[Paraneoplastic Cushing's syndrome. Pseudotumors of the thymus occurring after correction of hypercorticism. 3 cases].

Ectopic ACTH-secreting tumours responsible for paraneoplastic Cushing's syndrome are invisible at radiography in about 50 percent of the cases. In this situation, the current attitude is to correct the hypercorticism and then embark on a regular morphological monitoring in search of the initial tumour with the purpose of removing it. We report the cases of 3 patients who had a paraneoplastic Cushing's syndrome of unknown origin in 1 case and consecutive, in 2 cases, to a bronchial carcinoid tumour initially occult and discovered 30 and 42 months respectively after the onset of the disease. Six to 10 months after hypercorticism was cured with ketoconazole and bilateral adrenalectomy, a thymic mass 2 to 5 cm in length was detected by computerized tomography or magnetic resonance imaging in all 3 patients. At resection of the thymus, performed in 2 cases, a benign hyperplasia of this organ with negative immunohistostaining for ACTH was discovered. This abnormality, seldom reported, seems to result from the abrupt cessation of hypercorticism. It must be known to avoid an unnecessary thymectomy during supervision of patients with paraneoplastic Cushing's syndrome related to a radiologically occult tumour.