Abstract
The invasive encapsulated follicular variant of papillary thyroid carcinoma (IEFVPTC) is a subtype of papillary thyroid carcinoma (PTC) that is often clinically misdiagnosed as a benign lesion. This case report describes a case of IEFVPTC with lung metastasis, highlighting its pathological features and treatment process to enhance understanding of this disease. A female patient discovered to have a thyroid nodule during a routine physical examination sought evaluation and treatment at our hospital. Fine-needle aspiration of the left thyroid lobe and left cervical lymph node confirmed a diagnosis of the macrofollicular variant of IEFVPTC. Computed Tomography (CT) scans indicated pulmonary metastasis, and the patient underwent tumor excision followed by three courses of radioiodine-131 (I-131) therapy. After treatment, no new lymph node metastases were detected, and both the size and lung metastatic lesions significantly decreased. When thyroid lesions present as nodular hyperplasia, characterized by predominantly large follicles or macrofollicular structures rich in colloid, papillary proliferation of the follicular epithelium and cytological features such as ground-glass nuclei and nuclear grooves, one suspects the possibility of IEFVPTC. Clinical assessment, ultrasound examination, and immunohistochemical staining are often combined to aid in diagnosis, reducing the likelihood of missed cases of IEFVPTC.