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Objective: Retrotransverse foramen (RTF) and retrotransverse groove (RTG) are anatomic variations of the atlas (C1) vertebrae. RTF contains an anastomotic vein connecting atlanto-occipital and atlanto-axodian venous sinuses. The purpose of this study was to analyze the arterial vascular structures running though the RTF and RTG., Methods: Three-dimensional volume rendered computed tomography angiography (3D VR CTA) images of 427 patients (264 men, 163 women; age 17-87 years) were reviewed and evaluated using the RadiAnt DICOM Viewer (version 5.0.2; Medixant, Poznan, Poland). The incidence of RTF or RTG, the incidence of the V3 segment of vertebral artery variants, and the artery vascular structures inside the RTF and RTG anatomic variation of C1 were analyzed., Results: Fifty (11.7%) atlases presented RTF anatomical variant; 113 (26.5%) atlases presented RTG anatomical variants. The incidence of the V3 segment of vertebral artery variants was 0.94% (4 of 427). Three (0.7%) were persistent first intersegmental artery and 1 (0.2%) was the fenestration of the vertebral artery on left side. In 4 cases of C1 vertebral artery V3 segmental variants, there were no RTF and RTG. No artery vascular structure was found in RTF or RTG., Conclusions: The RTF or RTG of C1 was a common anatomical variant. No arterial vascular structure runs though the RTF or RTG. The presence of C1 RTF and RTG variants had no effect on the V3 segmental course of the vertebral artery. Preoperative understanding of these variations using 3D CTA are helpful for the safe execution of the upper cervical posterior approach surgeries., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Purpose: A skeleton named Iuzu has been unearthed from an exceptional middle Holocene burial in Toca dos Coqueiros site, in Serra da Capivara National Park (UNESCO World Heritage Site, Piauí State, Brazil). During a bioarchaeological analysis of its remains, we discovered that Iuzu was suffering from rare vertebral malformations. A double foramen transversaria, the agenesis of a foramen on the atlas and the hypoplasia of the transverse process of the axis have been highlighted. We aimed to deduce the clinical consequences of the malformation on the patient's health., Methods: We proceeded to macroscopic observation and radiography of the bones, then we search for other examples of such a pathology in archaeological litterature., Result: The malformation caused vascular insufficiency that may have led to neurological lesions leading to various pains and troubles. The very rare malformations Iuzu presented have not been found on a paleoindian skeleton from South America so far., Conclusion: This case allowed us to examine the conditions of selection of individuals buried in southern Piauí during the Middle Holocene, during which time this rite does not seem to predominate.

Background: The third part of the vertebral artery (VA) coursing in vertebral artery groove (VAG) may be injured during posterior craniocervical junction approaches., Objective: The current study classifies all possible variants of the posterior arch (PA) of the atlas vertebra (C 1 ), focusing on VAG and calculates their incidence. PA and VAG morphometry is studied in correlation with gender and age. Clinical and surgical implications of recorded variants are provided in an effort to explain associated pathology. The usefulness of three-dimensional computed tomography (3D-CT) in detecting PA variants is highlighted., Materials and Methods: Two hundred and forty-four Greek adult dry C 1 were classified in types according to PA morphology [i.e. presence of an imprint or a distinct VAG and occurrence of a partially or completely ossified dorsal (PDP or CDP) or lateral (PLP or CLP) ponticle unilaterally or bilaterally]. Combined variants were also included., Results: A VAG and an imprint were detected in 42.62% and 15.16%. A PDP and CDP were observed in 18.03% and 15.98%, while a CLP and PLP in 2.05% and 1.64%, respectively. Combined PDP and PLP were detected in 2.05%, a CDP and CLP similarly to a CDP and PLP in 1.23% and a PDP and CLP in 0.40%., Conclusions: Variants' classification will contribute to an in depth understanding of the complex C 1 anatomy and may explain cases of VA entrapment and injury during PA fixation. Surgeons should carefully study 3D-CT imaging to ensure type, location, size and shape of C 1 ponticles in combination with VAG morphology and VA course before screw insertion.

