Affected patients are typically in the fourth or fifth decades of life. There is a recognised male predominance with M:F ratios around 3:1 2,7.
The majority of patients present with symptoms related to mass effect or invasion of mediastinal and other thoracic structures 7. Carcinoid syndrome is uncommon 1,4.
Up to 50% of affected patients have hormonal abnormalities 2. Approximately 40% of patients have Cushing syndrome as a result of adrenocorticotropic hormone secretion by the tumour; these patients tend to have smaller lesions at the time of diagnosis since they present early with signs of corticosteroid excess. Up to 30% of patients with have advanced-stage disease at presentation 6.
Neuroendocrine tumours of the thymus are rare and believed to arise from thymic cells of neural crest origin (Kulchitsky cells).
Thymic carcinoid tumours are similar to lesions arising within the bronchi, ranges in differentiation and behavior from typical carcinoid to atypical carcinoid to small cell carcinoma 1,3.
Approximately 50% of thymic carcinoids are functionally active 6-7.
They generally tend to be large masses at presenation that range in size from 6-20 cm.
- non-functioning thymic carcinoids may be seen in association with multiple endocrine neoplasia syndrome type 1 2,6
Radiologically, these tumours typically manifest as large masses with a propensity for local invasion. Focal areas of necrosis and punctate calcification may be present 2,5.
On CT or MRI the masses are usually of heterogeneous attenuation or signal intensity, respectively.
The FDG uptake of carcinoid tumours on CT-PET is variable, with a tendency for the uptake to be low.
On cross sectional imaging thymic carcinoids may be indistinguishable from a thymomas 6. However, increased uptake has been reported to correlate with aggressive behaviour such as local invasion and distant metastases 2.
In-111–diethylenetriaminepentaacetic acid (DTPA)-D-Phe1]-octreotide
- accumulates in thymic carcinoids but is not specific as it also accumulated in thymomas and metastatic thymic tumours 7
Treatment and prognosis
They are generally thought to carry a poor prognosis due to high rates of recurrence and metastases. Follow up after resection (if resectable) if often recommended 10.
History and etymology
They are thought have been initially described by Rosai and Higa in 1972 as a distinct entity from thymomas 11.
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