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At least 19 recordsLinked to original sources
PubMedDate not supplied

[Redundancy of the main cerebral arteries in morphological variations of the Willis circle].

The study presents a computer simulation of the cerebral blood flow in three variants of the circle of Willis. The redundant function of the circle of Willis during occlusion of the internal carotid and basilar arteries was estimated. The major role of the circle of Willis in the redistribution of blood to certain areas of the brain in periods of flow disturbances is pronounced. Complete maintenance of the cerebral blood flow (without any additional autoregulatory mechanisms) during occlusion of the vertebro-basilar or internal carotid systems in some morphological variations of the circle of Willis was demonstrated.

Arterial Occlusive Diseases↗
PubMed2001

[Idiopathic sudden hearing loss: role of the posterior communicating cerebral arteries of the Willis' circle].

Sudden hearing loss (SHL) is a neurosensorial hearing loss of variable entity with an onset of less than three days. In most cases (85-90%) it is of unknown etiology (idiopathic sudden hearing loss--ISHL). The most accredited hypotheses for origin are: viral, immunitary and vascular. ISHL accounts for approximately 1% of all neurosensorial hearing loss; onset is most frequent in winter, i.e. January and February, and it most frequently affects women, particularly at 15 and between 40-50 years of age. In order to evaluate the role of vascular condition on the onset of ISHL, we focused our attention on the circle of Willis. The results confirm that, in the absence of cerebro-vascular pathology, posterior communicating arteries (PCAs) that cannot be activated--evaluated by transcranial Doppler (TCD)--are associated with ISHL. Moreover, hemodynamic alterations detected in the basilar artery in ISHL patients are correlated with the final prognosis for hearing. These observations highlight the importance of TCD in testing subjects at risk for idiopathic SHL and show that PCAs are essential in maintaining normal cochlear function.

Adult↗
PubMed1975

[Atherosclerosis of the vessels of Willis' circle in certain variants in its structure].

Random studies of the base of the brain vessels in 278 men who had died at the age of 50--64 years were carried out; 29 variants of the structure of the circle of Willis were established; the most common were threadlike connective arteries and posterior trifurcations of the inner carotid arteries. The investigation of atherosclerotic changes in every vessel of the base of the brain showed that in the so-called posterior trifurcations there was a statistically reliable growth of the average degree of atherosclerosis in the intracranial region of the inner carotid artery ensuring in these cases the blood supply for a considerably greater region of the brain. In posterior connective arteries atherosclerotic changes were revealed only when their diametre exceeded 0.1 cm which testified to the bloodflow in these arteries.

Carotid Artery, Internal↗
PubMed1997

Extended Willis circle model to explain clinical observations in periorbital arterial flow.

A fluid-dynamic model of the circle of Willis and its periorbital links with the external carotid arteries has been established and tested. It is based on anatomic data and takes Doppler measurements as flow input conditions. The model explains, on fluid-dynamic grounds, the clinical observations of periorbital reverse flow and arrival pulse time delay. It also obtains the velocity and pressure pulse at any point of the studied area. This allows the comparison between the normal or healthy condition and the flow distribution when an internal carotid is externally or pathologically occluded. Several combinations of the communicating artery sizes are explored to obtain the reduced cerebral flow. The combination of the communicating diameters can lead to insufficient irrigation which can be hydrodynamically assessed. No other physiological response is included, and the results must be considered as a minimum assured. These results show the need for a common evaluation of the alternative paths and explain some paradoxes found in literature.

Algorithms↗
PubMed1996

[Introduction to the study of the Willis circle with transcranial color Doppler: methodological notes and preliminary experience].

To date, adult intracranial circulation has been studied only with pulsed-wave Doppler US, which is a useful diagnostic tool even though several technical and practical limitations are related to the difficult location of intracranial vessels. Recently, dedicated color-Doppler transducers have been proposed, which can pass through the skull which makes a physiologic barrier for the US beam: this technique has been called transcranial color-Doppler (TCD). We report on our personal experience with TCD in 30 healthy volunteers (12 men and 18 women, age range: 17-75 years) submitted to TCD for Willis circle imaging. We used an ATL Ultramark 9HDI unit with a phased array transducer (3.5 MHz) and 2 MHz Doppler frequency; the PRF was 3000 Hz, with 80% color gain. 100 Hz wall filters were used. The middle cerebral artery was always shown correctly in all subjects, while the posterior one was depicted only in 7 cases (23.3%); in contrast, the anterior cerebral artery was demonstrated in 3 cases only (10%). Nowadays, TCD is mostly applied to normal intracranial circle studies, to assess normal blood speed values more accurately. To this purpose, both the direct visualization of blood vessels and the flowmetric values obtained measuring the incidence angle are useful pieces of information. TCD permits a more accurate study of intracranial local blood flow in the Willis circle and of its changes in pathologic conditions. In contrast, TCD yield is poor in characterizing intracranial tumor tissue.