Background: The retrotransverse foramen (RTF) is a nonmetric variant of the atlas vertebra that consists of an abnormal accessory foramen located on the posterior root of the transverse process and it extends from the posterior root of the transverse process to the root of the posterior arch. Its presence has been related to regional variations of the venous circulation. It is currently unknown whether the RTF is a modern or an ancient anatomic variation., Case Description: We analyzed the skeletal remains from the late-ancient Roman necropolis (II-VI centuries ad) of La Boatella (Valencia, Spain) and we found a well-preserved individual skeleton that presented with a left retrotransverse foramen in C1., Conclusions: The RTF is not a modern anatomic variation. As a result, ancient individuals had the same modifications in the regional circulation as modern subjects present today., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Study Design: Retrospective review., Objective: To evaluate the prevalence of anatomical variations of the vertebral artery at the craniovertebral junction and the posterior arch of the atlas in the US population., Summary of Background Data: Recent studies from Asia have reported a 5% to 10% prevalence of a persistent first intersegmental vertebral artery and 1% to 2% prevalence of a fenestrated artery. These anomalous vertebral artery courses lie directly over the starting point for atlas lateral mass screw insertion. The relatively high reported prevalence of these anomalies suggests that routine preoperative computed tomographic angiogram be considered prior to upper cervical fixation. We have not observed this anomaly as commonly as reported., Methods: The authors analyzed the records of 975 patients from a level I trauma center and adjacent university hospital who underwent computed tomographic angiography to evaluate the incidence of anomalous variations in the third segment of the vertebral artery. These results were compared with similar studies performed in Korea and Japan., Results: The mean age of the patients was 52.9 years. The ethnic distribution of the patients was as follows: 69.3% of the patients were Caucasian, 11% Asian, 10.8% African American, and 6% Hispanic. The prevalence of a persistent intersegmental artery was 0.01% (1/975); a fenestrated vertebral artery was 0.01% (1/975); and origin of a posterior inferior cerebellar artery was 0.4% (4/975). The incidence of these anomalies was significantly lower than those previously published from Korea and Japan., Conclusion: Vertebral artery course anomalies in the upper cervical spine were rare (0.42%) in our patient population. This finding contrasts with recent published reports from Asia, citing as high as a 10% rate of vertebral artery presence over the starting point for C1 lateral mass screw insertion. On the basis of the infrequent occurrence of this anomaly, we do not recommend routine computed tomographic angiography when planning upper cervical instrumentation., Level of Evidence: N/A

Several variations of the bony and vascular anatomy around the first and second cervical vertebrae have been reported. Failure to recognise these variations can complicate operations on the upper cervical spine. We present a patient with recent onset of cervical myelopathy due to stenosis at the C3-4 level. Preoperative evaluation identified Klippel-Feil syndrome with cervical fusion of C2-3, aplasia of posterior arch of C1, anomalous vertebral artery course and a "ponticulus posticus" of C2. The combination of these variations in a Klippel-Feil syndrome patient has never been reported. Thus, we recommend a thorough preoperative imaging evaluation, with CT scan and CT angiography or DSA, in addition to plain radiographs. This evaluation is imperative, before a cervical spine surgery, allowing a better understanding of the anatomy, in order to minimise the risks of misplacement of cervical instrumentation especially in such patients.

The current study evaluates the passage of the atlantal segment of the vertebral artery through the atlas to the cranial cavity in the case of occipitalisation, and searches for potential bony obstacles that constrict the lumen of the vertebral artery. Morphometric analysis was performed of the ossified atlanto-occipital articulation of the dry adult male skull, particularly in the region of the posterior arch of the atlas. The distance between the floor of the right groove for the vertebral artery and the occipital bone was measured using a digital sliding caliper. On the left side, measurements of the diameters of the inlet and outlet of the canal for the vertebral artery were performed using the same technique. Fusion of the left portion of the posterior arch of the atlas with the occipital bone caused significant narrowing of the space around the normally existing groove for the vertebral artery, and converted it into the canal. The size of the intracranial opening of the canal for the vertebral artery was measured as 3.8 mm x 4.7 mm, whereas the inlet to the canal was 5.4 mm x 7.0 mm. The diameter of the canal decreases, particularly at the entrance into the cranial cavity; therefore, compression of the vertebral artery within the canal seems to be possible.

