Update in diagnostic imaging of the thymus and anterior mediastinal masses

Imaging of Mediastinal Masses

A diverse group of conditions can present as a mediastinal mass, posing a diagnostic challenge for radiologists. As a first step toward an accurate diagnosis, precise localization of the mass to the appropriate compartment, followed by the assessment of its internal characteristics is important. The classification proposed by the International Thymic Malignancy Interest Group is the current practice standard for localizing mediastinal masses. Computed tomography remains the most widely used imaging modality for their diagnosis with an increasing use of MR imaging to problem solve owing to its superior tissue contrast and ability to characterize different tissue types.

Effectiveness of Adjuvant Chemo- and Radiotherapy in Thymic Carcinoma Stage II: A Systematic Review and Meta-Analysis

BACKGROUND

Thymic carcinoma is a rare tumor arising from the epithelial thymic tissue, yet among mediastinal tumors, it is the most common malignant entity. Thymic carcinoma often causes no symptoms and is incidentally discovered. Adjuvant radiotherapy is recommended, particularly in cases of incomplete resection and for stages III and IV, based on current guidelines and existing literature. In stage II (Masaoka-Koga system), the role of chemotherapy remains controversial, particularly in cases of incomplete resection. Therefore, this study aims to assess the effectiveness of adjuvant chemotherapy compared to adjuvant radiotherapy in the treatment of stage II (Masaoka-Koga system) thymic carcinoma after surgery.

METHODS

A comprehensive literature search was conducted in the Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and MEDLINE/PubMed databases for relevant studies published through April 30th, 2023.

RESULTS

The review identified a total of 101 studies in the Embase, Cochrane Library, and MEDLINE/PubMed databases. Of these, only eight retrospective studies met the inclusion criteria and were included in the meta-analysis. These eight studies encompassed a total of 323 patients with stage II (Masaoka-Koga system) thymic carcinoma, with an average patient age of 53.8 ± 5.0 years. There was no significant difference in the number of R0 resections between patients receiving adjuvant chemotherapy and those receiving adjuvant radiotherapy (P = 0.82). Patients who received adjuvant radiotherapy had a higher rate of recurrence, but this difference was not statistically significant (P = 0.93). The meta-analysis synthesized five-year overall survival data, with a combined hazard ratio (HR) of 0.881 (95% CI: 0.463 to 1.299), indicating no statistically significant difference between the treatment groups.

CONCLUSIONS

Although the results were not statistically significant, the findings suggest that adjuvant chemotherapy might be associated with a more favorable outcome for patients with stage II (Masaoka-Koga system) thymic carcinoma compared to adjuvant radiotherapy.

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.

Multiparametric Evaluation of Radiomics Features and Dual-Energy CT Iodine Maps for Discrimination and Outcome Prediction of Thymic Masses

RATIONALE AND OBJECTIVES

To investigate the diagnostic value of radiomics features and dual-source dual-energy CT (DECT) based material decomposition in differentiating low-risk thymomas, high-risk thymomas, and thymic carcinomas.

MATERIALS AND METHODS

This retrospective study included 32 patients (16 males, mean age 66 ± 14 years) with pathologically confirmed thymic masses who underwent contrast-enhanced DECT between 10/2014 and 01/2023. Two experienced readers evaluated all patients regarding conventional radiomics features, as well as DECT-based features, including attenuation (HU), iodine density (mg/mL), and fat fraction (%). Data comparisons were performed using analysis of variance and chi-square statistic tests. Receiver operating characteristic curve analysis and Cox-regression tests were used to discriminate between low-risk/high-risk thymomas and thymic carcinomas.

