Malignant Pleural Mesothelioma: Evaluation with CT


Malignant Pleural Mesothelioma: Evaluation with CT

Malignant pleural mesothelioma (MPM) is an uncommon neoplasm that arises from the pleura or, rarely, the pericardium or peritoneum. There are approximately 2,000–3,000 new cases diagnosed in the United States every year, the majority of which are associated with prior asbestos exposure (1). Patients frequently present with dyspnea, chest pain, cough, and weight loss. The tumor can invade both visceral and parietal pleura and frequently extends to adjacent structures. The prognosis is poor, with a median survival time of 12 months after diagnosis (2). Several factors have been shown to correlate with reduced survival time: intrathoracic lymph node metastases, distant metastatic disease, and extensive pleural involvement (3).

Various modalities have been used in the treatment of MPM. Radiation therapy alone is gener-ally used for palliation (4). Patients who undergo chemotherapy with a platinum- or doxorubicin-containing regimen have shown limited response without significant change in survival time (5). Aggressive surgical resection (extrapleural pneumonectomy or radical pleurectomy-decortication) used alone has also yielded disappointing results, with a median survival time of less than 1 year (6,7). However, multimodality therapy consisting of surgery followed by chemotherapy and radiation therapy has been shown to prolong survival. Sugarbaker et al (8) studied 183 patients who had undergone extrapleural pneumonectomy followed by adjuvant chemotherapy and radiation therapy and found a median survival time of 19 months at the most recent follow-up. More recently, Lee et al (9) showed a median survival time of 18.1 months for patients who had undergone radical pleurectomy-decortication with aggressive radiation therapy with or without chemotherapy. Proper patient selection is crucial in identifying those most likely to benefit from an aggressive multimodality regimen. Imaging studies, including computed tomography (CT), magnetic resonance (MR) imaging, and positron emission tomography (PET), play an essential role in the staging of disease in patients who are potential surgical candidates.

In this article, we discuss and illustrate the staging and diagnostic evaluation of MPM with CT, MR imaging, and PET.

StagingSection:
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The new staging system from the International Mesothelioma Interest Group is a TNM (tumor-node-metastasis) system that was initially developed to categorize like cases into homogeneous prognostic groups to aid in evaluating new treatment options (Tables 1–3) (3,10). This staging system emphasizes criteria used to determine the extent of local tumor and lymph node involvement, both of which factors have been shown to be related to the overall survival rate in MPM (3,11). With locally advanced tumors, it is important to distinguish between T3 (potentially resectable) and T4 (technically unresectable) disease. This distinction guides the choice of treatment options and implies significant differences in survival. The presence of N3 nodal disease or distant metastasis also precludes surgery. Although surgical staging is often required in patients with potentially resectable lesions, CT, MR imaging, and PET can aid in choosing whether to treat MPM surgically, medically, or both.

CT is usually the primary imaging modality used for disease staging in patients who are being considered for resection. CT is readily available and provides a significant amount of anatomic information. The results can be used to preclude surgery in patients with obviously unresectable tumors (eg, diffuse extension of tumor into the chest wall, mediastinum, or peritoneum or distant metastasis). MR imaging or PET can then be used as the final preoperative radiologic examination to complement CT, particularly in questionable cases. MR imaging with use of different pulse sequences and gadolinium-based contrast material can improve the detection of tumor extension, especially to the chest wall and diaphragm. PET is useful for the detection of nodal involvement and occult metastasis. Correlation of all imaging findings is essential in directing exploration to areas of possible invasion and selecting those patients who may benefit from aggressive therapy.

Diagnostic EvaluationSection:
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Computed Tomography
CT is the primary imaging modality used for the evaluation of MPM. Key CT findings that suggest MPM include unilateral pleural effusion (Fig 1), nodular pleural thickening (Figs 2–4), and interlobar fissure thickening (Fig 5). Growth typically leads to tumoral encasement of the lung with a rindlike appearance (Fig 3). Calcified pleural plaques are found at CT in approximately 20% of patients with MPM and may become engulfed by the pri-mary tumor, causing the tumor to mimic calcified MPM (Fig 6) (12). There is also frequent contraction of the affected hemithorax with associated ipsilateral mediastinal shift, narrowed intercostal spaces.