MR imaging of intracranial vertebral artery occlusion

Summary Magnetic resonance (MR) images of nine patients with intracranial vertebral artery occlusion (five proved, four presumed) have been reviewed. In two of nine, both vertebral arteries were occluded and in five of the nine, the basilar artery was also blocked. All occluded arteries showed absence of flow void and were clearly demonstrated as mildly hypo-mildly hyperintense structures to brainstem parenchyma on the T1-weighted images. In two of five patients with basilar artery occlusion, retrograde filling of the distal basilar artery was detected. Thus, MR imaging, in particular the T1-weighted image, is a pertinent diagnostic modality for evaluating intracranial vertebral artery occlusion. Angiography does not seem to be required for confirmation.     

MR imaging of intracranial tuberculomas

Eight patients with intracranial tuberculomas were studied with CT and magnetic resonance (MR) imaging. Large, ring enhancing, solid lesions on CT showed low intensity on T2-weighted images and intermediate intensity on T1-weighted images. Small lesions, with ring enhancement on CT, showed central bright signal on T2-weighted images with a peripheral low intensity rim surrounded by high intensity edema. The MR imaging features of the tuberculomas were found to be distinct from those of abscesses, metastases, and gliomas.     

MR imaging of carotid webs

Purpose

We propose a magnetic resonance (MR) imaging protocol for the characterization of carotid web morphology, composition, and vessel wall dynamics. The purpose of this case series was to determine the feasibility of imaging carotid webs with MR imaging.

Methods

Five patients diagnosed with carotid web on CT angiography were recruited to undergo a 30-min MR imaging session. MR angiography (MRA) images of the carotid artery bifurcation were acquired. Multi-contrast fast spin echo (FSE) images were acquired axially about the level of the carotid web. Two types of cardiac phase resolved sequences (cineFSE and cine phase contrast) were acquired to visualize the elasticity of the vessel wall affected by the web.

Results

Carotid webs were identified on MRA in 5/5 (100%) patients. Multi-contrast FSE revealed vessel wall thickening and cineFSE demonstrated regional changes in distensibility surrounding the webs in these patients.

Conclusion

Our MR imaging protocol enables an in-depth evaluation of patients with carotid webs: morphology (by MRA), composition (by multi-contrast FSE), and wall dynamics (by cineFSE).

     

MR imaging of hemorrhagic intracranial neoplasms

Thirty patients with intracranial tumors containing hemorrhage of varying stages were examined with high-field-strength MR imaging and CT to determine what differences might exist between hemorrhagic tumor and pure hemorrhage. Pathology was obtained in the six patients with primary tumors and in 14 of the 24 patients with metastases. Similar to evolving intraparenchymal hematomas, hemorrhagic neoplasms undergo changes in their appearance that can be categorized into three distinct intensity patterns, or stages. Stage 1 is characterized as iso- or hypointensity on short TR sequences and as hypointensity on long TR sequences; stage 2 as developing hyperintensity on both short and long TR sequences, without evidence of a well-defined black rim; and stage 3 as a hyperintense lesion with a well-defined black rim on long TR sequences. An additional mixed-intensity pattern was identified, which contained areas corresponding to more than one stage. In all of the cases exhibiting this pattern, pathology confirmed that the appearance was due to recurrent bleeding. We found several characteristics on MR that, when present, suggest an underlying neoplasm. These include delay in evolution between stages, central or eccentric hyperintensity in stage 2, and a mixed-intensity pattern. In addition, the presence of a hemosiderin rim does not exclude an underlying neoplasm. We found that the MR patterns that characterize hemorrhagic intracranial neoplasms should help to determine the cause of the hemorrhage.     

