Evaluation of renal masses by MR imaging

Magnetic resonance (MR) imaging was performed in 20 subjects, 10 of whom had benign or malignant renal masses, and 10 were normal volunteers. The purpose of the study was to evaluate the ability of MR to provide significant diagnostic information in the management of renal mass lesions. Ten normal patients were included to supply baseline data. Different pulse sequences were used and their contribution to the diagnosis was evaluated. The emphasis has been placed on evaluating MR against the pathological diagnosis rather than other imaging modalities.     

Gadolinium-enhanced MR imaging of renal masses.

Preliminary reports indicate that gadolinium-enhanced magnetic resonance (MR) imaging is highly accurate for diagnosis of renal masses. The authors demonstrate the clinical utility of MR imaging for evaluating renal masses in 26 patients for whom contrast material-enhanced computed tomography (CT) was contraindicated or inadequate for diagnosis or staging. Nine patients had complex cysts, one had a perinephric hematoma, and 16 had a solid mass (three of which were benign). All patients underwent MR imaging before and after administration of gadopentetate dimeglumine. Multiple imaging techniques and sequences were used. All tumors and no cysts enhanced with gadolinium. Even though the three benign tumors enhanced, two were differentiated from renal carcinoma on the basis of other imaging features. Unenhanced MR imaging was accurate in staging of renal carcinomas, and use of gadolinium did not improve staging accuracy. Gadolinium-enhanced MR imaging is indicated when results of CT and sonography are indeterminate for malignancy and when contrast-enhanced CT is contraindicated because of renal failure or adverse reaction to iodinated contrast material. In this latter instance, MR imaging is useful for both diagnosis and staging.     

Neurosarcoidosis: gadolinium-enhanced MR imaging

Two cases of neurosarcoidosis studied by Gd-diethylenetriamine pentaacetic acid-enhanced magnetic resonance imaging are reported. Both patients demonstrated multifocal white matter abnormalities that were clustered near regions of intense meningeal enhancement. Presumed spread of neurosarcoidosis along Virchow-Robin spaces was demonstrated, as evidenced by contrast enhancement along the course of vessels supplying some of the white matter abnormalities.     

Developing spinal column: gadolinium-enhanced MR imaging

Enhancement characteristics of the normally developing spinal column were examined in magnetic resonance (MR) images obtained in 58 children aged 7 days to 9 years. With a 1.5-T imager, short-repetition-time spin-echo images were obtained before and after the administration of 0.1 mmol/kg gadopentetate dimeglumine. Enhancement of normal bone marrow was seen in all patients aged less than 7 years; it was marked only in patients aged less than 2 years. Enhancement of normal cartilage, seen in all patients aged less than 1 1/2 years, may be the most striking feature of enhanced MR images of the infant spine. Enhancement of both bone marrow and cartilage in children appears to be due to the unusual prominence of vasculature, associated with permeability of the capillary endothelium and a plentiful extravascular space. Although marked and diffuse enhancement of vertebral bodies in adults is often thought to indicate a pathologic marrow state, caution must be used before the same criteria are applied to children.     

Parotid gland: plain and gadolinium-enhanced MR imaging

The purpose of this study was to show the typical appearance of lesions of the parotid gland with plain MR imaging and MR imaging enhanced with gadopentetate dimeglumine. Seventeen patients with inflammatory changes and 43 with benign and malignant tumors were studied. The examinations were carried out with plain T1-weighted sequences with a repetition time (TR) of 500 msec and an echo time (TE) of 25 msec (TR/TE = 500/25), T2-weighted sequences (1,600/90), and gadolinium-enhanced T1-weighted sequences in axial, coronal, and sagittal orientations. For identifying normal anatomic structures such as the facial nerve and the main duct, the administration of gadopentetate dimeglumine was helpful. In inflammatory changes, gadolinium-enhanced images showed no diagnostic advantages. Gadopentetate dimeglumine proved helpful in delineating tumorous lesions and in differentiating benign and malignant lesions. However, an exact differentiation of the different histologic types was not possible. Post-operative fibrosis could be differentiated from recurrent tumors after administration of gadolinium. If a question regarding infiltration or definition of the boundaries of a lesion cannot be answered with non-enhanced MR imaging, gadopentetate dimeglumine administration is advised. However, for routine imaging of the parotid gland, its use is not recommended.     