RESULTS

Of the 32 thymic tumors, 12 (38%) were low-risk thymomas, 11 (34%) were high-risk thymomas, and 9 (28%) were thymic carcinomas. Values differed significantly between low-risk thymoma, high-risk thymoma, and thymic carcinoma regarding DECT-based features (p ≤ 0.023) and 30 radiomics features (p ≤ 0.037). The area under the curve to differentiate between low-risk/high-risk thymomas and thymic cancer was 0.998 (95% CI, 0.915-1.000; p < 0.001) for the combination of DECT imaging parameters and radiomics features, yielding a sensitivity of 100% and specificity of 96%. During a follow-up of 60 months (IQR, 35-60 months), the multiparametric approach including radiomics features, DECT parameters, and clinical parameters showed an excellent prognostic power to predict all-cause mortality (c-index = 0.978 [95% CI, 0.958-0.998], p = 0.003).

CONCLUSION

A multiparametric approach including conventional radiomics features and DECT-based features facilitates accurate, non-invasive discrimination between low-risk/high-risk thymomas and thymic carcinomas.

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.

Cholesterol granuloma of the anterior mediastinum: A case report and literature review

INTRODUCTION

Cholesterol granulomas, which frequently present in the temporal bone of the skull, are recognized as benign lesions occurring due to chronic inflammation or hemorrhage. However, cholesterol granuloma of the mediastinum is extremely rare.

PRESENTATION OF CASE

An asymptomatic 43-year-old man with an incidental finding of anterior mediastinal mass by positron emission tomography scan was referred to our hospital. Preoperative computed tomography showed a well-circumscribed nodule 2 cm in size in the anterior mediastinum. A total tumor resection through a suprasternal approach was performed. Microscopically, numerous cholesterol clefts with an alveolar-like growth pattern and foreign body reaction were observed, indicating a pathological diagnosis of cholesterol granuloma.

DISCUSSION

Cholesterol granuloma is generally thought to be initiated by cell degeneration and hemorrhage resulting from trauma or inflammation. The patient's long-term rugby experience may have played a role in the development of cholesterol granuloma. It is difficult to diagnose a cholesterol granuloma based on preoperative imaging alone, and anatomy often makes preoperative biopsy or cytology difficult.

CONCLUSION

Complete resection and pathological examination may be unavoidable for diagnosis and treatment.

Pan-mediastinal neoplasm diagnosis via nationwide federated learning: a multicentre cohort study

BACKGROUND

Mediastinal neoplasms are typical thoracic diseases with increasing incidence in the general global population and can lead to poor prognosis. In clinical practice, the mediastinum's complex anatomic structures and intertype confusion among different mediastinal neoplasm pathologies severely hinder accurate diagnosis. To solve these difficulties, we organised a multicentre national collaboration on the basis of privacy-secured federated learning and developed CAIMEN, an efficient chest CT-based artificial intelligence (AI) mediastinal neoplasm diagnosis system.

METHODS

In this multicentre cohort study, 7825 mediastinal neoplasm cases and 796 normal controls were collected from 24 centres in China to develop CAIMEN. We further enhanced CAIMEN with several novel algorithms in a multiview, knowledge-transferred, multilevel decision-making pattern. CAIMEN was tested by internal (929 cases at 15 centres), external (1216 cases at five centres and a real-world cohort of 11 162 cases), and human-AI (60 positive cases from four centres and radiologists from 15 institutions) test sets to evaluate its detection, segmentation, and classification performance.

FINDINGS

In the external test experiments, the area under the receiver operating characteristic curve for detecting mediastinal neoplasms of CAIMEN was 0·973 (95% CI 0·969-0·977). In the real-world cohort, CAIMEN detected 13 false-negative cases confirmed by radiologists. The dice score for segmenting mediastinal neoplasms of CAIMEN was 0·765 (0·738-0·792). The mediastinal neoplasm classification top-1 and top-3 accuracy of CAIMEN were 0·523 (0·497-0·554) and 0·799 (0·778-0·822), respectively. In the human-AI test experiments, CAIMEN outperformed clinicians with top-1 and top-3 accuracy of 0·500 (0·383-0·633) and 0·800 (0·700-0·900), respectively. Meanwhile, with assistance from the computer aided diagnosis software based on CAIMEN, the 46 clinicians improved their average top-1 accuracy by 19·1% (0·345-0·411) and top-3 accuracy by 13·0% (0·545-0·616).