Spin-echo MR imaging of intracranial hemorrhage

Summary This retrospective study was performed to describe the appearance of intracranial hemorrhagic lesions on magnetic resonance (MR) imaging at 0.35 tesla using the spin-echo technique, and define the present clinical role of MRI in this particular pathology. Forty-eight examinations of forty-three patients with forty-seven intracranial hemorrhagic lesions (39 true hematomas and 8 hemorrhagic lesions mixed with other tissues) were reviewed for this study. Comparative CT studies were available for all the patients. In our limited experience with acute hematomas (less than 3 days old), low or isointense signal was seen with a short TR (0.5 s), but a relative increase in signal intensity was observed with a long TR (2.0 s). This appearance of acute hematoma was not specific. Chronic hematomas (more than 3 days old) were imaged as foci of bright signal intensity on both short and long TR. This pattern was characteristic of chronic hematoma. With a short TR (0.5 s), two hemorrhagic lesions (5 and 7 days old) were displayed as an isointense signal surrounded by a rim of high intensity signal. This peripheral zone most likely represented liquefaction at the clot's periphery and the initial formation of methemoglobin. T1 and T2 relaxation times were found to be very long for acute hematomas (first two days). T1 values of chronic hematomas (more than 3 days old) were compaaatively short and in the same range as T1 of white matter. T2 values of chronic hematomas decreased also but remained very long.     

MR imaging of intracranial metastatic melanoma

Ten patients with intracerebral metastases from malignant melanoma were evaluated with magnetic resonance (MR) imaging performed at 1.5 T using spin-echo techniques. On the basis of histopathologic findings in three of 10 cases and CT appearances in all 10 cases, three patterns were identified on analysis of MR signal intensities in both short repetition time/echo time (TR/TE) and long TR/TE spin-echo scans. In comparison to normal cortex, nonhemorrhagic melanotic melanoma appeared markedly hyperintense on short TR/TE images and isointense, mildly hypointense on long TR/TE images. Nonhemorrhagic, amelanotic melanoma appeared isointense or mildly hypointense on short TR/TE and isointense or mildly hyperintense on long TR/TE images. Hemorrhagic melanoma varied in appearance, depending on the stage of hemorrhage. Melanotic, nonhemorrhagic melanoma can be distinguished from early and late subacute hemorrhage by its signal intensity on long TR/TE images. Spin-echo MR appears to be the method of choice for diagnosing melanotic metastases.     

MR imaging of idiopathic intracranial hypertension

We report the case of a 9-year-old male patient with idiopathic intracranial hypertension without papilledema for which MR imaging of the optic nerves and pituitary gland provided important clues for the diagnosis of idiopathic intracranial hypertension and showed a return to normal appearance after normalization of CSF pressure.     

MR imaging of basilar artery occlusion

We studied six patients with basilar artery occlusion using magnetic resonance imaging. Two patients also had arteriography. All had signs consistent with pontine infarction; three had a "locked in" syndrome. Magnetic resonance imaging (five done within 24 h of onset of progression of neurologic symptoms) revealed a linear structure of increased signal intensity in the pontine cistern on T1-weighted parasagittal images and absence of flow void phenomena. Hyperintense signals at various brain stem levels corresponding to the course of the basilar artery were noted on T2-weighted images. Multiple parenchymal abnormalities were noted in the brain stem (six), cerebellum (four), occipital lobes (two), and thalamus (two). Magnetic resonance performed early in the course of basilar artery occlusion is a high-yield, safe procedure and might eliminate the need for arteriography.     

MR imaging of calcified intracranial lesions

Fifty calcified intracranial lesions diagnosed with computed tomography (CT) were evaluated with magnetic resonance (MR) using a spin-echo sequence. MR images demonstrated 41 of 50 lesions seen as calcified on CT scans, among them 29 of 30 cerebral neoplasms and all ten arteriovenous malformations. The presence of calcification was suspected prospectively in about 60% of calcified lesions but was also suspected in 45% of uncalcified lesions (reviewed as control cases). No fine calcifications and only 25% of punctate calcifications were disclosed on MR images. In the nine lesions undetected by MR, calcification was the only abnormal CT finding. The findings of calcification on MR images were nonspecific, ranging from signal void or signal dampening on all sequences to no alteration of signal intensity. The most common finding of calcification was a focus of signal diminution, rather than signal void, as commonly reported.     

