Prevalence and Clinical Implications of the Primitive Trigeminal Artery and its Variants: A Meta-Analysis.

BACKGROUND: The primitive trigeminal artery (PTA) is the most common and the largest persistent carotid-basilar anastomosis. Primitive trigeminal artery variants (PTAVs) are anastomoses between the internal carotid artery and cerebellar arteries. These vessels pose a risk of hemorrhagic or ischemic complications during neurosurgical procedures in the parasellar and intrasellar regions. The aim of this study was to determine the prevalence of both PTA and PTAVs and their clinically important anatomic features. METHODS: Major electronic databases were thoroughly searched for studies on PTA and PTAV. References in the included articles were also evaluated. Data regarding prevalence, laterality, origin, course patterns, and associated anomalies were extracted and pooled into a meta-analysis. RESULTS: A total of 39 studies (110,866 patients) were included in the meta-analysis. The total pooled prevalence estimate of PTA and PTAVs combined was 0.4% (95% confidence interval [CI], 0.3-0.5). Individually, PTA was present in 0.3% of patients and PTAV in 0.2%. Both arteries most often originated from the C4 internal carotid artery and took a course lateral to the dorsum sellae. The anterior inferior cerebellar artery type was the predominant PTAV (72.1%). Basilar artery hypoplasia was found in 42.5% of patients with a PTA. CONCLUSIONS: PTA and PTAVs are rare vessels, but they are clinically important because they can contribute to trigeminal neuralgia. Knowledge of the potential course of these arteries is essential in neuroradiology and neurosurgery, especially in minimally invasive procedures such as the endoscopic endonasal transsphenoidal approach to the pituitary gland and the percutaneous gasserian ganglion procedure.

Embryological basilar apex disposition as a risk factor of basilar apex aneurysm.

The pathogenesis of basilar apex aneurysm (BAA) are still poorly understood. Embryologically, basilar apex anatomical disposition is formed by the fusion of both caudal internal carotid divisions on the midline. To compare basilar apex morphology by embryological classification among patients with BAAs, anterior circulation aneurysms (ACAs), and controls. Prospectively collected data of 47 consecutive patients with unruptured BAAs (42 females and five males), age- and gender-matched 47 patients with unruptured ACAs, and 47 controls without any aneurysms were analyzed. Based on embryology, basilar apex morphology was classified into symmetric cranial fusion (SCrF), symmetric caudal fusion, and asymmetric fusion type. Posterior communicating artery (Pcom) was classified into hypoplastic, adult, or fetal type. The asymmetrical Pcom was defined as bilaterally different type Pcom. The ACAs located at the anterior communicating artery (n = 18), paraclinoid portion (n = 12), middle cerebral artery (n = 8), anterior cerebral artery (n = 5), the top of internal carotid artery (n = 2), and anterior choroidal artery (n = 2). Compared with the ACA group and controls, smoking, asymmetrical Pcom (fetal and adult type), and SCrF type were more prevalent in patients with BAAs by residual analysis. The multinomial logistic regression comparative analysis demonstrated that SCrF type was associated with BAAs (vs. ACA group; odds ratio, 13; 95% confidence interval, 3.8-41 and vs. controls; odds ratio, 25; 95% confidence interval, 5.4-121). The assessment of basilar apex morphology may aid in the understanding of the pathogenesis of BAA and the prediction of BAA formation.

Carotid-vertebrobasilar Anastomoses with Reference to Their Segmental Property.

The primitive carotid-vertebrobasilar anastomoses are primitive embryonic cerebral vessels that temporarily provide arterial supply from the internal carotid artery to the longitudinal neural artery, the future vertebrobasilar artery in the hindbrain. Four types known are the trigeminal, otic, hypoglossal, and proatlantal intersegmental arteries. The arteries are accompanied by their corresponding nerves and resemble an intersegmental pattern. These vessels exist in the very early period of cerebral arterial development and rapidly involute within a week. Occasionally, persistence of the carotid to vertebrobasilar anastomosis is discovered in the adult period, and is considered as the vestige of the corresponding primitive embryonic vessel. The embryonic development and the segmental property of the primitive carotid-vertebrobasilar anastomoses are discussed. This is followed by a brief description of the persisting anastomoses in adults.

