MR Imaging of Mediastinal Masses

Making an accurate diagnosis of anterior mediastinal lesions: a proposal for a new diagnostic algorithm from the BTOG Thymic Malignancies Special Interest Group

Due to the rising demand in cross-sectional thoracic imaging, anterior mediastinal lesions are being identified with increasing frequency. Following iterative and multidisciplinary discussions, the BTOG Thymic Malignancies Special Interest Group have developed an algorithm to standardise the diagnostic approach for these relatively uncommon but important conditions which span from benign (thymic remnant, thymic hyperplasia and thymic cysts) to suspected localised thymomas to suspected more aggressive malignancy (thymic carcinoma, lymphoma and germ cell tumours). For each condition, we provide a brief description, an overview of the key radiological findings and a description of the proposed algorithm including the rationale behind the recommendations. We also highlight the role of magnetic resonance (MR) imaging for the characterisation of anterior mediastinal masses in specific indications when the necessary local resources and expertise exist. In addition, we hope this provides the rationale for service development in MR of the anterior mediastinum where current resource and expertise requires development. Through this standardised pathway, we hope to drive improvements in patient care by rationalising surveillance schedules, avoiding unnecessary resections of benign entities with their associated morbidity and optimising the diagnostic work-up prior to the appropriate treatment of anterior mediastinal malignancies.

Chest Magnetic Resonance Imaging: Advances and Clinical Care

Many promising study results as well as technical advances for chest magnetic resonance imaging (MRI) have demonstrated its academic and clinical potentials during the last few decades, although chest MRI has been used for relatively few clinical situations in routine clinical practice. However, the Fleischner Society as well as the Japanese Society of Magnetic Resonance in Medicine have published a few white papers to promote chest MRI in routine clinical practice. In this review, we present clinical evidence of the efficacy of chest MRI for 1) thoracic oncology and 2) pulmonary vascular diseases.

Anastomosing haemangioma of the mediastinum: Clinicopathological series with radiological and genetic characterisation

AIMS

Anastomosing haemangiomas are benign tumours with anastomosing vascular channels that may mimic angiosarcoma. While anastomosing haemangiomas have been described in diverse locations, particularly the abdominal/paraspinal region, data on anastomosing haemangiomas in the mediastinum remain limited. We report the clinicopathological, radiological and molecular characteristics of the largest single-institutional series of mediastinal anastomosing haemangiomas.

METHODS AND RESULTS

In our pathology archives in 2011-23, we reviewed all vascular lesions involving the mediastinum and identified seven anastomosing haemangiomas. Clinical information was abstracted from medical charts; available radiological imaging was reviewed. Targeted DNA-based next-generation sequencing (447 genes, including GNAQ and GNA11) was performed on five cases. The seven patients included five women and two men, with an age range of 55-77 (median = 72) years. Of the six tumours with available radiology, two each were in the prevascular, visceral and paravertebral mediastinum, with lobulated peripheral enhancement in all tumours examined with contrast enhancement. Six patients underwent tumour resection; one patient received proton radiotherapy. Microscopically, each tumour was solitary and characterised by anastomosing capillary-sized vessels lined by hobnail endothelial cells. Fibrin microthrombi, hyaline globules and extramedullary haematopoiesis were common. In the five tumours analysed by next-generation sequencing, GNAQ p.Q209P was identified in one tumour; no additional reportable alterations were identified in the remaining cases. No recurrence was noted in the four patients with available follow-up of 3-58 (median = 9.5) months after resection.

CONCLUSION

While mediastinal anastomosing haemangiomas can microscopically mimic angiosarcoma, awareness of this entity and radiological correlation may help to circumvent this diagnostic pitfall.

T1 and T2 Mapping for Characterization of Mediastinal Masses: A Feasibility study

Purpose: To evaluate the feasibility and usefulness of T1 and T2 mapping in characterization of mediastinal masses. Methods: From August 2019 through December 2021, 47 patients underwent 3.0-T chest MRI with T1 and post-contrast T1 mapping using modified look-locker inversion recovery sequences and T2 mapping using a T2-prepared single-shot shot steady-state free precession technique. Mean native T1, native T2, and post-contrast T1 values were measured by drawing the region of interest in the mediastinal masses, and enhancement index (EI) was calculated using these values. Results: All mapping images were acquired successfully, without significant artifact. There were 25 thymic epithelial tumors (TETs), 3 schwannomas, 6 lymphomas, and 9 thymic cysts, and 4 other cystic tumors. TET, schwannoma, and lymphoma were grouped together as "solid tumor," to be compared with thymic cysts and other tumors ("cystic tumors"). The mean post-contrast T1 mapping (P < .001), native T2 mapping (P < .001), and EI (P < .001) values showed significant difference between these two groups. Among TETs, high risk TETs (thymoma types B2, B3, and thymic carcinoma) showed significantly higher native T2 mapping values (P = .002) than low risk TETs (thymoma types A, B1, and AB). For all measured variables, interrater reliability was good to excellent (intraclass coefficient [ICC]: .869∼.990) and intrarater reliability was excellent (ICC: .911∼.995). Conclusion: The use of T1 and T2 mapping in MRI of mediastinal masses is feasible and may provide additional information in the evaluation of mediastinal masses.

Approach to Imaging of Mediastinal Masses

Mediastinal masses present a diagnostic challenge due to their diverse etiologies. Accurate localization and internal characteristics of the mass are the two most important factors to narrow the differential diagnosis or provide a specific diagnosis. The International Thymic Malignancy Interest Group (ITMIG) classification is the standard classification system used to localize mediastinal masses. Computed tomography (CT) and magnetic resonance imaging (MRI) are the two most commonly used imaging modalities for characterization of the mediastinal masses.

Initial experience with robotic-assisted thoracic surgery for superior mediastinal masses

Objective

Minimally invasive surgery is challenging for masses located in the superior mediastinum, especially for those close to the chest outlet. This study aimed to evaluate the feasibility and safety of robotic-assisted thoracic surgery (RATS) for these masses.