MR imaging of intracranial tuberous sclerosis

The role of MR in evaluating tuberous sclerosis is reviewed in 15 patients. These studies were compared with CT scans, which were available in 14 patients. Four characteristic findings were noted on the MR images obtained. Subependymal nodules projecting into the lateral ventricles were seen in 12 of 15 patients on T1-weighted images. This was the most specific finding. Distortion of the normal cortical architecture was seen in 10 of 11 patients in whom T1-weighted images were obtained using a 256 X 256 matrix. These foci corresponded to multiple cortical areas of increased signal on T2-weighted images. Dilated ventricles were seen in five patients. In one patient, a known astrocytoma showed increased signal on the T2-weighted images, allowing differentiation from a benign subependymal nodule. MR depicted the cortical hamartomas more completely than did CT. The MR scans were abnormal in all cases, and a diagnosis could be confidently made in all 11 cases scanned using a 256 X 256 matrix. Our preliminary experience suggests that MR will at least equal and probably exceed CT, both for sensitivity and specificity, given the use of a 256 X 256 matrix.     

MR imaging of intracranial arachnoid cysts

The magnetic resonance characteristics of 16 intracranial arachnoid cysts were evaluated and several features identified that allowed the differentiation from other cystic lesions. Uncomplicated arachnoid cyst contents respond like CSF to both T1 and T2 weighted sequences. Signal from the contiguous brain is of normal intensity. The absence of signal from cortical bone and the ease of obtaining multiplanar views enable the margins of the cyst, its contents, and the full extent of the lesion to be easily defined.     

MR imaging of intracranial fluid levels

Six patients with seven intracranial fluid levels were evaluated with both CT and MR at 1.5 T. A surgical diagnosis was obtained in six of the seven instances. MR was found to be superior to CT in detecting intracranial fluid levels, and the MR signal characteristics were helpful in identifying their contents. These cases demonstrate the necessity for a slightly different approach to lesions with fluid levels. In one patient, imaging in the prone position allowed detection of a solid component; in several others, detection of the fluid level was dependent on the selection of nonroutine windows and levels. Fluid levels are classified with respect to their components and MR features. MR is superior to CT in imaging fluid levels. The appearance of fluid levels on MR varies with their composition, the ratio of the components, the sequence parameters, and the position of the patient.     

颈动脉粥样硬化斑块的MR成像

目的：探讨MR成像技术在颈动脉粥样硬化斑块检测中的应用，及其对斑块内成份进行定性分析的可能性。方法：采用3D-TOF、Double-IR(DIR)T1WI、T2WI、PDWI序列对11位高度疑诊颈动脉粥样硬化的患者及9位健康志愿者进行颈动脉成像。部分患者行彩超对照。结果：11例患者中9例可见明显颈动脉粥样硬化改变。TOF上表现为管腔内高信号血流中见低信号充盈缺损。DIR T1WI、T2WI、PDWI表现为管壁增厚，斑块呈等、低均匀信号或等、低、高混杂信号。与多普勒彩超对比，MRI对颈动脉粥样硬化的检出准确率较高。结论：MRI对颈动脉粥样硬化可达到满意的诊断，并提示MRI能分析斑块内成份，分析斑块成份及性质为临床选择治疗方案及估计预后提供有力的帮助。     

Arterial spin-labeling MR imaging measurements of timing parameters in patients with a carotid artery occlusion

