Mesothelioma – Fibrous and Malignant Mesothelioma

Mesothelioma

Mesothelioma (carcinosarcoma, malignant epithelioma, coelomic cancer, coelothelioma, sarcomatous endothelioma, carcinomatous endothelioma, endothelioma) is rare; it can be localized in the pleura, peritoneum, pericardium, as well as in the testicle and in the area of ​​the fallopian tubes (adenomatoid). There are benign and malignant variants of mesothelioma. The first includes the so-called adenomatous tumor of the genital organs, as well as fibrous mesothelioma. All other types of mesotheliomas are malignant.

Fibrous mesothelioma

Fibrous mesothelioma is a slowly growing, clearly demarcated node in the visceral pleura, dense, layered on the cut. Microscopically, it has the structure of a fibroma rich in cells. Only in tissue culture is it possible to prove the mesothelial origin of tumor cells.

Malignant mesothelioma

Malignant mesothelioma occurs in the pleura, peritoneum, and pericardium. Macroscopically, the tumor has the form of a dense infiltrate causing a sharp thickening. Less commonly, mainly in the abdominal cavity, where the omentum is mainly affected, the tumor may have the form of a loosely delimited node or several merging nodes, sometimes with a villous surface.

Metastases to regional lymph nodes are typical. The tumor often grows into the underlying organ with the formation of small nodules and strands of tumor tissue. When a large tumor node is formed in the organ, the assumption always arises of metastatic lesion of the serous membrane.

Serous membranes are represented by complex connective tissue membranes, their surface is lined with one layer of mesothelial cells located on the basement membrane.

Microscopically

Microscopically, the most common form is epithelioid mesothelioma with a predominantly tubular or papillary structure. The tumor resembles adenocarcinoma or hemangioendothelioma. The similarity with the latter is aggravated by the frequent presence of giant cells among the tubule lining. Lymorphic-giant cell variants, which are characterized by solid accumulations of tumor cells prone to phagocytosis, are also described.

papillary variant

In the papillary variant, the outgrowths are built from a cellular-fibrous base with vessels, covered with polymorphic cubic or tall prismatic cells with an admixture of giant ones. The lining of the tumor papillae sloughs off, often with the release of entire sheets of cells. The same papillae can cover the walls of cysts formed in the thickness of the tumor, apparently, as a manifestation of morphogenetic potencies. In this case, the tumor resembles a papillary cystadenoma with a well-developed fibrous stroma. In the papillary variant, tumor cells also filter the connective tissue structures of the serous membrane with the formation of tubules or trabeculae. In addition to the tubular and papillary variants, areas of sarcomatous, perithelial, and angiomatous structures are described. All this creates a significant polymorphism of the tumor structure.

Differentiating mesothelioma

Differentiating mesothelioma from adenocarcinoma on the basis of a single microscopic examination is difficult, dagnosis should be based primarily on the exclusion of a primary tumor in the lung, stomach, gallbladder, etc. »Sarcoma, etc., which is not characteristic of cancerous tumors.

benign cystic mesothelioma

In recent years, the so-called benign cystic mesothelioma has been identified as a variety , which is localized more often in the peritoneum of the small pelvis, less often in the greater omentum and is distinguished by an abundance of cysts with papillary outgrowths on their walls. Tumor nodes can reach 10-12 cm in diameter. The tumor can recur, which allows some authors to regard it as borderline.