Like a hole in the head: Development, evolutionary implications and diseases of the cranial foramina

Cranial foramina are holes in the skull through which nerves and blood vessels pass to reach both deep and superficial tissues. They are often overlooked in the literature; however they are complex structures that form within the developing cranial bones during embryogenesis and then remain open throughout life, despite the bone surrounding them undergoing constant remodelling. They are invaluable in assigning phylogeny in the fossil record and their size has been used, by some, to imply function of the nerve and/or blood vessel that they contained. Despite this, there are very few studies investigating the development or normal function of the cranial foramina. In this review, we will discuss the development of the cranial foramina and their subsequent maintenance, highlighting key gaps in the knowledge. We consider whether functional interpretations can be made from fossil material given a lack of knowledge regarding their contents and maintenance. Finally, we examine the significant role of malformation of foramina in congenital diseases such as craniosynostosis.

Aberrant Right Vertebral Artery with a Diverticulum of Kommerell: Review of a Rare Aortic Arch Anomaly

The normal aortic arch branching pattern is of a three-vessel arch with the vertebral arteries arising from the subclavian arteries. There are a variety of well-known symptomatic and asymptomatic aortic branching patterns widely reported in the literature. An anomalous right vertebral artery with a diverticulum of Kommerell is an extremely rare variant, with few other cases reported in the literature. Herein, we review the embryology of the aortic arch and vertebral artery, the various types of Kommerell's diverticula and the clinical significance of this anomaly.

Origin and course of the extracranial vertebral artery: CTA findings and embryologic considerations

PURPOSE

The aim of this study was to show the different origins and courses of the extracranial VA on CTA with special emphasis on embryological considerations. The duplicated VA is an anomaly that has been assumed to predispose for dissection and to be associated with aneurysms. We report its frequency and clinical significance.

METHODS

We retrospectively reviewed CTA of 539 patients by using a contrast-enhanced CTA protocol of the VA on CT.

RESULTS

Ninety-four-point-two percent of left VA originated from left subclavian artery and entered the transverse foramen at C6 in nearly all cases. Six-point-three-percent of left VA (m = 4 %, f  = 10 %) originated from the aortic arch and entered the transverse foramen either at C4, C5 or C7 but never at C6. One case of an aberrant retroesophageal right VA originated from the aortic arch distal to the left subclavian artery and entered at C7 (0.19 %). All other right VA originated from the right subclavian artery (99.8 %) and entered between C4 and C6. We diagnosed four cases of duplicated VA (0.74 %) with a female predominance (1.9 %) without any signs of dissection on CTA. Two cases with VA duplication had intracranial arterial aneurysms.

CONCLUSIONS

The VA is a longitudinal anastomosis of segmental metameric arteries. The level of entrance into the transverse foramen indicates which metameric artery or arteries persist. Duplication corresponds to persistence of two segmental arteries and is a rare phenomenon. VA duplication might be associated with vascular lesions.

Doppler study of the fetal vertebral artery in small for gestational age fetuses with intrauterine growth restriction

OBJECTIVES

The purposes of this study were to evaluate the Doppler resistive index of the fetal vertebral artery in small for gestational age (SGA) fetuses and to examine the ability of the vertebral artery resistive index in the diagnosis of intrauterine growth restriction (IUGR).

METHODS

A total of 437 Doppler examinations of the vertebral and umbilical artery resistive indices were performed in 437 fetuses between 26 and 41 weeks' gestation. According to birth weight, fetuses were classified into 5 groups: 1, above the 10th percentile; 2, between the 10th and 5th percentiles; 3, between the 5th and 3rd percentiles; 4, below the 3rd percentile; and 5, below the 3rd percentile with an umbilical artery resistive index above the 95th percentile. Subsequently, vertebral artery resistive index values were converted into multiples of the median, and box and whisker charts were generated to evaluate differences. Finally, receiver operating characteristic curves were calculated to assess the accuracy of the vertebral artery resistive index for predicting IUGR and a low Apgar score.

