肾脏囊性病变的MSCT表现及Bosniak分级在其中的应用

目的：讨论肾脏囊性病变的MSCT表现及Bosniak分级在肾脏囊性病变中的应用价值。方法：前瞻性分析我院肾脏囊性病变Mscr表现同时进行Bosniak分级,其中取得病理证实的有26例,将Bosniak分级结果与病理结果对照。结果：Bosniak Ⅰ级中2例都为良性,Ⅱ级4例都为良性,Ⅱ／F级3例,1例恶性（1／3）,Ⅲ级恶性3例（3／8）,Ⅳ级中9例都是恶性。结论：诊断肾脏囊性病变要注意影像特征,Bosniak分级对于诊断、指导治疗均有帮助,但Bosniak分级对于ⅡF级、Ⅲ级囊性病变存在不足之处。     

Bosniak分级在肾脏囊性病变MSCT诊断中的价值

目的 探讨Bosniak分级在肾脏囊性病变的MSCT诊断中的应用价值,提高对肾脏囊性占位的影像学特点的认识.方法 回顾近年来本院经手术、病理证实的肾脏囊性占位共42例,全部病例经过MSCT检查,结合Bosniak分级进行分类,并与病理诊断对照分析.结果 42例肾脏囊性肿物中,BosniakⅠ级4例均为良性,Ⅱ级11例中有1例为恶性,ⅡF级4例中1例为恶性,Ⅲ级13例中5例为恶性,Ⅳ级10例中9例为恶性.结论 Bosniak分级在肾囊性病变的MSCT诊断具有较高的应用价值,有助于肾囊性病变的诊断和鉴别诊断以及临床治疗方案的决策.     

多层螺旋CT结合Bosniak分级在肾囊性肿物诊断中的价值

目的 评价多层螺旋CT(MSCT)结合Bosniak分级对肾囊性肿物的诊断价值. 资料与方法 回顾性分析经手术、病理证实的109例患者共129个肾囊性占位术前MSCT的影像表现,并根据肾囊性占位的CT征象对其进行Bosniak分级;将MSCT的Bosniak分级结果与病理进行对照分析,判断各个级别中恶性囊肿的发生率;采用logistic回归分析预测Ⅰ～Ⅳ级中恶性肾囊肿的可靠CT征象. 结果 129个囊性肿物中,17个为恶性,112个为良性.对129个Ⅰ~Ⅳ级囊性病灶的CT特征进行logistic回归分析,结果显示实性成分强化是预测恶性肾囊肿的唯一可靠征象. 结论 高分辨CT结合Bosniak分级对大部分囊性肿物能够准确诊断;实性成分强化是预测恶性囊性肿物的唯一可靠征象.     

CT评估2019版Bosniak分级系统对肾囊性病变的诊断价值

目的 评估2019版Bosniak分级系统(Bosniak.v2019)对提高肾脏囊性病变影像诊断准确率的价值。方法 选取经手术治疗的肾脏囊性病变患者的病理和影像学资料，共纳入411例患者，发现囊性病变共495枚，2位医师分别使用2005版(Bosniak.v2005)和2019版Bosniak(Bosniak.v2019)分级系统对囊性病变进行影像学评估。使用Kappa检验评估2位医师评分结果间的一致性；使用ROC曲线评估Bosniak.v2005、Bosniak.v2019对肾恶性囊性病变的诊断效能；采用卡方检验对各级分级评分进行分析。结果 Bosniak.v2019的一致性较Bosniak.v2005有所提高(Kappa系数全部病变为0.851、0.887,肾恶性囊性病变为0.878、0.917);Bosniak.v2005、Bosniak.v2019诊断恶性囊性病变的敏感度差异无统计学意义(P>0.05);Bosniak.v2019诊断肾恶性病变的特异度、准确度和AUC值均高于Bosniak.v2005(P均<0.05)。Bosniak.v2019中对Ⅰ、Ⅱ类病变诊...     

