Usefulness of diffusion-weighted MRI in the diagnosis of transient ischemic attacks]

Diffusion-weighted imaging(DWI) has been demonstrated to be valuable for assessment of ischemic stroke patients. The aim of this study is to evaluate clinical usefulness of DWI in the diagnosis of transient ischemic attack(TIA). Nineteen patients with symptoms of TIA were studied. DWI was taken with 1.5 Tesla MRI system using spin echo EPI sequence. Seven patients revealed areas of hyperintensity (brightness) on DWI and of hypointensity on apparent diffusion coefficient(ADC) maps relative to normal brain. As the duration of TIA symptom elongated, the percentage of patients with DWI abnormalities became higher. DWI enabled to detect areas of hyperintense lesion in all three patients as early as 3 hours after the onset, while conventional T2 weighted imaging showed in one. All the DWI abnormalities were irreversible in spite of the complete recovery from TIA. DWI is an useful technique for the detection of responsible lesions in TIA. However, TIA cannot be ruled out even if DWI does not demonstrate any abnormal signals.     

Early diagnosis of bacterial brain abscesses: interest of diffusion-weighted MRI

Three cases of bacterial brain abscesses, in immunocompetent patients, are reported. In all these cases, the diffusion-weighted magnetic resonance (MRI) with apparent diffusion coefficient (ADC) map has permitted an early diagnosis and a rapid treatment. This emergency MRI showed in the three cases a low signal on TI-weighted images, a high signal on T2-weighted and echo-planar images, and a decrease of ADC (0.36- 0.49 x 10(-3) mm2/s). So, this new MRI technique provides an available and rapid element in the brain abscess diagnosis which often remains a complex clinical and radiological diagnosis.     

磁共振扩散加权成像在脑脓肿与脑内囊性肿瘤鉴别诊断中的价值

目的探讨磁共振扩散加权成像(DWI)以及表观扩散系数(ADC)在脑脓肿(BA)与脑内囊性肿瘤(BCT)鉴别诊断中的价值。方法收集经确诊的21例BA和33例BCT患者,所有病例行常规MRI及DWI检查,测量BA与BCT囊变区的ADC值。结果 21例BA患者在DWI上均呈不同程度的高信号,平均ADC值为(0.62士0.18)× 10~3mm~2/s;33例BCT患者中30例在DWI上呈低信号,另3例呈等信号,囊性肿瘤的平均ADC值为(2.37±0.34)× 10~3mm~2/s。BA与BCT的平均ADC值比较差异有统计学意义(P=0.000)。结论 DWI与ADC值能有效区分BA与BCT病灶内囊液的水分子扩散差别,对BA和BCT的鉴别诊断具有重要价值。     

Diffusion MRI findings in neonatal brain abscess

In neonates and infants, bacterial brain abscess is rare, and the diffusion weighted MR imaging appearance of such abscesses has not been reported. We report the diffusion weighted MR findings of a brain abscess in a 25-day-old boy. The lesion initially had a large cystic component with some high-signal pyogenic material inside on diffusion-weighted (b=1000 sec/mm(2))images. The ADC value of this material was low (0.59 x 10(-3) mm(2)/sec), compared to the value from normal cerebellar parenchyma (0.78 x 10(-3) mm(2)/sec). The unusual initial appearance mimicked a cystic tumor. The lesion markedly decreased in size over 20 days after antibiotic therapy with persistent high-signal pyogenic material. In addition, at the initial presentation b=1000 sec/mm(2) images revealed high-signal changes in the brain parenchyma compressed by markedly dilated ventricles, consistent with ischemia. Also, ADC values of perilesional vasogenic edema (1.74 x 10(-3) mm(2)/sec), and that of transependymal resorption of CSF (1.56 x 10(-3) mm(2)/sec) were noted at the initial stage.     