Methods

From June 2015 to January 2020, 35 patients (19 males, 16 females), with a mean age of 41.6 (range, 13-66) years, underwent RATS for the treatment of superior mediastinal masses. Data regarding the operation time, blood loss, pathology, conversion rate, morbidity, mortality, and cost were collected and analyzed.

Results

The mean (±standard deviation) operation time, blood loss, chest tube use duration, and postoperative hospital day were 117 ± 45.2 (range, 60-270) min, 59.7 ± 94.4 (range, 10-500) ml, 4.1 ± 2.1 (range, 1-10) days, and 5.1 ± 2.1 (range, 2-11) days, respectively. The pathological diagnoses included schwannoma (26 cases), ganglioneuroma (4 cases), bronchogenic cysts (3 cases), ectopic nodular goiter (1 case), and cavernous hemangioma (1 case). The mean diameter of the resected tumor was 4.6 ± 2.0 (range, 2.5-10) cm. No conversion or mortality occurred. Postoperative complications included Horner's syndrome (18 cases: 6 patients with preoperative Horner's syndrome), weakened muscular power (2 cases), and chylothorax (2 cases). The mean cost was $ 8,868.7 (range, $ 4,951-15,883).

Conclusions

Our experience demonstrated that RATS is safe and feasible for superior mediastinal mass resection. However, the high incidence of postoperative Horner's syndrome requires further research.

Utility of non-contrast-enhanced magnetic resonance imaging in predicting preoperative clinical stage and prognosis in patients with thymic epithelial tumor

PURPOSE

The purpose of this study was to find useful imaging features on non-contrast-enhanced magnetic resonance imaging (MRI) that can divide patients with thymic epithelial tumor (TET) into clinical stage I-II and III-IV groups under assumption that contrast media are contraindicated.

MATERIALS AND METHODS

This retrospective study included 106 patients (median age, 60 years; range, 27-82 years; 62 women) with surgically resected TET who underwent MRI between August 1986 and July 2015. All cases were classified according to the 2015 WHO classification and staged using the eighth edition of the TNM system. Two radiologists independently evaluated 14 categories of MRI findings; the findings in patients with stage I-II were compared with those of patients with stage III-IV using a logistic regression model. Disease-specific survival associated with significant findings was calculated using the Kaplan-Meier method.

RESULTS

Univariate analysis showed that stage III-IV patients were more likely to have tumors with an irregular contour, heterogeneity on T1WI, low-signal intensity on T2WI, irregular border with lung, findings of great vessel invasion (GVI) (hereafter, GVI sign), pericardial thickening/nodule, and lymphadenopathy (all, P < 0.01). On multivariable analysis, only two findings, irregular border between tumor and lung (odds ratio [OR], 272.8; 95% CI 26.6-2794.1; P < 0.001) and positive GVI sign (OR, 49.3; 95% CI 4.5-539.8; P = 0.001) remained statistically significant. Patients with one or both features had significantly worse survival (log-rank test, P < 0.001).

CONCLUSION

For patients with TET who are unable to receive contrast for preoperative staging, the two image findings of an irregular border between tumor and lung and the positive GVI sign on non-contrast-enhanced MRI could be helpful in determining stage III-IV disease which is associated with a worse survival.

The value of transthoracic echocardiography in the detection of extra-cardiac lesions

Objective

Transthoracic echocardiography (TTE) is generally recognized as the top choice for detecting myocardial and cardiac cavity lesions. Sonographers mostly focus on myocardium, cardiac cavity and cardiac hemodynamics, whereas the abnormal extra-cardiac lesions are easily remain unrecognized. The aim of this study was to investigate the ultrasonic image features in abnormal extra-cardiac lesions and the value of TTE in the detection of extra-cardiac lesions.

Methods

49 cases of abnormal extra-cardiac lesion detected by TTE from January 2014 to December 2019 were collected, which were confirmed by surgical pathology. The two-dimensional ultrasonic characteristics and the relationships with the cardiac and great vessels were summarized on the basis of multi-view by TTE. All patients were also examined by computed tomography (CT).

Results

In 49 patients with abnormal extra-cardiac lesions, 37 malignant cases and 12 benign cases were included. There were 41 cases (41/49, 86.67%) of mediastinal lesions and 8 cases (8/49, 16.33%) of lung lesions. The maximum diameter ranged from 3.2 cm to 13.66 cm, and the median diameter was about 7.4 cm, among which 29 cases (29/49, 59.18%) were larger than 5 cm. 4 cases (4/49, 8.16%) of cystic anechoic lesions were pericardial cyst. 2 cases (2/49, 4.08%) of cystic-solid echogenic lesions were teratoma. The remaining 43 cases (43/49, 87.76%) presented as solid hypoechoic or heterogeneous masses. 6 cases compressed the heart and 21 cases encroached on the heart and vessels. Diagnosis coincidence rates of TTE and CT were respectively 77.55% and 93.88%, with a statistical difference (p = 0.012).

Conclusion

Although the diagnostic coincidence rate of TTE is slightly lower than that of CT, TTE has certain diagnostic value for extra-cardiac lesions.

Imaging Evaluation of Thymoma and Thymic Carcinoma

Imaging is integral in the management of patients with thymoma and thymic carcinoma. At initial diagnosis and staging, imaging provides the clinical extent of local invasion as well as distant metastases to stratify patients for therapy and to determine prognosis. Following various modalities of therapy, imaging serves to assess treatment response and detect recurrent disease. While imaging findings overlap, a variety of CT, MRI, and PET/CT characteristics can help differentiate thymoma and thymic carcinoma, with new CT and MRI techniques currently under evaluation showing potential.