Adult↗
PubMedDate not supplied

The usefulness of dynamic CT in patients with aneurysm of Willis circle. Comparative study with the angiography.

The diagnosis of cerebral aneurysm is currently based on the angiographic data. We have tried to evaluate the usefulness of a less-invasive examination, such as the dynamic-CT, in the diagnosis of intracranial aneurysm and of the possible and concomitant subaracnoid haemorrhage. The CT examination is useful in the diagnosis of both subarachnoid haemorrhage and giant trombosed aneurysm. It is less reliable than the angiography as regard to aneurysm of small dimension.

Adult↗
PubMed1995

[Multiple intracranial aneurysms and asymmetrical circle of Willis].

In a consecutive series of 268 patients harboring saccular aneurysms confirmed by digital subtraction angiography (DSA) all major blood vessels of the brain, 36 patients (13.4%) with multiple aneurysms were identified. Majority of them (around 58%) were between 40 to 60 years of age, around 22% were below 40 years of age, but no was younger than 30 years of age. The asymmetric Willis circle was identified in 26 patients (74.2%) A hypoplastic A1 segment of the anterior cerebral artery was revealed in 10 patients; a combination of the hypoplastic A1 segment and the fetal type of the posterior communicating artery with a hypoplastic P1 segment of the posterior cerebral artery were found in 9 cases, while 7 patients had only the fetal posterior communicating artery. A suggestion was put that the asymmetric circle of Willis, prenatal or acquired in postnatal life is inclined of developing aneurysm (multiple aneurysms) only if there exist a hemodynamic stress in postnatal life producing degenerative lesions of the circle of Willis at the site of the augmented hemodynamic vascular wave.

Adult↗
PubMedDate not supplied

[Aneurysms of the anterior communicating artery and anomalies of the anterior part of the circle of Willis].

Aneurysms of the anterior communicating artery are much more frequently encountered in subjects with developmental anomalies of the anterior part of the Willis circle than in the general population. The most frequent anomaly is hypoplasia of the A1 ACa segment, duplication of the anterior communicating artery or accessory artery of the corpus callosum. In the material of the authors of 130 surgically treated cases of the aneurysm situated in the anterior communicating artery complex developmental anomalies were found in 37.7%.

Brain↗
PubMed1989

[Compression of structures in the visual pathway by arteries of the circle of Willis in suprasellar tumors].

The mechanical compression of optic nerves, of the chiasma of optic pathways by vessels of Willis circle was revealed in 12 of 34 necropsies of extensive craniopharyngiomas and pituitary adenomas and in three of 109 patients operated on account of these tumours. The localization of pressure changes, from shallow grooves on the surface of optic structures to almost complete interruption of their anatomical continuity, depended on the localization of the tumour in relation to the chiasma. This relation was influenced in particular by two factors, the site of the primary development of the tumour and the premorbid localization of the chiasma. Impaired optic functions were the result of the action of pressure of the tumour exerted on the area and pressure of firm vascular structures on a defined portion of the optic pathway, which begins to act only when the tumour is large and has a more malignant effect than the pressure of the tumour itself.

Circle of Willis↗
PubMed1988

[Study of the circle of Willis with digital angiography. Contribution to the detection of high-risk carotid clamping].

Radiological studies of Willis' circle morphology are mainly performed in search of intracerebral aneurysms, and for this purpose digital imaging has not superseded conventional radiology. In contrast, conventional imaging does not seem to have given satisfactory results in the functional study of this substitute vascular network, and it is in this field that digital angiography is of particular value. Between January, 1985 and June, 1986, we performed 300 digital angiographies of the supra-aortic vessels in patients with carotid artery stenosis. Each exploration included a stage of investigation for intracranial substitute vessels by compression of the carotid artery on the side of the lesion. Substitute vessels were found to be adequate in 93 p. 100 of the cases. The test showed that there was no alternative blood flow in 3.7 p. 100 of the cases, which made it imperative to use brain protection measures during clamping of the carotid artery. The substitute network was found to be insufficient in 1 p. 100 of the cases, and the method failed in 2.4 p. 100.

Carotid Arteries↗
PubMedDate not supplied

The anatomy of aneurysm-bearing circles of Willis.

The circle of Willis is known to exhibit considerable anatomical variability. The incidence of variations of the circle is said to be greater when an aneurysm is present, particularly one of the anterior communicating artery. In this study 40 circles of Willis bearing 51 saccular aneurysms were dissected and examined macroscopically. Forty circles from patients with other neurological diseases served as controls. Ninety-seven per cent of circles bearing aneurysms showed variations from a hypothetical "normal" structure, as did 85% of controls. The aneurysm group as a whole, and circles bearing anterior communicating aneurysms, showed a higher incidence of anterior cerebral artery asymmetry than controls (p less than 0.001), as did the latter when compared with circles bearing aneurysms at other sites (p less than 0.01), but there were no other significant differences.

Circle of Willis↗