Extensive lymph node metastases found by (18)F-FDG-PET/CT in a patient with diffuse sclerosing variant of papillary thyroid carcinoma.

To the Editor: The diffuse sclerosing variant of papillary thyroid carcinoma (DSPTC) is a relatively rare histologic subtype of papillary thyroid carcinoma (PTC). It was first described in 1985 [1] and accounts for 2%-10% of all PTC [2-5]. The major clinical features of DSPTC include: younger age at presentation, larger tumor size, greater incidence of cervical lymph node involvement, distant metastases (up to 25% lung metastases), and more frequent presence of high level serum antithyroglobulin antibody (TgAb) [6-8]. To date, few cases of DSPTC were reported in the literature [9]. Our case of DSPTC had extensive lymph node metastases including cervical, axillary, mediastinal and hilar lymph nodes found by 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT). A 44 years old man with thyroid carcinoma underwent total thyroidectomy with modified neck dissection. Surgical pathology revealed a 3.0Χ2.0Χ1.5cm PTC with diffuse sclerosing variants and 65 metastatic lymph nodes involvement. He was treated with oral administration of 3700MBq of iodine-131 (131I) for ablation of remnant thyroid tissue, one month after surgery and with 5550MBq of 131I for detection and treatment of potential metastatic disease, five months later. Iodine-131 whole-body scan (131I-WBS) demonstrated no evidence for residual active thyroid tissue or metastatic disease after two courses of 131I treatment (Fig. 1). Serum TgAb was higher than 4000IU/mL and thyroglobulin (Tg) was undetectable. The patient was suspected for high risk of metastatic disease and a 18F-FDG-PET/CT examination was performed, which showed extensive lymph node metastases (including cervical, axillary, mediastinal and hilar lymph nodes) and a single left lung metastasis (Fig. 2, 3). To identify the axillary lesions, ultrasound-guided transthoracic biopsy was performed and pathohistology features were consistent with metastatic DSPTC. Histopathology showed