Computed Tomography Correlated with Histology of Mesothelioma

Mesothelioma is a rare malignancy of the mesothelium, which is the thin serosal membrane that covers most of the internal organs of the body.  Mesothelioma is associated with exposure to asbestos, either occupationally, environmentally or second hand.  Malignant pleural mesothelioma, which affects the lining of the lungs, is the most common and accounts for 50 – 60 % of all mesotheliomas, followed by peritoneal (abdominal) and pericardial (heart).    Most rare is mesothelioma that affects the tunica vaginalis testis in males or tunica serosa uteri in females.  In the United States alone, approximately 2,500 to 3,000 cases of mesothelioma re diagnosed each year. 

Diagnosis of mesothelioma is complicated because of a long latency period and challenges in correlating presenting symptoms with accurate identification.    There are limited therapeutic options, especially since mesothelioma is often not diagnosed until it has reached advanced stages.  Prognosis is usually less than a year from time of diagnosis.

Computed tomography (CT) scans are one method used to identify mesothelioma.  A study from the University of British Columbia, Canada, reviewed and correlated CT imaging findings of malignant pleural mesothelioma with histological subtypes.  Prognosis of mesothelioma is strongly related to histological type, and therefore being able to identify this would help in guiding treatment and calculating survival times accurately.

There are three histological types of mesothelioma:

• Epithelial - composed of epithelial cells, which may be arranged in a particular pattern, hold different shapes, with cell cytology relatively monotonous
• Sarcomatous - resemble sarcomas, most commonly taking the form of malignant fibrous histiocytoma
• Mixed - biphasic, or a combination of epithelial and sarcomatous, showing any combination of patterns of the two forms

Identifying histological subtype by CT scan would help identify which patients would be best selected for surgery and determine therapeutic intervention options.  Although controversy exists over treatment of mesothelioma, most centers are more likely to operate with the epithelial histological subtypes of mesothelioma due to a better prognosis rate.  Mixed types have the next best prognosis, with sarcomatous having the worst. 

The aim of the BC study was to compare CT scan results with histology to guide treatment preoperatively.  In this study, researchers observed a higher incidence of bilateral disease and spontaneous pneumothorax than previously reported.  They also found that more patients had internal mammary, retropleural and cardiophrenic adenopathy which could be used for identify patients most suitable for surgery.  Epithelial mesothelioma was clearly associated with large pleural effusions, while CT findings of ipsilateral volume loss indicated sarcomatous or mixed subtypes. 

Accurate and early diagnosis is vitally important, however this study also showed that CT findings combined with identifying histological subtype can be utilized in deciding which are the best treatment options, whether surgery is recommended, and more accurately determining prognosis.