially illustrated steps depict this technique. The far lateral/combined supra- and infratentorial exposure is a comprehensive surgical approach that provides direct access to the entire anterior and lateral brain stem and craniovertebral junction. It minimizes brain-stem retraction and maximizes visualization of the neurovascular structures.

Microsurgical anatomy of the intracranial part of the vertebral artery

We studied the intracranial portion of the vertebral artery and its branches in 11 cadaveric specimens. We evaluated the course of vessels and their dimensions (external diameter and length), as well as relationships between each of them. The vertebral artery was larger on the left side in two cases, on the right in five cases, and equal on both sides in four cases. The right and left vertebral arteries joined each other forming the basilar artery at the level of the pontomedullary junction in four cases, 2 mm below it in one case, and 1 to 7 mm above it in six cases. We divided all branches of the intracranial vertebral artery into two groups: the medial branches and the lateral branches. Two major types of medial branches were observed: the anterior spinal artery and the branches of the foramen caecum. The origin of the anterior spinal artery was located 6.5 mm (5-11 mm) proximal to vertebrobasilar junction on the right and 8.5 mm (6-17 mm) on the left. The anterior spinal artery was absent on the right in two cases and on the left in one. Branches arising from the vertebral artery to the foramen caecum were found in four brains. Lateral branches originated from the posterolateral or lateral aspect of vertebral artery. The posterior inferior cerebellar artery, the largest branch of the vertebral artery, was included in this group. Other branches were mostly located between the origin of the posterior inferior cerebellar artery and the vertebrobasilar junction. Forty-six lateral branches originating from the vertebral artery were found in 11 brains (26 on the right and 20 on the left). Lateral branches widely anastomosed with perforators from the basilar artery, posterior inferior cerebral artery, and the anterior inferior cerebellar artery.

Blood flow dynamics in the vertebrobasilar system: correlation of a transparent elastic model and MR angiography

PURPOSE

To describe the flow patterns in a model of the vertebrobasilar artery and use these observations to explain the appearance of the flow on the MR images.

METHODS

We created an anatomically precise, transparent elastic model of the human vertebrobasilar artery containing a basilar tip aneurysm and perfused the model with non-Newtonian fluid which has similar rheologic properties to blood. Flow patterns in the vessels were directly observed. MR angiogram images were obtained with commercially available two-dimensional time-of-flight, three-dimensional time-of-flight, and 3-D phase-contrast MR angiographic pulse sequences, and they were correlated with the directly seen flow patterns. Quantitative flow velocity measurements were performed with 2-D cine phase-contrast MR angiography and correlated with the flow measured with an electromagnetic flow meter.

RESULTS

Visualization studies showed the dye stream patterns in the vertebrobasilar arteries to be extremely complex and variable. During the MR experiments we found that often the same segment of a vessel could appear very different depending on the pulse sequence. In some instances, the model experiments helped to explain the MR appearance of the vessels. Flow profiles measured with 2-D cine phase contrast were found to be consistent with those measured directly with an electromagnetic flow meter.

CONCLUSION

Clear elastic models can be used to duplicate the flow in human cranial vessels and thus provide a unique means to observe these flow patterns directly. The flow patterns helped to explain the variation in appearance of the vessels and the artifacts with different MR angiography pulse sequences. The artifacts depend on both the geometry of the vessel and the flow pattern within it. Two-dimensional cine phase-contrast MR provides temporal flow field information that is directly related to physiological information about flow volumes and velocity patterns.

Vertebral artery dissection due to minor neck trauma

Vertebral artery dissection has been previously reported following minor head and neck trauma. Such activities as rapid head turning, tennis, yoga, and vigorous exercise have been implicated. We report a case of vertebral artery dissection following minor neck trauma suffered in a volleyball game. The anatomy of the vertebral artery, pathophysiology of dissection, and emergency department recognition and treatment of this disorder are discussed.

Intracranial vertebrobasilar system: MR angiography

PURPOSE

To determine the reliability of magnetic resonance (MR) angiography in depicting normal vascular anatomy and its usefulness in detecting vascular disease compared with those of digital subtraction angiography (DSA).

MATERIALS AND METHODS

Sixty patients with symptoms referable to disease of the vertebrobasilar system were examined with MR angiography and DSA.

RESULTS

In patients with normal DSA results, all vertebral arteries (VAs) and basilar arteries (BAs) were also visualized with MR angiography. MR angiography demonstrated 117 of 120 superior cerebellar arteries and 80 of 90 posterior inferior cerebellar arteries but only 30 of 58 anterior inferior cerebellar arteries. MR angiography demonstrated disease of the VAs and BAs with 100% sensitivity. Stenoses were differentiated from occlusions in all cases. However, the degree of stenosis was overestimated in 63% of patients. In six patients with occlusive disease, collateral flow was correctly analyzed with selective saturation.