Bosniak分级在MRI诊断肾脏复杂囊性病变中的应用

目的：探讨Bosniak分级在MRI诊断肾脏复杂囊性病变中的应用.方法：41例经病理证实的肾脏复杂囊性病变,恶性28例,良性13例.观察其MRI表现,进行Bosniak分级.并与病理及手术结果进行对照.结果：恶性、良性两组分隔数量大于4的病变比例分别为67.9%和23.1%,差异有显著性意义（P=0.007）.恶性组中囊壁或分隔增厚的病变中88.2%可见不规则增厚,明显高于良性组的28.6%（P=0.009）.9例病变实性成分大于25%,6例有假包膜征象,病理证实均为恶性.恶性、良性组中病变有明显强化分别占85.7%扣23.1%,差异有显著性意义（P〈0.001）.强化征象诊断恶性的敏感度、特异度和符合率分别为82.6%、76.9%和82.9%.恶性组Ⅱ～Ⅳ级病变和Ⅱ～ⅡF级病变比例分别为89.3%和10.7%,良性组为30.8%和69.2%,差异有显著性意义（P〈0.001）.结论：增强仍是MRI Bosniak分级和良性鉴别的最可靠征象,囊壁和分隔的增厚、实性成分比、分隔数量及假包膜等征象也有重要诊断价值.     

超声造影、增强CT及增强MRI对肾脏占位性病变的诊断价值比较

目的：比较超声造影、增强CT及增强MRI对肾脏占位性病变的诊断价值。资料与方法对78例经常规超声诊断为肾脏占位性病变患者的80个病灶进行实时超声造影检查,39个行增强CT检查,28个行增强MRI检查,其中5个同时行增强CT及增强MRI检查。以病理结果为“金标准”,比较超声造影、增强CT及增强MRI诊断肾脏占位性病变良恶性的价值。结果80个病灶中,57个为恶性病变,23个为良性病变;超声造影诊断肾脏病变良恶性的敏感度、特异度、阳性预测值、阴性预测值分别为93.0%、69.6%、88.3%、80.0%;增强CT诊断肾脏病变良恶性的敏感度、特异度、阳性预测值、阴性预测值分别为96.4%、72.7%、90.0%、88.9%;增强MRI诊断肾脏病变良恶性的敏感度、特异度、阳性预测值、阴性预测值分别为86.4%、66.7%、90.5%、57.1%;3种检查诊断效果间差异无统计学意义（P>0.05）。结论超声造影、增强CT及增强MRI对于肾脏占位性病变良恶性的诊断效果相当,临床可以根据各个检查技术的特点,为不同的患者选择适宜的检查,联合应用两种检查方法为肾脏占位性病变的诊断提供了更丰富的信息。     

动态增强MRI检查分级评估良恶性乳腺团块型病灶的价值

目的 探讨鉴别乳腺良恶性病灶的客观评分方法,为乳腺团块型病灶的良恶性判断提供客观评价依据.方法 将第4版乳腺影像和报告系统(BI-RADS)的MR部分对团块型病灶的描述作为病灶评价指标对188个高血供团块型病灶评分,根据评分结果与病理结果进行ROC曲线分析,计算曲线下面积并计算最佳良恶性诊断阈值;根据最佳诊断阈值及病灶良恶性倾向将病灶归入Ⅰ～Ⅴ级(Ⅰ级阴性、Ⅱ级良性、Ⅲ级可能良性、Ⅳ级可疑恶性、Ⅴ级高度提示恶性),最后检测评分方法诊断恶性团块型病灶的敏感度和特异度.结果 病理证实188个高血供病灶中有91个恶性,97个良性.ROC曲线下面积为0.938±0.016,评分法鉴别病灶良恶性的最佳阈值为5分.病灶分级结果为Ⅱ级24例、Ⅲ级72例、Ⅳ级54例、Ⅴ级38例.评分法诊断恶性乳腺团块型病灶的敏感度为87.91％,特异度为87.62％.除去Ⅲ级中3例假阴性的导管原位癌,特异度提高到90.90％.结论 建立在多参数标准化分析基础上的评分方法有助于客观判读乳腺动态增强MR影像.     

超声及X线摄影BI-RADS诊断乳腺囊性及以囊性为主病变的价值

目的通过分析乳腺囊性肿块病变超声及钼靶表现并与病理对照,为临床提出进一步处理意见。方法回顾性分析乳腺囊性病变患者112例,共135个病灶。根据病灶内部囊性、实性成分比例和分布特点将其分为5型,计算每一类型恶性病灶阳性预测值,对这些病灶的良恶性行超声及X线摄影技术BI-RADS分级,分析相关性。结果超声分型中Ⅰ型39个(28.9%),Ⅱ型46个(34.1%),Ⅲ型13个(9.6%),Ⅳ型14个(10.4%),Ⅴ型23个(17.0%),阳性预测值分别为0、2.2%、30.8%、50.0%和56.5%,且各类型间阳性预测值有显著性差异,P=0.000,Ⅲ、Ⅳ、Ⅴ型阳性预测值明显高于Ⅰ型和Ⅱ型。超声和X线摄影技术BI-RADS分级之间具有显著性差异。结论超声与X线摄影技术BI-AIDS分级在诊断乳腺囊性病变中存在差异,联合应用有助于提高符合率。     

