Retroperitoneal masses: magnetic resonance imaging findings with pathologic correlation

Primary retroperitoneal masses are a rare but diverse group of benign and malignant processes. Magnetic resonance (MR) imaging is playing an increasing role in evaluating retroperitoneal soft-tissue masses. Since the MR imaging features of most retroperitoneal soft-tissue masses are nonspecific, prediction of a specific histologic diagnosis remains a challenge for the radiologist. However, there are certain specific MR imaging appearances that are helpful. Dynamic enhancement patterns can reflect the vascularity of masses, differentiating benign from malignant soft-tissue masses. This article pictorially illustrates the MR imaging features of various common and uncommon retroperitoneal masses.     

Diagnosis of soft-tissue masses with MR imaging: can benign masses be differentiated from malignant ones?

A blinded, retrospective review of 83 soft-tissue masses (49 benign and 34 malignant) was performed to evaluate the ability to distinguish benign from malignant soft-tissue masses with magnetic resonance (MR) imaging. The correct histologic diagnosis was reached in 31% of cases by one reader and in 16% of cases by the second reader. Mean sensitivity was 50% for benign masses and 80% for malignant masses. The majority of both benign and malignant masses had inhomogeneous signal intensity and at least partially irregular borders. Malignant masses uncommonly had smooth borders and homogeneous signal intensity. MR imaging can be used to evaluate the extent of soft-tissue masses, but most masses will require biopsy to determine if they are benign or malignant.     

MRI对软组织肿块的诊断价值

目的：探讨ＭＲＩ鉴别软组织肿块良、恶性的价值。方法：ＭＲＩ检查６７例软组织肿块,其中２５例肿块应用ＳＴＩＲ成像,４７例肿块Ｇｄ－ＤＴＰＡ增强造影。结果：６７例软组织肿块,良性５２例,恶性１５例。根据ＭＲＩ影像特征,１１例（２１．２％）良性肿块和１例（６．７％）恶性肿块正确诊断。当ＭＲＩ影像特征结合临床资料后,良性肿块定性准确率９４．２％,恶性肿块定性准确率８０％。结论：仅根据ＭＲＩ影像特征,大多数软组织肿块的良、恶性鉴别是不可靠的,当ＭＲＩ影像特征和临床资料结合后,大多数软组织肿块的良、恶性鉴别是可能的。     

Soft-tissue masses: histologic basis for decreased signal (short T2) on T2-weighted MR images

Most soft-tissue masses and tumors of various etiologies and histologies have high signal intensity on T2-weighted pulse sequences (long T2). Of 47 soft-tissue masses, seven had a low signal (short T2) on T2-weighted pulse sequences. All seven masses were tumors, and histologic review showed that their composition differed from that of the other 40 lesions with a long T2 in that the seven masses were relatively acellular and had more collagen. The tumors with a short T2 included one malignant and six benign soft-tissue tumors. Malignant fibrous histiocytoma and aggressive fibromatosis showed paradoxical signal intensities in that they showed both long and short T2. All of the tumors with low signal intensity on T2-weighted images had significant fibrous elements and marked hypocellularity. This study suggests that the less commonly encountered short T2 may be seen in both benign and malignant soft-tissue lesions. A part of the explanation for the low signal on T2-weighted sequences appears to be the relative acellularity and abundant collagen of these tumors in comparison with those that have the same histologic diagnoses but show a high signal. The histologic composition of the tumor rather than the histologic diagnosis appears to influence the MR signal on T2-weighted sequences.     

Inflammatory myofibroblastic tumor of the spleen: a case report

Inflammatory myofibroblastic tumors (IMTs), otherwise known as the inflammatory pseudotumor, is a rare solid mesenchymal tumor, simulating malignant neoplasms, histologically characterized by the proliferation of spindle cells in a fibrous myxoid stroma containing inflammatory cells. CT and MR imaging are the most used tools in their assessment. Clinical features are nonspecific and depend on the localization of the tumor, radiologic findings are polymorphic and no-conclusive and present a diagnostic challenge to the radiologist. Although histology remains obligatory for the final diagnosis. Heren, we report a case of splenic IMT with histological correlation.     