MR弥散加权成像与钆增强MRI对脑脓肿的诊断价值

目的 评估MR弥散加权成像(DWI)和含钆造影剂对比增强磁共振成像(CE-MRI)对脑脓肿的诊断价值.方法 对49例脑内单发囊实性病变行常规T1WI、T2WI、液体反转恢复序列(FLAIR)、弥散加权成像和钆增强MRI检查.分析脑脓肿(22例)与囊变坏死性脑肿瘤(27例)DWI信号及强化特征并进行囊变坏死区ADC值测量.所有图像分三组与病理结果进行对照分析:Ⅰ组为DWI结合常规序列;Ⅱ组为CE-MRI结合常规序列;Ⅲ组为DWI、CE-MRI两种序列联合并结合常规序列.结果 DWI上20例脑脓肿呈高信号,24例囊变坏死性脑肿瘤为低信号;14例脑脓肿、12例囊变坏死性脑肿瘤呈壁较薄而均匀环形强化.大部分脑脓肿的ADC值明显低于囊变坏死性脑肿瘤(P＜0.05).Ⅰ组、Ⅱ组、Ⅲ组诊断脑脓肿的敏感性分别为90.9％、63.6％、95.5％,Ⅰ、Ⅱ组间及Ⅱ、Ⅲ组间均具有明显统计学差异(P＜0.05),但Ⅰ、Ⅲ组间没有统计学差异(P＞0.05).结论 DWI较CE-MRI能更敏感地发现脑脓肿,ADC值的测量可以为脑脓肿与囊变坏死性脑肿瘤的鉴别提供有价值的诊断信息.     

实验性脑脓肿影像学改变的病理基础研究

目的：明确不同时期动物脑脓肿的影像学特征及其相应的病理学改变。方法：制备脑脓肿狗动物模型１４只，采用ＣＴ、ＭＲＩ检查结合多项病理学观测进行动态分析。结果：脑炎期ＭＲＩ对炎症坏死区及水肿范围的显示较ＣＴ扫描更为清晰准确。包膜形成期：ＣＴ上脑脓肿包膜强化是炎症区血脑屏障破坏和新生血管形成所致；ＭＲＩＴ２加权成像上包膜的低信号“暗带”与包膜上的巨噬细胞堆积有关，延迟扫描和ＭＲＩ均能有效地区分脑脓肿的急性脑炎期和包膜形成期，但ＭＲＩ更加准确、迅速。结论：脑脓肿的ＭＲＩ特征与其临床分期及病理学变化的相关性较好，能更加准确、简便、迅速地区别脓肿的脑炎期和包膜形成期，可作为临床诊治脑脓肿的有力参考。     

Role of diffusion-weighted imaging and proton MR spectroscopy in distinguishing between pyogenic brain abscess and necrotic brain tumor

Brain abscesses and brain tumors may have similar clinical presentations. For example, only 50% brain abscess patients have fever, which could be masked by corticosteroid therapy. Also, the differential diagnosis of brain abscesses versus cystic or necrotic tumors may be difficult based on computed tomography (CT) or magnetic resonance (MR) imaging findings. However, the strategies of management for abscess and neoplasm are very different, and it is especially imperative to have a correct diagnosis before any surgical intervention of cystic brain lesions. The MR special techniques, e.g. diffusion-weighted imaging (DWI) and proton (1H) MR spectroscopy, are useful as additional diagnostic modalities for differentiating brain abscesses from cystic or necrotic brain tumors. DWI shows high signal intensity in most cases of pyogenic abscesses and low signal intensity in most cases of cystic or necrotic tumors. MR spectroscopy shows characteristic metabolites in pyogenic abscesses, distinct from those in cystic or necrotic tumors.     

