Primary mediastinal ectopic thyroid in a 43-year-old woman

Rationale: Primary mediastinal ectopic thyroid (PMET) is exceedingly rare, and its imaging features often overlap with those of thymic epithelial tumors, lymphoma, Castleman disease, and paraganglioma. The absence of anatomical continuity with the cervical thyroid and the presence of an independent intrathoracic blood supply are important considerations in differential diagnosis and surgical planning. This report aims to highlight the diagnostic value of thyroid-like enhancement and the absence of cervical continuity and to demonstrate how preoperative computed tomography angiography (CTA)-based vascular mapping can guide selection of the surgical approach and intraoperative vascular control in PMET. Patient concerns: An asymptomatic 43-year-old woman was admitted after routine chest computed tomography (CT) revealed an anterior mediastinal mass. Physical examination showed no palpable cervical mass or thyromegaly, and thyroid function was normal. Diagnoses: Contrast-enhanced CT demonstrated an irregular soft-tissue lesion measuring approximately 49 × 37 × 56 mm, with heterogeneous density, scattered calcifications, and non-enhancing hypodense areas. The mass showed intense but heterogeneous enhancement and lacked anatomical continuity with the cervical thyroid. CTA revealed abundant vascularity, with multiple tortuous small-caliber vessels coursing over the tumor surface adjacent to the left innominate vein. Intraoperatively, no continuity with the cervical thyroid was observed. Histopathological examination confirmed benign ectopic thyroid tissue. Interventions: Based on the vascular anatomy and tumor location, median sternotomy was performed. The tumor, together with part of the adjacent thymus, was completely resected after sequential clipping and division of the feeding vessels using titanium clips and ultrasonic shears. Outcomes: The postoperative course was uneventful. At approximately 11 months after surgery, follow-up chest CT showed no evidence of recurrence, thyroid function remained normal, and cervical ultrasonography revealed no suspicious abnormalities. Lessons: PMET should be considered in the differential diagnosis of hypervascular anterior mediastinal masses, particularly when imaging demonstrates thyroid-like enhancement without anatomical continuity with the cervical thyroid. Preoperative CTA can delineate tumor vascularity and its relationship with adjacent mediastinal vessels, thereby facilitating selection of the surgical approach and planned vascular control. Complete excision is generally associated with a favorable outcome, although continued postoperative surveillance remains appropriate.