INTERPRETATION

For mediastinal neoplasms, CAIMEN can produce high diagnostic accuracy and assist the diagnosis of human experts, showing its potential for clinical practice.

FUNDING

National Key R&D Program of China, National Natural Science Foundation of China, and Beijing Natural Science Foundation.

Thoracic Diseases: Technique and Applications of Dual-Energy CT

Dual-energy computed tomography (DECT) is one of the most promising technological innovations made in the field of imaging in recent years. Thanks to its ability to provide quantitative and reproducible data, and to improve radiologists' confidence, especially in the less experienced, its applications are increasing in number and variety. In thoracic diseases, DECT is able to provide well-known benefits, although many recent articles have sought to investigate new perspectives. This narrative review aims to provide the reader with an overview of the applications and advantages of DECT in thoracic diseases, focusing on the most recent innovations. The research process was conducted on the databases of Pubmed and Cochrane. The article is organized according to the anatomical district: the review will focus on pleural, lung parenchymal, breast, mediastinal, lymph nodes, vascular and skeletal applications of DECT. In conclusion, considering the new potential applications and the evidence reported in the latest papers, DECT is progressively entering the daily practice of radiologists, and by reading this simple narrative review, every radiologist will know the state of the art of DECT in thoracic diseases.

Non-ST-segment elevation myocardial infarction with non-obstructive coronary arteries due to a type-A thymoma: A case report

Introduction

Myocardial infarction with non-obstructive coronary arteries (MINOCA) has become an increasingly recognized subgroup in patients with acute myocardial infarction, with a recent cohort study reporting a prevalence of 8.8%. This report describes a patient who presented with non-ST-segment elevation myocardial infarction (NSTEMI) due to an incidental anterior mediastinal mass.

Case presentation

An 80-year-old woman presented to our emergency department with a chief complaint of progressive shortness of breath associated with retrosternal chest pain for one day duration. Computed tomography (CT) angiogram of the chest was conducted, which revealed an anterior mediastinal mass. Upon admission, the patient developed an acute episode of recurrent severe chest pain, which was diagnosed as an NSTEMI. Emergent cardiac catheterization was performed because of unstable vital signs; however, the results showed no evidence of atherosclerotic changes in the major coronary arteries, compatible with the diagnosis of MINOCA. The mediastinal mass was later confirmed to be a type A thymoma on CT-guided biopsy.

Conclusion

Myocardial infarction in patent coronary arteries due to an anterior mediastinal mass is rare. Further studies are needed to standardize the diagnosis and management protocols for the potential etiologies of MINOCA.

From the archives of MD Anderson Cancer Center Castleman disease involving the thymus gland: Case report and literature review

Castleman disease is a nodal based disease and very rarely involves the thymus gland. We report a 52-year-old man who was found incidentally to have a single thymic mass by computerized tomography scan. Thymectomy was performed, and the gross specimen showed a well-circumscribed, multi-loculated cystic mass. Histologic examination showed thymus involved by Castleman disease, hyaline-vascular variant. The lesion was characterized by lymphoid follicles with wide mantle zones, variably lymphocyte-depleted germinal centers with sclerotic radial blood vessels, and prominent interfollicular/stromal changes including numerous endothelial venules with sclerotic walls and hyaline sclerosis, scattered and frequent dysplastic follicular dendritic cells and foci of dystrophic calcification. Immunohistochemical analysis showed that the follicle mantle zones were composed of numerous B-cells positive for CD20, PAX5, and IgD. Antibodies specific for CD21 and CD23 highlighted prominent follicular dendritic cell networks within follicles. There was no evidence of human herpes virus 8. We searched the literature and could identify only 10 additional cases of thymic CD. Previously reported cases included 8 unicentric and 2 multicentric, classified pathologically as plasma cell variant (n = 4), hyaline vascular variant (n = 3), and mixed (n = 3). Thymectomy, as was done in the currently reported case, most often leads to the diagnosis of Castleman disease and was a mainstay of treatment in other reported cases.

