Anterior mediastinal solid tumours in adults: characterisation using dynamic contrast-enhanced MRI, diffusion-weighted MRI, and FDG-PET/CT

Evaluation of the effect of PET/CT Fluorodeoxyglucose inclusion on mortality and survival in operated thymoma patients

PURPOSE

In recent years, the use of fluorodeoxyglucose PET-computed tomography (PET-CT) has become widespread to evaluate the diagnosis, metabolism, stage and distant metastases of thymoma. In this study, it was aimed to investigate the connection of malignancy potential, survival and maximum standardized uptake value (SUV max ) measured by PET-CT before surgery according to the histological classification of the WHO in patients operated for thymoma. In addition, the predictive value of the Glasgow prognostic score (GPS) generated by C-reactive protein (CRP) and albumin values on recurrence and survival was investigated and its potential as a prognostic biomarker was evaluated.

METHODS

Forty-five patients who underwent surgical resection for thymoma and were examined with PET-CT in the preoperative period between January 2010 and January 2022 were included in the study. The relationship between WHO histological classification, tumor size and SUV max values on PET-CT according to TNM classification of retrospectively analyzed corticoafferents were evaluated. Preoperative albumin and CRP values were used to determine GPS.

RESULTS

The cutoff value for SUV max was found to be 5.65 in the patients and the overall survival rate of low-risk (<5.65) and high-risk (>5.65) patients was compared according to the SUV max threshold value (5.65) and found to be statistically significant. In addition, the power of PET/CT SUV max value to predict mortality (according to receiver operating characteristics analysis) was statistically significant ( P  = 0.048). Survival expectancy was 127.6 months in patients with mild GPS (O points), 96.7 months in patients with moderate GPS (1 point), and 25.9 months in patients with severe GPS (2 points).

CONCLUSION

PET/CT SUV max values can be used to predict histological sub-type in thymoma patients, and preoperative SUV max and GPS are parameters that can provide information about survival times and mortality in thymoma patients.

The thymus: what's normal and what's not? Problem-solving with MRI

Anterior mediastinal masses can be difficult to characterise on computed tomography (CT) due to the wide spectrum of normal appearances of thymic tissue as well as the challenge of differentiating between benign and malignant pathologies. Additionally, attenuation of cystic mediastinal lesions can be misinterpreted on CT due to varying attenuation values. Anecdotally, non-vascular magnetic resonance imaging (MRI) of the thorax is underutilised across radiology departments in the UK, but has been shown to improve diagnostic certainty and reduce unnecessary surgical intervention. T2-weighted MRI is useful in confirming the cystic nature of lesions, whereas chemical shift techniques can be utilised to document the presence of macroscopic and intra-cellular fat and thus help distinguish between benign and malignant pathologies. In this review article, we present a practical approach to using MRI for the characterisation of anterior mediastinal lesions based on our clinical experience in a UK district general hospital.

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.

MRI Findings and Differential Diagnosis of Anterior Mediastinal Solid Tumors

The anterior mediastinum is the most common location of mediastinal tumors, and thymic epithelial tumors are the most common mediastinal tumors. It is important to differentiate thymic epithelial tumors from malignant lymphomas and malignant germ cell tumors because of the different treatment strategies. Dynamic contrast-enhanced MRI and diffusion-weighted imaging can provide additional information on the differential diagnosis. Chemical shift imaging can detect tiny fat tissues in the lesion and is useful in differentiating thymic hyperplasia from other solid tumors such as thymomas. MRI findings reflect histopathological features of mediastinal tumors, and a comprehensive evaluation of MRI sequences is important for estimation of the histopathological features of the tumor. In this manuscript, we describe the MRI findings of anterior mediastinal solid tumors and the role of MRI in the differential diagnosis.

Differentiating invasive thymic epithelial tumors from mediastinal lung cancer using spectral CT parameters

PURPOSE

The purpose of the study was to explore the importance of quantitative characteristics of spectral CT between invasive thymic epithelial tumors (TETs) and mediastinal lung cancer.

METHODS

We analyzed 54 patients (28 with invasive TETs and 26 with mediastinal lung cancer) who underwent spectral CT. During the arterial and venous phase, we measured the CT70keV, effective atomic number (Zeff), iodine concentration (IC), and water concentration (WC) and calculated the slope of the spectral curve (K100keV). We compared the clinical findings and spectral CT parameters of both groups and performed receiver operating characteristic analysis to evaluate the diagnostic efficacy and the optimal cutoff values of the spectral CT parameters.

RESULTS

During the AP and VP, the CT70keV, Zeff, IC, and K100keV were significantly higher in patients with invasive TETs than those in patients with mediastinal lung cancer (p < 0.05). WC was not statistically significantly different between the two groups (p > 0.05). ROC curve analysis revealed that all quantitative parameters combined in the AP and VP provided the best diagnostic performance in identifying invasive TETs from mediastinal lung cancer (AUC = 0.88, p = 0.002, sensitivity = 0.89 and specificity = 0.77). The cutoff values in the AP for CT70keV, IC, Zeff, and K100keV to differentiate invasive TETs from mediastinal lung cancer were 75.55, 15.86, 8.45, and 1.71, respectively. The cutoff values in the VP for CT70keV, IC, Zeff, and K100keV to differentiate them were 67.06, 15.74, 8.50, and 1.81, respectively.

CONCLUSIONS

Spectral CT imaging has potential value in the differential diagnosis of invasive TETs and mediastinal lung cancer.

Extracellular volume fraction derived from equilibrium contrast-enhanced CT as a diagnostic parameter in anterior mediastinal tumors

PURPOSE

To assess the usefulness of extracellular volume (ECV) fraction derived from equilibrium contrast-enhanced CT (CECT) for diagnosing anterior mediastinal tumors.

METHOD

This study included 161 histologically confirmed anterior mediastinal tumors (55 low-risk thymomas, 57 high-risk thymomas, 32 thymic carcinomas, and 17 malignant lymphomas) that were assessed by pretreatment CECT. ECV fraction was calculated using measurements obtained within the lesion and the aorta on unenhanced and equilibrium phase CECT. ECV fraction was compared among anterior mediastinal tumors using one-way ANOVA or t-test. Receiver-operating characteristic (ROC) curve analysis was performed to evaluate the ability of ECV fraction to differentiate thymic carcinomas/lymphomas from thymomas.

