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.
OBJECTIVE
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.


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.
Kuo
T-t
TT
Department of Pathology, Chang Gung University School of Medicine and Chang Gung Memorial Hospital, Kwei San, Tao Yuan, Taiwan. ttkuo@adm.cgmh.org.tw
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000328:Adult; D014408:Biomarkers, Tumor / Q000378:metabolism; D002276:Carcinoid Tumor / Q000150:complications / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D002277:Carcinoma / Q000473:pathology; D003480:Cushing Syndrome / Q000150:complications / Q000473:pathology; D003937:Diagnosis, Differential; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008544:Melanocytes / Q000378:metabolism / Q000473:pathology; D012509:Sarcoma / Q000473:pathology; D022142:Secretory Vesicles / Q000648:ultrastructure; D013945:Thymoma / Q000473:pathology; D013953:Thymus Neoplasms / Q000150:complications / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D014057:Tomography, X-Ray Computed
D014408:Biomarkers, Tumor; D000324:Adrenocorticotropic Hormone