Pigmented spindle cell carcinoid tumour of the thymus with ectopic adrenocorticotropic hormone secretion: report of a rare variant and differential diagnosis of mediastinal spindle cell neoplasms

Pigmented spindle cell carcinoid tumour of the thymus with ectopic adrenocorticotropic hormone secretion: report of a rare variant and differential diagnosis of mediastinal spindle cell neoplasmsAims : A variety of histological variants of thymic carcinoid tumour have been described. A rare case of pigmented spindle cell carcinoid tumour of the thymus is documented and compared with the reported cases of thymic pigmented carcinoid tumour in the literature, with a discussion of the differential diagnosis of spindle cell tumours of the mediastinum. Methods and results : A thymic tumour with ectopic adrenocorticotropic hormone (ACTH) secretion was resected from a 24‐year‐old man suffering from Cushing's syndrome. Histological, immunohistochemical, and ultrastructural studies revealed an ACTH‐producing spindle cell carcinoid tumour harbouring pigmented melanocytes. Among four thymic pigmented carcinoid tumours reported before, only one was similar to the present case by being also an ACTH‐secreting pigmented spindle cell thymic carcinoid tumour. The clinicopathological features of this tumour distinguish it from a spindle cell thymoma, spindle cell thymic carcinoma, and other mediastinal spindle cell tumours. Conclusions : This case illustrates an extremely rare variant of thymic carcinoid tumour exhibiting a spindle cell morphology and harbouring pigmented melanocytes. Awareness of this histological variant is important in the differential diagnosis of spindle cell tumours of the mediastinum.