Determinants of level Ib involvement in oral squamous cell carcinoma and implications for submandibular gland-sparing neck dissection.

Traditional neck dissection for oral squamous cell carcinoma (OSCC) involves removal of the submandibular salivary gland. Several studies have cited the low incidence of direct gland invasion by tumours and have recommended gland-sparing neck dissection. In this study, a detailed audit of level Ib involvement in OSCC was performed in order to assess the feasibility of submandibular gland-sparing in neck dissection; the rate of direct involvement by the primary tumours, the involvement of periglandular level Ib nodes, and their determinants were investigated. A total of 586 neck dissection specimens obtained between 2005 and 2014 from patients operated on at the study institution for floor of mouth, tongue, and buccal primaries, were evaluated for direct invasion of the gland and periglandular lymphadenopathy. Of 226 node-positive patients, 21 (9.3%) had direct gland invasion by tumour. Risk factors were tumour diameter >4cm (P=0.002) and depth of invasion >10mm (P=0.003). Determinants of periglandular lymphadenopathy were depth of invasion >10mm (P<0.001), perineural invasion (P=0.02), lymphovascular invasion (P=0.014), and moderate/poor differentiation (P<0.0001). Gland-sparing neck dissection is safe in early tumours (pT1pN0-1), with a good chance of minimizing xerostomia without radiotherapy. Larger tumours without clear evidence of submandibular gland invasion or suspicious level Ib lymphadenopathy may be considered for gland preservation, however the oncological safety is unclear.