Study Design: a series of 9 patients surgically treated with a novel combined pre-and retrovascular extraoral approach to lateral mass of the atlas (LMA) is examined., Objective: to describe the efficacy of combined pre- and retrovascular extraoral approach in achieving a wide exposure and aggressive resection of tumors at the LMA., Summary of Background Data: the anatomic complexity and closeness to vital neurovascular structures raise technical difficulties in the surgical access to the LMA. Although various approaches, such as transoral approach, high anterior cervical approach, anterior lateral approach, and far lateral approach, have been reported in literature, wide exposure for the tumors at the LMA remains a unique challenge., Methods: for our experience in the surgical exposure of the upper cervical spine, we have developed a combined pre- and retrovascular extraoral approach to the atlas since 2001. Nine patients with neoplastic lesions at the LMA were surgically treated through this combined approach. Reconstruction of stability was achieved by a posterior occipitocervical fusion through a posterior approach under the same anesthesia., Results: this combined approach provided an excellent surgical field exposure to ensure the successful tumor resection while preventing the vertebral artery or nerve from injury. There was no operative mortality or severe morbidity in this series. Complications included 1 instance of transient dysphagia and 2 instances of transient trouble swallowing liquids. The symptoms of local pain and pharyngeal discomfort relieved, and patients suffering from spinal cord compression recovered well with 1 level of the Frankel scale when reevaluated 3 months after operation. With a follow-up period of 16 to 100 months, 1 patient with chondrosarcoma developed local recurrence at the 14th month of postoperation and died of respiratory and circulatory failure 39 months after surgery. No evidence of local recurrence was found in other patients., Conclusion: the combined pre- and retrovascular extraoral approach provides an advantageous alternative to previous reported approaches. For selected cases with tumor lesions at the LMA, this combined approach offers more benefits, through which a wide exposure with well-protected vertebral artery favoring radical excision could be achieved without complications normally associated with transoral surgery.

Study Design: This is a technical note and review of the literature., Objective: We propose to describe a revised surgical technique of C1 lateral mass screw insertion with protection of C1-C2 venous sinus surrounding the C2 nerve root., Summary of Background Data: During C1 lateral mass screw insertion and in posterior C1-C2 fixation, iatrogenic injury of C1-C2 venous sinus results in bleeding, which is troublesome. Appropriate management of the venous sinus in this region is critical to successful surgery in this complex anatomic region., Methods: We reviewed 48 patients who underwent posterior C1-C2 fixation at our institution between September 2001 and October 2008. Twenty-four atlas screws were inserted by the originally described C1 lateral mass screw technique (group A), and 28 through a revised posterior arch and lateral mass screw technique (C1 transpedicular screw) (group B). The final group of 44 atlas screws was placed with our newly revised technique (group C)., Results: Bleeding of venous sinus was encountered in 3 group A, 2 group B, and 1 group C atlas screw insertions. The incidence rate was 12.50% (A), 7.14% (B), and 2.27% (C). Statistical comparison showed no significant difference between the groups. All the cases were followed for a mean period of 28.1 month. Four patients in group A complained of postoperative numbness in occipitocervical region. No patients in group B or group C voiced this complaint. A high fusion rate was found in all 3 groups with no signs of implant failure., Conclusion: Bleeding of C1-C2 venous sinus is vigorous and frustrating. The revised technique we describe provides theoretical and practical protection of venous sinus. In addition, the firm bony purchase of screws afforded by this technique contributes to achieving stabilization of the upper cervical spine and a high fusion rate.

Background: Patients with chronic cervical internal carotid artery occlusion (ICAO) and cerebral ischemia may benefit from revascularization. The feasibility of endovascular recanalization for chronic ICAO has been reported recently, but its safety is still unproven. We report the follow-up results of 54 chronic ICAO patients who underwent endovascular recanalization, focusing on potential vascular complications and corresponding management., Methods and Results: Endovascular recanalization for chronic ICAO was attempted in 54 consecutive patients (48 men; 69.2 + or - 9.8 years old) with either recurrent neurological deficit or objective ipsilateral hemisphere ischemia. Mean duration from occlusion documentation to the procedure was 237 + or - 327 days (range, 56 to 1424 days). Adverse events while in the hospital and during the 3-month follow-up were recorded. Successful recanalization was achieved in 35 of 54 patients (65%). Three-month cumulative stroke and death rate was 4% (2 of 54), including 1 in-hospital fatal nonipsilateral stroke and 1 in-hospital minor ipsilateral stroke secondary to systemic hypotension. Vascular complications developed in 3 of 54 patients (6%), including 1 late pseudoaneurysm formation 3 months after recanalization, 1 immediate carotid-cavernous fistula after recanalization, and 1 minor extravasation at carotid bifurcation after failed recanalization. However, no clinical sequela was noted with close follow-up and adequate management., Conclusions: Certain immediate or delayed vascular complications may develop during or after the endovascular recanalization for chronic ICAO. Although periprocedural death and stroke rate is limited in our study, further study combining neuroimaging tools and cognitive function evaluation is mandatory to assess its utility and appropriateness in patients with chronic ICAO.

