脑脂肪栓塞的MRI及CT诊断

目的 总结脑脂肪栓塞(CFE)的临床及MRI及CT的影像特点。方法 分析3例急性CFE的临床表现、影像特点。结果 (1)3例均为长骨骨折，在外伤后或骨折固定、复位数小时后突发精神状态改变。(2)醒状昏迷是主要临床表现。(3)3例患者MRI能明确显示病灶，1例CT显示了病灶。(4)MRI、CT显示脑内病灶均呈基本对称性分布，为边缘模糊的点、片状长T1、长T2信号，CT呈低密度。病灶均累及脑干、分水岭区脑白质、基底节区、胼胝体压部。2例病灶累及小脑。(5)1例患者发病康复治疗3个月后MRI复查示脑内病灶完全消失。结论 急性脑脂肪栓塞的临床及MRI、CT影像改变具有特征性，MRI在病灶显示上优于CT。     

Reversible MR changes in the cat brain after cerebral fat embolism induced by triolein emulsion

BACKGROUND AND PURPOSE: Clinical cerebral-fat embolism shows both reversible and irreversible changes. We used MR imaging to investigate the reversibility of embolized lesions induced with a fat-emulsion technique and to evaluate the histologic findings. METHODS: A fat emulsion was made with 0.05 mL of triolein and 20 mL of normal saline and vigorous to-and-fro movement through a three-way stopcock. In 50 cats, the internal carotid artery was infused with the fat emulsion. Cats were divided into six groups on the basis of time delay after embolization: 1 hour; 1 and 4 days; and 1, 2, and 3 weeks. MR imaging and histologic examination were performed at these times. RESULTS: Embolized lesions were hyperintense on T2-weighted images, isointense or mildly hyperintense on diffusion-weighted images, isointense on apparent diffusion coefficient maps, and enhancing on gadolinium-enhanced T1-weighted images at 1 hour. These MR imaging findings were less evident at day 1 and reverted to normal after day 4 (isointense on all images). Electron microscopy showed minimal findings in the cortical lesion in groups 1 and 2 (group 1 at 1 hour and group 2 at 1 hour and 1 day). Light microscopic findings revealed evidence of necrosis-small focal gliosis and demyelination in the periventricular white matter-in only one cat. The number of intravascular fat globules was not significantly different between groups, as visualized by oil red O staining. CONCLUSION: Cerebral-fat embolism induced by a triolein emulsion revealed reversible MR findings and minimal histologic findings.     

Experimental pulmonary fat embolism induced by injection of triolein in rats

The relationship between the volume of fat flowing in the bloodstream and the degree of pulmonary fat embolism has remained unclear. In this study, in order to examine whether the volume of fat particles in the bloodstream could be estimated from the degree of pulmonary fat embolism, 0.05, 0.1, 0.15, 0.2 and 0.25 ml of triolein were injected into male rats weighing 300-320 g, through the caudal vein. Consequently, it was noted that the severity of pulmonary fat embolism tended to gradually increase in proportion to the volume of injected triolein, with the severity of pulmonary fat embolism being significantly augmented by the injection of 0.2 and 0.25 ml of triolein, based on morphometric analysis. In application to human cases, about 60 ml of fat particles was estimated to flow into the bloodstream after the occurrence of a pelvic fracture. Moreover, the results of this study led to the hypothesis that the prognosis of pulmonary fat embolism is affected by the severity of preceding conditions which have caused fat embolism.     

Evaluation of particulate embolic materials with MR imaging,scanning electron microscopy,and phase-contrast microscopy.

