Malignant Pleural Mesothelioma CT Imaging: How to Measure It Correctly?

Abstract

Background: Malignant pleural mesothelioma is the most common primary tumor of the pleura. The unique growth pattern of malignant pleural mesothelioma makes it difficult to apply the Response Evaluation Criteria for Solid Tumors (RECIST). Hence the need to use modified RECIST (mRECIST) criteria, as they better fit the unique growth pattern of malignant pleural mesothelioma. The thickness of the tumor perpendicular to the chest wall or mediastinum is measured at 2 points at 3 separate levels at least 1 cm apart on chest CT scans, and summed to obtain a one-dimensional pleural measurement. The same criterion has also been used to assess response to treatment. RECIST 1.1 represents a further update, taking into account new concepts such as revised minimum dimensions for lymph nodes and an approach to lesions that become non-measurable. Based on experience and published literature, the hypothesis of merging the 2 above-mentioned criteria in mRECIST 1.1 for mesothelioma and the use of iRECIST for the application to immune-based therapies (iRECIST) was considered. Purpose: Support the importance of studying pleural mesothelioma in a reliable and reproducible way, through a scrupulous methodology, applying the mRECIST1.1 and iRECIST criteria. Conclusions: Adoption of a standardized study metodology can make the study of PM reproducible and correct.

Keywords: RECIST criteria; computed tomography; malignant pleural mesothelioma.

Figure 1.

Example of measurement of detectable lesions obtained by measuring the thickness of the tumor perpendicular to the chest wall. Pleural tumor thickness was measured at 2 different locations on each of 3 levels selected for unidimensionally measurable lesions (a, b, and c). Subsequently, a total measurement was calculated by adding the 6 measurements, thus obtaining the sum of the pleural crust (d).

Figure 2.

Example of malignant pleural mesothelioma studied with multidetector CT images in 3 planes with high spatial resolution (slice thickness of approximately 1-2 mm in the axial plane (a) and 2-3 mm in the sagittal and coronal planes (b and c).

Figure 3.

Example of measurements of pleural mesothelioma, present in sites consistent with clinical relevance, up to a maximum of 6 in no more than 3 sections at least 1 cm apart, preferably above the left atrium (a) and below the aortic arch (b and c) to try to standardize reproducibility.

Figure 4.

Example of advanced disease characterized by left circumferential pleural thickening, ipsilateral lung volume loss and “crusted” infiltration of the lung parenchyma (a) and chest wall infiltration (*) (b).

Figure 5.

Example of extrathoracic extension of the disease, with hepatic invasion (*) (a), peritoneal carcinomatosis (*) (b), and brain metastases (*) (c).

Figure 6.

Mediastinal (a), para-aortic (b), and laterocervical (c) lymph node involvement, with short axis of 10 mm or more, considered pathological.