1.WELL DIFFERENTIATED PAPILLARY MESOTHELIOMA:

2.LOCALIZED MALIGNANT MESOTHELIOMA:

3.MULTICYSTIC MESOTHELIOMA:

4.ADENOMATOID TUMOUR

WELL DIFFERENTIATED PAPILLARY MESOTHELIOMA:

Well-differentiated papillary mesothelioma (WDPM) is  considered  a specific clinico-pathologic entity distinct from conventional diffuse malignant mesothelioma.

The majority of cases have been reported in the peritoneum in women of reproductive age with no history of asbestos exposure and also in the tunica vaginalis of men. Cases have also been reported in the pleura.

WDPM is often discovered incidentally during abdominal or pelvic surgery.

The tumour has an indolent clinical course and with a good prognosis. Occasional cases are more aggressive and require long term clinical follow-up.

Macroscopic features:  Multiple grey white nodules usually less than 20mm in diameter.

Microscopic features:

Well defined stout papillary structures with myxoid cores, lined by bland, flattened, single layer of cuboidal or columnar mesothelial cells. Subnuclear vacuolation may be noted. Mitotic figures are rarely present. In some cases there may be limited invasion of the submesothelial layer. Deep invasion is usually not seen.

Differential diagnosis:

Reactive mesothelial hyperplasia (assocciated with inflammation) ;

Serous neoplasia of peritoneum ( cellular stratification, atypia and mitotic figures) ;

Primary and seconday adenocarcinoma (mucin histochemistry and immunohistochemistry are useful ) ;

Diffuse mesothelioma with a prominent tubulopapillary epithelial component (diffuse growth pattern & cytological atypia).

LOCALIZED MALIGNANT MESOTHELIOMA:

Localized malignant mesotheliomas are uncommon, sharply circumscribed tumours of the serosal membranes with the microscopic appearance of diffuse malignant mesothelioma but without any evidence of diffuse spread.  This lesion should not be confused with localized fibrous tumours as localized malignant mesothelioma has a more aggressive clinical behaviour.

MULTICYSTIC MESOTHELIOMA:

Multicystic mesothelioma is a rare form of mesothelioma. It is an extremely rare benign neoplastic disease with high tendency to recur locally, but no tendency to malignancy.

There is often history of previous surgery, pelvic inflammatory disease or endometriosis. The lesion is not associated with asbestos exposure.

Macroscopic features: Single or multiple thin-walled cysts.

Microscopic features: Cysts are multilocular thin-walled and lined by single layer of cuboidal mesothelial cells.

Differential diagnosis: Diffuse malignant mesothelioma with a cystic/angiomatoid component( multicystic mesothelioma is localized in nature) and cystic lymphangioma.

Correct diagnosis of multicystic mesothelioma can be made with histopathologic examination and always with immunohistochemical and ultrastructural evaluation.