原发性心脏血管肉瘤的CT及MRI表现

目的:探讨心脏原发性血管肉瘤的CT、MRI表现,以提高对该病的影像诊断水平。方法:回顾性分析5例经临床病理证实的心脏原发血管肉瘤患者的临床及影像资料。5例中男4例,女1例;年龄24~45岁,平均34.5岁。对肿瘤的部位、大小、形态、边缘、CT密度、MRI信号及强化形式进行分析。5例中,3例行胸部CT平扫加增强扫描,2例行CT平扫、MRI平扫及增强扫描。结果:5例心脏原发性血管肉瘤均发生在右心房游离壁,向心腔内或外生长。CT平扫表现为等或稍低密度;MRI平扫T1WI表现为与心肌信号相似的等或稍低信号,T2WI表现为不均匀稍高信号;如瘤体内有坏死、出血、钙化,则表现为混杂密度或混杂信号。CT及MRI增强扫描肿瘤呈明显不均匀延迟强化,CT增强扫描瘤体内见肿瘤血管或血管团。结论:心脏原发血管肉瘤具有一定的影像特征,掌握这些特征有助于病变的诊断及鉴别诊断。     

肾脏恶性肿瘤的MRI诊断(附15例报告)

目的 :探讨肾脏恶性肿瘤的MRI诊断价值。方法 :回顾性分析和比较 15例经手术病理证实的肾脏恶性肿瘤患者的MRI检查资料 ,其中 13例行增强扫描。结果 :术前MR诊断正确的 13例 ,2例分别误诊为肾周陈旧性血肿、肾血管源性肿瘤。 12例为肾细胞癌 ,3例为肾移行细胞癌。病变大多边缘光整 ,有完整包膜 ,T1 WI为等或低信号 ,T2 WI大多为高信号 ,仅 1例T2 WI为低信号 ,若伴囊变者为混杂信号。病变强化无明显特征 ,仅有 1例肾盂癌明显强化 ,不符合其常见的乏血管特征。 1例肾上盏的 2cm× 2cm的肿瘤CT平扫和增强扫描均漏诊 ,MR信号特征可鉴别之。结论 :MRI具有良好的软组织分辨率、多方位成像的技术特点 ,在诊断肾脏恶性肿瘤中 ,对明确诊断和确定手术范围有重要的价值     

CT和MRI动态强化在颈动脉体瘤中的诊断价值

目的:分析颈动脉体瘤的CT和MRI的动态强化特点,探讨CT与MR动态强化在诊断颈动脉体瘤中的作用,提高术前诊断水平。方法:回顾性分析经手术病理证实的颈动脉体瘤12例,术前均行64层CT动态强化及CT血管成像,注射速率4.5~5.0ml/s,有效层厚0.625mm;2例行MRI平扫,其中1例行MRI动态强化及MR血管成像。结果:12例病变均为单发,位于颈总动脉分叉处。9例病变颈内、外动脉夹角增大,呈典型的"杯口状"表现;3例病变较小,颈动脉分叉角度无明显变化。CT平扫10例病变密度均匀,呈等或略高密度,2例病变密度不均匀。增强后动脉期12例肿瘤均明显强化,CT值平均226.7HU,强化程度接近颈动脉血管,病灶均匀强化8例、不均匀强化4例,边界清楚;静脉期显示肿瘤进一步持续强化,强化程度稍低于颈动脉血管,均表现为均匀一致的强化。其时间-密度曲线峰值与颈内动脉峰值相比幅度稍小、出现稍晚。MR平扫T1WI呈等信号,T2WI呈略高信号,动态增强后病变显著均匀强化,变化规律与CT一致。结论:颈动脉体瘤动态强化影像学特征对颈动脉体瘤的诊断及鉴别诊断具有重要的临床实用价值。     

颅底软骨肉瘤的CT和MRI诊断

目的 分析颅底软骨肉瘤的CT和MRI表现，探讨CT和MRI的诊断价值和限度。资料与方法搜集经病理组织学证实的12例颅底软骨肉瘤，均行CT及MRI平扫。其中8例行MRI增强扫描。结果 11例CT上可见不同程度的钙化，MRTlWI呈低等信号，T2WI呈不均匀高信号；1例CT表现为囊性低密度，伴有高密度点状出血灶，T1WI呈以低信号为主夹杂高信号出血灶，T2WI呈均匀高信号，边界清晰。8例MRI增强扫描均表现为不均匀强化，信号及密度改变与病理相符。结论 颅底软骨肉瘤的CT和MRI表现与病理相符。CT和MRI是诊断颅底软骨肉瘤的有效方法。     