Myxoid liposarcoma: appearance at MR imaging with histologic correlation.

Although myxoid liposarcoma is a subtype of liposarcoma, it may be difficult to establish the correct diagnosis with magnetic resonance (MR) imaging due to the lack of fat signal intensity. Without the administration of gadolinium contrast material, the tumor may even mimic a cystic tumor. A spectrum of MR imaging abnormalities occur in myxoid liposarcoma, depending on the amount of fat and myxoid material, the degree of cellularity and vascularity, and the presence of necrosis. Most myxoid liposarcomas have lacy or linear, amorphous foci of fat. Some myxoid liposarcomas appear to be cystic at nonenhanced MR imaging, although they enhance like other solid masses at contrast material-enhanced MR imaging. The enhancing areas within the tumor represent increased cellularity and vascularity; the nonenhancing areas represent necrosis, reduced cellularity, and accumulated mucinous material. Gadolinium-enhanced imaging is important in differentiating myxoid liposarcoma from benign cystic tumors. Characterization of the tumor with MR imaging plays an important role in the management of myxoid liposarcoma.     

Soft-tissue tumors: MR imaging

We evaluated the suspected soft-tissue masses of 33 patients using magnetic resonance (MR) imaging. Thirty-two masses were defined, of which ten were malignant and 22 were benign. Specific characteristics that would allow us to distinguish the benign lesions from the malignant ones could not be identified on MR imaging. Lesions located within muscles or in the intramuscular septa were best seen with T2-weighted imaging sequences; those located within the subcutaneous fat were best outlined with T1-weighted imaging sequences. Both imaging sequences were necessary to provide the complete representation of the extent of the mass. We performed comparison studies using computed tomography (CT) in 24 of the cases. Of 92 possible comparisons and in four categories MR imaging yielded results that were superior to those obtained by CT scanning in 30 instances, equaled the results obtained by CT scanning in 62 instances, but never yielded results inferior to those obtained by CT scanning. However, MR imaging failed to demonstrate soft-tissue calcification and soft-tissue gas in one case each.     

MRI在涎腺肿物诊断中的作用

为了探讨不同涎腺肿物的ＭＲＩ特征，本文回顾性观察了２４例病理证实涎腺肿物的ＭＲＩ表现。结果发现良、恶性肿瘤在形态特征方面存在差异性，良性肿物多呈圆形、类圆形，可有清晰可见的包膜，肿瘤膨胀性生长，界线清楚；恶性肿瘤多浸润性生长，侵犯邻近肌肉，形态不规则，界线不清。对良性肿物的进一步组织学定性ＭＲＩ可提供一定价值的信息资料，增强扫描有助于涎腺肿瘤的定性诊断。     

Adrenal masses: characterization with T1-weighted MR imaging

The ability of a T1-weighted spin-echo magnetic resonance (MR) sequence to allow differentiation of benign from malignant adrenal masses at 0.5 T was investigated in 28 patients with 35 adrenal masses. All nine lesions with an adrenal mass-liver signal intensity ratio of 0.71 or less were metastases, and all 15 with a ratio of 0.78 or more were adenomas. Eleven masses (31%)--including six adenomas, three metastases, a pheochromocytoma, and a neuroblastoma--had ratios between these values. Nine of ten masses with adrenal mass-fat intensity ratios of 0.35 or less were metastases, and all 12 with ratios of 0.42 or more were benign. Eleven masses (31%), four malignant and one benign, had ratios between these values. The ratios for two masses could not be calculated due to lack of fat. The specificity of T1-weighted MR imaging in differentiating benign from malignant adrenal masses appears similar to that reported for T2-weighted imaging. However, significant overlap occurred, as has also been reported for T2-weighted imaging. While both imaging sequences may help distinguish benign from malignant adrenal masses in some cases, biopsy is still necessary when an accurate histologic diagnosis is essential.     

