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

Applied anatomy of the vertebral arteries for endovascular neurointerventions

The vertebral arteries (VAs) constitute most of the arterial supply to the posterior cerebral vascular circulation. They have anatomical specificities and may have variants that are critical for neurointerventionists to recognize in order to design open or endovascular surgical treatment. This review addresses each segment of the VA including its origin and discusses the branches and relevant anatomical features for neurointerventions.

Atypical posterior circulation strokes: a case-based review of rare anatomical variations involved

The circle of Willis is a very important vascular mechanism of protecting against cerebral ischemia, especially when circulation within the main arteries irrigating the brain is somehow impeded. As result of congenital malformation arising early in embryonic development, the fetal-type posterior circle of Willis remains as such during the rest of one’s life. Consequently, the posterior cerebral artery (PCA) becomes a branch of the internal carotid artery (ICA), rather than of the basilar artery (BA). Furthermore, the rest of collateral circulation, between the anterior and the posterior regions of the brain, is also negatively affected (e.g., leptomeningeal vessels). The anatomical variant represented by the artery of Percheron (AOP) has its origin on one of the PCAs, supplying singlehandedly both paramedian areas of the thalamus (right and left) and posterior regions of the midbrain. In the present study, we report a case of bilateral thalamic infarction with midbrain involvement, where the correct diagnosis was made retrospectively using computed tomography (CT) scan, magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI) and three-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA).

A unique variant of a right persistent hypoglossal artery arising from the common carotid artery with complex cardiovascular anomalies in a female neonatal patient

Persistent primitive hypoglossal artery is a carotid-vertebrobasilar anastomosis, which commonly arises from the internal carotid artery at the level of the C (cervical) 1-3 vertebrae. We describe a unique case of a female infant patient with this anomaly that has an unusually low origin from the distal common carotid artery just below the bifurcation at the level of roughly C5 and supplies the entire vertebrobasilar system. Additional cardiovascular anatomical variations were present: Tetralogy of Fallot and a right-sided aortic arch with mirror image branching. These singular variations are rare in the general population, but even rarer when combined. Awareness of these unusual vascular variants is clinically significant, as they may predispose the patients to early ischemic injury, hemorrhage, aneurysm formation, and can be essential in surgical planning. Therefore, radiographic imaging is of importance in proper diagnosis of such variants.

Unilateral segmental agenesis of the vertebral artery at the C2 level

PURPOSE

To report a case of unilateral segmental agenesis of the vertebral artery (VA).

METHODS

We describe the angiographic and MRI features of a segmental VA agenesis (C2 segment).

RESULTS

VA agenesis is caused by the absence of the anastomotic connection normally linking two adjacent intersegmental arteries; in the reported observation, a paravertebral extraforaminal anastomosis replaced the C2 segment normally joining the 1st and 2nd cervical intersegmental arteries through the C2 transverse foramen.

CONCLUSION

We present an observation of segmental VA agenesis. This variant is consistent with the developmental history of the VA. It appears exceptional but is more likely underappreciated.

Smaller Absolute Quantities but Greater Relative Densities of Microvessels Are Associated with Cerebellar Degeneration in Lurcher Mice

Degenerative affections of nerve tissues are often accompanied by changes of vascularization. In this regard, not much is known about hereditary cerebellar degeneration. In this study, we compared the vascularity of the individual cerebellar components and the mesencephalon of 3-month-old wild type mice (n = 5) and Lurcher mutant mice, which represent a model of hereditary olivocerebellar degeneration (n = 5). Paraformaldehyde-fixed brains were processed into 18-μm thick serial sections with random orientation. Microvessels were visualized using polyclonal rabbit anti-laminin antibodies. Then, the stacks comprised of three 5-μm thick optical sections were recorded using systematic uniform random sampling. Stereological assessment was conducted based on photo-documentation. We found that each of the cerebellar components has its own features of vascularity. The greatest number and length of vessels were found in the granular layer; the number of vessels was lower in the molecular layer, and the lowest number of vessels was observed in the cerebellar nuclei corresponding with their low volume. Nevertheless, the nuclei had the greatest density of blood vessels. The reduction of cerebellum volume in the Lurcher mice was accompanied by a reduction in vascularization in the individual cerebellar components, mainly in the cortex. Moreover, despite the lower density of microvessels in the Lurcher mice compared with the wild type mice, the relative density of microvessels in the cerebellar cortex and nuclei was greater in Lurcher mice. The complete primary morphometric data, in the form of continuous variables, is included as a supplement. Mapping of the cerebellar and midbrain microvessels has explanatory potential for studies using mouse models of neurodegeneration.

