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ACTH secreting neuroendocrine tumor arising from thymus with brachiocephalic vein infiltration

Aim/Introduction: Neuroendocrine tumors (NETs) arising from the thymus with brachiocephalic vein infltration are exceedingly rare and have been reported in only a handful of patients. Thymic NETs (TNETs) are more aggressive than NETs of other origin and are found to be malignant in 82% of cases. Patients with TNETs can present with symptoms related to compression of mediastinal structures, endocrinopathy and distant metastases. Infltration of adjacent vascular structures is seen in advanced disease, usually of superior vena cava, while brachiocephalic vein infltration is extremely rare. CASE PRESENTATION:A 49-year-old male patient was referred for evaluation of Cushing Syndrome (CS) in September 2018. Clinically he appeared cushingoid and presented with fatigue, abdominal weight gain and skin darkening. Laboratory fndings indicated ectopic CS. Conventional radiologic imaging and total body 18F-fuorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) showed sclerotic bone lesions in several vertebrae suggestive of bone metastases, as well as brachiocephalic vein thrombosis. Towards localization of the source of ACTH secretion, somatostatin receptor scintigraphy using 99mTc- EDDA/HYNIC-Tyr3- octreotide was performed, but showed only physiologic uptake. To characterize bone lesions, CT-guided bone biopsy of the L5 was performed and immunohistology indicated neuroendocrine tumor metastases with tumor cells showing partial ACTH expression and Ki-67 proliferation index of 20%. Furthermore, bilateral adrenalectomy was performed in order to control hypercortisolemia, but only normal adrenal tissue was found. Patient underwent several cycles of chemotherapy and palliative irradiation of the spine over the course of 3 years since the diagnosis of progressive metastatic NET while primary tumor site still remained occult. During follow-up in October 2021, still with unknown primary, Ga-68 DOTATATE PET/CT was performed unveiling a somatostatin receptor positive 2.2 cm tumor infltrate in the left brachiocephalic vein with direct spreading from the thymus that could be the primary tumor site and the source of ectopic ACTH secretion. Because of disease progression surgical resection is contraindicated and systemic chemotherapy is continued. Materials and Methods: / Results: / Conclusion: Thymic NETs with brachiocephalic vein infltration are exceedingly rare and aggressive malignant tumors that have been reported in only a few cases. Due to similar clinical and radiological presentation they can be mistaken for venous thrombosis.With this case we would like to point out the important role of Ga-68 DOTATATE PET/CT in diagnosis of this rare neuroendocrine tumor.

Ga68 DOTATATE, PET/CT, neuroendocrine tumor

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