Hypoplastic arteries of the cerebral arterial ring in the blind spot of computed tomography angiography

BACKGROUND

Some variations of the cerebral arterial circle (CAC) are associated with an increased risk for the development of various pathological conditions. This paper aimed to determine the prevalence of hypoplastic arteries of CAC and to emphasize the limited possibility of their visualization by computed tomography angiography (CTA).

MATERIALS AND METHODS

The research was performed on 400 adult cadavers by macro- and microdissection of the cerebral arteries. Each case was photographed and the diameter of the arteries was measured digitally, by analyzing photographs of the bases of the brain in the ImageJ program.

RESULTS

The largest prevalence of artery diameter <1mm (<0.6mm) in CAC had the posterior communicating artery (PCoA). PCoA on the left side was hypoplastic in 44.9% (11.4%) of cases, while the same artery on the right side was hypoplastic in 44.3% (6.6%) of cases. The posterior cerebral artery was hypoplastic on the left side in 3% (0.6%) and on the right side in 4.2% (0.6%) of cases. The anterior cerebral artery had a hypoplastic caliber only on the right side in 2.4% (0.6%) of the cases, while the internal carotid arteries did not have a diameter <1mm in any case. The anterior communicating artery showed the greatest variability in morphology. Studies on CTA describe the occurrence of aplasia in a statistically significantly higher percentage, and the occurrence of hypoplastic arteries in a statistically significantly lower percentage compared to studies on cadavers.

CONCLUSIONS

Due to significant differences between cadaveric and radiological studies, it is necessary to analyze their results regarding arterial hypoplasia and aplasia separately. A diameter of less than 1 mm has been suggested as a criterion for arterial hypoplasia.

Specifies of the fetal median callosal artery

BACKGROUND

A variable artery in the anterior cerebral circulation, named median callosal artery (MdCA) belongs to one of the three groups of anteromedial central branches of the anterior communicating artery (ACoA). The lack of information on MdCA in human fetuses inspired the authors to explore and present its morphological features.

METHODS

The arteries of the brain base were analyzed and measured on 193 specimens of human fetuses, whose values are preserved from the time of preparation of PhD thesis.

RESULTS

The median callosal artery was observed in 45% (87/193) of fetuses from 12.5 to 25 weeks of gestation. The MdCA originating from the single ACoA was found in 4.66% cases. MdCAs originating from the so-called anterior communicating rete (16.58%), as well from the partially duplicated (5.69%) and total duplicated ACoA (10.88%) were also found. A statistically significant difference of the artery OD between male and female fetuses was not found. There was a non-significant positive correlation between fetal age presented in gestational weeks and the artery OD (r = 0.214). The OD of the MdCA did not correlate with the diameters of the anterior cerebral artery (ACA). An unusual convergent union of initial ACA medial vessels and partial duplication at MdCA beginning and its trunk fenestrations were shown, along with bilateral distribution of MdCA branches.

CONCLUSIONS

The wide range of variability of the median callosal artery in human fetuses, presented in this paper, contributes to anatomical knowledge on the anterior part of cerebral circulation.

Congenital unilateral absence of the internal carotid artery associated with aneurysms of different arteries: a review

There are four hundred and sixty- six cases of absent unilateral (398) and bilateral (68) internal carotid artery (ICA) published in online books, abstracts and original articles from 2020. to 2021. Of the 398 cases of absent unilateral ICA, 95 were associated with aneurysm. The analysis of these cases includes age, nationality and gender, location of aneurysm(s), description, and scheme of carotid-vertebrobasilar angioarchitecture mode in the brain base, as well as hypothesis on embryonic background of accompanying vascular variations and abnormalities. Calculated ratio between number of absent unilateral ICA cases and number of absent bilateral ICA cases is 5.8:1. The ratio between the total number of cases of absent unilateral ICA and those associated with aneurysms is 4.2:1. The association between the posterior communicating-middle cerebral anastomosis and intercavernous (trans-sellar or intercarotid) channel with absence of both anterior cerebral and anterior communicating arteries is common. More than half of the cases with aneurysms are located at the anterior segment vessels of the cerebral arterial circle. This review is based on the description and explanation of embryology and morphology of absent unilateral ICA with aneurysms, which would be significant contribution to published literature on this topic, especially due to the fact that nothing similar has been published since 1957.