Background: One of the limiting factors of C1-C2 fixation is the location of the vertebral artery (VA). The authors sought to assess the potential variations in atlanto-axial VA anatomy using computed tomography angiography (CTA)., Methods: Detailed measurements were made on digital images of 106 patients undergoing CTA at our institution (54 males, 52 females; mean age 56, range 20-86). Distances, diameters and angles of osseous and vascular elements of the atlanto-axial complex were measured., Results: Optimal C1 and C2 screw trajectories demonstrated wide variations among patients. The size of the VA groove or foramen was not predictive of exact arterial location or size., Conclusions: The size, location and path of the VA cannot be precisely predicted by the appearance of osseous structures such as the transverse foramina and/or the VA groove. CTA provides additional information regarding the atlanto-axial complex, and should be considered as a useful adjunct in the preoperative evaluation of select patients., ((c) 2008 John Wiley & Sons, Ltd.)

Background: The location of the vertebral artery on a groove on the superior surface of the posterior arch of atlas makes it vulnerable to injury during surgical procedures in this region. Knowledge of the quantitative anatomy of the vertebral artery groove is therefore necessary., Methods: In 55 dry adult atlas vertebrae, the distance of the medial edges of the vertebral artery groove were measured from the posterior midline at both the inner and outer cortices of the posterior arch of atlas. In addition, the distance between the vertebral artery grooves on either side as well as the length of the vertebral artery groove was also measured., Results: It was found that a minimum of 1.5 cm of the posterior arch could be safely exposed at both the outer and inner cortices. In addition, with mobilization of the vertebral artery from its groove on both the sides, an additional 1 cm of posterior arch could be exposed on either side., Conclusions: Exposure of the posterior arch of the atlas is an important step in surgical procedures for treatment of diverse conditions of the upper spinal cord and foramen magnum region. Injury to the vertebral artery in its position on the vertebral groove may lead to disastrous complications. The present study reveals that the neurosurgeon can safely expose up to 3.5 cm of the posterior arch of atlas and knowledge of this anatomic fact may help in planning surgical approaches.

Object: The current study evaluates the incidence of anatomical variations of the V(3) segment of the vertebral artery (VA) and the posterior arch of the atlas (C-1). Failure to appreciate these types of anatomical variations can cause catastrophic injury to the VA during posterior approaches to the upper cervical spine., Methods: In the present study, the authors analyzed the records of 1013 Korean patients who underwent computed tomography (CT) angiography to evaluate the incidence of anomalous variations in the third segment of the VA and to determine the incidence and morphometric characteristics of any detected posterior ponticuli. The authors also hoped to determine any specific imaging features that might indicate a VA anomaly around the craniovertebral junction., Results: The mean age of the patients was approximately 55.7 years and the prevalence of a posterior ponticulus was 15.6%. The incidence rate of a posterior ponticulus in the male population was 19.3%, whereas in the female population it was 12.8%. The incomplete type of posterior ponticulus was more common than the complete type. The mean age of the patients with an incomplete posterior ponticulus (55.7 years) was significantly younger (p = 0.018) than the mean age of patients with a complete posterior ponticulus (57.6 years). The incidence rate of a persistent first inter-segmental artery was 4.7% and the incidence rate of a fenestrated VA was 0.6%. The area of the C-1 transverse foramen on the abnormal side was significantly smaller than that of the contralateral normal side., Conclusions: The shape of the C-1 posterior arch and the third segment of the VA are heterogeneous. Therefore, preoperative radiological studies should be performed to identify any anatomical variations. Using preoperative 3D CT angiography, we can precisely identify an anomalous VA and significantly reduce the risk of VA injury.

