대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Atypical carcinoid

Radiologic Findings

Fig. 1-3. On CT images of 8 years ago, a 1.9 cm enhancing ovoid nodule is in the left anterior mediastinum at the aortic arch level.
Fig. 4. On chest X-ray of 5 years ago, the left anterior mediastinal mass is not seen.
Fig5-8. Current. Chest X-ray and CT images show a 9.8 cm enhancing mass in the left anterior mediastinum. The mass has multiple non-enhancing portions. On the superior medial side of the mass, there are hypertrophied adjacent and intra-tumoral vessels. The mass compresses the inferior portion of left innominate vein. There is no definite adjacent structure invasion.


Thymus, total thymectomy, Neuroendocrine tumor, grade 2, (Atypical carcinoid)
partially capsulated and focally invasive; slightly increased mitotic activity: about 5 mitotic counts/50 HPFs; no necrosis present, multifocal hemorrhage, and cystic change; clear but abutting resection margin

Brief Review

Thymic neuroendocrine neoplasms account for 2-5% of all thymic neoplasms and only 0.4% of all neuroendocrine neoplasms. All thymic neuroendocrine neoplasms share a propensity for recurrence, lymph node or distant metastasis, and tumor-associated death, with increasing risk from low-grade to high-grade tumors. (typical carcinoids-> atypical carcinoids->large cell neuroendocrine carcinomasmall cell carcinoma)
Carcinoid/neuroendocrine tumor (NET) of the thymus is a neuroendocrine epithelial neoplasm of thymic origin with low-grade nuclear features; typical carcinoid (TC) has < 2 mitoses/2 mm2 and lacks of necrosis, whereas atypical carcinoid (AC) has 2-10 mitoses/2mm2 and/or foci of necrosis.
About 50% of patients present with chest pain, cough, dyspnea, or superior vena cava syndrome. Paraneoplastic manifestations due to hormone production include Cushing syndrome (17-30% of adult and > 50% of childhood carcinoids), with or without cutaneous hyperpigmentation; hypercalcemia/hypophosphataemia due to production of PTHrP or from primary hyperparathyroidism in the context of multiple endocrine neoplasia type 1 (MEN1); acromegaly; and inappropriate production of antidiuretic hormone or atrial natriuretic peptide. Carcinoid syndrome is exceedingly rare (<1%).
The clinical presentation of ACs is indistinguishable from that of TCs and includes the same paraneoplastic manifestations. About 40-50% of patients already have mediastinal, cervical, or supraclavicular lymph node metastasis at presentation. Invasion into adjacent organs (40-50%) or pleural or pericardial cavity (10%) is common. Sites of distant metastasis include lung, brain, lumbar spine, bone, liver, kidney, adrenals, skin, and soft tissues. Late recurrence occurring as late as 9 years after resection has been reported.
The average age at presentation for patients with typical carcinoids is 49 years, with marked male predominance. MEN1-associated thymic neuroendocrine neoplasms have all been carcinoids and occurred almost exclusively in adult men (age range: 31-66 years; mean: 44 years).
In the thymus, ACs are far more common than TCs, and they occur in a slightly older age group. They usually occur in adults, with an average patient age of 48-55 years (range: 18-82 years), but they have also been rarely observed in children. There is a strong male predominance, with the M:F ratio ranging from 2:1 to 7:1.
About 25% of patients with thymic carcinoids have a family history of MEN1. Conversely, among MEN 1 patients, thymic carcinoids occur in 8% of cases. In MEN1, smoking has been reported to be a risk factor in males but not in females.
There are few published data on the prognosis of thymic carcinoids. The available data suggest that the clinical course of TCs is similar to that of ACs. Reported 5-year overall survival rates of ACs vary in published series, from 20-70% up to 80%, with a median survival time of 59 months.
Surgery and postoperative radiotherapy improve the outcome. Published 5-year survival rates are in the range of 50-70%, with a median survival time of 126 months.
Thymic NET in comparison to lung: Smoking is not a risk factor for the development of pulmonary and thymic TCs and ACs. Thymic TC and AC show a strong male predominance, whereas pulmonary carcinoids occur more often in females. AC and LCNEC (large cell neuroendocrine carcinoma) are by far the most frequent subtypes in the thymus, whereas TC and SmCC (small cell carcinoma) prevail in the lung. Most patients with pulmonary LCNEC and SmCC are heavy smokers, whereas there is no established role of smoking in the development of any NET type in the thymus. Molecular findings indicate that thymic and pulmonary carcinoids are different at the molecular level, while thymic and pulmonary LCNEC and SmCCs appear to be more similar.
Radiographs typically demonstrate an anterior mediastinal mass. Multidetector CT findings range from a well-defined nodule to an ill-defined unencapsulated mass of 2–20 cm with internal necrotic and hemorrhagic foci. Lesions typically enhance heterogeneously with contrast and may demonstrate punctate and dystrophic calcification. However, differentiating thymic carcinoids and other thymic tumors on cross-sectional imaging is difficult, and reported case series are typically small.
In a study of CT images of eleven cases of atypical carcinoid tumor, authors suggest that marginal cystic/necrotic component (9/11) and hypervascular signs (5/11) (multiple vessels in the solid components of the tumors in the arterial phase) can be helpful for the diagnosis.

References

Neuroendocrine tumors, p391-394 In: Thoracic Tumours. 5th ed. WHO classification of tumours series. 5. WHO Classification of Tumours Editorial Board. International Agency for Research on Cancer, Lyon, France 2021

Mandegaran R, David S, Screaton N. Cardiothoracic manifestations of neuroendocrine tumours. Br J Radiol 2016; 89: 20150787.

Kan, Xiaojing MD*; Wang, Pengming MD*; Gong, Zhiquan MD†; Gao, Feifei MD*; Zhang, Yuxia MD*; Ge, Yinghui MD, PhD*. Investigation on Computed Tomography Features of Primary Thymic Atypical Carcinoid Tumors. Journal of Computer Assisted Tomography 41(6):p 990-994, 11/12 2017. | DOI: 10.1097/RCT.0000000000000615

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