Origin of a signal intensity loss artifact in fat-saturation MR imaging

Artifactual water signal intensity loss can be observed on fat-saturation magnetic resonance (MR) images of inhomogeneous regions such as the thorax. Magnetic effects of air inclusions on fat-saturation pulses were investigated as the possible origin of this artifact. Computer simulation results agreed well with observed production of water saturation by means of nominal fat suppression in MR imaging of phantoms and a representative clinical example.     

MR imaging of renal masses interpreted on CT to be suspicious

OBJECTIVE: Prior studies have shown that renal MR contrast enhancement improves the efficacy of mass and proximal vascular evaluation. This study assessed the usefulness of different sequences for characterization of masses that appeared suspicious on CT and for prediction of their potential for malignancy. SUBJECTS AND METHODS: In a prospective manner 32 patients (age range, 26-78 years: average age, 54 years), each with at least one suspicious mass on CT, were examined with MR imaging. The following sequences were performed: conventional spin-echo with and without fat saturation, fast spin-echo, and dynamic gadopentetate dimeglumine-enhanced infusion using a 1.5-T superconducting magnet. Results were analyzed and compared with pathologic results after resection. RESULTS: A total of 65 renal masses of average size 2.6 cm (range, 1-10 cm) were detected with dynamic MR imaging. Seventeen of the 65 masses were malignant. Of the 17 malignant masses, three did not enhance on dynamic MR imaging (because of hemorrhage). Sixteen of the 17 malignant masses were heterogeneous on T2-weighted images. Three enhancing masses contained fat and all were angiomyolipomas. Thirty-five of the 65 masses (four with hemorrhage) did not show enhancement, all of which were homogeneous on T2-weighted images and were proven to be cysts. Five masses resulted from infections and had heterogeneous T2 appearance. The remaining masses were three hematomas with hemorrhage, one column of Bertin, and one aneurysm. CONCLUSION: Renal masses that are interpreted as suspicious on CT may lack MR enhancement because of hemorrhage effects; heterogeneity of their T2 appearance is thus critical in differentiating malignancy from benign disease. Odds-ratio calculations give an adjusted estimate of a 3.36-fold increase (95% confidence interval, 1.8-6.27) in the likelihood of malignancy when masses are heterogeneous on T2-weighted images and a 29-fold increase (95% confidence interval, 3.67-241.8) for predicting malignancy when enhancement is present.     

Brain: gadolinium-enhanced fast fluid-attenuated inversion-recovery MR imaging

PURPOSE: To determine the clinical utility of gadolinium-enhanced fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging of the brain by comparing results with those at gadolinium-enhanced T1-weighted MR imaging with magnetization transfer (MT) saturation. MATERIALS AND METHODS: In 105 consecutive patients referred for gadolinium-enhanced brain imaging, FLAIR and T1-weighted MR imaging with MT saturation were performed before and after administration of gadopentetate dimeglumine (0.1 mmol per kilogram of body weight). Pre- and postcontrast images were evaluated to determine the presence of abnormal contrast enhancement and whether enhancement was more conspicuous with the FLAIR or T1-weighted sequences. RESULTS: Thirty-nine studies showed intracranial contrast enhancement. Postcontrast T1-weighted images with MT saturation showed superior enhancement in 14 studies, whereas postcontrast fast FLAIR images showed superior enhancement in 15 studies. Four cases demonstrated approximately equal contrast enhancement with both sequences. Six cases showed some areas of enhancement better with T1-weighted imaging with MT saturation and other areas better with postcontrast fast FLAIR imaging. Superficial enhancement was typically better seen with postcontrast fast FLAIR imaging. CONCLUSION: Fast FLAIR images have noticeable T1 contrast making gadolinium-induced enhancement visible. Gadolinium enhancement in lesions that are hyperintense on precontrast FLAIR images, such as intraparenchymal tumors, may be better seen on T1-weighted images than on postcontrast fast FLAIR images. However, postcontrast fast FLAIR images may be useful for detecting superficial abnormalities, such as meningeal disease, because they do not demonstrate contrast enhancement of vessels with slow flow as do T1-weighted images.     

Parotid masses: MR imaging

Over a 2-year period 20 patients who presented with masses in the parotid gland were evaluated with magnetic resonance (MR) imaging. T1-weighted images were obtained on a high-resolution, thin-section MR imaging system. When "cystic-appearing" lesions were found, T2-weighted images were obtained in order to better characterize the tumor. As in other areas of the body, MR images of parotid tumors are not usually histologically specific. MR findings may be distinctive in rare cases and define the internal architecture of complex parotid masses. Although poor tumor margination was a clue to malignancy, this was not a consistent finding. The real advantage of MR imaging in evaluating parotid masses was its ability to accurately reveal the extraparotid or intraparotid location of a tumor and demonstrate the relationship of the tumor to the facial nerve. Small and medium-sized mass lesions could be seen as superficial or deep to the facial nerve. Larger masses producing some distortion of the normal course of the nerve made identification of the nerve more difficult, if not impossible. In malignant tumors with gross invasion of the facial canal, MR images can show the extent of nerve involvement.     