RESULTS

ECV fraction differed significantly among the anterior mediastinal tumors (p < 0.001). ECV fraction of thymic carcinomas was significantly higher than those of low-risk thymomas, high-risk thymomas, and lymphomas (p < 0.001, p < 0.001, and p = 0.006, respectively). ECV fraction of lymphomas was significantly higher than that of low-risk thymomas (p < 0.001). ECV fraction was significantly higher in thymic carcinomas/lymphomas than in thymomas (40.1 % vs. 27.7 %, p < 0.001). The optimal cutoff value to differentiate thymic carcinomas/lymphomas from thymomas was 38.5 % (AUC, 0.805; 95 %CI, 0.736-0.863).

CONCLUSIONS

ECV fraction derived from equilibrium CECT is helpful in diagnosing anterior mediastinal tumors. High ECV fraction is indicative of thymic carcinomas/lymphomas, particularly thymic carcinomas.

Large mediastinal/thoracic benign teratoma presenting with haemoptysis: Report of a case and review of the literature

The mediastinal teratomas can grow to a large size before becoming symptomatic. The symptoms are usually due to the compression of adjacent structures. A computed tomographic scan of the chest is the investigation of choice for making a provisional diagnosis and planning for further management. Removal of large mediastinal/thoracic teratoma can be associated with various intraoperative and postoperative complications, which can be life-threatening sometimes. We operated on a patient with a large mediastinal mass extending into the right thoracic cavity up to the costo-phrenic angle. The postoperative period was eventful and required judicious intensive care. The patient eventually recovered with conservative treatment. A literature search was done on PubMed using the keywords benign mediastinal teratoma. Case series/original articles published in the last two decades, that is, after the year 2000, were evaluated. As per the review of the literature, the prevalence of benign mediastinal teratoma may be higher in eastern countries. Thoracoscopic surgery is the preferred modality except for cases with adhesions or infiltration into surrounding structures.

Feasibility of iodine concentration and extracellular volume fraction measurement derived from the equilibrium phase dual-energy CT for differentiating thymic epithelial tumors

PURPOSE

To assess the diagnostic feasibility of iodine concentration (IC) and extracellular volume (ECV) fraction measurement using the equilibrium phase dual-energy CT (DECT) for the evaluation of thymic epithelial tumors (TETs).

MATERIALS AND METHODS

This study included 33 TETs (11 low-risk thymomas, 11 high-risk thymomas, and 11 thymic carcinomas) that were assessed by pretreatment DECT. IC was measured during the equilibrium phases and ECV fraction was calculated using IC of the thymic lesion and the aorta. IC and ECV fraction were compared among TET subtypes using the Kruskal-Wallis H test and Mann-Whitney U test. Receiver-operating characteristic (ROC) curve analysis was performed to evaluate the ability of IC and ECV fraction to diagnose thymic carcinoma.

RESULTS

IC during the equilibrium phase and ECV fraction differed among the three TET groups (both p < 0.001). IC during the equilibrium phase and ECV fraction was significantly higher in thymic carcinomas than in thymomas (1.9 mg/mL vs. 1.2 mg/mL, p < 0.001; 38.2% vs. 25.9%, p < 0.001; respectively). The optimal cutoff values of IC during the equilibrium phase and of ECV fraction to diagnose thymic carcinoma were 1.5 mg/mL (AUC, 0.955; sensitivity, 100%; specificity, 90.9%) and 26.8% (AUC, 0.888; sensitivity, 100%; specificity, 72.7%), respectively.

CONCLUSION

IC and ECV fraction measurement using DECT are helpful in diagnosing TETs. High IC during the equilibrium phase and high ECV fraction are suggestive of thymic carcinoma.

Quantitative texture analysis based on dynamic contrast enhanced MRI for differential diagnosis between primary thymic lymphoma from thymic carcinoma

To evaluate the value of texture analysis based on dynamic contrast enhanced MRI (DCE-MRI) in the differential diagnosis of thymic carcinoma and thymic lymphoma. Sixty-nine patients with pathologically confirmed (thymic carcinoma, n = 32; thymic lymphoma, n = 37) were enrolled in this retrospective study. Ktrans, Kep and Ve maps were automatically generated, and texture features were extracted, including mean, median, 5th/95th percentile, skewness, kurtosis, diff-variance, diff-entropy, contrast and entropy. The differences in parameters between the two groups were compared and the diagnostic efficacy was calculated. The Ktrans-related significant features yielded an area under the curve (AUC) of 0.769 (sensitivity 90.6%, specificity 51.4%) for the differentiation between thymic carcinoma and thymic lymphoma. The Kep-related significant features yielded an AUC of 0.780 (sensitivity 87.5%, specificity 62.2%). The Ve-related significant features yielded an AUC of 0.807 (sensitivity 75.0%, specificity 78.4%). The combination of DCE-MRI textural features yielded an AUC of 0.962 (sensitivity 93.8%, specificity 89.2%). Five parameters were screened out, including age, Ktrans-entropy, Kep-entropy, Ve-entropy, and Ve-P95. The combination of these five parameters yielded the best discrimination efficiency (AUC of 0.943, 93.7% sensitivity, 81.1% specificity). Texture analysis of DCE-MRI may be helpful to distinguish thymic carcinoma from thymic lymphoma.

Multiparameter diagnostic model based on 18F-FDG PET and clinical characteristics can differentiate thymic epithelial tumors from thymic lymphomas

OBJECTIVE

To evaluate the diagnostic performance of combined multiparametric ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸FDG PET) with clinical characteristics in differentiating thymic epithelial tumors (TETs) from thymic lymphomas.

PATIENTS AND METHODS

A total of 173 patients with 80 TETs and 93 thymic lymphomas who underwent ¹⁸F-FDG PET/CT before treatment were enrolled in this retrospective study. All patients were confirmed by pathology, and baseline characteristics and clinical data were also collected. The semi-parameters of ¹⁸F-FDG PET/CT, including lesion size, SUVmax (maximum standard uptake value), SUVmean (mean standard uptake value), TLG (total lesion glycolysis), MTV (metabolic tumor volume) and SUVR (tumor-to-normal liver standard uptake value ratio) were evaluated. The differential diagnostic efficacy was evaluated using the receiver operating characteristic (ROC) curve. Integrated discriminatory improvement (IDI) and net reclassification improvement (NRI), and Delong test were used to evaluate the improvement in diagnostic efficacy. The clinical efficacy was evaluated by decision curve analysis (DCA).