RESULTS

Compared to normally grown fetuses, vertebral artery resistive index values were lower in fetuses with birth weight below the 3rd percentile, and this difference was greater in fetuses with birth weight below the 3rd percentile and Doppler anomalies of the umbilical artery. The receiver operating characteristic analysis showed that the vertebral artery resistive index diagnosed SGA fetuses and low Apgar scores poorly. However, it performed better in cases of severe IUGR with high umbilical artery resistive index values.

CONCLUSIONS

Preliminary data show that the vertebral artery resistive index diminishes in growth-restricted SGA fetuses. Doppler examination of the vertebral artery seems to identify a group of fetuses with brain sparing and severe IUGR.

Bilateral segmental agenesis of the vertebrobasilar junction: developmental and angiographic anatomy

BACKGROUND AND PURPOSE

Bilateral vertebrobasilar junction agenesis is an exceptional anatomic variation. This article explores the angiographic characteristics of this variant and its embryologic mechanisms.

MATERIALS AND METHODS

Two observations of bilateral agenesis of the vertebrobasilar junction are reported. A case of atheromatous disease of the vertebrobasilar junction is shown to highlight characteristics distinguishing such a lesion from the reported variant.

RESULTS

In the 2 reported cases, the distal segment of both vertebral arteries (VAs) and the proximal portion of the basilar artery (BA) were absent. In addition, distal connections of the BA with the posterior cerebral arteries (PCA) were also lacking. As a consequence, the remaining portion of the BA was isolated from its usual sources of blood supply, which was provided by a persistent carotid-basilar anastomosis.

CONCLUSION

The developmental mechanism underlying bilateral agenesis of the vertebrobasilar junction likely involves the anterior radicular artery of C1. This branch of the proatlantal artery normally becomes the adult distal VA and the proximal BA. The lack of cranial connection of the BA with the PCA may be secondary to the proximal vertebrobasilar agenesis and the resulting paucity of antegrade flow within the BA. Alternatively, the absence of both the proximal and distal connections of the BA could be the result of a similar, yet unknown, developmental mechanism. From a clinical standpoint, this vascular anomaly was discovered incidentally in our 2 patients, a finding consistent with the assumed congenital nature of the variant.

Association of cervical internal carotid artery aneurysm with ipsilateral vertebrobasilar aneurysm in two children: a segmental entity?

INTRODUCTION

A combination of cervical and intradural aneurysm in children in the absence of systemic disorders has previously not been reported.

CASE REPORT

We report two boys with an identical combination of fusiform cervical internal carotid aneurysm and ipsilaterally located vertebrobasilar aneurysm. They had no history of trauma, they did not display any personal or familial signs of systemic disease, and the testing for collagen disease was negative. The location and appearance of the aneurysms and the identical anatomical disposition in the patients indicated a non-randomly distributed segmental vulnerability.

CONCLUSION

The cases demonstrate primary morphological signs of a developmental error being expressed in two seemingly separate segments but linked by the hypoglossal artery. It suggests a segmental error related to this embryonic vessel. They also show that few phenotypes are specific for a genotypic disorder and highlight the importance of analysing different etiologies for aneurysm formation and anatomical disposition when taking treatment strategy decisions.

MR angiographic demonstration of bilateral duplication of the extracranial vertebral artery: unusual course and review of the literature

Duplication of the vertebral artery is a rare developmental anomaly. Duplication and fenestration are terms often used incorrectly and interchangeably in the literature. To the best of our knowledge, this is the first report to describe bilateral duplication of the extracranial vertebral artery. Bilaterally, there are 2 separate origins of each vertebral artery from the corresponding subclavian artery, with one duplicated segment entering the C7 foramen transversarium bilaterally and the other segment entering the carotid space on either side. The duplicated vessels join together at C5-C6 disk level on the left and at C4-C5 disk level on the right before continuing as one vessel in the foramina transversaria on either side. Duplication is thought to represent failure of controlled regression of 2 intersegmental arteries and a segment of the primitive dorsal aorta. This case was discovered on a 2D time-of-flight and contrast-enhanced neck MR angiogram in an 83-year-old man with cognitive decline and appears as an incidental finding without obvious clinical implications.

