Collateral ability of the circle of Willis in patients with unilateral internal carotid artery occlusion: border zone infarcts and clinical symptoms.

BACKGROUND AND PURPOSE: The circle of Willis is regarded as the major source of collateral flow in patients with severe carotid artery disease. The purpose of the present study was to assess whether the presence of border zone infarcts is related to the collateral ability of the circle of Willis in symptomatic (transient ischemic attack, minor stroke) and asymptomatic patients with unilateral occlusion of the internal carotid artery (ICA). METHODS: Fifty-one patients (35 symptomatic, 16 asymptomatic) and 53 control subjects were investigated. Patients had unilateral occlusion of the ICA and contralateral ICA stenosis between 0% and 69%. The directions of flow, on the side of the ICA occlusion, and the size of the component vessels in the circle of Willis were investigated with MR angiography. RESULTS: On average, 92% of the patients without border zone infarcts (n=26) had willisian collateral flow compared with 60% of patients with border zone infarcts (n=25; P<0.05). This increase in collateral flow was caused by the high prevalence of collateral flow via the posterior communicating artery in patients without border zone infarcts (50% versus 12%; P<0.05). No statistically significant relation was found between the pattern of collateral flow via the circle of Willis and the presence of clinical symptoms. Nevertheless, asymptomatic patients with ICA occlusion demonstrated an increased diameter of the anterior communicating artery (P<0.05). CONCLUSIONS: In patients with unilateral ICA occlusion, the presence of collateral flow via the posterior communicating artery in the circle of Willis is associated with a low prevalence of border zone infarcts. Asymptomatic patients with an ICA occlusion do not have an increased collateral function of the circle of Willis.

Circle of Willis collateral flow investigated by magnetic resonance angiography.

BACKGROUND AND PURPOSE: The circle of Willis (CW) is considered an important collateral pathway in maintaining adequate cerebral blood flow in patients with internal carotid artery (ICA) obstruction. We aimed to investigate the anatomic variation of the CW in patients with severe symptomatic carotid obstructive disease and to analyze diameter changes of its components in relation to varying grades of ICA obstruction and in relation to the presence or absence of (retrograde) collateral flow. METHODS: Seventy-five patients with minor disabling neurological deficits and with ICA stenoses or occlusions were categorized into 4 groups according to the severity of ICA obstruction. This patient population reflected a relatively favorable subgroup of cerebral infarction (considering their minor neurological deficits). All subjects underwent magnetic resonance angiography, including magnetic resonance angiography sensitive to flow direction. CW morphology and the size of its components were determined and compared with those values in control subjects (n=100). RESULTS: Compared with control subjects, patients demonstrated a significantly higher percentage of entirely complete CW configurations (55% versus 36%, P=0.02), complete anterior configurations (88% versus 68%, P=0.002), and complete posterior CW configurations (63% versus 47%, P=0.04). Patients with severe ICA stenosis did not show significantly increased CW vessel diameters. Patients with ICA occlusion demonstrated a high prevalence of collateral flow through the anterior CW and significantly increased diameters of the communicating channels. Patients with bilateral ICA occlusion relied on collateral flow via the posterior CW and demonstrated a bilateral increase in posterior communicating artery diameters (P<0.05). CONCLUSIONS: The anatomic and functional configuration of the CW reflects the degree of ICA obstruction.

Effect of age on cerebral blood flow: measurement with ungated two-dimensional phase-contrast MR angiography in 250 adults.

PURPOSE: To determine the normal values and effects of age and sex on total cerebral blood flow (CBF) as measured with ungated two-dimensional phase-contrast magnetic resonance (MR) angiography. MATERIALS AND METHODS: Volume flow rates in the basilar artery and both internal carotid arteries were measured on two-dimensional phase-contrast MR angiograms obtained in 250 subjects (age range, 19-88 years; mean age, 50 years) undergoing MR imaging because of indications other than cerebrovascular disease. Volume flow rates for the three arteries were summed to obtain the total CBF, and the values were analyzed in terms of age and sex. RESULTS: Mean total CBF was 616 mL/min +/- 143. There was a significant yearly decrease with age in total CBF of 4.8 mL/min (P < .001). Mean total CBF ranged from 748 mL/min +/- 121 to 474 mL/min +/- 105 in subjects aged 19-29 and 80-89 years, respectively. No sex differences were found. Mean relative contributions of the right and left internal carotid arteries and the basilar artery to total CBF were 41%, 40%, and 19%, respectively, with no substantial change due to age. CONCLUSION: Ungated two-dimensional phase-contrast MR angiography is a useful, noninvasive technique for assessing total CBF. By using this technique, a significant decrease in total CBF with age was demonstrated.

Circle of Willis: morphologic variation on three-dimensional time-of-flight MR angiograms.

PURPOSE: To establish normal reference values for the presence of the anatomic variants of the circle of Willis and average diameters for its component vessels by using three-dimensional time-of-flight magnetic resonance (MR) angiography and to determine whether age- or sex-related differences exist in the circle's anatomy. MATERIALS AND METHODS: One hundred fifty volunteers were grouped according to age: those aged 20-25 years (n = 50) and those aged 60-88 years (n = 100). All subjects underwent three-dimensional time-of-flight MR angiography of the arterial circle at 1.5 T. The anatomic variants of the anterior and posterior parts of the circle were determined separately, the completeness of the entire circle was assessed, and the diameters of all component vessels were measured. RESULTS: On MR angiograms, 111 (74%) subjects demonstrated a complete anterior part of the circle, 78 (52%) demonstrated a complete posterior part of the circle, and 63 (42%) demonstrated an entirely complete circle of Willis (complete anterior and posterior parts of the circle combined). The presence of an entirely complete circle of Willis was slightly higher in younger persons and in women. Most vessel diameters were smaller in women, except for the diameter of the posterior communicating artery. Statistically significant differences were found in vessel diameters between the younger and the older age groups. CONCLUSION: The authors determined normal reference values for morphologic variants and diameter measurements of the circle of Willis specific to three dimensional time-of-flight MR angiography.