Comparative Study of Multilocular Cystic Renal Cell Carcinoma and Other Complex Renal Cystic Lesions

目的 比较多房囊性肾癌(multilocular cystic renal cell carcinoma,MCRCC)与其他复杂性肾囊性病变在临床、病理及影像学方面的不同特点.方法 搜集本院2007年至2011年经手术病理证实的复杂性肾囊性病变64例,包括MCRCC患者17例,囊性肾癌(cystic renal cell carcinoma,CRCC) 28例,肾脏囊性良性病变19例,回顾性分析三组病例的临床资料、病理及CT特征.结果 (1)MCRCC组与良性病变组囊液性状均以浆液状为主(分别为82.4％,52.6％),CRCC囊液以浑浊坏死为主(64.3％);MCRCC组临床T分期明显低于CRCC组(P=0.001);(2) MCRCC与肾良性病变主要分布在BosniakⅢ级(64.7％∶57.9％),CRCC主要分布在BosniakⅣ级(67.8％).CRCC组囊液CT值中位数明显高于MCRCC与良性囊性病变组(30.6∶ 15.8∶10.6,P=0.019).MCRCC与CRCC病灶内软组织影大小存在明显差异(P=0.000).结论 MCRCC在临床、病理及影像学方面均显示其恶性程度低于CRCC,甚至在某些方面与肾脏囊性良性病变有相似的特点.     

多层螺旋CT鉴别诊断肾脏混合性上皮和间质肿瘤与囊性肾癌

目的探讨肾脏混合性上皮和间质肿瘤与囊性肾癌的多层螺旋CT(MSCT)表现及鉴别诊断要点,以提高二者术前影像诊断的准确性。资料与方法采用盲法研究,回顾性分析6例肾脏混合性上皮和间质肿瘤及14例囊性肾癌的MSCT表现,并与手术病理结果进行对照。结果 6例肾脏混合性上皮和间质肿瘤均为囊实性病变,但实性成分多少不等;其中BosniakⅢ型5例,BosniakⅣ型1例。14例囊性肾癌中,8例为透明细胞癌囊变,BosniakⅢ型7例,BosniakⅣ型1例;6例为多房性透明细胞性肾细胞癌,均为BosniakⅡF型。增强扫描示:肾脏混合性上皮和间质肿瘤实性部分在皮髓期呈轻度或中等程度强化,并随时间延迟强化程度增加;多房性透明细胞性肾细胞癌皮髓期菲薄间隔轻至中度延迟强化;7例BosniakⅢ型透明细胞癌囊变,皮髓期增厚间隔明显强化,1例BosniakⅣ型透明细胞癌囊变增厚间隔及结节皮髓期显著强化,二者强化程度较高,实质期强化程度均减退。结论肾脏混合性上皮和间质肿瘤囊性肾癌MSCT鉴别诊断有一定困难,但肿瘤实性成分的多少、间隔的形态以及增强方式可以为诊断及鉴别诊断提供依据。     

Assessment of cystic renal masses based on Bosniak classification: comparison of CT and contrast-enhanced US

OBJECTIVES: To compare retrospectively the imaging features of computed tomography (CT) and contrast-enhanced US (CEUS) imaging for the assessment of cystic renal masses using the Bosniak classification system. MATERIALS AND METHODS: The CT and CEUS images of 31 pathologically confirmed cystic renal masses in 31 patients were retrospectively analyzed for septa numbers, wall and/or septa thickness, enhancement degree, and for the presence of a solid component by consensus between two radiologists using the Bosniak classification. Diagnostic accuracies of CT and CEUS for malignant cystic tumor were calculated and compared using McNemar test. RESULTS: Diagnostic accuracies of CT and CEUS for malignant renal tumor were 74% and 90%, respectively, but there were not statistically different (P>0.05). CEUS and CT images showed same Bosniak classification in 23 (74%) lesions and there were differences in 8 (26%) lesions, all of which were upgraded by CEUS; one lesion from I to IV, two lesions from II to IV, two lesions from IIF to III, and three lesions from III to IV. CEUS images depicted more septa in 10 (32%) lesions, more thickened wall and/or septa in 4 (13%) lesions, and stronger enhancement in 19 (61%) lesions. Moreover, for six lesions, solid component was detected by CEUS but not by CT. CONCLUSION: CEUS might better visualize septa number, septa and/or wall thickness, solid component and the enhancement of some renal cystic masses than CT, resulting in upgrade of Bosniak classification and affecting their treatment plan.     

