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MR Imaging of Benign and Malignant Pleural Disease

Thursday, June 26, 2008

Source: Magnetic Resonance Imaging Clinics of North America

Radiological imaging technologies are among the most important tools available for the diagnosis of mesothelioma and other forms of cancer, as they can render the status and structure of the interior landscape of a patient’s body without the need for invasive, exploratory surgery. Since the original discovery of x-ray technology in 1895, a number of elaborations on imaging technology have taken place and contemporary medicine regularly utilizes the following imaging modalities for cancer diagnosis in general and mesothelioma diagnosis in particular: x-ray, computed axial tomography (CAT or CT scanning), magnetic resonance imaging (MRI) and positron emission tomography (PET). Each technology has its own individual strengths and weaknesses and its own appropriate use in the diagnosis of disease.

Research into the efficacy of these technologies for the diagnosis of pleural mesothelioma and peritoneal mesothelioma is regularly being conducted, as improvements in a physician’s ability to diagnose mesothelioma can often mean the difference between an early-stage diagnosis and a late-stage one. When these technologies are compared as a group, x-ray generally represents the first technology used for a diagnosis of chest-related issues and then CT is used to investigate whatever is found on the chest x-ray. CT is much more sensitive than is x-ray to tissue structures and represents the first level at which abnormalities in the pleural surfaces can actually be visualized. CT is considered the standard diagnostic tool for mesothelioma and is used in multiple ways in the management of the disease. However, CT does have limitations in its ability to resolve fine tissue structures, so MRI can be used post-CT to confirm CT findings and/or to answer questions that CT is unable to answer.

The extent to which MRI should be used in the diagnosis of mesothelioma is a particularly active area of investigation and physicians from Boston’s Brigham and Women’s Hospital have recently added to the literature on the subject with an article summarizing the use of MRI for pleural imaging in general and for mesothelioma in particular.

Introduction

The pleura are thin, finely-structured tissues that are difficult to visualize in the absence of disease. The parietal pleura lines the chest wall, while the visceral pleura encases the lungs. Each surface is separated by a small area, known as the pleural space, where a lubricating fluid is secreted into. This fluid allows the lungs to more easily expand and contract and move around the restricted space in which it lives. Taken together, the pleural space and the individual tissues have a combined thickness of only .2–.4 mm, which means that technologies attempting to image these areas must demonstrate high enough resolution to provide adequte detail of the pleural structures if the scans are to serve a diagnostic function. Traditional x-ray does not have sufficient resolution for this purpose, but CT and MRI have both demonstrated great utility for the diagnosis of pleural mesothelioma, as well as other diseases and disorders of the pleural cavity.

CT and MRI work according to different underlying technologies, but they share a common goal of providing doctors with important information about the interior structures of certain parts of the body. CT is the standard modality employed as a first-line tool for the diagnosis of mesothelioma, while MRI often represents the next step in the management workflow. The principal difference between the quality of the images generated by each technology revolves around contrast—specifically, soft tissue contrast. For this purpose, MRI is a markedly superior technology. Both technologies can visualize the basic structure of the body’s interior surfaces, but MRI’s better contrast makes it more effective for diagnosing the differences between and within tissue structures, as well as for visualizing the extent to which these structures have been infiltrated by pleural mesothleioma.

Overview of the Article

The article describes the use of MRI and CT for imaging a number of disorders within the pleural cavity, from pleural effusions to pleural mesothelioma, and it makes a number of recommendations regarding the role that each technology plays within this framework. The authors state that both technologies can be used to image pleural plaques, which are localized, abnormal patches of tissue commonly associated with asbestos exposure, as well as benign and malignant cases of diffuse pleural thickening. In fact, they specifically note that CT and MRI provide similar information in most cases, but MRI’s superior soft tissue contrast means that it can be used as an elaboration of whatever findings are first demonstrated on CT:

MR Imaging is useful to confirm and characterize CT findings, particularly diffuse pleural thickening, pleural effusion, and involvement of adjacent spaces.
(MR Imaging of Benign and Malignant Pleural Disease, p. 335)

The authors also note that MRI’s enhanced contrast makes it especially important for surgical planning.

The article closes with a brief discussion of the use of integrated CT/PET for mesothelioma diagnosis. While certain studies have shown great value in this recent innovation, especially in its ability to visualize distant metastases and occult disease, the authors remained concerned with PET’s ability to finely render specific body structures, which is a clear concern for visualizing the pleura and the other tissues involved with mesothelioma.

The authors conclude their article by asserting CT’s primary role in the medical management of pleural diseases; but they follow this with an explicit affirmation of the importance that MRI plays in the diagnosis, staging and treatment of pleural mesothelioma.

Labels: mesothelioma

posted by Belluck & Fox at 4:11 PM
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