Transabdominal Insonation of Fetal Basilar Artery: A Feasibility Study.

BACKGROUND: Fetal anterior, middle, and posterior cerebral arteries have been studied using transabdominal Doppler ultrasound. We performed a feasibility study to determine whether basilar artery can be identified and blood flow velocities measured using transabdominal fetal Doppler ultrasound. METHODS: The basilar artery was identified in sagittal plane behind the clivus bone using directional color Doppler with 6-2 and 7-4 MHz curved array probes. The clivus was identified by hyperechoic linear signal anterior to junction of vertebral processes and occipital bone and superior to first vertebral body. The flow direction was away from the probe in the basilar artery consistent with caudo cephalic orientation. The Doppler ultrasound probe was placed at insonation angles of less than 30° at the visualized segment of the basilar artery. Peak systolic and end diastolic velocities were measured. RESULTS: We attempted insonation of the basilar artery in 20 fetuses. The basilar artery was adequately insonated in 18 fetuses with a mean gestational age of 27 weeks (range 19 to 38 weeks). The mean value (±SD) of peak systolic velocity of the basilar artery was 22.1 ± 8.5 cm/second (range 10.4-36.7 cm/second). The mean value (±SD) of end diastolic velocity was 6.8 ± 2.8 cm/second (range 3.5-13.5 cm/second). There was an increase in peak systolic velocity values according to gestational age of fetus. CONCLUSIONS: We demonstrate the feasibility of fetal basilar artery insonation using directional color Doppler ultrasound via transabdominal approach.

Human basilar artery abnormalities in the prenatal and postnatal period.

OBJECTIVE: Although complex and varied, adult cerebral angioarchitecture has its origins in embryologic development, where normal components, variations, and abnormalities evolve from modifications of primitive vessels. Therefore, the aim of this report was the study of the morphologic features of the basilar fenestrations in prenatal and postnatal period and associated variants and/or pathologies. METHODS: We studied the brain vessels of 120 fetuses microscopically (i.e., with an operative microscope) and 112 adult cadavers macroscopically. RESULTS: We described 10 cases of basilar abnormalities, five fetal and four adult fenestrations, as well as one adult case with a basilar aneurysm. The location of the vertebrobasilar junction on a caudal myelencephalon and a prolongation of the basilar trunk followed both fetal and adult forms of fenestrations. The same caliber values of the basilar and internal carotid arteries, a variation in the number and origin of some of the basilar side branches, and a tendency of fenestrations to be multiple in number, as particular fetal features, were mostly present in adults. CONCLUSION: The fact that basilar fenestrations in adult specimens shared similar features with fetal ones and without aneurysms, as well as the fact that a basilar aneurysm was without fenestration in its base, lead us to hypothesis that the basilar fenestration is a vascular developmental variant related to the maintenance of vascular symmetry in the midline of the human brain base.

Middle meningeal artery arising from the basilar artery: report of a case and its probable embryological mechanism.

An extremely rare variation of the (left) middle meningeal artery (MMA) originating from the basilar artery, detected incidentally during cerebral angiography, is reported. The right MMA was normal and an accessory meningeal artery arising from the maxillary artery was present on both the sides. The foramen spinosum on the variant side was absent. This abnormal origin of the MMA can be explained by the presence of a perineural arterial network in the region of the Gasserian ganglion, formed by branches of the developing basilar and stapedial arterial systems; the middle meningeal-basilar arterial channel opening up in the absence of a normally developing MMA.

Normal subtypes of the posterior part of the cerebral arterial circle in human fetuses.