Complex cystic renal masses: characterization with contrast-enhanced US

PURPOSE: To prospectively compare contrast material-enhanced ultrasonography (US) with computed tomography (CT) in the classification of complex cystic renal masses with the Bosniak system. MATERIALS AND METHODS: Ethics committee approval and written informed consent were obtained. Forty patients (17 women, 23 men; age range, 31-77 years) with 44 complex cystic renal masses detected with conventional US were prospectively examined by using second-harmonic US with a second-generation contrast agent and multiphasic helical CT. Thirty-six patients had one lesion, and four patients had two lesions. Surgical resection in nine patients and imaging follow-up in 31 patients were used to determine the outcome. RESULTS: On contrast-enhanced US images, masses were classified as Bosniak category II (n = 18), IIF (ie, lesions were classified as category II and follow-up was needed) (n = 16), III (n = 7), or IV (n = 3) lesions. On CT images, masses were classified as Bosniak category II (n = 24), IIF (n = 10), III (n = 7), or IV (n = 3) lesions. Interobserver agreement was high (kappa = 0.86, P < .001) for classification with US. Complete concordance between the readers was found for classification with CT. Complete concordance between contrast-enhanced US and CT was observed in the differentiation of surgical and nonsurgical complex cysts. Complete concordance among the three readers in the assessment of vascularity with contrast-enhanced US was found. Interobserver agreement in the evaluation of enhancement on CT images was high (kappa = 0.88, P < .001). Concordance between contrast-enhanced US and CT in the evaluation of vascularization was high (kappa = 0.77, P < .001). CONCLUSION: The study data suggest that contrast-enhanced second-harmonic US is appropriate for renal cyst classification with the Bosniak system.     

Evaluation of cystic renal masses: comparison of CT and MR imaging by using the Bosniak classification system

PURPOSE: To compare computed tomography (CT) and magnetic resonance (MR) imaging in the evaluation of cystic renal masses by using the Bosniak classification system. MATERIALS AND METHODS: Images of 69 renal masses in 59 patients (38 men, 21 women; mean age, 60.4 years; range, 30-86 years), who had undergone both CT and MR imaging examinations within 1 year (average, 60.5 days; range, 0-356 days), were retrospectively analyzed by two radiologists in consensus. For each lesion, images were compared for thickness of wall and septa, number of septa, and presence of enhancement. Each mass was categorized (Bosniak classification) first on CT images and then on MR images, and results were compared. Pathologic correlation was available in 25 lesions. RESULTS: On CT images, there were 15 category I, 16 category II, 10 category IIF, 19 category III, and nine category IV lesions. Findings on CT and MR images were similar in 56 (81%) lesions; in 13 (19%) lesions, there were differences. In eight (12%) lesions, MR imaging depicted more septa than did CT, which resulted in an upgrade of the classification at MR imaging in two cases. In seven (10%) lesions, MR imaging depicted increased wall and/or septa thickness compared with CT, resulting in a classification upgrade in six cases. Three lesions had both increased numbers of septa and thickening of the wall and/or septa. In two (3%) lesions, enhancement characteristics at CT and MR imaging were different. One of these lesions also had an increased number of septa. Overall, MR imaging results led to a cyst classification upgrade of seven lesions, from category II to IIF (n = 2), IIF to III (n = 3), or III to IV (n = 2). Pathologic correlation in 25 lesions revealed 20 malignant and five benign lesions. CONCLUSION: CT and MR imaging findings were similar in the majority of cystic renal masses. In some cases, however, MR images may depict additional septa, thickening of the wall and/or septa, or enhancement, which may lead to an upgraded Bosniak cyst classification and can affect case management.     

