[Risk for metastasis of lymph node between sternocleidomastoid and sternohyoid muscle in papillary thyroid cancer]

Objective: To analyze the risk factors for metastasis of lymph nodes between sternocleidomastoid and sternohyoid muscle (LNSS) in papillary thyroid cancer (PTC). Methods: Papillary thyroid cancer patients with clinically positive lateral lymph node metastasis (cN1) who underwent surgery including LNSS dissection between May 1, 2013 and May 31, 2016 at the Department of Head and Neck Surgery, Fudan University Shanghai Cancer Center were retrospectively studied. Logistic regression analysis was performed to evaluate possible clinicopathological factors related to LNSS metastasis. Results: In 85 patients, 54 patients (63.5%) showed LNSS in their surgical specimen, and 20 patients (23.5%) had pathologically positive LNSS metastasis. Patients with LNSS showed preoperatively higher levels of serum thyroid stimulating hormone (TSH) and thyroid peroxidase antibody (TPO-Ab) compared to patients only with fibrofatty tissues between sternocleidomastoid and sternohyoid muscle (P<0.05), and they also displayed a higher proportion of multifocality in ipsilateral thyroid lobe (P<0.05). Multi-factor analysis indicated that LNSS metastasis was correlated with original tumor size (OR=1.819, 95%CI 1.050-3.850, P=0.002) and Level Ⅳ lymph node metastasis (OR=2.190, 95%CI 1.132-2.334, P=0.005). Furthermore, the number of positive LNSS was tightly correlated to that of level Ⅳ lymph node metastasis(P<0.05). Conclusion: LNSS metastasis is occult but not quite rare in PTC. Patients with extensive lymph node metastasis in Level Ⅳhave a higher risk for metastasis of LNSS.