Our aim was to describe the technique and clinical results of preoperative embolization of cervical spine osteoblastomas. We treated 3 patients with these tumors with transarterial embolization and subsequent surgical excision. In all 3 patients, distal access to the tumor-supplying vessels was gained with a microcatheter and embolization was performed with polyvinyl alcohol particles. No complications occurred. Surgical resection was performed in all patients without relevant bleeding. The postoperative course was uneventful in all patients. Preoperative embolization is a valuable adjunct to the surgical treatment of osteoblastomas of the cervical spine.

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.

During color Doppler examination of a 41-year-old man who presented with vertigo, a right vertebral artery could not be found. Both MR angiography and digital subtraction angiography revealed a large anastomotic vessel between the right internal carotid and vertebral artery. It was thought to be type I proatlantal artery. Furthermore, the external carotid arteries were bilaterally absent. Although each vascular anomaly mentioned above is rare, it even more rare for these variations to occur simultaneously., (Copyright American Society of Neuroradiology)

Objective and Importance: Aneurysmal bone cysts (ABCs) are benign and expansile osteolytic lesions that can occur in any location in the spine, including the craniovertebral junction. Aggressive resection followed by bone grafting has been the mainstay of treatment, with selective arterial embolization as a presurgical adjunct. Complete excision of these lesions at the craniovertebral junction is associated with high surgical morbidity. We report a case of successful treatment of an ABC of the atlas in a child with selective arterial embolization alone., Clinical Presentation: A 10-year-old girl presented with persistent neck pain after a snowboarding accident. Computed tomography and magnetic resonance imaging of the cervical spine revealed an expansile cystic mass involving the right lateral mass of C1. Digital subtraction angiography revealed a tumor blush, which, along with the cystic appearance of the lesion, was consistent with an ABC., Intervention: The arterial feeders to the lesion were selectively embolized with polyvinyl alcohol particles. Three sessions of embolization were required to eradicate the blood supply to the lesion completely., Conclusion: Complete surgical resection of ABCs at the craniovertebral junction can be associated with high morbidity secondary to the highly vascular and destructive nature of these lesions. The case discussed here demonstrates the viability of selective arterial embolization as a primary and stand-alone modality of treatment.

Persistent proatlantal artery type 1 is one of the four anastomotic vessels between the carotid and vertebrobasilar arterial systems. Persistence of this embryonic anastomosis is extremely rare. We present such a case with bilateral persistent proatlantal arteries that arose from internal carotid arteries, entered the skull via the foramen magnum and united with the horizontal portions of vertebral arteries. We also mention its embryology, potential clinical implications, and differentiating features between two types of proatlantal arteries., (Copyright American Society of Neuroradiology)

The atlas of a 52-year-old male Japanese cadaver, which had been removed and macerated, presented a bilateral unknown bone bridge forming a foramen (Case 1). The bone bridge connected the ponticulus lateralis (PL) and posterior (PP) to form an oval foramen between the superior roots of both ponticuli. The atlas of a 69-year-old male Japanese cadaver was found to have similar variations in situ (Case 2). In this case, the right bone bridge connected the superior root of the incomplete PL and the inferior root of the also incomplete PP to form a long ellipsoid foramen opening medially. The medial opening of the foramen was closed by a ligamentous connective tissue in situ. The condylar emissary vein passed this complete foramen to join the cervical epidural venous plexus. The similar bilateral foramen in case 1 was supposed to pass the same vein as in case 2. The bone bridge between the two ponticuli and the resulting foramen mentioned above have not been described previously, as far as we know. We propose that these structures be called the ponticulus interponticularis atlantis and the foramen atlantoideum interponticulare, respectively.

