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 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 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 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.     

MR imaging of intracranial carotid occlusion

The MR scans of seven patients with intracranial carotid occlusion (five proved, two presumed) were reviewed to evaluate the MR signal characteristics seen in this disorder. Five patients had clinical signs of cerebral infarction. Of the remaining two patients, one was asymptomatic and the other had a long-standing occlusion and headaches. We correlated the MR findings with cerebral angiography in five patients and with CT scans in six patients. All occluded vessels demonstrated MR signal predominantly isointense to brain on proton-density- T1- and T2-weighted images. Since there is an absence of flow, the MR signal is based on the intrinsic properties of the arterial thrombus and possibly on the chronicity of the occlusion. The pathogenesis and histopathology of intravascular thrombus differ significantly from extravascular hematoma, which accounts for the differences in their MR signal characteristics. The demonstration of occluded intracranial vessels may solidify the diagnosis of stroke in cases in which clinical and/or CT findings are equivocal. In patients presenting with infarction, an occluded carotid artery by MR may obviate the need for angiography; however, the demonstration of a patent carotid in conjunction with infarction suggests the possibility of an embolus, which may require angiography. We believe that MR is a valuable adjunct to CT in evaluating patients with cerebrovascular infarction.     

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.     

颅内脑室外室管膜瘤的MRI诊断

目的 探讨颅内脑室外室管膜瘤的MRI表现.方法 结合10例经手术证实的颅内脑室外室管膜瘤,回顾性分析其MRI表现.结果 10例颅内脑室外室管膜瘤,其中室管膜瘤5例,间变性室管膜瘤5例,共10个病灶,枕叶3例,颞叶2例,额叶2例,跨叶生长3例,肿瘤均位于脑皮质区.肿瘤实质T1呈等或稍低信号,T2呈等或稍高信号,FLAIR呈等或稍高信号,肿瘤内部见多发囊变、坏死区;本组病例室管膜瘤5例均以实质性为主,间变性室管膜瘤5例均以囊性为主,其中2例室管膜瘤内可见长T1短T2钙化灶,1例间变性室管膜瘤内见出血;增强后肿瘤实质明显强化,囊变、坏死或钙化区不强化,囊壁可见环状强化.结论 进行颅内脑室外室管膜瘤的MRI表现研究,有助于本疾病诊断及鉴别诊断.     

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     

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.     

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.     

Gd-DTPA enhanced MR imaging in intracranial tuberculosis

Summary Twenty-six patients with intracranial tuberculosis (Tb) (10 with acute meningitis, 5 with chronic meningitis, 5 with meningitic sequelae and 6 with localized tuberculoma(s) were examined with MR before and after Gd-DTPA enhancement (0.1 mmol/kg), using 2.0T superconducting unit, and the images were retrospectively analyzed and compared with CT scans. Without Gd-DTPA enhancement, the MR images were generally insensitive to detection of active meningeal inflammation and granulomas. The signal intensity of granulomas was usually isointense to gray matter on both T1- and T2-weighted images, whether they were associated with diffuse meningitis or presented as localized tuberculoma(s). A few granulomas showed focal hypointensity on T2-weighted images. Calcifications seen on CT of the meningitic sequelae group usually appeared markedly hypointense on all spin-echo sequences. On Gd-DTPA enhanced T1-weighted images, abnormal meningeal enhancement indicating active inflammation was conspicuous, and the granulomas often appeared as conglomerated ring-enhancing nodules, which seems to be characteristic of granulomas. Thin rim enhancement around the suprasellar calcifications were observed in two out of 5 patients with meningitic sequelae. Compared with CT, MR detected a few more ischemic infarcts, hemorrhagic infarcts, meningeal enhancement and granulomas in the acute meningitis group, but missed small calcifications in the basal cisterns well shown on CT in the sequelae group. Otherwise, MR generally matched CT scans. MR imaging appears to be superior to CT in evaluation of active intracranial Tb only if Gd-DTPA is used, while CT is better than MR in evaluating meningitic sequelae with calcification.     

MR imaging in paranasal and intracranial aspergillosis

The MR findings in three patients with paranasal and intracranial aspergillosis were analyzed. Two patients had sphenoid sinus aspergillosis with mucocele, and one had aspergillosis in the maxillary sinus and pachymeningitis in the posterior fossa. In all patients with aspergillosis of the paranasal sinuses, a markedly hypointense area was present within the lesion on T2-weighted images. In the patient with pachymeningitis, contrast-enhanced MR images clearly demonstrated the extent of the lesion.     

颅内脱髓鞘假瘤的MRI表现

目的：探讨颅内脱髓鞘假瘤(DPTs)的 MRI 影像表现。方法回顾性分析10例经临床最终诊断为 DPTs 的 MRI 影像资料,所有患者均行 MRI 平扫,其中9例行增强扫描,7例行扩散加权成像(DWI),2例行单体素短回波1 H-MRS。结果其中8例患者病灶周围伴有轻~中度水肿,5例表现为多发病灶,3例表现为单发结节灶,2例表现为单发片状病灶。增强扫描中4例为开环形强化,3例为环形强化,1例结节状强化,1例斑片状强化。病灶在 DWI 上均表现为高信号,1 H-MRS 示2例均有 NAA 峰不同程度降低,Cho 峰、Lac 和 Lip 峰升高,1例谷氨酸/谷氨酰胺复合物(Glx 峰)明显升高。结论DPTs 在 MRI 影像上有一定特点,特征性表现为开环形强化,结合 DWI 及1 H-MRS 技术有助于 DPTs 和其他病变鉴别。