颞下窝原发肿瘤的CT及MR表现

目的：探讨颞下窝原发肿瘤CT及MRI表现。方法回顾性分析20例经病理证实的颞下窝原发肿瘤的CT及MR资料。结果颞下窝肿瘤形态多不规则。神经鞘瘤多边界清楚（5/6）,MR T1WI为等信号,T2WI为高信号肿物伴线状分隔样低信号,2例通过卵圆孔伸入中颅窝呈哑铃状生长。恶性外周神经鞘膜肿瘤边界多不清楚（4/5）,MR T1WI为等信号,T2WI为不均匀高信号,病变可侵犯邻近肌肉及骨质。横纹肌肉瘤MR T1WI为等信号,T2WI为高信号。孤立性纤维性肿瘤边界清楚,MR T1 WI等信号,T2 WI为混杂略高信号,增强后较明显强化。腺样囊性癌边界不清,沿神经浸润生长。侵袭性多形性腺瘤MR T1 WI为等、低信号,T2 WI为高信号,侵犯邻近肌肉。淋巴瘤形态不规则,边界清楚,MR T1WI为低信号,T2WI为中高信号,轻度强化,内有线样血管影穿行。结论熟悉颞下窝原发肿瘤CT及MRI表现,有助于提高该部位病变诊断及鉴别诊断水平。     

儿童韧带样纤维瘤的影像学表现

目的 探讨儿童韧带样纤维瘤(DT)的影像诊断价值.方法 回顾性分析14例经病理证实的儿童DT的临床及影像特点.9例行CT平扫及增强扫描,2例行MRI平扫及增强扫描,3例同时行CT及MR检查.结果 儿童DT主要为腹壁外型,病灶呈梭形、卵圆形,沿肌纤维间隙浸润性生长.CT平扫表现为等、稍低密度肿物,动脉期呈轻度不均匀强化,延迟扫描强化程度显著增高.MRI表现为软组织肿物,T1WI等/稍低信号,T2WI多为不均匀稍高信号,T1WI及T2WI均见索条状稍低信号,增强后不均匀强化.结论 儿童DT CT/MRI表现为梭形、卵圆形沿肌肉间隙生长的软组织肿物,延迟强化明显增高;MRI能显示其中的纤维成分,其影像特征为正确诊断提供重要依据.     

肝血管源性恶性肿瘤的CT和MRI诊断

【摘要】目的：总结分析肝血管源性恶性肿瘤的CT及MRI表现,提高其影像诊断水平。方法:回顾性分析经手术病理证实的11例肝血管源性恶性肿瘤患者的临床及影像学资料,其中10例行MRI扫描,1例行CT扫描,所有患者均行平扫及三期动态增强扫描。结果：11例肝血管源性恶性肿瘤中,肝上皮样血管内皮瘤(EHE)5例,肝血管肉瘤(PHA)3例,肝血管外皮细胞瘤(HPC)3例。5例肝EHE边界均清晰,其中3例为孤立结节,2例为多发结节并相互融合,3例病灶位于包膜下;1例出现肝“包膜凹陷”征,2例出现“晕”征;1例CT平扫呈低密度,中心见更低密度区;2例T1WI平扫呈高低混杂信号,2例呈低信号;2例T2WI呈高低混杂信号,2例呈高信号;增强扫描动脉期3例肿瘤边缘强化,2例肿瘤内出现片状或点状不均匀强化;延迟期均表现为持续强化,其中2例强化范围扩大。3例肝PHA边界均清晰,其中2例为单发巨块型;在T1WI及T2WI中均表现为高低混杂信号,增强扫描动脉期2例肿瘤内出现片状或点状不均匀强化及非周边强化,1例肿瘤边缘花边样强化;延迟期均表现为持续强化,强化范围均扩大。3例肝HPC中2例边界清晰,1例边界不清;在T1WI及T2WI中均表现为高低混杂信号;增强扫描动脉期3例肿瘤边缘均出现环状不均匀强化;延迟期2例边缘持续填充强化,未向中心填充;1例向内略填充。结论：肝血管源性恶性肿瘤的影像表现复杂多样,CT和MRI表现对判定肿瘤起源及与其它肿瘤的鉴别诊断有一定价值,确诊需依靠免疫病理检查。     