BACKGROUND AND PURPOSE: Arterial spin-labeling (ASL) with image acquisition at multiple delay times can be exploited in perfusion MR imaging to visualize and quantify the temporal dynamics of arterial blood inflow. In this study, we investigated the consequences of an internal carotid artery (ICA) occlusion and collateral blood flow on regional timing parameters.MATERIALS AND METHODS: Seventeen functionally independent patients with a symptomatic ICA occlusion (15 men, 2 women; mean age, 57 years) and 29 sex- and age-matched control subjects were investigated. ASL at multiple delay times was used to quantify regional cerebral blood flow (CBF) and the transit and trailing edge times (arterial timing parameters) reflecting, respectively, the beginning and end of the labeled bolus. Intra-arterial digital subtraction angiography and MR angiography were used to grade collaterals.RESULTS: In the hemisphere ipsilateral to the ICA occlusion, the CBF was lower in the anterior frontal (31 ± 4 versus 47 ± 3 mL/min/100 g, P < .01), posterior frontal (39 ± 4 versus 55 ± 2 mL/min/100 g, P < .01), and frontal parietal region (49 ± 3 versus 61 ± 3 mL/min/100 g, P = .04) than that in control subjects. The trailing edge of the frontal-parietal region was longer in the hemisphere ipsilateral to the ICA occlusion compared with that in control subjects (2225 ± 167 versus 1593 ± 35 ms, P < .01). In patients with leptomeningeal collateral flow, the trailing edge was longer in the anterior frontal region (2436 ± 275 versus 1648 ± 201 ms, P = .03) and shorter in the occipital region (1815 ± 128 versus 2388 ± 203 ms, P = .04), compared with patients without leptomeningeal collaterals.CONCLUSION: Regional assessment of timing parameters with ASL may provide valuable information on the cerebral hemodynamic status. In patients with leptomeningeal collaterals, the most impaired territory was found in the frontal lobe.

An obstructive lesion in the internal carotid artery (ICA) causes a reduction of the perfusion pressure in the cerebral circulation. As the cerebral perfusion pressure decreases, pressure is initially maintained by a compensatory vasodilation of the arterioles, followed by an increase in the oxygen extraction fraction.¹ Regionally, the cerebral hemodynamic status depends not only on the degree of carotid obstruction but also on other factors, such as the contribution of collateral pathways.^2,3The collateral circulation can provide alternative routes for oxygenated blood to reach the brain tissue, either through the primary pathways via the circle of Willis or the secondary pathways via leptomeningeal and ophthalmic collaterals.⁴ The combination of a decreased cerebral perfusion pressure and an insufficient primary collateral blood supply may lead to hemodynamic impairment, which eventually can result in a limited clearance of emboli and ischemia.^5,6 Recruitment of the secondary collaterals is associated with further impairment, and its presence may be considered a marker of inadequacy of the primary collateral pathways.^7,8 Because the recruitment of collateral perfusion in patients with an ICA occlusion will lead to longer blood flow routes and a delayed arrival time of the blood, regional knowledge of the arrival times of arterial blood may provide additional information to characterize the collateral flow and may potentially be used to identify hemodynamically impaired regions. The most widely used methods to measure arrival times of blood use dynamic sampling of an injected bolus of contrast agent. However, due to the current concerns regarding contrast use in patients with poor renal function⁹ and ionizing radiation, an alternative without detrimental effects would be of great benefit.Recently, arterial spin-labeling (ASL) was introduced as a noninvasive method capable of assessing cerebral perfusion and the temporal dynamics of arterial blood inflow.¹⁰ The purpose of our study was, first, to investigate hemodynamic parameters in different areas of the brain in patients with an occlusion of the ICA and, second, to evaluate the effect of collateral flow on regional hemodynamics. We used an ASL MR imaging technique with image acquisition at multiple delay times to quantify regionally cerebral blood flow (CBF) and arterial timing parameters (transit and trailing edge times).     