Longitudinal CT and MRI Characteristics of Unilocular Thymic Cysts

Background Isoattenuating and hyperattenuating thymic cysts at CT are often misinterpreted as lymphadenopathy or thymic epithelial neoplasms. Purpose To evaluate the longitudinal change in thymic cyst appearance at CT and MRI. Materials and Methods All chest MRI studies showing thymic cysts between July 2008 and December 2019, identified from a retrospective search of a quality assurance database, were included in this study if initial CT depicted a thymic lesion, the patient was referred for follow-up MRI for characterization, and the baseline (ie, index) MRI indicated a cystic lesion. Follow-up CT scans and/or MRI scans were identified through July 2020. Thymic cyst characteristics, such as size, location, and morphologic features, as well as CT and MRI characteristics, were recorded. Change in size, attenuation, and T1-weighted MRI signal was assessed longitudinally. Descriptive statistics of longitudinal change were tabulated. Results A total of 244 chest MRI studies in 140 patients with 142 unique cysts and 392 CT examinations (636 total examinations and 645 thymic cysts-nine examinations with two cysts each) were evaluated. The median follow-up duration was 2.2 years. Thirty-three patients with 34 unique cysts (34 of 142 cysts [24%]) underwent imaging follow-up for more than 5 years. Thymic cysts followed up for more than 5 years were most commonly saccular (189 of 274 cysts [69% axially]) and retrosternal (14 of 34 cysts [41%]). Craniocaudal dimension was larger than transverse and anteroposterior dimensions in 223 of 274 cysts (81%). Mean thymic cyst attenuation was 25 HU (range, 15-100 HU). Five of 31 cysts (16%) exhibited wall calcification. The median cyst wall thickness was 2.0 mm (range, 0.9-3.0 mm). Most thymic cysts changed in volume (31 of 34 cysts [91%]), CT attenuation (15 of 35 cysts [43%]), and T1-weighted MRI signal (12 of 18 cysts [67%]) over time. None developed mural irregularity, nodularity, or septations. Conclusion Unilocular thymic cysts, defined at index MRI, never developed irregular wall thickening, mural nodularity, or septations that would raise concern for malignant transformation. However, these cysts showed mural calcification and change in size, CT attenuation, and MRI signal over more than 5 years of follow-up. © RSNA, 2021 Online supplemental material is available for this article.

Fat content quantification using dual-energy CT for differentiation of anterior mediastinal lesions from normal or hyperplastic thymus

BACKGROUND

Detection of fat content in thymic lesions is crucial to differentiate thymic hyperplasia from thymic tumors or other anterior mediastinal pathologies.

PURPOSE

To assess the feasibility of dual-energy CT (DECT) fat content quantification for the differentiation of anterior mediastinal lesions from benign thymic lesions and the normal spectrum of the thymus.

MATERIALS AND METHODS

Chest DECT images of 465 patients (median 61 years, 63% female) were visually evaluated by two radiologists and semiquantitatively scored based on the degree of fatty degeneration ranging from completely fatty (score 0) to predominantly soft-tissue (score 3), and anterior mediastinal mass (score 4). A subset of scans (n =134 including all cases with scores 2-4 and 20 randomly-selected cases from scores 0 and 1) underwent quantitative DECT analysis (fat fraction, iodine density, and conventional CT value). DECT values were compared across the semiquantitative scores.

RESULTS

Results of visual evaluation included 35 with predominantly solid thymus (score 3) and 15 with anterior mediastinal mass (score 4). The most common clinical diagnoses of the 15 masses (including 8 with pathologic confirmation) were metastases (n = 10) and lymphoma (n = 4). CT values in the abnormal thymus were significantly higher than those in score 3 (median: 69.7 HU versus 19.9 HU, P <0.001). There was no significant difference in iodine density values (median: 1.7 mg/ml versus 1 mg/ml, P = 0.09). However, the fat fraction value was significantly lower in the abnormal thymus (score 4) than in the predominantly soft-tissue attenuation thymuses (score 3) (median: 12.8% versus 38.7%, P <0.001). ROC curve analysis showed that fat fraction had an AUC of 0.96 (P <0.001), with a cutoff of <39.2% fat fraction yielding 100% sensitivity and 85% specificity.

CONCLUSION

DECT fat fraction measurements of the thymus may provide additional value in distinguishing anterior mediastinal lesions from benign thymus. Use of DECT may reduce the need for subsequent imaging evaluation.

ACR Appropriateness Criteria® Imaging of Mediastinal Masses

Mediastinal masses can present with symptoms, signs, and syndromes or incidentally. Selecting the appropriate diagnostic imaging study for mediastinal mass evaluation requires awareness of the strengths and weaknesses of the various imaging modalities with regard to tissue characterization, soft tissue contrast, and surveillance. This publication expounds on the differences between chest radiography, CT, PET/CT, ultrasound, and MRI in terms of their ability to decipher and surveil mediastinal masses. Making the optimal imaging choice can yield diagnostic specificity, avert unnecessary biopsy and surgery, guide the interventionist when necessary, and serve as a means of surveillance for probably benign, but indeterminate mediastinal masses. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Canadian Society of Thoracic Radiology/Canadian Association of Radiologists Clinical Practice Guidance for Non-Vascular Thoracic MRI

Historically thoracic MRI has been limited by the lower proton density of lung parenchyma, cardiac and respiratory motion artifacts and long acquisition times. Recent technological advancements in MR hardware systems and improvement in MR pulse sequences have helped overcome these limitations and expand clinical opportunities for non-vascular thoracic MRI. Non-vascular thoracic MRI has been established as a problem-solving imaging modality for characterization of thymic, mediastinal, pleural chest wall and superior sulcus tumors and for detection of endometriosis. It is increasingly recognized as a powerful imaging tool for detection and characterization of lung nodules and for assessment of lung cancer staging. The lack of ionizing radiation makes thoracic MRI an invaluable imaging modality for young patients, pregnancy and for frequent serial follow-up imaging. Lack of familiarity and exposure to non-vascular thoracic MRI and lack of consistency in existing MRI protocols have called for clinical practice guidance. The purpose of this guide, which was developed by the Canadian Society of Thoracic Radiology and endorsed by the Canadian Association of Radiologists, is to familiarize radiologists, other interested clinicians and MR technologists with common and less common clinical indications for non-vascular thoracic MRI, discuss the fundamental imaging findings and focus on basic and more advanced MRI sequences tailored to specific clinical questions.