MRI diagnosis of neurodegenerative disorders]

Routine use of high field MRI has greatly contributed to the clinical diagnosis of neurodegenerative disorders, because MRI enables to visualize degenerative process showing either atrophy of the specific areas or degeneration of specific structures. Among many specific MRI signs which have been hitherto proposed to be diagnostic for certain neurodegenerative disorders, the author discussed here some clinically useful ones with neuropathological interpretations. "Humming-bird sign" is highly diagnostic for progressive supranuclear palsy (PSP) because it represents focal atrophy of the rostro-dorsal portion of mid-brain tegmentum where the neural centers for vertical gaze specifically affected in PSP are located. Un-treated Wilson disease patients show frequently "face of giant panda sign" of mid-brain which disappears after successful treatment. Although the sign is pathognomonic for Wilson disease, neuropathological entity of this MRI abnormality has not been known yet. MRI enables to discriminate two types of cerebellar atrophies; cerebellipetal atrophy in which ponto-, spino- and olivo-cerebellar fibers are lost, and cerebellofugal atrophy in which loss of Purkinje cells is the main pathological process. In cerebellipetal atrophy, cerebellar white matter shows T2 high signal due to the degeneration of nerve fibers in it but T2 low signal of dentate nucleus is usually well preserved. This combination of degenerative process realized" black teeth sign" of dentate nucleus in MRI. On the other hand, cerbellofugal atrophy shows "white teeth sign" of dentate nucleus, because the loss of Purkinje cell axons causes signal change of dentate nucleus where the axons of Purkinje cells are concentrating. "White teeth sign" could also be observed in case of the degeneration of dentate nucleus itself, like in DRPLA, but differential diagnosis between Purkinje cell loss and dentate degeneration is not so difficult, because the atrophy of the superior cerebellar peduncle is detectable in the latter but never seen in the former condition.     

Nocardia brain abscess mimicking high-grade necrotic tumor on perfusion MRI

Differentiating a pyogenic cerebral abscess from a cystic brain tumor can be a challenge when using morphological and functional imaging techniques. Several studies on MRI perfusion-weighted imaging (PWI) have demonstrated that enhancing abscess capsules have lower cerebral blood volume ratios (rCBV) than the enhancing rims of necrotic tumors. We report a 67-year-old male with a Nocardia cerebral abscess showing restricted diffusion in the necrotic center, but high values for rCBV in the enhancing capsule on PWI, therefore mimicking a high-grade necrotic tumor. Differential diagnosis between cerebral abscesses and necrotic tumors is greatly improved by the adjunct of diffusion-weighted imaging (DWI) and PWI to the morphological magnetic resonance findings; yet there is still overlap. That an abscess may show increased rCBV along the capsule, therefore mimicking a hypervascular brain tumor on PWI, should be considered when attempting a radiological diagnosis of a ring-enhancing brain lesion.     

Nocardia abscess during treatment of brain toxoplasmosis in a patient with aids, utility of proton MR spectroscopy and diffusion-weighted imaging in diagnosis

We report the case of a 30-year-old man with known HIV-positive status who developed, 4 months prior to admission, recurrent left partial motor seizures followed by left hemiparesis. At another hospital, contrasted CT scan of the head revealed right frontal hypodense lesion with mass effect and focal contrast enhancement. A small left occipital lesion was also present. HIV-associated brain toxoplasmosis was considered and phenytoin, pyrimethamine, clindamycin and antiretrovirals were administered. Hemiparesis improved but, 3 weeks prior to admission, he developed progressive headache and bilateral visual defects. Upon admission to our center, he was found with left homonymous hemianopsia, right hemiparesis and a large hypodense left occipital lesion on a head CT scan. Proton MR spectroscopy showed lactate at 1.3ppm, amino acids at 0.9ppm, and diffusion-weighted imaging (DWI) revealed hyperintensity at the lesion, suggesting a pyogenic abscess. Aspiration yielded purulent material and Nocardia asteroides grew in culture. The patient was treated with trimethoprim-sulfametoxazole and recovered with a mild visual field residual defect.     