CONCLUSION

Despite its limitations, MR angiography is a clinically important noninvasive technique for screening patients for macroangiopathy of the posterior arterial supply to the brain.

Carotid and vertebral artery blood flow in left- and right-handed healthy subjects measured with MR velocity mapping

The goal of the study was to establish normal carotid artery flow rates in left-handed and right-handed individuals as a standard against which patients with carotid artery disease could be compared. Antegrade and retrograde flow were measured in the ascending aorta, in the right and left common, internal, and external carotid arteries, and in the vertebral arteries of 12 healthy subjects. Five subjects were right-handed, five left-handed, and two ambidextrous. Measured flow rates were as follows: common carotid arteries, 360-557 mL/min (mean [+/- standard deviation], 465 mL/min +/- 52); internal carotid arteries, 132-367 mL/min (mean, 265 mL/min +/- 60); external carotid arteries, 113-309 mL/min (mean, 186 mL/min +/- 51); vertebral arteries from 133-308 mL/min (mean, 244 mL/min +/- 43); and cerebral circulation, 546-931 mL/min (mean, 774 mL/min +/- 134). All right-handed subjects had higher flow rates in the left internal carotid artery than in the right, and all left-handed subjects had higher flow rates in the right internal carotid artery (P = .007). There were no significant differences in left and right common carotid artery flow rates between left- and right-handed subjects. The standard deviation of a single measurement was 5%. The flow rates were similar to those obtained previously with other techniques and could be used as a normal standard.

Endolymphatic sac blood flow versus cochlear blood flow following intravenous administration of isosorbide in guinea pigs

Endolymphatic sac (ES) blood flow (ESBF) and cochlear blood flow (CBF) were measured in different groups of guinea pigs by laser-Doppler flowmetry (Advance Laser Flowmeter, Model ALF 2100) after the intravenous administration of 70% isosorbide (1.6 ml/kg). The measurements were made under general anesthesia with intraperitoneal pentobarbital sodium. Respiration was controlled by a respirator after tracheotomy, and blood pressure was monitored through the femoral artery (Gould Statham P23 ID Pressure Transducer). For ESBF measurements, a probe was placed on the right ES after entering the posterior cranial fossa via the dorsal approach. For CBF measurements, a probe was placed on the basal turn of the right cochlea via the ventral approach. Isosorbide was administered intravenously through the jugular vein for 60 s. Both ESBF and CBF increased immediately after administration, reached a peak within 3-6 min and decreased gradually to their initial baseline levels in 11-15 min. Both blood flow changes almost always corresponded to systemic blood pressure changes, although a slight delay was observed in blood pressure compared to the blood flow. The magnitude of the CBF response tended to be greater than that of the ESBF response (p < 0.1). This may result from the anatomical differences in the two blood supplies, i.e., from the vertebral artery (CBF) and the external carotid artery (ESBF).

Use of histomorphometry in the assessment of fatal vertebral artery dissection

AIM

To assess morphometrically the structural changes, which occur with ageing, along the length of the vertebral artery.

METHODS

A series of 36 vessels were removed at necropsy from subjects aged between 9 months and 86 years. Image analysis was used to measure the medial width, the circumference, the intimal: medial area ratio and the adventitial: medial area ratio along each artery. The artery from a case of fatal vertebral artery dissection, which occurred after a game of cricket and then chiropractic neck manipulation, was also examined in the same manner. The proteoglycan accumulation in the media was quantified using an eyepiece graticule.

RESULTS

The vertebral arteries were, on average, larger around the origin of the vessel from the subclavian artery, and the adventitia were relatively thicker at this point, and also after piercing the dura mater. The media were much thinner within the intracranial segment and pronounced intimal thickening occurred with increasing age. The dissected artery showed undoubtable pre-existent structural abnormalities, in the form of massive proteoglycan accumulation, which predisposes an artery to dissection.

CONCLUSIONS

These data should help pathologists faced with the task of assessing the underlying structural integrity of the vessel wall in cases of vertebral artery injury.