A rare variation of the vertebral artery

Variations of the vertebrobasilar arterial complex are important with regard to their potential clinical impact. We present an unusual case of the vertebral artery, in which the left vertebral artery in its ascent in the neck through the transverse foramina passed posteriorly between the transverse processes of C3 and C4 and supplied the posterior muscles of the neck without continuing intracranially. Albeit speculatively, we hypothesise that the variation of the vertebral artery reported here was caused by degeneration of the proximal portion of the left postcostal longitudinal anastomosis (i.e. C1 and C2 intersegmental arteries) in the context of a persistent third cervical intersegmental artery. Our case is unique in that the left vertebral artery terminated extracranially. Knowledge of the variations of the vertebrobasilar arterial complex is important for surgeons operating at the skull base, craniocervical junction, and cervical region, and for clinicians interpreting the imaging of this region.

Morphogenesis of the posterior inferior cerebellar artery with three-dimensional reconstruction of the late embryonic vertebrobasilar system

The posterior inferior cerebellar artery (PICA) shows the most variable course among the cerebellar arteries, mainly at the level of the lateral medullary segment. Based on the correlation between the level of origin and the characteristics of the lateromedullary segment, we have proposed three patterns of course of the PICA. With the aim of understanding their embryological basis we review the interrelations between the developing cerebellum and the primitive hindbrain arterial plexus through the analysis of transverse serial sections of human embryos of 22.5 and 23 mm crown-rump length. Three-dimensional reconstruction of the vertebrobasilar system has been performed to study the morphology of the vascular networks. The cerebellar primordium is vascularized by the metencephalic plexus that will form the basilar artery and the superior cerebellar arteries. Due to the development of the pontine flexure the rhomboid lips approach and the cerebellum comes into contact with the myelencephalon; thus the myelencephalic plexus represents an acquired source of vascularization for the cerebellum with respect to the metencephalic plexus. The examination of the transverse sections shows that the vertebral and basilar arteries, superior cerebellar arteries, anterior inferior cerebellar arteries, and primitive lateral vertebrobasilar anastomoses are well recognizable. The three-dimensional reconstruction of the vessels shows that the PICA is not yet defined due to the persistence of a plexus of many thin vessels at the level of the lateral aspect of the myelencephalon, indicating that its origin and course are established at the end of the embryonic period. Based on the evolution of the primitive hindbrain plexus, we suggest that in synchrony with the progressive descent of the cerebellum the branches of the myelencephalic plexus succeed with a rostrocaudal progression in feeding the cerebellum and the morphogenesis of the PICA results from the selection of portions of this plexus. The high origin of the PICA from the basilar artery could be ascribed to its development from a rostral collateral of the plexus due to an early development of the vessel at the beginning of its embryonic lifetime. Moreover, the three patterns of course of the PICA could reflect the variable retention of the primitive lateral vertebrobasilar anastomosis in the trunk of the definitive PICA, which may be related to its level of origin.

Persistent carotid-vertebrobasilar anastomoses

The persistent carotid-vertebrobasilar anastomoses (PCVBA) can be explained by an interruption of the vertebrobasilar system (VBS) embryogenesis. We present two very rare cases of persistent anastomoses: a hypoglossal artery and a type I proatlantal artery, insisting on the angiographic criteria allowing differentiation. After a brief review of the embryogenesis of the VBS, we describe the different types of persistent anastomoses (hypoglossal, type I and II proatlantal, trigeminal and otic arteries). We will insist on the potential risks, not well-known, but typical of each anastomosis. PCVBA usually are incidental findings but imaging follow-up may be required since aneurysms may develop.

[Origin and clinical significance of the vertebral arterial fenestration: report of a case]

Fenestration of the vertebral artery, different from duplication, is a rare vascular variation, which can be usually classified into extracranial, intracranial and extracranial-intracranial types. We report a case of extracranial fenestration detected by cerebral angiography, and analyze the embryologic pathogenesis and clinical significance of this variation.

