MR Imaging of Benign and Malignant Pleural Disease

Predictive potential of MRI in differentiating the predominant component in biphasic pleural mesothelioma

PURPOSE

To assess the potential of apparent diffusion coefficient (ADC) values derived from diffusion weighted (DW) MRI preoperatively to predict the predominant histologic component among biphasic pleural mesothelioma (PM) tumors.

METHODS

ADC maps were generated from DW MRI scans. Histology and predominant component of biphasic PM were confirmed following surgical resection. Statistical analyses were done with R (R Foundation for Statistical Computing, Vienna, Austria). Average ADC values corresponding to epithelioid- and sarcomatoid-predominant tumors were compared. ADC thresholding was accomplished by recursive partitioning and confirmed with ROC analysis.

RESULTS

Eighty-four patients with biphasic PM's, 69 (82 %) epithelioid-predominant (BE) and 15(18 %) sarcomatoid-predominant (BS) tumors were evaluated. Thirty-eight (45 %) patients underwent extrapleural pneumonectomy (EPP), 39 (46 %) had extended pleural decortication (ePDC) and 7 (8 %) had pleural decortication (PDC). ADC values ranged between 0.696 x 10-3 to 1.921 x 10-3 mm2/s. BE tumors demonstrated significantly higher ADC values than BS tumors (p = 0.026). ADC values above 0.94 x 10-3 mm2/s were associated with a significant increase of relative risk of being in group BE over group BS (relative risk: 1.47, 95 %CI: 1.05-2.06, p = 0.027) CONCLUSION: Average ADC values of BE tumors were higher than BS tumors and the two groups can be separated by a cut off value of 0.94 X 10-3 mm2/s.

Diffusion-weighted Imaging of the Chest: A Primer for Radiologists

Diffusion-weighted imaging (DWI) is a fundamental sequence not only in neuroimaging but also in oncologic imaging and has emerging applications for MRI evaluation of the chest. DWI can be used in clinical practice to enhance lesion conspicuity, tissue characterization, and treatment response. While the spatial resolution of DWI is in the order of millimeters, changes in diffusion can be measured on the micrometer scale. As such, DWI sequences can provide important functional information to MRI evaluation of the chest but require careful optimization of acquisition parameters, notably selection of b values, application of parallel imaging, fat saturation, and motion correction techniques. Along with assessment of morphologic and other functional features, evaluation of DWI signal attenuation and apparent diffusion coefficient maps can aid in tissue characterization. DWI is a noninvasive noncontrast acquisition with an inherent quantitative nature and excellent reproducibility. The outstanding contrast-to-noise ratio provided by DWI can be used to improve detection of pulmonary, mediastinal, and pleural lesions, to identify the benign nature of complex cysts, to characterize the solid portions of cystic lesions, and to classify chest lesions as benign or malignant. DWI has several advantages over fluorine 18 (18F)-fluorodeoxyglucose PET/CT in the assessment, TNM staging, and treatment monitoring of lung cancer and other thoracic neoplasms with conventional or more recently developed therapies. © RSNA, 2023 Quiz questions for this article are available in the supplemental material. Supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article.

Pleural Neoplasms-What Could MRI Change?

The primary pleural neoplasms constitute around 10% of the pleural tumors. The currently recommended method for their imaging is CT which has been shown to have certain limitations. Strong development of the MRI within the last two decades has provided us with a number of sequences that could potentially be superior to CT when it comes to the pleural malignancies' detection and characterization. This literature review discusses the possible applications of the MRI as a diagnostic tool in patients with pleural neoplasms. Although selected MRI techniques have been shown to have a number of advantages over CT, further research is required in order to confirm the obtained results, broaden our knowledge on the topic, and pinpoint the sequences most optimal for pleural imaging, as well as the best methods for reading and analysis of the obtained data.