胸膜外孤立性纤维性肿瘤MSCT与MRI征象

目的:探讨胸膜外孤立性纤维性肿瘤(ESFT)的MSCT与MRI影像诊断。方法:分析12例ESFT的CT与MRI资料,5例行CT平扫和增强,4例MR平扫和增强,1例行CT平扫及MR平扫和增强,2例MR平扫。结果:腹盆部5例,头面部5例,四肢2例;单发11例,双发1例,共13处病灶;瘤体呈类圆形5例,不规则形8例;边缘清楚6例,边缘呈浸润或模糊状7例;实性10例,囊实性3例。CT平扫呈均匀及混杂密度各3例,5例增强后动脉期均匀强化2例,不均匀强化3例,强化呈斑片状和线条状,静脉期进行性增强或减低,3例见钙化及坏死。MR平扫肿瘤实质部分4例T1WI等信号,T2WI等及稍高信号;4例T1WI等、低信号,T2WI等、低或稍高混杂信号;增强后肿瘤实质明显强化。结论:ESFT影像学有一定特征,典型征象为孤立的明显进行性强化的软组织肿瘤,当肿瘤实质区T1WI或T2WI出现等低信号且增强明显强化时应考虑SFT诊断可能。     

周围型胆管细胞癌的MSCT和MRI诊断

目的:探讨肝内周围型胆管细胞癌(IHPCC)的CT及MRI诊断。方法:回顾性分析经手术或活检病理证实的IHPCC 24例,20例行CT平扫和三期增强扫描,5例行MR扫描。结果:CT三期增强扫描强化曲线19例表现为"慢进慢退",1例表现为"快进慢退";MRI T2WI及T1WI上无特异性,3例双回波T1WI同反相位信号未见衰减,DWI上为高信号。结论:IHPCC的CT、MRI有其特征性表现,特别三期增强扫描强化曲线"慢进慢退"表现对于IHPCC诊断尤为重要。MRI同反相位扫描对于IHPCC与含脂质肝脏肿瘤相鉴别可能有帮助。     

颅内血管平滑肌瘤的影像表现(附2例讨论)

目的探讨颅内血管平滑肌瘤的CT及MRI表现。资料与方法结合文献回顾性分析2例经手术病理证实的位于颅内鞍旁的血管平滑肌瘤的CT及MRI表现。2例均行MRI平扫及增强,1例行MRI动态增强,1例行CT平扫。结果 2例均位于右侧鞍旁。例1行CT平扫示中颅窝鞍旁类圆形稍高密度肿块,密度均匀,周围未见水肿,MRI平扫T1WI呈低信号,扩散加权成像(DWI)呈低信号,T2WI呈不均高信号,内可见条状低信号。病灶周围见薄层环状水肿带,增强扫描肿块明显均匀强化,局部可见脑膜尾征;例2 MRI平扫示鞍旁卵圆形肿块,T1WI呈等信号,T2WI呈高信号,右三叉神经受压,增强扫描早期示病灶中心斑片状强化,增强晚期示病灶逐渐从中心向周边强化。结论动态增强扫描呈中心性渐进性强化可能为颅内血管平滑肌瘤特征性表现,有助于其诊断与鉴别诊断。     

MRI of anterior mediastinal tumors.

To compare the abilities of MRI (magnetic resonance imaging) and CT to provide information about anterior mediastinal tumors, we retrospectively evaluated the MR (n = 28) and CT images (n = 25) of patients with anterior mediastinal tumors. T1-weighted and T2-weighted images were obtained with spin echo sequences using cardiac gating. Six of 12 thymomas and seven of nine teratomas showed characteristic findings by MRI, while four of the 10 thymomas and five of the eight teratomas were correctly diagnosed by CT. The other tumors did not show a characteristic MR appearance. All nine malignant tumors were correctly diagnosed as malignant lesions on MR images, while one false positive case and one false negative case were recorded on CT images. We conclude that MRI and CT provide nearly the same information for the evaluation of anterior mediastinal tumors. However, in some cases, only MRI can provide information about malignancy or a specific diagnosis.     