Diagnostic approach for mediastinal masses with radiopathological correlation

PURPOSE

Mediastinal masses have various histopathological and radiological findings. Although lymphoma is the most common type of tumor, thymic epithelial and neurogenic tumors are common in adults and children, respectively, but several other types are difficult to distinguish. No previous review has simply and clearly shown how to differentiate mediastinal masses.

METHOD

We conducted a review of the latest mediastinal classifications and mass differentiation methods, with a focus on neoplastic lesions. Both older and recent studies were searched, and imaging and histopathological findings of mediastinal masses were reviewed. Original simple-to-use differentiation flowcharts are presented.

RESULTS

Assessing localizations and internal characteristics is very important for mediastinal mass differentiation. The mass location and affected organ/tissue should be accurately assessed first, followed by more qualitative diagnosis, and optimization of the treatment strategy. In 2014, the International Thymic Malignancy Interest Group presented a new mediastinal clinical classification. In this classification, mediastinal masses are categorized into three groups according to location: prevascular (anterior)-, visceral (middle)-, and paravertebral (posterior)-compartment masses. Then, the internal characteristics and functional images are evaluated.

CONCLUSIONS

Differentiation of mediastinal masses is very difficult. However, if typical imaging findings and clinical characteristics are combined, reasonable differentiation is possible. In each patient, proper differential diagnosis may contribute to better treatment selection.

SEOM-GECP-GETTHI Clinical Guidelines for the treatment of patients with thymic epithelial tumours (2021)

Thymic epithelial tumours (TET) represent a heterogeneous group of rare malignancies that include thymomas and thymic carcinoma. Treatment of TET is based on the resectability of the tumour. If this is considered achievable upfront, surgical resection is the cornerstone of treatment. Platinum-based chemotherapy is the standard regimen for advanced TET. Due to the rarity of this disease, treatment decisions should be discussed in specific multidisciplinary tumour boards, and there are few prospective clinical studies with new strategies. However, several pathways involved in TET have been explored as potential targets for new therapies in previously treated patients, such as multi-tyrosine kinase inhibitors with antiangiogenic properties and immune checkpoint inhibitors (ICI). One third of patient with thymoma present an autoimmune disorders, increasing the risk of immune-related adverse events and autoimmune flares under ICIs. In these guidelines, we summarize the current evidence for the therapeutic approach in patients with TET and define levels of evidence for these decisions.

Hyperthyroidism secondary to a primary mediastinal goiter with normal functional cervical thyroid gland

Primary mediastinal goiter is extremely uncommon. The majority of primary mediastinal goiters were reported as incidental findings on chest imaging of asymptomatic patients. Symptoms related to compression of adjacent structures or hyperthyroidism were rarely described. Herein we report a case of hyperthyroidism secondary to a primary mediastinal goiter.

CT texture analysis in evaluation of thymic tumors and thymic hyperplasia: correlation with the international thymic malignancy interest group (ITMIG) stage and WHO grade

OBJECTIVES

To evaluate the effectiveness of CT texture analysis (CTTA) in (1) differentiating Thymoma (THY) from thymic hyperplasia (TH) (2) low from high WHO grade, and (3) low from high Masaoka Koga (MK)/International Thymic Malignancy Interest Group (ITMIG) stages.

METHODS

After institute ethical clearance, this cross-sectional study analyzed 26 patients (THY-18, TH-8) who underwent dual energy CT (DECT) and surgery between January 2016 and December 2018. CTTA was performed using TexRad (Feedback Medical Ltd., Cambridge, UK- www.fbkmed.com) by a single observer. Free hand regions of interest (ROIs) were placed over axial sections where there was maximum enhancement and homogeneity. Filtration histogram was used to generate six first-order texture parameters [mean, standard deviation (SD), mean of positive pixels (MPP), entropy, skewness, and kurtosis] at six spatial scaling factors "SSF 0, 2, 3, 4, 5, and 6". Mann-Whitney test was applied among various categories and p value < 0.05 was considered significant. Three-step feature selection was performed to determine the best parameters among each category.