Added Value of Magnetic Resonance Imaging for the Evaluation of Mediastinal Lesions

The high soft tissue contrast and tissue characterization properties of magnetic resonance imaging allow further characterization of indeterminate mediastinal lesions on chest radiography and computed tomography, increasing diagnostic specificity, preventing unnecessary intervention, and guiding intervention or surgery when needed. The combination of its higher soft tissue contrast and ability to image dynamically during free breathing, without ionizing radiation exposure, allows more thorough and readily appreciable assessment of a lesion's invasiveness and assessment of phrenic nerve involvement, with significant implications for prognostic clinical staging and surgical management.

Contrast-Enhanced Ultrasonography versus Contrast-Enhanced Magnetic Resonance Imaging in the Diagnosis of Mediastinal Tumors

The aim of the study was to evaluate and compare contrast-enhanced ultrasound (CEUS) and contrast-enhanced magnetic resonance imaging (CE-MRI) with respect to their value in the differential diagnosis between benign and malignant mediastinal tumors. Forty-two patients with mediastinal tumor underwent CEUS and CE-MRI respectively. The sensitivity, specificity, diagnostic coincidence rate, positive predictive value (PPV) and negative predictive value of the two methods were compared. The value of different enhancement patterns in the differential diagnosis of benign and malignant mediastinal tumors was analyzed. SonoLiver software was used to obtain the dynamic vascular pattern curve (DVPC) of the lesions, and parameters such as arrival time (AT), rise time (RT), time to peak (TTP), maximum intensity/peak intensity (IMAX) and quality of fit (QOF) were extracted from time-intensity curves for quantitative analysis. We found that (i) the specificity of CEUS was higher than that of CE-MRI, and the PPV and diagnostic coincidence rate of CEUS were equal to those of CE-MRI; (ii) the enhancement patterns and DVPC of CEUS differed between the benign and malignant groups, while there was no difference in CE-MRI enhancement intensity; and (iii) AT, RT and TTP in the malignant groups were significantly shorter, while IMAX was significantly higher. In conclusion, the application of quantitative parameters and DVPC of CEUS is worth popularizing. CEUS can be used as an effective alternative and complementary examination for patients who cannot undergo CE-MRI.

Imaging of the Middle and Visceral Mediastinum

The visceral mediastinum contains important vascular and non-vascular structures including the heart, great vessels, lymph nodes, and portions of the esophagus and trachea. Multiple imaging modalities, including chest radiography, computed tomography, MR imaging, and nuclear medicine studies, can be used to detect, diagnose, and characterize masses in this compartment. Lymphadenopathy is the most common process involving the visceral mediastinum and can be seen with a wide variety of diseases. Less commonly seen entities include foregut duplication cysts, neoplasms and other lesions arising from the trachea and esophagus, paragangliomas as well as other mesenchymal tumors.

First things first: A late robotic approach to anamnesis, in a patient with a thymus hematoma

Anterior mediastinal masses are generally asymptomatic until they grow and compress surrounding structures. Chest X-rays only suggest a mediastinal abnormality and contrast-enhanced CT scan and MRI are necessary for a better definition of the lesion. The classification of the anterior mediastinal masses is based on their etiology and it is sometimes a challenge to have an accurate differential diagnosis based only on radiological examinations: therefore, only the histopathological examination makes the correct diagnosis. Surgeons generally agree that symptomatic masses or those with progressive growth should undergo surgical resection. We report a case of an accidental finding of an organized thymic hematoma in a 46-year-old female. At first totally asymptomatic, the hematoma was misdiagnosed for a thymic cyst and resected when it increased in size and compressed surrounding mediastinal structures. A detailed anamnesis highlighted a minor thoracic trauma which turned out to be the cause. Retrosternal hematoma generally grows several months after trauma and initial stabilization; therefore, it is mandatory to include an organized hematoma in the differential diagnosis of the retrosternal neoformations.

Invasive thymoma extending into the superior vena cava and right atrium: The value of multimodal cardiac magnetic resonance

The purpose of this case report is to describe the multimodal cardiac magnetic resonance (CMR) imaging features of an invasive thymoma extending into the superior vena cava and right atrium. This unusual case indicates that multimodal CMR can not only reveal the morphological features of thymoma but also enable the identification of histological types, which provides a reasonable surgical plan in the perioperative management. <Learning objective: Invasive thymoma can invade the superior vena cava and extend into the right atrium. Multimodal cardiac magnetic resonance images have certain characteristics in the diagnosis of invasive thymoma.>.

Magnetic resonance imaging characteristics of thymoma in Vietnamese patients with myasthenia gravis in relation to histopathological type and disease staging

INTRODUCTION

Myasthenia gravis (MG) is a relatively uncommon neuromuscular disease. The thymus plays an important role in the pathogenesis of MG, with 70% of patients presenting with thymic follicular hyperplasia and 20% presenting with thymoma. This study aimed to characterize magnetic resonance (MR) images of thymomas in patients with MG, associated with various stages and types.

MATERIAL AND METHODS

A prospective study was performed in 46 MG patients with thymoma, who underwent surgery between August 2014 and September 2018, in Vietnam. Differences in MR imaging (MRI) images, according to type and stage, were assessed by the χ2 test or Fisher's exact test and Student's t-test. A p-value < 0.05 was considered significant.

RESULTS

The proportions of each type of thymomas found to be invasive were 28.6%, 61.1%, 66.7%, 90.9%, and 100%, for type A, AB, B1, B2, and B3 thymomas, respectively. Heterogeneous signal intensities on T1- and T2-weighted images, necrosis, and cysts were more commonly observed in high-risk thymomas than in low-risk thymomas. Non-invasive thymomas were more likely to display smooth margins than invasive thymomas (p < 0.05). Only 16.7% of invasive thymomas were detected in MR findings.

