Inclusions of benign tissues in lymph nodes are most often aberrant glandular tissue, including endosalpingiosis, the thyroid, parotid, breast, and pancreas. Nonglandular inclusions are rare and include nevus cells and decidua. Mesothelial cells in lymph nodes are exceedingly rare; only eight cases have been reported in mediastinal lymph nodes and three cases in abdominal lymph nodes. The incidence of benign mesothelial cells in mediastinal lymph nodes in patients with a history of pericarditis or pleuritis is reported in this study. A retrospective search showed eight cases with removal of mediastinal lymph nodes in the absence of neoplasm. Hematoxylin and eosin-stained sections were examined in all cases. Immunohistochemical stains for CAM 5.2 were performed in all cases, and stains for AE1/AE3, Ber-EP4, carcinoembryonic antigen, Leu-M1, B72.3, and S-100 were performed in one case. CAM 5.2-positive cells with features of mesothelial cells were present in five of eight cases. In all cases, the cells were present in nodal sinuses and appeared as single cells or small clusters. The cells were missed on routine hematoxylin and eosin sections in all cases but one, in which they were numerous and mimicked metastatic carcinoma. Malignancy was not found in any of the cases preoperatively, at the time of surgery, or during the follow-up period. Benign mesothelial cells may embolize to regional lymph nodes in pleuritis or pericarditis. In most cases, these cells are few and undetectable on routine sections. Rarely, hyperplastic mesothelial cells may be present and must be distinguished from metastatic carcinoma, mesothelioma, and melanoma.
Germ cell tumors of the mediastinum can be divided into three categories: 1) mature teratomas which have all elements at a mature level; 2) immature teratomas which are similar to the mature teratomas, but also contain immature epithelial or mesenchymal elements or blastema; and 3) embryonal tumors which contains elements which are recognized as dysgerminoma, embryonal carcinoma with or without yolk sac elements, and choriocarcinoma. Immature teratomas are the rarest type, accounting for only about 1% of mediastinal teratomas. Two cases of immature teratoma of the mediastinum occurring in infants are reported. One tumor was completely excised. The child is well without evidence of disease two years later. The other immature teratoma was unresectable. Biopsy showed it to be similar to the teratoma that was excised. No postoperative treatment was given. The tumor has not changed appreciably in size, but the child has grown normally for six years so that the tumor mass, which initially filled his chest, is now evidenced as mediastinal widening. A review of the reported cases of immature teratomas in the mediastinum shows that the prognostic value of the histologic appearance of these tumors has not been developed to the same degree as it has for teratomas in the ovary or the sacrococcygeal region. The immature teratomas that occur in infants behave as mass lesions as do the mature teratomas. Immature teratomas in the mediastinum of children in their late teens and in young adults behave as highly malignant tumors similar to the embryonal carcinomas.
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