A vertebral artery (VA) coursing below the posterior arch of the atlas (C1) without passing through the transverse foramen of C1, combined with a tortuous course within the spinal canal has rarely been reported in the literature. This article describes a case encountered during an anatomical study of the far-lateral approach, and reviews its embryonic development and clinical significance. The suboccipital triangle was filled with numerous venous plexures. After exiting from the transverse foramen of C2, instead of passing upwards through the transverse foramen of C1, the VA turned directly medially towards the spinal canal. At the spinal canal, it first formed an angle downwards, then turned upwards, piercing and entering the lateral part of the dura at C1 level. The diameter of this VA seemed to be within its normal limits. The course of the contralateral (right) VA was normal but with a small caliber and mainly supplied the posterior inferior cerebellar artery (PICA); after PICA, it became much thinner and dysplastic, the basilar artery was mainly supplied by the left VA. The bilateral posterior communicating arteries were large in diameter but there was dysplasia of the P1 segment of the posterior cerebral arteries bilaterally. Marked tortuosity of the bilateral intracavernous internal carotid artery (ICA) was also found. We did not find any osseous abnormality in the occipito-axial region or of C1-C2 joint. An abnormal course of the VA should be kept in mind during exposure of the craniocervical junction, especially in the variety of lateral approaches; due to compression of the nerve roots or the spinal cord, this abnormal course of the VA could give rise to clinical symptoms, which could be resolved by microvascular decompression technique.

This case report demonstrates a rare vascular pattern of a left external carotid artery (ECA) that arises directly from the aortic arch (AA), along with a type II proatlantal-vertebral artery anastomosis. Our research shows no report of an ECA arising from the AA. This, in association with a type II proatlantal anastomosis, is interesting because of its apparent rarity.

The posterolateral tunnel on the superior surface of the first cervical (atlas) vertebra is of normal occurrence in monkeys and other lower animals, but its presence in the form of a tunnel-like canal, for the passage of the third part of the vertebral artery over the posterior arch of the human atlas vertebra is not reported. The aim of the present study was to detect the presence of such a canal, in addition to other types of ponticuli (little bridges) reported by earlier investigators, in macerated atlas vertebrae and routine cadaveric dissections. The posterolateral tunnel was detected in 1.14%, and the posterior and lateral ponticuli in 6.57 and 2% of vertebrae. Probably the bony roof of the posterolateral tunnel serves the purpose of additional lateral extension for the attachment of the posterior atlanto-occipital membrane in quadrupeds, where the load of the head is supported by the extensor muscles of the neck, ligaments and posterior atlanto-occipital membrane. In man, where the weight of the head is borne by the vertical loading of the superior articular process of the atlas, the roof of the tunnel has disappeared.

A case of bilateral persistence of the proatlantal arteries with occlusion of both internal carotid arteries is reported.

A 65-year-old man, who suffered from recurrent syncopal attacks after a minor stroke, was treated by percutaneous transluminal angioplasty using the kissing balloon technique (KBT) in which two angioplasty balloons were inflated simultaneously for the right carotid bifurcation stenoses. Because they involved the right internal carotid artery and the right external carotid artery coupled with the right proatlantal intersegmental artery, neither of them should close after the angioplasty. Bifurcation stenoses were sufficiently dilated with KBT and no syncopal attacks have recurred since the treatment.

Study Design: An evaluation of the vertebral artery groove of the atlas vertebra using dry bony vertebrae., Objectives: To measure the dimension of the vertebral artery groove of the atlas and to define its relation to the posterior midline., Summary of Background Data: Anatomic descriptions of the vertebral artery groove of the atlas exist, but very little quantitative data focused on this groove have been reported., Methods: Fifty dry atlas vertebrae were obtained for this study. Anatomic evaluation focused on the vertebral artery groove and its relation to the midline. A total of eight linear and two angular measurements were made bilaterally. The mean, range, and standard deviation were calculated for all of the specimens and for male and female specimens separately., Results: Differences in dimensions of male and female specimens were found to be statistically significant in one linear and two angular parameters. The average depths of the medial and lateral entrances, lengths of the axis, and thicknesses of the vertebral artery groove for male and female specimens were 9 mm, 6 mm, 14 mm, and 4 mm, respectively. The average angle of the vertebral artery groove axis for both genders was 64 degrees lateral to the sagittal plane. The distances from the midline to the medial-most edge of the vertebral artery groove on the inner and outer cortexes for male and female specimens averaged 10 mm, with a minimum of 8 mm, and 18 mm, with a minimum of 12 mm, respectively., Conclusions: The results of this study suggest that dissection on the posterior aspect of the posterior ring should remain within 12 mm lateral to the midline, and dissection on the superior aspect of the posterior ring should remain within 8 mm of the midline.