CONCLUSIONS

Only a few characteristic MRI features could be used to differentiate thymomas by stage or type.

Pictorial Review of Mediastinal Masses with an Emphasis on Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) has become a crucial tool for evaluating mediastinal masses considering that several lesions that appear indeterminate on computed tomography and radiography can be differentiated on MRI. Using a three-compartment model to localize the mass and employing a basic knowledge of MRI, radiologists can easily diagnose mediastinal masses. Here, we review the use of MRI in evaluating mediastinal masses and present the images of various mediastinal masses categorized using the International Thymic Malignancy Interest Group's three-compartment classification system. These masses include thymic hyperplasia, thymic cyst, pericardial cyst, thymoma, mediastinal hemangioma, lymphoma, mature teratoma, bronchogenic cyst, esophageal duplication cyst, mediastinal thyroid carcinoma originating from ectopic thyroid tissue, mediastinal liposarcoma, mediastinal pancreatic pseudocyst, neurogenic tumor, meningocele, and plasmacytoma.

Role of diffusion weighted MR-imaging in the evaluation of malignant mediastinal lesions

Background

Conducted studies showed that the ADC (apparent diffusion coefficient) values of malignant mediastinal lesions are significantly lower than those of benign lesions. Investigators determined cut-off ADC values to differentiate the two; concluding that ADC value is a promising noninvasive, imaging parameter that helps assess and characterize mediastinal tumors.

Taking this a step forward, the primary objective of our prospective study was to investigate the potential of DW-MRI (diffusion-weighted magnetic resonance imaging) to characterize malignant mediastinal lesions using their ADC values.

Thirty-three patients that underwent MRI of the chest with DWI and latter pathologically diagnosed with a malignant mediastinal lesion were included in this study. Lesions’ ADC values were measured and correlated with the histopathological results. The statistical significance of differences between measurements was tested using the one-way ANOVA (analysis of variance) test; p values equal to or less than 0.05 were considered significant.

Results

There was no statistically significant difference between the ADCmean values of the histopathological groups of lesions assessed with the overlap of their ADCmean values. The average ADCmean value of NHL (non-Hodgkin lymphoma) was evidently lower than that of HD (Hodgkin disease) with no overlap between their ADCmean values. DWI failed at characterizing one lesion in this study as a malignant tumor, namely an immature teratoma (germ-cell tumor). Again DWI could not be used to evaluate a mass, latter pathologically diagnosed as an angiosarcoma, because of its overall hemorrhagic nature showing no definite non-hemorrhagic soft tissue components. The aforementioned results did not differ considerably when minimum ADC was used instead of mean ADC.

Conclusion

There was no statistically significant difference between the ADC values of the malignant mediastinal lesions evaluated. However, regarding lymphoma subtypes, our limited sample study of lymphoma suggested a considerable difference between the ADC values of Hodgkin disease and non-Hodgkin lymphoma.

Quantitative Thoracic Magnetic Resonance Criteria for the Differentiation of Cysts from Solid Masses in the Anterior Mediastinum

Objective

To evaluate quantitative magnetic resonance imaging (MRI) parameters for differentiation of cysts from and solid masses in the anterior mediastinum.

Materials and Methods

The development dataset included 18 patients from two institutions with pathologically-proven cysts (n = 6) and solid masses (n = 12) in the anterior mediastinum. We measured the maximum diameter, normalized T1 and T2 signal intensity (nT1 and nT2), normalized apparent diffusion coefficient (nADC), and relative enhancement ratio (RER) of each lesion. RERs were obtained by non-rigid registration and subtraction of precontrast and postcontrast T1-weighted images. Differentiation criteria between cysts and solid masses were identified based on receiver operating characteristics analysis. For validation, two separate datasets were utilized: 15 patients with 8 cysts and 7 solid masses from another institution (validation dataset 1); and 11 patients with clinically diagnosed cysts stable for more than two years (validation dataset 2). Sensitivity and specificity were calculated from the validation datasets.

Results

nT2, nADC, and RER significantly differed between cysts and solid masses (p = 0.032, 0.013, and < 0.001, respectively). The following criteria differentiated cysts from solid masses: RER < 26.1%; nADC > 0.63; nT2 > 0.39. In validation dataset 1, the sensitivity of the RER, nADC, and nT2 criteria was 87.5%, 100%, and 75.0%, and the specificity was 100%, 40.0%, and 57.4%, respectively. In validation dataset 2, the sensitivity of the RER, nADC, and nT2 criteria was 90.9%, 90.9%, and 72.7%, respectively.

Conclusion

Quantitative MRI criteria using nT2, nADC, and particularly RER can assist differentiation of cysts from solid masses in the anterior mediastinum.

PET/MRI attenuation estimation in the lung: A review of past, present, and potential techniques

Positron emission tomography/magnetic resonance imaging (PET/MRI) potentially offers several advantages over positron emission tomography/computed tomography (PET/CT), for example, no CT radiation dose and soft tissue images from MR acquired at the same time as the PET. However, obtaining accurate linear attenuation correction (LAC) factors for the lung remains difficult in PET/MRI. LACs depend on electron density and in the lung, these vary significantly both within an individual and from person to person. Current commercial practice is to use a single‐valued population‐based lung LAC, and better estimation is needed to improve quantification. Given the under‐appreciation of lung attenuation estimation as an issue, the inaccuracy of PET quantification due to the use of single‐valued lung LACs, the unique challenges of lung estimation, and the emerging status of PET/MRI scanners in lung disease, a review is timely. This paper highlights past and present methods, categorizing them into segmentation, atlas/mapping, and emission‐based schemes. Potential strategies for future developments are also presented.