A Functional Perspective on the Embryology and Anatomy of the Cerebral Blood Supply

The anatomy of the arterial system supplying blood to the brain can influence the development of arterial disease such as aneurysms, dolichoectasia and atherosclerosis. As the arteries supplying blood to the brain develop during embryogenesis, variation in their anatomy may occur and this variation may influence the development of arterial disease. Angiogenesis, which occurs mainly by sprouting of parent arteries, is the first stage at which variations can occur. At day 24 of embryological life, the internal carotid artery is the first artery to form and it provides all the blood required by the primitive brain. As the occipital region, brain stem and cerebellum enlarge; the internal carotid supply becomes insufficient, triggering the development of the posterior circulation. At this stage, the posterior circulation consists of a primitive mesh of arterial networks that originate from projection of penetrators from the distal carotid artery and more proximally from carotid-vertebrobasilar anastomoses. These anastomoses regress when the basilar artery and the vertebral arteries become independent from the internal carotid artery, but their persistence is not uncommon in adults (e.g., persistent trigeminal artery). Other common remnants of embryological development include fenestration or duplication (most commonly of the basilar artery), hypoplasia (typically of the posterior communicating artery) or agenesis (typically of the anterior communicating artery). Learning more about the hemodynamic consequence that these variants may have on the brain territories they supply may help understand better the underlying physiopathology of cerebral arterial remodeling and stroke in patients with these variants.

Bilateral segmental agenesis of carotid and vertebral arteries with rete mirabile and the prominent anterior and posterior spinal arteries as compensations

Agenesis of carotid or vertebrobasilar arteries with rete formation is rare. The anterior spinal artery or posterior spinal arteries supplying the posterior circulation with steno-occlusion or agenesis of bilateral vertebral arteries is also uncommon. Here, we describe a very rare case of concomitant segmental agenesis of bilateral carotid and vertebral arteries with collateral compensations from the prominent anterior spinal artery and posterior spinal arteries, as well as some transdural arterial networks which were considered a rete mirabile. We discuss its embryological and anatomic significance.

Circle of Willis configuration as a determinant of intracranial dolichoectasia

BACKGROUND

Circle of Willis (COW) variants might influence arterial caliber in the brain. We hypothesized that these variants would be associated with the prevalence of intracranial dolichoectasia (DE).

METHODS

We examined COW variants and DE in a sample of stroke-free participants (n = 436) undergoing magnetic resonance angiography (MRA) as part of a population-based study. Large intracranial arterial diameters were obtained when available; if not, the artery was defined as hypoplastic or absent according to its visibility on MRA. Subscores for the anterior and the posterior circulations were created. DE was defined as arterial diameters ≥2 SD above the population mean for that artery, adjusting for intracranial volume. Generalized linear models with a Poisson distribution were used to evaluate predictors of both absent and hypoplastic vessels, and logistic regression was used to assess the odds ratio (OR) and 95% confidence interval (95% CI) of DE depending on COW variants.

RESULTS

Only 44% of the sample had all 14 arteries present, 32% lacked 1 artery, 18% lacked 2 and 6% lacked 3 or more. DE of at least 1 artery was not associated with the total number of hypoplastic or absent arteries, but DE in a posterior circulation artery was weakly associated with the number of absent arteries in the posterior circulation (β coefficient = 0.36, p = 0.06). DE of at least 1 artery was more frequent in those with 1 or more absent arteries (OR 1.27, 95% CI 1.03-1.57). Posterior circulation DE was more frequent in participants with at least 1 or more absent arteries at any location (OR 1.35, 95% CI 1.02-1.78). Participants with an incomplete posterior COW were more likely to have DE in the anterior circulation (OR 1.52, 95% CI 1.01-2.33). Having an absent left anterior cerebral artery (ACA) A1 segment was associated with right ACA DE (OR 34.1, 95% CI 3.16-368.2); an absent right ACA was associated with left ACA DE (OR 14.1, 95% CI 1.69-118.28). Absence of 1 (OR 1.9, 95% CI 1.1-3.4) or 2 (OR 3.0, 95% CI 1.4-6.6) of the 2 arteries connecting the anterior to the posterior circulation was associated with basilar artery DE.