[Persistent fetal carotid-vertebrobasilar anastomoses]

The primitive trigeminal, otic (acoustic), hypoglossal, and proatiantal intersegmental arteries are persistent fetal anastomoses between the carotid and vertebrobasilar circulations. These fetal anastomoses regress at roughly the rate at which the posterior communicating and vertebral arteries develop. The purpose of this study is to review the persistent fetal carotid-vertebrobasilar anastomoses with MRI and DSA.

Abnormal origin of internal thoracic and vertebral arteries

The aim of this study was to evaluate the variability of the origin of the internal thoracic and vertebral arteries after a cadaver demonstrated abnormal origins for both vessels. The arteries were studied in 60 adult cadavers and measurements taken to adjacent structures. In one cadaver the right internal thoracic artery originated from the third part of the subclavian artery (one of 120 arteries; 0.83%). The same cadaver presented with the left vertebral artery originating directly from the aortic arch between the left common carotid and left subclavian arteries. Two other cadavers also presented with abnormal vertebral arteries, making it three of 60 left vertebral arteries (5%). These results are comparable to the established range in the literature. The internal thoracic artery is used for revascularization in coronary artery diseases and as this area is also used for subclavian vein catheterization, it is important to be aware of this rare variation concerning the internal thoracic artery. This study reports an important variation in the origins of the internal thoracic and vertebral artery in a singular cadaver.

Cartilaginous development of the human craniovertebral junction as visualised by a new three-dimensional computer reconstruction technique

Serial transverse histological sections of the human craniovertebral junction (CVJ) of 4 normal human embryos (aged 45 to 58 d) and of a fetus (77 d) were used to create 3-dimensional computer models of the CVJ. The main components modelled included the chondrified basioccipital, atlas and axis, notochord, the vertebrobasilar complex and the spinal cord. Chondrification of the component parts of CVJ had already begun at 45 d (Stage 18). The odontoid process appeared to develop from a short eminence of the axis forming a third occipital condyle with the caudal end of the basioccipital. The cartilaginous anterior arch of C1 appeared at 50-53 d (Stages 20-21). Neural arches of C1 and C2 showed gradual closure, but there was still a wide posterior spina bifida in the oldest reconstructed specimen (77 d fetus). The position of the notochord was constant throughout. The normal course of the vertebral arteries was already established and the chondrified vertebral foramina showed progressive closure. The findings confirm that the odontoid process is not derived solely from the centrum of C1 and that there is a 'natural basilar invagination' of C2 during normal embryonic development. On the basis of the observed shape and developmental pattern of structures of the cartilaginous human CVJ, we suggest that certain pathologies are likely to originate during the chondrification phase of development.

Persistent primitive hypoglossal artery complicated by atrial septal defect and congenital intrahepatic shunts

During early embryogenesis, anastomoses are formed between the carotid artery and the basilar or the vertebral artery, and subsequently, these anastomoses regress. In some cases, these anastomoses remain as persistent carotid-basilar or carotid-vertebral anastomoses. Atrial septal defect (ASD), a communication between the atria at the septal level, is a congenital heart anomaly. Intrahepatic venous shunts between the portal and hepatic veins are very rare and only some are considered congenital. We present the first case report of a patient with an ASD, a persistent primitive hypoglossal artery, and congenital portahepatic shunts.

Surgical treatment of spasmodic torticollis: is there a role for microvascular decompression? With an illustrative case report

Spasmodic torticollis (ST) is a puzzling movement disorder, characterized by involuntary tonic or clonic contractions of various neck muscles. From time to time, psychogenic, extrapyramidal and neuroperipheral origins have been postulated and reflecting the variety of theories proposed, as many different treatments have been attempted, none of which has shown absolute effectiveness. Surgery of ST classically includes destructive procedures such as myotomies, stereotactically placed lesions, rhizotomies and neurectomies. The recent application of the concept of "neurovascular conflict" to ST induced several authors to perform microvascular decompression (MVD) in these patients, with encouraging and in some cases long-lasting results. Our case report joins this group. From the analysis of pertinent literature we conclude that: a. Spasmodic torticollis is probably a collection of separate clinical entities; b. Even in the so-called "ST of neuroperipheral origin" some coexising central factor must be admitted; c. Neurovascular compression underlies at least some cases of ST. Historical, anatomical, physiopathological and clinical aspects of ST are extensively discussed.