Double unilateral fenestration of the anterior cerebral artery in the pre-communicating segment: a report of a unique case

A unique example of two fenestrations of the pre-communicating (A1) segment of the right anterior cerebral artery (ACA) in a 78-year-old woman was a special case among 388 cadaveric specimens. It was found by a retrospective review of the personal data obtained during graduate and undergraduate studies at the Faculty of Medicine. Two unequal fenestrations of the right A1 segment were associated with the presence of a pseudo anterior communicating artery, hypoplasia of the right posterior communicating artery and the left superior cerebellar artery, absence of the right anterior inferior cerebellar artery, and ectasia of the basilar artery; however, the cerebral arteries were without aneurysm(s) or other pathology. The reason could be the almost equal ACA diameter on both sides.

Congenital absence of the bilateral internal carotid artery: a review of the associated (ab)normalities from a newborn status to the eighth decade of life

PURPOSE

Due to the fact that the internal carotid artery (ICA) is responsible for nourishing two thirds of the brain volume, our aim was to inspect the morphofunctional consequences of the bilateral lack of this artery.

METHODS

In order to examine this condition, we referred to both the library archive of our Faculty of Medicine and electronic databases of anatomical and clinical reports that included the following keywords: "absence," "aplasia," or "agenesis" in combination with "internal carotid artery," "common carotid artery," or only "carotid artery."

RESULT

We found 60 recorded cases of the bilateral ICA absence in the subjects of newborn status to the eighth decade of life, which had been discovered in 20 countries. The following ten parameters were described: the embryological base, terminology, history, incidence, general data, differential diagnosis, collateral circulation, the associated vascular aplasia and/or other variants, pathophysiology, and the importance in praxis.

CONCLUSION

This review noted all the cases of the bilateral ICA aplasia published for the past 104 years. Although there were 11.6% of cases of the associated cerebral aneurysms and 1-4 cases of 16 other diseases, approximately one quarter of the cases was without any pathology.

Unilateral Aplasia versus Bilateral Aplasia of the Vertebral Artery: A Review of Associated Abnormalities

Morphological characteristics of 108 cases of uni- and bilateral aplasia of the vertebral artery (VA) in reports or images of retrospective studies, including one recent case, published between 1967 and 2016 are analyzed. Incidence, gender, persistence of carotid-vertebrobasilar anastomosis (CVBA), associated with other vascular variants, and vascular pathology in each group of uni- and bilateral VA aplasia are mutually compared. Most of the cases of VA aplasia in ages 31 to 80 were discovered in USA, Japan, and India. The bilateral VA aplasia is more common in the male gender than in the female one. The side of the VA aplasia had a significant effect on the side of CVBA persistence. Associated aplasia of other arteries was more common in cases of unilateral VA aplasia. The left VA was more commonly hypoplastic in cases of single right VA aplasia than the right VA in cases of single left VA aplasia. Aneurysms of definitive arteries were more frequent in cases of single right VA aplasia than in cases of single left VA aplasia. We claim that the aplasia of the VA probably depends on genetic factors in some races, while diseases are expressed usually in persons over 30 years of age.

Association of Two Primitive Carotid-Basilar Anastomoses and Cerebrovascular Abnormalities on the Brain Base: A Case Report

Simultaneous presence of the persistent primitive trigeminal artery and so-called intermediate communicating artery was discovered in a 77-year-old cadaver autopsied due to the myocardial infarction. Many vascular variants and abnormalities such as aplasia of the right vertebral artery (VA), presence of two right posterior cerebral arteries (PCAs), partial duplication of the right superior cerebellar artery, hypoplasia of the pre-communicating part (A1) of the right anterior cerebral artery and the right PCA of basilar origin, a special configuration of the anterior communicating artery (ACoA), and a small aneurysm at the right A1-ACoA junction were associated. The finding of an incipient cerebral aneurysm at the junction of the hypoplastic A1 and embryonal configuration of the ACoA in the eight decade of life indicates that its development was caused by long-term pressure of blood flow at branching points of this artery independent from its caliber. However, it is not yet clear whether the persistence of the first and/or the second carotid-basilar anastomoses in this case was the condition for an aplasia of one VA or vice versa.

Fenestrations and Various Duplications of the Posterior Communicating Artery in the Prenatal and Postnatal Periods

BACKGROUND

The 2 paired arteries-the posterior communicating arteries (PCoAs) and the precommunicating parts of the posterior cerebral arteries-form the so-called posterior segment of the cerebral arterial circle on the base of the brain. A number of (ab)normal morphologic features were described in the literature (e.g., unusual kinking, or extreme elongations, hypoplasia, duplications, fenestrations, the infundibular widening, or aplasia of the PCoA in the prenatal and/or postnatal periods). The aim of this study was to analyze an incidence of various fenestrations and duplications of the PCoA, and describe their general features and their association with other vascular abnormalities.