RESULTS

Age, clinical symptoms, and metabolic parameters differed significantly between patients with TETs and thymic lymphomas. The ROC curve analysis of SUVR showed the highest differentiating diagnostic value (sensitivity = 0.763; specificity = 0.888; area under the curve [AUC] = 0.881). The combined diagnostics model of age, clinical symptoms and SUVR resulted in the highest AUC of 0.964 (sensitivity = 0.882, specificity = 0.963). Compared with SUVR, the diagnostic efficiency of the model was improved significantly. The DCA also confirmed the clinical efficacy of the model.

CONCLUSIONS

The multiparameter diagnosis model based on ¹⁸F-FDG PET and clinical characteristics had excellent value in the differential diagnosis of TETs and thymic lymphomas.

An MRI-Based Clinical-Perfusion Model Predicts Pathological Subtypes of Prevascular Mediastinal Tumors

This study aimed to build machine learning prediction models for predicting pathological subtypes of prevascular mediastinal tumors (PMTs). The candidate predictors were clinical variables and dynamic contrast–enhanced MRI (DCE-MRI)–derived perfusion parameters. The clinical data and preoperative DCE–MRI images of 62 PMT patients, including 17 patients with lymphoma, 31 with thymoma, and 14 with thymic carcinoma, were retrospectively analyzed. Six perfusion parameters were calculated as candidate predictors. Univariate receiver-operating-characteristic curve analysis was performed to evaluate the performance of the prediction models. A predictive model was built based on multi-class classification, which detected lymphoma, thymoma, and thymic carcinoma with sensitivity of 52.9%, 74.2%, and 92.8%, respectively. In addition, two predictive models were built based on binary classification for distinguishing Hodgkin from non-Hodgkin lymphoma and for distinguishing invasive from noninvasive thymoma, with sensitivity of 75% and 71.4%, respectively. In addition to two perfusion parameters (efflux rate constant from tissue extravascular extracellular space into the blood plasma, and extravascular extracellular space volume per unit volume of tissue), age and tumor volume were also essential parameters for predicting PMT subtypes. In conclusion, our machine learning–based predictive model, constructed with clinical data and perfusion parameters, may represent a useful tool for differential diagnosis of PMT subtypes.

Comparison of Interobserver Agreement and Diagnostic Accuracy for IASLC/ITMIG Thymic Epithelial Tumor Staging Among Co-registered FDG-PET/MRI, Whole-body MRI, Integrated FDG-PET/CT, and Conventional Imaging Examination with and without Contrast Media Administrations

RATIONALE AND OBJECTIVES

The purpose of this study was to compare the interobserver agreements and diagnostic accuracies for IASLC/ITMIG (International Association for the Study of Lung Cancer/International Thymic Malignancies Interest Group) thymic epithelial tumor staging of co-registered fluorodeoxyglucose positron emission tomography/magnetic resonance imaging (FDG-PET/MRI), MRI, integrated fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT), and conventional imaging examination.

MATERIALS AND METHODS

Prospective whole-body MRI including diffusion-weighted imaging, integrated PET/CTs, conventional imaging examinations, pathological examinations, and surgical reports, as well as follow-up examinations, were performed for 64 consecutive patients with thymic epithelial tumor. All FDG-PET/MRIs were co-registered PET data with MRI. TNM staging was evaluated by two radiologists on the basis of the IASLC/ITMIG thymic epithelial tumor staging system. Kappa statistics were determined for evaluations of agreements of all factors between each of the methods and final diagnosis. Finally, the diagnostic accuracy of each factor and of determination of the clinical stage was statistically compared to each other using McNemar test.

RESULTS

Agreements for all factors between each method and final diagnosis were assessed as fair, moderate, substantial, or almost perfect (0.28 ≤ kappa value ≤ 0.80; P < .0001). Diagnostic accuracy for N factor of PET/MRI (93.8% [60/64]) and MRI (93.8% [60/64]) was significantly higher than that of conventional imaging examination (81.3% [52/64] vs PET/MRI and MRI; P = .008). In addition, diagnostic accuracy for staging of PET/MRI (84.4% [54/64]) and MRI (84.4 [54/64]) was significantly higher than that of conventional imaging examination (71.9% [46/64] vs PET/MRI and MRI; P = .008).

CONCLUSIONS

Whole-body PET/MRI, MRI, and PET/CT have better interobserver agreements and accuracies than conventional imaging examination for the new IASLC/ITMIG thymic epithelial tumor staging.

Using CT to evaluate mediastinal great vein invasion by thymic epithelial tumors: measurement of the interface between the tumor and neighboring structures

OBJECTIVES

For thymic epithelial tumors, simple contact with adjacent structures does not necessarily mean invasion. The purpose of our study was to develop a simple noninvasive technique for evaluating organ invasion using routine pretreatment computed tomography (CT).

METHODS

This retrospective study analyzed the pathological reports on 95 mediastinal resections performed between January 2003 and June 2020. Using CT images, the length of the interface between the primary tumor and neighboring structures (arch distance; Adist) and maximum tumor diameter (Dmax) was measured, after which Adist/Dmax (A/D) ratios were calculated. Receiver operating characteristic (ROC) curves were used to analyze the Adist and A/D ratios.

RESULTS

An Adist cut-off of 37.5 mm best distinguished between invaded and non-invaded mediastinal great veins based on ROC curves. When Adist > 37.5 mm was used for diagnosis of invasion of the brachiocephalic vein (BCV) or superior vena cava (SVC), the sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and area under the ROC curve for diagnosis of invasion were 61.9%, 92.5%, 81.25%, 82.2%, 81.97%, and 0.76429, respectively. Moreover, there were significant differences between BCV/SVC Adist > 37.5 mm and ≤ 37.5 mm for 10-year relapse-free survival and 10-year overall survival (p < 0.01).