PURPOSETo analyze the properties and embolic effect of microfibrillar collagen (MFC), Gelfoam powder, and polyvinyl alcohol (PVA) materials that are used in embolization procedures in the head and neck.METHODSThe shape and surface of these embolic agents were examined with scanning electron microscopy and phase-contrast microscopy. The mean number of areas of T2-weighted high signal intensity was measured on MR images in a rat embolization model to estimate the embolic effect.RESULTSBy scanning electron microscopy and phase-contrast microscopy, MFC appears fibriform and has various sizes and an irregular surface. Gelfoam is of uniform size and has a smooth surface. PVA materials are granulated and have a rough surface. MFC is somewhat suspendable and its shape changes moderately after suspension. Gelfoam is very suspendable and its shape changes rapidly. PVA showed only mild swelling. The embolic effect of MFC was the lowest of the materials examined. Large PVA particles (250 to 500 microns) showed a lesser embolic effect than Gelfoam or small PVA particles (50 to 150 microns) or medium-sized PVA particles (150 to 250 microns). No significant differences were observed among the embolic effects of Gelfoam, small PVA particles (50 to 150 microns), and medium PVA particles (150 to 250 microns).CONCLUSIONSMFC and large PVA particles (250 to 500 microns) should be used for embolization of vascular anatomy involving potentially dangerous anastomoses. Gelfoam, PVA particles of 150- to 250-micron diameter, and PVA particles of 50- to 150-micron diameter are adequate for embolization involving homogeneous and peripheral anatomy.     

Contrast-enhanced MR imaging of cerebral fat embolism: case report and review of the literature

We report a case of cerebral fat embolism (CFE) that was imaged with T2- and T2*-weighted, fluid-attenuated inversion recovery, and contrast-enhanced T1-weighted images. Multiple white matter lesions demonstrated contrast enhancement, with little evidence of hemorrhage. The patient regained complete neurologic function. CFE can cause capillary inflammation and breakdown of the blood-brain barrier, without associated hemorrhage or permanent neurologic deficit. In this case, both contrast-enhanced T1-weighted and gradient-echo T2*-weighted images were important in diagnosing CFE and in determining the severity of the patient's condition.     

Magnetic resonance imaging of cerebral fat embolism

Summary The cerebral fat embolism is a potentially serious complication of fractures but clinical cases often go undiagnosed. Two cases of clinically diagnosed cerebral fat embolism are reported, and MR images of these patients are described. While brain CT revealed no abnormality, MR imaging showed relative low-intensity areas on T1-weighted images and high-intensity areas on T2-weighted images. In one patient follow-up MR showed nearly complete resolution of the abnormal signal. MR imaging appears to be valuable for detecting the lesions in these patients.     

MR imaging and differentiation of cerebral fat embolism syndrome from diffuse axonal injury: application of diffusion tensor imaging

Introduction

Cerebral fat embolism syndrome (CFES) mimics diffuse axonal injury (DAI) on MRI with vasogenic edema, cytotoxic edema, and micro-hemorrhages, making specific diagnosis a challenge. The objective of our study is to determine and compare the diagnostic utility of the conventional MRI and DTI in differentiating cerebral fat embolism syndrome from diffuse axonal injury.

Methods

This retrospective study was performed after recruiting 11 patients with severe CFES and ten patients with severe DAI. Three trauma radiologists analyzed conventional MR images to determine the presence or absence of CFES and DAI. DTI analysis of the whole-brain white matter was performed to obtain the directional diffusivities. The results were correlated with clinical diagnosis to determine the diagnostic utility of conventional MRI and DTI.

Results

The sensitivity, specificity, and accuracy of conventional MRI in diagnosing CFES, obtained from the pooled data were 76, 85, and 80 %, respectively. Mean radial diffusivity (RD) was significantly higher and the mean fractional anisotropy (FA) was lower in CFES and differentiated subjects with CFES from the DAI group. Area under the receiver operating characteristic (ROC) curve for conventional MRI was 0.82, and for the differentiating DTI parameters the values were 0.75 (RD) and 0.86 (FA), respectively.

Conclusions

There is no significant difference between diagnostic performance of DTI and conventional MRI in CFES, but a difference in directional diffusivities was clearly identified between CFES and DAI.     