METHODS

The research was performed on the brains of 200 human fetuses and 377 adult cadavers of both genders and different ages using microdissection and macrodissection methods.

RESULTS

There were 0.34% cases with PCoA fenestrations and 3.12% cases with various PCoA duplications. Their morphologic features were described and compared with the similar PCoA abnormalities recorded in the scientific literature. There was no association between the PCoA and either duplication or aneurysm in adult cases.

CONCLUSIONS

After thorough examination, the fenestrations and duplications of the PCoA are distinguished as 2 special forms of vascular abnormalities, and the PCoA duplications are characterized as partial and total. Furthermore, whereas the low incidence of a fenestration of the PCoA suggests it to be a sufficiently rare phenomenon, the duplications of the PCoA trunk are fairly frequent, especially concerning its terminal segment.

Fenestrations of the human posterior cerebral artery

BACKGROUND

The posterior cerebral artery (PCA), as a paired terminal branch of the basilar artery, runs through four segments (P1 to P4) to the inferior and medial surfaces of the occipital and a part of the temporal lobes. There are many PCA variants in its course. The literature data indicated that a fenestration of the PCA was very rare and that its clinical significance is unknown. The purpose of this investigation was to present the frequency, location, and some morphological features of PCA fenestration in the prenatal and postnatal period.

METHOD

Using brain bases of 468 (200 fetal and 268 adult) cadavers, we applied macroscopic and microscopic investigation.

RESULTS

We found four (0.85 %) cases of PCA fenestrations-two at the left and right P1 segment of fetuses, respectively, then one adult at the left P2 segment, as well as one adult at one right PCA of the two existing arteries. There were associated multiple vascular abnormalities in one adult case. We did not find any case of PCA aneurysm originating from fenestration, as well as from PCA without fenestration.

CONCLUSION

The frequency, segment, and side location, as well as the size and shape of PCA fenestrations in specimens of our population did not significantly differ from the same in other populations. PCA fenestrations in our adult specimens were not the bases of aneurysms.

Morphology of the cerebral arterial circle in the prenatal and postnatal period of Serbian population

BACKGROUND

In the literature, there are descriptions of morphological types of the cerebral arterial circle (CAC) of different human populations around the world, but not the Serbian population. This additionally inspired the authors to present the results of previous and current researches of CAC's configuration in the prenatal, as well as in the postnatal period.

METHOD

The study was performed on CACs of 190 human fetuses and 143 adult cadavers. The caliber and configuration of fetal vessels were examined under the operating microscope, while the same of adults were studied using the ImageJ. Statistical analysis of CACs vessels' calibers was performed. Classification into one of CAC morphological types was based on the presence of hypoplasia of corresponding vessel(s).

RESULTS

There was not only significant difference of the three communicating arteries calibers before and beyond the 16th week of gestation. Calibers of the right pre-communicating part of the posterior cerebral artery and right cerebral part of the internal carotid artery were significantly higher in male than in female adults. There were 13 morphological types of CACs from the prenatal to the postnatal period. Most frequent CAC types were the type I (normal CAC) prenatally and type IV (unilateral hypoplasia of the posterior communicating artery) in the postnatal period. There were not relationships between the cerebral cause of death and a presence of aneurysm.

CONCLUSION

Results of this study will be the basis for future investigation of CACs according to the same or different ages and causes of disease and/or death.

Vertebral and/or basilar dolichoectasia in human adult cadavers

BACKGROUND

Intracranial arterial dolichoectasia is a condition in which arteries demonstrate an increase in length and diameter, with the vertebrobasilar system being the most commonly affected segment. Because the criteria for and degree of vertebrobasilar dolichoectasia are usually established on three-dimensional time-of-flight MR angiography, we presented the results of an anatomic study of vertebrobasilar dolichoectasia cadaveric specimens.

METHOD

Examination was carried out on the brains of human adult cadavers, routinely dissected at the Institute of Forensic Medicine. Measurement of the outer diameter and length of vertebral and/or basilar arteries was performed using the ImageJ processing program.