Giant intracranial aneurysms: MR imaging

Fifteen patients with giant intracranial aneurysms were examined with magnetic resonance (MR) imaging, computed tomography (CT), and angiography. MR imaging revealed a rounded extraaxial mass with evidence of intraluminal blood flow in 12 of the 15 cases. Signal void within the lumen was seen in all 12 of these cases. Other flow effects, such as even-echo rephasing, were seen in some cases. Complete thrombosis was seen in three giant aneurysms in which high signal intensity on T1- and T2-weighted images filled the lumen, and no flow effects were seen. Partial thrombosis was detected in four aneurysms as persistent areas of medium to high signal intensity within the lumen on T1- and T2-weighted images. In five cases, the cause of the intraluminal signal that was present was difficult to determine. The ability of MR to indicate flow within the lumen in 12 of 15 cases provided for greater diagnostic confidence than with CT, which was strongly suggestive of an extraaxial tumor in nine patients. Calcification of the wall of the aneurysm was better detected with CT.     

MR diffusion imaging of human intracranial tumours

We used MRI for in vivo measurement of brain water self-diffusion in patients with intracranial tumours. The study included 28 patients (12 with high-grade and 3 with low-grade gliomas, 7 with metastases, 5 with meningiomas and 1 with a cerebral abscess). Apparent diffusion coefficients (ADC) were calculated in a single axial slice through the tumours; the sequence was sensitive to diffusion along the cephalocaudal axis. Our main finding was that ADC in contrast-enhancing areas within cerebral metastases was statistically significantly higher than ADC in contrast-enhancing areas in high-grade gliomas (P≤ 0.05). Furthermore, the ADC in oedema surrounding metastases were statistically significantly higher the ADC in oedema around high-grade gliomas (P≤ 0.02). The ADC in patients with meningiomas did not differ significantly from those seen with high-grade gliomas or cerebral metastases. The highest ADC were found within cystic or necrotic tumour areas. In one patient with a cerebral abscess, suspected of having a high-grade glioma, the ADC was similar to that in high-grade gliomas. The finding of higher ADC in cerebral metastases than in high-grade gliomas may be helpful in trying to distinguish between these tumours preoperatively; it suggests increased free extracellular and/or intracellular water fraction in cerebral metastases. The method seems to hold potential for further noninvasive characterisation of intracranial tumours. Received: 10 June 1996 Accepted: 6 August 1996     

Gadolinium-DOTA enhanced MR imaging of intracranial lesions

Gadolinium 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (Gd-DOTA) is the first of a new class of macrocyclic paramagnetic magnetic resonance (MR) contrast agents (gadolinium cryptelates) to be used in clinical practice. Gadolinium-DOTA possesses relaxation properties similar to those of gadolinium diethylene triamine pentaacetic acid (Gd-DTPA). We report our initial clinical experience in 38 patients with intracranial lesions studied with MR before and after injection of Gd-DOTA. Diseases included primary and metastatic brain tumor, cerebral infarct, vascular malformation, meningioma, hemangiopericytoma, schwannoma, and pituitary macroadenoma. Gadolinium-DOTA was administered intravenously in a dosage of 0.1 mmol/kg body weight. All studies were performed on a superconductive 0.5 T system. As compared to noncontrast T1- and T2-weighted images (WI), Gd-DOTA enhanced T1 WI were useful in defining the anatomy of malignant intraaxial tumors (high-grade glioma, metastasis) and in tumor versus edema differentiation. Low-grade gliomas did not enhance; in these cases the precontrast T2-weighted sequence was found to be more informative. In post-operative patients, Gd-DOTA allowed us to demonstrate residual tumor or tumor recurrence. Extraaxial tumors (meningioma, hemangiopericytoma, neuroma) enhanced markedly, presumably reflecting tumor vascularity. In our experience, the use of Gd-DOTA improves the anatomic definition of cerebral lesions and in some cases increases both MR sensitivity and specificity. We found Gd-DOTA to be a well tolerated and effective paramagnetic contrast agent. Gadolinium-DOTA can be considered as an alternative water-soluble MR contrast agent to Gd-DTPA.