Measuring blood flow by nontriggered 2D phase-contrast MR angiography.

This study was done to assess the validity of nontriggered 2D phase contrast MR angiography for measuring blood flow in human arteries and veins. Volume in the popliteal and internal carotid arteries was measured by nontriggered and triggered 2DPC in 1.3 normal volunteer (mean age 27, range 18-46). Parameter selection was guided by previous phantom experiments. Results were compared by linear regression analysis. Measurement error was determined by one-way analysis of variance of repeated measurements. In the internal carotid arteries, good agreement was found between the volume flow, Q, as determined by a triggered measurement and a nontriggered measurement: Qntr = 0.988 (+/- 0.006) Qtr, r = 0.98, SEE = 0.16 ml/s. The estimated measurement errors of both techniques were of the same order: 0.27 vs. 0.31 ml/s. Substantial deviations between triggered and nontriggered 2DPC were found in the popliteal artery: Qntr = 0.827 (+/- 0.028) Qtr, r = 0.97, SEE = 0.12 ml/s. The estimated measurement error of nontriggered 2DPC turned out to be twice as large as of triggered 2DPC here: 0.22 vs. 0.13 ml/s. We believe that nontriggered 2DPC is a valid technique for measuring blood flow in stationary vessels with weakly pulsatile flow, but merely provides a rough estimation for strongly pulsatile flow. In its current implementation, nontriggered 2DPC provides the data in 40 s, whereas triggered 2DPC requires 3-4 min, and offers additional time savings with regard to patient preparation and data processing.

Arterial tortuosity in the femoropopliteal region during knee flexion: a magnetic resonance angiographic study.

Dynamic changes in curvature are expected in the femoropopliteal region during knee flexion. The location of the artery dorsal to the axis of movement implicates a relative length excess that may influence local morphology. To study arterial morphology in vivo, magnetic resonance angiography was performed in 22 healthy volunteers (aged 23-68 y). The curvature of the femoral vessels was studied and quantified in stretched and flexed positions. During knee flexion the vessel followed the movement of the leg and in the sagittal plane one curve was visible distal to the adductor hiatus. Three or more small curves were seen proximal to the knee joint in all volunteers. In the group aged under 30 y these minor curves were located proximal to the adductor hiatus as if the artery curls up in Hunter's canal. In the group aged over 45 y one or more curves were located distal to the adductor hiatus in the popliteal fossa. In volunteers aged 60 y and older some of these curves did not disappear during knee extension. In older individuals, natural elongation and loss of arterial elasticity will contribute to the formation of these curves. Impairment of the free gliding mechanism of the femoral vessels in the adductor canal could explain the differences in location of these minor curves between younger and older subjects. It is concluded that morphological changes in the femoral artery occur during knee flexion and that this tortuosity is age dependent. This may influence local haemodynamics and therefore possibly contribute to atherogenesis.

Accuracy and precision of time-averaged flow as measured by nontriggered 2D phase-contrast MR angiography, a phantom evaluation.

The purpose of this study was to assess the accuracy and precision of time-averaged flow as measured by nontriggered 2D PC. Mono-, bi-, and triphasic flow patterns, modelling waveforms encountered in the human vascular system, were generated by a computer-controlled flow system. Time-averaged flow velocity was measured by conventional 2D cardiac-triggered cine PC and by nontriggered 2D PC for different settings of the excitation flip angle and the velocity sensitivity. Accuracy and precision were determined by repeating the measurements (N = 6) and comparing the results against precisely known calibration values. Measurements revealed waveform-specific deviations between triggered and nontriggered acquisitions that depended on the velocity sensitivity and, more strongly, on the flip angle of the nontriggered experiment. This confirmed the theoretically predicted predominance of amplitude over phase effects. Systematic errors could be reduced by decreasing the flip angle and the velocity sensitivity, although at the expense of signal-to-noise, so that additional signal averaging was required to maintain a specified precision. The attainable accuracy appeared to be acceptable only for waveforms with a relatively low pulsatility index. The study demonstrates the feasibility of accurate and precise nontriggered velocity measurements for weakly pulsatile flow and indicates a route towards improving the reliability for highly pulsatile flow.

Spinal deformities in deferoxamine-treated homozygous beta-thalassemia major patients.

A new constellation of spinal changes are observed in homozygous beta-thalassemia major (HBT) patients receiving deferoxamine (DF), an iron-chelating drug used in combination with transfusion therapy in certain anemic syndromes. In a retrospective study of 22 HBT patients who were receiving DF therapy, morphological deformities (decreased spinal height, increased thoracic kyphosis, vertebral flattening and elongation anteriorly, and disk calcification) were found in 16 of 22 patients. These changes are believed to be caused by interference with spinal growth-plate development. Investigation of DF-dose correlation supports the conclusion that the spinal changes were DF-induced. Spinal changes observed in DF-treated patients differ both morphologically and pathogenetically from earlier reports of vertebral deformities occurring as a sequel to compensatory marrow hyperplasia in poorly transfused patients.

Occluding staghorn calcification of the aortic arch and left subclavian artery: case report.

A calcified thrombus resembling a staghorn was found in the aortic arch, cast into this shape by the aorta and its branching vessel, the left subclavian, into which it projected for a short distance. Unique, in this case, is the extraordinarily large size of the calcification which was mostly free of the vessel wall, its radiological image, and its location. Digital subtraction angiography led to the diagnosis and was confirmed on computed tomography.