RESULTS

There were 14 cases (14/216) of vertebral and/or basilar (dolicho)ectasia. Their classification into special (sub)types is made according to the basilar and/or vertebral diameter. The basilar length ranged from 32.91-59.37 mm, and the basilar outer diameter ranged from 3.51-8.92 mm in relation to the corresponding point of its measurement. The outer diameter of the vertebral arteries ranged from 0.67-5.91 mm. The Games-Howell post hoc test additionally showed that a basilar outer diameter of grade III and IV was significantly larger than in grade II (p < 0.05).

CONCLUSIONS

We noted a predisposition of males older than 40 years to arterial dolichoectasia in the vertebrobasilar system, independently from population group, as well as its asymptomatic appearance, independently from the presence of atherosclerotic plaques.

Trigeminal artery: a review of normal and pathological features

OBJECTS

Carotid-vertebrobasilar anastomoses-the trigeminal, otic, hypoglossal, and proatlantal intersegmental arteries-serve as transitory channels between primitive internal carotid arteries and bilateral longitudinal neural arterial plexus, which is the precursor of future basilar artery, when the human embryo reaches about 4-mm length.

MATERIAL AND METHODS

Normal and/or abnormal morphofunctional aspects of the prenatal and postnatal forms of the trigeminal artery are described according to personal and literature data. Many arteries of similar origin and course are also noted in the differential diagnosis of the trigeminal artery.

CONCLUSIONS

The persistent primitive trigeminal artery, as the most commonly carotid-vertebrobasilar anastomosis, has a reported incidence of 0.03-2.2% in the literature. There is female sex predilection, and it may be discovered in patients of any age, on either side, and in association with many vascular variants. Although the significance of persistent primitive trigeminal artery regarding the development of an aneurysm or association with another pathological condition may not be clear, its (ab)normal morphology is the inspiration for anatomists, especially for neurosurgeons, before planning diagnostic and therapeutic procedures.

Morphometric analysis of human sciatic nerve perineurial collagen type IV content

OBJECTIVES

Aging is the process which unavoidably alters structure and function of the basal membranes in humans. Though, collagen type IV presents the most prominent component of the basal membranes, we estimated its presence in the perineurium of the human sciatic nerve samples during the aging process.

MATERIALS AND METHODS

Material was 12 sciatic nerve samples, obtained from cadavers whose age ranged from 36 to 84 years. Cadavers were classified into three age groups: first which age ranged from 35 to 54 years, second which age ranged from 55 to 74 years and third which included cases older than 75 years. Tissue slices were further stained by labeled streptavidin-biotin method with collagen type IV monoclonal antibody and analyzed with light microscope under 100× lens magnification with oil immersion. Digital images of sciatic nerve perineurium were further processed and analyzed with ImageJ software.

RESULTS

Our results showed that there is statistically significant increase of perineurial area, perimeter, collagen type IV area, and collagen type IV area per perineurial perimeter unit in the third age group. These parameters also increased in the second age group, but this increase was not significant. Multiple regression analysis showed that beside fascicular size, age more significantly predict perineurial collagen type IV content.

CONCLUSIONS

Results of morphometric and statistical analysis pointed to the conclusion that there is significant increase of sciatic nerve perineurial thickness during the aging process. This increase might represent the consequence of perineurial collagen type IV deposition with aging.

An excess vessel in the posterior part of the human cerebral arterial circle (CAC): a case series

BACKGROUND

As a continuation of the previous findings in human fetuses, accidental finding of an accessory vascular component in the posterior part of CAC of human adult cadavers inspired the authors to present and compare its posterior part configuration.

CASE PRESENTATION

Examination was carried out on brains of 48 human adult cadavers, routinely dissected at the Institute of Forensic Medicine. The aberrant vessel in the posterior part of four CACs was discovered.Vascular components of the posterior segment of CAC or of the whole CAC were described and photographed. A comparison between fetal and adult cases was also presented.

CONCLUSIONS

Based on the fact that the age of the four presented cases ranged from 73 to 84 and based on the causes of their death, we concluded that the angioarchitecture of the posterior part of the CAC is a consequence of the embryonic or primitive arterial stabilization and interaction with normal adult vessels.

Human bony jugular foramen: some additional morphological and morphometric features

BACKGROUND

The jugular foramen, the bony opening on the basis of skull, is an opening through which pass the ninth, tenth, and eleventh cranial nerves, two dural sinuses, and the meningeal branches of the occipital and ascending pharyngeal arteries. The increasing use of modern diagnostic procedures and new surgical approaches has created a need for much more detailed anatomical studies and explanations. This article reveals some additional features.