Mediastinal masses: MR imaging

Seventy-five patients with mediastinal masses were imaged with magnetic resonance (MR). Results were analyzed with regard to the ability of MR to demonstrate the masses, their morphology, and their encroachment or displacement of blood vessels and airways. T1 values were determined in 53 patients and T2 values in 59. Hydrogen density and percentage of contrast relative to muscle and fat were also obtained in 53 and 59 patients, respectively. MR images were compared with computed tomography (CT) scans, which were available in 45 patients. MR depicted all masses and demonstrated compromise of vessels and cardiac chambers owing to the inherent contrast between the masses and cardiovascular structures. Bronchogenic carcinoma had very long relaxation values for T1 and T2, while chronic inflammatory processes had intermediate values for T1 and T2, thus appearing less intense than bronchogenic carcinoma on T2-weighted images. Other neoplasms demonstrated T1 and T2 values between these two disease groups. Masses appeared less homogeneous on MR images than on CT scans, and vascular compromise was better assessed with MR. Thus, MR imaging is a completely noninvasive technique for the evaluation of mediastinal masses. While the anatomic information is comparable to that produced by CT, MR provides some insight into the composition of the mass.     

Thymic masses on MR imaging

MR imaging is an excellent technique for identifying and defining the extent of thymic tumors. T1-weighted spin-echo MR images (e.g., 600/15 [TR/TE]) best demonstrate tumor extent, and T2-weighted images (e.g., 2500/90 [TR/TE]) help differentiate "cystic" from solid thymic masses. Cyst formation and/or hemorrhage appear as areas of high signal intensity (greater than that of fat) on T2-weighted images. Focal areas of low signal intensity (less than that of muscle) correspond pathologically to fibrous capsules and septa, air, or calcification. In this report, the MR appearance of the normal thymus is reviewed briefly, and the gamut of abnormal thymic masses on MR is illustrated.     

Osteomyelitis in children: gadolinium-enhanced MR imaging.

Fifteen pediatric patients with biopsy- or culture-proved nonspinal osteomyelitis were studied with magnetic resonance (MR) imaging. Osteomyelitis was acute in seven patients, subacute in three, and chronic in five. Four patients had subperiosteal abscesses, one had a large associated soft-tissue abscess, and one had an intraosseous (Brodie) abscess. Areas of active inflammation had decreased marrow signal intensity on T1-weighted images, increased signal intensity on T2-weighted images, and enhancement on T1-weighted images obtained after gadopentetate dimeglumine administration (n = 10). Abscesses were rim enhancing (n = 3) or not (n = 2) with gadolinium-enhanced MR imaging. Nonenhancing areas presumably represented necrotic material. Gadolinium-enhanced MR imaging assisted in definition of the presence and extent of nonvascularized fluid collections within the bone and/or adjacent soft tissues and the extent of bone involvement in patients with chronic osteomyelitis. It also helped guide surgical debridement of intraosseous disease (n = 7) and open or percutaneous drainage of subperiosteal or soft-tissue fluid collections (n = 5).     