Regional cerebral flow velocity waveforms in the human fetus

The purpose of this study was to determine regional cerebral flow velocity waveforms in the human fetus. Flow velocity waveforms were determined at the level of the middle cerebral artery, vertebral artery, and intracerebellar arteries in 25 fetuses between 23 and 39 weeks' gestation. The pulsatility index was used to quantify the waveforms. Technically acceptable waveforms were obtained at all three vessels in 20 fetuses. The pulsatility index was lowest for the intracerebellar artery in all the fetuses studied. The pulsatility indices of the vertebral artery and middle cerebral artery were not significantly different. These data suggest that significant fetal regional cerebral blood flow differences occur in utero, with intracerebellar arterial resistance being lower than resistance in other regions of the brain.

Right proatlantal artery type I, right internal carotid occlusion, and left internal carotid stenosis: case report and review of the literature

A 66-year-old man presented with right cerebellar infarction and ischemic lesions in the left dorsal thalamus and right upper parietal lobe. Angiography showed occlusion of the right internal carotid artery proximal to an ipsilateral proatlantal artery type I, 70% stenosis of the left internal carotid artery, and aplasia of both posterior communicating arteries. The carotid occlusion was successfully treated by thrombendarterectomy. Persistence of a proatlantal artery is a rare condition. In relation to the 38 literature reports on proatlantal arteries, this case demonstrates the clinical significance of a persistent proatlantal artery in the evolution of atypical ischemic cerebrovascular disease.

Persistent hypoglossal artery

During embryological development, the hypoglossal artery serves as a transient anastomosis between the internal carotid artery and the vertebro-basilar system. This artery occasionally persists into adult life. Two cases of persistent hypoglossal artery we have recently encountered are reported here. The embryology, diagnosis and potential problems for carotid surgery are discussed.

Ruptured saccular aneurysm associated with duplication of the vertebral artery

A case of a ruptured aneurysm arising from a duplicated segment of the intracranial portion of the vertebral artery is reported. This particular association, which can be explained by the embryological development of the vertebral artery, has not been described previously.

Circle of Willis variant analogous to fetal type primitive trigeminal artery

Primitive caroticobasilar anastomoses are uncommon embryonic arterial connections between the carotid (anterior) and vertebrobasilar (posterior) circulations. With the exception of extracranial proatlantal intersegmental arteries, these embryonic arterial anastomoses are named according to the cranial nerves which they parallel. In this report, a previously undescribed variant circle of Willis with supraclinoid caroticobasilar anastomosis, functionally equivalent to a fetal type primitive trigeminal artery, is presented.

Persistent hypoglossal artery encountered during carotid endarterectomy

The hypoglossal artery is present as an anastomotic channel between the carotid and vertebrobasilar system for approximately one week during embryologic development. Rarely, it may persist into adulthood and may be encountered during cerebrovascular operations. We report a 76-year-old woman with a persistent hypoglossal artery and a symptomatic internal carotid stenosis treated successfully by carotid endarterectomy. A discussion of the embryology, radiology, and operative pitfalls follows.