MATERIAL/METHODS

Fifty jugular foramina of skulls of persons of unknown age and gender were examined. The morphological characteristics of all the investigated jugular foramina were described, measured, and compared, taking into consideration their side.

RESULTS

All quantitative mean values, except for the width of the anteromedial compartment, were greater on the right side; of these, the lengths and widths of the posterolateral compartment were significantly greater. The bipartite form of the jugular foramen dominated. Complete bony bridging of the jugular foramen was found in 24% of cases. There is no rule of simultaneous complete bony bridging of the jugular foramen and splitting of the hypoglossal canal.

CONCLUSIONS

A detailed examination of the jugular foramen anatomy was performed. The main types of jugular foramina and the frequencies of bipartite or tripartite division were established. Several dimensions of the parts of the jugular foramen were measured. Some new data could provide important information about the anatomy of the jugular foramen for reliable surgical interventions in this area.

Otic artery: a review of normal and pathological features

Three primitive arteries - the trigeminal, otic and hypoglossal take the names according to their close relation with the V, VIII and XII cranial nerves, while at the cervical level, the first segmental artery is named the primitive proatlantal intersegmental artery. When the human embryo is 4 mm long, these arteries serve as transitory anastomoses between primitive internal carotid arteries and bilateral longitudinal neural arterial plexus, which is the precursor of future basilar artery. Normal and/or abnormal morphofunctional aspects of the prenatal and postnatal forms of the otic artery are described according to the personal and literature data. Many (ab) normal arteries are also noted in differential diagnosis of the otic artery. Postnatally, individual incidence rates of the carotid-vertebrobasilar anastomoses have been found to be inversely related to their order of disappearance. The persistent trigeminal artery has a reported incidence from 0.06-0.6%, whereas the persistent primitive otic artery has been convincingly documented only in minor rates. Persistent carotid-vertebrobasilar anastomoses between the anterior and posterior cranial circulation are important to recognize during angiography for endovascular and surgical planning. Most frequently, the otic artery was an incidental finding.

Proatlantal intersegmental artery: a review of normal and pathological features

OBJECTS

Primitive carotid-vertebral and carotid-basilar anastomoses are formed early during human embryogenesis at approximately 24 days. From cephalic to caudal direction, these anastomoses are cranial extensions of the primitive internal carotid, trigeminal, otic, hypoglossal and proatlantal intersegmental arteries.

MATERIALS AND METHODS

Normal and/or abnormal morphofunctional aspects of prenatal and postnatal forms of the proatlantal intersegmental artery, from the 24th day of gestation to postnatal eight decades, are described according to personal and literature data. Many (ab) normal carotid-vertebral anastomoses are also marked in differential diagnosis of the proatlantal intersegmental artery.

CONCLUSIONS

The proatlantal intersegmental artery maintains the posterior circulation until the vertebral arteries are fully developed between the seventh and eighth gestational weeks. When this artery fails to obliterate, it becomes persistent one. The proatlantal intersegmental artery, most commonly, is an incidental finding or it may be of clinical significance in some patients.

Human fetal medial striate artery or artery of Heubner

OBJECT

The authors describe some of the features of the medial striate branch or recurrent artery of Heubner (RAH). This structure has indisputable functional, neurological, and neurosurgical significance, and originates from the A(1) and/or A(2) segments of the anterior cerebral artery.

METHODS

Microdissection of 94 human fetal specimens was performed. The RAH was observed in 97.3% (single in 71.6%, double in 25.1%, and triple in 3.3%) of the cases. Its origin was from A(2) in 42.3% of specimens, from the A(1)-A(2) junction in 25.7%, and from A(1) in 20%.

RESULTS

Five types and 14 subtypes of the RAH were identified, determined based on vessel origin and number. In its course, the RAH gave 1-12 branches, and the terminal part most frequently penetrated into the brain through the anterior perforated substance at the level of the sphenoid segment of the middle cerebral artery. The specimens with a single RAH fenestration, abnormal double RAH anastomosis, and unusual RAH origin and relationship to the surrounding vessels represented new data.

CONCLUSIONS

The authors' observations of common anatomical variations in the number and origin of the RAH, as well as its abnormalities, may assist neuroradiologists in the interpretation of diagnostic test results and neurosurgeons in performing procedures in the anterior cerebral circulation.