CONCLUSIONS

When diagnosing invasion of the mediastinal great veins based on Adist > 37.5 mm, we achieved a higher performance level than the conventional criteria such as irregular interface with an absence of the fat layer. Measurement of Adist is a simple noninvasive technique for evaluating invasion using CT. Key Points • Simple contact between the primary tumor and adjacent structures on CT does not indicate direct invasion. • Using CT images, the length of the interface between the primary tumor and neighboring structures (arch distance; Adist) is a simple noninvasive technique for evaluating invasion. • Adist > 37.5 mm can be a supportive tool to identify invaded mediastinal great veins and surgical indications for T3 and T4 invasion by thymic epithelial tumors.

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.

Role of diffusion MRI in diagnosis of mediastinal lymphoma: initial assessment and response to therapy

Background

Malignant lymphoma accounts for nearly 20% of all mediastinal neoplasms in adults and 50% in children. Hodgkin’s disease is the most common primary mediastinal lymphoma. In non-Hodgkin’s lymphoma, the two most common forms of primary mediastinal lymphoma are lymphoblastic lymphoma and diffuse large B-cell lymphoma. The aim of this study is to implement diffusion MRI in the algorithm of diagnosis of mediastinal lymphoma, differentiating Hodgkin's from non-Hodgkin's lymphoma and assessment of post therapeutic response.

Results

Using Diffusion weighted magnetic resonance imaging DWI-MRI, there were statistic significant difference between ADC values in lymph nodes and mediastinal masses in Hodgkin and non-Hodgkin lymphomas. ADC range in non-treated Hodgkin lymphoma cases was 0.774 to 1.4, while ADC range in in non-treated non-Hodgkin lymphoma was 0.476 to 0.668. In this study, there was statistically significant difference of ADC values in lymphoma cases presented by mediastinal masses with and without chemotherapy.

Conclusions

Diffusion weighted magnetic resonance imaging DWI-MRI is a promising functional technique in diagnosis of Hodgkin's and non-Hodgkin's lymphoma and assessment of response to treatment with no need for special preparation, contrast injection or radiation exposure.

Differentiating thymoma, thymic carcinoma and lymphoma based on collagen fibre patterns with T2- and diffusion-weighted magnetic resonance imaging

OBJECTIVES

The amount and distribution of intratumoural collagen fibre vary among different thymic tumours, which can be clearly detected with T2- and diffusion-weighted MR images. To explore the incidences of collagen fibre patterns (CFPs) among thymomas, thymic carcinomas and lymphomas on imaging, and to evaluate the efficacy and reproducibility of CFPs in differential diagnosis of thymic tumours.

MATERIALS AND METHODS

Three hundred and ninety-eight patients with pathologically diagnosed thymoma, thymic carcinoma and lymphoma who underwent T2- and diffusion-weighted MR imaging were retrospectively enrolled. CFPs were classified into four categories: septum sign, patchy pattern, mixed pattern and no septum sign. The incidences of CFPs were compared among different thymic tumours, and the efficacy and reproducibility in differentiating the defined tumour types were analysed.

RESULTS

There were significant differences in CFPs among thymomas, thymic squamous cell carcinomas (TSCCs), other thymic carcinomas and neuroendocrine tumours (OTC&NTs) and thymic lymphomas. Septum signs were found in 209 (86%) thymomas, which differed between thymomas and any other thymic neoplasms (all p < 0.005). The patchy, mixed patterns and no septum sign were mainly seen in TSCCs (80.3%), OTC&NTs (78.9%) and thymic lymphomas (56.9%), respectively. The consistency of different CFP evaluation between two readers was either good or excellent. CFPs achieved high efficacy in identifying the thymic tumours.

CONCLUSION

The CFPs based on T2- and diffusion-weighted MR imaging were of great value in the differential diagnosis of thymic tumours.

KEY POINTS

• Significant differences are found in intratumoural collagen fibre patterns among thymomas, thymic squamous cell carcinomas, other thymic carcinomas and neuroendocrine tumours and thymic lymphomas. • The septum sign, patchy pattern, mixed pattern and no septum sign are mainly seen in thymomas (86%), thymic squamous cell carcinomas (80.3%), other thymic carcinomas and neuroendocrine tumours (79%) and thymic lymphomas (57%), respectively. • The collagen fibre patterns have high efficacy and reproducibility in differentiating thymomas, thymic squamous cell carcinomas and thymic lymphomas.

Usefulness of 18F-FDG PET/CT in treatment-naive patients with thymic squamous cell carcinoma

OBJECTIVE

Thymic squamous cell carcinoma (TSCC) is very rare. This study aims to investigate the clinical utility of fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) in treatment-naive patients with TSCC.

METHODS

The tumor metabolic parameters of ¹⁸F-FDG PET/CT, including maximum standard uptake value (SUVmax), metabolic tumor volume of primary lesion (MTV-P) and combination of primary lesion and metastases (MTV-C), and total lesion glycolysis of primary lesion (TLG-P) and combination of primary lesion and metastases (TLG-C) were collected. Age, sex, smoking, serum tumor markers, tumor size, Masaoka-Koga stage, TNM stage, contrast-enhanced CT scan, and tumor immunity were also reviewed. Moreover, progression-free survival (PFS) and overall survival (OS) of these patients were analyzed.

RESULTS

Forty-two treatment-naive patients with TSCC were enrolled in this study. All primary tumors were FDG-avid with the average SUVmax of 10.0 ± 4.5 (range, 1.5-20.4). Higher SUVmax, MTV-C, and TLG-C were observed in advanced Masaoka-Koga stage than early stage, and higher SUVmax was found in advanced TNM stage than early stage. Next, 36 out of 42 patients performed chest contrast-enhanced CT scan, which showed SUVmax associated with the enhancement degree of CT. Moreover, 27 out of 42 lesions were assessed tumor immunity, and the detective rates of PD-L1, PD-1, CD4, CD8, and Foxp3 were 59.3%, 37.0%, 59.3%, 100%, and 77.8%, respectively. Higher SUVmax was observed in lesions with lower CD4-positive tumor-infiltrating lymphocytes. Furthermore, 12- and 24-month PFS and OS rates were 62.0% vs 32.8% and 84.5% vs 68.9%, respectively. Multivariate Cox regression analysis showed that only MTV-C was an independent predictor of PFS.

CONCLUSION

¹⁸F-FDG PET/CT is useful in evaluating tumor staging, assessing CT enhancement degree, and detecting tumor immunity of TSCC before treatment. ¹⁸F-FDG PET/CT could also be a promising tool to provide prognostic information for treatment-naive patients with TSCC.

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.