Primary malignant fibrous histiocytoma of the chest wall: CT and MR appearance

PURPOSE: The purpose of this work is to describe the CT and MR appearance of primary malignant fibrous histiocytoma (MFH) of the chest wall. METHOD: Eleven men and eight women (45-76 years old) with primary MFH of the chest wall who underwent both CT and MRI were enrolled, and the imaging interpretation was retrospectively compared to the pathologic specimen. RESULTS: All tumors were inhomogeneous in appearance on CT scans. All tumors showed high signal intensity on T2-weighted images. On T1-weighted MR images, tumors displayed inhomogeneous isosignal intensity in 15 cases (79%) and low signal intensity in 5 (21%) compared with the surrounding muscle. Tumors exhibited inhomogeneous enhancement in all except three localized tumors on enhanced CT and MRI. Invasion of intercostal muscle was noted on MR images in 18 patients (95%) and on CT in 11 patients (58%). CONCLUSION: There might be various radiologic appearances of MFH. However, CT and MRI are able to demonstrate the exact localization and disease extent of MFH arising in the chest wall.     

Computed tomography and magnetic resonance imaging findings of solitary fibrous tumors in the pelvis: Correlation with histopathological findings

Objective

We aimed to analyze the computed tomography (CT) and magnetic resonance imaging (MRI) findings of pelvic solitary fibrous tumors (SFTs) and to improve the diagnostic efficacy for such tumors.

Methods

Six cases of pelvic SFTs confirmed by histopathology were analyzed retrospectively. Of the 6 patients, 4 had undergone CT scanning, and 2 had undergone magnetic resonance imaging. All the patients had undergone unenhanced and contrast-enhanced examinations, and 2 had also undergone dynamic CT enhancement examination. Image characteristics such as shape, size, number, edge, attenuation or intensity for each lesion before and after contrast enhancement were analyzed and compared with the pathomorphology of the tumors.

Results

All the 6 cases showed oval or rounded and well-defined masses. Unenhanced CT images showed heterogeneous masses with patchy, necrotic foci in 3 cases and homogeneous mass in 1 case. None of the tumors showed calcification. Contrast-enhanced CT images showed marked, heterogeneous enhancement in the first and second cases. Dynamic enhancement scan demonstrated mild homogeneous enhancement in the third case and mild prolonged, delayed enhancement and washout in the fourth case. T1-weighted MR images showed heterogeneous mild hypointense lesion with linear hyperintensity in 1 case, and homogeneous isointensity in the other. T2-weighted images showed heterogeneous mixed intensity in 1 case and mostly hyperintensive lesion with hypointense foci in another case. A case showed marked heterogeneous enhancement and another showed marked homogeneous enhancement on contrast-enhanced T1-weighted images.

Conclusion

Radiological findings of pelvic SFTs are variable and nonspecific. However, a well-defined, ovoid or rounded mass with hypointense on MR T2-weighted images and variable enhancement on CT and MR images may suggest the diagnosis of SFTs. Pelvic SFTs should be included in the differential diagnosis of regional tumors.     

Differentiation of phyllodes breast tumors from fibroadenomas on MRI

OBJECTIVE: The purpose of our study was to evaluate the MRI appearance of phyllodes breast tumors and to differentiate them from fibroadenomas. MATERIALS AND METHODS: MR images were obtained on a 1.5-T imager. T1- and T2-weighted sequences and dynamic 2D fast-field echo T1-weighted sequences were performed. MR images of 23 patients with 24 phyllodes breast tumors (one malignant, 23 benign) were analyzed with respect to morphology and contrast enhancement. The tumors were compared with the MRI appearance of 81 fibroadenomas of 75 patients. RESULTS: Well-defined margins were seen in 87.5% of the phyllodes tumors and 70.4% of the fibroadenomas, and a round or lobulated shape in 100% and 90.1%, respectively. A heterogeneous internal structure was observed in 70.8% of phyllodes tumors and in 49.4% of fibroadenomas. Nonenhancing internal septations were found in 45.8% of phyllodes tumors and 27.2% of fibroadenomas. A significantly greater increase in signal was seen on T2-weighted images in the tissue surrounding phyllodes tumors (21%) compared with fibroadenomas (1.2%). Most of both lesions appeared with low signal intensity on T1- and T2-weighted images. After the administration of contrast material, 33.3% of phyllodes tumors and 22.2% of fibroadenomas showed a suspicious signal intensity-time course. CONCLUSION: Phyllodes breast tumors and other fibroadenomas cannot be precisely differentiated on breast MRI. Phyllodes tumors have benign morphologic features and contrast enhancement characteristics suggestive of malignancy in 33% of cases.     