肾肿物的动脉自旋标记MR成像:与组织病理结果的对照研究

目的以组织病理学结果为参照,评价肾脏实性肿物的动脉自旋(ASL)MRI灌注特征与价值。材料与方法这项前瞻性研究符合HIPAA原则,获得单位伦理委员会的批准。所有病人均于检查前签署了知情同意书。42例怀疑肾肿物的病人在进行常规1.5T临床MRI检查前,进行了ASL检查。1名放射医师在不知最终病理结果的情况下,通过对兴趣区的分析,计算肿瘤灌注的平均值和峰值水平。通过方差分析检验灌注值与病理学结果的相关性。采用线性模型评价肾透明细胞癌的肿瘤体积与灌注值之间的相关性。P<0.05为差异具有统计学意义。结果 34例病人[男28例,女6例;(60.4±11.7)岁]获得组织病理学结果。乳头型肾细胞癌的平均灌注值[(27.0±15.1)mL/(min.100g)]低于透明细胞型[(171.6±61.2)mL/(min.100g),P=0.001]、嫌色细胞型[(152.9±80.7)mL/(min.100g),P=0.04]、未分类型肾细胞癌[(208.0±41.1)mL/(min.100g),P=0.001]和肾嗜酸细胞瘤[(373.9±99.2)mL/(min.100g),P<0.001]。肾嗜酸细胞瘤的灌注平均值和峰值水平[分别为(373.9±99.2)mL/(min.100g)和(512.3±146.0)mL/(min.100g)]高于乳头型[(27.0±15.1)mL/(min.100g)和(78.2±39.7)mL/(min.100g),两者P<0.001],嫌色细胞型[分别为(152.9±80.7)mL/(min.100g),P<0.001和(260.9±61.9)mL/(min.100g),P=0.02]和未分类型肾细胞癌[分别为(208.0±41.1)mL/(min.100g),P=0.01和(273.3±83.4)mL/(min.100g),P=0.03]。肾嗜酸细胞瘤的平均肿瘤灌注值高于透明细胞癌(P<0.001)。结论动脉自旋标记MR成像可在灌注水平上区分和诊断不同病理类型的肾脏肿物。肾嗜酸细胞瘤的灌注水平高于肾细胞癌,乳头型肾细胞癌的灌注水平低于其他亚型的肾细胞癌。     

Renal lesion characterization with gadolinium-enhanced MR imaging: efficacy and safety in patients with renal insufficiency

Five patients with renal insufficiency were studied with T1-weighted magnetic resonance (MR) imaging before and after intravenous administration of gadopentetate dimeglumine (0.1 mmol/kg) to characterize renal lesions that were detected with nonenhanced computed tomography (CT) and were considered indeterminate. Four patients demonstrated renal lesions that enhanced after gadolinium administration. A total of five lesions in these four patients were surgically resected and found to be renal cell carcinoma at pathologic examination. The fifth patient was spared surgery because a hyperattenuated lesion noted at nonenhanced CT did not enhance with intravenous gadolinium, indicating a benign cyst. Five incidentally occurring benign cysts removed at the time of nephrectomy in two of the patients did not demonstrate enhancement with gadolinium on MR images. Serial serum creatine levels were obtained before and after gadolinium administration in all patients; no changes were noted after gadolinium administration. Gadolinium-enhanced MR imaging is an effective method for characterizing renal lesions in patients with renal insufficiency. At the usual dosage, there appears to be no nephrotoxic reaction in these patients.     

Imaging of osteoid osteoma with dynamic gadolinium-enhanced MR imaging

PURPOSE: To compare dynamic gadolinium-enhanced T1-weighted magnetic resonance (MR) imaging with nonenhanced T1-weighted and T2-weighted MR imaging and thin-section computed tomography (CT) for the demonstration of osteoid osteomas. MATERIALS AND METHODS: The images of 11 patients with pathologically proven osteoid osteomas who underwent nonenhanced MR imaging, dynamic gadolinium-enhanced MR imaging, and CT were retrospectively reviewed. Images obtained with all three techniques were scored for conspicuity of the osteoid osteoma relative to the surrounding bone. Time-enhancement curves were generated from signal intensity measurements of these lesions and the adjacent bone marrow. The mean imaging scores of the four techniques were compared, and the statistical significance was calculated by using a linear model with terms for method and patient. Pairwise comparisons were made by using the Tukey-Kramer adjustment for multiple comparisons. RESULTS: Compared with CT, dynamic gadolinium-enhanced MR imaging demonstrated the osteoid osteoma equally well in eight of 11 patients and with better conspicuity in three of 11 patients, although this difference was not statistically significant (P =.69). The dynamic gadolinium-enhanced MR images demonstrated the osteoid osteomas significantly better than the nonenhanced T1-weighted (P <.001) and T2-weighted (P <.001) MR images. On the dynamic gadolinium-enhanced MR images, nine (82%) of 11 patients had peak enhancement of the osteoid osteoma in the arterial phase with early partial washout, compared with slower, progressive enhancement of the adjacent marrow. This resulted in greatest lesion to marrow contrast material enhancement in the arterial phase. One osteoid osteoma had peak enhancement in the venous phase, and one showed progressive enhancement through all phases to 150 seconds. CONCLUSION: Osteoid osteomas can be imaged with greater conspicuity by using dynamic gadolinium-enhanced instead of nonenhanced MR imaging and with conspicuity equal to or better than that obtained with thin-section CT.