Check the chest: review of chest findings on abdominal MRI

Magnetic resonance imaging (MRI) of the abdomen may include lower chest findings which may be overlooked or misinterpreted due to their location outside the area of main exam focus or lack of familiarity with the image appearance of these findings. This article will review the utility of abdominal MRI sequences to diagnose lower chest pathology while providing a systematic pictorial review of imaging findings in the lungs, pleura, mediastinum and chest wall. We will discuss the MRI appearance of lung nodules and masses, lung infiltrates, pulmonary infarction, pulmonary embolism, empyema, pleural effusions and thickening, mediastinal lesions and lymphadenopathy, cardiac thrombus and masses, and breast lesions. The purpose of this article is to increase awareness to the diagnostic advantages of abdominal MRI sequences for lower chest findings and encourage abdominal MRI readers to meticulous scrutinize the lower chest for concomitant pathology.

Pediatric Chest MRI: A Review

Chest radiographs and CT scans have been the cornerstone of pulmonary imaging given their advantages of being rapid and easily available techniques. However, a significant concern with their use in the pediatric population is the associated ionisation radiation. The use of magnetic resonance imaging (MRI) in pulmonary imaging has lagged behind its adoption in other organ systems. Previously, the lung parenchyma was considered difficult to evaluate by magnetic resonance due to low proton density in the pulmonary tissue, susceptibility artefacts within the lungs, and respiratory motion artefacts. However, in recent years, there have been a multitude of technical advancements to overcome these limitations. MRI can be an excellent radiation-free alternative in patients who require protracted follow-up like in cases such as cystic fibrosis, complicated pneumonias, tuberculosis and mediastinal neoplasms. An added advantage of MRI is that it can provide functional information in addition to the structural information provided by traditional imaging techniques. One of the major reasons of limited use of MRI despite its established utility is the lack of clarity regarding its indications, and a paucity of data on tailored MRI protocols customised to clinical needs. This article aims to review the basic MRI techniques, indications and terminologies used in chest imaging, with special emphasis on imaging findings of common pathologies in the pediatric population.

Role of advanced magnetic resonance imaging in the assessment of malignancies of the mediastinum

In the new era of functional magnetic resonance imaging (MRI), the utility of chest MRI is increasing exponentially due to several advances, including absence of ionizing radiation, excellent tissue contrast and high capability for lesion characterization and treatment monitoring. The application of several of these diagnostic weapons in a multiparametric fashion enables to better characterize thymic epithelial tumors and other mediastinal tumoral lesions, accurate assessment of the invasion of adjacent structures and detection of pathologic lymph nodes and metastasis. Also, “do not touch lesions” could be identified with the associated impact in the management of those patients. One of the hot-spots of the multiparametric chest MR is its ability to detect with acuity early response to treatment in patients with mediastinal malignant neoplasms. This has been related with higher rates of overall survival and progression free survival. Therefore, in this review we will analyze the current functional imaging techniques available (¹⁸F-Fluorodeoxiglucose positron emission tomography/computed tomography, diffusion-weighted imaging, dynamic contrast-enhanced MRI, diffusion tensor imaging and MR spectroscopy) for the evaluation of mediastinal lesions, with a focus in their correct acquisition and post-processing. Also, to review the clinical applications of these techniques in the diagnostic approach of benign and malignant conditions of the mediastinum.

Management of incidental anterior mediastinal lesions: summary of relevant studies

With the increasing use of chest computed tomography (CT) imaging, the detection of asymptomatic incidental lesions in the anterior mediastinum has become more frequent. The prevalence of incidental nodular lesions in the anterior mediastinum is 0.49% to 0.89%. Most of these lesions manifest as soft tissue nodules measuring between 10 and 30 mm on non-contrast CT images. Thymic epithelial tumors are mainly responsible for larger lesions, while smaller lesions are primarily benign cysts. Most incidental thymic epithelial tumors are early-stage and have a favorable outcome. During follow-up, most lesions are stable, but some show indolent growth. Incidental lesions can be managed by a conservative patient-tailored approach with regular follow-up and the use of non-invasive imaging modalities such as magnetic resonance imaging.

Growth of thymic epithelial tumors and thymic cysts: Differential radiological points

BACKGROUND

The growth rate of thymic epithelial tumors (TETs) and thymic cysts was investigated to determine whether they can be differentiated and clinico-radiological predictors of interval growth was identified.

METHODS

This retrospective study included 122 patients with pathologically proven thymic cysts (n = 56) or TETs (n = 66) who underwent two serial chest computed tomography scans at least eight weeks apart. Average diameters and attenuation were measured, volume-doubling times (VDTs) were calculated, and clinical characteristics were recorded. VDTs were compared using the log-rank test. Predictors of growth were analyzed using the log-rank test and Cox regression analysis.

RESULTS

The frequency of growth did not differ significantly between TETs and thymic cysts (P = 0.279). The VDT of thymic cysts (median 324 days) was not significantly different from that of the TETs (median 475 days; P = 0.808). Water attenuation (≤ 20 Hounsfield units) predicted growth in thymic cysts (P = 0.016; hazard ratio 13.2, 95% confidence interval 1.6-107.3), while lesion size (> 17.2 mm) predicted growth in TETs (P = 0.008 for size, P = 0.029 for size*time). For the growing lesions, the positive and negative predictive values of water attenuation for thymic cysts were 93% and 80%, respectively.

CONCLUSION

The frequencies of interval growth and VDTs were indistinguishable between TETs and thymic cysts. Water attenuation and lesion size predicted growth in thymic cysts and TETs, respectively. Among the growing lesions, water attenuation was a differential feature of thymic cysts.

Diagnostic Value of Transthoracic Echocardiography Combined With Contrast-Enhanced Ultrasonography in Mediastinal Masses

OBJECTIVES

Multiple types of mediastinal masses, especially masses in the anterior mediastinum, may be encountered in routine echocardiographic examinations for symptomatic or asymptomatic patients. The aim of this study was to evaluate the diagnostic value of transthoracic echocardiography combined with contrast-enhanced ultrasonography in determining the location, composition, and vascularization of mediastinal masses.