State-of-the-art MR Imaging for Thoracic Diseases

Since thoracic MR imaging was first used in a clinical setting, it has been suggested that MR imaging has limited clinical utility for thoracic diseases, especially lung diseases, in comparison with x-ray CT and positron emission tomography (PET)/CT. However, in many countries and states and for specific indications, MR imaging has recently become practicable. In addition, recently developed pulmonary MR imaging with ultra-short TE (UTE) and zero TE (ZTE) has enhanced the utility of MR imaging for thoracic diseases in routine clinical practice. Furthermore, MR imaging has been introduced as being capable of assessing pulmonary function. It should be borne in mind, however, that these applications have so far been academically and clinically used only for healthy volunteers, but not for patients with various pulmonary diseases in Japan or other countries. In 2020, the Fleischner Society published a new report, which provides consensus expert opinions regarding appropriate clinical indications of pulmonary MR imaging for not only oncologic but also pulmonary diseases. This review article presents a brief history of MR imaging for thoracic diseases regarding its technical aspects and major clinical indications in Japan 1) in terms of what is currently available, 2) promising but requiring further validation or evaluation, and 3) developments warranting research investigations in preclinical or patient studies. State-of-the-art MR imaging can non-invasively visualize lung structural and functional abnormalities without ionizing radiation and thus provide an alternative to CT. MR imaging is considered as a tool for providing unique information. Moreover, prospective, randomized, and multi-center trials should be conducted to directly compare MR imaging with conventional methods to determine whether the former has equal or superior clinical relevance. The results of these trials together with continued improvements are expected to update or modify recommendations for the use of MRI in near future.

Extracellular volume fraction measurement correlates with lymphocyte abundance in thymic epithelial tumors

Background

Recent advance in tissue characterization with parametric mapping imaging has the potential to be a novel biomarker for histopathologic correlation with thymic epithelial tumors (TETs). The purpose of our study is to evaluate MRI T1 mapping with the calculation of extracellular volume (ECV) fraction for histologic correlation with thymic epithelial tumor based on lymphocyte abundance.

Methods

A retrospective study including 31 consecutive patients (14 men and 17 women, median age, 56 years; interquartile range, 12 years) with TETs was performed. The T1 values and ECV were assessed by using quantitative MRI mapping techniques. Mann-Whitney U test, Kruskal-Wallis H test, and receiver operating characteristic curve analyses were used to assess discrimination between different types of TETs based on lymphocyte abundance.

Results

Extracellular volume was significantly higher in TETs with sparse lymphocyte, including type A, type B3, and thymic carcinoma, compared with those with abundant lymphocyte, including type B1, B2, and AB thymomas (42.5% vs 26.9%, respectively; p < 0.001). Extracellular volume was significantly higher in thymic carcinoma compared with low grade and high grade thymomas (48.6% vs 31.1% vs 27.6%, respectively; p = 0.002).

Conclusions

T1 mapping with the calculation of extracellular volume (ECV) fraction correlate with the WHO histologic classification of thymic epithelial tumor based on lymphocyte abundance.

Anterior mediastinal lesions: CT and MRI features and differential diagnosis

Anterior mediastinum is the most common location of mediastinal tumors, which include various solid and cystic lesions. The lesion location and CT and MRI features are important in the differential diagnosis. Recently, CT-based mediastinal compartment classification systems were proposed and suggested to be useful for accurate evaluation of mediastinal lesions. CT and MRI reflect the pathological findings of mediastinal lesions, and knowledge of the pathological features is important for the differential diagnosis. In this article, we review the CT and MRI features of anterior mediastinal lesions and describe important points in the differential diagnosis.

[Imaging of Mediastinal Tumors]

In computed tomography, the mediastinum is split into ventral prevascular, middle visceral and dorsal paravertebral compartments. Each compartment contains specific tumours which will be presented and discussed briefly. The focus is on image-based analysis of morphological signs to differentiate between entities using X-rays, ultrasound, CT and MRI. It is however difficult to differentiate between various types of lesions based on morphology and to estimate the grade of malignancy. For this reason, functional imaging techniques like PET and MRI are essential tools for detailed and non-invasive work-up. If a histological tissue examination is required, these tissue samples can be acquired using CT guided biopsies with high diagnostic yield and low complication rates.

Value of metabolic parameters in distinguishing primary mediastinal lymphomas from thymic epithelial tumors

Objective: A high rate of unnecessary thymectomies has been reported. This study aimed to distinguish primary mediastinal lymphomas (PMLs) from thymic epithelial tumors (TETs) by evaluating volumetric and metabolic parameters with ¹⁸F-FDG PET/CT.

Methods: A total of 136 patients who were pathologically diagnosed with TETs or PMLs were enrolled, and ¹⁸F-FDG PET/CT was performed before therapy. Volumetric parameters, including the mean SUV (SUVmean), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and SUVmax, were determined and compared between the 2 subtypes. The diagnostic performance of these parameters was evaluated with receiver operating characteristic (ROC) curve analysis.

Results: All parameters significantly differed between patients with PMLs and TETs. Patients with lymphomas were younger and had higher SUVmean, SUVmax, TLG, and MTV values than patients with TETs. The MTV and TLG values had similar diagnostic performance. ROC analysis indicated that the areas under the curves of the SUVmean and SUVmax values performed similarly (approximately 0.76) in differentiating patients with PMLs from TETs, and both values were better than the MTV and TLG values. When age was included with the SUVmax in differentiating TETs from PMLs, the AUC was 0.91, and the sensitivity and specificity increased to 80% and 93%, respectively.

Conclusions: The SUVmax and volumetric parameters of ¹⁸F-FDG PET/CT can be used to distinguish patients with PMLs versus TETs, and thus may aid in preventing unnecessary thymectomies or other invasive operations.

Feasibility of using dynamic contrast-enhanced MRI for differentiating thymic carcinoma from thymic lymphoma based on semi-quantitative and quantitative models

AIM

To evaluate the value of using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) derived parameters to differentiate thymic carcinoma and thymic lymphoma based on semi-quantitative and quantitative models.