Cystic renal masses: usefulness of the Bosniak classification

To determine the usefulness of the Bosniak classification of cystic renal masses, the computed tomographic (CT) and ultrasound findings of 16 pathologically proven cystic renal masses were retrospectively reviewed. All imaging studies were reviewed and categorized utilizing the Bosniak classification without knowledge of the final pathologic diagnosis. There were no category I lesions (classical simple cyst), four category II (minimally complicated), seven category III lesions (more complicated), and five category IV lesions (probable malignant). All category II lesions were benign, all category IV lesions were malignant. Of the seven category III lesions, three were benign and four were malignant. We conclude that the Bosniak classification is extremely useful in the management of cystic renal masses.     

Assessment of cystic renal masses in children: Comparison of multislice computed tomography and ultrasound imaging using the Bosniak classification system

To retrospectively compare contrast-enhanced multislice computed tomography (MSCT) and ultrasound (US) imaging for the assessment of cystic renal masses in children using the Bosniak classification system. Twenty-two consecutive patients (age 1 month to 5.2 years, mean 2.4 years) with 24 cystic renal masses (7 benign, 17 malignant) pathologically confirmed after surgical resection underwent both MSCT and US imaging, and were retrospectively analyzed using the Bosniak classification. A senior and a junior radiologist retrospectively and independently reviewed imaging findings. The sensitivity, specificity, positive predictive value and negative predictive values of MSCT and US were assessed using diagnostic statistics. The statistical significance of differences was determined by the McNemar test. Both radiologists accurately predicted lesions of categories I and IV with the Bosniak classification using MSCT and US. All masses classified as Bosniak classes I and II were proven to be benign, and all malignant lesions were correctly characterized in all cases both on ultrasound images and on the contrast-enhanced CT (CECT) images. Two benign multilocular cystic nephromas and one multicystic dysplastic kidney were classified into category III or even IV based on the classification scheme because of their multilocular nature and thick septation. The diagnostic accuracy of CECT was slightly better than ultrasound (CECT vs. US: senior reader, 92% vs. 88%; junior reader, 88% vs. 83%). However, there was no statistically significant difference between the two sets (p > 0.05). The two radiologists had perfect inter-observer agreement on the two modalities. Both MSCT and US provide highly accurate diagnosis for the malignant renal cystic masses in children using the Bosniak classification system, but assessment of benign masses still needs improvement. We would recommend US is the best screening modality in Bosniak I and II, In Bosniak III and IV, MSCT are first the choice.     

Cystic renal masses: Usefulness of the bosniak classification

To determine the usefulness of the Bosniak classification of cystic renal masses, the computed tomographic (CT) and ultrasound findings of 16 pathologically proven cystic renal masses were retrospectively reviewed. All imaging studies were reviewed and categorized utilizing the Bosniak classification without knowledge of the final pathologic diagnosis. There were no category I lesions (classical simple cyst), four category II (minimally complicated), seven category III lesions (more complicated), and five category IV lesions (probable malignant). All category II lesions were benign, all category IV lesions were malignant. Of the seven category III lesions, three were benign and four were malignant. We conclude that the Bosniak classification is extremely useful in the management of cystic renal masses. The opinions expressed herein are those of the authors and are not to be construed as official or as reflecting the views of the Uniformed Services University of the Health Sciences, the Department of Defense, or the United States Navy     

Calcification in cystic renal masses: is it important in diagnosis?

PURPOSE: To determine whether the presence of calcifications in cystic renal masses is important in diagnosis and to suggest an approach to the management of calcified cystic renal masses. MATERIALS AND METHODS: Eighty-one cystic renal masses containing calcification in a wall or septum were evaluated by means of review of computed tomographic (CT) images (n = 81), follow-up CT images (n = 28), and results of pathologic examination (n = 40) by the authors in consensus. Images were evaluated for lesion size, amount and morphology of calcification, and any association of calcification with soft-tissue structures. Lesions were categorized according to the Bosniak cyst classification system; the amount of calcification was determined with a subjective grading system. Progression of calcification was qualitatively determined with available follow-up CT scans. RESULTS: Twenty-one lesions were Bosniak category II (benign) and showed small amounts and thin strands of calcification. Nineteen lesions containing more extensive calcification but no enhancing tissue were category IIF. Follow-up CT results available for 16 of these lesions (average follow-up length, 5 years 8 months) showed no substantial change. The three remaining lesions were proved benign at surgery. Twenty-five lesions were category III; surgical intervention was performed in 21 of these (benign, n = 12; malignant, n = 9). Sixteen lesions that contained obvious areas of enhancing soft tissue were category IV and proved malignant at surgery. CONCLUSION: Calcification in a cystic renal mass is not as important in diagnosis as is the presence of associated enhancing soft-tissue elements. This information should enable a reasonable approach to the management of calcium-containing renal cystic lesions.     

