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Benign mesothelioma is a tumor that originates in the mesothelium, but is benign rather than malignant. A malignant tumor has the ability to metastasize or spread and attack other tissues and organs. A benign tumor may grow larger, but will not spread to other tissues. Benign, or noncancerous, mesothelioma is very rare. The vast majority of cases of tumors arising from mesothelial tissues are malignant.

Diagnosing this type of mesothelioma is similar to malignant tumors, but it is during the biopsy examination that a doctor should be able to see that cells are benign not malignant. Treatment is straightforward, usually involving surgery to remove the tumor, and prognosis for this condition is generally very good.

Malignant vs. Benign Mesothelioma

The main difference between these two types of tumors is that malignant mesothelioma has the potential to spread to other tissues while a benign tumor does not. Mesothelioma is rare as a type of cancer, but benign tumors of the mesothelium is even rarer. Another difference is that malignant mesothelioma is strongly connected to asbestos exposure, while the benign form seems to be totally unrelated.

There are several subtypes of each kind of mesothelioma. Benign tumors can come in a few different forms including benign tumors of the pleura, benign multicystic peritoneal mesothelioma, and papillary mesothelioma. Of these, the benign tumors in the pleura are most common. The peritoneal form is rare, with only about 150 cases ever reported, and papillary mesothelioma has only been reported about 60 times.

Benign Fibrous Pleural Mesothelioma

The most common of these rare benign mesotheliomas is the type that forms in the pleura, the lining of the lungs. About 500 cases of this were reported by 2004. Most cases of these tumors first grow in the visceral layer of the pleura, which is the inner layer that surrounds the lungs. Benign pleural tumors can range from small to large, are typically smooth, may have fluid-filled cysts, and are often partially calcified. The cell type in this kind of tumor may be one of three types: fibrous, cellular, and mixed, or a combination of fibrous and cellular.

Benign Multicystic Peritoneal Mesothelioma

Even rarer among benign mesotheliomas is the type that originates I the peritoneum, the epithelium that lines abdominal organs. It is most common in women of reproductive age, although it can occur in anyone at any age. Benign peritoneal mesothelioma is usually multicystic; these tumors contain multiple, fluid-filled cysts.

Well-Differentiated Papillary Mesothelioma

Very few cases of well-differentiated papillary mesothelioma have ever been diagnosed and reported. They are mostly benign tumors, but sometimes have malignant cells as well. They are more common in women between the ages of 30 and 40 and are most likely to arise in the peritoneum. In a few cases this type of tumor has developed in the pericardium, the lining around the heart. Papillary mesothelioma tumors are characterized by papillary structures, which can be seen under the microscope.

Adenomatoid Tumors

These are tumors of the glands, often seen in the testis or uterus. They are often classified as benign mesotheliomas because they originate in the mesothelium around a gland. It is possible for this type of tumor to become malignant, but most often they are benign and can be found in the pleura or peritoneum as well as in the testis and uterus.

Complications

Although benign tumors are not cancerous and do not spread to other tissues, they can cause problems. The problems usually arise as these tumors grow larger. Benign pleural tumors, for instance, can cause some of the same symptoms as malignant pleural mesothelioma: tightness in the chest, shortness of breath, chest pains, and pleural effusion, or the buildup of fluid between the two layers of the pleura. If the tumor grows even larger it can ultimately cause more serious complications including seizures and coma.

Benign mesothelial tumors of the peritoneum or pericardium may cause similar complications. Usually this happens when the tumor has grown large enough to cause fluid buildup, which may result in pain or discomfort. In many cases of peritoneal or pericardial benign tumors, there are no symptoms. The tumor may be found coincidentally if the patient is being screened for something else.

Diagnosis

Diagnosis for benign mesotheliomas may be accidental if no symptoms are apparent, but in some cases the tumor grows large enough to cause discomfort. Diagnosis begins with a physical exam and then continues with imaging scans. These scans may show that there is an unusual mass or lesion, which is expected to be a tumor.

The next step is to determine if that mass is a benign or malignant tumor, whether it is a mesothelioma, and what cell types are involved. A biopsied sample of the tumor can be investigated under the microscope by a pathologist who may be able to determine if the cells are in fact benign, if they seem to be of a papillary type, or if they are adenomatoid.

This histological approach is not always accurate, but immunohistochemical staining can improve that accuracy. This technique uses antibodies to target specific antigens in tumor cells. It can rule out or find cancerous cells with good accuracy.

Treatment

If there are no symptoms and a benign mesothelial tumor is not very large, no treatment may be necessary. If it is growing larger and causing discomfort, treatment is usually surgery to remove the mass. Most of these are straightforward surgeries with modest recovery times. In some cases of benign pleural mesothelioma, depending on the size and placement of the tumor, a segment of a lung or an entire lobe may need to be removed, which means more recovery time and a greater possibility of complications.

Prognosis

The prognosis for benign mesotheliomas is overwhelmingly positive. There are risks with any type of surgery, but in most cases the surgical removal of one of these tumors is curative. A few patients may experience a recurrence, but this is often years later and with a tumor that is still benign. Survival rates of benign mesothelioma are near 100 percent.

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