Advantages of color Doppler imaging for the evaluation of vertebral arteries

Assessment of the vertebral arteries is often difficult with conventional duplex ultrasonography. This study of 60 patients aimed to determine the potential advantages of color Doppler imaging over conventional duplex ultrasonography in the evaluation of vertebral arteries, specifically three extracranial segments of these vessels. Both methods allowed visualization of the vertebral artery in the midcervical course (V2 and distal V1 segments) in all subjects. Color Doppler imaging appeared more effective for visualization of the V0 and the proximal V1 segments (on the right side in 88% of patients and on the left side in 73%). Conventional duplex ultrasonography imaged the ostium on the right side in 80% of patients and on the left side in 65%, but was difficult and time-consuming. Visualization at the atlas loop (V3 segment) was rarely successful with duplex sonography, whereas color Doppler imaging visualized the vertebral artery on the right side in 87% of patients and on the left side in 85%. Color Doppler imaging allows better visualization of the proximal and distal segments of the vertebral arteries, compared to conventional duplex ultrasonography.

[Visualization of the normal basilar artery and its branches using magnetic resonance angiography (MRA)]

MRA (magnetic resonance angiography) is besides duplex sonography at present the only noninvasive method for vascular visualisation. The technical fundamentals and our initial experiences with this new technique of angiography in the visualisation of the basilar artery are presented in the following article.

The measurement of the calibers of the branches of the aortic arch: a statistical investigation of 430 living subjects using ultrasonic tomography

Using Doppler ultrasound, we have measured the calibers of the branch arteries of the aortic arch in 430 subjects (230 men and 200 women; age range: 18 to 84 years). These included: the brachiocephalic trunk, the subclavian arteries, the common carotid arteries, the internal and external carotid arteries, and the vertebral arteries. Statistical analysis of the values obtained yielded a number of interesting results. The average caliber of the arteries of the women examined was lower than that of the men. Nonetheless, the statistical difference in the arterial diameters of the two sexes was not significant, with the exception of the left subclavian artery. In the case of this artery, its caliber was larger among the men than the women. However, this relationship was not confirmed in the right subclavian artery. The left vertebral artery was larger than the right one. This difference was statistically significant among the women (p < 0.05), but not among the men (p = ns). The right subclavian artery was larger than the left one by a statistically significant margin (p < 0.05), but the statistical significance may be accounted for by the values in the women alone (p < 0.02). When the men were considered separately, the difference between right and left did not achieve statistical significance (p = ns). There was no statistically significant correlation between arterial caliber and either height or body weight. Furthermore, the caliber of the arteries examined increased with age, but not in a statistically significant manner. The mean values of the single arteries examined were lower than those described by the principal investigators of the cadaveric studies to which we have referred. However, with three exceptions, the differences were not statistically significant. In the case of the subclavian and internal and external carotid arteries, our values were lower by a statistically significant margin.

The vertebral artery: its relationship with adjoining tissues in its course intra and inter transverse processes in man

The authors study the vertebral artery from its origin to termination, especially in its course inter and intra transverse process and show its relation to venous and nervous structures, as well as its behavior toward adjacent conjunctive tissue. They discuss the relation of the anatomy to the physiopathology of the vertebral artery and come to the conclusion that the vertebral artery is fixed to adjacent structures in the fibrous osteomuscular tunnel by means of a continuous lamina of collagen along its entire course and that there is considerable independence between the artery and the branches of these final nerves.

Imaging of the intracranial vertebrobasilar system using color-coded ultrasound

BACKGROUND

Anatomic variety and difficult accessibility of the vertebrobasilar arteries pose considerable problems to conventional ultrasound. We evaluated the diagnostic potential of transcranial color-coded sonography in the distal part of this system.

METHODS

We insonated the intracranial section of the vertebrobasilar arteries through the foramen magnum window in 24 healthy individuals using a Doppler color flow imaging system in connection with a 2.5-MHz sector transducer. Magnetic resonance images in special inclination planes were performed and compared with the color-coded duplex images in five cases.

RESULTS

The B-mode image of the craniocervical junction and the intracranial parenchymal structures in addition to the color-coded blood flow allowed an unambiguous identification of the vertebrobasilar arteries (vertebral artery, 96%; basilar artery, 79%; and posterior inferior cerebellar artery, 50%). Blood flow velocities were measured considering the insonation angles: vertebral arteries, 50/24 cm/sec (30 degrees); basilar artery, 59/28 cm/sec (4 degrees); and posterior inferior cerebellar artery, 56/30 cm/sec (20 degrees) [peak systolic/end diastolic blood flow velocity (mean angle correction)].

CONCLUSIONS

Transcranial color-coded sonography enables accurate identification and differentiation of the intracranial vertebrobasilar arteries and improves accuracy of Doppler measurements. It may prove useful for evaluation of tortuosity and for hemodynamic studies in this vascular territory.