METHODS

A retrospective analysis was conducted on 48 consecutive patients who first had a diagnosis of mediastinal masses by echocardiography. The location of the mass, tissue components, and relationships with the heart and great vessels were analyzed on the basis of multiple transthoracic echocardiographic views. Further contrast-enhanced ultrasonography was performed to determine the vascularization of masses in 25 patients. The clinical, computed tomographic, and histopathologic findings were all recorded and analyzed.

RESULTS

The localization, ultrasonographic characteristics of the mass, degree of vascularization, and relationships with the heart and great vessels assessed on echocardiography allowed a correct diagnosis in most of the cases.

CONCLUSIONS

Transthoracic echocardiography is a useful method for diagnosing mediastinal. Further contrast-enhanced ultrasonography could provide more details on the degree of vascularization, which could facilitate accurate diagnosis and differentiation diagnosis.

Mediastinal and Pleural MR Imaging: Practical Approach for Daily Practice

Radiologists in any practice setting should be prepared to use thoracic magnetic resonance (MR) imaging for noncardiac and nonangiographic applications. This begins with understanding the sequence building blocks that can be used to design effective thoracic MR imaging protocols. In most instances, the sequences used in thoracic MR imaging are adapted from protocols used elsewhere in the body. Some modifications, including the addition of electrocardiographic gating or respiratory triggering, may be necessary for certain applications. Once protocols are in place, recognition of clinical scenarios in which thoracic MR imaging can provide value beyond other imaging modalities is essential. MR imaging is particularly beneficial in evaluating for benign features in indeterminate lesions. In lesions that are suspected to be composed of fluid, including mediastinal cysts and lesions composed of dilated lymphatics, MR imaging can confirm the presence of fluid and absence of suspicious enhancement. It can also be used to evaluate for intravoxel lipid, a finding seen in benign residual thymic tissue and thymic hyperplasia. Because of its excellent contrast resolution and potential for subtraction images, MR imaging can interrogate local treatment sites for the development of recurrent tumor on a background of post-treatment changes. In addition to characterization of lesions, thoracic MR imaging can be useful in surgical and treatment planning. By identifying nodular sites of enhancement or areas of diffusion restriction within cystic or necrotic lesions, MR imaging can be used to direct sites for biopsy. MR imaging can help evaluate for local tumor invasion with the application of "real-time" cine sequences to determine whether a lesion is adherent to an adjacent structure or surface. Finally, MR imaging is the modality of choice for imaging potential tumor thrombus. By understanding the role of MR imaging in these clinical scenarios, radiologists can increase the use of thoracic MR imaging for the benefit of improved decision making in the care of patients. ^©RSNA, 2018.

Magnetic resonance imaging of the pediatric mediastinum

The mediastinum, the central anatomical space of the thorax, is divided by anatomical landmarks but not by physical boundaries. The mediastinum is a conduit, a space through which cranial nerves, important nerve branches, the sympathetic chain, vascular structures, and visceral structures, the trachea and esophagus pass. This arrangement allows contiguous extension or communication of disease along facial planes and through potential spaces to and from the head and neck or cervical spine, to and from the superior mediastinum, between superior and inferior mediastinal levels, and between inferior mediastinal spaces into the intra- and retroperitoneal spaces. Magnetic resonance imaging (MRI) of the mediastinum in children poses technical challenges, in particular cardiac and respiratory motion, and diagnostic challenges, including a broad range of tissue types and possible diagnoses. In this paper we review mediastinal anatomy, MRI sequences and protocol choices and include a short discussion of features and MRI findings of some of the congenital and acquired pathologies that are most often encountered in the pediatric mediastinum.

MR Imaging of Thymic Epithelial Neoplasms

Thymic epithelial neoplasms are malignant lesions that originate from the thymus and include thymoma, thymic carcinoma, and thymic neuroendocrine tumors. Although computed tomography (CT) is typically considered the imaging modality of choice for identifying thymic tumors, characterizing the primary neoplasm, and staging of disease, the role of magnetic resonance (MR) imaging continues to expand. MR imaging is effective in distinguishing thymic epithelial neoplasms and other malignant tumors from benign lesions in the prevascular mediastinum, can be used to characterize and stage thymic tumors in those patients with contraindications to contrast-enhanced CT, and can reveal morphologic features of thymic tumors. At least 15 different stage classifications have been proposed for thymic epithelial neoplasms and used to varying degrees in clinical practice. Recently, an official, consistent tumor node metastasis (TNM) staging system has been recognized by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC), based on an analysis of a retrospective database performed by the International Association for the Study of Lung Cancer (IASLC) and the International Thymic Malignancy Interest Group (ITMIG). In this article, we discuss the appropriate utilization of MR imaging in the evaluation of patients with thymic epithelial neoplasms, key imaging features of the tumors, and the impact of imaging findings on overall staging.

Incidental Anterior Mediastinal Nodular Lesions on Chest CT in Asymptomatic Subjects

OBJECTIVE

The aim of this study was to investigate the prevalence and characteristics of nodular lesions in the anterior mediastinum that had been found incidentally on screening chest computed tomography (CT) in asymptomatic subjects.

METHODS

We included 56,358 consecutive participants (mean age 52.4 ± 10.5 years; male-female ratio 35,306:21,052) who underwent a baseline low-dose chest CT scan as part of a health checkup from 2006 through 2013. After the presence of anterior mediastinal nodular lesion had been confirmed, their CT findings, confirmatory diagnosis, and interval CT scan were reviewed. The standardized prevalence ratio for thymic epithelial tumor was calculated on the basis of the Republic of Korea cancer statistics for 2014.

RESULTS

Of the 56,358 participants, 413 (0.73%) had lesions (95% confidence interval: 0.66-0.80%); the prevalence increased with age (p <0.001) and a history of malignancy (p = 0.005). Of the lesions, 85.2% were smaller than 2 cm, 61.3% were round, and 80.2% had CT attenuation higher than 20 Hounsfield units. Among 51 proven cases, 39 lesions (76.9%) were benign and 12 (23.1%) were malignant. The standardized prevalence ratio for thymic epithelial tumor was 2.04 (95% confidence interval: 1.01-3.42). Of 11 resected thymic epithelial tumors, five were carcinomas, 10 were stage I or II, and all were completely resected without recurrence. Of the 237 unconfirmed cases with a follow-up CT scan, 82.2% were stable, 8.9% had increased, and the other 8.9% had decreased.

