대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Thymic neuroendocrine tumor (typical carcinoid)

Radiologic Findings

Fig 1. Chest PA shows suspicious nodular lesion in aortic arch.
Fig 2-4. CT scans reveal a well-defined ovoid mass in anterior mediastinal mass with abutting to aortic arch and heterogeneous enhancement (average 40 HU). No evidence of parenchymal abnormality in the lung.
Fig 5. This lesion is measured about 3.1 X 5.1 cm in diameter on coronal image.

Brief Review

Thymic carcinoid tumors are uncommon neoplasms originating from the thymus, derived from the foregut. In 2015, the World Health Organization (WHO) categorized thymic carcinoid tumors into four distinct groups. These include typical and atypical carcinoids, characterized by well-differentiated neoplasms, and small-cell and large-cell carcinoid tumors, distinguished by poorly differentiated neoplasms. Mediastinal carcinoid tumors are exceedingly rare malignancies with aggressive behavior and a poor prognosis. The etiology lacks conclusive evidence, but there is a higher incidence of thymic carcinoid in multiple endocrine neoplasia (MEN-1) patients with heavy smoker. Thymic NETs have links to paraneoplastic syndromes like Cushing’s syndrome and hyperparathyroidism. There is no evidence of paraneoplastic syndrome in this patient.
Most cases emerge in adults around 54 years old, with a notable male predilection (3:1 ratio). These malignancies often remain undetected until reaching advanced stages. CT findings of thymic NETs include a large, heterogeneous, lobulated, and frequently invasive anterior mediastinal mass with areas of hemorrhage or necrosis. Similar to other NETs, thymic NETs exhibit an overexpression of somatostatin receptors. Consequently, the use of radiolabeled somatostatin analogs like gallium Ga-68 DOTATOC (OctreoScan) aids in distinguishing thymic NETs from other anterior mediastinal malignancies.
Official guidelines for thymic neuroendocrine tumors are currently lacking. The preferred therapy is a complete surgical resection, if possible, similar to other thymic carcinoma in anterior mediastinum. Due to their large size and invasion, most thymic NETs are considered unresectable at the time of diagnosis. The role of neoadjuvant chemotherapy or radiation therapy (RT) remains unclear, primarily based on case reports.

References

1. Filosso PL, Ruffini E, Solidoro P, Roffinella M, Lausi PO, Lyberis P, Oliaro A, Guerrera F. Neuroendocrine tumors of the thymus. J Thorac Dis. 2017 Nov;9(Suppl 15):S1484-S1490.
2. Chaer R, Massad MG, Evans A, Snow NJ, Geha AS. Primary neuroendocrine tumors of the thymus. Ann Thorac Surg. 2002 Nov;74(5):1733-40

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