RESULTS

The best performing parameters were (1) THY vs TH- Mean at "SSF 0" (AUC: 0.8889) and MPP at "SSF 0" (AUC: 0.8889), (2) Low vs high WHO grade - no parameter showed statistical significance with good AUC, and (3) Low vs high MK/ITMIG stage- SD at "SSF 6" (AUC: 0.8052 and 0.8333 respectively]).

CONCLUSION

CTTA revealed several parameters with excellent diagnostic performance in differentiating thymoma from thymic hyperplasia and MK/ITMIG high vs low stages. CTTA could potentially serve as a non-invasive tool for this stratification.

ADVANCES IN KNOWLEDGE

This study has employed texture analysis, a novel radiomics method on DECT scans to determine the best performing parameter and their corresponding cut-off values to differentiate among the above-mentioned categories. These new parameters may help add another layer of confidence to non-invasively stratify and prognosticate patients accurately which was only previously possible with a biopsy.

Advancement in Diagnostic Imaging of Thymic Tumors

Thymic tumors are rare neoplasms even if they are the most common primary neoplasm of the anterior mediastinum. In the era of advanced imaging modalities, such as functional MRI, dual-energy CT, perfusion CT and radiomics, it is possible to improve characterization of thymic epithelial tumors and other mediastinal tumors, assessment of tumor invasion into adjacent structures and detection of secondary lymph nodes and metastases. This review aims to illustrate the actual state of the art in diagnostic imaging of thymic lesions, describing imaging findings of thymoma and differential diagnosis.

Case Report: Multidisciplinary Approach for a Rare Case of Thymic Vascular Malformation

We report the rare case of a 2.5 cm in size mass diagnostic for residual thymus associated with venous vascular malformation (ISSVA classification, 2008) in a 58 years old man. Diagnosis was obtained only after surgical removal that was complicated by a sudden massive bleeding (about 1,500 cc) requiring emergency conversion to median sternotomy. Difficulty in preoperative diagnosis, rarity of histologic pattern, and surgical challenges make this case very interesting for surgeons, pathologists and radiologist. Our message, dealing with mediastinal masses, is: (a) differential diagnosis between the more frequent solid antero-superior mediastinal tumors and vascular malformation should be always considered (b) preoperative angiography should always be performed in case of uncertain diagnosis (c) coil embolization should always be considered to reduce potentially fatal bleeding (d) histologic differentiation with other thymic neoplasms must be always considered.

Dual energy CT in gland tumors: a comprehensive narrative review and differential diagnosis

Dual energy CT (DECT)with image acquisition at two different photon X-ray levels allows the characterization of a specific tissue or material/elements, the extrapolation of virtual unenhanced and monoenergetic images, and the quantification of iodine uptake; such special capabilities make the DECT the perfect technique to support oncological imaging for tumor detection and characterization and treatment monitoring, while concurrently reducing the dose of radiation and iodine and improving the metal artifact reduction. Even though its potential in the field of oncology has not been fully explored yet, DECT is already widely used today thanks to the availability of different CT technologies, such as dual-source, single-source rapid-switching, single-source sequential, single-source twin-beam and dual-layer technologies. Moreover DECT technology represents the future of the imaging innovation and it is subject to ongoing development that increase according its clinical potentiality, in particular in the field of oncology. This review points out recent state-of-the-art in DECT applications in gland tumors, with special focus on its potential uses in the field of oncological imaging of endocrine and exocrine glands.

Anterior chest wall non-traumatic diseases: a road map for the radiologist

The anterior chest wall (AWC) non-traumatic pathologies are largely underestimated, and early detection through imaging is becoming increasingly important. This paper aims to review the major non-traumatic ACW pathologies, with a particular interest in imaging features and differential diagnosis.