Diagnosis: Carcinoid tumor of the thymus with extensive recent ischemic necrosis. Satellite tumor (probable lymph node metastasis).
Comment: Although focal
necrosis is a common features of thymic carcinoid tumors, extensive
infarction has not been described. Furthermore, necrosis was absent
in the satellite tumor. It is probable that the infarction of the
tumor resulted from vasoconstriction associated with smoking crack
cocaine several hours before the chest pain developed.
Thymic Carcinoid Tumors
Classification: Thymic carcinoid tumors are rare tumors that most closely resemble well-differentiated neuroendocrine carcinomas (atypical carcinoid tumors) of the lung in their histologic appearance and behavior. In the thymus, they have a category of their own separate from thymic carcinoma, which includes small cell neuroendocrine carcinoma (table). It has been argued by some that carcinoid tumors should also be classified as a type of thymic carcinoma for the following reasons .
Table: Tumors of the Thymus 
Well-differentiated squamous carcinoma
Well-differentiated mucoepidermoid carcinoma
Small cell neuroendocrine carcinoma
Other: Adenocarcinoma, undifferentiated, sarcomatoid, and clear cell types
Germ cell tumors
Clinical features: Patients with thymic carcinoid tumors may present with symptoms related to compression of normal structures, or tumors may be found incidentally on chest radiographs (see table). The average age is 48.3 y, and the ratio of men to women is 4.3 to 1. About 10% of patients have Cushing's syndrome, and a similar fraction have a multiple endocrine neoplasia syndrome. Weight loss or the superior vena caval syndrome may be present. Other rare manifestations include Eaton-Lambert syndrome, the syndrome of inappropriate production of antidiuretic hormone, and hypertrophic osteoarthropathy . An incidental thymic carcinoid tumor was described in a man with a thymoma that was associated with myasthenia gravis . The carcinoid syndrome has not been described.
Differential diagnosis includes tumors of the thyroid or ectopic thyroid tissue, parathyroid tumors, paragangliomas, metastatic tumors, thymolipoma, soft tissue tumors, germ cell tumors, and the thymic tumors listed above. Carcinoid tumors metastatic to the thymus from another site are usually not occult, but search for an extrathymic primary site should be done before diagnosing a thymic carcinoid tumor .
Gross features: Tumors do not have a capsule and the cut surface is homogeneous rather than lobulated, as is characteristic of thymomas. The cut surfaces are usually firm and grey. Focal necrosis and hemorrhage are common .
Histologic features: Several variants include a usual form and diffuse, spindled, desmoplastic (fibrotic), and mucinous types, as well as a variant resembling medullary carcinoma of the thyroid . A proliferation of pigmented thymic melanocytes darkened the gross appearance of one tumor .
Immunohistochemistry: Tumors react with antibodies to cytokeratin and chromogranin A, as well as other neuroendocrine markers including synaptophysin and Leu-7. Additionally, tumors may show reactivity for ACTH, serotonin, calcitonin, gastrin, cholecystokinin, or somatostatin, even if there is no clinical evidence of their presence. Parathyroid tumors can be distinguished by their staining with antibody to parathormone. Paragangliomas express neuroendocrine markers but do not react with cytokeratin. Lymphomas will show reactivity with leukocyte common antigen, and germ cell tumors will react with placental alkaline phosphatase .
Electron microscopy: Just as carcinoid tumors of the lung, thymic carcinoid tumors have neurosecretory granules. These range in size from 100 to 400 nm .
Treatment and outcome: Surgical excision is the preferred method of treatment with postoperative radiation and/or chemotherapy for tumors that cannot be removed completely [9,10]. Response to chemotherapy or radiation alone is poor. Embolic metastases occur in up to 3/4 of patients. Metastatic sites include mediastinal lymph nodes, but distant metastases (bone, liver, skin) occur in 30-40% of cases . Five-year survival for cases without an associated endocrinopathy was about 70% and for those with an endocrinopathy was 35% in one report . A more recent report indicated an overall survival of 31% at 5 years; all 14 patients were dead of disease by 109 months . Late recurrence after 8 years has been reported .
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Copyright 1998 by Martha L. Warnock. All rights reserved.
Last revised 9/30/00
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