Embryonic vascular development: immunohistochemical identification of the origin and subsequent morphogenesis of the major vessel primordia in quail embryos

The development of the embryonic vasculature is examined here using a monoclonal antibody, QH-1, capable of labelling the presumptive endothelial cells of Japanese quail embryos. Antibody labelling is first seen within the embryo proper at the 1-somite stage. Scattered labelling of single cells appears ventral to the somites and at the lateral edges of the anterior intestinal portal. The dorsal aorta soon forms a continuous cord at the ventrolateral edge of the somites and continues into the head to fuse with the ventral aorta forming the first aortic arch by the 6-somite stage. The rudiments of the endocardium fuse at the midline above the anterior intestinal portal by the 3-somite stage and the ventral aorta extends craniad. Intersomitic arteries begin to sprout off of the dorsal aorta at the 7-somite stage. The posterior cardinal vein forms from single cells which segregate from somatic mesoderm at the 7-somite stage to form a loose plexus which moves mediad and wraps around the developing Wolffian duct in later stages. These studies suggest two modes of origin of embryonic blood vessels. The dorsal aortae and cardinal veins apparently arise in situ by the local segregation of presumptive endothelial cells from the mesoderm. The intersomitic arteries, vertebral arteries and cephalic vasculature arise by sprouts from these early vessel rudiments. There also seems to be some cell migration in the morphogenesis of endocardium, ventral aorta and aortic arches. The extent of presumptive endothelial migration in these cases, however, needs to be clarified by microsurgical intervention.

[Thoracic vertebral nerve]

When studying phylogenetic transformations of the sympathetic trunk, a theoretical possibility has been substantiated that in Mammalia a caudal continuation of the vertebral nerve in the thoracic area can exist. By means of some embryological and anatomical methods, in man and in certain animals (cat, dog), together with the cervical, the thoracic vertebral nerve has been revealed. The latter has an appearance of a plexus situating on the rudimentary thoracic vertebral artery wall and is formed at the expense of the multisegmentary distribution of the gray connective branches fibers. Anatomical manifestation of multisegmentarity of the gray connective branches connections is a division of these branches into cranial and caudal fasciculi and their spreading in the foramens between the transversal processes of the thoracic vertebrae and the necks of the corresponding ribs. In Mammalia the neck and the thoracic vertebral nerves combine into the vertebral neural trunk homologous to the secondary sympathetic trunk in birds. The thoracic vertebral nerve is a roundabout way for innervation of many somatic and vegetative structures. The pathogenetic mechanisms responsible for disturbances in the cervical vertebral nerve function, probably, somehow influence the thoracic vertebral nerve.

Dysplastic vertebral artery with paradoxical infarction

A rare abnormality of the vertebral artery is described in a 63-year-old male. The right vertebral artery consisted of several minute endothelial lined channels which failed to perfuse at autopsy. The anterior spinal artery showed areas of muscular media dysplasia. These anomalies were associated with large posterior communicating arteries. The terminal event was precipitated by thrombotic occlusion of the left vertebral artery. The embryological aspect of these anomalies are discussed.

[The developmental mechanism of occipital-vertebral anastomosis (author's transl)]

Four cases of the occipital-vertebral anastomosis, demonstrated on vertebral arteriogram, were reported; three on the left side and one on the right side. The occlusion in the vertebral artery at the posterior end of the horizontal segment or the more distal segment of the vertebral artery was found in two cases and no occlusion involving the carotid and vertebral arteries was present in the remaining two cases. The direct type of the occipital-vertebral anastomosis was found in all of the four cases in the atlanto-occipital space. The developmental mechanism of the anastomosis was explained based upon the author's hypothesis on the embryonic development of the occipital artery.

Sites of transition between functional systemic and cerebral arteries of rabbits occur at embryological junctional sites

The vascular smooth muscle of cerebral blood vessels is relatively insensitive to sympathomimetic stimulation compared with muscle from systemic vessels. The transition in the vertebral artery occurs just rostral to the emergence of that artery from the foramen of the lateral process of the atlas and in the internal carotid artery just before it enters the carotid canal. These sites in the adult correspond to embryological junctions between segments of the vertebral and internal carotid arteries derived from the primitive dorsal aortas and their branches with vessels originating locally from the bilateral longitudinal neural arteries. Topographic patterns of vascular properties may in some cases be explained by the different sites of origin of their primordial mesodermal cells.