New Era for Malignant Pleural Mesothelioma: Updates on Therapeutic Options

Malignant pleural mesothelioma (MPM) is a rare malignancy with few treatment options. Recent advances have led to US Food and Drug Administration approvals and changes in the standard of care with a novel biomedical device approved for use with platinum-pemetrexed, and also for immunotherapy agents to be included as a frontline treatment option in unresectable disease. Although predictive biomarkers for systemic therapy are not currently in use in clinical practice, it is essential to correctly identify the MPM histology to determine an optimal treatment plan. Patients with nonepithelioid MPM may have a greater magnitude of benefit to dual immunotherapy checkpoint inhibitors and this regimen should be preferred in the frontline setting for these patients. However, all patients with MPM can derive benefit from immunotherapy treatments, and these agents should ultimately be used at some point during their treatment journey. There are ongoing studies in the frontline unresectable setting that may further define the frontline therapy space, but a critical area of research will need to focus on the immunotherapy refractory population. This review article will describe the new developments in the areas of biology with genomics and chromothripsis, and also focus on updates in treatment strategies in radiology, surgery, radiation, and medical oncology with cellular therapies. These recent innovations are generating momentum to find better therapies for this disease.

Clinical Implementation of a Free-Breathing, Motion-Robust Dynamic Contrast-Enhanced MRI Protocol to Evaluate Pleural Tumors

OBJECTIVE. The purpose of this study was to develop a motion insensitive clinical dynamic contrast-enhanced MRI (DCE-MRI) protocol to assess the response of pleural tumors in clinical trials. MATERIALS AND METHODS. Thirty-two patients with pleura-based lesions were administered contrast material and imaged with gradient-recalled echo DCE-MRI sequence variants: either a traditional cartesian k-space acquisition (FLASH), a time-resolved imaging with stochastic trajectories acquisition (TWIST), or a radial stack-of-stars acquisition (radial) sequence in addition to other standard-of-care imaging sequences. Each image acquisition's sensitivity to motion was evaluated by comparing the motion of the thoracic border in 3D throughout the acquisition. One-way ANOVA was used to compare the image quality between different acquisitions. The 95% CIs were calculated for mean thoracic border displacement. The effects of motion on kinetic parameter estimation were explored with simulations according to clinically acquired data. RESULTS. Radial was the most motion-robust sequence with subvoxel mean displacement in the superior-inferior direction (0.4 ± 1.2 [SD] mm). FLASH showed intermediate displacement (4.6 ± 2.0 mm), whereas TWIST was most sensitive to motion (6.4 ± 3.4 mm). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the images acquired with the radial sequence were on par or better than the FLASH and TWIST sequences when reconstructed with an improved density compensation algorithm. Simulations showed that motion on scans showing pleural-based lesions can lead to markedly inaccurate kinetic parameter estimation and inappropriate kinetic model convergence within a nested model analysis. CONCLUSION. A practical radial k-space trajectory sequence that provides motion-insensitive pharmacokinetic parameters was incorporated as part of the DCE-MRI protocol of pleural tumors. Validation and usefulness in clinical trials assessing response to therapy is needed.

Interobserver Variability of Quantitative and Qualitative Assessment Using MRI in Malignant Pleural Mesothelioma

PURPOSE

To evaluate the interobserver variability associated with quantitative and qualitative MRI assessments of malignant pleural mesothelioma (MPM).

MATERIALS AND METHODS

Patients with MPM who underwent uniform-protocol preoperative MRI between 2009 and 2014 were included. The MRI-derived tumor volume was estimated. Unidimensional measurements of maximal pleural thickness (P _max) and average pleural thickness (P _avg) on axial MR images; maximal fissural thickness (F _max); maximal diaphragmatic thickness (D _max); and average diaphragmatic thickness (D _avg) on sagittal reconstructed images were acquired. Interobserver agreement regarding the American Joint Committee on Cancer (AJCC) tumor stage at each criterion level was assessed by using Cohen κ statistics. Agreement between quantitative measurements was assessed by using Bland-Altman plots and intraclass correlation coefficients (ICCs).

RESULTS

The study cohort included 349 patients (median age, 68 years [age range, 30-90 years), 273 (78%) of whom were men and 203 (58%) of whom had epithelioid-subtype tumors. Qualitative assessment performed by using the AJCC staging criteria (eighth edition) was concordant in 31% of cases and yielded considerable disagreement (κ = 0.177). Inspection of the Bland-Altman plots led to decisive agreement between the two reviewers regarding MRI-derived tumor volume (ICC, 0.979). There was also a good degree of agreement between the two reviewers regarding unidimensional measurements of D _max (ICC, 0.807), D _avg (ICC, 0.823), P _max (ICC, 0.787), P _avg (ICC, 0.787), and F _max (ICC, 0.659).