Primitive embryonic anastomotic vessels between the carotid and vertebrobasilar arterial systems occasionally persist into adult live. Coincidence with cerebrovascular disease may be of functional relevance. We report a case of segmental internal carotid occlusion and aplasia of both vertebral arteries in combination with persistence of proatlantal artery type I. Recurrent cerebral ischemia required revascularization of the segmental occluded internal carotid artery. Disobliteration was successfully performed with an uneventful postoperative course. The patient recovered well from his neurological deficits. Clinically, the combination of persistent proatlantal artery with occlusive disease of the carotid arteries may lead to atypical neurological deficits. In cerebrovascular surgery, a persisting proatlantal artery, as a main supply vessel of the vertebrobasilar system, is of great importance if the carotid artery is clamped.

We report on a rare case of aplasia of the left vertebral artery, while the basilar artery is supplied by the proatlantal artery, a persistent carotid-basilar anastomosis. The right vertebral artery appears to be hypoplastic.

A case of asymptomatic common carotid artery occlusion with direct vertebrocarotid anastomosis (proatlantal intersegmental artery) in a 70-year-old male is reported. Despite the acquired left common carotid artery occlusion, there was no demonstrable neurologic deficits that would occur by the involvement of the area supplied by the occluded carotid system. Cerebral angiography revealed, in addition to efficient collateral circulation from the contralateral carotid system through the anterior communicating artery, a collateral channel from the left vertebral artery to the ipsilateral external carotid artery via the proatlantal intersegmental artery. These collateral circulations were indicated to be important in prevention of possible grave neurologic consequences. The proatlantal intersegmental artery, though rarely visualized by ordinary cerebral angiographic procedures, was thus demonstrated to be capable of serving as a collateral channel of potential usefulness in the event of severe intracranial hemodynamic alterations, including acquired common carotid artery occlusion.

A case of persistent primitive proatlantal intersegmental artery (PPPIA) is reported. A 65-year-old male with treated hypertension was admitted to our clinic complaining of dysarthria and hemiparesis of sudden onset two days after the ictus. CT revealed spotty low-density lesions in the left corona radiata and bilateral thalami with bilateral watershed infarction. MRI findings were also compatible with cerebral infarction. Left common carotid angiography demonstrated a large anastomosis between the external carotid artery and the vertebral artery at the proatlantal region. Neither of the vertebral arteries were visualized on digital subtraction aortography. All the blood circulation of the vertebro-basilar system was through this anastomotic artery (PPPIA). A flow study revealed hypoperfusion in the territory of the left middle cerebral artery on 133Xe SPECT. Bone window CT of cervical vertebrae revealed hypoplasia of the left transverse foramen in C2, C3, C4, C5, C6 vertebrae. This case is very suggestive of an anaplasia or hypoplasia of the vertebral arteries. The etiology of his left frontal infarction seemed to be a blood-stealing phenomenon of long standing, from the anterior to the posterior circulation through the PPPIA.

A 57-year-old male was hospitalized with stroke on the day of onset. An initial computed tomography revealed a hemorrhage in the left caudate nucleus. Common carotid angiography demonstrated a carotid-vertebral anastomosis. Complete selective external carotid angiography disclosed the proatlantal intersegmental and occipital arteries arising from the external carotid artery at the level of the atlas. The proatlantal intersegmental artery, which is one type of persistent primitive carotid-vertebrobasilar anastomosis, is rarely associated with hypertensive intracerebral hemorrhage, according to the literature.

The arterial supply to the cervical vertebrae of the ox was studied in 22 animals (Friesland, Jersey and Guernsey cross-breeds), ranging from near full-term foetuses to adults. Various techniques, including angiography and clearing of bone, were employed to expose the extra- and intraosseous distribution of the arteries and a description is given of a modified Spalteholtz clearing technique. The extraosseous nutrient arteries are described and illustrated. A uniform pattern emerged from the investigation and it is suggested that the main branches be named: (1) the artery of the vertebral arch; (b) the artery of the transverse process; (c) the basivertebral arteries. Frequent anastomoses between epi- and metaphysial vessels in young animals are reported, and stress is laid on the effective collateral supply maintained by the extra- and intraosseous nutrient vessels.