软组织肿块的MRI诊断价值探讨

目的：探讨MRI在软组织肿块的诊断及良恶性鉴别中的价值。方法：软组织肿块82例,男44例,女38例,年龄2-63岁。术前分析MRI征象并结合临床作出MRI诊断,与手术、病理结果对照。结果：82例中45例（54.84%）术前MRI诊断与病理相符。67例肿瘤中,MRI诊断良性肿瘤的敏感性、特异性、准确性分别为93.48%、76.79%、82.14%,诊断恶性肿瘤分别为38.10%、72.73%、52.38%。肿块局部边界不清或浸润邻近组织结构并局部水肿是最可靠的恶性征象。结论：软组织恶性肿瘤特别是其早期的MRI恶性征象尚需进一步研究、总结。     

Soft-tissue tumors of the foot: value of MR imaging for specific diagnosis

We reviewed MR imaging findings in 14 patients with primary soft-tissue tumors of the foot and compared them with surgical and pathologic findings to determine the value of MR imaging in anatomic localization, delineation, and characterization of such lesions. Nine tumors (64%) were benign, and five (36%) were malignant. The anatomic location (compartment, space, relation to specific tendon) and extent of all tumors were accurately shown by MR imaging. Twelve tumors (86%) were correctly characterized as benign or malignant. Eight (89%) of nine benign lesions showed distinctive MR imaging features that correctly suggested a specific diagnosis. These included hemangioma (high T2-weighted intensity and internal septa), ganglion cyst (homogeneous, high T2-weighted weighted intensity and peritendinous location), plantar fibromatosis (nodularity of plantar aponeurosis with low intensity on all sequences), and pigmented villonodular synovitis (low T2-weighted intensity and lower intensity rim). Aggressive fibromatosis (one case) could not be characterized. Four (80%) of five malignant neoplasms had MR imaging findings suggesting soft-tissue sarcoma. Two synovial sarcomas were inhomogeneous and showed extensive peritendinous growth. Two clear cell sarcomas arose at the origin of the plantar aponeurosis and infiltrated adjacent muscle. A small clear cell sarcoma could not be characterized as benign or malignant. MR imaging of the foot is accurate in showing the extent of soft-tissue tumors, which is helpful for surgical planning. Determination of their specific anatomic location may help characterize some tumors. Although our series is small, it appears that MR imaging often suggests a specific diagnosis in certain benign soft-tissue tumors of the foot and may often correctly distinguish benign from malignant tumors.     

Pitfalls in diagnosing female genital tract: ovarian disease

Because the ovaries are composed of surface epithelial cells, germ cells, sex-cord stromal cells and stroma, tumors of various histopathologies arise from this organ. In addition, a number of non-tumorous diseases form adnexal masses such as endometriosis and tubo-ovarian abscess. Furthermore, tumors arising from other pelvic organs are sometimes mis-diagnosed as ovarian tumors. Therefore, it is difficult to predict the histological type of an adnexal mass prior to surgery even though the MR characteristics of various ovarian tumors have been reported. Because of the large number of patients, there are two 'common sense' considerations in diagnosing female intrapelvic masses in daily practice: 1) solid adnexal masses are malignant ovarian tumors, 2) predominantly cystic intrapelvic masses originate from the ovaries. However, certain tumors do not conform to common sense. For example, fibrothecomas and benign teratomas are exceptions to 1), and subserosal pedunculated leiomyomas and cystic adenomyosis are exceptions to 2). The MR characteristics, pitfalls to diagnosis, and clues to correct imaging diagnosis are discussed in this review.     