CONCLUSION

Quantitative assessment can enhance the clinical staging of MPM. Compared with qualitative assessment, quantitative assessment has low interobserver variability and could yield a tumor size criterion that is currently lacking in the AJCC clinical staging of MPM.Supplemental material is available for this article.© RSNA, 2020.

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.

Radiologic Considerations and Standardization of Malignant Pleural Mesothelioma Imaging Within Clinical Trials: Consensus Statement from the NCI Thoracic Malignancy Steering Committee - International Association for the Study of Lung Cancer - Mesothelioma Applied Research Foundation Clinical Trials Planning Meeting

Detailed guidelines pertaining to radiological assessment of malignant pleural mesothelioma are currently lacking due to the rarity of the disease, complex morphology, propensity to invade multiple planes simultaneously, and lack of specific recommendations within the radiology community about assessment, reporting, and follow-up. In March 2017, a multidisciplinary meeting of mesothelioma experts was co-sponsored by the National Cancer Institute Thoracic Malignancy Steering Committee, International Association for the Study of Lung Cancer, and the Mesothelioma Applied Research Foundation. One of the outcomes of this conference was the foundation of detailed, multidisciplinary consensus imaging and management guidelines. Here, we present the recommendations for radiologic assessment of malignant pleural mesothelioma in the setting of clinical trial enrollment. We discuss optimization of imaging parameters across modalities, standardized reporting, and response assessment within clinical trials.

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.

Volumetric assessment in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a highly malignant pleural neoplasm with a dismal prognosis. Multimodality approach including surgery and chemotherapy are utilized to treat patients with resectable disease. Clinical staging allows for selection of patients for treatment strategies, but has not been found to be prognostic and is plagued by high interobserver variability. Tumor volume measurement on cross-sectional imaging has emerged as a potential quantitative tool with prognostic significance. This review focuses on volumetric assessment from cross-sectional imaging (CT, MRI, ¹⁸F-FDG PET/CT) and the potential prognostic benefit and applications.

Novel MR Imaging Applications for Pleural evaluation

Computed tomography is the first-line modality for evaluation of chest diseases primarily because of its spatial resolution. Magnetic resonance (MR) imaging is used as a problem-solving tool to answer key questions that are vital to optimal patient management. MR has the potential to provide qualitative, quantitative, anatomic, and functional information without the use of ionizing radiation or nephrotoxic contrast administration. With new advances in proton MR techniques, MR imaging can overcome some of the inherent problems associated with imaging the lung. This article describes novel MR applications for evaluation of the pleura and pleural diseases.

Response evaluation in mesothelioma: Beyond RECIST

Malignant pleural mesothelioma (MPM) typically demonstrates a non-spherical growth pattern, so it is often difficult to accurately categorize change in tumour burden using size-based tumour response criteria (e.g., WHO (World Health Organisation), RECIST (Response Evaluation Criteria in Solid Tumours) and modified RECIST). Functional imaging techniques are applied to derive quantitative measurements of tumours, which reflect particular aspects of the tumour pathophysiology. By quantifying how these measurements change with treatment, it is possible to observe treatment effects. In this review, we survey the existing roles of CT and MRI for the management of MPM, including the currently applied size measurement criteria for the assessment of treatment response. New functional imaging techniques, such as positron emission tomography (PET), diffusion-weighted MRI (DWI) and dynamic contrast-enhanced MRI (DCE-MRI) that may potentially improve the assessment of treatment response will be highlighted and discussed.

Imaging of mesothelioma

Malignant pleural mesothelioma (MPM) is an asbestos-related neoplasm that originates in pleural mesothelial cells and progresses locally along the pleura until it encases the lungs and mediastinum, ultimately causing death. Imaging plays a crucial role in diagnosis and optimal management. Computed tomography (CT) continues to be the primary and initial imaging modality. Magnetic resonance imaging (MRI) complements CT scan and is superior in determining chest wall and diaphragmatic invasion. FDG18-PET/CT provides anatamo-metabolic information and is superior to both CT and MRI in overall staging and monitoring response to therapy. This chapter will detail the imaging finding of MPM and role of imaging in guiding management.