CONCLUSION

The COW is a pleomorphic structure that allows collateral flow to compensate for an insufficient or absent arterial component at the base of the skull. By presumed flow diversion, arteries might undergo outward remodeling. Whether this compensatory arterial dilatation is beneficial or not remains unknown.

Extracranial Segments of the Vertebral Artery: Insight in the Developmental Changes up to the 21st Year of Life

The vertebral artery (VA) bilaterally arises usually from the subclavian artery and courses within the bony canals of cervical vertebrae, and then it reverses directions on the first vertebra before piercing the dura to enter the cranium.The aim was to follow (ab)normal developmental changes of extracranial VA from prenatal status to age 21. This chapter included a brief description of the arterial embryology and morphofunctional specificity of the VA in prevertebral, cervical, and atlantic parts, during prenatal and postnatal period.The authors concluded that the subclavian origin of the VA was in most of fetal and adult cases. The incidences of variable VA origins and domination of one of the VAs were different from one series of human specimens to the second one. Although in most of cases, anomalous origin and/or variable course of the extracranial VA had little or did not result in clinical symptoms in infants and young adults, the true value of their discovery is in the diagnostic gain before vascular surgery of supra-aortic arteries.

Monolateral type I proatlantal artery with bilateral absence of vertebral arteries: description of a case and review of the literature

We report a case of a patient with right type I proatlantal intersegmental artery associated with right fetal posterior cerebral artery and absence of both vertebral arteries and of the left posterior communicating artery. We also describe the clinical relevance of these findings for this patient. A 56-year-old woman with vertigo and tinnitus underwent contrast enhanced Magnetic Resonance Angiography (MRA) of the supra-aortic arteries using a 1.5 Tesla scanner. Maximum intensity projection and volume rendering reconstructions were obtained. MRA demonstrated the persistence of an anastomotic artery between the right internal carotid artery and basilar artery, passing through the foramen magnum, suggesting a type I proatlantal intersegmental artery. The examination also showed the absence of both vertebral arteries and the presence of a right fetal-type posterior cerebral artery. To our knowledge, this is the first report of a type I proatlantal intersegmental artery associated with an omolateral fetal-type posterior cerebral artery and the absence of both vertebral arteries and of the left posterior communicating artery. This condition requires a watchful monitoring of the patient and has to be considered in case of surgical procedures of the carotid arteries.

Basilar artery hypoplasia

A rare case of segmental hypoplasia of the basilar artery is described in a 49-year-old man with transient vertebrobasilar ischemia, explored by magnetic resonance imaging (MRI) and digital angiography (DA). The embryology, clinical relevance and magnetic resonance findings of this arterial anomaly are discussed, with a review of six previously reported cases. Segmental aplasia was suggested in our case by magnetic resonance, and subsequently confirmed not only by time-of-flight magnetic resonance, but also by DA. Only ultrathin-slice T2-weighted images revealed the real finding of basilar artery hypoplasia. This sequence, not employed in previously reported cases, is mandatory to allow a clear differential diagnosis between basilar artery aplasia and hypoplasia.

Normal and abnormal embryology and development of the intracranial vascular system

The brain vascular system develops in such a way that it continuously adapts the supply of oxygen and other nutrients to the needs of the parenchyma. To accompany the developing brain vesicles, it evolves in several steps: superficial meningeal network first; intraventricular choroid plexuses which determine the arterial pattern; penetrating capillaries from the surface to the ventricular germinal matrix forming simple transcerebral arteriovenous loops; cortical capillaries last, mainly in the last trimester. The venous return becomes connected to both the surface and to the choroidal veins, so forming distinct meningeal and subependymal venous drainage systems, while the arteries are on the surface only. While the arterial system was determined early (week 8), the venous system is continuously remodeled by the morphological changes of the base of the skull and the expansion of the brain vesicles. Until late in gestation, the vascular system is made of simple endothelial channels in which the arterial or venous fate is determined primarily by the direction of flow.