BACKGROUND: Although centuries of the human CAC research are behind us, still there is a stimulus for the authors to describe something new or to add to the "archive" of already known facts about its angioarchitecture. METHODS: With normal configurations of the posterior part of the CAC in early prenatal status, 172 brains of human fetuses from the 13th to the 24th week were used in the purpose of investigation. Brain arteries were injected and microdissected using a surgical microscope. RESULTS: According to diameter values of vascular components in the posterior part of the CAC, 6 basic types and the corresponding number of their subtypes are formed. Incidences of bilateral transitory (18.6%), fetal (9.3%), and adult (33.1%) types, as well bilateral asymmetric types (fetal-transitory in 5.8%, adult-transitory in 14.5%, and adult-fetal in 18.6% of cases), proved that dominant configuration of posterior part had not been present in the period from the fourth to the sixth gestational month. CONCLUSION: The finding of normal subtypes of the posterior part of the CAC, as well as the absence of some subtypes, is a challenge for future studies of the posterior arterial pattern within vascular abnormalities or diseases.

The posterior part of the human cerebral arterial circle (CAC): arterial caliber from gestational weeks 13 to 24.

Numerous studies have reported that all components of the cerebral arterial circle in the 4-month-old human fetus are more slender than adult vessels, and of equal caliber. After that period, a degree of caliber differentiation is present, especially at the level of the posterior communicating arteries. The aim of this study was to determine arterial diameters in the posterior part of the fetal cerebral arterial circle from the 4th month (IV) to the 6th (VI). One hundred and seventy-two fetal cerebral arterial circles were examined by means of a surgical microscope. It was determined that average diameters of the left (right) pre-communicating parts of the posterior cerebral artery ranged from 0.30 +/- 0.03 (0.29 +/- 0.02) mm in month IV, to 0.36 +/- 0.04 (0.36 +/- 0.03) mm during month V and up to 0.55 +/- 0.22 (0.50 +/- 0.18) mm in month VI. The average diameters of the left (right) posterior communicating artery ranged from 0.24 +/- 0.02 mm (0.25 +/- 0.02) in month IV, to 0.30 +/- 0.03 mm (0.29 +/- 0.05) during month V and up to 0.38 +/- 0.08 (0.44 +/- 0.10) in month VI. Gender differences between posterior cerebral artery and posterior communicating artery diameters were not significant. Average posterior cerebral artery diameters were significantly larger than posterior communicating artery diameters in months IV and V, but not in month VI. It was established that caliber differentiation in the posterior part of the cerebral arterial circle began from gestational month IV, and that gender differences in arterial diameters were not significant until month VI of gestation.

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.

Basilar trunk aneurysms with associated fenestration treated by using Guglielmi detachable coils: two cases reports.

Basilar trunk saccular aneurysms associated with fenestration are infrequent. Surgical treatment of a basilar trunk aneurysm is difficult because of its anatomic environment and complicated surgical exposure. We experienced two cases of basilar fenestration aneurysm, and the patients were treated using Guglielmi detachable coils. The usefulness of 3-dimensional digital subtraction angiography and efficacy of endovascular treatment for basilar trunk aneurysms with associated fenestration is discussed in this article, and the relevant literature is reviewed.

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.

Persistencia de arterias embrionarias / Persistent embryonic arteries

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Chronic hypoxia modulates relations among calcium, myosin light chain phosphorylation, and force differently in fetal and adult ovine basilar arteries.