A case of interhemispheric subdural empyema with sinusitis diagnosed by diffusion-weighted MRI]

The patient was a 29-year-old man with sinusitis. He was admitted with high grade fever, headache, vomiting and disturbance of consciousness. Neurological examination revealed nuchal rigidity, aphasia, right hemiparesis, right sensory disturbance and bilateral Babinski signs. A nonenhanced CT on admission showed a low density area in the interhemispheric fissure. Gadolinium-enhanced MRI and DWI showed an interhemispheric subdural empyema and sinusitis. Neurological deficits gradually improved, after he underwent urgent surgical drainage of sinusitis followed by antibiotics therapy. About three weeks later, he developed right hemiparesis and disturbance of consciousness, and MRI demonstrated the expansion of interhemispheric subdural empyema. Therefore, he underwent surgical drainage of interhemispheric subdural empyema. He was discharged from our hospital without neurologic deficit. We suggest that MRI, in particular DWI, is a useful additional imaging modality for the diagnosis of interhemispheric subdural empyema.     

Case of Hashimoto's encephalopathy with diffuse white matter lesions on diffusion-weighted MRI]

A 65-year-old woman was admitted to our hospital because of subacute deterioration of cognitive function. On admission, she presented with marked disorientation of time and place and inability to carry out commands. Mini-Mental State Examination score was 5/30. Although routine laboratory examinations including thyroid function, vitamin B1 and B12, serum syphilitic reaction, sIL-2 receptor level, titers of herpes simplex and zoster viruses, and HIV antibody were normal, titers of anti-thyroglobulin (TG) antibodies and thyroid peroxidase (TPO) antibodies were elevated. Cerebrospinal fluid showed normal findings. Brain MRI revealed diffuse high intensity in the white matter on diffusion- and T2-weighted images, mimicking leukoencephalopathy. We made a diagnosis of Hashimoto's encephalopathy, based on clinical features and high titers of anti-thyroid antibodies. Following administration of steroid hormone, her cognitive impairment gradually improved, associated with decrease of the white matter abnormality on MRI. Hashimoto's encephalopathy should be kept in mind in the differential diagnosis of subacute leukoencephalopathy with cognitive decline.     

A case of Japanese encephalitis presenting with unilateral lesions in diffusion-weighted MRI]

We report the findings of diffusion-weighted MRI (DWI) taken serially in a patient with Japanese encephalitis (JE). The patient was a 43-year-old woman presenting with headache, high fever and consciousness disturbance. The diagnosis of JE was made based on more than fourfold elevation of serum complement fixation antibody titer for JE virus in the convalescent phase of illness. The DWI on the second day of illness (Day-2) disclosed high-signal intensity lesions in the left thalamus, substantia nigra and frontal lobe cortex. The signal intensity of these lesions on the DWI increased on Day-3 but gradually decreased thereafter and normalized on Day-28. The improvement of the DWI findings was paralleled with that of the consciousness level and the cell number and neuron specific enolase concentration in the CSF, suggesting that DWI is useful for evaluation of the disease activity in JE. The lesions in the brain suffering from Japanese encephalitis are usually bilateral and diffuse. To our knowledge, this is the first report of JE presenting with unilateral lesions on MRI, of which phathomechanism remains to be elucidated.     

脑脓肿45例诊治体会

脑脓肿在颅内感染中较为常见，随着生活和卫生保健水平的提高，其流行病学已发生了变化，在诊治方面亦有了新的认识。我院自1990年至2003年收治脑脓肿45例，现将临床诊断和治疗体会介绍如下：     

The physical basis of diffusion-weighted MRI

Diffusion-weighted (DW) magnetic resonance imaging (MRI) is the only technique that permits a non-invasive in vivo assessment of water molecular diffusion, which reflects tissue configuration at a microscopic level. Therefore, this technique appears to be particularly useful in monitoring brain abnormalities. However, the quantitative measurement of diffusion is not without problems, which may limit the widespread use of diffusion-weighted MRI. In this report, the phenomenon of diffusion is described, together with its effect on the nuclear magnetic resonance signal. The concepts of diffusion anisotropy and diffusion tensor are also introduced, and the technical and hardware requirements are discussed.