侧脑室内脑膜瘤的CT和MRI诊断

目的分析侧脑室内脑膜瘤的CT和MRI表现,以提高诊断准确性。方法回顾性分析8例手术病理证实的侧脑室内脑膜瘤的CT和MRI资料。结果肿瘤呈圆形或分叶状软组织肿块,CT平扫多呈稍高或高密度,MRI多表现为T1WI等信号、T2WI等高信号,除1例因肿瘤坏死致信号和强化不均匀外,余7例肿瘤密度、信号及强化较均匀;周围脑组织可见不同程度水肿。1例肿瘤稍向周围脑组织呈浸润性生长,病理诊断为恶性脑膜瘤。结论侧脑室内脑膜瘤的CT、MRI表现具有一定的特征性,结合临床资料可提高诊断准确性。     

Small bowel neoplastic disease: Demonstration by MRI

This study demonstrates the appearance of small bowel tumors on MR images. Sixteen patients with tumors involving small bowel were studied by MRI. All tumors were proven with histopathology. Eleven patients had primary tumors of the small bowel, which included the following: four carcinoid tumors, three adenocarcinomas, two lymphomas, one leiomyosarcoma, and one leiomyoma. Five patients had recurrent or metastatic disease to small bowel: two patients had colon cancer, one patient had pancreatic cancer, one patient had uterine leiomyosarcoma, and one patient had chloroma (leukemia). MR examination included breath-hold T1-weighted spoiled gradient echo (all patients), immediate postgadolinium-spoiled gradient echo (10 patients), and 2 to 4 minutes postgadolinium T1-weighted, fat-suppressed images (all patients). Tumor size, local extent, signal intensity, and enhancement features of tumor and adjacent tissue were determined. Tumor ranged in diameter from 1 to 9 cm (mean, 4.0 cm). Tumors had similar signal intensity to normal small bowel on precontrast images. Fourteen malignant tumors showed heterogeneous enhancement greater than adjacent bowel on gadolinium-enhanced images. Tumor local extent was best shown on precontrast-spoiled gradient-echo images and postgadolinium T1-weighted fat-suppressed images. Image quality was most consistent on breath-hold images. The results of this study show that small bowel tumors are demonstrable on MR images. Precontrast breath-hold T1-weighted spoiled gradient-echo images and gadolinium-enhanced fat suppressed images demonstrate tumor extent most reliably.     

MR imaging in the diagnosis of desmoplastic infantile tumor: retrospective study of six cases

BACKGROUND AND PURPOSE: Desmoplastic infantile tumors (DITs) are rare supratentorial tumors of infancy with a favorable prognosis. Radiologic and histologic features of DIT are misleading, and DIT may be misinterpreted as a malignant lesion. We have studied the usefulness of MR imaging in the diagnosis of these tumors. METHODS: Between 1995 and 2002, six DITs were diagnosed in young children at our institution. Neuroimaging, age at diagnosis, sex, clinical presentation, symptoms duration, follow-up, and development were studied retrospectively. Contrast-enhanced CT and MR images were available. MR study included T1-, T2-, and postgadolinium T1-weighted sequences in the axial, sagittal, and coronal planes. RESULTS: These tumors were massive and predominantly cystic, with preferential frontal and parietal involvement. Typically, a DIT appears as a hypointense cystic mass with an isointense peripheral solid component on T1-weighted MR images. The peripheral solid component enhances after gadolinium administration. On T2-weighted MR images, the cystic component is hyperintense and the solid portion isointense or heterogeneous. The cystic portion is usually located deep inside the lesion, whereas its solid portion is peripheral. Meningeal enhancement and thickening adjacent to the solid portion of the tumor, calcifications, bone abnormalities adjacent to the tumor consisting of thinning and deformation were noted in 50% of our cases. Edema was usually absent or moderate. Median follow-up was 32 months, and no recurrence was noted except for one atypical case with incomplete excision, which led to the patient's death. CONCLUSION: Despite their malignant appearance, MR imaging features of DIT may help in the diagnosis and obviate unnecessary chemotherapy or radiation therapy.     

