C51-38 A Case of Superior Vena Cava Syndrome in a Patient With Follicular Thyroid Cancer

Introduction Superior vena cava (SVC) syndrome arises from SVC obstruction due to thrombosis or external compression. Most cases (60-80%) are caused by thoracic malignancies such as lung cancer or lymphoma. We report a rare case of SVC syndrome in a young woman caused by a large, noninvasive follicular thyroid carcinoma. Case Presentation A 22-year-old woman with scoliosis presented with orthopnea and progressive enlargement of neck and left breast veins. CT of the neck and thorax demonstrated a large substernal thyroid gland compressing the left brachiocephalic vein, along with significant narrowing of the SVC, consistent with SVC syndrome (Figures 1-2). The thyroid mass also caused moderate tracheal compression and deviation (Figure 3). Fine-needle aspiration was nondiagnostic. Total thyroidectomy confirmed an 8.5-cm follicular thyroid carcinoma (pT3a, Nx) with negative margins and no invasion. Postoperative imaging showed normalization of SVC caliber. She was started on calcium and levothyroxine (100 mcg daily) for TSH suppression.At two months, TSH was 9.1 IU/mL and thyroglobulin 2.9 ng/mL, suggesting residual tissue. Radioiodine therapy was deferred due to uncertain localization. TSH suppression with surveillance was continued. Subsequent scans showed mild I-131 uptake at the surgical bed. At six months, thyroglobulin declined to 1.7 ng/mL, and the patient remained asymptomatic under routine follow-up. Discussion Surgery in SVC syndrome carries risks of hemorrhage, nerve injury, and hypoparathyroidism. Despite mild thyroglobulin elevation and I-131 uptake, negative margins and noninvasive pathology justified conservative management. Standard therapy includes surgery with selective radioiodine and TSH suppression, but prolonged suppression risks atrial fibrillation and osteoporosis. Unlike invasive tumors requiring radical resection, noninvasive, margin-negative cases may be safely managed with TSH suppression and close follow-up. Conclusion This case illustrates follicular thyroid carcinoma as a rare cause of SVC syndrome in a young, low-risk patient. Conservative management with TSH suppression achieved biochemical and clinical stability, avoiding morbidity from additional interventions.