Surgical Management of Poorly Differentiated Thyroid Carcinoma Extending Into the Superior Vena Cava: A Case Report

Poorly differentiated thyroid carcinoma (PDTC) is a rare histological type with a poorer prognosis than well-differentiated thyroid carcinoma. Herein, we report a case of a tumor extending from the left thyroid lobe into the superior vena cava (SVC), which was successfully resected in a joint operation with cardiovascular surgeons. A 75-year-old man was referred to our department after a left thyroid lobe tumor was incidentally found on a CT scan. Contrast-enhanced CT revealed that the entire left thyroid lobe was replaced by a tumor, which extended through the left inferior thyroid vein and brachiocephalic vein into the SVC. Bilateral cervical lymph node metastases and multiple pulmonary metastases were also observed. A needle biopsy led to a suspected diagnosis of PDTC. Total thyroidectomy, bilateral neck dissection, and resection of the tumor in the SVC via thoracotomy were performed. The patient had an uneventful recovery and was discharged on postoperative day 9. The histopathological diagnosis of the surgical specimen confirmed PDTC. Postoperatively, radioactive iodine (RAI) therapy was considered, but it was not administered due to the absence of iodine uptake. Instead, treatment with lenvatinib was initiated. With lenvatinib treatment, the multiple pulmonary metastases have shown regression, and no recurrence has been observed locally, in the cervical lymph nodes, or in the SVC. PDTC is rare, and only one other case report of PDTC extending into the SVC has been published. This case suggests that even for a tumor thrombus from poorly differentiated carcinoma, surgical resection can be a viable option if imaging studies show no evidence of invasion into the vessel wall.