肝脏炎性肌纤维母细胞瘤的影像表现

目的 探讨肝脏炎性肌纤维母细胞瘤(IMT)的影像表现特征,以提高影像诊断水平.方法 回顾性分析经手术病理证实的12例肝脏IMT的影像表现,其中12例均行CT扫描,2例行MR检查.结果12例单发病灶均位于肝右叶.6例肿块为实性,4例肿块为囊实混合性,2例表现为门静脉周围浸润性病灶.CT图像上呈实性或囊实性低密度影,MR T1WI为低信号,T2WI为略高信号;增强扫描肿块实性部分呈均匀或不均匀中重度强化,囊实混合性病灶周边及灶内实性间隔呈蜂窝样强化.结论CT及MR检查能为临床诊断及鉴别诊断肝脏IMT提供有价值的信息.     

原发性骨恶性纤维组织细胞瘤的CT和MRI诊断

目的:探讨原发性骨恶性纤维组织细胞瘤(BMFH)的CT和MRI表现,以提高影像诊断水平。方法:收集经手术病理证实的原发性BMFH 13例,9例行CT检查,其中行增强扫描3例;6例行MRI检查,其中行增强扫描2例;2例同时行CT和MRI检查。分析原发性BMFH的CT和MRI表现,并与组织病理学表现相对照。结果:13例中,长骨骨端11例,长骨骨干1例,髂骨1例。骨质表现为溶骨性破坏,其中6例病灶边缘有轻度骨硬化,7例骨质破坏区间夹杂粗细不等的骨嵴,骨膜反应1例;MRI表现为T1WI等低信号,T2WI混杂高信号。13例均见超过骨破坏范围的软组织肿块,钙化1例;T1WI表现为等或等低信号,T2WI为等高或混杂高信号。CT、MRI增强扫描病变不均匀强化。结论:原发性BMFH的CT、MRI表现有一定的特征,能较好地反映病变的病理特点,对术前明确诊断具有重要意义。     

Neuroendocrine tumors of the pancreas: spectrum of appearances on MRI

We reviewed our 8.5 year experience with magnetic resonance imaging (MRI) in the demonstration of neuroendocrine tumors of the pancreas using precontrast fat-suppressed T1-weighted, fat-suppressed T2-weighted, and serial post-gadolinium T1-weighted images, to describe the spectrum of appearances of these tumors. All MR examinations of patients with histologically proven neuroendocrine tumors were retrospectively reviewed. Histological type, tumor location, tumor diameter, signal intensity on precontrast images, enhancement patterns, and presence and appearance of metastases were determined. Twenty-two patients had histologically proved neuroendocrine tumors detected by MRI over the 8.5 year period. Histological types were gastrinoma (n = 8), insulinoma (n = 3), glucagonoma (n = 2), somatostatinoma (n = 1), VIPoma (n = 1), ACTHoma (n = 1), carcinoid (n = 1), and five untyped tumors. Primary tumors ranged in diameter from 1 to 6.2 cm. There was one histopathology-proven false-positive neuroendocrine tumor. The positive predictive value for MRI in the detection of these tumors was 96%. The most common appearance on precontrast images was low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, which was observed in tumors in 18 of 22 patients. Moderate or intense early enhancement of all or portions of the primary tumors was observed in tumors in 19 of 22 patients either as uniform homogeneous, ring, or diffuse heterogeneous enhancement. Enhancement was minimal on these images in the other three patients. Gastrinomas enhanced in a ring pattern in 7 of 8 patients whereas the majority (9 of 11 patients) of noninsulinoma-nongastrinoma and untyped tumors enhanced in a diffuse heterogeneous fashion. Liver metastases were present in 13/22 patients including 3/8 with gastrinoma and 9/11 with noninsulinoma-nongastrinoma tumors. Most neuroendocrine tumors of the pancreas are low signal intensity on fat-suppressed T1-weighted images and moderately high in signal intensity on fat-suppressed T2-weighted images, although variations do exist. Tumors most often enhance in an early moderately intense fashion. Gastrinomas are often different in appearance than other neuroendocrine tumors in that they usually enhance in a ring fashion whereas nongastrinoma-noninsulinoma tumors usually enhance in a heterogeneous fashion.