Cerebellar stroke in elderly patient with basilar artery agenesia: a case report

We report a case of a 76-year-old woman admitted to our institution with sudden onset of dizziness and vertigo followed by vomiting and blurred vision. Her medical history was remarkable for hypertension, diabetes, and ischemic stroke in the territory of the left cerebral median artery. Her symptoms were suggestive of a cerebellar stroke. Computed tomography brain scan and neck vessel ultrasounds produced normal findings. A 24-hour blood pressure monitoring showed a reverse dipping pattern. Magnetic resonance imaging examination was performed, showing a hyperintense ischemic focus involving pons and left middle cerebellar peduncle, on T2-weighted images. On Time-of-flight (TOF)-3-dimensional magnetic resonance angiography, there was a marked reduction of basilar artery signal. The digital subtraction angiography showed a vertebrobasilar system anomaly. The right vertebral artery was hypoplastic with few thin terminal spinal branches. The left vertebral artery was vicarious to the right one in intracranial tract. V3 to V4 tract showed multiple atherosclerotic wall irregularities. The basilar common trunk was absent. An abnormal posterior inferior cerebellar artery replaced the anterior inferior cerebellar artery and superior cerebellar artery. Right posterior inferior cerebellar artery, anterior inferior cerebellar artery, and superior cerebellar artery arose from ipsilateral V4 tract. This case is the first description of pure basilar agenesia. The symptoms might be related to temporary decrement of the flow in the left vertebral artery. Furthermore, the reverse dipping pattern together with the aging, hypertension, and diabetes had probably contributed to a hemodynamic malfunction of the cerebral vascular system.

Bilateral vertebral artery occlusion with retrograde basilary flow in three cases of giant cell arteritis

Vertebrobasilar ischaemia is a rare life-threatening complication in giant cell arteritis (GCA). We report three patients with bilateral vertebral artery occlusion. Neurovascular imaging, including CT-angiography, MR-angiography and colour-coded duplex sonography revealed flow reversal in the basilar artery as well as inflammation of the vertebral vessel wall. The first patient died from massive brainstem infarction, the other two patients survived the initial inflammatory phase of GCA. No stroke recurrence at 12 months' follow-up on warfarin and steroid treatment was observed. Bilateral distal vertebral artery occlusion and retrograde basilar artery flow persisted.Outcome in these patients is dependant on potent immunosuppression, concurrent atherosclerotic steno-occlusive disease and presence and/or rapid development of sufficient collateral pathways into the vertebrobasilar circulation. The identification of patients with high risk of ischaemia due to compromised vertebrobasilar flow may be important to select adjunct treatment to immunosuppression, such as anticoagulation in GCA.

Ultrasound findings of bilateral hypoplasia of the vertebral arteries associated with a persistent carotid-hypoglossal artery

We present a 31-year-old female who was admitted to our neurology department for vertigo, partial left-sided hemihypesthesia and nuchal headache of subacute onset. Colour-duplex ultrasound disclosed bilateral low flow with a high resistance flow pattern in both vertebral arteries in the V2 segments, while the basilar artery had normal flow. CT angiography and MRI ruled out any ischaemic cerebral infarct and disclosed a persistent hypoglossal artery (PHA) originating from the left internal carotid artery (ICA). The patient was eventually treated for cervicobrachialgia. Persistent carotid-basilar anastomosis such as PHA may account for an atypical stroke pattern in carotid disease, aneurysms and arterovenous malformations. In retrospect, PHA is amendable to colour-Duplex investigation due to an abnormal ICA flow and a discrepancy between the vertebral and basilar flow patterns. Ultrasound investigation of the vertebrobasilar system remains a challenge as variants appear frequently; hypoplasia of the vertebral arteries should thus be confirmed using CT or MR angiography.