The study of cerebral hemodynamics in the hyperacute stage of fat embolism induced by triolein emulsion

PURPOSE: The purpose of this study was to evaluate the cerebral hemodynamic change in the hyperacute stage of cerebral fat embolism induced by triolein emulsion, by using MR perfusion imaging in cat brains. METHODS: By using the femoral arterial approach, the internal carotid arteries of 14 cats were infused with an emulsion of triolein 0.05 mL. T2-weighted (T2WI), diffusion-weighted (DWI), apparent diffusion coefficient (ADC) map, perfusion-weighted (PWI), and gadolinium-enhanced T1-weighted (Gd-T1WI) images were obtained serially at 30 minutes and 2, 4, and 6 hours after infusion. The MR images were evaluated qualitatively and quantitatively. Qualitative evaluation was performed by assessing the signal intensity of the serial MR images. Quantitative assessment was performed by comparing the signal-intensity ratio (SIR) of the lesions to the contralateral normal side calculated on T2WIs, Gd-T1WIs, DWIs, and ADC maps at each acquisition time and by comparing the relative cerebral blood volume (rCBV), cerebral blood flow (CBF), and mean transit times (MTT) of the lesions to the contralateral normal side calculated on PWI. RESULTS: In the qualitative evaluation of the MR images, the lesions showed hyperintensity on T2WIs, enhancement on the Gd-T1WIs, and isointensity on DWIs and the ADC maps. In the quantitative studies, SIRs on the Gd-T1WIs, DWIs, and ADC maps peaked at 2 hours after infusion. The SIRs on the T2WIs peaked at 4 hours after infusion and decreased thereafter. On PWIs, the rCBV, rCBF, and MTT of the lesion showed no significant difference from the contralateral normal side (P = .09, .30, and .13, respectively) and showed no significant change of time course (P = .17, .31, and .66, respectively). CONCLUSION: The embolized lesions induced by triolein emulsion showed no significant difference in cerebral hemodynamic parameters from those on the contralateral normal side. The result may suggest that consideration of the hemodynamic factor of embolized lesions is not necessary in further studies of the blood-brain barrier with triolein emulsion.     

MR imaging of the brain in fat embolism syndrome

Fat embolism syndrome (FES) is an uncommon but serious complication of traumatic injury and is frequently diagnostically challenging. In this paper, the authors present four patients who sustained lower extremity long bone injury and who had a normal Glasgow Coma Scale before orthopedic surgical intervention. However, postoperatively, significant neurological deterioration developed in these patients. While cranial computed tomography (CT) obtained immediately after surgery for acutely altered mental status was negative in two of the four patients, brain magnetic resonance imaging (MRI) demonstrated white and gray matter abnormalities accounting for the impaired neurological status in all cases. MRI findings in conjunction with clinical presentation established the diagnosis in all patients. MRI is indicated in any patient with orthopedic injuries who manifests an unexplained acute alteration in mental status, despite a normal head CT.     

Magnetic resonance imaging and histologic findings of experimental cerebral fat embolism

RATIONALE AND OBJECTIVES: The purpose of this study was to determine whether cerebral fat embolism demonstrated reversible or irreversible findings in magnetic resonance (MR) imaging over time and to compare the features in MR images with histologic findings in a cat model. MATERIALS AND METHODS: MR images were obtained serially at 2 hours, 1 and 4 days, and 1, 2, and 3 weeks after embolization with 0.05 mL of triolein into the internal carotid artery in 19 cats. Any abnormal signal intensity and change in the signal intensity were evaluated on T2-weighted images, T1-weighted images, diffusion-weighted images (DWIs; including apparent diffusion coefficient [ADC] maps), and gadolinium-enhanced T1-weighted images (Gd-T1WI) over time. After MR imaging at 3 weeks, brain tissue was obtained and evaluated for light microscopic (LM) examination using hematoxylin-eosin and Luxol fast blue staining. For electron microscopic examination, the specimens were obtained at the cortex. The histologic and MR findings were compared. RESULTS: The embolization lesions showed hyperintensity on T2-weighted images, hyperintensity, or isointensity on DWIs, hypointensity, or isointensity on ADC maps and contrast enhancement on Gd-T1WIs at 2 hours. The T2-weighted hyperintensity extended to the white matter at day 1 and decreased thereafter. Contrast enhancement decreased continuously from day 1, and hyperintensity on DWI decreased after day 4. Hypointensity on ADC maps became less prominent after day 4. By week 3, most lesions had reverted to a normal appearance on MR images and were correlated with LM findings. However, small focal lesions remained in the gray matter of 8 cats and in the white matter of 3 cats on MR images, and this correlated with the cystic changes on LM findings. Electron microscopic examination of the cortical lesions that reverted to normal at week 3 in MR images showed that most of these lesions appeared normal but showed sporadic intracapillary fat vacuoles and disruption of the endothelial walls. CONCLUSIONS: The embolized lesions of the hyperacute stage were of 2 types: type 1 lesions, showing hyperintensity on DWIs and hypointensity on ADC maps, have irreversible sequelae, such as cystic changes; whereas type 2 lesions, showing isointensity or mild hyperintensity on DWIs and ADC maps, reverted to a normal appearance in the subacute stage.     