[Right vertebral artery originating from the right common carotid (author's transl)]

In the study of 273 aortic arch angiograms, one case of right vertebral artery arising from the right common carotid artery was encountered. The embryology of this anomaly and its clinical significance are discussed.

[A case of cerevical canal stenosis accompanied with congenital cervical fusion and extracranial occlusion of vertebral artery--a clinical and embryological study (author's transl)]

A case of cervical canal stenosis accompanied by congenital cervical fusion and extracerebral occlusive disease of the verebral artery was reported. A 39-year-old male was admitted to our hospital on June 5, 1976, because of his shoulder strain, motor weakness and numbness of his left hand, and gait disturbance for a couple of months. Neurological examination disclosed spastic paraparesis with positive pyramidal signs in the four extremities which was greater on the left side, and the superficial and deep sensations were diminished below C-4 dermatomes bilaterally. Spinal tap revealed crystal clear fluid under an initial pressure equivalent to 120 mm of water with a protein content of 20 mg/dl. Plain X-P and laminogram of the cervical spine showed congenital fusion of C 2-3, cervical canal stenosis and cervical spondylosis. Posterior spurring of C 3-4 was demonstrated only on the laminogram. Myelogram showed incomplete myelographic block at the site of C 3-4-5. The left retrograde brachial angiogram disclosed occlusion of the vertebral artery at the site of C3-4. where the proxymal vertebral artery anastomosed with the well developed muscular branch of the vertebral artery, taking a tortuous course at the leve of the transverse foramen of the atlas, and were opacified the distal vertebral artery and basilar artery. Each collateral flow extending from the deep cervical artery and ascending cervical artery anastomosed with the proxymal and distal portion of the occluded vertebral artery. In spite of conservative treatment for two weeks, the cord compression syndromes rather deteriorated. Posterior decompression, that is, C 2-7 laminectomy and C 3-4 partial facetectomy were performed for relieving the symptoms. The postoperative course was uneventfull and there was progressive improvement of the sensory, motor and gait disturbance. The relationship betwen the cervical canal stenosis and cervical spondylosis and their clinco-radiological problem were discussed. The close embryological relationship was very suggestive of the pathogenesis between the cervical bony lesion and congenital cervical fusion and the occlusive vascular lesion of the vertebral artery.

[The primitive otic artery, a very rare, persistent, primitive artery (author's transl)]

A very rare carotid-basilar anastomosis, the primitive otic artery, is described. In the presence of hypoplasia of the vertebral and basilar arteries and dorsal interruption of the circle of Willis, an attempt is made to explain the situation embryologically and to discuss the disadvantages associated with this condition.

Rare carotid-vertebrobasilar anastomoses with notes on the differentiation between proatlantal and hypoglossal arteries

Two cases of persistent anastomoses between the carotid and vertebrobasilar systems which have only once been previously reported are described. These are a proatlantal intersegmental artery which arises from the external carotid artery and a primitive trigeminal artery with direct anastomosis to the superior cerebellar artery. Angiographic criteria for differentiation of the proatlantal and more common hypoglossal arteries, as well as the rare persistent cervical intersegmental artery are also presented.

[Atypical termination of the vertebral artery and of the inferior posterior cerebellar artery (author's transl)]

A rare varient in the termination of the vertebral artery is described associated with a low origin of an unpaired inferior posterior cerebellar artery lying between C. 1 and C. 2. This is illustrated radiographically. An attempt is made to explain this radiologically and to classify it. Possible clinical significant of this anomaly, particularly in relation to subarachnoid haemorrhage, is discussed.

Segmental intervertebral anastomosis in subclavian steal

Segmental intervertebral arterial connections originate from normal vascular channels which are commonly seen on selective vertebral arteriography. In subclavian steal, these vessels can hypertrophy and form important collateral pathways. The significance of their haemodynamic contributions may be assessed by their multiplicity and calibre. Lateral or oblique projections in addition to frontal visualization may be required to differentiate the various transcervical channels which lie either anterior or posterior to the vertebral bodies.

The persistent hypoglossal artery

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