Age-Related Changes of the Human Fetal Kidney Size

Early prenatal diagnostics and the importance of genetic counseling are of great interest for echosonographic evaluation of normal fetus anatomy. Development of the human fetal kidney runs through a series of continual and mutually dependent changes during which the kidney obtains its morphological and functional maturity. This study was created to estimate the changes in kidney size during gestation in fetuses from the 4th to the 10th lunar month, to evaluate the dynamics of their growth, as well as to establish the validity of the volume calculated from these dimensions. Serial measurements of kidney dimensions (length, width, thickness) were performed in 110 fetuses. Photomicrographs of kidneys from the 4th, 6th, 8th and 10th lunar months are also presented. On the basis of the results obtained by our examination, we concluded that the period from the 14th to 16th week of intrauterine life is the fastest period of kidney growth during fetal development. Using the ellipsoid formula for calculating the fetal renal volume offers an underestimation of about 32-33% on average. The importance of this study lies in determining the average fetal kidney dimensions, which could be used as standard values in obstetrics.

The level of the sciatic nerve division and its relations to the piriform muscle

Background. The sciatic nerve, as the terminal branch of the sacral plexus, leaves the pelvis through the greater sciatic foramen beneath the piriform muscle. Afterwards, it separates into the tibial and the common peroneal nerve, most frequently at the level of the upper angle of the popliteal fossa. Higher level of the sciatic nerve division is a relatively frequent phenomenom and it may be the cause of an incomplete block of the sciatic nerve during the popliteal block anesthesia. There is a possibility of different anatomic relations between the sciatic nerve or its terminal branches and the piriform muscle (piriformis syndrome). The aim of this research was to investigate the level of the sciatic nerve division and its relations to the piriform muscle. It was performed on 100 human fetuses (200 lower extremities) which were in various gestational periods and of various sex, using microdissection method. Characteristic cases were photographed. Results. Sciatic nerve separated into the tibial and common peroneal nerve in popliteal fossa in 72.5% of the cases (bilaterally in the 66% of the cases). In the remainder of the cases the sciatic nerve division was high (27.5% of the cases) in the posteror femoral or in the gluteal region. Sciatic nerve left the pelvis through the infrapiriform foramen in 192 lower extremities (96% of the cases), while in 8 lower extremities (4% of the cases) the variable relations between sciatic nerve and piriform muscle were detected. The common peroneal nerve penetrated the piriform muscle and left the pelvis in 5 lower extremities (2.5% of the cases) and the tibial nerve in those cases left the pelvis through the infrapiriform foramen. In 3 lower extremities (1.5% of the cases) common peroneal nerve left the pelvis through suprapiriform, and the tibial nerve through the infrapiriform foramen. The high terminal division of sciatic nerve (detected in 1/3 of the cases), must be kept in mind during the performing of popliteal block anesthesia. Conclusion. Although very rare, anatomical abnormalities of common peroneal nerve in regard to piriform muscle are still possible.

Morphological aspect of the thyroid ima artery in human fetuses

Some morphological characteristics of the variable thyroid ima artery were investigated on the injected fetal arteries and explained on their 106 static images. Thyroid ima artery of different origin was proven in 18 (16.9%) cases. With respect to the vascular sources of the investigated artery, the branching of the brachiocephalic trunk and right common carotid artery was found in 72.1% of the cases. At the same time, the thyroid ima and superior or inferior thyroid arteries were obvious in all cases, as well as the presence of single or multiple variations and abnormalities of neighbouring arteries in 38.8% of the cases. No major anatomical difference was noted between the fetal form of the variable thyroid artery reported in this paper and the postnatal form reviewed from the literature. Thyroid ima artery probably represents an example of the arterial self-differentiation and induced differentiation of the unilateral vascular trunk.

Comparative morphological variations and abnormalities of circles of Willis: a minireview including two personal cases

Two rare cases of the circle of Willis are presented. One of them represents a fetal circle of Willis (crown-rump length, or CRL, 17 cm), the other one is adult circle from a male cadaver 65 years of age. Arterial variations and abnormalities of the represented circles of Willis are described. Interpretation of the appearance of variations and abnormalities is based on the acceptable embryological, anatomical, and clinical reports. Summarizing these opinions, we have supplemented them with a hypothesis that arterial variations and abnormalities could preserve their relationships because of constant interaction between primitive arterial remnants and cerebral arteries in postnatal life, unless some pathological lesions appear.