The most common clinical presentation of mesothelioma is diffuse malignant pleural mesothelioma, where the mesothelioma cells arise in the parietal or visceral pleura and then spread through the pleural surfaces. This form of the disease is seen in 70% or 80% of all cases and is often characterized by the aggressive spread of the malignancy to tissue structures adjacent to the pleura, such as the lungs and diaphragm. However, there are a number of other forms of the disease as well. Alternative forms typically arise among different origin sites, with peritoneal mesothelioma the next most common form of the disease after pleural mesothelioma. Even when the disease arises from these different origin sites, it’s normal behaviour pattern is described as a diffuse disorder where the cancerous cells spread throughout large surface areas. In very rare cases though, individuals may present with a localized version of the disease, where the histological analysis of the tumor cells reveals mesothelioma, but the presentation is characterized by a single, solitary tumor instead of a large malignancy. These cases rank among the rarest of all forms of mesothelioma and articles that describe these single presentations are often the only way that knowledge of these variants can be shared among physicians.

The newest case of localized mesotehlioma to appear in the literature was recently published in the journal Surgery Today. In the article, the authors describe the presentation, treatment and response to treatment of a patient who presented in their institution with very rare case of localized pericardial mesothelioma.

Overview of the Case

The authors report on a 52 year-old man admitted to their institution to discover the cause of an unexplained shadow on a chest x-ray that was incidentally found by the patient’s dentist during a dental examination. After receiving a follow-up chest radiograph, a contrast-enhanced CT disclosed the cause of the shadow: a middle mediastinal tumor, approximately 43 x 36mm in size. Further examination revealed a localized tumor, without evidence of metastasis or local spread, nor pleural or peritoneal effusion. The man then underwent surgery and the tumor was resected with surgical margins from the pericardium.

The tumor was then examined microscopically and histologically. Microscopic analysis revealed the presence of “large atypical epithelial tumor cells” that were “admixed with dense lymphoplasmahistiocytic infiltrates.” Histological examination revealed that the tumor cells were positive for calretinin, thrombomodulin and CAM5.2, which are part of the panel used in mesothelioma diagnoses, while negative for carcinoembryonic antigen (CEA) and LeuM1, which are common markers for adenocarcinoma. Based on these findings, the authors diagnosed the man with localized epithelial lymphohistiocytoid pericardial mesothelioma.

The tumor returned a year later and the follow-up thoracotomy also revealed a localized tumor, but in this case, the tumor had invaded the aorta and the superior vena cava. Because the tumor could not be resected, a bypass of the superior vena cava was performed instead and, pursuant to the patient’s request, he was treated solely with radiotherapy. Follow-up at 27 months from diagnosis revealed significant lung metastases. The patient attempted an alternative therapy, but this was not successful and he finally died three years after his initial thoracotomy.

Discussion

In this article, the authors describe a very rare presentation of mesothelioma. As we said above, the most common presentation of mesothelioma is diffuse malignant pleural mesothelioma, which accounts for 70% to 80% of all diagnoses. When pleural mesothelioma is not the case, peritoneal mesothelioma is the next most common diagnosis, with pericardial mesothelioma and mesothelioma of the tunica vaginalis considered very rare presentations. In the few cases of localized mesothelioma that have been described, most of them arise form the pleura. The authors note that localized forms of pericardial mesothelioma have only been described in five other cases, making their patient the sixth person in which this variant has been seen and described.

Due to their extreme rarity, localized mesotheliomas are easily misdiagnosed as different malignant developments than what they actually are. In these cases, immunohistochemical analysis is probably the best way to return a definitive diagnosis. Localized forms of the disease also seem to have a better prognosis than do the typical forms of the disease, but that conclusion could be based more on the small number of cases that have been reported on than on any actual prognostic differences between the various behavior patterns involved.

The authors also state that their patient’s presentation was quite rare for another reason as well: lymphohistiocytoid mesothelioma is a proposed term for a variant of sarcomatoid mesothelioma that has only been identified in 10 other cases besides the present case.

Conclusion

Mesothelioma remains a difficult to understand disease. Even as more is being learned about its most common forms, it continues to evade effective treatment. When it comes to management of the disease’s rarest forms, physicians must deploy whatever treatments are available, or what their patients request, because so little is known about them. Journal articles remain the primary way in which knowledge of these rare forms can be shared.

Labels: mesothelioma, pericardialmesothelioma