Occult Lymph Node Metastasis in cN0 Tongue Squamous Cell Carcinoma: A Prospective Observational Study

Abstract

Tongue squamous cell carcinoma (TSCC) is prone to occult lymph node metastasis, and preoperative evaluation of cervical nodes is critical for determining treatment strategies. There is scarce report of detecting occult lymph node metastasis in TSCC by using multi-parameter magnetic resonance imaging (mpMRI), spectral computed tomography (spectral CT) or other diagnostic functional imaging. In this study, we aimed to analyze the incidence and risk factors of occult lymph node metastasis in cN0 TSCC by comparing preoperative imaging with postoperative pathology results. This study prospectively enrolled newly-diagnosed cN0 TSCC patients admitted to the Hunan Cancer Hospital between May, 2022 and December, 2022. All patients underwent primary resection and selective dissection of cervical lymph nodes. MpMRI and spectral CT scan of oral cavity and neck were performed prior to surgery. Preoperative evaluation of lymph node metastasis was conducted by two senior radiologists independently. The location of cervical lymph nodes was assigned based on the 2013 consensus guidelines. A total of 26 cN0 TSCC patients (6 cT1 stage, 13 cT2 stage, and 7 cT3 stage) were enrolled. The median age was 53 (range, 36-64), and there were 25 males. Among all patients, 13 patients underwent unilateral cervical lymph node dissection, while 13 patients underwent bilateral cervical lymph node dissection. A total of 208 lymphatic drainage areas were resected, and 1003 lymph nodes were removed. There were 7 of pT1, 12 of pT2, 7 of pT3 based on postoperative pathological stages. Besides, there are 21 cases staged pN0, 2 cases staged pN1, 2 cases staged pN2, and 1 case staged pN3. Among the 26 patients, 5 (19.23%) cases had occult lymph node metastasis. A total of 8 metastatic lymph nodes (4 in ipsilateral Ib level, 1 in contralateral Ib level, 3 in IIa level ipsilateral side) were detected in the whole group. No lymph node metastasis was detected in level IIb, III and IV. The median maximum diameter of metastatic lymph nodes was 12 mm (range 5 to 15 mm), and 1 extra-nodal extension was observed. Moreover, all occult lymph node metastases occurred in patients with a primary invasion depth of ≥ 5 mm (29.41%, 5/17). The incidence of occult lymph node metastasis in cN0 TSCC remains high under functional imaging diagnostic technology. Preventive neck dissection is necessary for patients with cN0 disease, especially those with primary tumor invasion depth exceeding 5 mm.