Thyroid cancer is the most common endocrine malignancy. It is estimated that 96% of all new endocrine organ cancers will originate from the thyroid gland, resulting in approximately 63,000 new cases in 2014 in the US1. Among them, papillary thyroid cancer (PTC) is the most common subtype of thyroid cancer, accounting for more than 90% of all thyroid cancers. The incidence of PTC has been increasing in recent years, largely because of advances in early detection with ultrasonography and fine-needle aspiration biopsy1-4. The most effective treatment for PTC is the complete removal of the primary tumor and the metastatic regional lymph nodes, which is a prerequisite for other adjuvant therapies. Cervical lymph node metastases are quite common in PTC and have been reported to occur in 12-81% of patients with PTC5. The most common site of PTC nodal metastases is the central neck, which has a reported rate of lymph node metastases as high as 50%\~70%5. Lymph node metastases in this area are difficult to identify preoperatively because the lymph nodes typically do not appear abnormal on preoperative imaging6,7.

Routine dissection of the central neck compartment is still controversial due to uncertain prognostic value of preserving clinically non-apparent lymph node metastasis1,8, central neck dissection has important value to ensure accurate clinical staging and surgical planning. According to previously published data, prophylactic central dissection has been suggested to improve disease-specific survival and to decrease local recurrence9,10 as well as post-treatment thyroglobulin levels9,11. Neck dissection also informs postoperative treatment, follow-up programs, assessment of recurrence risk, and prognosis12. However, routine neck dissection is controversial because of the uncertain effect on prognosis of clinically non-apparent lymph node metastases and because of complications, such as damage to the parathyroid glands, hypoparathyroidism, temporary/permanent recurrent laryngeal nerve injury, and tracheal or esophageal injury, that may profoundly influence a patient's qual¬ity of life.

Methylene blue has been used in the detection of sentinel lymph nodes in thyroid cancer, but methylene blue can also stain parathyroid glands, thyroid tissue, and fat, which can make the anatomic boundaries unclear and thereby restrict the use of methylene blue in PTC. As a novel lymphatic tracer13,14, carbon nanoparticles (CN) have been applied successfully in the detection of sentinel lymph nodes in breast and gastric cancers, while not been used as a lymphatic tracer for PTC. Thus, investigators hypothesized that CN may have clinical value in thyroid cancer as a novel lymph node tracer to guide central neck dissection. The goal of this study was to evaluate whether the use of CN facilitates the detection of lymph nodes, increases the number of metastatic lymph nodes removed, accurately reflects the metastatic condition of the central neck, and has the potential to protect the parathyroid glands. In this study, investigators evaluated the clinical value of CN in acquiring a more accurate reflection of the central neck lymph node status and in guiding central neck dissection.