In vitro MR imaging of hyaline cartilage: correlation with scanning electron microscopy

OBJECTIVE: Our goal was to determine how the three-dimensional structure of hyaline cartilage affects its MR appearance and to correlate this appearance with detailed structural analysis using scanning electron microscopy and freeze-fracture sectioning techniques. MATERIALS AND METHODS: In vitro 7-T spin-echo MR images of hyaline cartilage specimens from four patients undergoing above-knee amputations were obtained parallel and perpendicular to the main magnetic field. Specimens were imaged with low- and high-power scanning electron microscopy after freeze fracturing. The corresponding images from both techniques were analyzed with specific attention to the three-dimensional structure of the cartilage, collagen fibril orientation, and respective changes in the MR appearance. RESULTS: Freeze fracturing of cartilage reveals a curved fracture plane. Expected changes in signal intensity predicted by the magic angle effect correlated with observed changes in signal intensity across the thickness of the sample. Changes in individual collagen fibril orientation did not correspond to MR layering. CONCLUSION: The three-dimensional organization of collagen in cartilage has a strong influence on the MR appearance of cartilage. This influence is caused by the restriction of water mobility and the resulting magic angle effect caused by curvature of the collagen network, possibly because of the influence on proteoglycan orientation.     

Simultaneous quantification of fat content and fatty acid composition using MR imaging

Not only the fat content but also the composition of fatty acids (FAs) in stored triglycerides might be of interest in the research on nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. In this study, a novel reconstruction approach is proposed that uses theoretical knowledge of the chemical structure of FAs to simultaneously quantify the fat fraction (FF) and the FAs composition (chain length cl, number of double bonds ndb, and number of methylene‐interrupted double bonds nmidb) from multiple gradient echo images. Twenty phantoms with various fat contents (FF = 9–100%) and FA compositions (cl = 12.1–17.9, ndb = 0.23–5.10, and nmidb = 0.04–2.39) were constructed and imaged in a 3‐T Siemens scanner. In addition, spectra were acquired in each phantom. Slopes and “standard deviations from true values” were used to investigate the accuracy of the two methods. The imaging method holds well in a comparison to the previously suggested spectroscopy method and showed similar overall accuracy. The in vivo feasibility was demonstrated in the thigh adipose tissue of a healthy volunteer. In conclusion, our developed method is a promising tool for FF and FA composition quantification. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Evaluation of cerebral abscesses by diffusion-weighted MR imaging and MR spectroscopy.

Cerebral abscess may sometimes mimic necrotic tumor and cystic metastases both clinically and radiologically. The imaging findings may be indistinguishable on conventional magnetic resonance imaging. Although recent studies have shown that cerebral abscess displays restricted diffusion on diffusion-weighted imaging (DWI), it is not pathognomic. Necrotic tumor and cystic metastases may occasionally have restricted diffusion on DWI. Since the urgency of surgical intervention and approach of surgery is different, MR Spectroscopy may be used in conjunction with DWI in establishing the correct diagnosis.     