MR imaging of soft-tissue masses: Role of gadopentetate dimeglumine

To assess the effectiveness of gadopentetate dimeglumine in the magnetic resonance (MR) imaging evaluation of soft-tissue masses without osseous involvement, 30 patients underwent MR imaging before and after administration of contrast material (0.1 mmol/ kg) of the 30 lesions, 22 were benign and eight were malignant; histologic confirmation was available in all lesions except one benign lesion. Overall, enhancement was detected in 26 (87%) of 30 lesions: 18 (82%) of the 22 benign lesions and eight (100%) of eight malignant lesions. Enhancement was characterized as homogeneous (two [11%] benign lesions, two [25%] malignant lesions), inhomogeneous (11 [61%] benign lesions, six [75%] malignant lesions), or peripheral (five [28%] benign lesions, no malignant lesions) of the 19 lesions assessed for a change in enhancement over time, seven (37%) showed an increase and two (11%) showed a decrease in signal intensity. The authors conclude that benign and malignant soft-tissue lesions could not be differentiated solely on the basis of enhancement (pattern, degree, or time course).     

Differentiation of soft tissue benign and malignant peripheral nerve sheath tumors with magnetic resonance imaging

PURPOSE: The objective of this study was to differentiate the magnetic resonance (MR) imaging appearance of benign peripheral nerve sheath tumors (PNSTs) from that of malignant PNSTs. MATERIALS AND METHODS: Twenty-six patients who underwent MR imaging and had a histologic diagnosis of benign (schwannoma, n=16; neurofibroma, n=1) or malignant (n=9) PNST were retrospectively reviewed. The size, location, shape, margin, and signal intensities of the tumors on precontrast and gadolinium-enhanced MR imaging were analyzed. In each patient, the presence or absence of split fat, target, and fascicular signs was determined. RESULTS: The mean size of the benign PNSTs (3.4 cm, S.D.=2.5 cm) was significantly smaller than that of the malignant tumors (8.2 cm, S.D.=3.1 cm) (P<.001). Seventeen (65.4%) of the 26 tumors were spindle shaped or ovoid (12 benign and 5 malignant tumors). Contiguity with specific nerves was identified in 15 (88.2%) of the 17 benign PNSTs but in none of the malignant tumors (P<.05). Well-defined margins were noted in all 17 benign PNSTs but in only 3 (33.3%) of the 9 malignant tumors (P<.001). Five (55.6%) of the 9 malignant PNSTs but none of the benign tumors showed signal intensity change in adjacent soft tissue (P<.05). There was no significant difference in signal intensity between the benign and malignant tumors on T(1)-weighted, T(2)-weighted, and contrast-enhanced MR images. The split fat and target signs were present more frequently in the benign PNSTs than in the malignant PNSTs (P<.05).Conclusions: Benign and malignant PNSTs are often spindle shaped. Recognition of contiguity with adjacent nerves, a well-defined margin, and the presence of the split fat sign may suggest benignity. Imaging features suggestive of malignancy can be a larger size and an infiltrative margin.     

MR imaging of extraabdominal desmoids: differentiation from other neoplasms.

A retrospective review of MR images of 36 patients with histologically proved extraabdominal desmoids was done to define the MR characteristics of these tumors and to determine if MR could be used to differentiate desmoids from other benign and malignant soft-tissue neoplasms. The desmoids evaluated included eight primary and 30 recurrent lesions. Our study was conducted in parallel with another study in which the MR appearance of 95 benign and malignant soft-tissue masses was evaluated, and the MR images of these masses were compared with our findings. The four desmoids from that study are included in our data. The signal intensity of the tumor on T1- and T2-weighted images was graded relative to the intensities of muscle and fat. Homogeneity, margin, neurovascular and bone involvement, and fibrosis (low-signal regions within the tumor on both T1- and T2-weighted images) were evaluated. On MR imaging, the desmoids showed inhomogeneous signal (97%), poor margination (89%), neurovascular involvement (58%), and bone involvement (37%). Fibrosis was present in 88% of primary desmoids and 90% of recurrent ones, and intermediate signal (greater than that of muscle and less than that of fat) was present in 75% and 50% of these, respectively. Our results show that the MR features of desmoids have characteristics that are commonly found in malignant tumors (inhomogeneous signal, poor margination, and neurovascular involvement). MR features of desmoids that distinguish them from malignant neoplasms are the presence of fibrosis and intermediate signal in the regions of the tumor.     