MATERIALS AND METHODS

Twenty-nine pathologically confirmed anterior mediastinum tumours in 29 patients were enrolled in this retrospective study, including 15 thymic carcinoma and 14 lymphoma patients. All the patients underwent pre-treatment mediastinum DCE-MRI. Both semi-quantitative and quantitative parameters were calculated and the volume transfer constant K^trans, the flux rate constant between extravascular extracellular space and plasma k_ep, the extravascular extracellular volume fraction v_e were obtained based on a modified Tofts model. DCE-MRI derived parameters were compared between thymic carcinoma and thymic lymphoma groups.

RESULTS

Thymic carcinoma had significantly lower k_ep (p=0.040) and higher v_e (p=0.018) than thymic lymphoma; however, there were no significant differences on K^trans and semi-quantitative parameters between the two groups. v_e had the highest area under the curve (cut-off value, 0.282; area under the curve, 0.748; sensitivity, 71.4%; specificity, 80%). The combination of k_ep and v_e could increase the diagnostic performance significantly (area under the curve, 0.752; sensitivity, 57.1%; specificity, 93.3%).

CONCLUSION

DCE-MRI derived parameters may have value in the differentiating thymic carcinoma and thymic lymphoma.

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 analysis of metabolic parameters at 18F-fluorodeoxyglucose positron emission tomography in predicting malignant potential of anterior mediastinal tumors

To evaluate the utility of ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) for predicting the malignancy of anterior mediastinal tumors, the present study retrospectively examined a total of 105 consecutive patients who underwent surgical resection of anterior mediastinal tumors at Gunma University Hospital after undergoing a preoperative FDG-PET scan. Patients were divided into benign and malignant groups in accordance with the following three classification systems: i) Clinical classification, benign or malignant (thymoma and carcinoma); ii) recurrence-based classification, low-risk recurrence (benign and low-risk thymoma) or high-risk recurrence (high-risk thymoma and carcinoma); and iii) pathological classification, benign (benign and thymoma) or malignant (carcinoma). The present study analyzed the differences between the benign and malignant groups in terms of FDG-PET parameters, including maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV) and total lesion glycolysis (TLG). The malignant group exhibited a significantly greater SUVmax than the benign group according to all classification systems. By contrast, there was only a slight difference between groups in volume-based metabolic parameters (MTV and TLG) using the clinical classification, and no intergroup differences using the recurrence-based and pathological classifications. The area under the curve in receiver-operating characteristic curve analysis for predicting malignancy was significantly greater for SUVmax than for volume-based metabolic parameters using all classification methods. The respective optimal cut-off value, sensitivity and specificity of SUVmax to predict malignancy were 1.77, 92.0 and 87.0% for the clinical classification, 2.54, 93.6 and 60.3% for the recurrence-based classification, and 5.15, 78.9 and 90.7% for the pathological classification. SUVmax was the most useful parameter for predicting the malignancy of anterior mediastinal tumors.

Contrast-enhanced ultrasound features of mediastinal lymphomas and thymic epithelial tumors

OBJECTIVES

To summarize the contrast-enhanced ultrasound (CEUS) features of mediastinal lymphomas and thymic epithelial tumors (including thymomas and thymic carcinomas) and to explore the value of CEUS in the differential diagnosis of lymphomas and thymic epithelial tumors.

METHODS

Sixty-nine patients with 69 mediastinal lesions who underwent CEUS and had disease confirmed by histopathology were enrolled in the study. There were 33 cases of lymphoma, 19 cases of thymic carcinoma, and 17 cases of thymoma. CEUS features, including the enhancement pattern, enhancement distribution, enhancement time, inner necrosis status, wash out pattern, and vascular morphology, were evaluated in each group.

RESULTS

Thymomas often presented with homogeneous (88.2%, 15/17) and late (88.2%, 15/17) enhancement and a low rate of inner necrosis (17.6%, 3/17). Late (73.7%, 14/19), heterogeneous (68.4%, 13/19), and centripetal (63.2%, 12/19) enhancement were more often observed in thymic carcinoma, as was a high rate of inner necrosis (78.9%, 15/19). Lymphomas showed a homogeneous enhancement rate of 57.6% (19/33) and a late enhancement rate of 54.5% (18/33). The rate of inner necrosis for lymphomas was 45.5% (15/33). The diagnostic accuracy of this finding for distinguishing thymic epithelial tumors from lymphomas was 63.8%, the sensitivity was 80.6%, and the specificity was 45.5%. Enlarged blood vessels were a feature specific to lymphomas, while small vessels arranged in a comb shape was a feature specific to thymic epithelial tumors.

CONCLUSION

This study describes the CEUS features of common mediastinal tumors and may stimulate further studies in this field.

Comparison between CT and MRI in the Diagnostic Accuracy of Thymic Masses

Purpose: The aim of this study was to compare diagnostic accuracy between CT and MRI for thymic masses.

Methods: We searched literature and collected information on first author, publication year, cases of different types of thymic lesions, correct diagnostic cases of CT and MRI and results of quantitative analysis of CT and MRI. The ROC curve was applied to compare the diagnostic performance of different imaging modalities.

Results: Eight literatures were finally included and analyzed in this study. There were 253 cases examined by CT and 340 cases by MRI in total. We showed outcomes of quantitative analysis of each study in this article. The sensitivity of CT and MRI was both 100%, while the specificity was 75% and 80%, respectively. AUC of CT was 0.875 [95%CI: 0.473, 0.997] and that of MRI was 0.880 [95%CI: 0.531, 0.995].

Conclusion: The diagnostic accuracy of MRI is superior to CT in detecting thymomas, thymic cysts or thymic hyperplasia but that of CT and MRI is still unclear in differentiating thymic carcinomas and lymphomas/germ cell tumors.

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.

Building blocks for thoracic MRI: Challenges, sequences, and protocol design

Thoracic MRI presents important and unique challenges. Decreased proton density in the lung in combination with respiratory and cardiac motion can degrade image quality and render poorly executed sequences uninterpretable. Despite these challenges, thoracic MRI has an important clinical role, both as a problem-solving tool and in an increasing array of clinical indications. Advances in scanner and sequence design have also helped to drive this development, presenting the radiologist with improved techniques for thoracic MRI. Given this evolving landscape, radiologists must be familiar with what thoracic MR has to offer. The first step in developing an effective thoracic MRI practice requires the creation of efficient and malleable protocols that can answer clinical questions. To do this, radiologists must have a working knowledge of the MR sequences that are used in the thorax, many of which have been adapted from use elsewhere in the body. These sequences can be broadly divided into three categories: traditional/anatomic, functional, and cine based. Traditional/anatomic sequences allow for the depiction of anatomy and pathologic processes with the ability for characterization of signal intensity and contrast enhancement. Functional sequences, including diffusion-weighted imaging, and high temporal resolution dynamic contrast enhancement, allow for the noninvasive measurement of tissue-specific parameters. Cine-based sequences can depict the motion of structures in the thorax, either with retrospective ECG gating or in real time. The purpose of this article is to review these categories, the building block sequences that comprise them, and identify basic questions that should be considered in thoracic MRI protocol design. Level of Evidence: 5 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2019;50:682-701.