[Three-dimensional analysis of arteriography in human posterior circulation (preliminary report)]

In earlier articles it was suggested that there is a relation between vertigo and the posterior circulation. This study was designed to ascertain the course of the branches of the vertebral artery and the basilar artery, as well as the principal blood vessels of the vestibular nucleus by using radiographic three-dimensional observation. We studied 27 human brains (17 males, 10 females) fixed with the arterial embalming method at the Department of Anatomy of Kawasaki Medical School. The results were as follows: 1. Many variations in the course of the anterior inferior cerebellar artery and the posterior inferior cerebellar artery were observed, but the most frequent pattern, observed in 56% of our subjects, was the anterior inferior cerebellar arteries originating from the basilar artery and the posterior inferior cerebellar arteries from the vertebral artery. 2. Measurement of the inside diameter of both vertebral arteries showed the diameter of the left side to be thicker than that of the right side. 3. Perforating branches in the brain stem consisted of the pontine branches from the basilar artery and small branches from the anterior inferior cerebellar artery. Moreover, the transverse section showed a large number of them to originate from the ventral part of the brain stem.

Practical choices of fast spin echo pulse sequence parameters: clinically useful proton density and T2-weighted contrasts

With the development of fast spin echo (FSE) MRI techniques, T2-weighted images of the brain may be obtained much more quickly than when using conventional spin echo techniques (CSE), because made the individual echoes on the FSE pulse sequence are phase encoded, allowing acquisition of the same spatial information as in CSE with less excitations. The pulse sequence parameters (echo train length, bandwidth, echo spacing) are discussed. Images were obtained on four volunteers using both CSE and FSE while varying repetition time, echo time and matrix. Comparison for signal intensity gray-white differentiation, fat and CSE signal, arifacts and vascular resolution showed that FSE images comparable in quality to those of CSE can be obtained in less than half the time. A practical choice of FSE parameters is recommended for clinical use. However, artifacts, possibly related to CSF and vascular pulsation, of which the radiologist should be aware, were identified on the FSE images.

Microscopic anatomy of the human vertebro-basilar system

Concerning the structure of connective-muscular components the authors studied the walls of the terminal segments of the vertebral arteries as well as the basilar artery, utilizing the following staining methods: Azan modified by Heidenheim, Weigert's resorcin-fuchsin, and Weigert modified by van Gieson. It was established that wall of the vertebro-basilar system exhibits a mixed structure, muscular and elastic, by means of which the vessels are adjusted to the specific blood circulation conditions. Thus, vertebral arteries show in the most external layer of tunica media an evident external elastic lamina. In contrast, in the basilar artery the elastic tissue is localized mainly in the tunica media, and is distributed heterogeneously. In its caudal segment the elastic fibers are situated in the most internal layer of tunica media, and in the cranial segment the elastic component is homogeneously distributed in the whole of tunica media.

Microvascular anatomy of foramen caecum medullae oblongatae

The foramen caecum (FC) is a triangular-shaped fossa situated in the midline on the base of the brain stem, at the pontomedullary junction. Although this area is known to have a very high concentration of brainstem perforating vessels, its microvascular anatomy has not been studied in detail. The purpose of this study was to detail the microvasculature of this territory. Twenty unfixed brains were injected with silicone rubber solution and dissected under a microscope equipped with a camera. The origin, course, outer diameter, and branching pattern of the perforators were examined. The total number of perforators found in the 20 brains was 287, with an average (+/- standard deviation) of 14.35 +/- 1.24 perforators per brain (range seven to 28). Their origin was as follows: right vertebral artery in 52 perforators (18.11%); left vertebral artery in 35 (12.19%); basilar artery below the anterior inferior cerebellar artery (AICA) in 139 (48.43%); basilar artery above the AICA in 46 (16.02%); AICA in 10 (3.48%); and anterior spinal artery in five (1.74%). Most of the perforators arose as sub-branches of larger trunks; their average outer diameter was 0.16 +/- 0.006 mm while that of trunks was 0.35 +/- 0.02 mm. These anatomical data are important for those wishing 1) to study the pathophysiology of vascular insults to this area caused by atheromas, thrombi, and emboli; 2) to plan vertebrobasilar aneurysm surgery; 3) to plan surgery for vertebrobasilar insufficiency; and 4) to study foramen magnum neoplasms.

[Comparative anatomical characteristics of the histological structure of the arteries at the base of the brain in various mammalian orders and species]

In 30 mammalian species specific peculiarities of the arterial structure has been revealed and their dependence on the type of the brain blood supply has been demonstrated. The architectonics of the blood supply sources is correlated with the structure of the wall in the arteries, immediately participating in dumping the blood stream during its transport to the brain.