Effects of lithotripsy on rat kidney: evaluation with MR imaging, histology, and electron microscopy

Magnetic resonance (MR) imaging at 1.5 T was used to evaluate the effects of extracorporeal shock wave lithotripsy (ESWL) in 30 rats and the findings on T1- and T2-weighted (spin echo 600/22, 1,600-2,000/90) images were compared with histology and scanning microscopy. The observed pathologic changes increased in severity with the number of shock waves given (500-5,000 15 kV). Post-ESWL MR findings in 54 kidneys included perirenal and subcapsular fluid (n = 30), diffuse loss of corticomedullary junction definition (n = 28), intrarenal foci of increased (n = 7) or decreased (n = 6) signal intensity, focal indentation of the renal contour (n = 5), and loss of distinction between the renal, splenic, or hepatic contour (n = 7). The subcapsular and intrarenal findings corresponded pathologically to areas of hemorrhage and hematoma formation--the contour changes to foci of renal scarring or perirenal adhesions. Electron microscopy demonstrated marked alterations of the renal tubules and vasculature. The study shows the feasibility of assessing the nature and chronology of renal damage post-ESWL in a rat model by MR.     

Early development of vasogenic edema in experimental cerebral fat embolism in cats: correlation with MRI and electron microscopic findings

RATIONALE AND OBJECTIVES: To evaluate the magnetic resonance imaging and electron microscopic findings of the hyperacute stage of cerebral fat embolism in cats and the time needed for the development of vasogenic edema. METHODS: Magnetic resonance imaging was performed at 30 minutes (group 1, n = 9) and at 30 minutes and 1, 2, 4, and 6 hours after embolization with triolein (group 2, n = 10). As a control for group 2, the same acquisition was obtained after embolization with polyvinyl alcohol particles (group 3, n = 5). Magnetic resonance images were analyzed qualitatively and quantitatively. Electron microscopic examination was done in all cats. RESULTS: In group 1, the lesions were iso- or slightly hyperintense on T2-weighted (T2W) and diffusion-weighted (DWIs) images, hypointense on the apparent diffusion coefficient (ADC) map image, and markedly enhanced on the gadolinium-enhanced T1-weighted images (Gd-T1WIs). In group 2 at 30 minutes, the lesions were similar to those in group 1. Thereafter, the lesions became more hyperintense on T2WIs and DWIs and more hypointense on the ADC map image. The lesions were enhanced on Gd-T1WIs at all acquisition times. In group 3, the lesions showed mild hyperintensity on T2WIs at 6 hours but hypointensity on the ADC map image from 30 minutes, with a tendency toward a greater decrease over time. The lesions were not enhanced on Gd-T1WIs at any time point. Electron microscopic findings revealed discontinuity of the capillary endothelial wall, perivascular and interstitial edema, and swelling of glial and neuronal cells in groups 1 and 2. Cellular swelling and interstitial edema were more prominent in group 2. In group 3, interstitial edema was seen; however, discontinuity of the endothelial wall was absent. CONCLUSIONS: The lesions were hyperintense on T2WIs and DWIs, hypointense on the ADC map image, and enhanced on Gd-T1WIs. On electron microscopy, the lesions showed cytotoxic and vasogenic edema with disruption of the blood-brain barrier. Vasogenic edema seems to develop within 30 minutes in cerebral fat embolism in cats.     

Heterogeneity of cerebral cavernous hemangiomas diagnosed by MR imaging

The cavernous hemangioma (cavernoma) is increasingly recognized as a vascular malformation of the brain that may present with seizures, hemorrhage, or progressive neurological deficit. Since 1985 we have identified 13 cases of presumed cavernoma of the brain based on the findings on CT, selective angiography, and magnetic resonance (MR) imaging. In each case CT showed a high density lesion that was "occult" or "cryptic" on angiography. However, within all lesions MR revealed a complex internal structure consisting of reticulated patches of high and low intensity signal surrounded by a hypointense rim on T1- and T2-weighted pulse sequences. Of the nine operated cases, five resected specimens were compatible with pure arteriovenous malformations (AVMs), and the other four were mixtures of cavernoma with either AVM or venous angioma. Our experience strongly suggests that the above complex of radiographic findings is not at all specific for the cavernoma. We propose that the major common factor shared by such "cavernomatoid" malformations is low blood flow. We believe low flow lesions follow a relatively benign clinical course, and they readily lend themselves to surgical resection.