Iodine Quantification Using Dual-Energy Computed Tomography for Differentiating Thymic Tumors

The aim of the study was to explore the efficacy of iodine quantification with dual-energy computed tomography (DECT) in differentiating thymoma, thymic carcinoma, and thymic lymphoma.

MATERIALS AND METHODS

Fifty-seven patients with pathologically confirmed low-risk thymoma (n = 16), high-risk thymoma (n = 15), thymic carcinoma (n = 14), and thymic lymphoma (n = 12) underwent chest contrast-enhanced DECT scan were enrolled in this study. Tumor DECT parameters including iodine-related Hounsfield unit (IHU), iodine concentration (IC), mixed HU (MHU), and iodine ratio in dual phase, slope of energy spectral HU curve (λ), and virtual noncontrast (VNC) were compared for differences among 4 groups by one-way analysis of variance. Receiver operating characteristic curve was used to determine the efficacy for differentiating the low-risk thymoma from other thymic tumor by defined parameters.

RESULTS

According to quantitative analysis, dual-phase IHU, IC, and MHU values in patients with low-risk thymoma were significantly increased compared with patients with high-risk thymoma, thymic carcinoma, and thymic lymphoma (P < 0.05/4).The venous phase IHU value yielded the highest performance with area under the curve of 0.893, 75.0% sensitivity, and 89.7% specificity for differentiating the low-risk thymomas from high-risk thymomas or thymic carcinoma at the cutoff value of 34.3 HU. When differentiating low-risk thymomas from thymic lymphoma, the venous phase IC value obtained the highest diagnostic efficacy with the area under the curve of 0.969, and sensitivity, specificity, and cutoff value were 87.5%, 100.0%, and 1.25 mg/mL, respectively.

CONCLUSIONS

Iodine quantification with DECT may be useful for differentiating the low-risk thymomas from other thymic tumors.

Incremental Value of Magnetic Resonance Imaging in Further Characterizing Hypodense Mediastinal and Paracardiac Lesions Identified on Computed Tomography

Mediastinal and paracardiac lesions are usually first diagnosed on a chest radiograph or echocardiogram. Often, a computed tomography is obtained to further delineate these lesions. CT may be suboptimal for evaluation of enhancement characteristics and direct extension into the adjacent mediastinal structures. With its intrinsic superior soft-tissue characterization, magnetic resonance imaging (MRI) can better delineate these lesions, their internal tissue characteristics, and identify adhesion/invasion into adjacent structures. This pictorial essay provides a brief synopsis of the key MRI sequences and their utility in further characterizing mediastinal and paracardiac lesions.

Radiographic Predictors of Resectability in Thymic Carcinoma

BACKGROUND

The aim of this study was to assess preoperative computed tomography characteristics of thymic carcinomas and to investigate which features could predict an incomplete surgical resection. A secondary aim was to correlate preoperative imaging features with Masaoka stage.

METHODS

In this study, approved by our Institutional Review Board, two readers retrospectively reviewed preoperative computed tomography scans at our tertiary referral oncology center between 1994 and 2014. Imaging features analyzed included tumor morphology, infiltration of surrounding mediastinal fat, loss of surrounding fat plane, degree of contact between tumor and great vessels, and associated pulmonary or pleural abnormality. Surgical and pathologic records were reviewed for completeness of surgical resection and Masaoka stage.

RESULTS

Forty-one patients were included, with Masaoka stage I (n = 3), stage II (n = 4), stage III (n = 12), and stage IV (n = 22). Twenty-one patients (51%) had a complete surgical resection. Ten had microscopic residual disease (R1) with involved surgical margins at pathology, and 10 patients had macroscopic residual disease (R2) at surgery. In addition to lesion size, the feature associated with incomplete surgical resection was the degree of tumor contact with adjacent mediastinal vessels on the preoperative computed tomography image (p = 0.038). Many of the more common features associated with incomplete resection were also more likely to be present in patients with late Masaoka stage (III/IV), including infiltration of the mediastinal fat, which was present in all 34 patients with Masaoka stage III/IV compared with 5 patients (71%) with stage I/II (p = 0.03).

CONCLUSIONS

Preoperative computed tomography imaging features may help to identify patients at risk for an incomplete surgical resection.

A Whole-Tumor Histogram Analysis of Apparent Diffusion Coefficient Maps for Differentiating Thymic Carcinoma from Lymphoma

Objective

To assess the performance of a whole-tumor histogram analysis of apparent diffusion coefficient (ADC) maps in differentiating thymic carcinoma from lymphoma, and compare it with that of a commonly used hot-spot region-of-interest (ROI)-based ADC measurement.

Materials and Methods

Diffusion weighted imaging data of 15 patients with thymic carcinoma and 13 patients with lymphoma were retrospectively collected and processed with a mono-exponential model. ADC measurements were performed by using a histogram-based and hot-spot-ROI-based approach. In the histogram-based approach, the following parameters were generated: mean ADC (ADC_mean), median ADC (ADC_median), 10th and 90th percentile of ADC (ADC₁₀ and ADC₉₀), kurtosis, and skewness. The difference in ADCs between thymic carcinoma and lymphoma was compared using a t test. Receiver operating characteristic analyses were conducted to determine and compare the differentiating performance of ADCs.

Results

Lymphoma demonstrated significantly lower ADC_mean, ADC_median, ADC₁₀, ADC₉₀, and hot-spot-ROI-based mean ADC than those found in thymic carcinoma (all p values < 0.05). There were no differences found in the kurtosis (p = 0.412) and skewness (p = 0.273). The ADC₁₀ demonstrated optimal differentiating performance (cut-off value, 0.403 × 10^-3 mm²/s; area under the receiver operating characteristic curve [AUC], 0.977; sensitivity, 92.3%; specificity, 93.3%), followed by the ADC_mean, ADC_median, ADC₉₀, and hot-spot-ROI-based mean ADC. The AUC of ADC₁₀ was significantly higher than that of the hot spot ROI based ADC (0.977 vs. 0.797, p = 0.036).

