Peritonel Mesothelioma

Malignant peritoneal mesothelioma (MPM) is a rare aggressive tumor of the peritoneum, regarded as a universally fatal disease. It is poorly described and the knowledge of its natural history is very limited. The incidence has increased in the past 2 decades.In the United States, the overall prevalence is 1-2 cases per million, with an estimated incidence of 200-400 new cases annually. It was exceedingly rare until 1930, when industry increased the use of asbestos, which is the principal risk factor for the disease. It can occur in any age group, although the 50- to 69-year age group is the most affected: only an estimated 2% to 5% of all cases present in the first 2 decades of life. It is more common in men, possibly because of the higher male occupational exposure to asbestos. The main risk factor is asbestos exposure, primarily the crocidolite variety, although some tumors have arisen in ports of prior radiation, or after thorium, talc, erionite or mica exposure, as well as in patients affected by familial Mediterranean fever and diffuse lymphocytic lymphoma. Only 50% of patients with a peritoneal origin of MPM have a history of asbestos exposure.This association increases to 80% in mesotheliomas with the more common pleural origin. Only 20% to 33% of all mesotheliomas arise from the peritoneum itself; the pleura is the most common site of origin.A reported association with simian virus (SV) 40 remains controversial.  The median survival range is from 5 to 12 months in untreated cases with little improvement seen in patients receiving multimodality therapy.

Peritoneal Symptoms

Peritoneal mesothelioma is diagnosed in advanced stages in most cases, and it often takes considerable time to arrive at the correct diagnosis, as the mean symptoms-to-diagnosis time reported is 122 days. The most frequently reported initial symptoms are abdominal pain (35%), abdominal swelling (31%), anorexia, marked weight loss, and ascites; less frequently night sweats and hypercoagulability. Clinical presentation with fever of unknown origin, intestinal obstruction, or surgical emergency (due to acute inflammatory lesions) have been reported. In particular, compression of the gastrointestinal tract can complicate the disease, but it is rarely the presenting symptom. Occasionally the diagnosis has been made incidentally during laparoscopy. Paraneoplastic syndromes associated with mesothelioma, and in particular with peritoneal mesothelioma, are thrombocytosis, hypoglycemia, venous thrombosis, paraneoplastic hepatopathy, and a wasting syndrome.

Diagnosis

The clinical and radiologic presentation of mesotheliomas is nonspecific. History can be very elusive because the most frequent symptom at presentation is abdominal pain. Routine laboratory tests are not useful in making the diagnosis, and abdominal radiographs will show signs such as abdominal distension. Potentially useful serum markers for diagnosis and follow-up are the serum mesothelin-related protein (SMRP), which is elevated in more than 84% of mesotheliomas, and has a 60% sensitivity at diagnosis; CA-125, CA 15-3, hyaluronic acid, and osteopontin are other potential markers.

Computed tomography (CT) findings of peritoneal mesothelioma are nonspecific and not sufficient to establish a diagnosis; however, CT is useful for the detection, characterization, staging, and guiding biopsy of peritoneal masses. At CT, MPM appears as solid, heterogeneous, enhancing soft-tissue masses. Its growth pattern is expansive more than infiltrating. There are 3 types of CT appearances described. 'Dry-painful' type is the most common, in which CT shows 1 large mass or multiple small peritoneal masses in 1 abdominal quadrant, with no signs of ascites. The 'wet' type is associated with intestinal distension and ascites, widespread small nodules and plaques, and no solid masses. Finally, there is the 'mixed' type. Few data have been published about the sonographic and magnetic resonance imaging manifestations of peritoneal mesothelioma. A precise diagnosis based on imaging findings alone is not possible. Furthermore, distinguishing a benign from a malignant process as well as a primary from a metastatic process is also challenging. Therefore, the definitive diagnosis of peritoneal mesothelioma depends on histologic and immunohistochemical examination.

Cytologic analysis of ascites has a low diagnostic potential, due to high cytologic diversity of tumor cells and to small number of malignant cells within the fluid. When there is no effusion, sampling by fine-needle aspiration of the tumour can be used to reach a diagnosis. Immunohistochemistry uses some cytological markers: calretinin and Wilms' tumor 1 antigen (WT1) are used to determine whether the tissue is mesothelial; epithelial membrane antigen (EMA) is used to determine whether the tissue is malignant. In experienced hands, the diagnosis of malignant peritoneal mesothelioma can be made in approximately 80% of cases with an adequate cytologic sample of the tumor.When cytologic findings are inconclusive or ascitic fluid is absent, tumor biopsy is more likely to yield a diagnosis. Immunohistochemical expression of tumor markers is not homogeneous within the same solid tumor section, so diagnostic accuracy increases with core sample size.