CONCLUSIONS

The prevalence of incidental nodular lesion was 0.73%. Most lesions had CT features that were indistinguishable from thymic epithelial tumors, but a considerable portion of the lesions were suspected to be benign. Incidental thymic epithelial tumors were more prevalent than clinically detected tumors, were early-stage cancer, and showed favorable outcomes.

MR Imaging of Mediastinal Masses

The mediastinum contains vital vascular and nonvascular structures and organs, and a wide variety of abnormalities may arise from this region of the thorax. Although mediastinal masses may be initially detected on chest radiography, cross-sectional imaging plays an important role in the identification and evaluation of mediastinal lesions, enabling the formulation of focused differential diagnoses and ultimately guiding management. Computed tomography (CT) is considered the imaging modality of choice for evaluating most mediastinal masses; however, the role of magnetic resonance (MR) imaging continues to expand, as it is superior to CT in differentiating between cystic and solid masses, identifying cystic and solid components within complex lesions, and distinguishing thymic hyperplasia and normal thymus from thymic epithelial neoplasms and other neoplasms. In addition, it facilitates the staging and restaging of patients with thymic epithelial neoplasms and other tumors that cannot undergo contrast-enhanced CT imaging due to severe contrast allergy and/or impaired renal function. As division of the mediastinum into specific compartments is beneficial for diagnostic and treatment planning purposes and facilitates communication between clinicians in a multidisciplinary setting, a new classification model based on cross-sectional imaging has been developed by the International Thymic Malignancy Interest Group (ITMIG) and accepted as a new standard. In this article, we describe the role of MR imaging in the evaluation of mediastinal masses in conjunction with the new mediastinal compartment classification system introduced by ITMIG.

ITMIG Classification of Mediastinal Compartments and Multidisciplinary Approach to Mediastinal Masses

Division of the mediastinum into specific compartments is beneficial for a number of reasons, including generation of a focused differential diagnosis for mediastinal masses identified on imaging examinations, assistance in planning for biopsies and surgical procedures, and facilitation of communication between clinicians in a multidisciplinary setting. Several classification schemes for the mediastinum have been created and used to varying degrees in clinical practice. Most radiology classifications have been based on arbitrary landmarks outlined on the lateral chest radiograph. A new scheme based on cross-sectional imaging, principally multidetector computed tomography (CT), has been developed by the International Thymic Malignancy Interest Group (ITMIG) and accepted as a new standard. This clinical division scheme defines unique prevascular, visceral, and paravertebral compartments based on boundaries delineated by specific anatomic structures at multidetector CT. This new definition plays an important role in identification and characterization of mediastinal abnormalities, which, although uncommon and encompassing a wide variety of entities, can often be diagnosed with confidence based on location and imaging features alone. In other scenarios, a diagnosis may be suggested when radiologic features are combined with specific clinical information. In this article, the authors present the new multidetector CT-based classification of mediastinal compartments introduced by ITMIG and a structured approach to imaging evaluation of mediastinal abnormalities. ^©RSNA, 2017.

Pulmonary relaxometry with inversion recovery ultra-fast steady-state free precession at 1.5T

PURPOSE

To present a technique for simultaneous mapping of T₁ , T₂ , and relative spin density (M₀ ) in human lung using inversion recovery ultra-fast steady-state free precession (IR-ufSSFP) imaging.

METHODS

Pulmonary relaxometry with IR-ufSSFP is based on an interleaved time series acquisition of 2D images acquired at 1.5T. The technique was tested in a phantom and in four healthy volunteers using breath-hold and electrocardiogram triggering. Typically, 30 transient state images were acquired in a single breath-hold within < 10 s. From the signal time course, voxel-wise nonlinear fitting yielded T₁ , T₂ , and M₀ parameter maps. Furthermore, off-resonance and B1 effects were investigated in a phantom.

RESULTS

In the phantom, the observed T₁ of 829 ± 2 ms and T₂ of 105 ± 4 ms were in agreement with the reference T₁ of 858 ± 1 ms and T₂ of 104 ± 1 ms using spin echo methods. In volunteers, the average T₁ of 1375 ± 102 ms and T₂ of 66 ± 26 ms of lung tissue were in good agreement with the literature and were observed to be independent of the respiratory phase. Overall, high reproducibility was shown in a volunteer, yielding coefficient of variations of 0.03 for M₀ , 0.004 for T₁ , and 0.04 for T₂ measurements.

CONCLUSION

IR-ufSSFP allows for fast and simultaneous quantitative mapping of the human lung. Magn Reson Med 77:74-82, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Magnetic resonance imaging of the mediastinum, chest wall and pleura in children

The acceptance of applications for the use of chest MRI in children has been somewhat slow and selective. The use of MRI to image chest wall lesions is likely the most common and widely used indication, aside from the widespread and somewhat sophisticated use of MRI in imaging the cardiovascular structures of the chest. In this respect, fairly standard variations of T1-W, T2-W and contrast-enhanced imaging can be used, similar to the sequences used for musculoskeletal lesions elsewhere in the body. Imaging of the anterior mediastinal masses should be performed in conjunction with a detailed pre-test clinical examination to determine potential cardiovascular compromise. MRI in the setting of middle mediastinal adenopathy, congenital mediastinal cysts or posterior mediastinal masses, however, has been shown to be more effective and more comprehensive than multidetector CT. Although sonographic imaging is the initial modality of choice for pleural abnormalities, MR imaging is extremely effective and clinically useful in the setting of a potentially ambiguous sonographic examination. Faster imaging protocols are likely to increase the acceptance of MRI to replace multidetector CT for many pediatric chest lesions.