Conclusion

Compared with the commonly used hot spot ROI based ADC measurement, a histogram analysis of ADC maps can improve the differentiating performance between thymic carcinoma and lymphoma.

Histogram analysis of apparent diffusion coefficient maps for assessing thymic epithelial tumours: correlation with world health organization classification and clinical staging

OBJECTIVE

To investigate the value of apparent diffusion coefficients (ADCs) histogram analysis for assessing World Health Organization (WHO) pathological classification and Masaoka clinical stages of thymic epithelial tumours.

METHODS

37 patients with histologically confirmed thymic epithelial tumours were enrolled. ADC measurements were performed using hot-spot ROI (ADC_HS-ROI) and histogram-based approach. ADC histogram parameters included mean ADC (ADC_mean), median ADC (ADC_median), 10 and 90 percentile of ADC (ADC₁₀ and ADC₉₀), kurtosis and skewness. One-way ANOVA, independent-sample t-test, and receiver operating characteristic were used for statistical analyses.

RESULTS

There were significant differences in ADC_mean, ADC_median, ADC₁₀, ADC₉₀ and ADC_HS-ROI among low-risk thymoma (type A, AB, B1; n = 14), high-risk thymoma (type B2, B3; n = 9) and thymic carcinoma (type C, n = 14) groups (all p-values <0.05), while no significant difference in skewness (p = 0.181) and kurtosis (p = 0.088). ADC₁₀ showed best differentiating ability (cut-off value, ≤0.689 × 10^-3 mm² s^-1; AUC, 0.957; sensitivity, 95.65%; specificity, 92.86%) for discriminating low-risk thymoma from high-risk thymoma and thymic carcinoma. Advanced Masaoka stages (Stage III and IV; n = 24) tumours showed significant lower ADC parameters and higher kurtosis than early Masaoka stage (Stage I and II; n = 13) tumours (all p-values <0.05), while no significant difference on skewness (p = 0.063). ADC₁₀ showed best differentiating ability (cut-off value, ≤0.689 × 10^-3 mm² s^-1; AUC, 0.913; sensitivity, 91.30%; specificity, 85.71%) for discriminating advanced and early Masaoka stage epithelial tumours.

CONCLUSION

ADC histogram analysis may assist in assessing the WHO pathological classification and Masaoka clinical stages of thymic epithelial tumours. Advances in knowledge: 1. ADC histogram analysis could help to assess WHO pathological classification of thymic epithelial tumours. 2. ADC histogram analysis could help to evaluate Masaoka clinical stages of thymic epithelial tumours. 3. ADC₁₀ might be a promising imaging biomarker for assessing and characterizing thymic epithelial tumours.

Nonsuppressing normal thymus on chemical-shift MR imaging and anterior mediastinal lymphoma: differentiation with diffusion-weighted MR imaging by using the apparent diffusion coefficient

OBJECTIVES

To prospectively evaluate usefulness of the apparent diffusion coefficient (ADC) in differentiating anterior mediastinal lymphoma from nonsuppressing normal thymus on chemical-shift MR, and to look at the relationship between patient age and ADC.

METHODS

Seventy-three young subjects (25 men, 48 women; age range, 9-29 years), who underwent chemical-shift MR and diffusion-weighted MR were divided into a normal thymus group (group A, 40 subjects), and a lymphoma group (group B, 33 patients). For group A, all subjects had normal thymus with no suppression on opposed-phase chemical-shift MR. Two readers measured the signal intensity index (SII) and ADC. Differences in SII and ADC between groups were tested using t-test. ADC was correlated with age using Pearson correlation coefficient.

RESULTS

Mean SII±standard deviation was 2.7±1.8% for group A and 2.2±2.4% for group B, with no significant difference between groups (P=.270). Mean ADC was 2.48±0.38x10^-3mm²/s for group A and 1.24±0.23x10^-3mm²/s for group B. A significant difference between groups was found (P<.001), with no overlap in range. Lastly, significant correlation was found between age and ADC (r=0.935, P<.001) in group A.

CONCLUSIONS

ADC of diffusion-weighted MR is a noninvasive and accurate parameter for differentiating lymphoma from nonsuppressing thymus on chemical-shift MR in young subjects.

KEY POINTS

• SII cannot differentiate mediastinal lymphoma from nonsuppressing normal thymus at visual assessment • ADC is useful for distinguishing nonsuppressing normal thymus from mediastinal lymphoma • ADC is more accurate than transverse-diameter and surface-area in this discrimination • ADC of normal thymus is age dependent and increases with increasing age.

Evaluation of anterior mediastinal solid tumors by CT perfusion: a preliminary study

PURPOSE

We aimed to assess the role of computed tomography (CT) perfusion in differentiation of thymoma from thymic hyperplasia, lymphoma, thymic carcinoma, and lung cancer invading anterior mediastinum.

METHODS

In this study, 25 patients with an anterior mediastinal lesion underwent CT perfusion imaging from January 2015 to February 2016. Diagnoses included thymoma (n=7), thymic hyperplasia (n=8), lymphoma (n=4), thymic carcinoma (n=3), and invasive lung cancer (n=3). Lymphoma, thymic carcinoma, and lung cancer were grouped as malignant tumors for statistical analysis. Values for blood flow, blood volume, and permeability surface were measured in CT perfusion.

RESULTS

Blood flow and blood volume values were higher in thymoma in comparison to thymic hyperplasia; however, the difference was not statistically significant. Blood volume values were significantly higher in thymoma (mean, 11.4 mL/100 mL; range, 5.2-20.2 mL/100 mL) compared with lymphoma (mean, 5.3 mL/100 mL; range, 2.5-7.2 mL/100 mL) (P = 0.023). Blood flow and blood volume values were significantly higher in thymoma compared with non-thymoma malignant tumors (P = 0.025).

CONCLUSION

CT perfusion is helpful in differentiating thymoma from non-thymoma malignancies including lymphoma, thymic carcinoma, and invasive lung cancer involving the anterior mediastinum.