The present study tests the hypothesis that age-related differences in contractility of cerebral arteries from hypoxic animals involve changes in myofilament Ca2+ sensitivity. Basilar arteries from term fetal and nonpregnant adult sheep maintained 110 days at 3,820 m were used in measurements of cytosolic calcium concentration ([Ca2+]i), myosin light chain phosphorylation, and contractile tensions induced by graded concentrations of K+ or serotonin (5-HT). Slopes relating [Ca2+]i to tension were similar in fetal (0.83 +/- 0.07) and adult (1.02 +/- 0.08) arteries for K+ contractions but were significantly greater for fetal (3.77 +/- 0.64) than adult (2.00 +/- 0.13) arteries for 5-HT contractions. For both K+ and 5-HT contractions, these relations were left shifted in fetal compared with adult arteries, indicating greater Ca2+ sensitivity in fetal arteries. In contrast, slopes relating [Ca2+]i and %myosin phosphorylation for K+ contractions were less in fetal (0.37 +/- 0.08) than adult (0.81 +/- 0.07) arteries, and the fetal curves were right shifted. For 5-HT contractions, the slope of the Ca2+-phosphorylation relation was similar in fetal (0.33 +/- 0.09) and adult (0.33 +/- 0.23) arteries, indicating that 5-HT depressed Ca2+-induced myosin phosphorylation in adult arteries. For slopes relating %myosin phosphorylation and tension, fetal values (K+: 1.52 +/- 0.22, 5-HT: 7.66 +/- 1.70) were less than adult values (K+: 2.13 +/- 0.30, 5-HT: 8.29 +/- 2.40) for both K+- and 5-HT-induced contractions, although again fetal curves were left shifted relative to the adult. Thus, in hypoxia-acclimatized basilar arteries, a downregulated ability of Ca2+ to promote myosin phosphorylation is offset by an upregulated ability of phosphorylated myosin to produce force yielding an increased fetal myofilament Ca2+ sensitivity. Postnatal maturation reprioritizes the mechanisms regulating hypoxic contractility through changes in the source of activator Ca2+, the pathways governing myosin light chain phosphorylation, and its interaction with actin.

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 nonfused segments of the basilar artery: longitudinal versus axial nonfusion.

Embryologic development of the basilar artery occurs along two axis systems: longitudinal fusion and axial fusion. Longitudinal fusion consists of midline fusion of paired ventral arteries and reflects the simplified pattern of arterial anatomy found in the spinal cord. Axial fusion consists of fusion of the distal basilar artery, which arises from the caudal division of the internal carotid artery, to the midbasilar agenesis to the posterior inferior cerebellar artery termination of the vertebral arteries. Persistent longitudinal nonfusion (or complete duplication) of the basilar artery is very rare, and persistent axial nonfusion is even rarer. We report one case of persistent longitudinal nonfusion of the basilar artery in a 3-year-old boy and a case of persistent axial nonfusion of the basilar artery in a 43-year-old man.

[Persistent fetal carotid-vertebrobasilar anastomoses]. / Persistan fetal karotid-vertebrobaziler anastomozlar.

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.

Developmental changes in ryanodine- and IP(3)-sensitive Ca(2+) pools in ovine basilar artery.

To explore the hypothesis that cerebrovascular maturation alters ryanodine- and inositol 1,4,5-trisphosphate (IP(3))-sensitive Ca(2+) pool sizes, we measured total intracellular Ca(2+) with (45)Ca and the fractions of intracellular Ca(2+) released by IP(3) and/or caffeine in furaptra-loaded permeabilized basilar arteries from nonpregnant adult and term fetal (139-141 days) sheep. Ca(2+) mass (nmol/mg dry weight) was similar in adult (1.60 +/- 0.18) and fetal (1.71 +/- 0.16) arteries in the pool sensitive to IP(3) alone but was significantly lower for adult (0.11 +/- 0.01) than for fetal (1.22 +/- 0.11) arteries in the pool sensitive to ryanodine alone. The pool sensitive to both ryanodine and IP(3) was also smaller in adult (0.14 +/- 0.01) than in fetal (0.85 +/- 0.08) arteries. Because the Ca(2+) fraction in the ryanodine-IP(3) pool was small in both adult (5 +/- 1%) and fetal (7 +/- 4%) arteries, the IP(3) and ryanodine pools appear to be separate in these arteries. However, the pool sensitive to neither IP(3) nor ryanodine was 10-fold smaller in adult (0.87 +/- 0.10) than in fetal (8.78 +/- 0.81) arteries, where it accounted for 72% of total intracellular membrane-bound Ca(2+). Thus, during basilar artery maturation, intracellular Ca(2+) mass plummets in noncontractile pools, decreases modestly in ryanodine-sensitive pools, and remains constant in IP(3)-sensitive pools. In addition, age-related increases in IP(3) efficacy must involve factors other than IP(3) pool size alone.