软组织病变磁共振短T2信号的病理基础

目的：分析软组织病变在T2WI出现低信号区的病理基础。材料和方法：对在TzWI出现低信号区的45个软组织肿块(良性27个，恶性18个)进行组织学检查，分析其与MR表现之间的关系。结果：神经鞘瘤、黏液性脂肪肉瘤、软骨肉瘤等为局限性低信号，色素性绒毛结节性滑膜炎(PVNS)呈弥漫性低信号。低信号区与病灶内胶原纤维增多，细胞成分较少，含铁血黄素沉着以及钙化、骨化等相对应。结论：胶原纤维、钙化和骨化等多种因素都可造成病灶在T2WI出现低信号区，分析低信号的病理基础有助于部分肿瘤的诊断。     

MRI of ganglioneuroma: histologic correlation study

PURPOSE: The purpose of this study was to evaluate the MR findings of ganglioneuroma and to correlate imaging and histologic features. METHOD: Conventional SE and contrast-enhanced dynamic MRI was used to examine 10 patients with pathologically confirmed ganglioneuroma. The morphologic features, signal intensity, and dynamic enhancement pattern of the tumors were retrospectively analyzed and correlated with histologic features. RESULTS: Capsules were present in all tumors histologically and were also detected in five tumors on postcontrast T1-weighted images. A whorled appearance corresponding to interlacing bundles of Schwann cells and collagen fibers on histologic specimens was visualized in five tumors on T1-and/or T2-weighted images. Tumors with markedly high signal intensity on T2-weighted images consisted histologically of a large amount of myxoid stroma and relatively few cellular and fibrous components. Tumors with intermediate to high signal intensity consisted of numerous cellular and fibrous components and little myxoid stroma. Early enhancement of tumors was usually lacking in dynamic MR studies; however enhancement gradually increased. CONCLUSION: The results suggest that the MR features of ganglioneuroma are well correlated with histologic findings.     

MR Imaging of Soft Tissue Tumors: An Overview

Over the past decade, magnetic resonance (MR) imaging has been established as the most widely used examination for the detection of a suspected soft tissue mass and often for depiction of the extent and the characterization of the mass. Sensitivity of the examination for the detection of soft tissue masses is high but specificity is limited. With experience accrued over the past decade, radiologists are increasingly able to predict the histology of lesions based on MR imaging criteria. However, because of the overlap of morphologic features of benign and malignant soft tissue masses, a benign-appearing mass should not be considered benign unless the tumor can be specifically named and its histology predicted by well-established MR imaging features. When a mass is not thought to be an overt sarcoma and there is uncertainty as to whether it is benign or malignant, the tumor should be characterized as indeterminate and approached as a sarcoma until proven otherwise. This article reviews MR imaging in diagnosing and staging soft tissue masses and briefly discusses the radiologist?s approach to percutaneous biopsy of indeterminate soft tissue masses.     

Masses of the anterior mediastinum: CT and MR imaging

CT and MR imaging allow earlier diagnosis and more specific characterization of anterior mediastinal masses than is possible with plain film radiographs. This review describes state-of-the-art CT and MR imaging of the anterior mediastinum. After a discussion of CT and MR imaging and indications for their use, normal and abnormal CT and MR findings in the anterior mediastinum are reviewed. Abnormalities include benign and malignant neoplasms, cysts, and mediastinal thyroid. Several masses such as thymolipomas, goiters, cysts, and lymphangiomas often do not require removal and now can be diagnosed with reasonable accuracy when imaging results are combined with clinical history. Detection, diagnosis, staging, and follow-up of malignant anterior mediastinal masses are important and have been improved with CT and MR imaging.