Differentialdiagnose fokaler Nierenläsionen in CT und MRT

The great majority of renal masses are found incidentally as a result of the use of ultrasonography, computed tomography (CT) and magnetic resonance imaging (MRI). If ultrasonography is not diagnostic CT or MRI should be initiated to differentiate lesions of the kidney that need surgical intervention from those that do not and from those that need follow-up examinations.Cystic renal masses are characterized by using the Bosniak classification, including category IIF. In solid lesions of the kidney first non-surgical lesions as well as lymphoma, renal infarction and nephritis should be excluded. Identifying fatty components in renal lesions is very important because in angiomyolipoma they are almost always present.CT and MRI are exellent for tumor detection. Careful evaluation of imaging finding combined with the patient′s history should assist the radiologist in making the proper diagnosis or recommending the appropriate treatment in most cases.This article provides a review about renal masses, the imaging methods for their evaluation and their characteristic features at CT and MR imaging. Different lesions are demonstrated like xantogranulomatous pyelonephritis, acute pyelonephritis, renal infarction, lymphoma, angiomyolipoma, renal oncocytoma, cystic lesion and polycystic disease the kidney, echinococcosis, renal cystadenoma, metastases, renal cell carcinoma (RCC), and multiple bilateral RCC in patients with Hippel-Lindau-Syndrome.This article should help to differentiate complex cystic lesions of the kidney by using the Bosniak-classification, especially Bosniak Category IIF. Solid masses should be characterized and the major question to be answered is whether the mass represents a surgical or nonsurgical lesion or if follow-up studies are necessary.     

Cystic tumors of the kidney in adults: radio-histopathologic correlations

The purpose of this study is to provide an updated pathologic-radiologic classification of cystic renal tumors and to assess imaging diagnostic capabilities. Eighty seven cases of cystic renal tumors explored with multimodality imaging (ultrasonography, CT, MRI, arteriography) and with histopathologic correlation are reported. The most common cystic carcinomas were multilocular cystic renal cell carcinoma (33%) and the pseudocystic necrotic carcinoma (31%), which usually belong to category IV. Less common cystic carcinomas were unilocular cystic renal cell carcinoma (6%) and renal cyst wall carcinoma (6%). The association of thin septa and large locules are suggestive findings for multilocular cystic nephroma, but such criteria are not specific enough to recognize benign multilocular cystic nephroma and to exclude multilocular cystic renal cell carcinoma. Since carcinomatous degeneration may occur within the wall of such tumors, especially in von Hippel Lindau disease, surgery is still required. The results of our study corroborate the Bosniak classification of cystic renal masses: no tumors belonged to the category I or II, all cystic masses which belonged to the category IV were malignant tumors, category III included benign and malignant tumors.     

Cystic renal masses: accurate Bosniak classification requires adequate renal CT

OBJECTIVE: The objective of this study was to assess the practical usefulness of the Bosniak classification system for separating surgical from nonsurgical cystic renal masses in a large number of patients examined with properly performed renal CT. The study included only patients whose scans were technically adequate to allow proper assignment of the lesion to a category. MATERIALS AND METHODS: The scans of 109 patients were gathered from two large teaching institutions both prospectively and retrospectively, yielding a total of 116 analyzable renal cystic lesions. Eighty-two masses were resected from 77 of these patients, retrospectively categorized by two experienced uroradiologists using the Bosniak classification system, and correlated with pathology reports. A second group of 34 lesions in 32 patients with atypical cysts was followed up prospectively for periods ranging from 3 months to 10 years. RESULTS: The results were similar for the two institutions: 15 resected categories I and II lesions were correctly identified as benign, and all 18 category IV lesions were malignant. Twenty-nine (59%) of 49 pooled category III masses were malignant. No malignancies have been identified in the prospectively monitored group of patients. CONCLUSION: Our results are compared with earlier, smaller series and support those that show that the Bosniak classification system is useful in separating lesions requiring surgery from those that can be safely followed up, provided proper CT techniques are used.